JP3353294B2 - Optical transmission monitoring device, optical transmission monitoring method, optical amplification system, optical amplification system control method, and optical transmission system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a monitoring device, a monitoring method, and an optical amplification system including the monitoring device for monitoring a transmission state in an optical transmission line on which light including one or more signal lights having different wavelengths propagates. A control method of the optical amplification system,
And an optical transmission system.

[0002]

2. Description of the Related Art WDM (Wavelength Division Multiple)
xing) An optical transmission system employing a communication system includes an optical fiber transmission line network through which a WDM signal including one or more signal lights having different wavelengths propagates, and enables large-capacity and high-speed communication. This optical transmission system includes an optical fiber transmission line that is a transmission medium for signal light, an optical amplifier that collectively amplifies a WDM signal, and an optical ADM (a light ADM that extracts and adds some signal light included in the WDM signal). Add-Drop M
ultiplexer).

In an optical transmission system having the above-described structure, monitoring and controlling an optical amplifier is one of important issues. That is, when the wave number of the signal light transmitted from the transmitter fluctuates, the wave number of the signal light propagating through the optical transmission line fluctuates due to the extraction and addition of the signal light from the optical ADM provided in the optical transmission line. In this case, or when the transmission loss in an optical transmission line or the like fluctuates, each amplified light (each signal light) optically amplified by the optical amplifier.
It is desired that the optical power of the light is controlled to be constant. Various proposals have been made to solve this problem.

[0004] For example, the "WD proposed in the 1996 IEICE Communication Society Conference B-1096" has been proposed.
Output level control method for M optical amplifier (Control of Optic
al Output Level for WDM Optical Fiber Amplifie
r) "(first conventional example), an acousto-optic filter whose passing wavelength characteristic changes according to a change in the frequency of an ultrasonic wave is applied as an optical wavelength selection element. The acousto-optic filter is controlled by a sweep circuit, and has a period of
The band of 1557 nm is swept, and the WDM signal is converted into a pulse train on the time axis. This pulse train is optically / electrically converted and the wave number counter detects the wave number of the signal light included in the WDM signal. Then, based on the information on the detected wave number, the output constant control of the optical amplifier (ALC: Automatic Level
Control) has been done. In addition, the "Wide Tunable Range and Low S
idelobe Level of Double-stage Polarization Indepen
dent Acousto-optic Tunable Filter) describes the acousto-optic filter described above.

[0005] The "Characteristics of EDFA with Automatic Level Con- trol" proposed in "1996 IEICE Communications Society Conference B-1092" was proposed.
trol for change of number of the wavelengths and in
put signal level) (second conventional example), the pilot light in the amplification band of the optical amplifier is extracted from the optical transmission line by the branching element provided on the output side of the optical amplifier, and the extracted pilot light is output. A method has been proposed in which the optical power is detected and the optical amplifier is controlled so that the optical power of the pilot light becomes constant. As a technique similar to the second conventional example, for example, Seo Yeon Park and Sa
ng-Yung Shin "Gain and power controlled EDFA and W
DM optical networds ", 2nd Optoelectronics & Comm
unications Conference (OECC '97) Technical Digest.
July 1997, Seoul KOREA is known.

[0006] In addition, Takashi Ono, "Fiber grating wa
velength monitor for optical amplifier control and
administration in WDM transmission systems ", Firs
t Optoelectronics and Communications Conference (O
ECC '96) Technical Digest, July 1996, Makuhari Mess
In e, 17B3-2 (third conventional example), a part of the WDM signal (part of each signal light) is extracted by a branching element provided on the output terminal side of the optical amplifier, and a short pulse is output by an acousto-optic switch. Is output as Further, a delay corresponding to the wavelength of each signal light is given to each short pulse signal light by an optical circulator and an optical fiber grating. The signal lights having different wavelengths thus delayed are converted into pulses arranged on the time axis. From the number, position, and optical power of the pulses, the wave number of the signal light included in the WDM signal, the used wavelength band, and the power of each signal light can be obtained. In the third conventional example, constant output control (ALC) of the optical amplifier is performed based on the wave number of the signal light included in the obtained WDM signal.

[0007]

However, the first and third prior arts use special optical elements such as an acousto-optic filter, an acousto-optic switch, and an optical circulator. Uses a pilot light, these conventional systems become complicated and expensive.

In the first and third conventional examples, an acousto-optic filter and an acousto-optic switch are used.
Although the wave number of the signal light included in the DM signal can be detected, the power fluctuation of the signal light of the specific wavelength in the WDM signal cannot be detected. Further, the second conventional example using the pilot light cannot detect the wave number of the signal light included in the WDM signal, and can detect the optical power fluctuation of the signal light of a specific wavelength in the WDM signal. Can not. Therefore, the first to third prior art examples have the WDM
It is not possible to identify whether the optical power fluctuation of the signal is caused by the optical power fluctuation of the signal light of the specific wavelength or the loss fluctuation in the optical transmission line. Such a problem is particularly serious in an optical transmission system using an optical ADM.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has an optical transmission monitoring apparatus, a monitoring method, and an optical transmission method having a simple structure capable of identifying the cause of optical power fluctuation of a WDM signal. It is an object to provide an optical amplification system including a monitoring device, a control method for the optical amplification system, and an optical transmission system.

[0010]

According to the present invention, there is provided an optical transmission monitoring apparatus for transmitting an optical signal on an optical transmission line through which a WDM signal including at least one signal light having a wavelength within a signal light wavelength band and different wavelengths from each other propagates. This is a device for monitoring the state, and uses light in the signal light wavelength band or light in a wavelength band different from the signal light wavelength band as monitoring light.

Specifically, the optical transmission monitoring device according to the present invention comprises a first photodetector, a second photodetector, and the first photodetector.
And a monitoring unit that monitors a transmission state in the optical transmission line using a detection result of the second photodetector.

The first photodetector is included in a monitoring light wavelength band in a monitoring light wavelength band in which light propagating in an optical transmission line and including one or more monitoring lights having different wavelengths from each other exists. At least one of the optical power of one or more monitoring lights in the light in the first wavelength band and the optical power of noise light in the light in the first wavelength band is detected. In addition, the second photodetector includes an optical power of at least one monitor light among the lights in the second wavelength band included in the monitor light wavelength band and the second power.
At least one of the optical powers of the noise light is detected among the light within the wavelength band.

The monitoring light wavelength band may be a wavelength band different from the signal light wavelength band or a wavelength band partially overlapping the signal light wavelength band. When the monitoring light wavelength band is different from the signal light wavelength band, light in the monitoring light wavelength band propagating in the optical transmission line is extracted from the optical transmission line by the demultiplexer. The extracted light in the monitoring light wavelength band is guided to the optical transmission monitoring device and used for optical transmission monitoring. On the other hand, when the monitoring light wavelength band and the signal wavelength band overlap, the signal light can be used as the monitoring light in the overlapping wavelength band. Therefore, by providing at least one demultiplexer in the optical transmission line, a part of light in the signal light wavelength band propagating in the optical transmission line is extracted. The extracted light is guided to the optical transmission monitoring device and used for the optical transmission monitoring. in this way,
At least a part of the light component of the signal light extracted from the optical transmission path can be used as monitoring light.

In the monitoring light wavelength band, the first wavelength band and the second wavelength band may be different wavelength bands. Also, these first and second wavelength bands are:
Some may overlap, provided that they do not match each other. As an aspect in which the first wavelength band and the second wavelength band overlap, the bandwidth of the first wavelength band is wider than the bandwidth of the second wavelength band, and the second wavelength band is included in the first wavelength band. It is preferable that the setting is made.

The monitoring unit may further include an optical power variation per unit time in the first wavelength band detected by the first photodetector, and a unit in the second wavelength band detected by the second photodetector. Compare the optical power fluctuation amount per time. Then, the monitoring unit identifies the cause of the optical power fluctuation in the optical transmission line to be monitored based on the obtained comparison result. Specifically, when the optical power fluctuation in the first wavelength band and the optical power fluctuation in the second wavelength band show the same tendency, the fluctuation of the transmission loss of the optical transmission line (the optical amplifier is installed in the optical transmission line). When the optical amplifier is provided, the fluctuation of the gain of the optical amplifier is also included). When the optical power fluctuation in the first wavelength band and the optical power fluctuation in the second wavelength band show different tendencies, it is determined that the wave number of the signal light propagating in the optical transmission line has increased or decreased. In addition, since this monitoring unit uses the fluctuation of the optical power in both the first and second wavelength bands,
The light to be detected by the first and second photodetectors is monitoring light in the monitoring light wavelength band and spontaneous emission light (ASE: Amplified Sp
Any noise light, such as ontaneous emission, or light containing these may be used. In another aspect, the light component detected by the first photodetector and the light component detected by the second photodetector do not need to be the same type.
For example, the first photodetector detects the optical power of signal light (monitoring light), while the second photodetector detects the optical power of noise light such as ASE excluding the signal light, and detects each detected optical component. May be used for monitoring the optical transmission path.

However, in the monitoring of the wave number change by the above configuration, when the same light level fluctuation occurs in the first wavelength band and the second wavelength band in the monitoring light wavelength band, the loss fluctuation in the optical transmission line is reduced. Will be mistaken. In an optical transmission line monitoring device that solves such a problem, light in a wavelength band other than the signal light wavelength band is propagated as a part of the monitoring light, and at least three types of light (light contained in each other) are monitored in the monitoring light wavelength band. By detecting the optical powers of the components having different components, the transmission state in which the wave number change as described above has occurred can be monitored.

In the above aspect, the light in the signal light wavelength band corresponds to the light in the first wavelength band of the monitoring light wavelength band, and the light propagating in the optical transmission path separately from the signal light is transmitted in the second wavelength band. Corresponding to the light inside. The optical transmission monitoring device further includes a third detector that detects at least the optical power of the light including the noise light in the first wavelength band. Accordingly, the optical transmission monitoring device uses the first detector to detect the optical power of the first light (the noise light in the first wavelength band and the second wavelength) including at least the monitoring light (signal light) in the first wavelength band. And the second detector may detect at least the optical power of the second light including the monitoring light in the second wavelength band, and the third detector may detect at least the second power of the second light including the monitoring light in the second wavelength band. The optical power of the third light including the noise light within one wavelength band is detected. The monitoring unit is configured to determine an optical power variation per unit time for the first light obtained by the first detector, an optical power variation per unit time for the second light obtained by the second detector, The variation of the optical power per unit time of the third light obtained by the third detector is compared, and the cause of the optical power variation in the optical transmission line is identified based on the comparison result.

On the other hand, the optical transmission monitoring device according to the present invention
The configuration may be such that the optical transmission state is monitored by using signal light for one channel in the signal light wavelength band as pilot light. In this case, light in the signal light wavelength band corresponds to light in the monitoring light wavelength band, and a wavelength band that includes pilot light for one channel and is included in the signal light wavelength band corresponds to the second wavelength band. That is, in this configuration, the monitoring light wavelength band is set so that the second wavelength band is included in the first wavelength band. The monitoring unit obtains the optical power fluctuation amount per unit time obtained for the signal light and the noise light as the monitoring light in the first wavelength band and the pilot light as the monitoring light in the second wavelength band. The optical power fluctuation per unit time is compared, and the cause of the optical power fluctuation in the optical transmission line is identified based on the comparison result. Preferably, the optical transmission monitoring device detects a transmission abnormality of at least one channel of signal light selected from signal lights in a wavelength band overlapping the first wavelength band in the second wavelength band. A first system and, based on a detection result obtained by the first system, monitor light in a second wavelength band from signal light in a wavelength band overlapping the first wavelength band in the signal light wavelength band. And a second system for reselecting the signal light to be selected as the control signal. This is because there is a case where the monitoring target channel is damaged for some reason or its use is stopped.

Next, the optical transmission monitoring device according to the present invention comprises:
When an optical amplifier is provided in the optical transmission line, it can be used as a control device for the optical amplifier. That is, the optical transmission monitoring device is arranged at a predetermined position on the optical transmission path to which the amplified light output from the optical amplifier reaches. Also,
When the amplification characteristic of the optical amplifier depends on the wavelength, the center wavelength of the first wavelength band and the center wavelength of the second wavelength band are set to the signal light wavelength in order to minimize the influence of the wavelength dependency of the optical amplifier. It is preferable that the wavelength is set so as to match the wavelength at which the gain is substantially equal to the average gain of the optical amplifier in the band. Further, each bandwidth of the first and second wavelength bands is based on at least one of a shift between the amplification wavelength band of the optical amplifier and the monitoring light wavelength band, and a wave number of the monitoring light included in the monitoring light wavelength band. Is preferably set.

An optical transmission monitoring method according to the present invention is realized by utilizing the above-described optical transmission monitoring device. That is, the monitoring method includes, in a monitoring light wavelength band in which light propagating through an optical transmission line and including light including one or more monitoring lights having different wavelengths from each other, a first wavelength included in the monitoring light wavelength band. Detecting at least one of the optical power of one or more supervisory lights among the light in the band and the optical power of the noise light among the lights of the first wavelength band, and detecting the amount of optical power fluctuation per unit time; The optical power fluctuation amount is detected for at least one of the optical power of one or more monitoring lights among the light within the second wavelength band included in the wavelength band and the optical power of the noise light among the light within the second wavelength band. I do. And
The monitoring method compares the detected optical power fluctuation amount per unit time in the first wavelength band with the detected optical power fluctuation amount per unit time in the second wavelength band, and based on the comparison result. The cause of the fluctuation of the optical power in the optical transmission line is identified.

Further, the optical amplification system according to the present invention comprises:
At least an optical amplifier for collectively amplifying light of a signal light wavelength band propagated in an optical transmission line, and an optical transmission monitoring device disposed at a predetermined position on the optical transmission line to which the amplified light output from the optical amplifier reaches And This optical transmission monitoring device has the above-described structure. Further, the optical amplification system is located on an optical transmission path, where the signal light in the signal light wavelength band passes before reaching the optical transmission monitoring device,
And a variable optical attenuator disposed at at least one of positions where the signal light passes after passing through the optical transmission monitoring device and attenuates the signal light by a predetermined amount. in this case,
The monitoring unit of the optical transmission monitoring device adjusts the attenuation of the variable attenuator according to the transmission state in the optical transmission path.

In the control method of the optical amplification system having such a structure, as described above, even if the light including the one or more monitoring lights having different wavelengths from each other propagates in the optical transmission line. In the optical wavelength band, at least one of the optical power of one or more supervisory lights out of the light in the first wavelength band included in the monitoring optical wavelength band and the optical power of noise light out of the light in the first wavelength band. And the optical power fluctuation amount per unit time is detected, and among the light within the second wavelength band included in the monitoring light wavelength band, the optical power of at least one monitoring light and the light power within the second wavelength band. An optical power fluctuation per unit time is detected for at least one of the optical powers of the noise light. The detected optical power fluctuation amount per unit time in the first wavelength band is compared with the detected optical power fluctuation amount per unit time in the second wavelength band, and the wave number of the signal light is calculated based on the comparison result. The increase or decrease is determined. Then, based on the determination result, at least one of gain adjustment of the optical amplifier and adjustment of the variable attenuator corresponding to the increase or decrease of the wave number of the signal light is performed.

Further, the optical transmission system according to the present invention comprises:
At least one relay station is provided at a predetermined position on an optical transmission path through which light including at least one signal light having a wavelength within a signal light wavelength band and different from each other propagates. Each relay station includes a section monitoring device having the same structure as the above-described optical transmission monitoring device. Each relay station may further include an optical amplifier that collectively amplifies light in the signal light wavelength band that has propagated in the optical transmission line. In this configuration, the monitoring unit of the optical transmission monitoring device includes an optical transmission line. , The gain of the optical amplifier is adjusted according to the transmission state.

Each of the relay stations may further include a variable optical attenuator for attenuating the signal light within the signal light wavelength band by a predetermined amount. In this configuration, the monitoring unit of the optical transmission monitoring device adjusts the variable optical attenuator according to the transmission state in the optical transmission path. In addition, each relay station may include an optical input / output element such as an optical ADM that extracts a part of the signal light from the signal light propagating in the optical transmission line and adds a new signal light. In particular, in this optical transmission system, one of the first and second wavelength bands may include a part of the signal light in which either the extraction or the addition of the signal light is performed by the optical input element. This is more preferable because it is not necessary to prepare monitoring light separately from signal light.

In the optical transmission system, in each of the relay stations having the above-described structure, the light per unit time of a part separated from the light in the monitoring light wavelength band that reaches the relay station. The optical power fluctuation in the entire optical transmission system based on the power fluctuation amount and the light power fluctuation amount per unit time for a part of the light in the monitoring light wavelength band output from the relay station and separated from the light. May be further provided. In this configuration, the system control unit corrects the control performed by the monitoring unit of the optical transmission monitoring device in each of the relay stations based on the optical power fluctuation amount of the input / output light in each of the relay stations.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical transmission monitoring device and the like according to the present invention will be described below with reference to FIGS. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. In the following description, eight WDM signals will be mainly described, but the wave number of the signal light included in the WDM signal is not limited to this.

First, an optical transmission system to which the optical transmission monitoring device according to the present invention is applied will be described. FIG. 1 (a)
FIG. 1 is a diagram showing a schematic configuration of the optical transmission system. FIGS. 1B and 1C show signal light wavelength bands (W1 and W2) at respective parts in FIG. FIG. 3 is a diagram illustrating an optical spectrum of a used wavelength band (WDM signal wavelength band). The optical transmission system shown in FIG. 1A collectively transmits a transmitter 10 for transmitting eight signal lights (λ1 to λ8) having different wavelengths from each other and an eight-wave signal light transmitted from the transmitter 10. An optical amplifier 20 for optically amplifying the optical signal, and an optical transmission monitoring device 30 for monitoring eight signal lights output from the optical amplifier 20. These components 10, 2
0 and 30 are optically connected by optical fiber transmission lines 41 to 43, respectively.

At the portion of the optical transmission system indicated by W1, light transmitted from the transmitter 10 is shown in FIG.
As shown in FIG. 5, while including eight signal lights (λ1 to λ8), spontaneous emission light (ASE: Amplified Spontaneous Emis)
)). The signal light passing through the point W1 reaches the optical amplifier 20 via the optical fiber transmission line 41, and is collectively optically amplified. As shown in FIG. 1C, the amplified light output from the optical amplifier 20 at the portion indicated by W2 includes not only signal light (.lambda.1 to .lambda.8) but also noise light that has been collectively optically amplified. Including. Further, the amplified light output from the optical amplifier 20 reaches the optical transmission monitoring device 30 via the optical fiber transmission line 42, and a part of the amplified light further propagates through the optical fiber transmission line 43.

In the case where light in the above-mentioned signal wavelength band is used as the monitoring light, the optical transmission monitoring apparatus 30 uses a part of the light in the signal light wavelength band including the inputted eight signal light (separated light) as the monitoring light. And the separated light is used for monitoring the transmission state in the optical transmission line. That is, the optical power (the optical power of the signal light, the optical power of the noise light, and the optical power of the light including these) in the first wavelength band included in the signal light wavelength band (corresponding to the monitoring light wavelength band). And the optical power in the second wavelength band included in the signal light wavelength band (the optical power of the signal light, the optical power of the noise light, and the optical power of the light including these). ) Are detected by separately provided photodetectors. Then, the variation of the optical power per unit time in the first wavelength band is compared with the variation of the optical power per unit time in the second wavelength band. The transmission status on the path is monitored based on the comparison result.

The setting of the monitoring light wavelength band and the setting of the first wavelength band and the second wavelength band in the monitoring light wavelength band have various aspects as described later.

(First Embodiment of Optical Transmission Monitoring Apparatus) FIG. 2
FIG. 2A is a diagram illustrating a configuration of an optical transmission monitoring device according to a first embodiment, and FIG. 2B is a diagram illustrating a configuration substantially equivalent to the configuration illustrated in FIG. It is. FIG.
(A) to FIG. 3 (d) show FIG. 2 indicated by W3 to W6.
It is a figure which shows the optical spectrum of the signal light wavelength band (it matches a monitoring light wavelength band) in each part in (a) and (b).

The optical transmission monitoring device 31 shown in FIG.
(Equivalent to the optical transmission monitoring device 30 in (a)) includes an optical branching element 311 provided on the optical fiber transmission line 42 and an optical branching element provided on a branch line through which the light separated by the optical branching element 311 propagates. Branch element 312 and optical branch element 3
Photodetector 31 optically connected to one of the outgoing ends of 12
3, a band-pass filter 314 (optical fiber grating) having one end optically connected to the other of the emission ends of the light splitting element 312, and a photodetector 315 optically connected to the other end of the optical fiber grating 314. And a monitoring unit 316 using detection signals from the photodetectors 313 and 315.
And

Incidentally, the above-mentioned light splitting element 312
As shown in (b), it may be provided on the optical fiber line 42. In this case, the photodetector 313 is optically connected to the light splitting element 311 and the bandpass filter 314
Is optically connected to the light splitting element 312.

Each of the optical branching elements 311 and 312 includes, for example, an optical fiber coupler or the like, and
A part of the light within the signal light wavelength band including the eight signal lights (λ1 to λ8) propagating therethrough is separated. Photodetector 313
Includes, for example, a photo diode, etc.
The optical power of the light separated by 1 and passed through the optical branching element 312 is detected. Optical fiber grating 31
Reference numeral 4 denotes an optical component built in the optical fiber by periodically changing the refractive index along the optical axis of the optical fiber, and is disposed between the optical branching element 312 and the photodetector 315. ing. The optical fiber grating 314 has a function of transmitting light in a wavelength band including four signal lights (λ5 to λ8) among the lights separated by the optical branching element 312. The photodetector 315 includes, for example, a photodiode and detects the optical power of the light transmitted through the optical fiber grating 314. The monitoring unit 316 includes the light detector 31
Data on the optical power detected by each of the third and 315 is input, and the transmission state in the signal light wavelength band is monitored based on the comparison result of the variation of each optical power per unit time.

The optical transmission line to be monitored includes at least the transmitter 10, the optical amplifier 20, and the optical fiber transmission line 42. The monitoring of the transmission state by the monitoring unit 316 is performed by identifying the cause of the fluctuation of the optical power in the optical transmission line. In particular, when light in a signal light wavelength band, which is a used wavelength band, is used as the monitoring light, it is possible to monitor an increase or decrease in the wave number of the signal light propagating in the optical transmission line.

The light that reaches the optical transmission monitor 31 via the optical fiber transmission line 42 is output from the optical amplifier 20 and is shown in FIG. 3B (same as FIG. 1C). As described above, in addition to the eight-wave signal light (λ1 to λ8) collectively optically amplified by the optical amplifier 20, ASE is included as noise light. Most of the light reaching the optical transmission monitoring device 31 passes through the optical branching device 311 (passes through the optical branching devices 311 and 312 in the configuration of FIG. 2B) and is output from the optical transmission monitoring device 31. . As shown in FIG. 2D, the spectrum of the light output from the optical transmission monitoring device 31 matches the spectrum of the light reaching the optical transmission monitoring device (FIG. 2A).

On the other hand, part of the light reaching the optical transmission monitoring device 31 is separated by the optical branching element 311, further passes through the optical branching element 312, and its optical power is detected by the photodetector 313. The light received by the photodetector 313 (first light)
As shown in FIG. 3B, the light in the wavelength band includes ASE in addition to the eight signal lights (λ1 to λ8). On the other hand, the light splitting element 312 extracts a part of the light split by the light splitting element 311. Of this extracted light,
Of the extracted light, light in a wavelength band including four signal lights (λ5 to λ8) reaches the photodetector 315 via the optical fiber grating 314. The optical detector 315 detects the optical power of the light that has passed through the optical fiber grating 314. As shown in FIG. 3C, the light (light in the second wavelength band) received by the photodetector 315 includes, in addition to the four signal lights (λ5 to λ8), the second wavelength band. Also includes ASE. Then, the monitoring unit 316 determines the amount of change per unit time of the optical power in the first wavelength band detected by the photodetector 313 and the unit of the optical power in the second wavelength band detected by the photodetector 315. The fluctuation amount per time is compared, and based on the comparison result, the transmission state of the signal light wavelength band that matches the monitoring light wavelength band is monitored.

The above-mentioned monitoring of the transmission state is performed, for example, by
As shown in FIG. 4A, the wavelengths λ _{a1 to} λ _n1 are different from the light within the signal light wavelength band (including the signal lights λ _{a2 to} λ _n2 ).
This is also realized by propagating the monitoring light through the optical transmission line and monitoring the fluctuation of the optical power in the monitoring band.
Further, as described above, since the optical transmission monitoring is performed by monitoring the optical power fluctuation of the light propagating in the optical transmission line, the light within the signal light wavelength band (it is not necessary to be the signal light).
Can be used as monitoring light. That is,
As shown in FIG. 4B, when at least a part of the monitoring light wavelength band and the signal light wavelength band overlap (may coincide with each other), the monitoring light within the signal light wavelength band is used. Light (including at least one of signal light and noise light) of a wavelength band overlapping the wavelength band can be used as the monitoring light wavelength band (including at least one of monitoring light and noise light).

The monitoring light wavelength band and the signal light wavelength band overlap each other, for example, as shown in FIG. 4C, so that the signal light wavelength band is included in the monitoring light wavelength band. As shown in FIG. 4E, the set mode and the mode in which the monitoring light wavelength band is set to be included in the signal light wavelength band are included. Further, in a mode in which the monitoring light wavelength band is set to a wavelength band different from the signal light wavelength band, for example, as shown in FIG. 4D, the monitoring light wavelength band is configured by a plurality of wavelength bands. Embodiments are included.

On the condition that the first wavelength band defining the light received by the photodetector 313 and the second wavelength band defining the light received by the photodetector 315 do not coincide with each other,
Settings in various modes as shown in FIGS. 5A to 5D are possible. That is, the first wavelength band and the second wavelength band are mutually different wavelength bands, one or more of the eight signal lights to be captured are included in one of the first and second wavelength bands, and It is possible to set so as not to be included in the other wavelength band (see FIG. 5A). Further, since the monitoring light wavelength band can be set to be constituted by a plurality of wavelength bands as shown in FIG. 4C, as shown in FIG. Second
It is also possible to set each wavelength band. In addition, the first wavelength band and the second wavelength band are different from each other in that the wavelength bands do not overlap each other as shown in FIG.
As shown in (e), it can be set in a state where at least a part thereof overlaps. In addition, even when the wavelength bands overlap, the bandwidth of the second wavelength band is set to be narrower than the bandwidth of the first wavelength band so that the wavelength bands do not match each other. The setting may be made to include the second wavelength band (see FIGS. 5C and 5D). When the first wavelength band and the second wavelength band overlap, the second wavelength band may be composed of a plurality of wavelength bands as shown in FIG.

As shown in FIG. 6, the light including the signal light having the wavelength λ0 as the center wavelength generally includes noise light such as ASE and the signal light. In the optical transmission monitoring device according to the present invention, the transmission state in the optical transmission line is monitored by focusing on the fluctuation of the optical power in each of the first and second wavelength bands. It is not necessary to compare the optical power of all light components in the second wavelength band with the optical power of all light components in the second wavelength band. For example, the optical power between signal light in the first wavelength band and the signal light in the second wavelength band, the optical power between noise light such as ASE in the first wavelength band and the noise light in the second wavelength band, the first power Optical power between signal light in the wavelength band and noise light in the second wavelength band,
Alternatively, the transmission state in the optical transmission line can be monitored by comparing the optical power between the noise light in the first wavelength band and the signal light in the second wavelength band.

The separation of signal light and noise light from light within a predetermined wavelength band can be realized by the optical device shown in FIG. The device illustrated in FIG. 7 includes an optical splitter 401 that splits and extracts a part of light propagating through the optical transmission line 400, and a light A including the signal lights λ1 to λ32 separated by the optical splitter 401. , And an optical fiber coupler 402 for branching into light propagating through the optical fiber transmission path 403 and light propagating through the optical fiber transmission path 404. The optical fiber transmission line 403 has a chirped grating 405 for reflecting signal light of wavelengths λ1 to λ32.

FIG. 8A shows the spectrum of light A taken in by the apparatus shown in FIG. 7, and FIG. 8B shows the spectrum of light A reflected by the optical fiber grating 405 and transmitted through the coupler 402. FIG. 8C shows the spectrum of the light B propagating in the optical fiber grating 404, and FIG. 8C shows the spectrum of the noise light not including the signal light, which has passed through the optical fiber grating 405.

FIG. 9 is a graph for explaining an optical transmission monitoring method in the optical transmission monitoring device according to the first embodiment. 9, a solid line shows a graph of a time change of the optical power P1 in the first wavelength band detected by the photodetector 313, and a broken line shows the optical power P2 in the second wavelength band detected by the photodetector 315. 3 shows a graph of the time change of FIG. Note that, in FIG. 9, the second
The optical power P2 in the wavelength band is doubled. The monitoring unit 316 of the optical transmission monitoring device 31 compares the fluctuation amounts Δ (change rates) per unit time Δt of these optical powers P1 and P2, and based on the comparison result, changes the transmission state as follows. to decide.

That is, time t <t1, t1 <t <t
2 and t2 <t, the change rates of the optical powers P1 and P2 in the first and second wavelength bands are substantially the same, so that the wave number of the signal light propagating through the optical fiber transmission line 42 changes. You can see that it is not. From this, the monitoring unit 316 monitors the transmission loss fluctuation in the optical transmission line including the optical fiber transmission line 42 and upstream of the optical transmission device 31 or the output level fluctuation of the upstream optical amplifier or the like. It is determined that optical power fluctuation has occurred.

At time t1 and time t2, the variation Δ1 of the optical power P1 in the first wavelength band is clearly different from the variation Δ2 of the optical power P2 in the second wavelength band. The monitoring unit 316 determines that the wave number of the propagating signal light has changed.

(Second Embodiment of Optical Transmission Monitoring Apparatus) FIG.
10A is a diagram illustrating a configuration of an optical transmission monitoring device according to a second embodiment, and FIGS. 10B to 10E illustrate W7 to W.
FIG. 11 is a diagram illustrating an optical spectrum of a signal light wavelength band (corresponding to a monitoring light wavelength band) in each unit in FIG.

The optical transmission monitoring device 32 (corresponding to the optical transmission monitoring device 30 in FIG. 1A) includes at least the optical branching element 321 provided on the optical fiber transmission line 42 and the optical branching element 321. Optically connected demultiplexing filter 322
And optical detectors 323 and 324 optically connected to the demultiplexing filter 322, respectively, and a monitoring unit 325 for inputting data relating to the optical power detected by the optical detectors 323 and 324.

The optical branch element 321 is connected to the optical fiber transmission line 4
A part of the light (see FIG. 10B) in the signal light wavelength band including the eight signal lights (λ 1 to λ 8) propagating through 2 is branched and extracted. The demultiplexing filter 322 includes a dichroic mirror, for example, and converts the light extracted by the optical branching element 321 into light of a first wavelength band including four signal lights (λ1 to λ4) (see FIG. 10D). And the remaining four signal lights (λ5 to λ
The light is demultiplexed into light of the second wavelength band including (8) (see FIG. 10C). The photodetector 323 includes, for example, a photodiode and detects optical power in a second wavelength band including four signal lights (λ5 to λ8) output from the demultiplexing filter 322. The photodetector 324 also includes, for example, a photodiode, and detects the optical power in the first wavelength band including the four signal lights (λ1 to λ4) output from the demultiplexing filter 322. The monitoring unit 325 includes the photodetectors 323 and 32
4 to compare the amount of change in the optical power detected per unit time, and monitor the transmission state in the signal light wavelength band based on the comparison result.

The light that reaches the optical transmission monitoring device 32 via the optical fiber transmission line 42 is output from the optical amplifier 20 and is shown in FIG. 10B (same as FIG. 1C). As described above, 8
In addition to wave signal light (λ1 to λ8), noise light such as ASE is included. Most of the light reaching the optical transmission monitoring device 32 passes through the optical branching element 321 and is transmitted to the optical transmission monitoring device 32.
Output from The spectrum of the light output from the optical transmission monitoring device 32 is, as shown in FIG.
This is similar to the spectrum shown in FIG.

A part of the light reaching the optical transmission monitoring device 32 is branched and extracted by the optical branching element 321, and the first wavelength band including four signal lights (λ 1 to λ 4) is output by the branching filter 322. And the light of the second wavelength band including the four signal lights (λ5 to λ8). Demultiplexing filter 3
The light of the second wavelength band output from the second detector 22 is
3, the optical power is detected. The light of the second wavelength band received by the photodetector 323 includes, as shown in FIG. 10C, ASE which is noise light in addition to four signal lights (λ5 to λ8). . The optical power of the light of the first wavelength band including the remaining four signal lights (λ1 to λ4) output from the demultiplexing filter 322 is detected by the photodetector 324. The light of the first wavelength band received by the photodetector 324 includes FIG.
As shown in (d), ASE that is noise light is included in addition to the four signal lights (λ1 to λ4). Then, the monitoring unit 325
Then, the fluctuation amount per unit time of the optical power in the second wavelength band detected by the photodetector 323 and the fluctuation amount per unit time of the optical power in the first wavelength band detected by the photodetector 324 are calculated. The transmission status in the signal light wavelength band is monitored based on the comparison result.

FIG. 11 is a graph for explaining an optical transmission monitoring method in the optical transmission monitoring device according to the second embodiment. In this figure, the solid line shows a graph of the time change of the optical power P1 in the first wavelength band detected by the photodetector 323, and the broken line shows the optical power P2 in the second wavelength band detected by the photodetector 324. 3 shows a graph of the time change of FIG. Note that the optical power P2 in the second wavelength band is shown as being doubled. Monitoring unit 32 of optical transmission monitoring device 31
5 compares the fluctuation amounts Δ (change rates) per unit time Δt of these optical powers P1 and P2, and determines the transmission state based on the comparison result as follows.

In this figure, time t <t1, t1 <t
In the respective time ranges of <t2 and t2 <t, the change rates of the optical powers P1 and P2 in the first and second wavelength bands are substantially the same, so that the signal light transmitted through the optical fiber transmission line 42 is transmitted. It can be seen that the wave number of does not change. From this, the monitoring unit 325 controls the transmission of the signal light due to the transmission loss fluctuation in the transmission line including the optical fiber transmission line 42 and upstream of the optical transmission monitoring device 32 or the output level fluctuation of the upstream optical amplifier or the like. It is determined that optical power fluctuation has occurred.

On the other hand, at time t1 and time t2, the variation Δ1 of the optical power P1 in the first wavelength band.
And the variation Δ2 of the optical power P2 in the second wavelength band are different from each other, so that the monitoring unit 325 determines that the wave number of the signal light propagating through the optical fiber transmission line 42 has changed. (Optical amplification system) FIGS. 12 (a) and 12 (b)
FIG. 13 is a diagram illustrating a schematic configuration of an optical amplification system according to the present invention, and FIG. 13 is a diagram illustrating a specific configuration of the optical amplification system illustrated in FIG. Further, FIG.
4 is a flowchart for explaining a control method of the optical amplification system shown in FIG.

The optical amplification system 3 shown in FIG.
In the first embodiment, the optical amplifier 350 and the optical amplifier 3
And an optical transmission monitoring device 30 for performing a gain adjustment of 50. The optical amplification system 300 according to the first embodiment is configured such that the optical transmission monitoring device 30 monitors the state of optical transmission upstream and adjusts the output of the optical amplifier 350 according to the transmission state. On the other hand, the optical amplification system 300 shown in FIG. 12B collectively optically amplifies the light transmitted through the optical transmission monitoring device 30 and the optical transmission monitoring device 30 that monitors the state of upstream optical transmission. An optical amplifier 350 and a variable attenuator 351 arranged so as to sandwich the optical transmission monitoring device 30 with the optical amplifier 350 are provided. In the optical amplification system 300 according to the second embodiment, the optical transmission monitoring device 30 monitors the upstream optical transmission state, and controls the optical power of the input light to the optical amplifier 350 according to the transmission state.
The attenuation of the variable attenuator 351 is adjusted.

FIG. 13 is a diagram showing a specific configuration of the optical amplification system 300 shown in FIG. 12 (a). In this figure, in particular, in this figure, the optical transmission monitoring device 3 according to the first embodiment is described.
1 (FIG. 2A) shows a configuration in which the optical transmission monitoring device 30 is applied.

In FIG. 13, the optical amplification system 30
0, the optical transmission monitoring device 31 includes the optical branching elements 311, 312, the optical fiber grating 314 as a bandpass filter, the photodetectors 313, 3
15 and a monitoring unit 316. Note that the configuration of the optical transmission monitoring device 31 in the optical amplification system 300 is not limited to the configuration illustrated in FIG. 2A, and may be the configuration illustrated in FIG.

The optical amplifier 350 located downstream of the optical transmission monitoring device 31 is provided with the Er-added optical fiber 20.
1, an excitation light source 204 for supplying excitation light to the amplification optical fiber 201, and a signal light propagating through the optical fiber transmission line 41 guided to the amplification optical fiber 201 and the excitation light from the excitation light source 204 is An optical isolator 202 for guiding the amplification optical fiber 201, an optical isolator 203 for guiding the optically amplified signal light to the optical fiber transmission line 42 and guiding the excitation light from the excitation light source 204 to the amplification optical fiber 201; And a drive system 205. The monitoring unit 316 of the optical transmission monitoring device 31
The drive system 205 is controlled in accordance with the transmission state of the monitored signal light, and the gain of the optical amplifier 20 is adjusted.

Next, the optical amplification system 30 according to the present invention
The operation of the optical transmission monitoring device 31 is mainly described in FIG.
This will be described with reference to the flowchart shown in FIG. In the following description, it is assumed that the monitoring light wavelength band monitored by the optical transmission monitoring device 31 matches the signal light wavelength band. The first wavelength band in the monitoring light wavelength band is the entire monitoring light wavelength band (including the signal lights λ1 to λ8), and the photodetector 313 detects the optical power in the first wavelength band. On the other hand, the second wavelength band has four signal lights (λ
5 to λ8), and the photodetector 315 detects the optical power in the second wavelength band.

The electrical signals corresponding to the optical powers of the first and second wavelength bands detected by the photodetectors 313 and 314 are sequentially input to the monitoring unit 316. Monitoring unit 31
In step 6, the variation Δ1 per unit time of the optical power in the first wavelength band and the variation Δ2 per unit time of the optical power in the second wavelength band are calculated from the input electric signals (step ST1). .

Subsequently, the monitoring unit 316 determines whether or not the difference | Δ1−Δ2 | between the obtained fluctuation amounts Δ1 and Δ2 is equal to or smaller than the allowable value e (step ST2).

Generally, the wave number of a signal light propagating in an optical transmission line is proportional to the signal level (optical power).
For example, it is known that when the number of signals of 16 channels is reduced to 8 channels in WDM transmission, the signal level is reduced by about 3 dB. However, since a signal level fluctuation of about 3 dB occurs even in the transmission loss in the optical transmission line, even if only the signal level of the light input to the optical transmission monitoring device 31 is monitored, the signal level actually varies. It was not possible to judge whether the fluctuation was caused by an increase or decrease in the number of signal lights, or simply a fluctuation in loss in an optical transmission line. According to the present invention, two kinds of wavelength bands are prepared as wavelength bands to be monitored, and the transmission state is monitored by independently monitoring the two wavelength bands. Specifically, as described above, in the case of the transmission loss in the optical transmission line, it is common that there is a loss over the entire signal light wavelength band (the transmission loss has no wavelength dependency).
There is no large difference in loss fluctuation between the two wavelength bands.
Therefore, each photodetector 3 determined by the monitoring unit 316
13, Δ315 |
If 1−Δ2 | is equal to or smaller than the allowable value e, the optical transmission monitoring device 31
It can be determined that the fluctuation is a loss fluctuation of the optical transmission line upstream of the optical transmission line (event 1). When the signal level of the output light is monitored by the optical amplifier 20 located upstream, whether the optical power fluctuation (loss fluctuation) in the optical transmission line is the amplification level fluctuation of the optical amplifier 20 (event 4) Alternatively, it can be determined whether the loss is in the transmission line 42. When it is determined that the fluctuation is loss, the monitoring unit 316 adjusts the gain of the optical amplifier 350 located downstream in order to realize the ALC operation by adjusting the gain for the loss fluctuation (step ST3). The gain adjustment by the monitoring unit 316 is performed by the monitoring unit 316 controlling the drive system 205 in the optical amplifier 20 according to the difference between the fluctuation amounts obtained in step ST2. Specifically, the monitoring unit 316 outputs an electric signal for drive control to the drive system 205. The drive system 205 supplies a drive voltage to the excitation light source 204 in response to the applied electric signal. By adjusting the driving voltage in this manner, the excitation light source 204
The optical power of the pumping light output from is adjusted, and the gain of the optical amplifier 20 can be adjusted. That is,
The gain adjustment of the optical amplifier 350 is performed by the amplification optical fiber 20.
This is realized by adjusting the power of the pumping light supplied to the light source 1.

In step ST2, when it is determined that the difference between the fluctuation amounts of the respective optical powers detected by the photodetectors 313 and 315 exceeds the allowable value e, the monitoring light wavelength band 2 is prepared. It can be determined that there was a change in the number of different components in each type of wavelength band (event 2). As described above, when it is determined that the difference between the fluctuation amounts of the respective optical powers detected by the photodetectors 313 and 315 exceeds the allowable value e, the gain adjustment of the optical amplifier 350 is not performed.

(Third Embodiment of Optical Transmission Monitoring Apparatus) Next, an optical transmission monitoring apparatus according to a third embodiment will be described. FIG.
FIG. 5A is a diagram showing a configuration of an optical transmission monitoring device according to a third embodiment, and FIGS. 15B and 15C are diagrams of FIG.
It is a figure showing composition equivalent to composition shown in Drawing 5 (a).
FIGS. 15A to 14D show W11 to W14.
FIG. 16 is a diagram showing an optical spectrum of a signal light wavelength band (corresponding to a monitoring light wavelength band) in each unit in FIG.

The optical transmission monitoring device 33 shown in FIG. 15A includes an optical branching element 331 provided on the optical fiber transmission line 42.
A light branching element 332 provided on a branch line through which light separated from the light branching element 331 propagates, and a photodetector 333 optically connected to one of the emission ends of the light branching element 332. A bandpass filter 334 having one end optically connected to the other of the emission ends of the light branching element 332,
A photodetector 335 optically connected to the other end of the bandpass filter 334 and a monitoring unit 336 that uses detection signals from the photodetectors 333 and 335 are provided.

Note that the optical branching element 332 is configured as shown in FIG.
As shown in (b), it may be provided on the optical fiber transmission line 42. In the configuration of FIG. 15 (b), the photodetector 333 is optically connected to the optical branching element 331, and , The band-pass filter 334 is optically connected to the optical branching element 332. On the other hand, the monitoring light wavelength band is composed of the first and second wavelength bands, but the light other than the signal light wavelength band is used as the monitoring light in the first wavelength band or the monitoring light in the second wavelength band. Alternatively, as shown in FIG. 15C, a configuration in which a dichroic mirror 350 is provided on the optical fiber transmission line 42 may be adopted. This FIG.
In the configuration (c), the light detector 335 is optically connected to the dichroic mirror 350, and the light detector 333 is optically connected to the light branching element 331.

Each of the optical branching elements 331 and 332 includes, for example, an optical fiber coupler, etc.
Are separated in the signal light wavelength band including the eight signal lights (λ1 to λ8) transmitted through the optical path. The light detector 333 is
For example, it includes a photodiode or the like, and detects the optical power of the light separated by the optical branching element 331 and passing through the optical branching element 332. The band-pass filter 334 is provided between the optical branching element 332 and the photodetector 335, and four signal lights (λ3 to
It has a function of transmitting light in a wavelength band including λ6).
The light detector 335 includes, for example, a photodiode or the like,
The optical power of the light transmitted through the bandpass filter 334 is detected. The monitoring unit 336 inputs data on the optical power detected by each of the photodetectors 333 and 335, and monitors the transmission state in the signal light wavelength band based on the comparison result of the fluctuation amount of each optical power per unit time. I do.

In the third embodiment, the monitoring light wavelength band coincides with the signal light wavelength band. Light that reaches the optical transmission monitoring device 33 via the optical fiber transmission line 42 is
FIG. 16A shows an output from the optical amplifier 20.
As shown in FIG. 1 (c), the optical amplifier 20
Signal light (λ1 to λ)
In addition to 8), ASE is included as noise light. Most of the light reaching the optical transmission monitoring device 33 is the optical branching elements 331, 33.
2 and is output from the optical transmission monitoring device 33. The spectrum of the light output from the optical transmission monitoring device 33 matches the spectrum of the arriving light (FIG. 16A), as shown in FIG.

Further, a part of the light reaching the optical transmission monitoring device 33 is separated by the optical branching element 331, further passes through the optical branching element 332, and its optical power is detected by the photodetector 333. The light (light in the first wavelength band) received by the photodetector 333 is, as shown in FIG.
ASE is included in addition to the eight signal lights (λ1 to λ8). On the other hand, light in a wavelength band including the four signal lights (λ3 to λ6) separated by the optical branching element 332 reaches the detector 335 via the bandpass filter 334. Photodetector 3
At 35, the optical power of the light passing through the bandpass filter 334 is detected. The light (light in the second wavelength band) received by the photodetector 335 is, as shown in FIG.
In addition to the four signal lights (λ3 to λ6), ASE noise light in the wavelength band of these signal lights is also included. And the monitoring unit 3
At 36, the variation per unit time of the optical power within the first wavelength band detected by the photodetector 333 and the variation per unit time of the optical power within the second wavelength band detected by the photodetector 335 Are compared, and based on the comparison result, the transmission state of the signal light wavelength band that matches the monitoring light wavelength band is monitored.

The mode of this optical transmission monitoring is the same as that described with reference to FIG.

In the optical amplifier 20, it is generally desired that there is no gain deviation for each signal light.
When a WDM signal having a small difference between signal lights is input, the optical amplifier 20 amplifies each signal light uniformly and sends out the amplified light to the optical fiber transmission line 42. In the optical amplifier 20, constant output control (ALC) is performed to maintain each signal light included in the output amplified light at a constant value. This output constant control is performed when the optical power in the signal light wavelength band (corresponding to the monitoring light wavelength band) is determined to fluctuate due to transmission loss fluctuation in the optical fiber transmission line 42 or the like. Is performed by resetting. When a new gain is set in this way, a new gain deviation occurs, and there is a possibility that gains for the respective signal lights will be different from each other (wavelength dependence of the optical amplifier 20). At this time, signal light having uniform optical power is transmitted to the optical amplifier 2.
Even if the signal is input to 0, the optical amplifier 20 outputs amplified light (WDM signal) having a different gain between the signal lights.

FIG. 17 is a diagram showing an output light spectrum of the optical amplifier. As shown in this figure, when the input light power changes, the output light spectrum of the optical amplifier 20 also changes. However, in the signal light wavelength band in which the optical amplifier 20 collectively amplifies the light, the gain at the wavelength near the center is approximately equal to the average gain of the optical amplifier 20 in the signal light wavelength band. Therefore, the optical transmission monitoring device 33 according to the third embodiment sets the first and second wavelength bands around the wavelength at which the gain is substantially equal to the average gain of the optical amplifier 20 in the signal light wavelength band (monitoring light wavelength band). Each is set.

The operation of the optical transmission monitoring device 33 according to the third embodiment will be described below in comparison with the optical transmission monitoring device 31 (FIG. 2A) according to the first embodiment.
FIGS. 18A to 18E are diagrams for explaining the operation of the optical transmission monitoring device 33 according to the third embodiment.
2 shows a spectrum of light output from the optical amplifier 20.

When the optical amplifier 20 has no gain deviation, the rate of change of the optical power P1 of the light existing in the first wavelength band and the rate of change of the optical power P2 of the light existing in the second wavelength band are: Approximately equal (see FIG. 18A). Therefore, in this case, the optical transmission monitoring device 31 according to the first embodiment described above.
However, even in the optical transmission monitoring device 33 according to the third embodiment,
In both cases, it is possible to distinguish between a case where the wave number of the signal light (monitoring light) propagating through the optical fiber transmission line 42 fluctuates and a case where a transmission loss fluctuation or the like occurs in the optical fiber transmission line 42.

However, the optical transmission monitoring device 31 according to the first embodiment is not limited to the case where the wave number of the signal light transmitted through the optical fiber transmission line 42 fluctuates, but also due to the transmission loss fluctuation in the upstream transmission line. Even when a gain deviation occurs in the optical power P20, the optical power P in the first wavelength band (λ1 to λ8)
1 and the change rate of the optical power P2 in the second wavelength band (λ5 to λ8) (FIG. 18B,
FIG. 18 (c)). Therefore, the optical transmission monitoring device 31 according to the first embodiment cannot determine which of the above two cases is the case.

On the other hand, the optical transmission monitoring device 33 according to the third embodiment has the first configuration centering on the wavelength at which the gain is substantially equal to the average gain of the optical amplifier 20 in the signal light wavelength band (monitoring light wavelength band). And the second wavelength band is set, even if a gain deviation occurs in the optical amplifier 20,
The change rate of the optical power P1 in the first wavelength band (λ1 to λ8) and the optical power P in the second wavelength band (λ3 to λ6)
2 become substantially equal (FIG. 18D, FIG. 18).
(E)). Therefore, the optical transmission monitoring device 33 according to the third embodiment determines whether the signal wave number of the signal light transmitted through the optical fiber transmission line 42 fluctuates and the transmission loss fluctuation or the like occurs in the upstream transmission line. It can always be determined.

If the signal light wavelength band or the wave number of the WDM signal changes, the signal light wavelength band substantially matching the average gain of the optical amplifier 20 also changes. The wavelength band is the bandwidth of the signal light wavelength band and W
Preferably, it is set according to the wave number of the DM signal.

FIG. 19A is a diagram showing a configuration of a modification of the optical transmission monitoring apparatus according to the third embodiment, and FIG. 19B is substantially the same as the configuration of FIG. It is a figure which shows the structure equivalently. The difference between the configurations shown in these drawings is that the optical branching element 332 in the optical transmission monitoring device 33A shown in FIG.
On the other hand, in the optical transmission monitoring device 33A shown in FIG. 19B, the optical branching element 332 is provided on the branch line through which the light separated by the light propagates. Is provided on the optical fiber line 42 so as to selectively separate light having a desired wavelength. 20 (a) to 20 (d) show W15 to
It is a figure which shows the optical spectrum in each part in FIG.19 (a) and FIG.19 (b) shown by W18. These modifications include a wavelength selection element 334A separately from the optical transmission monitoring device main body 33A. This wavelength selection element 334A
The optical transmission monitoring device 33A is detachably disposed between the optical branching element 332 and the photodetector 335 of the main body 33A, and can be exchanged according to the wave number of the signal light and the bandwidth of the signal light wavelength band.

When a band-pass filter is applied as the wavelength selection element 334A, FIGS.
The device of the first modification shown in FIG.
The configuration is substantially the same as that of the optical transmission monitoring device 33 shown in FIG. When an optical fiber grating is applied as the wavelength selection element 334A, the light (light existing in the second wavelength band) received by the photodetector 335 is as shown in FIG.
As shown in (c), in addition to the signal lights of the four wavelengths λ1, λ2, λ7, and λ8, ASE in the wavelength band of these signal lights is included. As described above, the optical transmission monitoring device having the configuration shown in FIG. 19A not only has the same operation and effect as the device shown in FIG. There is also an effect that the selected wavelength range of the optical transmission monitoring device can be optimally set without disconnection.

In the optical transmission system to which these modifications are applied, the light output from the optical amplifier 20 is
As shown in FIG. 20A, the optical transmission monitoring device 33A includes an ASE in addition to the signal light (also used as the monitoring light in this embodiment).
While detecting light having a spectrum as shown in FIG. 20B, light similar to that shown in FIG.
(D)).

(First Embodiment of Optical Transmission System) Next, a first embodiment of an optical transmission system to which the optical transmission monitoring device according to the present invention is applied will be described. FIG. 21 is a diagram showing a part of the configuration of an optical transmission system to which the optical transmission monitoring device according to the present invention is applied, and FIGS.
FIG. 22 is a diagram showing a spectrum of light in each part of the optical transmission system shown in FIG. 21.

The optical transmission system according to the first embodiment shown in FIG. 21 comprises an optical amplifier 21, an optical ADM 50, an optical amplifier 2
2, an optical amplifier 23, an optical transmission monitoring device 30, and an optical amplifier 24 are sequentially connected in cascade via optical fiber transmission lines 41 to 47. Here, the optical amplifiers 21 and 2
2. The first relay station 1 is configured by the optical ADM 50, the receiver 61, and the transmitter 11, and the second relay station 2 is configured by the optical amplifiers 23 and 24 and the optical transmission monitoring device 30. Each of the first and second relay stations 1 and 2 has an optical amplifier stage configuration. In this figure, a point Wa is a point near the input terminal of the optical amplifier 21 of the first relay station 1, a point Wb is a point near the output terminal of the optical amplifier 22 of the first relay station 1, and a point Wc is the second relay. This is a point near the input terminal of the optical amplifier 23 of the station 2.

The optical amplifiers 21 to 24 are optical components that amplify and output the input light, respectively,
When a DM signal is input, it is collectively optically amplified. The optical transmission monitoring device 30 is disposed between the optical amplifier 23 and the optical amplifier 24. The optical ADM 50 is disposed between the optical amplifier 21 and the optical amplifier 22,
1 and the optical amplifier 22, and is optically connected to the receiver 61 and the transmitter 11.

The optical ADM 50 has an optical coupler 501,
502 and an optical fiber grating 503. The optical coupler 501 includes eight signal lights (λ1 to λ) that have arrived from the optical amplifier 21 via the optical fiber transmission line 42.
8), and the four signal lights (λ1 to λ4) are
1 and output the remaining four signal lights (λ
5 to λ8) are output to the optical fiber grating 503. The optical fiber grating 503 transmits the four signal lights (λ5 to λ8) from the optical coupler 501 and blocks the four signal lights (λ1 to λ4).
The optical coupler 502 multiplexes the four signal lights (λ5 to λ8) from the optical fiber grating 503 and the new four signal lights (λ1 to λ4) output from the transmitter 11. This mixed light is guided to the optical amplifier 22 via the optical fiber transmission line 43.

In this optical transmission system, eight signal lights (λ 1 to λ 8) input to the optical amplifier 21 via the optical fiber transmission line 41 are collectively optically amplified by the optical amplifier 21 and transmitted through the optical fiber transmission line 42. The light is then guided to the ADM 50. The eight signal lights (λ1 to λ) that have reached the optical ADM 50
8), four signal lights (λ1 to λ4) are received by the receiver 61 via the optical coupler 501, and the remaining four signal lights (λ5 to λ8) are converted into the optical coupler 501 and the optical fiber grating 503. Is input to the optical coupler 502. Then, in the optical coupler 502, the four signal lights (λ5 to λ8) and the four signal lights (λ1 to λ4) newly output from the transmitter 11 are multiplexed.

The eight signal lights (λ 1 to λ 8) output from the optical coupler 502 of the optical ADM 50 propagate through the optical fiber transmission line 43 and are collectively optically amplified at a predetermined gain in the optical amplifier 22. The amplified signal light propagates through the optical fiber transmission line 44 and is further amplified by the optical amplifier 23 with a predetermined gain. The eight signal lights (λ1 to λ8) output from the optical amplifier 23 are input to the optical transmission monitoring device 30 via the optical fiber transmission line 45. Monitor the status of optical transmission. On the other hand, eight signal lights (λ1 to λ1) excluding light used for monitoring
λ8) is the optical monitoring device 30 and the optical fiber transmission line 46.
After passing through the optical amplifier 24, the optical amplifier 24 collectively amplifies the light with a predetermined gain and outputs the amplified light to the optical fiber transmission line 47.

As shown in FIG. 22A, the light reaching the input point Wa of the first relay station 1 is composed of eight signal lights (λ1 to λ8) having substantially the same power level and signal light. Includes ASE that exists throughout the wavelength band. Assuming that the optical transmission system is normal, the light at the output point Wb of the first relay station 1 has eight signal lights (about the same level) as shown in FIG. λ1 to λ8) and an ASE in a band defined by wavelengths λ5 to λ8. At this time, the reason that the ASE in the band defined by the wavelengths λ1 to λ4 is not included is that the light in this wavelength band is transmitted to the receiver 61 by the optical coupler 501 of the optical ADM 50 and cut off by the optical fiber grating 503. Because it is done.
Similarly, light reaching the input point Wc of the second relay station 2
As shown in FIG. 22C, eight signal lights (λ1 to λ8) having substantially the same power level and wavelengths λ1 to λ
4 includes the ASE of the band specified in FIG.

However, when the transmission loss increases upstream of the point Wa, the light reaching the point Wa is
As shown in FIG. 2 (d), the signal power includes eight signal lights (λ1 to λ8) having substantially the same power level and ASE existing in the entire signal light wavelength band. The total optical power is lower than that of FIG. When the optical amplifiers 21 and 22 perform a constant gain operation at a predetermined gain, the light at the point Wb is output as shown in FIG.
As shown in (e), in the wavelength band of wavelengths λ1 to λ4, it consists of only four signal lights (λ1 to λ4) having the same optical power as the normal optical power (see FIG. 22B). In the bands of wavelengths λ5 to λ8, the optical power is lower than that in the normal case (see FIG. 22B). This is because while the light in the wavelength band of wavelengths λ5 to λ8 passing through the optical ADM 50 is affected by the increase in the transmission loss upstream of the point Wa and the optical power is reduced, the wavelength inserted by the optical ADM 50 is reduced. This is because light in the wavelength band of λ1 to λ4 is not affected by the transmission loss. Similarly,
As shown in FIG. 22 (f), the light that has reached the point Wc has the same optical power as the normal optical power (see FIG. 22 (c)) in the band defined by the wavelengths λ1 to λ4. Wave signal light (λ1 to λ4) only, wavelength λ5 to λ5
In the band defined by λ8, the optical power is lower than that in the normal case (see FIG. 22C).

The optical ADM output from the transmitter 11
When the optical power of the four signal lights (λ1 to λ4) to be multiplexed by the 50 optical couplers 502 decreases due to the failure of the transmitter 11 or the optical coupler 502, the light at the point Wb and the point Wc are changed to The light that has arrived is shown in FIG.
As shown in FIG. 22, in the band defined by the wavelengths λ1 to λ4, the optical power in the normal case (FIG.
(C), and the same optical power as the normal optical power (see FIGS. 22 (b) and 22 (c)) in the band defined by the wavelengths λ5 to λ8. (4) signal light (λ1 to λ4) and ASE. When the transmission loss increases between the point Wb and the point Wc, the light reaching the point Wb
As shown in (h), the light power is lower than the light power in the normal case (FIG. 22 (c)).

As described above, when the transmission loss increases upstream of the point Wa, the optical power of the four signal lights (λ1 to λ4) to be inserted in the optical ADM 50 is reduced, and the distance between the point Wb and the point Wc is reduced. In each of the transmission loss increases, even if the total optical power of the light reaching the point Wc is substantially the same, the optical power change rate of the light in the band defined by the wavelengths λ1 to λ4 and the wavelength λ5 to λ8 The rate of change of the optical power of the light in the band is different from each other.

That is, when the transmission loss increases upstream of the point Wa, the change in the optical power in the band defined by the wavelengths λ5 to λ8 of the light reaching the point Wc is larger at the wavelengths λ1 to λ4. It is larger than the change in optical power in the specified band (see FIG. 22 (f)). When the optical power of the signal light (λ1 to λ4) of four wavelengths to be inserted in the optical ADM 50 decreases, the change in the optical power in the band defined by the wavelengths λ1 to λ4 of the light reaching the point Wc. But,
It is larger than the optical power change in the band defined by the wavelengths λ5 to λ8 (see FIG. 22 (g)). Also, the point Wb and the point Wc
When the transmission loss increases between the wavelengths λ1 to λ4, the change in the optical power in the band defined by the wavelengths λ1 to λ4 of the light reaching the point Wc is substantially equal to the change in the optical power in the band defined by the wavelengths λ5 to λ8. (See FIG. 22 (h)).

Therefore, the optical transmission monitoring device 30 provided in the second relay station 2 is capable of controlling the optical power change in the band defined by the wavelengths λ1 to λ4 and the optical power change in the band defined by the wavelengths λ5 to λ8. Are compared, based on the comparison result, in which region in the optical transmission system transmission loss increased,
It can be determined whether the insertion of the four signal lights (λ1 to λ4) in the optical ADM 50 is normal or not, or whether the wave number has changed. Then, the optical transmission monitoring device 30
Controls the gains of the optical amplifiers 23 and 24 based on the monitoring result.

(Second Embodiment of Optical Transmission System) Next, a second embodiment of the optical transmission system to which the optical transmission monitoring device according to the present invention is applied will be described. FIG. 23A is a configuration diagram of an optical transmission system to which the optical transmission monitoring device according to the present invention is applied, and FIGS. 23B to 23D show W1.
It is a figure which shows the optical spectrum in each part in FIG.23 (a) shown by 9-W21. FIGS. 24A and 24B are diagrams showing the configuration of each relay station shown in FIG.

[0094] The optical transmission system shown in FIG. 23 (a), the transmitter 10 and the relay station 1 _j is the optical fiber transmission line 40
j, and each relay station 1 _j includes at least an optical amplifier (j = 0, 1, 2,...).
The transmitter 10 and the relay station 1 ₀ are connected through the optical fiber transmission line 40 _0, are connected via an optical fiber transmission path 40 _j to the relay station 1 _j-1 and the relay station 1 _j (J = 0,
1, 2, 3, ...). Here, each optical fiber transmission line 40 _j
P _{a, j,} output terminals of the relay station 1 _j the optical power of the input light at the input end of the transmission loss alpha _j, the optical amplification gain in each relay station apparatus 1 _j G _{t, j,} each relay 1 _j in _Let P _{d, j} be the optical power of the output light at. Between these parameters,
If ASE is not considered, there is a relationship represented by the following equations (1) and (2).

Α _j = P _{a, j} / P _{d, j-1} (1) G _{t, j} = P _{d, j} / P _{a, j} (2) However, in practice, ASE is transmitted from each relay station. Output (Fig. 2
3 (b)), the ASE is optically amplified by the next-stage relay station, and a new ASE generated in the relay station is also added (see FIG. 23 (b)). Then, the added ASE is further optically amplified by the next-stage relay station, and an ASE newly generated at the relay station is added (see FIG. 23D). Considering the occurrence of such an ASE, a relationship expressed by the following equation (3) is established between the parameters instead of the equation (2).

P _{d, j} = G _{t, j} · (K + P _{a, j} ) (3) where K is proportional to the optical amplification bandwidth and the noise figure in the optical amplifier in the relay station, respectively, and Is a value that depends on the optical power of

[0097] As shown in FIG. 24 (a), an optical amplifier 101, as follows, if the optical transmission monitoring apparatus 130, and optical amplifier 102 are cascaded to the relay station 1 _j is constituted . The light power is set to P _{b, j} at the output of the previous amplifier 101, to the optical power at the input of the subsequent stage of the optical amplifier 102 P _c, and _j. Further, the transmission loss of the transmission path from the output terminal of the optical amplifier 101 at the preceding stage to the input terminal of the optical amplifier 102 at the _subsequent stage is α _{thru, j} , the optical amplification factor of the optical amplifier 101 at the preceding stage is G _{b, j} , The optical amplification factor of the subsequent optical amplifier 102 is defined as G _{c, j} . At this time, the optical amplification gain G _{t, j} in each relay station 1 _j is represented by the following equation (4).

G _{t, j} = G _{b, j} · α _{thru, j} · G _{t, j} (4) As shown in FIG. 24B, the optical amplifier 101 and the light A
DM 150, optical transmission monitoring device 130, and optical amplifier 10
If the 2 cascaded with repeater 1 _j is formed is as follows. Here, the optical ADM 150 includes the optical couplers 103 and 105 and the optical fiber grating 1.
04. Further, the relay station 1 _j is connected to the optical ADM 15
0 and a receiver 106 and a transmitter 107 connected thereto. It is assumed that the optical power of the output light at the output terminal of the optical amplifier 101 at the preceding stage is P _{b, j} , and the optical power of the input light at the input terminal of the optical amplifier 102 at the subsequent stage is P _{c, j} . Further, the transmission loss of the transmission path from the output terminal of the optical amplifier 101 in the preceding stage to the input terminal of the optical amplifier 102 in the subsequent stage through the optical coupler 103, the optical fiber grating 104, and the optical coupler 105 in order is α _{thru, j} , The optical amplification factor of the optical amplifier 101 at the preceding stage is G _{b, j} , and the optical amplification factor of the optical amplifier 102 at the subsequent stage is G _{c, j} . Again, the optical amplification gain G _t in each relay station 1 _{j, j}
Is represented by the above equation (4).

In the case of the relay station shown in each of FIGS. 24 (a) and 24 (b), the optical transmission monitoring device 130 operates in the first and second wavelength bands different from each other in the signal light wavelength band. The optical power is detected, the optical power change in the first wavelength band is compared with the optical power change in the second wavelength band, and the upstream optical transmission state is monitored based on the comparison result. Here, as shown in FIG. 24 (b), when the light ADM150 is provided in the relay station 1 _j, it is one of the first and second wavelength band,
It is preferable that the wavelength band includes the signal light extracted or added by the optical ADM 150.

In each of the relay stations shown in FIGS. 24A and 24B, the fluctuation of the transmission loss α _j of the optical fiber transmission line 40 _j and the fluctuation of the wave number of the transmitted signal light are reduced. , Are detected by the optical transmission monitoring device 130. The optical transmission system is transmitted by setting the reciprocal of the transmission loss α _j in the optical fiber transmission line 40 _j in the preceding section in the optical amplification gain G _{t, j} of each relay station 1 _j based on the detection result. WD
The total optical power of the M signal is kept equal to each other at the output terminal of each relay station 1 _j . The target optical power of the output light of each relay station 1 _j is obtained by multiplying the product of the optical power Pa _{, j} of the input light and the optical amplification gain G _{t, j} by the AS generated at the relay station 1 _j.
This is set by adding the optical power of E.

Next, the specific configuration and operation of the optical transmission system according to the second embodiment will be described with reference to FIGS. 25 and 26 (a).
26 (h) (part 1), FIGS. 27 and 28 (a)
FIG. 28 (h) (part 2), and FIGS. 29 and 28
This will be described with reference to FIGS.

FIG. 25 and FIG. 27 correspond to FIG.
The relay station 1 and the relay station 2 having the configuration shown in FIG.
Optical transmission system connected via fiber transmission line 40
Is shown. 26 (a) to 26 (h).
Is the ground near the input end of the relay station 1 in the preceding stage in FIG.
Optical power P at point W22_w22, In the preceding relay station 1
At a point W23 near the output terminal of the pre-stage optical amplifier 101
Optical power P_w23, A post-stage optical amplifier 1 in the pre-stage relay station 1
02 at the point W24 near the input end
P_{w2 Four}, And a point W25 near the output end of the pre-stage repeater 1.
Optical power P_w25Each time change is shown
And a point W26 near the input end of the relay station 2 at the subsequent stage.
Optical power P at_w26, The upstream optical amplifier in the downstream relay station 2
Optical power at a point W27 near the output end of the band 201
P_w27Input of the post-stage optical amplifier 202 in the post-stage relay station 2
Optical power P at point W28 near the end_w28And later
Power at a point W29 near the output end of the repeater 2 of FIG.
P_w29Each time change is shown. FIG.
8 (a) to FIG. 28 (h) similarly show W3 in FIG.
Optical power P at each part indicated by 0 to W37_w30~ P_w37
Is shown over time.

FIGS. 26 (a) to 26 (h) and FIG.
In each of the graphs showing the time variations of the optical power in (a) to FIG. 28 (h), the hatched portions indicate four-wave signals that are extracted or added by the optical ADMs 150 and 250 in each relay station. Indicates the optical power of the band defined by the light (λ1 to λ4). In the optical transmission system shown in FIG. 25, a point W2 in the preceding relay station 1
Optical transmission monitoring devices 130 and 230 are provided at the point W28 in the relay station 4 and the relay station 2 at the subsequent stage, respectively. FIG.
In the optical transmission system shown in FIG. 7, optical transmission monitoring devices 130 and 230 are provided at a point W32 in the upstream relay station 1 and a point W36 in the downstream relay station 2, respectively.

In the optical transmission system shown in FIG. 25, eight signal lights (λ1 to λ8) to be input to the repeater 1 in the preceding stage.
Will be described at the time t1 due to an increase in the transmission loss of the upstream optical fiber transmission line. In this case, the optical power P _w22 at the point W22 of the preceding repeater 1 decreases after the time t1. Point W
Light power P in 23 _w23 are those multiplied by the signal light gain of the optical amplifier 101 to the optical power P _w22 at the point W22, although decreases at time t1, the output constant control (AL
C) The optical amplifier 101 gradually increases after time t1.

Of the optical power P _w24 at the point W24, the optical power in the band where the four signal lights ( _{λ1 to λ4} ) exist is cut off by the optical fiber grating 104, but is newly output from the transmitter 107. The added signal light is substantially constant since the added signal light is added, whereas the optical power of the band in which the four signal lights (λ5 to λ8) are present decreases at time t1 and gradually increases after time t1. To go. Optical power P at point W25
_w25 is an optical amplifier 1 at the optical power P _w24 at the point W24.
02 multiplied by the signal light gain, and gradually increases after time t1 by the optical amplifier 102 whose output is controlled to be constant.

However, the optical transmission monitoring device 130 provided at the point W24 in the preceding relay station 1
When it is detected that the optical power of the wave signal light (λ1 to λ8) has decreased, the signal transmission gain of each of the optical amplifiers 101 and 102 is controlled by the optical transmission monitoring device 130. Thus, after time t2 (> t1) when the signal light gain is controlled, the output light of the optical amplifier 101 becomes almost zero, and the four signal lights (λ1 to λ4) output from the optical amplifier 102 are output.
Each optical power is maintained at substantially the same value as before time t1.

[0107] The optical power P _w26 at the point W26 in the subsequent stage of the relay station 2 is a value obtained by multiplying the transmission loss of the optical fiber transmission line 40 with respect to the optical power P _w25 at the point W25.
Optical power P _W27 at a point W27 becomes a value obtained by multiplying the signal light gain of the optical amplifier 201 to the optical power P _w26 at the point W26, although decreases in time t1, after the time t1 by the optical amplifier 201 that is output constant control It gradually increases.

Of the optical power P _w28 at the point W28, the optical power in the band where the four signal lights ( _{λ1 to λ4} ) exist is cut off by the optical fiber grating 204, but is newly output from the transmitter 207. It is substantially constant because the added signal light is added. On the other hand, the optical power of the band in which the four signal lights (λ5 to λ8) are present decreases at time t1, and gradually increases after time t1. Optical power P _W29 at a point W29 becomes a value obtained by multiplying the signal light gain of the optical amplifier 202 to the optical power P _W28 at the point W28, after the time t1 by the optical amplifier 202 that is output constant control is gradually increased.

However, when the optical transmission monitoring device 230 provided at the point W28 in the relay station 2 at the subsequent stage detects a decrease in the wave number of the signal light at time t1, the optical amplifiers 201 and 20 are turned off.
The signal light gain of each of the two is controlled. Thus, after time t2 (> t1) when the signal light gain is controlled, the optical power of each of the four signal lights (λ1 to λ4) output from each of the optical amplifier 201 and the optical amplifier 202 is substantially the same as before time t1. It is kept the same.

In the optical transmission system shown in FIG. 27, all four signal lights (λ1 to λ44) to be added by the optical ADM 150 in the relay station 1 in the preceding stage all transmit at time t1 due to a failure of the transmitter 107 or the like. A case in which no input is made will be described. In this case, the points W30 and W
The optical powers P _w30 and P _w31 at the time 31
It is substantially constant before and after 1.

Of the optical power P _w32 at the point W32, the optical power in the band where the four signal lights (λ1 to λ4) exist is cut off by the optical fiber grating 104, and after time t1, the transmitter 107 Since the signal light output from is not newly added, it becomes substantially zero. On the other hand, the optical power of the band in which the four signal lights (λ5 to λ8) exist is substantially constant before and after time t1. Optical power P at point W33
_w33 is an optical amplifier 1 at the optical power P _w32 at the point W32.
The value is a value obtained by multiplying the signal light gain of No. 02 by a signal light gain. The value is reduced by the decrease in the wave number generated at time t1, but is gradually increased after time t1 by the optical amplifier 102 whose output is controlled to be constant.

However, when the optical transmission monitoring device 130 provided at the point W32 in the preceding relay station 1 detects that the wave number has changed at the time t1, the optical amplifier 101,
The signal light gain of each of the optical transmission monitoring devices
Is controlled by Thus, after time t2 (> t1) when the signal light gain is controlled, the intensity of each of the four wavelengths .lambda.5 to .lambda.8 output from the optical amplifier 202 is maintained at substantially the same value as before time t1.

[0113] The optical power P _W34 at the point W34 in the subsequent stage of the relay station 2 is a value obtained by multiplying the transmission loss of the optical fiber transmission line 40 with respect to the optical power P _w33 at the point W33.
Point light power P _W35 in W35 becomes a value obtained by multiplying the signal light gain of the optical amplifier 201 to the optical power P _W34 at the point W34, although temporarily lowered by the wave number decreases occurring at time t1, the output level control light amplifier Due to 201, it gradually increases after time t1.

Optical power P at point W36_w36Horse
That is, the optical path of the band in which four signal lights (λ1 to λ4) exist.
Power is determined by the optical fiber grating 204.
Is interrupted, but the signal newly output from the transmitter 207 is interrupted.
Since the light is added, it is substantially constant. On the other hand, four waves
Optical power in the band where the signal light (λ5 to λ8)
Then, after time t1, it gradually increases. Point W3
Power P at 7_{w3 7}Is the light intensity at point W36.
Word P_w36Multiplied by the signal light gain of the optical amplifier 202
At time t by the optical amplifier 202 whose output is controlled to be constant.
From 1 onwards, the signal light of four waves (λ1 to λ4) gradually increases
And the remaining signal light (λ5 to λ8)
Gradually increases.

However, the optical transmission monitoring device 230 provided at the point W36 in the relay station 2 at the subsequent stage
When it is detected that the optical power of the wave signal light (λ1 to λ4) does not fluctuate and the optical power of the remaining signal light (λ5 to λ8) is increased, the signal light gain of each of the optical amplifiers 201 and 202 is increased. Controlled. Thus, after time t2 (> t1) when the signal light gain is controlled, eight wave signal lights (λ1
~ Λ8) Each optical power is maintained at substantially the same value as before time t1.

FIG. 29 shows that the relay station 1 having the structure shown in FIG.
0 is an optical transmission system connected to the system. FIGS. 30 (a) to 30 (h) _show the optical power P _w38 at the point W38 near the input terminal of the preceding relay station 1 and the pre-optical amplifier 10 in the preceding relay station 1 in FIG.
1, the optical power P _w39 at a point W39 near the output end,
Is a graph showing the respective time changes the optical power P _w41 at the light power P _W40, and the previous stage of the output point in the vicinity W41 relay station 1 at the input point in the vicinity W40 of the rear-stage optical amplifier 102 in the preceding stage in the repeater station 1 Further, the optical power P _w42 at a point W42 near the input terminal of the _subsequent relay station 3 and the pre-optical amplifier 30 in the rear-stage relay station 3 are shown.
1, the optical power P _w43 at a point W43 near the output end,
It is a graph showing the respective time changes the optical power P _W45 in the optical power P _W44, and the subsequent output point near W45 of the relay station 3 at the input point in the vicinity W44 of the rear-stage optical amplifier 302 in the subsequent stage in the repeater station 3 It is shown. In each of the graphs showing the time change of the optical power, the hatched portions indicate four signal lights (λ1) extracted or added by the optical ADM 150 in the relay station 1.
~ Λ4) represents the optical power of the band in which it exists. An optical transmission monitoring device 130 is provided at a point W40 in the relay station 1 at the preceding stage.

In the optical transmission system shown in FIG. 29, the operation of the preceding relay station 1 is the same as the operation of the preceding relay station 1 in the optical transmission system shown in FIG.

[0118] The optical power P _W42 at the point W42 in the subsequent stage of the relay station 3, a value obtained by multiplying the transmission loss of the optical fiber transmission line 40 with respect to the optical power P _w41 at the point W41.
Optical power P _W43 at a point W43 becomes a value obtained by multiplying the signal light gain of the optical amplifier 301 to the optical power P _W42 at the point W42, although decreases in time t1, after the time t1 by the optical amplifier 301 that is output constant control It gradually increases.

[0119] The optical power P _W44 at a point W44 is the value obtained by multiplying the transmission loss between the optical amplifiers 301 and an optical amplifier 302 to the optical power P _W43 at the point W 43. Optical power P _W45 at a point W45 is the value obtained by multiplying the signal light gain of the optical amplifier 302 to the optical power P _W44 at the point W 44, once reduced at time t1, then, the output level controlled light amplifier 302 It gradually increases and approaches a predetermined value. Further, it decreases at time t2 and thereafter gradually increases again by the optical amplifier 302 whose output is controlled to be constant, and gradually approaches a predetermined value.

As described above, when the optical transmission monitoring device is not provided in the relay station, the total optical power of the light output from the relay station is kept constant, but the optical power is output from the relay station. The optical power of each signal light of each wavelength is not constant. However, changes in the optical power of each of the first and second wavelength bands different from each other in the monitoring light wavelength band (coincident with the signal light wavelength band in this embodiment) using the optical transmission monitoring device provided in each relay station. The transmission state is monitored by comparing the rates, and the wave number fluctuation and the transmission loss fluctuation are identified based on the monitoring result. As described above, the optical transmission monitoring device according to the present invention appropriately controls the signal light gain of the optical amplifier in the relay station according to the case of the wave number fluctuation and the case of the transmission loss fluctuation, so that the output from each relay station is The optical power of each signal light of each wavelength is maintained constant. (Fourth Embodiment of Optical Transmission Monitoring Apparatus) In the optical transmission monitoring apparatus according to each of the above-described embodiments, in monitoring the change in the wave number, a signal light is used as the monitoring light, and the group of the monitoring light is a monitoring light wavelength band. This is possible when signal light increases or decreases in one of the first wavelength band and the second wavelength band.
However, the first wavelength band and the second
When the signal light having the same wave number increases and decreases over the wavelength band, the optical power fluctuates similarly in any wavelength band, and thus is erroneously recognized as a loss fluctuation in the optical transmission line. The optical transmission monitoring device according to the fourth embodiment has a structure that solves the above problems. That is, the optical transmission monitoring device monitors the state of the upstream optical transmission by using light of another wavelength in addition to the signal light.

The optical transmission monitoring apparatus according to the fourth embodiment uses light having a wavelength different from that of the signal light as a part of the monitoring light as described above. The limitation on the wavelength selection of the signal light added / extracted upstream that occurs can be avoided. Also, as compared with the conventional case where the transmission loss or the like is monitored based only on the level fluctuation of the monitoring light prepared separately from the signal light,
Even if a level change occurs in the light source itself that supplies the monitoring light, it is necessary to distinguish between the level change caused by the loss change in the transmission path and the level change caused by the light source without separately providing a means for reporting the presence or absence of the change. Becomes possible. Further, according to the fourth embodiment, even if transmission of the signal light wavelength band (transmission of signal light) is interrupted, the level fluctuation of the separately prepared monitoring light is regarded as the level fluctuation of the optical transmission line. Thus, there is an advantage that the monitoring of the transmission state can be continued.

FIG. 31A is a diagram showing the configuration of an optical transmission system to which the optical transmission monitoring device according to the fourth embodiment is applied. In this optical transmission system, the signal lights S having different wavelengths output from the transmitter 10 reach the optical amplifier 20 via the optical fiber transmission line 41. The optical amplifier 20 collectively amplifies the input signal light S and collectively amplifies the light in the signal light wavelength band (as described in the above embodiments, the amplified light includes the signal light S and the other light). Noise light N such as ASE) is transmitted through the optical fiber transmission line 42 and reaches the optical transmission monitoring device 30. In the optical transmission line between the optical amplifier 20 and the optical transmission monitoring device 30, a new monitoring light M having a wavelength band different from the signal light wavelength band used as a part of the monitoring light is transmitted through the optical fiber transmission line. The monitoring light (hereinafter referred to as M light) so that it can be supplied to the optical transmission monitoring device 30 via the path 42.
And a multiplexer 40 for multiplexing the M light and light in the signal light wavelength band (hereinafter referred to as (S + N) light).
0 is provided. An optical amplifier 25 whose gain is controlled by the optical transmission monitoring device 30 is provided downstream of the optical transmission monitoring device 30. The amplified light output from the optical amplifier 25 is sent to the optical fiber transmission line 43.

The optical transmission monitoring device 30 according to the fourth embodiment differs from the optical transmission monitoring devices of the above-described embodiments in that at least three types of light (light components included in each other) are monitored in the monitoring light wavelength band. ) Is monitored while monitoring the upstream optical transmission state while detecting optical power fluctuations.

That is, in the fourth embodiment, FIG.
As shown in (b), light in the signal light wavelength band is used as light in the first wavelength band of the monitoring light wavelength band,
Light (light supplied by the light source 601) propagating in the optical transmission path separately from the signal light is used as light in the second wavelength band. The optical transmission monitoring device 30 further includes a third detector that detects at least the optical power of light including ASE in the first wavelength band. Thereby, the optical transmission monitoring device uses the first detector to detect the optical power of the first light including the monitoring light (signal light) in at least the first wavelength band (the first power).
ASE in the wavelength band), the second detector detects the optical power of the second light including the monitoring light in at least the second wavelength band, and the third detector detects at least the first wavelength. The optical power of the third light including the ASE in the band is detected. The monitoring unit is configured to determine an optical power fluctuation amount per unit time for the first light obtained by the first detector, an optical power fluctuation per unit time for the second light obtained by the second detector, The optical power fluctuation amount per unit time of the third light obtained by the three detectors is compared, and the cause of the optical power fluctuation in the optical transmission line is identified based on the comparison result.

Specifically, in the optical transmission monitoring device 30 according to the fourth embodiment, an optical fiber transmission line 4
2 (including the signal light S, the newly supplied monitoring light M, and the noise light N such as ASE generated in the optical amplifier 20) used for monitoring the transmission state. Is done. Part of the separated light (light including signal light S, noise light N, and monitoring light M; hereinafter, (S + N + M)
Light or T light) is converted into an electric signal by the photoelectric conversion element 603, and a part of the
The light is separated into the monitoring light M (hereinafter, referred to as M light) and the signal light S (hereinafter, referred to as (S + N) light) including the M light by 04. In the configuration of FIG. 31A, the light separated from the optical fiber transmission line is T light (at least ASE in the first wavelength band).
), (S + M) light (at least the first light
It is separated into M light (corresponding to a second light including at least the monitoring light in the second wavelength band) and M light (corresponding to the first light including the monitoring light in the wavelength band). The monitoring unit monitors the light transmission state using the information on each light. 32 (a) to 32
FIG. 32C is a diagram showing optical components that are optically or electrically separated and to be monitored, and FIG.
The monitor light (M light) of the second wavelength band separated from the light of the monitor light wavelength band shown in (b), and FIG. 31 (b) is the ASE (N light) separated from the light of the first wavelength band. , FIG. 32 (c)
FIG. 3 is a diagram showing signal intensities of T light, M light, and S light converted into electric signals, respectively. However, each optical component is separated by frequency decomposition, and a unique code component (C
m, Cs) may be added in advance and detected.

The signal light wavelength band (including (S + N) light) is set as the first wavelength band of the monitoring light wavelength band, and the wavelength band containing M light is set as the second wavelength band of the monitoring light wavelength band. (See FIG. 31 (b)), monitoring using two types of light, M light in the second wavelength band and (S + N) light in the first wavelength band, detects loss fluctuation on the transmission line. Optical amplifier 2 located upstream
It is not possible to distinguish between a case where a uniform level fluctuation of the signal occurs due to a gain fluctuation of 0 and a case where the wave number of the S light changes. In the fourth embodiment, attention is paid to the fact that ASE (N light) included in the signal light wavelength band does not change even when the wave number of the signal light (S light) changes, and further, the ASE (N light) is monitored. The optical transmission state is monitored by detecting optical power fluctuations of three types of light components including N light within the first wavelength band of the band. Therefore, the first light detected by the first detector only needs to include at least the monitoring light (signal light) in the first wavelength band, and is the T light as described with reference to FIG. May also be the (S + N) light.

Next, the monitoring operation of the optical transmission monitoring apparatus according to the fourth embodiment will be described with reference to FIGS. 33 (a) to 33 (d) (the horizontal axis represents time t, and the vertical axis represents signal strength). . In the following description, for simplicity, the first detector detected by the first detector will be described.
The light is only monitoring light (S light) in the first wavelength band, and the second light detected by the second detector is monitoring light (M light) in the second wavelength band.
Only, and the third light detected by the third detector is only ASE (N light) in the first wavelength band. In addition, FIG.
In FIG. 33D, the solid line indicates the S optical signal intensity (or (S +) in the first wavelength band detected by the first detector.
N) may be signal intensity of light or T light).
The dashed line indicates the time variation of the M optical signal intensity in the second wavelength band detected by the second detector, and the dashed line indicates the time variation of the N optical signal intensity in the first wavelength band detected by the third detector. ing.

First, as shown in FIG. 33 (a), in the time zone D1, when a change in the signal intensity is detected for any of the S light, the M light, and the N light, the change is detected on the upstream optical transmission line. It is determined that a loss fluctuation has occurred. Also,
As shown in FIG. 33 (b), in the time zone D2,
Fluctuations in signal intensity were detected for S light and N light,
If no change in signal intensity is detected for light (that is, a change in optical power is detected only in the first wavelength band), it is determined that an output change has occurred in the upstream optical amplifier 20.

Further, as shown in FIG.
In the time zone D3, a change in the signal intensity is not detected for the S light and the N light, while a change in the signal intensity is detected for the M light, a loss-dependent change in wavelength occurs in the upstream optical transmission line. It is determined that this has occurred. In addition,
In order to minimize the influence of the wavelength-dependent loss fluctuation, it is preferable that the wavelength of the monitoring light in the second wavelength band is set near the first wavelength band in which the signal light as the monitoring light exists. Specifically, the signal light of the first wavelength band is 1.55 μm.
When the light is in the m wavelength band, the monitoring light in the second wavelength band is
Preferably, the light is in the 1.51 μm wavelength band, the 1.48 μm wavelength band, or the 1.60 μm wavelength band.

As shown in FIG. 33D, in the time zone D4, a change in the signal light intensity is detected for the S light, and a change in the signal light intensity is detected for the other M light and N light. If there is no such change, it is determined that there is a change in the wave number of the signal light propagating at the time when the change in the S light signal intensity occurs.

The structure of the optical transmission monitoring apparatus according to the fourth embodiment is not limited to the structure shown in FIG. 31 (a), but is shown in FIGS. 34 (a) and 34 (b). As shown, various modifications are possible.

FIG. 34A is a diagram showing the configuration of a first modification of the optical transmission monitoring device according to the fourth embodiment. The optical transmission monitoring device 30 shown in FIG. In, a part separated from the T light (including the S light, the M light, and the N light) transmitted through the optical fiber transmission line by the optical branching element 602 is used for monitoring the transmission state. The separated T light is further divided into S light and (M
+ N) light and separated into photoelectric conversion elements 606 and 6 respectively.
07 is converted into an electric signal. Further, the (M + N) light is further separated into an M light and an N light ((M + N) light) including the M light by the electrical separation device 608.
Also in the first modified example, the monitoring unit includes a first light (detected by the first detector) including at least the S light in the first wavelength band and a second light (detected by the first detector) including the M light in the second wavelength band. Detected by a second detector), and at least the first
The optical transmission state is monitored using information on light including N light (detected by the third detector) included in the wavelength band.

FIG. 34B is a diagram showing the configuration of a second modification of the optical transmission monitoring apparatus according to the fourth embodiment.
In the optical transmission monitoring device 30 shown in FIG. 4B, T which has been propagated through the optical fiber
From light (including S light, M light and N light) to (M + N)
The light is separated, and the light splitting element 611 is used to split the light.
Only the S light is separated from the T light passing through 0. Further, the separated S light is converted into an electric signal by the photoelectric conversion element 613. On the other hand, the separated (M + N) light is converted into an electric signal by the photoelectric conversion element 612, and further separated into M light and N light ((M + N) light) including the M light by the electric conversion device 614. Is done. The monitoring unit is an optically or electrically separated S light, (M + N)
The optical transmission state is monitored using information on the light and the M light.

(Fifth Embodiment of Optical Transmission Monitoring Apparatus) Next, a fifth embodiment of the optical transmission monitoring apparatus according to the present invention will be described. The fifth embodiment differs from the fourth embodiment in that the signal light for one channel in the signal light wavelength band is used as pilot light.

That is, in the fifth embodiment, the light in the signal light wavelength band corresponds to the light in the monitor light wavelength band, includes one channel of pilot light, and is included in the signal light wavelength band. Corresponds to the second wavelength band (FIG. 5 (c)).
As shown in FIG. 35B, the monitoring light wavelength band is set so that the second wavelength band is included in the first wavelength band. The monitoring unit obtains the optical power fluctuation amount per unit time obtained for the signal light and the noise light as the monitoring light in the first wavelength band and the pilot light as the monitoring light in the second wavelength band. The optical power fluctuation per unit time is compared, and the cause of the optical power fluctuation in the optical transmission line is identified based on the comparison result. In the fifth embodiment, preferably, the optical transmission monitoring device includes at least one signal light selected from signal lights in a wavelength band overlapping the first wavelength band in the second wavelength band. A first system for detecting a transmission abnormality of the first wavelength, and a second wavelength based on a detection result obtained by the first system, from a signal light within a wavelength band overlapping the first wavelength band in the signal light wavelength band. A second system for reselecting signal light to be selected as monitoring light in the wavelength band may be further provided. This is because there is a case where the monitoring target channel is damaged for some reason or its use is stopped.

FIG. 35A is a diagram showing the configuration of an optical transmission system to which the optical transmission monitoring device according to the fifth embodiment is applied. In this optical transmission system, the transmitter 10 outputs pilot light P (hereinafter, referred to as P light) together with signal light (S light) having different wavelengths. The S light and P light output from the transmitter 10 reach the optical amplifier 20 via the optical fiber transmission line 41. The optical amplifier 20 collectively optically amplifies the input (S + P) light, and amplifies the light in the signal light wavelength band (as described in each of the above embodiments, the amplified light includes (S + P) light. N light such as ASE) propagates along the optical fiber transmission line 42 and reaches the optical transmission monitoring device 30. An optical amplifier 25 whose gain is controlled by the optical transmission monitoring device 30 is provided downstream of the optical transmission monitoring device 30. The amplified light output from the optical amplifier 25 is sent to the optical fiber transmission line 43.

More specifically, in the optical transmission monitoring device 30 according to the fifth embodiment, the optical fiber transmission line 4
2 (signal light S as monitoring light in the first wavelength band, pilot light P as monitoring light in the second wavelength band, and noise light N such as ASE generated in the optical amplifier 20). ) Is used for monitoring the transmission status. A part of the separated T light is converted into an electric signal by the photoelectric conversion element 603, and a part thereof is further separated into the T light and the P light by the electric separation device 604. FIG. 36A is a diagram showing the spectrum of the pilot light P. Since the pilot light P is once optically amplified by the optical amplifier b20, ASE is included in the second wavelength band. Further, in the electrical separation device 604, as shown in FIG. 36B, T light ((S + P +
N) light) and pilot light have respective signal intensities fs and f
It is detected in a separated state as information of p.
As described above, one channel is arbitrarily selected from the signal light, and the signal light is used as the monitoring light in the first wavelength band.
By monitoring the signal light of the selected one channel together as the monitoring light of the second wavelength band, the adverse effect of fixedly dividing the signal light to be monitored (the monitoring wavelength band is set to the first wavelength band).
And upstream optical AD for monitoring by dividing into the second wavelength band
The extraction and addition of the signal light by M or the like are restricted).

The structure of the optical transmission monitoring device according to the fifth embodiment is not limited to the structure shown in FIG. 35 (a), but is shown in FIGS. 37 (a) and 37 (b). As shown, various modifications are possible.

FIG. 37 (a) is a diagram showing the configuration of a first modification of the optical transmission monitoring device according to the fifth embodiment. The optical transmission monitoring device 30 shown in FIG. In, a part separated from the T light (including the S light, the P light, and the N light) transmitted through the optical fiber transmission line by the optical branching element 602 is used for monitoring the transmission state. The separated T light is further divided into P light and (S
+ N) separated into light. The separated P light further passes through a band-pass filter 623, and then the photoelectric conversion element 624.
Is converted into an electric signal. On the other hand, the separated (S +
N) The light is converted into an electric signal by the photoelectric conversion element 622. The monitoring unit determines (S +
N) light (signal light as monitoring light detected by the first detector) as light, and information on P light (monitoring light detected by the second detector) in the second wavelength band are used for the optical transmission state. Perform monitoring.

FIG. 37 (b) is a diagram showing the configuration of a second modification of the optical transmission monitoring apparatus according to the fifth embodiment.
In the optical transmission monitoring device 30 shown in FIG. 7B, the optical branching element 625 transmits the T
While the P light is separated from the light, the (S + N) light is separated from the T light passing through the light branching element 625 by the light branching element 626. The separated P light passes through the band-pass filter 627 and is converted into an electric signal by the photoelectric conversion element 629. On the other hand, the separated (S + N) light is also converted into an electric signal by the photoelectric conversion element 628. Monitoring of the optical transmission state is performed based on the obtained information.
(Third Embodiment of Optical Transmission System) Next, FIG.
A third embodiment of the optical transmission system will be described with reference to FIG. 38 (b), FIG. 39 and FIG.

The optical transmission system according to the third embodiment, as shown in FIG. 38A, has at least one or more signal lights within the signal light wavelength band and different wavelengths from each other. And at least one relay station R1 to R4 arranged at a predetermined position on an optical transmission line between a transmitter 10 that outputs light including the light and a receiver 100 that receives the light. R4 function as a section monitoring device including the optical transmission monitoring device according to each of the above embodiments. Further, in this optical transmission system, a system control unit 700 for controlling the section monitoring in each of the relay stations R1 to R4 as a whole system.
It has.

FIG. 38B shows the above-mentioned section monitoring devices R1 to R1.
FIG. 4 is a diagram illustrating a specific configuration of R4, wherein each section monitoring device includes a monitoring light detection unit 30a that detects monitoring light M that has propagated in a monitoring section (upstream optical fiber transmission line); A signal light detector 30b for detecting the propagated signal light S and noise light N such as ASE, and a two-stage optical amplifier 7
01, 703, a variable amplifier 702 disposed between the optical amplifiers 701, 703, an output light detector 30c for detecting light transmitted to a downstream optical fiber transmission line, and the monitor light detector 30a, Based on the detection results from the signal light detection unit 30b and the output light detection unit 30c, the variable attenuator 702 and the two-stage optical amplifiers 701 and 703 are set to A
And a section control section 30d for performing LC (constant output control).

The above-mentioned optical transmission monitoring device 30 is composed of the monitoring light detection unit 30a, the signal light detection unit 30b, the output light detection unit 30c, and the section control unit 30d. Each of the detection units 30a, 30b, and 30c includes an optical splitter for separating a desired light component from the transmitted light, and a photoelectric splitter that converts the light component split by the optical splitter into an electric signal. A conversion element.

In the above configuration, the variable attenuator 7
02 is preferably equal to or more than the difference between the maximum loss fluctuation and the minimum loss fluctuation in the optical transmission line in the monitoring section,
The section monitoring section 30 controls the transmission loss in the monitoring section and the sum of the loss in the variable attenuator 702 to be a predetermined value based on the preset attenuation amount and the monitoring result of the variable attenuator 702. This is because the transmission devices such as the optical amplifiers 701 and 703 and the receiver 100 installed in each section monitoring device may be limited in an allowable input signal level to an extremely narrow range. That is, when such a transmission device is arranged in an optical transmission line where loss fluctuation is severe,
By applying the variable attenuator 702 that provides an attenuation equal to or more than the difference between the maximum value and the minimum value of the loss variation in the optical transmission line, it is possible to operate while maintaining the input signal level within a narrow allowable range. It is. Note that such control of the variable attenuator is similarly performed in the optical amplification system shown in FIG.

The system control section 700 sequentially receives information detected by the optical transmission monitoring device 30 in each section monitoring device, and monitors the entire optical transmission line. The optical transmission monitoring device 30 in each section monitoring device is capable of controlling the loss fluctuation of the optical transmission path,
Output fluctuations of optical amplifiers and monitoring light installed upstream
It is possible to make a determination in a short time without transmitting information on each of these situations to a device installed downstream. However, the monitoring accuracy cannot always be maintained at a high level due to the wavelength dependency of the optical amplifier and the detection accuracy of loss fluctuation. In particular, when monitoring is performed for a long time, accumulation of the error may be a problem. Also,
In the case where monitoring is performed only with monitoring light having a different wavelength band when the signal light is cut off, the monitoring result also lacks reliability. On the other hand, even if it takes some time, if the monitoring results of the relay stations (section monitoring devices) R1 to R4 are sequentially collected and the entire optical transmission path is monitored, it is difficult to obtain sufficient accuracy in a short time. In long-term monitoring, highly accurate monitoring results can be obtained.

Further, the system control section 700 may have a function of transmitting information obtained from one of the section monitoring apparatuses to another section monitoring apparatus. In this case, a desired monitoring effect can be obtained even if an optical transmission monitoring device having no monitoring function is installed in the optical transmission path.

Note that, upstream of a section where the wave number of the signal light is controlled (for example, a position where the optical ADM is installed),
When the wave number of the signal light propagating rapidly changes due to disconnection of the optical transmission line or the like, a short-time control is required even if the accuracy is low. In such a situation, it is desired that the optical transmission monitoring device 30 provided in the section monitoring device, which is each of the relay stations R1 to R4, performs control (ALC) immediately based on the obtained monitoring result. However, when the loss of the optical transmission line changes at a relatively slow speed simultaneously with the change of the wave number, the control in the optical transmission monitoring device 30 as described above includes an unexpected error. Therefore, in the optical transmission system according to the third embodiment, the optical transmission control by the optical transmission monitoring device 30 is performed in each of the relay stations R1 to R4, and the respective relay stations R obtained by the system control unit 700 are obtained.
1 to R4, each optical transmission monitoring device 30
Is corrected. As described above, if the optical transmission control is performed based on the double monitoring result, the accuracy of the optical transmission control becomes coarse in a short time, but a sufficiently high control result is obtained in the optical transmission control for a long time. Can be

Based on the above configuration, this third
Monitoring operation of optical transmission system according to the embodiment (optical transmission control)
This will be described below with reference to FIGS. 39 and 40. FIG. 39 is a flowchart for explaining a control operation in each of the relay stations (section monitoring devices) R1 to R4.
0 is a flowchart for explaining a control operation in the system control unit 700. Also, the following explanation
Each section monitoring device has the structure shown in FIG. 38B (including the optical transmission monitoring device according to the fourth embodiment shown in FIG. 31A), and a signal light wavelength band as the monitoring light. This is limited to the case of using signal light of a wavelength band (corresponding to the first wavelength band in the monitoring light wavelength band) and light of a wavelength band different from the signal light wavelength band (corresponding to the second wavelength band in the monitoring light wavelength band). Will be explained.

First, in each section monitoring device, during the monitoring period,
The input level value of the light to be monitored is monitored. Specifically, the section monitoring unit 30d captures the input level value of the monitoring light in the second wavelength band from the monitoring light detection unit 30a, and also monitors the monitoring light (signal light and ASE) in the first wavelength band from the signal light detection unit 30b. ) Is taken in (step ST4). The section monitoring unit 30d determines whether or not the input level value has changed by 1 dB or more while taking in the detection signals from the monitoring light detection unit 30a and the signal light detection unit 30b (step ST5).
When determining that the input level has changed by 1 dB or more in step ST5, the section monitoring unit 30d shifts to the constant output control (ALC) process (step ST6).

In the ALC process in the section monitoring unit 30d, first, the steady value of the input level of the monitoring light in the first and second wavelength bands to be monitored is updated (step ST).
7), a judgment is made as to the change content of the input level value (step ST8). At this stage, monitoring of the input level value is also performed, and the input level value of each monitoring light in the first and second wavelength bands is taken into the sequential section monitoring unit (steps ST4 to ST6).

If it is determined in step ST8 that the change in the input level value is a change due to the wavelength dependency and not a loss change, the signal level value of the output light output from the section monitor (output level value) ) Is captured from the output light detection unit 30c (step ST10), and it is monitored whether or not the level of the input level value sequentially captured continues (step ST11). On the other hand, when it is determined that there is a loss fluctuation, ALC is first performed (step ST9). The ALC adjusts the amount of attenuation of the variable attenuator 702 to control the optical power of the light input to the optical amplifier 703, and adjusts the gain of each of the optical amplifiers 701 and 703. The signal level value (output level value) of the output light output from the section monitoring device after the ALC ends is output to the output light detection unit 3.
It starts from 0c (step ST10), and shifts to a monitoring operation (step ST11) for checking whether or not the level change of the input level value that is successively taken continues.

The capture of the output level value (step ST10) is performed while the change of the input level value continues. Then, when the change of the input level value stops, the section monitoring unit 30d notifies the system control unit 700 of the input level value of the own station, and also sets the target gain value (gain target value) of the own station. An inquiry is made (step ST12).

When the gain target value of the own station is fetched from the system control section 700 (step ST13), the section monitoring section 30
d captures the gain value (gain monitor value) actually obtained in the own station (step ST14), and compares the obtained gain monitor value with the gain target value notified from the system control unit 700 (step ST15). If the gain monitor value does not match the gain target value, the current gain monitor value is notified to the system control unit 700 (step ST1).
7) Perform ALC again (step ST18). These steps ST17 and ST18 are repeated until the actual gain monitor value of the own station matches the gain target value. On the other hand, if the gain monitor value matches the gain target value,
The actual gain monitor value of the own station is notified to the system control section 700 (step ST16), and this ALC process is terminated.

The system control section 700 takes in the input / output level values of the signal light in each station sequentially (step S).
T20), the transmission loss value in each section is calculated, and the obtained loss value is stored (step ST21).
When the obtained section loss value and the prepared initial value exceed a predetermined allowable value e (step ST22), it is determined that the section loss is abnormal and a warning is issued to the administrator (step ST24). .

On the other hand, when the obtained section loss value and the prepared initial value are equal to or smaller than a predetermined allowable value e (step ST22), the gain target value of each station is determined based on the optical transmission state of the entire transmission system. (Step ST2)
3). The system control unit 700 notifies the section monitoring unit 30d of each station of the calculated gain target value (Step S
T25), and waits for the notification of the gain monitor value from the section monitoring unit 30d of each station (step ST26). Then, the system control unit 700 compares the received gain monitor value with the already calculated gain target value. Here, if the received gain monitor value does not match the gain target value, the gain target value of the station where the excess or deficiency of the gain monitor value has occurred (the station that has notified the gain monitor value) is corrected. (Step ST28), the above-mentioned steps ST25 to ST25
Repeat T27.

When the gain monitor value received in step ST27 matches the target gain value of the target station, system control section 700 newly notifies the input monitor value and inquires about the gain target value. It waits until (step ST29). If any of the stations receives a notification of an input monitor value or an inquiry about a gain target value (step ST29), the system control unit 700 fetches an output monitor value of a station located upstream of the notified or inquired station. (Step ST30), the above-mentioned steps ST21 to ST29 are repeated.

[0157]

As described above, according to the present invention, a monitoring light wavelength band for monitoring the state of optical transmission is set to 2 in advance.
One wavelength band is set, and the transmission state of the optical transmission line is monitored while comparing the fluctuation amounts of the optical powers of a plurality of types of light different from each other in the two wavelength bands. Can identify the cause of the optical power fluctuation of the WDM signal. In addition, in an optical amplification system or an optical transmission system to which the optical transmission monitoring device is applied, appropriate transmission control that matches the state of optical transmission can be performed.

[Brief description of the drawings]

FIG. 1A is a diagram showing a configuration of an optical transmission line system to which an optical transmission monitoring device according to the present invention is applied;
(B) and (c) show FIG. 1 (a) indicated by W1 and W2.
It is a figure which shows the optical spectrum of the signal light wavelength band in each part in the middle.

FIG. 2A is a diagram illustrating a configuration of an optical transmission monitoring device according to a first embodiment, and FIG. 2B is a diagram illustrating a configuration substantially equivalent to the configuration illustrated in FIG. It is.

3 (a) to 3 (d) are diagrams of FIG. 2 indicated by W3 to W6.
It is a figure which shows the optical spectrum of the signal light wavelength band (it matches a monitoring light wavelength band) in each part in (a) and (b).

FIGS. 4A to 4E are conceptual diagrams for explaining a relationship between a monitoring light wavelength band and a signal light wavelength band.

FIGS. 5A to 5E are conceptual diagrams for explaining a relationship between a first wavelength band and a second wavelength band in a monitoring light wavelength band.

FIG. 6 is a conceptual diagram for explaining the optical power of signal light and noise light existing within a predetermined wavelength band.

FIG. 7 is a diagram showing a structure of an apparatus for separating signal light (monitoring light) and noise light from light in a predetermined wavelength band.

8A is a diagram showing an optical spectrum of incident light input to the device shown in FIG. 7, and FIGS.
FIG. 8 is a diagram illustrating optical spectra of signal light and noise light separated by the device illustrated in FIG. 7.

FIG. 9 is an optical transmission monitoring device according to the first embodiment (FIG. 2A)
6 is a graph for explaining an optical transmission monitoring method using (b) and (b).

FIG. 10A is a diagram illustrating a configuration of an optical transmission monitoring device according to a second embodiment, and FIGS. 10B to 10E are diagrams illustrating W7 to W1.
FIG. 11 is a diagram illustrating an optical spectrum of a signal light wavelength band (coincident with a monitoring light wavelength band) in each unit in FIG.

11 is an optical transmission monitoring device according to a second embodiment (FIG. 10)
6 is a graph for explaining an optical transmission monitoring method using (a)).

FIGS. 12A and 12B are diagrams showing a schematic configuration of an optical amplification system according to the present invention.

FIG. 13 is a diagram showing a specific configuration of the optical amplification system shown in FIG.

14 is a flowchart for explaining a control method of the optical amplification system shown in FIG.

FIG. 15A is a diagram showing a configuration of an optical transmission monitoring device according to a third embodiment, and FIGS. 15B and 15C are substantially equivalent to the configuration shown in FIG. FIG. 3 is a diagram illustrating a configuration.

FIGS. 16 (a) to (d) show the optical spectrum of the signal light wavelength band (matching the monitoring light wavelength band) in each part in FIGS. 15 (a) and 15 (b) indicated by W11 to W14. FIG.

FIG. 17 is a diagram showing an output light spectrum in the optical amplifier.

FIGS. 18A to 18E are diagrams for explaining the operation of the optical transmission monitoring device according to the third embodiment (FIGS. 15A and 15C).

FIG. 19A is a diagram illustrating a configuration of a first modification of the optical transmission monitoring device according to the third embodiment, and FIG. 19B is a diagram illustrating the configuration of FIG.
FIG. 3 is a diagram showing a configuration substantially equivalent to the configuration shown in FIG.

20 (a) to (d) are optical spectra of light in a signal light wavelength band (matching a monitoring light wavelength band) in each part in FIGS. 20 (a) and (b) indicated by W15 to W18. FIG.

FIG. 21 is a diagram showing a configuration of a first embodiment in an optical transmission system to which the optical transmission monitoring device according to the present invention is applied.

FIGS. 22 (a) to (h) are diagrams showing optical spectra in respective parts of the optical transmission system shown in FIG. 21.

23A is a diagram showing a configuration of a second embodiment in an optical transmission system to which the optical transmission monitoring device according to the present invention is applied, and FIGS. 23B to 23D are W19 to W21; FIG. FIG. 24 is a diagram showing an optical spectrum of a signal light wavelength band (coincident with a monitoring light wavelength band) in each section in FIG. 23A.

FIGS. 24A and 24B are diagrams showing a configuration of a relay station arranged in an optical transmission line, respectively.

FIG. 25 is a diagram illustrating a specific configuration of the optical transmission system (second embodiment) illustrated in FIG. 23A (part 1).

FIGS. 26 (a) to (h) are graphs showing changes over time of optical power in respective parts in FIG. 25 indicated by W22 to W29.

FIG. 27 is a diagram illustrating a specific configuration of the optical transmission system (second embodiment) illustrated in FIG. 23A (part 2).

FIGS. 28 (a) to (h) are graphs showing the time change of the optical power in each part in FIG. 27 indicated by W30 to W37.

FIG. 29 is a diagram showing a specific configuration of the optical transmission system (second embodiment) shown in FIG. 23A (part 3).

FIGS. 30 (a) to (h) are graphs showing the time change of the optical power in each part in FIG. 29 indicated by W38 to W345.

FIG. 31A is a diagram illustrating a configuration of an optical transmission system to which a fourth embodiment of the optical transmission monitoring device according to the present invention is applied, and FIG. 31B is a diagram illustrating a monitoring light wavelength band and a signal light wavelength; FIG. 4 is a diagram for explaining a relationship between the first wavelength band and a second wavelength band in the monitoring light wavelength band.

FIGS. 32 (a) to (c) are diagrams showing an optical spectrum and the like of a light component detected by the optical transmission monitoring device shown in FIG. 31 (a).

FIGS. 33 (a) to (d) are diagrams for explaining the monitoring operation of the optical transmission monitoring device (FIG. 31 (a)) according to the fourth embodiment.

FIG. 34A is a diagram illustrating a configuration of a first modification of the optical transmission monitoring device according to the fourth embodiment, and FIG. 34B is a diagram illustrating a second configuration of the optical transmission monitoring device according to the fourth embodiment. It is a figure showing composition of a modification.

FIG. 35A is a diagram showing a configuration of an optical transmission system to which a fifth embodiment of the optical transmission monitoring device according to the present invention is applied, and FIG. 35B is a diagram showing a monitoring light wavelength band and a signal light wavelength; FIG. 4 is a diagram for explaining a relationship between the first wavelength band and a second wavelength band in the monitoring light wavelength band.

FIGS. 36 (a) and (b) are diagrams showing optical spectra of light components detected by the optical transmission monitoring device according to the fifth embodiment.

FIG. 37A is a diagram illustrating a configuration of a first modification of the optical transmission monitoring device according to the fifth embodiment; FIG. 37B is a diagram illustrating a second configuration of the optical transmission monitoring device according to the fifth embodiment; It is a figure showing composition of a modification.

38A is a diagram showing a configuration of a third embodiment of the optical transmission system to which the optical transmission monitoring device according to the present invention is applied, and FIG. 38B is a diagram showing FIG. 38A. FIG. 3 is a diagram illustrating a configuration of each relay station (section monitoring device) in the optical transmission system according to the embodiment.

FIG. 39 is a flowchart illustrating a monitoring operation in each relay station in the optical transmission system according to the third embodiment.

FIG. 40 is a flowchart illustrating a monitoring operation of a system control unit in the optical transmission system according to the third embodiment.

[Explanation of symbols]

20 to 25, 101, 102, 201, 202, 350
... optical amplifiers, 41-43 ... optical fiber transmission lines, 30-3
3, 33A, 130, 230 ... optical transmission monitoring device, 300
... optical amplification system, 316, 325, 336 ... monitoring unit,
313, 315, 324, 323, 333, 335, 6
03, 606, 607, 622, 624: first to third detectors, 351, 702: variable attenuators, 700: system control unit, R1 to R4: relay stations.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04B 10/00-10/28 H04L 14/00-14/08

Claims (23)

(57) [Claims] 1. A optical transmission monitoring apparatus for monitoring the transmission state in the optical transmission path through which light propagates containing signal light is light in the wavelength band and one or more of signal lights of different wavelengths from each other, the light In a monitoring light wavelength band in which light propagating in a transmission path and including one or more monitoring lights having different wavelengths from each other, at least one of light in a first wavelength band included in the monitoring light wavelength band is included. A first detector for detecting at least one of the optical power of the monitoring light and the optical power of the noise light among the light of the first wavelength band; and a first detector included in the monitoring light wavelength band and one of the first wavelength band.
A second detector for detecting at least one of the optical power of one or more monitoring lights out of the light in the second wavelength band and the optical power of noise light out of the light in the second wavelength band; Comparing the amount of optical power fluctuation per unit time in the first wavelength band detected by the detector with the amount of optical power fluctuation per unit time in the second wavelength band detected by the second detector; An optical transmission monitoring device comprising: a monitoring unit that identifies a cause of a change in optical power in the optical transmission path based on a comparison result. 2. The optical transmission monitoring apparatus according to claim 1, wherein the monitoring light wavelength band is a wavelength band at least part of which overlaps the signal light wavelength band. 3. The monitoring light within the monitoring light wavelength band,
3. The optical transmission monitor according to claim 2, wherein signal light included in a part of the signal light wavelength band separated from light in a wavelength band overlapping the monitor light wavelength band is used. apparatus. 4. In the monitoring light wavelength band, the first
The optical transmission monitoring device according to claim 1, wherein the wavelength band is a wavelength band that does not overlap with the second wavelength band. 5. The first wavelength band is a wavelength band at least a part of which overlaps with the signal light wavelength band,
As the monitoring light in the first wavelength band, light in a wavelength band overlapping with the first wavelength band in the signal light wavelength band is used, and the first detector includes at least the light in the first wavelength band. 5. The optical power of the first light including the monitoring light is detected, and the second detector detects the optical power of the second light including the monitoring light in at least the second wavelength band. The optical transmission monitoring device as described in the above. 6. The apparatus further comprising a third detector for detecting an optical power of a third light including at least a noise light in the first wavelength band, wherein the monitoring unit is a unit obtained for the first light. Comparing the optical power variation per unit time, the optical power variation per unit time obtained for the second light, and the optical power variation per unit time obtained for the third light,
6. The optical transmission monitoring device according to claim 5, wherein a cause of a change in optical power in the optical transmission line is identified based on the comparison result. 7. In the monitoring light wavelength band, the first
2. The optical transmission monitoring device according to claim 1, wherein the wavelength band is a wavelength band at least partially overlapping the second wavelength band. 8. In the monitoring light wavelength band, the first
The optical transmission monitoring device according to claim 7, wherein the bandwidth of the wavelength band is wider than the bandwidth of the second wavelength band, and the second wavelength band is included in the first wavelength band. 9. The first wavelength band is a wavelength band at least part of which overlaps the signal light wavelength band,
As the monitoring light in the first wavelength band, a signal light included in a part of the signal light wavelength band separated from light in a wavelength band overlapping the first wavelength band is used, and the second wavelength As the monitoring light in the band, signal light of at least one channel selected from signal light in a wavelength band overlapping the first wavelength band in the signal light wavelength band is used, and the monitoring unit includes: An optical power variation per unit time obtained for the monitoring light and the noise light in the first wavelength band;
Comparing the optical power fluctuation per unit time obtained for the monitoring light in the second wavelength band, and identifying the cause of the optical power fluctuation in the optical transmission path based on the comparison result. The optical transmission monitoring device according to claim 8. 10. The optical transmission line, wherein at least one first optical amplifier is disposed on the optical transmission line, and the optical transmission monitoring device is arranged on the optical transmission line to which the amplified light output from the first optical amplifier reaches. While being arranged at a predetermined position, the center wavelength of the first wavelength band and the center wavelength of the second wavelength band are the first wavelength in the signal light wavelength band.
2. The optical transmission monitoring device according to claim 1, wherein the optical transmission monitoring device is set so as to coincide with a wavelength at which the gain becomes substantially equal to the average gain of the optical amplifier. 11. A first system for detecting transmission abnormality of at least one channel of signal light selected from signal light in a wavelength band overlapping the first wavelength band in the signal light wavelength band; Based on the detection result obtained by the first system, from the signal light in the wavelength band overlapping with the first wavelength band in the signal light wavelength band, the signal light is selected as monitoring light in the second wavelength band. The optical transmission monitoring device according to claim 9, further comprising a second system for reselecting a signal light to be transmitted. 12. Each of the first and second wavelength bands has a difference between an amplification wavelength band of the first optical amplifier and the monitor light wavelength band and a monitor light included in the monitor light wavelength band. The optical transmission monitoring device according to claim 1, wherein the setting is performed based on at least one of the wave numbers. 13. An optical amplification system disposed at a predetermined position on an optical transmission path through which light in a predetermined signal light wavelength band including one or more signal lights having different wavelengths from each other propagates. At least a second optical amplifier that collectively amplifies the light of the signal light wavelength band that has propagated in the optical transmission line; and a gain of the second optical amplifier according to a transmission state in the optical transmission line. An optical amplification system comprising the optical transmission monitoring device according to claim 1. 14. A position on the optical transmission line where signal light within the signal light wavelength band passes before reaching the optical transmission monitoring device, and a position where signal light passes after passing through the optical transmission monitoring device. And a first variable optical attenuator arranged to attenuate the signal light by a predetermined amount, wherein the monitoring unit of the optical transmission monitoring device is configured to: 14. The optical amplification system according to claim 13, wherein the amount of attenuation of one variable attenuator is adjusted. 15. The control method for an optical amplification system according to claim 13, wherein at least one of the monitoring lights is light that propagates in the optical transmission line and has different wavelengths from each other. In the monitoring light wavelength band in which light including the following exists, the optical power of at least one monitoring light among the light in the first wavelength band included in the monitoring light wavelength band and the noise light among the light in the first wavelength band Detecting the amount of optical power variation per unit time for at least one of the optical powers of the second and third wavelengths, and among the light within the second wavelength band included in the monitoring light wavelength band, the optical power of at least one of the monitoring light and the second Detecting at least one of the optical power of the noise light among the light within the wavelength band, the optical power variation per unit time in the detected first wavelength band, and detecting the optical power variation per unit time in the first wavelength band; With the calculated optical power fluctuation amount per unit time in the second wavelength band, and based on the comparison result, determines whether or not the wavelength channel of the signal light has increased or decreased. And controlling a gain of the second optical amplifier when there is no optical amplifier. 16. At least one relay station disposed at a predetermined position on an optical transmission line through which light containing at least one signal light having a wavelength within a signal light wavelength band and different from each other propagates. An optical transmission system, wherein each of the relay stations includes a section monitoring device having the same structure as the optical transmission monitoring device according to claim 1. 17. Each of the relay stations further includes an optical amplifier that collectively amplifies light of the signal light wavelength band that has propagated in the optical transmission line, and a monitoring unit of the optical transmission monitoring device includes: 17. The optical transmission system according to claim 16, wherein a gain of the optical amplifier is adjusted according to a transmission state in a transmission path. 18. Each of the relay stations further includes a second variable optical attenuator for attenuating a predetermined amount of signal light within the signal light wavelength band, and a monitoring unit of the optical transmission monitoring device includes the optical transmission line. 17. The optical transmission system according to claim 16, wherein the second variable optical attenuator is adjusted according to a transmission state in the optical transmission system. 19. An optical power variation per unit time for a part of the relay station separated from light within the monitoring light wavelength band that has reached the relay station, and the output power from the relay station. A system control unit that monitors the optical power fluctuation in the entire optical transmission system based on the optical power fluctuation amount per unit time for a part separated from the light in the monitoring light wavelength band. The optical transmission system according to claim 16, wherein 20. The system control unit according to claim 13, wherein the control performed by the monitoring unit of the optical transmission monitoring device in each of the relay stations is corrected based on each optical power fluctuation amount of the input / output light in each of the relay stations. Claim 19
The optical transmission system according to the above. 21. An optical input / output element for extracting a part of the signal light from the signal light propagating in the optical transmission line and adding a new signal light. The optical transmission system according to the above. 22. One of the first and second wavelength bands includes a part of the signal light from which signal light is extracted or added by the optical input / output element. The optical transmission system according to claim 21, wherein: 23. An optical transmission monitoring method and a light signal wavelength in the band light including one or more of signal lights of different wavelengths from each other to monitor the transmission state in the optical transmission path for propagating the light In a monitoring light wavelength band in which light propagating in a transmission path and including one or more monitoring lights having different wavelengths from each other, at least one of light in a first wavelength band included in the monitoring light wavelength band is included. Detecting at least one of the optical power of the monitoring light and the optical power of the noise light out of the light of the first wavelength band, and detecting one of the optical power included in the monitoring light wavelength band and the first wavelength band.
One or more monitoring light detecting at least one of the optical power of the noise light in the light power and the first wavelength band of light, the first wavelength band the detected out of the light in the absence match the second wavelength band comparing an optical power variation amount per unit time, and an optical power variation amount per unit time in the detected second wavelength band in the ratio
An optical transmission monitoring method for identifying a cause of a change in optical power in the optical transmission path based on a comparison result .