JP3189199B2 - Wavelength monitoring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength monitoring device suitable for a wavelength monitoring circuit in wavelength division multiplex communication or a wavelength discriminator of a stabilization circuit for a wavelength division multiplex light source.

[0002]

2. Description of the Related Art A light source used in wavelength division multiplexing communication is mainly a semiconductor laser, and its oscillation wavelength fluctuates due to aging and temperature change. Therefore, an apparatus for simultaneously and accurately measuring the wavelengths of a plurality of semiconductor lasers is required.

A conventional wavelength monitoring apparatus that monitors each wavelength of wavelength-multiplexed light sweeps the transmission center wavelength of a sweep-type optical filter (for example, a sweep-type Fabry-Perot interferometer) temporally, and converts a wavelength error into a time domain. And performs wavelength discrimination.

FIG. 1 shows an example of the configuration of a conventional wavelength monitoring apparatus (Shiragaki, et al., "622 Mbit / s-16ch FDM coherent optical transmission system using two-electrode MQWDFB-LD", IEICE Biology, Vol.J77-
BI, No. 5, pp. 294-303,199
4).

In the figure, reference wavelength light R and wavelength multiplexed light M
Are multiplexed by the optical coupler 71 and input to the sweep type Fabry-Perot interferometer 72. Swept Fabry-Perot interferometer 7
2 is swept by a sawtooth wave (FIG. 2A) generated by a sawtooth generator 76 synchronized with the oscillator 75, and light having a wavelength corresponding to the transmission center wavelength is received by the photodetector 73. The peak position of the output pulse of the photodetector 73 (FIG. 2B) is differentially detected by the differentiator 78 (FIG. 2C), and the sampling pulse corresponding to the peak position is detected by the sampling circuit 79 (FIG. 2C). (D)). The sampling pulse and the output signal of the oscillator 75 (FIG. 2 (e)) are input to the synchronous detector 80, and the output thereof is output to the sample hold circuit 8
1 is input. Since the sawtooth wave and the output signal of the oscillator 75 are synchronized, the phase of the output signal of the oscillator 75 is detected by the sampling pulse, and the detection output is held by the sample-and-hold circuit 81 to generate an error signal (FIG. 2 (f)). ) Can be obtained. The selector 74 sequentially switches and outputs a relative error signal between each wavelength of the reference wavelength light R and the wavelength multiplexed light M and the transmission center wavelength of the swept Fabry-Perot interferometer 72.

The error signal corresponding to the reference wavelength light R is added to the sawtooth wave output from the sawtooth wave generator 76 by an adder 77 and applied to the sweep type Fabry-Perot interferometer 72, where the error signal corresponding to the reference wavelength light R The position of the output pulse of the photodetector 73 is controlled so as to be at a specified position. Thereby, the transmission center wavelength of the sweep type Fabry-Perot interferometer 72 is changed to the reference wavelength light R.
, And a temperature compensation function against fluctuations in the ambient temperature can be provided.

Further, an error signal corresponding to each wavelength of the wavelength multiplexed light M is negatively fed back to each light source of the wavelength multiplexed light M, and the injection current or temperature thereof is controlled to stabilize the wavelength of the wavelength multiplexed light M. be able to.

The sweep type Fabry-Perot interferometer used in the conventional configuration described above requires a mechanism for sweeping the resonator length by a piezoelectric element, but can be realized by a relatively simple optical circuit. Further, by appropriately selecting the transmission center wavelength and the pass band width of the swept Fabry-Perot interferometer, there is an advantage that a wide-range wavelength change can be monitored with a desired resolution.

[0009]

By the way, in the conventional configuration, the displacement of the piezoelectric element and the transmission center wavelength are proportional to the voltage applied to the piezoelectric element of the sweep type Fabry-Perot interferometer. However, actually, FIG.
As shown in (1), the displacement of the piezoelectric element is not proportional to the applied voltage, and has a hysteresis. Therefore, an attempt to set the transmission center wavelength corresponding to the displacement of the piezoelectric element at regular intervals, the applied voltage does not become equal intervals (V ₁ ~V _6), 3
It is necessary to apply a correction voltage (V ₂ ′ to V ₄ ′) indicated by a broken line in FIG.

That is, when the sweep voltage is a linear waveform of a sawtooth wave as in the conventional configuration, the transmission center wavelength cannot be swept correctly. Therefore, in the conventional configuration in which the sweep and the sampling are synchronized with the same clock, it is difficult to strictly discriminate the wavelength over a wide wavelength range, and it is impossible to monitor the wavelength multiplexed light multiplexed at an arbitrary wavelength interval with high accuracy. Was.

In the configuration using the Fabry-Perot interferometer, it is possible to relatively monitor each wavelength change of the wavelength multiplexed light with reference to the wavelength of the reference wavelength light, but the wavelength of the reference wavelength light is strictly stable. It was difficult to measure the absolute wavelength because it was not converted.

According to the present invention, a predetermined wavelength interval (frequency interval)
It is an object of the present invention to provide a wavelength monitoring device which can discriminate each wavelength of the wavelength multiplexed light multiplexed with high accuracy with high accuracy, and which is suitable for optical integration.

[0013]

In order to achieve the above object, the present invention provides a method for controlling the transmission center wavelengths of a plurality of channels based on a reference wavelength having a predetermined wavelength. A wavelength monitoring apparatus for simultaneously monitoring the wavelength error of each signal light Sk (k = 1-N: N is a positive integer) of the output wavelength multiplexed light, wherein the reference wavelength light and the wavelength multiplexed light are input. At least one of the first, which outputs at least a part of the reference wavelength light,
And an arrayed waveguide grating including at least one second channel for outputting at least a part of the signal light Sk, and a second detector for detecting reference wavelength light output from the first channel. 1 light receiving means, second light receiving means for detecting the signal light Sk output from the second channel, and transmission center wavelength of the first channel based on the output of the first light receiving means. Control means for stabilizing, and a wavelength error detecting means for outputting an error signal representing a wavelength error of the signal light Sk based on an output of the second light receiving means , wherein the arrayed waveguide grating comprises:
Two said first channels corresponding to reference wavelength light;
And the two second channels corresponding to the signal light Sk.
The wavelength monitoring device further comprises the first channel
Ratio comparing the intensities of two output lights output from the first
Comparing means, and two outputs from the second channel.
And second comparing means for comparing the intensity of the force light,
The control means is configured to perform a previous operation based on the output of the first comparing means.
Stabilizing the transmission center wavelength of the first channel;
The error detecting means is based on an output of the second comparing means.
And detecting a wavelength error of the signal light Sk .

[0014]

[0015]

[0016]

[0017]

[0018]

[0019]

The wavelength monitoring apparatus may further include input means for simultaneously inputting the wavelength multiplexed light and the reference wavelength light to one channel of the arrayed waveguide grating.

The wavelength monitoring apparatus may further include input means for inputting the wavelength multiplexed light and the reference wavelength light to separate channels of the arrayed waveguide grating.

The wavelength monitoring apparatus further includes input means for splitting a signal obtained by multiplexing the wavelength-division multiplexed light and the reference wavelength light, and simultaneously inputting the signals to separate channels of the arrayed waveguide grating. Is also good.

[0023] The two first channels may be adjacent to each other, and the two second channels may be adjacent to each other.

The two first channels are mutually FS
The channels are separated by R (Free Spectral Range), and the two second channels may be channels separated by FSR from each other.

The first comparing means is a logarithmic amplifier,
The second comparing means may also be a logarithmic amplifier.

The first comparing means may include an A / D converter and a digital signal processor, and the second comparing means may include an A / D converter and a digital signal processor.

The first comparing means is a differential light receiver,
The second comparing means may also be a differential light receiver.

[0028]

[0029]

[0030]

[0031]

[0032]

According to the present invention, the transmission center wavelength or the cross wavelength of the reference channel of the arrayed waveguide grating is controlled so that the relative wavelength error of the reference wavelength light becomes zero. Is stabilized at the wavelength of the reference wavelength light. On the other hand, the relative accuracy of the periodic transmission center wavelength or cross wavelength of the arrayed waveguide grating is extremely high. Therefore, by stabilizing the transmission center wavelength or crossed wavelength of the reference channel to the wavelength of the reference wavelength light, the arrayed waveguide grating is stabilized. The overall transmission characteristics can be stabilized. Then, by detecting the relative wavelength error of each wavelength of the wavelength multiplexed light, a highly accurate and stable wavelength discrimination operation can be performed.

Further, the wavelength monitoring apparatus of the present invention controls the zero-crossing wavelength of the Mach-Zehnder interferometer to the reference wavelength light stabilized at a predetermined wavelength, thereby enabling a wavelength discrimination operation synchronized with the absolute wavelength. .

[0035]

[0036]

[0037]

[0038]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 4 shows the configuration of a first embodiment of the wavelength monitoring apparatus according to the present invention.

In the figure, the reference wavelength light (wavelength λ ₀ ) and the wavelength-division multiplexed light (wavelengths λ _{1 to} λ _n ) to be monitored are coupled to the optical coupler 1.
The signals are multiplexed by 1 and input to a predetermined input waveguide of the arrayed waveguide grating 12. The arrayed waveguide grating 12 includes an input waveguide array 32 formed on a substrate 31, an input concave slab waveguide 33, an array waveguide 34 including a plurality of waveguides that are sequentially elongated by a waveguide length difference ΔL, and an output. The configuration is such that a side concave slab waveguide 35 and an output waveguide array 36 are sequentially connected. In this embodiment, the heater 13 is attached to the array waveguide 34. The reference signal Sa output from the oscillator 14 is input to the current circuit 15, and controls the temperature of the heater 13.

Output waveguides # 0 to # 0 of the arrayed waveguide grating 12
In #n, photodetectors 16-0 and 16-i (i is 1 to n)
Are connected (FIG. 5A). Photodetectors 16-0, 16
The output of -i is connected to phase comparators 18-0 and 18-i via amplifiers 17-0 and 17-i, respectively. The reference signals Sa output from the oscillator 14 are input to the phase comparators 18-0 and 18-i, and the outputs are input to low-pass filters (LPF) 19-0 and 19-i, respectively. The output of the low-pass filter 19-0 is output to the integrator 20-0.
Is input to A temperature control circuit 21 is connected to the output of the integrator 20-0. The temperature control circuit 21 controls a Peltier cooler 22 that adjusts the temperature of the arrayed waveguide grating 12.

FIG. 6 is a block diagram showing the structure of the temperature control circuit 21. In the figure, reference numeral 12T denotes a thermistor for detecting the temperature of the arrayed waveguide grating 12. The output of the thermistor 12T is sent to the thermistor bridge circuit 211 in the temperature control circuit 21. The thermistor bridge circuit 211 outputs a temperature signal TS corresponding to the temperature of the arrayed waveguide grating 12 from the resistance value of the thermistor 12T, and supplies the same to the comparator 212. The other input terminal of the comparator 212 is supplied with the reference voltage RV from the reference voltage source 213. The comparator 212 compares the temperature signal TS with the reference voltage RV, and generates an error signal T between the measured temperature and the set temperature.
E is output. The error signal TE is supplied to a loop filter 214 having a preset time constant. The loop filter 214 converts the error signal TE into a temperature control signal T
Convert to C

On the other hand, a wavelength error signal S for the reference wavelength light
d is supplied to the adding circuit 215. This wavelength error signal Sd is a wavelength error between the wavelength of the reference wavelength light and the transmission center wavelength of the channel of the reference wavelength light. On the other hand, if there is a preset offset between the set value of the transmission center wavelength and the wavelength of the reference wavelength light, the sum of the wavelength error signal Sd and the offset signal FS is equal to the set transmission center wavelength and the actual transmission. It becomes an error with the center wavelength. The addition circuit 215 adds the offset signal FS supplied from the offset circuit 216 and the wavelength error signal Sd, and supplies the error signal ES to the next addition circuit 217. The addition circuit 217 takes the difference between the error signal ES and the temperature control signal TC, and controls the Peltier cooler 22 via the Peltier element driving circuit 218. As described above, by using the offset signal indicating the amount of deviation between the set transmission center wavelength of the arrayed waveguide grating 12 and the wavelength of the reference wavelength light, control can be performed using reference wavelength light having a wavelength different from the set transmission center wavelength. Becomes possible.

As shown in FIG. 5 (B), a set of components below the photodetectors connected to the output waveguides # 1 to #n of the arrayed waveguide grating 12 is used as one set, and the optical switch 23 is used. You may switch and connect.

Here, the function of the arrayed waveguide grating 12 will be described.

Light incident from a predetermined input waveguide array 32 spreads by diffraction in the input concave slab waveguide 33 and is guided to a waveguide array 34 arranged perpendicular to the diffraction plane. In the waveguide array 34, since each waveguide is sequentially elongated by the waveguide length difference ΔL, light propagating through each waveguide and reaching the output side concave slab waveguide 35 corresponds to the waveguide length difference ΔL. A phase difference occurs. Since this phase difference depends on the wavelength (optical frequency),
When the light is focused on the input end of the output waveguide array 36 by the lens effect of the output concave slab waveguide 35, the light is focused on a different position for each wavelength.

As described above, the arrayed waveguide grating 12 can function as an optical demultiplexer. Its transmission characteristics are
As shown in FIG. 7, the transmission center wavelengths are arranged at predetermined intervals corresponding to the output waveguides. If the position of the input waveguide is shifted by one, the correspondence between the transmission center wavelength and the output waveguide is cyclically shifted by one channel.

In this embodiment, the temperature of the heater 13 for heating the waveguide array 34 is changed according to the reference signal Sa. Thereby, the transmission characteristics of the arrayed waveguide grating 12 can be minutely vibrated on the wavelength axis (FIGS. 8 and 10).
(A) and FIG. 10 (B)). By performing synchronous detection of a change in light intensity obtained according to the vibration, a relative wavelength error with respect to the transmission center wavelength can be detected.
Based on this principle, the transmission characteristics of the arrayed waveguide grating 12 are first stabilized at the wavelength of the reference wavelength light.

FIGS. 8 and 9 are diagrams for explaining the wavelength discrimination of the reference wavelength light and the stabilization of the transmission characteristics in the first embodiment.

The reference wavelength light is emitted from the output waveguide # 0 of the arrayed waveguide grating 12, is received by the photodetector 16-0, and the received light signal Sb is amplified by the amplifier 17-0 and is output by the phase comparator 18. Input to −0. At this time, the transmission center wavelength of the output waveguide # 0 is one of the states [1], [2], and [3] shown in FIGS. 8 and 9 with respect to the wavelength λ ₀ of the reference wavelength light. In a relationship.

In the state [3] where the transmission center wavelength of the output waveguide # 0 is on the short wavelength side with respect to the wavelength λ ₀ of the reference wavelength light,
The light receiving signal Sb is a signal having the same frequency and phase as the reference signal Sa. In the state [1] on the long wavelength side, the light receiving signal Sb is a signal having the same frequency as the reference signal Sa and shifted in phase by π. Further, in the state [2] where the two coincide with each other, the light receiving signal Sb is the reference signal Sa.
Is a signal of twice the frequency of Such a light receiving signal Sb
Is synchronously detected by the phase comparator 18-0 using the reference signal Sa, the minute vibration component is removed by the low-pass filter 19-0, and the signal component is extracted to obtain the wavelength λ ₀ of the reference wavelength light and the output waveguide # 0. An error signal Sc corresponding to the relative wavelength error with respect to the transmission center wavelength can be obtained. The error signal Sc becomes positive in the state [3], becomes negative in the state [1], and becomes 0 in the state [2].

The error signal Sc is time-integrated by the integrator 20-0 to obtain a control signal Sd, which is negatively fed back to the arrayed waveguide grating 12 via the temperature control circuit 21 and the Peltier cooler 22. Array waveguide grating 12
The transmission characteristics change also due to temperature control by the Peltier cooler 22. As a result, a loop that makes the relative wavelength error zero works, and the output waveguide # of the arrayed waveguide grating 12
The transmission center wavelength of ₀ can be stabilized to the wavelength λ ₀ of the reference wavelength light.

On the other hand, since the relative accuracy of the transmission center wavelength of each of the output waveguides # 0 to #n of the arrayed waveguide grating 12 is extremely high, stabilizing the transmission center wavelength of the output waveguide # 0 allows the array waveguide to be stabilized. The transmission characteristics of the entire waveguide grating can be stabilized.

Here, the transmission center wavelengths of the output waveguides # 1 to #n of the arrayed waveguide grating 12 are designed to be the respective wavelengths λ ₁ , λ ₂ ,..., Λ _n of the wavelength multiplexed light to be monitored. Then, each wavelength error of the wavelength multiplexed light can be detected from the output light of each output waveguide by the same synchronous detection. In addition,
Each wavelength of the wavelength-division multiplexed light may be equally spaced or irregularly spaced. The arrayed waveguide grating 12 can handle either case.

FIGS. 10A and 10B show the first embodiment.
FIG. 4 is a diagram illustrating a wavelength discriminating operation of wavelength multiplexed light according to the embodiment.

The transmission characteristics of the arrayed waveguide grating 12 are stabilized at the wavelength λ ₀ of the reference wavelength light. Therefore, the error signal, relative to the respective wavelengths lambda ₁ to [lambda] _n wavelength-multiplexed light with the transmission center wavelength of the output waveguide #. 1 to # n which is detected by the synchronous detection in the phase comparator 18-1 to 18-n This corresponds to the wavelength error.

For example, in the state of [1] in which the signal light of wavelength λ ₁ fluctuates to the short wavelength side, the transmission center wavelength of the output waveguide # 0 shown in FIGS. 8 and 9 becomes the wavelength λ ₀ of the reference wavelength light. On the other hand, it is equivalent to the state [1] on the long wavelength side. The state [3] in which the signal light having the wavelength λ ₁ fluctuates toward the long wavelength side corresponds to the state where the transmission center wavelength of the output waveguide # 0 is on the short wavelength side with respect to the wavelength λ ₀ of the reference wavelength light [3]. ]. Therefore, an error signal corresponding to the fluctuation of the wavelength can be obtained by synchronous detection, centering on the state [2] corresponding to the transmission center wavelength λ ₁ of the output waveguide # 1. The error signal corresponding to each wavelength error of the wavelength multiplexed light may be quantified as a wavelength error amount, or may be fed back to the wavelength control circuit of each light source of the wavelength multiplexed light for stabilization. .

As described above, the wavelength monitoring apparatus of the present embodiment
Utilizing the relative accuracy of the transmission center wavelength of each output waveguide of the arrayed waveguide grating 12 and stabilizing one transmission center wavelength to the wavelength λ ₀ of the reference wavelength light, the wavelength multiplexed light to be monitored Can be discriminated with high accuracy.

In the present embodiment, the reference wavelength light and the wavelength multiplexed light are multiplexed and incident on a predetermined input waveguide of the arrayed waveguide grating 12. The light may be incident from a waveguide. As described above, since the output waveguide is cyclically shifted by shifting the input waveguide, the reference wavelength light is input from another input waveguide and the reference wavelength light is output from the output waveguide # 0. Is
The wavelength λ ₀ of the reference wavelength light may be the same as one wavelength of the wavelength multiplexed light. For example, in the wavelength arrangement of FIG. 5A, when the wavelength of the reference wavelength light is λ ₁ (or λ _n ), the input waveguide of the reference wavelength light is shifted next to the input waveguide of the wavelength multiplexed light. I just need. Thus, the arrayed waveguide grating 1
By using 2, the wavelength λ ₀ of the reference wavelength light can be arbitrarily set including the wavelength used in the wavelength multiplexed light. This will be described later in detail.

(Second Embodiment) FIG. 11 shows the configuration of a wavelength monitoring apparatus according to a second embodiment of the present invention.

In the first embodiment, the transmission characteristic of the arrayed waveguide grating 12 is modulated by the reference signal Sa. In this embodiment, the phase modulation or the frequency modulation of the incident light of the arrayed waveguide grating 12 is performed by the reference signal Sa. Features.

In the figure, a phase modulator or a frequency modulator 24 is provided between an optical coupler 11 and an arrayed waveguide grating 12.
And the reference signal Sa output from the oscillator 14 is supplied to the phase modulator or the frequency modulator 24, and the reference wavelength light and the wavelength multiplexed light are phase-modulated or frequency-modulated.
Other configurations and the principle of wavelength error detection are the same as those of the first embodiment. However, in this embodiment, the arrayed waveguide grating 1
2, the reference wavelength light and the wavelength multiplexed light are minutely vibrated on the wavelength axis, and a change in the light intensity (light receiving signal Sb) obtained according to the vibration is synchronously detected. Detect relative wavelength error. Therefore, the sign of the error signal Sc has the opposite meaning to that of the first embodiment.

FIG. 12 and FIG. 13 are diagrams for explaining the wavelength discrimination and the stabilization operation of the transmission characteristic in the second embodiment.

The transmission center wavelength of the output waveguide # 0 has any one of the states [1], [2] and [3] with respect to the wavelength λ ₀ of the reference wavelength light. In a state [1] in which the transmission center wavelength of the output waveguide # 0 is on the long wavelength side with respect to the wavelength λ ₀ of the reference wavelength light, the received light signal Sb is a signal having the same frequency and phase as the reference signal Sa, and is on the short wavelength side. In the state [3], the signal has the same frequency as the reference signal Sa and the phase is shifted by π. Further, in the state [2] where the two coincide with each other, the light receiving signal Sb is a signal having twice the frequency of the reference signal Sa. Such a light receiving signal Sb is synchronously detected by the phase comparator 18-0 using the reference signal Sa, and the low-pass filter 19
By removing the modulation frequency component at −0 and extracting the signal component, it is possible to obtain an error signal Sc corresponding to the relative wavelength error between the wavelength λ ₀ of the reference wavelength light and the transmission center wavelength of the output waveguide # 0. it can. The error signal Sc becomes positive in the state [1], becomes negative in the state [3], and becomes 0 in the state [2]. By controlling the Peltier cooler 22 with the control signal Sd obtained by time-integrating the error signal Sc with the integrator 20-0, a loop for making the relative wavelength error zero works, and the output waveguide of the arrayed waveguide grating 12 is output. The transmission center wavelength of # 0 can be stabilized at the wavelength λ ₀ of the reference wavelength light.

The same applies to the wavelength discrimination operation of the wavelength division multiplexed light.
That is, since the transmission characteristics of the arrayed waveguide grating 12 are stabilized at the wavelength λ ₀ of the reference wavelength light, the phase comparator 18-1
Error signal detected by the synchronous detection in ~18~n the output waveguides # 1 and the wavelength lambda ₁ to [lambda] _n wavelength-multiplexed light
This corresponds to a relative wavelength error with the transmission center wavelength of #n.

(Third Embodiment) FIG. 14A shows a configuration of a third embodiment of the present invention.

In the figure, the reference wavelength light (wavelength λ ₀ ) and the wavelength-division multiplexed light (wavelengths λ _{1 to} λ _n ) to be monitored are coupled to the optical coupler 1.
The signals are multiplexed by 1 and input to a predetermined input waveguide of the arrayed waveguide grating 12. Output waveguide # of arrayed waveguide grating 12
Balanced light receiving elements 25-0 and 25-i (i is up to n) are connected to 0 to # 2n + 1 for every two adjacent output waveguides (FIG. 15A). Balanced light receiving element 25
−0, 25-i are output from amplifiers 17-0, 1
7-i. The output of the amplifier 17-0 is input to the integrator 20-0. A temperature control circuit 21 is connected to the output of the integrator 20-0. The temperature control circuit 21 includes a Peltier cooler 22 for adjusting the temperature of the arrayed waveguide grating 12.
Control.

As shown in FIG. 15 (B), the configuration below the balanced light receiving elements connected to the output waveguides # 2 to # 2n + 1 of the arrayed waveguide grating 12 constitutes one set, and the optical switch 23-1 , 23-2 for connection.

The feature of this embodiment is that, as shown in FIG. 16A, the transmission characteristics are stabilized so that the intersection (crossing wavelength) of adjacent transmission characteristics matches the wavelength λ ₀ of the reference wavelength light.
This is to discriminate each wavelength of the wavelength multiplexed light. When the transmission characteristics of the arrayed waveguide grating 12 are set in this way, as shown in FIG. 16B, the light intensity of the reference wavelength light has a Gaussian distribution between the output waveguides # 0 and # 1. (Gaussian beam) spreads. The coupling between the Gaussian beam and the output waveguides # 0 and # 1 occurs at a portion where the two are indicated by oblique lines in the figure. Therefore, when the transmission characteristic fluctuates to the long wavelength side or the short wavelength side, the light intensity coupled to the output waveguides # 0 and # 1 becomes uneven according to the relative wavelength error with respect to the wavelength λ ₀ of the reference wavelength light, The difference between them is detected as an error signal.

FIG. 17 (A) and FIG. 17 (B)
FIG. 6 is a diagram for explaining wavelength discrimination of reference wavelength light and stabilization of transmission characteristics in the example.

The transmission characteristics of the output waveguides # 0 and # 1 indicate the state [1], the state [2], and the state [2] with respect to the wavelength λ ₀ of the reference wavelength light.
The relationship is any one of the states [3]. In the state [1] where the transmission characteristic is on the long wavelength side with respect to the wavelength λ ₀ of the reference wavelength light, the light intensity coupled to the output waveguide # 0 increases,
In the state [3] on the short wavelength side, the light intensity coupled to the output waveguide # 1 increases. Further, in the state [2] where the two coincide, the light intensity is evenly coupled to the output waveguides # 0 and # 1. Therefore, the respective light receiving signals Sa0, Sa0 of the balanced light receiving element 25-0 connected to the output waveguides # 0, # 1.
Sa1 changes according to states [1], [2], and [3]. The balanced light receiving element 25-0 outputs each light receiving signal Sa.
Since the difference between 0 and Sa1 is output as the error signal Sc,
The error signal Sc indicates a positive voltage in the state [3], and the state [1]
Indicates a negative voltage, and becomes 0 in the state [2]. A control signal S obtained by time-integrating the error signal Sc with the integrator 20-0.
By controlling the Peltier cooler 22 with d, a loop that makes the relative wavelength error zero works, and the array waveguide grating 1
2 can be stabilized at the wavelength λ ₀ of the reference wavelength light.

The same applies to the wavelength discrimination operation of the wavelength division multiplexed light.
That is, since the transmission characteristic of the arrayed waveguide grating 12 is stabilized at the wavelength λ ₀ of the reference wavelength light, the error signal output from each of the balanced light receiving elements 25-1 to 25 -n is different from the wavelength multiplexed light. This corresponds to the relative wavelength error between the wavelengths λ _{1 to} λ _n and the transmission characteristics.

In this embodiment, the configuration using the balanced light receiving element and the amplifier is shown. However, as shown in FIG. 14B, the two output waveguides are provided with the photodetectors 16-1 and 16-1, respectively.
The same operation and effect can be obtained even if the light receiving signal is processed by the differential amplifier 26 by connecting the light receiving signal 16-2.

In this embodiment, the wavelength error is detected from the difference between the light intensities of the adjacent output waveguides of the arrayed waveguide grating 12. However, as shown in FIG. 16B, the pitch between the output waveguides cannot be ideally set to zero, so that the light intensity component between them cannot be effectively used, and the light intensity coupled to the output waveguide decreases. . That is, the transmission intensity at the crossing wavelength decreases. A configuration for solving this problem will be described below.

(Fourth Embodiment) FIG. 18 shows the configuration of a fourth embodiment of the present invention.

In the figure, the reference wavelength light (wavelength λ ₀ ) and the wavelength-division multiplexed light (wavelengths λ _{1 to} λ _n ) to be monitored are multiplexed by the 2 × 2 optical coupler 27, and the two inputs to the arrayed waveguide grating 12. Input to the waveguide. For one of the input waveguides reference wavelength light and the wavelength-multiplexed light inputted from the reference wavelength light and the wavelength lambda ₁ to [lambda] _n wavelength lambda ₀ in the output waveguide # 0 to # n of the arrayed waveguide grating 12 Signal light is output. Further, for the reference wavelength light and the wavelength multiplexed light input from the other input waveguide, the reference wavelength light of wavelength λ ₀ and the wavelengths λ _{1 to} λ are output to the output waveguides # n + 1 to # 2n + 1 of the arrayed waveguide grating 12. _{The n} signal lights are respectively output.
Balanced light receiving elements 25-0 and 25-i (i is 1 to n) are connected to each of two output waveguides corresponding to each wavelength (FIG. 19A). Balanced light receiving element 25-0, 25
The output of −i is input to amplifiers 17-0 and 17-i, respectively. The output of the amplifier 17-0 is input to the integrator 20-0. A temperature control circuit 2 is connected to the output of the integrator 20-0.
1 is connected. The temperature control circuit 21 controls a Peltier cooler 22 that adjusts the temperature of the arrayed waveguide grating 12.

As shown in FIG. 19B, the output waveguides # 1 to #n and # n + 2 to #n of the arrayed waveguide grating 12
The configuration below the balanced light receiving element connected to 2n + 1 may be set as one set, and switched and connected using the optical switches 23-1 and 23-2.

The feature of this embodiment is that by adjusting the distance between the output waveguides # 0 to #n and the output waveguides # n + 1 to # 2n + 1, as shown in FIG. One half of the light intensity is coupled to two output waveguides. For example, the output waveguide # 0 is designed to couple with the short wavelength half of the reference wavelength light (λ ₀ ), and the output waveguide # n + 1 is designed with the long wavelength half of the reference wavelength light (λ ₀ ). . This is because the distance between the output waveguides #n and # n + 1 is 6Δλ as shown in FIG.
Is set to λ ₀ −Δλ, and the transmission center wavelength of the output waveguide # n + 1 is set to λ ₀ + Δλ. Where Δ
λ is ４ of the wavelength interval of the wavelength multiplexed light. Conversely, half of the long wavelength side of the reference wavelength light (λ ₀ )
A half of the reference wavelength light (λ ₀ ) on the short wavelength side may be coupled to the output waveguide # n + 1. The same applies to signal light having wavelengths λ _{1 to} λ _n of wavelength multiplexed light. As described above, the interval between the waveguides of the output waveguides # 0 to #n is 4Δλ, and the interval between the waveguides of the output waveguides # n + 1 to # 2n + 1 is also 4Δλ.
On the other hand, the feature of this embodiment is that the interval between the output waveguides #n and # n + 1 is set to 6Δλ. In other words, while the normal output waveguide interval is set to the wavelength interval of the multi-wavelength light (4Δλ), the output waveguide group I (#
0 to #n) and II (# n + 1 to # 2n + 1)
It is characterized in that it is further shifted by a half wavelength interval (2Δλ) from the wavelength interval (4Δλ) of the wavelength multiplexed light, and is 1.5 times (6Δλ).

When such a transmission characteristic shifts in a direction in which Δλ increases, for example, due to temperature fluctuation, the coupling strength to the output waveguide # 0 decreases, and the output waveguide # n + 1
The bonding strength to the wire increases. By detecting the difference between them and controlling the Peltier cooler 22 in the same manner as in the third embodiment, a loop for making the relative wavelength error zero works, and the transmission characteristic of the arrayed waveguide grating 12 is reduced by the wavelength of the reference wavelength light. λ ₀
Can be stabilized.

The same applies to the wavelength discrimination operation of wavelength multiplexed light.
That is, since the transmission characteristic of the arrayed waveguide grating 12 is stabilized at the wavelength λ ₀ of the reference wavelength light, the error signal output from each of the balanced light receiving elements 25-1 to 25 -n is different from the wavelength multiplexed light. This corresponds to the relative wavelength error between the wavelengths λ _{1 to} λ _n and the transmission characteristics.

In the above embodiment, as shown in FIG. 21A, the reference wavelength light and the wavelength multiplexed light are multiplexed and input into the input waveguides (a) and (b), and the output waveguide # 0 is output. To #n, and a branch wavelength group II to the output waveguides # n + 1 to # 2n + 1.

However, the present embodiment is not limited to such a configuration. For example, as shown in FIG. 21B, the output waveguides # 0 to #n have 0-order light (diffraction order n) and output waveguides # N + 1 to # 2n + 1 are first-order light (diffraction order n +
It is also possible to design so that light can be extracted as in 1). However, in this case, the differential amplifier 26 is used instead of the balanced light receiving element, and the wavelength difference processing is performed by correcting the output intensity difference between the zero-order light and the primary light. Further, the output waveguide group is further increased to prepare several times the FSR, and the zero-order light and 1
It is also possible to take out light such as secondary light (diffraction order n + 2) in addition to the secondary light. Also in this case, the interval between the output waveguide groups of each order is 1.times. The wavelength interval of the wavelength multiplexed light.
It is characterized by a factor of 5 (6Δλ). In each of the embodiments described above, wavelength discrimination of wavelength-division multiplexed light has been described. However, optical frequency discrimination can be similarly described.

(Fifth Embodiment) FIGS. 22 and 23 are block diagrams showing a wavelength monitoring apparatus according to a fifth embodiment of the present invention. This fifth embodiment is different from the third embodiment shown in FIG. 14A in that the third embodiment takes the difference between the outputs of the adjacent output ports. The point is that the output ratio is taken. Therefore, in this embodiment,
Outputs of the light receiving elements 16-ia and 16-ib forming a pair are supplied to a first input terminal and a second input terminal of the logarithmic amplifier 40-i, respectively. The logarithmic amplifier 40-i calculates the difference between the two input signals after logarithmic conversion. Therefore, in this embodiment, the output ratio of the adjacent output port is output as a wavelength error signal.

The arrayed waveguide grating (AWG) 1 of this embodiment
Reference numeral 2 denotes a 16 × 16 arrayed waveguide grating, and the transmission center wavelength interval of each adjacent channel is 1 nm. Therefore, the FSR (Free Spectral Range) is 16 nm. However, only the central eight ports are used as input ports. The transmission center wavelength of each channel of the arrayed waveguide grating 12 changes depending on the position of the input port of the multiplexed wave of the wavelength multiplexed light and the reference wavelength light.

FIG. 24A is a view corresponding to FIG. 22, and shows a transmission characteristic of the arrayed waveguide grating 12 when a multiplexed wave of wavelength multiplexed light and reference wavelength light is input from the input port # 1. FIG. The horizontal axis of FIG.
The vertical axis represents the transmittance. As can be seen from this figure, when the output port number increases by one, the transmission center wavelength becomes one.
Shifts to the longer wavelength side by nm. Therefore, as shown in FIG. 22, each output port is connected to a logarithmic amplifier on the long wavelength side as the number increases. That is, the output ports # 1 and # 2 are
It is connected to the first input terminal and the second input terminal of the logarithmic amplifier 40-1 (output #G) on the shortest wavelength side via 6-1a and 16-1b. Similarly, output ports # 3 and # 4 are paired with light receiving elements 16-2a and 16-2b.
Are connected to a first input terminal and a second input terminal of the logarithmic amplifier 40-2 (output #F). Thereafter, the same connection is repeated, and the output ports # 13 and # 14 are connected to the first input terminal of the logarithmic amplifier 40-7 (output #A) on the longest wavelength side via the light receiving elements 16-7a and 16-7b. And a second input terminal. In addition, output port #
Reference numerals 15 and # 16 denote output ports for the reference wavelength light, and the first input terminal and the second input terminal of the logarithmic amplifier 40-0 (output #H) via the light receiving elements 16-0a and 16-0b.
Each is connected to an input terminal.

On the other hand, FIG. 24B is a diagram corresponding to FIG. 23, wherein the multiplexed wave of the wavelength multiplexed light and the reference wavelength light is represented by # 7.
7 is a graph showing transmission characteristics when input is made from an input port of FIG. As the input port number increases by one, the output port shifts by 1 nm to the longer wavelength side. Therefore, when the input port is changed from # 1 to # 7, the transmission center wavelength of the output port # 1 shifts to the longer wavelength side by 6 nm and changes from 1549 nm to 1555 nm. Therefore, each output port is connected as shown in FIG. That is, the output ports # 1 and # 2 are connected to the first input terminal and the second input terminal of the logarithmic amplifier 40-4 (output #D), and the output ports # 3 and # 4 are connected to the logarithmic amplifier 40-5 ( The output #C) is connected to a first input terminal and a second input terminal. Hereinafter, the same connection is repeated, and output ports # 15 and # 16 are connected to logarithmic amplifier 40-3.
(Output #E) are connected to the first input terminal and the second input terminal. The output ports # 9 and # 10 are connected to the first input terminal and the second input terminal of the logarithmic amplifier 40-0 (output #H) for the reference wavelength light, respectively.

As can be seen from FIGS. 24 (A) and 24 (B), the input / output characteristics of the arrayed waveguide grating 12 have periodicity (Periodic Assignment). For example, the output of output port # 15 in FIG.
And 1563 nm and the FSR component (in this case, 16n
The wavelength shifted by m) also has a transmission center wavelength. The same applies to an intersection wavelength defined as a point where two adjacent transmission center wavelength characteristic curves intersect.

FIG. 25 shows this state. FIG. 25 (A)
To (H) are the outputs # of the logarithmic amplifiers 40-7 to 40-0.
The zero-crossing outputs of A to #H are shown. As is clear from this figure, the zero-crossing points are shifted by 2 nm. This is because each logarithmic amplifier uses two output ports.

According to such a configuration, since the wavelength error signal is obtained in the form of the ratio of the two output lights, even if the intensity of the input light varies, highly accurate and stable wavelength discrimination is performed. be able to.

FIGS. 26A and 26B show the case where the difference between the outputs from the two output ports is taken (FIG. 26).
27 (A) is a graph showing a difference between the case where the ratio is taken (FIG. 26 (B)). The horizontal axis of these graphs is a value obtained by normalizing the deviation from the crossing wavelength, and the vertical axis is a value obtained by normalizing the difference output or the specific output with the input intensity. As can be seen from these figures, the difference output is the light input intensity P
While the output varies depending on 0 and P0 / 2, the specific output has a constant characteristic independent of the input intensity.

The measurement range of the wavelength multiplexed light is a range where the output of the logarithmic amplifier is determined and the ratio of the two output lights can be obtained. As shown in FIG. 26B, the output of the logarithmic amplifier is
It becomes 0 at the zero crossing wavelength and increases as the distance from this point increases, but a range of about 0.5 nm before and after the crossing wavelength can be set as the measurement range. That is, the measurement range is a straight line portion before and after the crossing wavelength, and for example, is in a range of 1547 to 1548 nm in FIG.

Also, the wavelength of the reference wavelength light is
It can be set arbitrarily in the output range of 0-0 (output #H). That is, the offset circuit 216 shown in FIG.
By adding, to the wavelength error signal, an offset corresponding to the difference between the set cross wavelength and the wavelength of the reference wavelength light, the reference wavelength light having a wavelength different from the set cross wavelength can be used.

In practice, the crossing wavelength of the arrayed waveguide grating 12 is set to 1547.5 nm, and the wavelength of the reference wavelength light output from the semiconductor laser light source 10 is 1547.4485.
There is a difference of 0.015 nm (1.8 GHz in terms of frequency) from the nm, but by giving an offset, this difference is compensated and stable control of the transmission center wavelength is enabled.

(Sixth Embodiment) FIG. 27 is a block diagram showing a wavelength monitoring apparatus according to a sixth embodiment of the present invention. This embodiment differs from the fifth embodiment shown in FIGS. 22 and 23 in that wavelength multiplexed light and reference wavelength light are input from separate input ports. That is, wavelength multiplexed light is input to input port # 5, and reference wavelength light is input to input port # 7.

The wavelength-division multiplexed light input to input port # 5 shifts the transmission center wavelength by 2 nm to the shorter wavelength side as compared with the case of FIG. 22 input to input port # 7. Therefore, each cross wavelength also shifts by 2 nm. For example, the output #A of the logarithmic amplifier 40-7 is
In the case of input port # 7, the cross wavelength is 1561.5
nm, but 155 from input port # 5.
Shift to 9.5 nm.

According to such a configuration, even if one wavelength light of the wavelength multiplexed light is the same as the wavelength of the reference wavelength light, the wavelength can be monitored. These lights have the same wavelength,
This is because the data is output from another output port.

FIGS. 28, 29, 30A and 3
0 (B) is a diagram for explaining this. The wavelength multiplexed light and the reference wavelength light are multiplexed, and input port # 0 of FIG.
29, if there is a constraint that the number of output ports is twice the number of input wavelengths (1 (reference wavelength) + the number of wavelength multiplexes), the wavelength arrangement is as shown in FIG. That is, the wavelength Ref (i) allowed as the reference wavelength is limited to a wavelength range that is an integral multiple of the FSR and does not overlap the wavelength range of the wavelength multiplexed light.

On the other hand, as shown in FIG. 28, when wavelength multiplexed light and reference wavelength light are input from different input ports, the wavelength multiplexed light shown in FIG.
The reference wavelength light in the range indicated by the white square is allowed. Also,
The hatched portion in FIG. 30B indicates the reference wavelength allowed when the wavelength multiplexed light and the reference wavelength light are input from the same input port. Therefore, by changing the input port of the reference wavelength light, the reference wavelength light of any wavelength can be used.

Note that in the fifth and sixth embodiments,
A logarithmic amplifier was used to determine the ratio of the output from the output port of the arrayed waveguide grating 12, but is not limited to this.
For example, as shown in FIG. 31, instead of a logarithmic amplifier, A / D converters 41-0a to 41-7b, a DSP (digital signal processor) 43, and D / A converters 45-0 to 45-7 are provided. Even when used, similar actions and effects can be obtained. In this case, the A / D converter 41-0a
The input terminals of 41-7b are the light receiving elements 16-0a of FIG.
To 16-7b, respectively.

The D / A converters 45-0 to 45-7
Is not always necessary, and a wavelength error signal obtained in the form of a digital signal can be used as an output.

(Seventh Embodiment) FIG. 32 shows an embodiment in which the wavelength monitoring apparatus according to the present invention is applied to the wavelength control of a semiconductor laser for transmission.

In the figure, lights having wavelengths of λ1 to λ7 output from semiconductor lasers 51 to 57 are multiplexed by a multiplexer 91 to become a wavelength multiplexed light and supplied to an optical coupler 92. The optical coupler 92 branches a part of each wavelength light of the wavelength-division multiplexed light, supplies it to the wavelength monitoring device 93, and outputs the rest. Wavelength monitoring device 93, set the wavelength lambda ₀₁ to a predetermined, lambda _02, ..., and lambda _07, the error amount lambda ₁ to [lambda] ₀₁ and each wavelength of a wavelength-multiplexed light, ..., lambda ₇ to [lambda] ₀₇ output I do. The error amount is negatively fed back to the injection current control circuits 61 to 67 of the semiconductor lasers 51 to 57 to control the error amount to zero. As a result, the oscillation wavelength of the semiconductor laser is stabilized at the set values λ ₀₁ ,..., Λ ₀₇ .

Further, instead of the injection current control circuit, a configuration in which negative feedback is performed to the temperature control circuit of the semiconductor laser can be realized.

(Eighth Embodiment) FIG. 33 shows the configuration of an eighth embodiment of the present invention.

In the figure, reference wavelength light is wavelength light stabilized to absorption lines of atoms or molecules. The wavelength-division multiplexed light (8-wave multiplex in this embodiment) to be monitored is input to the optical demultiplexer 111 and demultiplexed for each wavelength. Each wavelength light obtained by demultiplexing the reference wavelength light and the wavelength multiplexed light is input to a Mach-Zehnder interferometer array 113 in which a plurality of Mach-Zehnder interferometers 112 are integrated. Each Mach-Zehnder interferometer 112
Outputs two intensity output lights, the phases of which are inverted with respect to the wavelength, which are converted into electric signals by the photodetector 114, respectively. The level ratio of the two electrical signals for one wavelength is determined by a logarithmic amplifier (log amplifier) 115 and output as a wavelength error signal. The wavelength error signal for the reference wavelength light is input to the temperature control circuit 116. The temperature control circuit 116 controls the Peltier cooler 117 that adjusts the temperature of the Mach-Zehnder interferometer array 113.

Here, the wavelength error detecting operation in the eighth embodiment will be described with reference to FIG.

FIG. 34A shows one Mach-Zehnder interferometer 112 in the Mach-Zehnder interferometer array 113, and FIG.
Photodetectors 114-1 and 114-2 corresponding to outputs A and B of a Mach-Zehnder interferometer, respectively, and a logarithmic amplifier 115 which outputs a wavelength error signal by taking a level ratio of an electric signal output from each photodetector are shown. . The Mach-Zehnder interferometer has transmission characteristics at equal intervals with respect to the wavelength (or optical frequency) as shown in FIG. 34B, and the light output from the outputs A and B is different from the wavelength (or optical frequency). This indicates that the phase is inverted. The solid line indicates the transmission characteristic of the output A, and the broken line indicates the transmission characteristic of the output B. FIG. 34 (C)
The reference wavelength light (wavelength λ ₀ ) and the wavelength multiplexed light (wavelength λ ₁ , λ
₂ , ...) are shown. The wavelength multiplexed light is split into each wavelength light according to the transmission characteristics of the optical splitter (or the variable optical filter described later) shown in the figure.

Outputs A and B of Mach-Zehnder interferometer 112
The wavelength error signal according to the level ratio of the light output from
As shown in FIG. 34 (D), the output changes from a positive value to a negative value according to the input wavelength, and the output becomes zero at a zero crossing wavelength where the transmittances of the outputs A and B are equal (both are 0.5). That is, the relative wavelength error between the input wavelength and the zero-crossing wavelength can be detected according to the polarity and level of the wavelength error signal (electric signal) output from the logarithmic amplifier 115.

In this embodiment, since the zero-crossing wavelength for each half cycle is associated with each wavelength of the reference wavelength light and the wavelength multiplexed light, adjacent wavelengths are set as shown in FIG. The output A of the Mach-Zehnder interferometer 112 that discriminates
The connection relationship between B and the positive terminal and the negative terminal of the logarithmic amplifier 115 is alternately switched. Thus, the wavelength error can be detected for all the wavelengths according to the characteristic shown in FIG.

Now, the wavelength error signal output from the logarithmic amplifier corresponding to the Mach-Zehnder interferometer receiving the reference wavelength light is input to the temperature control circuit 116, and the Peltier cooler 117 is controlled so that it becomes zero. To adjust the temperature of the Mach-Zehnder interferometer array 113. As a result, the transmission characteristics of the Mach-Zehnder interferometer are shifted, and the zero-crossing wavelength can be matched with the wavelength of the reference wavelength light. At this time, the transmission characteristics of the other Mach-Zehnder interferometers of the Mach-Zehnder interferometer array 113 are simultaneously controlled, so that the configuration of this embodiment can function as a wavelength discriminator having the same degree of accuracy as the reference wavelength light. . That is, for each wavelength of the wavelength division multiplexed light demultiplexed by the optical demultiplexer 111, a corresponding predetermined wavelength (zero-crossing wavelength).
Can be obtained with high accuracy.

As another method for controlling the transmission characteristics of the Mach-Zehnder interferometer, for example, a transmission characteristic sweeping means utilizing an electro-optic effect such as a lithium niobate (LiNbO ₃ ) substrate is negatively applied to the applied voltage. A feedback control circuit can be used. The same applies to the following embodiments.

In this embodiment, since the level ratio of the two transmitted output lights of the Mach-Zehnder interferometer is determined by the logarithmic amplifier, the power is stable (independent of the input light power) even if the power of the input signal light fluctuates. Wavelength discrimination is possible. On the other hand, when the power of the input signal light is stable, the same wavelength discrimination is possible even in a configuration in which a level difference between two transmitted output lights is detected using a differential amplifier instead of a logarithmic amplifier. Further, if the output of the differential amplifier is corrected by the input optical power, stable wavelength discrimination can be performed even if the power of the input signal light fluctuates as in the case of using the logarithmic amplifier. The same applies to the following embodiments.

(Ninth Embodiment) FIG. 35 shows the configuration of a ninth embodiment of the present invention.

The present embodiment is characterized in that the optical demultiplexer 111 in the eighth embodiment is replaced by a variable optical filter 121, and two sets of Mach-Zehnder interferometers are provided as the Mach-Zehnder interferometer 113. In the eighth embodiment, the wavelength-division multiplexed light to be monitored is spatially divided for each wavelength and wavelength discrimination is performed at the same time. In the present embodiment, the variable optical filter 121 whose transmission center wavelength is switched at a predetermined cycle. The wavelength division multiplexed light is separated by time division to discriminate the wavelength.

FIG. 36 shows a sweep signal applied to the variable optical filter 121. The sweep signal applied to the tunable optical filter 121 is a multi-level step signal adjusted so that its transmission center wavelength changes according to the wavelength multiplexing interval. Thus, the signal light (channel) of each wavelength of the wavelength multiplexed light can be sequentially switched and input to the Mach-Zehnder interferometer.

As described above, the sweep signal (multi-level step signal) for calibrating the nonlinearity of the transmission center wavelength with respect to the voltage applied to the variable optical filter 121 is used, and the variable optical filter 121 is used.
By accurately sweeping the transmission center wavelength at the wavelength multiplexing interval, the signal light of each wavelength can be sequentially demultiplexed. Further, since the zero-crossing wavelength of the Mach-Zehnder interferometer array 113 is stabilized to the wavelength of the reference wavelength light, similarly to the eighth embodiment, the Mach-Zehnder interferometer array 113 functions as a wavelength discriminator synchronized with the absolute wavelength. Can be.
Therefore, the combination of the tunable optical filter 121 and the Mach-Zehnder interferometer array 113 of this embodiment also
The wavelength error of the wavelength multiplexed light to be monitored can be distinguished with high accuracy.

(Tenth Embodiment) FIG. 37 shows the first embodiment of the present invention.
0 shows the configuration of the embodiment.

This embodiment is characterized in that the variable optical filter 121 in the ninth embodiment is replaced by an optical splitter 111 and an optical switch 131.

In this embodiment, the wavelength division multiplexed light is demultiplexed for each wavelength by the optical demultiplexer 111 as in the eighth embodiment, and the signal light of each wavelength is sequentially output by the optical switch 131, and the Mach-Zehnder interferometer is used. Input to one Mach-Zehnder interferometer of array 113. The wavelength discrimination operation is the same as in the ninth embodiment.

(Eleventh Embodiment) FIG. 38 shows the first embodiment of the present invention.
1 shows a configuration of one embodiment.

This embodiment is different from the ninth or tenth embodiment in that the polarization of the reference wavelength light and the polarization of the wavelength multiplexed light are made orthogonal to each other, so that one Mach-Zehnder interferometer can discriminate both wavelengths. Is made possible.

The wavelength division multiplexed light is supplied to the variable optical filter 121 shown in the ninth embodiment or the optical demultiplexer 11 shown in the tenth embodiment.
1 and are sequentially demultiplexed for each wavelength via the optical switch 131 and output. The signal light of each wavelength and the reference wavelength light are multiplexed by orthogonal polarization multiplexing means (for example, a polarization beam splitter) 141 and input to one Mach-Zehnder interferometer 112. Outputs A and B of the Mach-Zehnder interferometer 112 are respectively orthogonal polarization separation means (for example, a polarization beam splitter).
Polarization separation is performed at 142-1 and 142-2. The polarized light is the signal light of each wavelength and the reference wavelength light, respectively, and the wavelength error is detected by the wavelength error detecting means (photodetector 114, logarithmic amplifier 115). The control system for stabilizing the Mach-Zehnder interferometer 112 to the absolute wavelength is the same as in the eighth to tenth embodiments.

[0122]

As described above, the wavelength monitoring apparatus of the present invention can cope with a change in the transmission center wavelength of the arrayed waveguide grating due to a change in the ambient temperature, and thus performs stable wavelength discrimination over a long period of time. be able to.

In the configuration in which the output light intensity difference between the two output waveguides of the arrayed waveguide grating is compared to perform wavelength discrimination,
Since an electric circuit required for synchronous detection is not required, the entire configuration can be simplified.

Further, since the arrayed waveguide grating is realized by a combination of optical waveguides integrated on a solid substrate such as quartz or a semiconductor, the transmission characteristics are improved by utilizing the thermo-optic effect or the electro-optic effect. Extremely stable control is possible. Moreover, since it is an integrated device, it is small and suitable for mass production, so that the cost of the wavelength monitoring device can be reduced.

Further, unlike the case of the sweep type Fabry-Perot interferometer, the arrayed waveguide grating is stable against mechanical vibration because it does not require a movable part.

Further, in the wavelength monitoring apparatus of the present invention, not only the reference wavelength light and the wavelength multiplexed light are arranged at equal wavelength intervals, but also in the case of unequal intervals, by using the corresponding arrayed waveguide grating, Discrimination processing becomes possible.

Further, by inputting the reference wavelength light and the wavelength multiplexed light from different input ports, it is possible to discriminate even if the reference wavelength light matches the wavelength multiplexed light. As described above, by using the arrayed waveguide grating, wavelength multiplexed light and reference wavelength light set at arbitrary wavelength intervals can be easily distinguished.

Further, the wavelength monitoring apparatus of the present invention uses the stabilized reference wavelength light to negatively feed back the relative wavelength error between the zero-crossing wavelength and the reference wavelength of the Mach-Zehnder interferometer array or Mach-Zehnder interferometer. Accordingly, the transmission characteristics can be stabilized with high accuracy even when the environment changes.

By using the stabilized Mach-Zehnder interferometer array or Mach-Zehnder interferometer as a wavelength discriminator, each wavelength of the wavelength-division multiplexed light to be monitored can be monitored with high accuracy. Further, by arraying Mach-Zehnder interferometers having the same characteristics on the same substrate, the relative wavelength accuracy can be increased. Further, the vibration resistance performance of the integrated structure can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of a conventional wavelength monitoring device.

FIG. 2 is a waveform chart showing the operation of a conventional wavelength monitoring device.

FIGS. 3A and 3B are graphs showing a relationship between an applied voltage of a sweep type Fabry-Perot interferometer, a displacement amount of a piezoelectric element, and a transmission center wavelength.

FIG. 4 is a block diagram showing a first embodiment of a wavelength monitoring device according to the present invention.

FIG. 5A is a diagram showing a configuration of a main part of the first embodiment;
(B) is a diagram showing a configuration of a main part of a modification of the first embodiment.

FIG. 6 is a block diagram illustrating a configuration of a temperature control circuit.

FIG. 7 is a graph showing transmission characteristics of an arrayed waveguide grating.

FIG. 8 shows wavelength discrimination of reference wavelength light in the first embodiment,
FIG. 9 is a diagram for explaining an operation of stabilizing transmission characteristics.

FIG. 9 shows wavelength discrimination of reference wavelength light in the first embodiment,
FIG. 9 is a diagram for explaining an operation of stabilizing transmission characteristics.

FIGS. 10A and 10B are diagrams for explaining the wavelength discriminating operation of the wavelength division multiplexed light in the first embodiment.

FIG. 11 is a block diagram showing a second embodiment of the wavelength monitoring device according to the present invention.

FIG. 12 is a diagram for explaining wavelength discrimination of reference wavelength light and operation of stabilizing transmission characteristics in the second embodiment.

FIG. 13 is a diagram for explaining wavelength discrimination of reference wavelength light and operation of stabilizing transmission characteristics in the second embodiment.

FIG. 14A shows a third example of the wavelength monitoring apparatus according to the present invention.
FIG. 13B is a block diagram illustrating an embodiment, and FIG. 13B is a diagram illustrating an example in which a photodetector and a differential amplifier are used instead of the balanced light receiving element and the amplifier in the third embodiment.

FIG. 15A is a diagram illustrating a configuration of a main part of the third embodiment, and FIG. 15B is a diagram illustrating a configuration of a main part of a modification of the third embodiment.

FIGS. 16A and 16B are diagrams showing a relationship between transmission characteristics and reference wavelength light in the third embodiment.

17A and 17B are diagrams for explaining wavelength discrimination of reference wavelength light and stabilizing operation of transmission characteristics in the third embodiment.

FIG. 18 is a block diagram showing a fourth embodiment of the wavelength monitoring device according to the present invention.

FIG. 19A is a diagram illustrating a configuration of a main part of a fourth embodiment, and FIG. 19B is a diagram illustrating a configuration of a main part of a modification of the fourth embodiment.

FIG. 20 is a diagram for explaining a wavelength discrimination operation in the fourth embodiment.

FIGS. 21A and 21B are diagrams illustrating input / output states according to a fourth embodiment and a modified example thereof.

FIG. 22 is a block diagram illustrating a wavelength monitoring apparatus according to a fifth embodiment of the present invention.

FIG. 23 is a block diagram showing a wavelength monitoring apparatus according to a fifth embodiment of the present invention.

FIGS. 24A and 24B are graphs for explaining the circulating property of an arrayed waveguide grating. FIG. 24A shows a case where input light is input to an input port # 1, and FIG. )
The case where the input light is input to the input port # 7 is shown.

FIG. 25 is a graph showing the zero-crossing wavelength of the output of each logarithmic amplifier when input light is input to input port # 1.

26A is a graph showing that an output difference between two output ports depends on input light intensity, and FIG. 26B is a graph showing that an output ratio of two output ports does not depend on input light intensity. FIG.

FIG. 27 is a block diagram showing a sixth embodiment of the wavelength monitoring device according to the present invention.

FIG. 28 is a diagram illustrating a state of output light when wavelength multiplexed light is input from an input port # 0 and reference wavelength light is input from another input port.

FIG. 29 is a diagram illustrating a wavelength arrangement of the wavelength multiplexed light and the reference wavelength light when the wavelength multiplexed light and the reference wavelength light are input after being multiplexed.

FIGS. 30A and 30B are diagrams showing wavelength allocation when wavelength multiplexed light and reference wavelength light are input to different input ports, and FIG. 30A is a diagram showing the wavelength allocation of wavelength multiplexed light. (B) shows the wavelength arrangement of the reference wavelength light.

FIG. 31 In the fifth and sixth embodiments, an A / D converter and a DSP are used instead of a logarithmic amplifier at the output end of a photodetector.
FIG. 2 is a block diagram illustrating a configuration when a (digital signal processor) and a D / A converter are connected.

FIG. 32 is a block diagram showing an embodiment in which the wavelength monitoring device according to the present invention is applied to a multi-wavelength transmission semiconductor laser.

FIG. 33 is a diagram showing a configuration of an eighth embodiment of the present invention.

FIG. 34 is a diagram illustrating a wavelength error detection operation in the eighth embodiment.

FIG. 35 is a diagram showing a configuration of a ninth embodiment of the present invention.

FIG. 36 is a diagram showing a sweep signal applied to the variable optical filter 121.

FIG. 37 is a diagram showing a configuration of a tenth embodiment of the present invention.

FIG. 38 is a diagram showing a configuration of an eleventh embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Optical coupler 12 Arrayed waveguide grating 13 Heater 14 Oscillator 15 Constant current circuit 16 Photodetector 17 Amplifier 18 Phase comparator 19 Low-pass filter (LPF) 20 Integrator 21 Temperature control circuit 22 Peltier cooler 23 Optical switch 24 Phase modulator 25 Balanced light receiving element 26 Differential amplifier 27 2 × 2 optical coupler 31 Substrate 32 Input waveguide array 33 Input concave slab waveguide 34 Array waveguide 35 Output concave slab waveguide 36 Output waveguide array 111 Optical demultiplexing Device 112 Mach-Zehnder interferometer 113 Mach-Zehnder interferometer array 114 Photodetector 115 Logarithmic amplifier (log amplifier) 116 Temperature control circuit 117 Peltier cooler 121 Variable optical filter 131 Optical switch 141 Quadrature polarization multiplexing means 142 Quadrature polarization separator

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kenichi Sato Nippon Telegraph and Telephone Corporation, 1-6-1, Uchisaiwai-cho, Chiyoda-ku, Tokyo (56) References JP-A-5-323247 (JP, A) JP-A-3-64084 (JP, A) JP-A-5-323246 (JP, A) JP-A-7-79212 (JP, A) JP-A-8-237203 (JP, A) JP-A-8-97775 (JP, A) A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04B 10/00-10/28 H04J 14/00-14/08 G01J 9/00

Claims (9)

(57) [Claims] 1. A signal light Sk (k = 1) of wavelength-division multiplexed light output from a plurality of channels while controlling transmission center wavelengths of the plurality of channels based on reference wavelength light having a predetermined wavelength. -N: N is a positive integer), which is a wavelength monitoring device that simultaneously monitors the wavelength error, wherein when the reference wavelength light and the wavelength multiplexed light are input,
An array waveguide grating including at least one first channel that outputs at least a part of the reference wavelength light, and at least one second channel that outputs at least a part of the signal light Sk; A first light receiving unit that detects the reference wavelength light output from the first channel; a second light receiving unit that detects the signal light Sk output from the second channel; and the first light receiving unit Control means for stabilizing the transmission center wavelength of the first channel based on the output of the first channel; and the signal light Sk based on the output of the second light receiving means.
Wavelength error detection means for outputting an error signal representing the wavelength error of the reference wavelength light , wherein the arrayed waveguide grating has a wavelength error signal corresponding to the reference wavelength light.
Corresponding to one of the first channels and the signal light Sk.
The wavelength monitoring device further includes two second channels, and the wavelength monitoring device further includes two output light intensities output from the first channel.
And first light comparing means for comparing the intensities of two output lights output from the second channel.
And a second comparing means for comparing the first and second comparing means , based on an output of the first comparing means.
Thus, the transmission center wavelength of the first channel is stabilized, and the wavelength error detecting means outputs the output of the second comparing means.
Detecting a wavelength error of the signal light Sk based on the
Characteristic wavelength monitoring device. 2. The wavelength monitor according to claim 1 , further comprising:
Multiplexing light and the reference wavelength light into the arrayed waveguide grating
Input means for inputting simultaneously to one channel of
The wavelength monitoring device according to claim 1, wherein: 3. The wavelength monitoring apparatus according to claim 1 , further comprising:
Multiplexing light and the reference wavelength light with the arrayed waveguide grating
Have input means for inputting in separate channels of
The wavelength monitoring device according to claim 1, wherein 4. The wavelength monitoring apparatus according to claim 1 , further comprising:
Multiplexed light and a signal obtained by multiplexing the reference wavelength light
Simultaneously into separate channels of the arrayed waveguide grating
The wavelength monitoring apparatus according to claim 1, further comprising input means for inputting . 5. The two first channels are adjacent to each other.
Tangent channels, said two second channels also:
Claims: Channels adjacent to each other
5. The wavelength monitoring device according to 2, 3, or 4 . 6. The two first channels are connected to each other by F
Channels separated by SR (Free Spectral Range)
The two second channels are also separated by FSR from each other.
4. The channel according to claim 2, wherein
Is a wavelength monitoring device according to 4 . 7. The first comparing means is a logarithmic amplifier.
Wherein the second comparing means is also a logarithmic amplifier.
The wavelength monitoring device according to any one of claims 2 to 6 . 8. The first comparing means includes an A / D converter and an A / D converter.
And a digital signal processor, said second ratio
The comparison means also includes an A / D converter and a digital signal processor.
7. A method according to claim 2, wherein said heat exchanger has a heat sink.
A wavelength monitoring device according to any of the preceding claims. 9. The first comparing means is a differential photo detector.
Wherein the second comparing means is also a differential photodetector.
The wavelength monitoring device according to any one of claims 2 to 6 .