JP4002245B2 - Fiber transmission system diagnostic equipment - Google Patents

Description

  In the present invention, when the bandwidth of a fiber transmission system is realized using the fundamental mode of a multimode optical transmission line, it is possible to easily and quickly diagnose whether or not the bandwidth can be increased. The present invention relates to a fiber transmission system diagnostic apparatus.

  So far, a method has been proposed in which only a fundamental mode of a multimode optical transmission line is excited to transmit a signal having a bandwidth wider than that of an actual multimode optical transmission line (see, for example, Patent Document 1). .

  According to the present invention, the apparent multimode optical transmission band is widely used by transmitting the laser light that has been excited only in the fundamental mode, that is, by preventing the higher-order mode from being excited as much as possible. Will be able to.

  Furthermore, a configuration has been proposed in which only the fundamental mode is received again among the laser beams transmitted by this configuration (see, for example, Patent Document 2).

  As a result, the bandwidth of the multimode optical transmission line can be further widely used.

  However, when attempting to increase the bandwidth of a fiber transmission system using such a method, the actual situation is that no technology has been proposed yet for diagnosing whether or not the bandwidth extension is actually possible. .

  Therefore, here, for comparison, a conventional technique for measuring a band of a fiber transmission system constructed by using a multimode optical transmission line and using many modes or all modes will be described.

  FIG. 5 illustrates the configuration of this prior art. In the figure, 100 is a multimode optical transmission line (MMF), 101 is a lens, 102 is a photodiode, and 103 is an oscilloscope.

  The principle of the conventional band measurement configured as described above is as follows.

  Pulse-shaped laser light for bandwidth measurement is incident from the left end of the multimode optical transmission line 100 and propagates through the multimode optical transmission line 100 toward the right. When the laser light is emitted from the right end of the multimode optical transmission line 100, the laser light is focused on the photodiode 102 by the lens 101. The photodiode 102 converts the laser light into an electric signal, and the oscilloscope 103 can display and store the electric signal waveform.

  At this time, the delay of light and the spread of the pulse in the multimode optical transmission line 100 vary depending on the incident location at the time of incidence, and also vary depending on the angle of incidence. The location and angle at the time of incidence correspond to the mode in the multimode optical transmission line 100.

  In conventional usage modes of multimode optical transmission lines, it is not known in what mode the optical signal is transmitted. Therefore, conventionally, when measuring the bandwidth of a multimode optical transmission line, the delay of every mode is considered. We measured and tried to add them together.

  That is, the incident location is fixed, and the optical pulse is displayed and accumulated on the oscilloscope 103 while changing the incident angle. Subsequently, the incident pulse is slightly shifted and the optical pulse is changed on the oscilloscope 103 while changing the incident angle. It was trying to repeat displaying and accumulating. That is, both the scan of the incident place and the scan of the incident angle are performed, and the shape of the optical pulse is displayed and accumulated on the oscilloscope 103, and the length of the pulse is measured.

Since both the frequency characteristic of the incident laser light and the frequency characteristic of the accumulated data of the outgoing laser light are obtained by Fourier transform, by normalizing the frequency characteristic of the accumulated data of the outgoing laser light with the frequency characteristic of the incident laser light, The frequency characteristics and band of the multimode optical transmission line 100 itself can be obtained.
US Patent US6185346 JP2003-21723

  There are various types of optical fibers used as multimode optical transmission lines, such as graded index optical fibers (GI optical fibers) and step index optical fibers (SI optical fibers).

  By exciting only the fundamental mode of the multimode optical transmission line, a method of transmitting a signal wider than the bandwidth of the actual multimode optical transmission line, or only the fundamental mode of the laser light transmitted by this configuration However, not all optical fibers used as multimode optical transmission lines can be used.

  If a certain type of GI optical fiber is used, the effect of using such a method can be expected. However, even if it is a GI type optical fiber, the effect cannot be obtained. I can't expect anything.

  Therefore, when applying such a method, it is necessary to investigate in advance whether or not the multimode optical transmission line scheduled to be used is applicable.

  However, to date, the actual situation is that no technology has been proposed for enabling this preliminary survey.

  In other words, the conventional technique for measuring the bandwidth of a multimode optical transmission line that uses many modes excited is as described above, but the band measurement when only the fundamental mode of the multimode optical transmission line is used is still proposed. It has not been. In addition, when only the fundamental mode of a multimode optical transmission line is used, the band is wider than when many modes are used, so a laser light source with better frequency characteristics is required. It has not been.

  The present invention has been made in view of such circumstances, and in the case of realizing a wide band of a fiber transmission system using a base mode of a multimode optical transmission line, a diagnosis of whether or not the wide band is possible. It is an object of the present invention to provide a new fiber transmission system diagnostic apparatus that can easily and quickly perform the above.

[1] Configuration for use in diagnosis of a fiber transmission system configured by exciting only the fundamental mode of a multimode optical transmission line (but not configured to receive only the fundamental mode)
To achieve the above Symbol purpose, fiber transmission system diagnostic apparatus of the present invention, (a) branches and short pulse laser light source for emitting light short pulses, the two output light (b) the short pulse laser light source An optical demultiplexer, (c) a first optical receiver that photoelectrically converts one output light from the optical demultiplexer, and (d) analyzing a high-frequency signal from the first optical receiver. (E) a single-mode optical transmission line in which only the fundamental mode of the other output light from the optical demultiplexer is incident on one end of the multimode optical transmission line to be measured; A second optical receiver that photoelectrically converts output light from the other end of the measured multimode optical transmission line; and (g) a second spectrum analyzer that analyzes a high-frequency signal from the second optical receiver. It comprises so that.

  In adopting this configuration, the short pulse laser light source may be composed of a mode-locked laser.

  Further, when adopting this configuration, the short pulse laser light source includes a semiconductor laser (sometimes a wavelength tunable laser diode) and an optical modulator that externally modulates the output light of the semiconductor laser. Sometimes.

[2] Configuration for use in diagnosing a fiber transmission system configured by exciting only the fundamental mode of a multimode optical transmission line and receiving only the fundamental mode
To achieve the above Symbol purpose, fiber transmission system diagnostic apparatus of the present invention, (a) branches and short pulse laser light source for emitting light short pulses, the two output light (b) the short pulse laser light source An optical demultiplexer, (c) a first optical receiver that photoelectrically converts one output light from the optical demultiplexer, and (d) analyzing a high-frequency signal from the first optical receiver. (E) a single-mode optical transmission line in which only the fundamental mode of the other output light from the optical demultiplexer is incident on one end of the multimode optical transmission line to be measured; A mode filter that transmits only the base mode light out of the output light from the other end of the measured multimode optical transmission line; (g) a second optical receiver that photoelectrically converts the transmitted base mode light; ) Solve the high frequency signal from the second optical receiver Configured to and a second spectral analyzer for.

  In adopting this configuration, the short pulse laser light source may be composed of a mode-locked laser.

  Further, when adopting this configuration, the short pulse laser light source includes a semiconductor laser (sometimes a wavelength tunable laser diode) and an optical modulator that externally modulates the output light of the semiconductor laser. Sometimes.

  By using the diagnostic apparatus for a fiber transmission system according to the present invention configured as described above, the band can be predicted in advance when the base mode excitation method is applied to the multimode optical transmission line to achieve a wide band. . This method is a very simple method, and applicability can be confirmed at a remarkably small cost compared with noticing a lack of bandwidth after system introduction.

  As described above, if the fiber transmission system diagnostic apparatus of the present invention is used, can an optical network facility, an optical LAN, and an optical access system using an existing multimode optical transmission line be broadened by a base mode excitation method? The diagnosis of whether or not can be performed easily and quickly.

  Hereinafter, the present invention will be described in detail according to embodiments.

Prior to the description of the present invention, techniques related to the present invention will be described.
[First related technology ]
FIG. 1 illustrates a first related technique related to the present invention.

  In the figure, 10 is a laser diode, 11 is a photodiode, 12 is a multimode optical fiber to be measured, 13a is a single mode optical fiber, which connects the multimode optical fiber 12 and the laser diode 10, and 13b A single-mode optical fiber that connects the multi-mode optical fiber 12 and the photodiode 11; 14a, an optical connector that is used to connect the multi-mode optical fiber 12 and the single-mode optical fiber 13a; 14b is an optical connector, which is used to connect the multimode optical fiber 12 and the single mode optical fiber 13b, 15 is a constant current source which generates a direct current, 16 is a synthesizer, One that generates high-frequency current in the form of sweeping frequency, A steer that generates a drive current for the laser diode 10 by superimposing a direct current generated by the constant current source 15 and a high-frequency current generated by the synthesizer 16, and 18 is a spectrum analyzer that includes a photodiode 11. 19 is a synchronizing circuit that controls the frequency of the high-frequency current generated by the synthesizer 16 and the frequency analyzed by the spectrum analyzer 18 to be the same.

Next, the operation of the first related technique configured as described above will be described. First, the configuration on the optical signal generation side will be described.

In the first related technique , the laser diode 10 is driven by direct modulation with a current on which a high-frequency signal is superimposed, thereby obtaining laser light subjected to high-frequency amplitude modulation. For this purpose, the constant current source 15 and the synthesizer 16 are connected to the laser diode 10 via the bias tee 17.

  The light emitted from the laser diode 10 is incident on the single mode optical fiber 13a, and is incident on the multimode optical fiber 12 that is the object of band measurement via the optical connector 14a. With the system thus far, it is possible to introduce into the multimode optical fiber 12 a laser beam in which a high-frequency signal is superimposed and only the fundamental mode is excited at the incident end face of the multimode optical fiber 12.

  This laser light is pumped only in the fundamental mode at the incident end face of the multimode optical fiber 12, but as it travels toward the photodiode 11 (receiving / measuring side), a part of the fundamental mode light and It gradually changes to scattered light. The higher order mode narrows the transmission band of the multimode optical fiber 12, and the scattering reduces the energy of light reaching the photodiode 11.

The first related technique is to measure the transmission band of the multimode optical fiber 12 excited by the fundamental mode.

  Part of the laser light transmitted through the multimode optical fiber 12 remains in the fundamental mode, and part of the laser light is converted into a higher-order mode and reaches the photodiode 11. Furthermore, there is a component that is converted from a fundamental mode to a higher-order mode and further converted to a fundamental mode again.

  As a result, when the frequency of the synthesizer 16 is high, the reception / measurement side determines the difference in arrival time between the component transmitted in the base mode and the component once converted to the base mode after being converted to the base mode. Due to the influence, the high-frequency signal is measured small.

  Next, the configuration on the reception / measurement side will be described.

  The multimode optical fiber 12 is connected to the single mode optical fiber 13b via the optical connector 14b in order to extract only the fundamental mode from the laser light reaching the reception / measurement side. The output of the single mode optical fiber 13b is input to the photodiode 11 for bandwidth measurement.

  The laser beam that has reached the reception / measurement side is photoelectrically converted by the photodiode 11 and the power of the high-frequency component transmitted by the spectrum analyzer 18 is measured. At this time, the synchronization circuit 19 controls the frequency generated by the synthesizer 16 and the frequency measured by the spectrum analyzer 18 to be the same, and scans the frequency temporally.

  According to this configuration, the frequency characteristic and band of the multimode optical fiber 12 to be measured are measured.

The measurement principle according to the first related technique will be described with reference to FIG.

  2A shows an example in which the modulation frequency of the high-frequency current applied to the laser diode 10 is low, FIG. 2B shows an example in which the modulation frequency is medium, and FIG. 2C shows a high modulation frequency. This is an example.

  (A) to (c) show the time transition of the light intensity of the laser light modulated at high frequency and the time transition of the current of the photodiode 11 demodulated on the receiving side. Further, (d) shows the frequency dependence of the amplitude of the current measured by the photodiode 11. Here, points (a) to (c) shown in (d) indicate points corresponding to the frequencies (a) to (c) in FIG.

  The behavior in the case of the low frequency shown in (a) is as follows. This frequency is assumed to be lower than the half-value frequency (referred to as a band) of the multimode optical fiber 12 to be measured. In this case, the current demodulated by the photodiode 11 is sufficiently large and has almost no frequency dependence in the vicinity of the frequency. Also in (d), the result in the vicinity of the point (a) is displayed, and it can be understood that the frequency dependence is small.

  On the other hand, the modulation frequency is increased to the frequency shown in (b). This corresponds to sweeping the modulation frequency. The current of the photodiode 11 is smaller than in the example of (a). In the example of (c), the modulation frequency is further increased.

  The result of plotting the measurement results of (a) to (c) is (d), and (d) just shows the frequency characteristics of the multimode optical fiber 12.

  In this way, the high frequency signal is applied to the laser diode 10 by the synthesizer 16, the frequency characteristics are displayed on the spectrum analyzer 18, and the band can be read immediately. The synthesizer 16 and the spectrum analyzer 18 are synchronously operated by a trigger signal supplied from the synchronization circuit 19.

In the first related technology , the laser diode 10 uses an oscillation wavelength of 1.550 μm, the multimode optical fiber 12 is a graded index optical fiber having a core diameter of 50 μm, and the measurement frequency is 1 MHz to 10 GHz. It was confirmed.

As a result, it is confirmed that the band when only the fundamental mode is excited is 1 GHz or more with respect to the multimode optical fiber 12 with a bandwidth of 200 MHz / km in the specification, and according to the first related technique , the multimode optical fiber 12 It was confirmed that the bandwidth could be measured.

[Second related technology ]
The second related technique realizes the wavelength variability of the laser light and the high frequency of the measurement band.

FIG. 3 illustrates a second related technique related to the present invention.

  In the figure, reference numeral 20 denotes a tunable optical sweeper, which is a laser light source having a variable optical wavelength and capable of temporally sweeping the modulation frequency, 21 is a photodiode, 22 is a multimode optical fiber to be measured, and 23a is A single mode optical fiber that connects the multimode optical fiber 22 and the tunable optical sweeper 20, 23b is a single mode optical fiber that connects the multimode optical fiber 22 and the photodiode 21, An optical connector 24a is used for connecting the multimode optical fiber 22 and the single mode optical fiber 23a, and 24b is an optical connector for connecting the multimode optical fiber 22 and the single mode optical fiber 23b. What is used, 25 is a spectrum analyzer, photo Analyzing the electrical signal output from the ion 21, 26 is a sawtooth wave oscillator, and the sawtooth wave shape is such that the modulation frequency of the tunable optical sweeper 20 and the frequency analyzed by the spectrum analyzer 25 are the same. A current is generated.

  The tunable light sweeper 20 includes a laser diode 200, a first wavelength tunable laser diode 201, a first wavelength control circuit 202, a photodiode 203, a high frequency amplifier 204, and a second wavelength tunable laser diode 205. The second wavelength control circuit 206 and a Mach-Zehnder optical modulator 207 are included.

  Although not shown in this figure, in reality, the laser diode 200, the first wavelength tunable laser diode 201, and the second wavelength tunable laser diode 205 each have a constant current source for driving the laser diode. It is connected.

  The tunable light sweeper 20 is a laser light source having a variable optical wavelength and capable of temporally sweeping the modulation frequency, and its mechanism is as follows.

  The optical frequency oscillated by the laser diode 200 is f1, and the optical frequency oscillated by the first wavelength tunable laser diode 201 is f2. Note that f1 is a fixed optical frequency, and f2 is a variable optical frequency. The first wavelength control circuit 202 supplies a current for determining the oscillation light frequency of the first wavelength tunable laser diode 201 to a wavelength tunable terminal (generally a DBR section or the like) of the first wavelength tunable laser diode 201. Applied to the terminal for controlling the refractive index of the DFB portion.

  If the laser beam output from the laser diode 200 and the laser beam output from the first wavelength tunable laser diode 201 are incident on the photodiode 203, the frequency of | f1-f2 | A beat is obtained from the photodiode 203 as a current output. However, this conversion efficiency is at most about 1 A / W, which is not sufficient to drive the Mach-Zehnder optical modulator 207 connected to the next stage, and is therefore amplified by the high-frequency amplifier 204. Here, fRF = | f1-f2 |.

  The second wavelength tunable laser diode 205 is also a wavelength tunable laser diode, and is connected to a second wavelength control circuit 206 for tunable wavelength. Laser light (wavelength is λLD and variable) output from the second wavelength tunable laser diode 205 is input to the Mach-Zehnder optical modulator 207 and intensity-modulated at the frequency fRF.

  In this way, the tunable light sweeper 20 outputs light having the wavelength λLD and the modulation frequency fRF.

  At this time, if the sawtooth wave oscillator 26 is connected to the first wavelength control circuit 202 and the first wavelength control circuit 202 outputs a sawtooth current, fRF is changed from a low frequency to a high frequency. And (or vice versa) the modulation frequency is swept.

  The laser light output from the tunable light sweeper 20 in this way is incident on the multimode optical fiber 22 to be measured through the single mode optical fiber 23a and the optical connector 24a. Thereby, only the fundamental mode is excited at the incident end of the multimode optical fiber 22.

  The multimode optical fiber 22 is connected to the single mode optical fiber 23b via the optical connector 24b in order to extract only the fundamental mode from the laser light that has reached the reception / measurement side. The output of the single mode optical fiber 23b is input to the photodiode 21 for bandwidth measurement.

  The laser light reaching the reception / measurement side is photoelectrically converted by the photodiode 21, and the power of the high frequency component transmitted by the spectrum analyzer 25 is measured. At this time, the sawtooth wave oscillator 26 controls the modulation frequency fRF of the tunable light sweeper 20 and the frequency analyzed by the spectrum analyzer 25 to be the same, and scans the frequency temporally.

  According to this configuration, the frequency characteristic and band of the multimode optical fiber 22 to be measured are measured.

In the first related technology , it was impossible to change the wavelength when measuring the band of the multimode optical fiber 22, but in the second related technology , the tunable optical sweeper 20 was used as the light source. The wavelength can be changed during the measurement of the 22 bands, so that the band of the multimode optical fiber 22 can be diagnosed over a wide wavelength band.

We have also prototyped a related technology that uses a tunable laser diode on the optical signal generation side instead of the tunable optical sweeper 20. According to the result, although it was inferior in terms of sweep speed as compared with the related art using the tunable optical sweeper 20, it was confirmed that the band measurement of the multimode optical fiber 22 functions sufficiently.

[Embodiment of the present invention ]
In the first and second related technologies , the band of the multimode optical fiber 22 is diagnosed by sweeping the modulation frequency for the laser. However, in the embodiment of the present invention , the wavelength variable mode containing a wideband frequency component is used. A configuration for performing band diagnosis using a lock laser diode (MLLD) is adopted.

Figure 4 illustrates an implementation embodiment of the present invention.

  In the figure, 30 is a wavelength-tunable mode-locked laser diode, 31 is an optical demultiplexer that demultiplexes the laser light emitted from the wavelength-tunable mode-locked laser diode 30, and 32 is a single-mode optical fiber. The wavelength tunable mode-locked laser diode 30 and the optical demultiplexer 31 are connected, 33 is a photodiode, 34 is a multi-mode optical fiber to be measured, and 35a is a single-mode optical fiber. A fiber 34 and an optical demultiplexer 31 are connected, 35b is a single mode optical fiber, a multimode optical fiber 34 and a photodiode 33 are connected, 36a is an optical connector, and a multimode light What is used to connect the fiber 34 and the single mode optical fiber 35a, and 36b is an optical connector. The multi-mode optical fiber 34 and the single-mode optical fiber 35b are connected to each other, 37 is a constant current source and generates a direct current, and 38 is a synthesizer, which sweeps the frequency. A high-frequency current is generated in the form of a bias tee 39. The driving current of the wavelength-tunable mode-locked laser diode 30 is superimposed by superimposing a DC current generated by the constant current source 37 and a high-frequency current generated by the synthesizer 38. , 40 is an input side photodiode, which converts the laser beam demultiplexed by the optical demultiplexer 31 into an electric signal, 41 is a single mode optical fiber, and the optical demultiplexer 31 Connected to the input-side photodiode 40, 42 is an input-side spectrum analyzer, and the output of the input-side photodiode 40 Which analyzes the electrical signals that, 43 is a spectrum analyzer is for analyzing the electrical signal output by the photodiode 33.

  Next, the operation of this embodiment configured as described above will be described. First, the configuration on the optical signal generation side will be described.

  In this embodiment, the wavelength tunable mode-locked laser diode 30 is a technique called active synchronization (an optical pulse that includes an applied high-frequency fundamental wave or higher-order harmonics directly modulated by a current superimposed with a high-frequency signal). To obtain a laser beam that has been amplitude-modulated by a high frequency and its harmonics. For this purpose, the constant current source 37 and the synthesizer 38 are connected to the wavelength tunable mode-locked laser diode 30 via the bias tee 39.

  The light emitted from the wavelength-tunable mode-locked laser diode 30 travels to the single mode optical fiber 32, the optical demultiplexer 31, and the single mode optical fiber 35a, and passes through the optical connector 36a to the multimode optical fiber 34 that is the target of band measurement. Incident. With the system described so far, it is possible to introduce into the multimode optical fiber 34 laser light on which a high-frequency signal is superimposed and only the fundamental mode is excited at the incident end face of the multimode optical fiber 34.

  Further, in order to grasp in advance the spectrum of the laser beam intensity used for the measurement, half of the laser beam emitted from the wavelength tunable mode-locked laser diode 30 is divided into the optical demultiplexer 31, the single mode optical fiber 41, and the input side. The light is incident on the photodiode 40 and converted into an electric signal, and the spectrum is measured and displayed by the input side spectrum analyzer 42.

  On the other hand, the laser light emitted from the wavelength-tunable mode-locked laser diode 30 is excited only in the fundamental mode at the incident end face of the multimode optical fiber 34, but proceeds toward the photodiode 33 (receiving / measuring side). Some of the fundamental mode light gradually changes to higher order modes and scattered light. The higher order mode narrows the transmission band of the multimode optical fiber 34, and the scattering reduces the energy of light reaching the photodiode 33.

  In the present invention, the transmission band of the multimode optical fiber 34 excited by the fundamental mode is measured.

Similar to the first and second related technologies , a part of the laser light transmitted through the multimode optical fiber 34 remains in the fundamental mode, and a part thereof is converted into a higher-order mode to be a photodiode. 33 is reached. Furthermore, there is a component that is converted from a fundamental mode to a higher-order mode and further converted to a fundamental mode again.

  Next, the configuration on the reception / measurement side will be described.

  The multimode optical fiber 34 is connected to the single mode optical fiber 35b via the optical connector 36b in order to extract only the fundamental mode from the laser light that has reached the reception / measurement side. The output of the single mode optical fiber 35b is input to the photodiode 33 for bandwidth measurement.

The laser light reaching the reception / measurement side is photoelectrically converted by the photodiode 33, and the high-frequency component power transmitted by the spectrum analyzer 43 is measured. At this time, when performing band measurement by sweeping as in the first related art , it is necessary to drive the synthesizer 38 and the spectrum analyzer 43 in synchronism with each other. In this embodiment, however, the mode always includes a wide high-frequency component. Since the lock laser beam is used, there is no need for synchronization, and the apparatus becomes simpler as much.

  The intensity spectrum of the optical pulse emitted from the tunable mode-locked laser diode 30 is measured by the input-side spectrum analyzer 42, while the intensity spectrum of the optical pulse that has passed through the multimode optical fiber 34 to be measured is measured by the spectrum analyzer 43. Measured. If the frequency characteristic measured by the spectrum analyzer 43 is normalized by the frequency characteristic measured by the input-side spectrum analyzer 42 (a device (not shown) that automatically performs the normalization may be provided), multimode light may be provided. The frequency characteristics of the fiber 34 itself can be obtained, and the band can be obtained immediately.

  According to this configuration, the frequency characteristic and band of the multimode optical fiber 34 to be measured are measured.

The prototype device according to the present embodiment worked well. The oscillation wavelength of the wavelength tunable mode-locked laser diode 30 was determined by making the current driven from the constant current source 37 variable.

Furthermore, the operation of the other two types of related technologies in which the optical signal generation side was changed was also confirmed.

  One of them is a substitute for the tunable mode-locked laser diode 30 by generating a short optical pulse using a laser diode and an electroabsorption semiconductor optical modulator. This is a method for generating a short optical pulse using the fact that the voltage vs. transmittance of the electroabsorption semiconductor optical modulator is nonlinear, and unlike the case where the wavelength variable mode-locked laser diode 30 is used, the spectrum of the light source is unnecessary. There is an advantage of not spreading.

  The other uses a tunable laser diode and an electroabsorption semiconductor optical modulator. By using a wavelength tunable laser diode, it also has a wavelength tunable feature.

It was confirmed that these two types of related technologies also work well.

  As can be seen from the above description, by using the fiber transmission system diagnostic apparatus of the present invention, optical network equipment, an optical LAN, and an optical access system using an existing multimode optical transmission line can be broadened by a base mode excitation method. It is possible to easily and quickly make a diagnosis as to whether or not it can be realized.

  In the embodiment described above, the fiber transmission system configured by exciting only the fundamental mode of the multimode optical transmission line and receiving only the fundamental mode is targeted for diagnosis. Even when a fiber transmission system configured by exciting only the fundamental mode (not used for a configuration that receives only the fundamental mode) is to be diagnosed, the present invention can be applied as it is.

When such a fiber transmission system is to be diagnosed, in the first related technology , the multimode optical fiber 12 to be measured is directly connected to the photodiode 11 without being connected to the single mode optical fiber 13b. I will take the configuration. In the second related technique , the multimode optical fiber 22 to be measured is directly connected to the photodiode 21 without being connected to the single mode optical fiber 23b. In the embodiment of the present invention, the multimode optical fiber 34 to be measured is directly connected to the photodiode 33 without being connected to the single mode optical fiber 35b.

It is a device block diagram of the 1st related art . It is explanatory drawing of the band measurement by a 1st related technique . It is an apparatus block diagram of 2nd related technology . It is a device block diagram of the example of an embodiment of the present invention . It is explanatory drawing of a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Laser diode 11 Photodiode 12 Multimode optical fiber 13a Single mode optical fiber 13b Single mode optical fiber 14a Optical connector 14b Optical connector 15 Constant current source 16 Synthesizer 17 Bias tee 18 Spectrum analyzer 19 Synchronous circuit

Claims (5)

A fiber transmission system diagnostic device used for diagnosis of a fiber transmission system that performs data transmission by exciting only the fundamental mode of a multimode optical transmission line,
A short pulse laser light source that emits an optical short pulse;
An optical demultiplexer for branching the output light of the short pulse laser light source into two;
A first optical receiver that photoelectrically converts one output light from the optical demultiplexer;
A first spectrum analyzer for analyzing a high-frequency signal from the first optical receiver;
A single-mode optical transmission line that enters only one fundamental mode of the other output light from the optical demultiplexer into one end of the multimode optical transmission line to be measured;
A second optical receiver that photoelectrically converts output light from the other end of the measured multimode optical transmission line;
A second spectrum analyzer for analyzing a high-frequency signal from the second optical receiver ;
Normalizing means for normalizing the analysis result of the second spectrum analyzer with the analysis result of the first spectrum analyzer ;
A fiber transmission system diagnostic device. A fiber transmission system diagnostic device used for diagnosis of a fiber transmission system that performs data transmission by exciting only the fundamental mode of a multimode optical transmission line,
A short pulse laser light source that emits an optical short pulse;
An optical demultiplexer for branching the output light of the short pulse laser light source into two;
A first optical receiver that photoelectrically converts one output light from the optical demultiplexer;
A first spectrum analyzer for analyzing a high-frequency signal from the first optical receiver;
A single-mode optical transmission line that enters only one fundamental mode of the other output light from the optical demultiplexer into one end of the multimode optical transmission line to be measured;
A mode filter that transmits only base mode light out of output light from the other end of the measured multimode optical transmission line;
A second optical receiver for photoelectrically converting the transmitted fundamental mode light;
A second spectrum analyzer for analyzing a high-frequency signal from the second optical receiver ;
Normalizing means for normalizing the analysis result of the second spectrum analyzer with the analysis result of the first spectrum analyzer ;
A fiber transmission system diagnostic device. In the fiber transmission system diagnostic apparatus according to claim 1 or 2 ,
The short pulse laser light source is composed of a mode-locked laser,
A fiber transmission system diagnostic device. In the fiber transmission system diagnostic apparatus according to claim 1 or 2 ,
The short pulse laser light source is
A semiconductor laser;
Comprising an optical modulator for externally modulating the output light of the semiconductor laser,
A fiber transmission system diagnostic device. In the fiber transmission system diagnostic apparatus according to claim 4 ,
The semiconductor laser is composed of a tunable laser diode,
A fiber transmission system diagnostic device.

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