JP2003106943A - PMD detector and WDM optical transmission system - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To be able to detect a time variation of a PMD amount in an optical transmission line. SOLUTION: A wavelength multiplexed data signal light (λ1 ... λm ... λn ... λz) including data signal lights of two wavelengths (λn, λm) whose polarization relation is known is transmitted to an optical transmission line 10. . A part of the wavelength multiplexed data signal light is extracted from the optical transmission line 10 by the optical tap 11 and split into two by the optical demultiplexer 12. Optical demultiplexer 13, optical filters 14, 15, PD1
In the paths 6 and 17 and the paths of the polarizer 18, the optical demultiplexer 19, the optical filters 20 and 21, and the PDs 22 and 23, data signals of two wavelengths (λn and λm) whose polarization relationship is known are known. Light intensity is detected. From the comparison of the two types of signal light intensities, it is possible to analyze the time variation of the PMD amount in the optical transmission line 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PMD detector for detecting a polarization mode dispersion characteristic that deteriorates the quality of a transmission signal in a wavelength division multiplexing optical transmission system for performing ultra-high speed optical transmission, and a wavelength having a PMD compensation function. The present invention relates to a multiplex optical transmission system.

[0002]

2. Description of the Related Art When light travels through substances having different refractive indices, the propagation speed of light in the substances varies depending on the magnitude of the refractive indices. In addition, the propagation of light in a material (anisotropic material) having a different refractive index depending on the polarization direction of incident light causes a phenomenon that the delay time after passing through the material differs depending on the state of polarization in the material. . Here, the polarization mode dispersion (hereinafter referred to as “PMD” (Polarizati)
on Mode Dispersion))).

In general, a single mode fiber used in an optical transmission line has a slight anisotropy locally along its longitudinal direction. Therefore, when light propagates through a fiber having such an anisotropy, a delay difference depending on the polarization direction of an optical signal is generated at a portion where refractive index anisotropy exists in this propagation path. Occurs. When the delay difference due to this polarization difference is accumulated in the optical transmission line,
This causes deterioration of the signal waveform at the receiving end.

FIG. 6 shows that the pulse width is equal to N
1d in optical transmission of RZ (Non-Return to Zero) signal
It is a figure which shows the relationship between the magnitude | size of PMD of the optical transmission line which causes B penalty, and optical transmission speed (bit rate).
The relationship shown in Fig. 6 is based on the document "Fading in lightwave syst".
ems due to polarization-mode dispersion "" (CD
Poole, RW Tkach, AR Chraplyvy and DA Fishm
an, IEEE Photonics Technol. Lett. vol.3, no.1,
pp.68-70, 1991) based on the relational expression.

That is, in the above document, the magnitude Δτ of PMD when the power penalty deteriorates by 1 dB and NRZ
The relationship with the signal pulse width T (T = 1 / B: B is the bit rate) is shown as the following expression (1). That is, Δτ
/ T to 0.4 (1). When the relationship between the PMD magnitude Δτ when the power penalty deteriorates by 1 dB and the bit rate B of the NRZ signal is obtained based on this equation (1), the result shown in FIG. 6 is obtained. For example, 4
It can be seen that when transmitting a 0 Gbit / s NRZ signal, the PMD of the transmission line must be suppressed to 10 ps or less.

On the other hand, in an actual transmission line, PMD having an average of about 0.1 ps / √km exists even with a low PMD fiber. This means that PMD of 10 ps occurs after transmission of 10,000 km. Further, the PMD in the transmission line has a characteristic that its size fluctuates with time. Therefore, after laying the optical fiber, P
It is necessary to perform PMD compensation according to the temporal variation of MD.

When performing PMD compensation according to time fluctuation,
A highly accurate PMD detection method that follows time fluctuations is required. Also, when considering implementation in a transmission system,
Miniaturization of the PMD detector is required.

As a PMD detection method capable of following a time change and performing a highly accurate measurement, for example, Japanese Patent Laid-Open No. 27308/1993.
Jones Matrix (Jones Ma) disclosed in Japanese Patent Publication No. 2 (Polarization Mode Dispersion Judgment Apparatus and Method for Optical Device)
The trix) method is the best known. In this Jones Matirix method, P is calculated from the polarization analysis results for a few wavelengths.
High-speed, high-accuracy PMD to determine the size of MD
It can be detected. Further, since the PMD detection is performed by calculation, it is suitable for downsizing the PMD detector.

As other means for detecting PMD based on ellipsometry, the Poincare sphere method, SOP method, FA
The (fixed analyzer) method is known. The Poincaré sphere method and the SOP method calculate the PMD based on the polarization analysis result at each wavelength, so that P
This method is suitable for the purpose of MD detection.

On the other hand, the FA method is a method of performing PMD analysis from wavelength characteristics using a variable wavelength light source. FIG. 7 is a diagram for explaining the PMD detection method by the FA method. This is based on Wavelength Division Multiplexing (W
An example of a conventional PMD compensation method in a DM) optical transmission system is shown.

In FIG. 7, the transmitting side is a variable wavelength light source 4
1 and a polarizer 42. The receiving side is a polarizer 43
And an optical power meter 44. An optical transmission line 45 connects between the polarizer 42 and the polarizer 43.

On the transmission side, the variable wavelength light source 41 generates signal light of various wavelengths at a predetermined sweep period and outputs it to the polarizer 42. The polarizer 42 adds a known polarization state to the signal light sent from the variable wavelength light source 41 and sends the signal light to the optical transmission line 45. On the receiving side, the signal light input from the optical transmission line 45 is input to the optical power meter 44 via the polarizer 43. In the optical power meter 44, the wavelength characteristic of the light intensity of the signal light input from the optical transmission line 45 is observed through the polarizer 43. The PMD amount is approximately calculated by analyzing the observed wavelength characteristics. As described above, the FA method shown in FIG. 7 can detect the amount of PMD in the optical transmission line.

[0013]

However, in the conventional FA method, the PMD amount is calculated by measuring the wavelength characteristic of the delay amount of the measured light by the variable light source, and therefore, there is another signal light. In the operating state, it is difficult to detect the time variation of the PMD amount.

The present invention has been made in view of the above,
An object of the present invention is to obtain a PMD detector capable of detecting the time variation of the amount of PMD in the optical transmission line and being miniaturized, and a wavelength multiplexing optical transmission system capable of PMD compensation using the PMD detector.

[0015]

In order to achieve the above object, a PMD detector according to the present invention transmits a wavelength-multiplexed data signal light including data signal lights of arbitrary two wavelengths whose polarization relations are known. Measuring light obtaining means for extracting a part of the wavelength-multiplexed data signal light from the optical transmission line, and first wavelength selecting means for extracting each of the two-wavelength data signal light from the output light of the measuring light obtaining means, First light intensity detecting means for receiving the output light of the first wavelength selecting means and detecting the signal light intensity of each of the data signal lights of the two wavelengths, and a predetermined polarization component of the output light of the measuring light obtaining means. A polarizer to be passed through, a second wavelength selecting means for extracting each of the data signal light of the two wavelengths from the output light of the polarizer, and a data signal of the two wavelengths for receiving the output light of the second wavelength selecting means. Light each Characterized by comprising a second light intensity detection means for detecting the issue light intensity.

According to the present invention, the measuring light acquisition means comprises:
A part of the wavelength-multiplexed data signal light is extracted from the optical transmission line through which the wavelength-multiplexed data signal light including the data signal lights of arbitrary two wavelengths whose polarization relations are known is transmitted. When the first wavelength selecting means extracts each of the two wavelengths of the data signal light from the output light of the measuring light acquiring means, the first light intensity detecting means extracts the extracted two wavelengths of the data signal. The signal light intensity of each light is detected. On the other hand, in the polarizer,
When a predetermined polarization component is extracted from the output light of the measurement light acquisition unit, the second wavelength selection unit extracts each of the two-wavelength data signal light from the output light of the polarizer,
The light intensity detecting means detects the signal light intensity of each of the data signal lights of the two wavelengths in a predetermined polarization state.

A PMD detector according to the next invention is characterized in that, in the above invention, the first wavelength selecting means and the second wavelength selecting means are wavelength variable selecting means.

According to the present invention, the wavelength tunable selecting means is used as the first wavelength selecting means and the second wavelength selecting means.

A PMD detector according to the next invention is a part of wavelength-multiplexed data signal from an optical transmission line through which wavelength-multiplexed data signal light including data signal light of arbitrary two wavelengths whose polarization relations are known is transmitted. The measurement light acquisition means for extracting light, a polarizer for passing a predetermined polarization component of the output light of the measurement light acquisition means, and the wavelength multiplexed data including the data signal light of the two wavelengths from the output light of the polarizer. And a light intensity detecting means for detecting the intensity of each signal light.

According to the present invention, the measuring light acquisition means comprises:
When a part of the wavelength-division-multiplexed data signal light is extracted from the optical transmission line through which the wavelength-division-multiplexed data signal light including the data-signal light of arbitrary two wavelengths whose polarization relationship is known, is measured by the polarizer. A predetermined polarization component is extracted from the output light of the acquisition means, and the light intensity detection means extracts the above-mentioned 2 from the output light of the polarizer.
The signal light intensity of each wavelength multiplexed data signal light including the data signal light of the wavelength is detected.

The PMD detector according to the next invention is characterized in that a polarization beam splitter is used in place of the polarizer.

According to the present invention, a polarization beam splitter is used instead of the polarizer. In the polarization beam splitter, the input wavelength-multiplexed data signal light is split into polarization components having an orthogonal relationship, and the light intensity is detected.

A wavelength-division-multiplexing optical transmission system according to the next invention is a wavelength-division-multiplexing optical transmission system for transmitting a wavelength-division-multiplexing data signal light containing data signal lights of arbitrary two wavelengths whose polarization relations are known. The part of wavelength-multiplexed data signal light is taken out from an optical transmission line through which the data signal light is transmitted, and the signal light intensity of at least the two-wavelength data signal light is detected. PM
A D detector, a first PMD compensating means arranged to perform a PMD compensating operation on the output light of the measuring light acquiring means in the PMD detector, and the wavelength-multiplexed data signal light transmitted through the optical transmission line. Second PMD compensation means arranged to perform a PMD compensation operation, said PM
The first PMD compensating means is controlled so that the PMD analyzed from the signal light intensity detected by the D detector is minimized, and the condition of the first PMD compensating means for minimizing the PMD is given to the second PMD compensating means. And a control means.

According to the present invention, the first PMD compensating means is
The PMD detector is arranged to perform a PMD compensation operation on the output light of the measurement light acquisition means, and the second PMD compensation means is arranged to perform a PMD compensation operation on the wavelength-multiplexed data signal light on the optical transmission line. The control means controls the first PMD compensating means so that the PMD analyzed from the signal light intensity detected by the PMD detector is minimized, and the condition of the first PMD compensating means for minimizing the PMD is the second PMD compensating means. Given to.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of a PMD detector and a wavelength division multiplexing optical transmission system according to the present invention will be described in detail below with reference to the accompanying drawings.

Embodiment 1. 1 is a block diagram showing the configuration of a PMD detector that is Embodiment 1 of the present invention. In FIG. 1, a wavelength-multiplexed data signal light (λ1 ... λm ... λn ... λz) including two wavelengths (λn, λm) whose polarization relationship is known is transmitted to the optical transmission line 10.

The PMD detector shown in FIG.
Optical tap 1 for extracting a part of WDM data signal light from
1 and an optical demultiplexer 12 that splits the output light of the optical tap 11 into two
And an optical demultiplexer 13 that further divides one branched light of the optical demultiplexer 12 into two, and receives each branched light of the optical demultiplexer 13 and extracts the data signal light of a specific wavelength (λm, λn). The optical filters 14 and 15 and a photodiode (hereinafter referred to as “PD”) 16, which electrically converts the output light of the optical filters 14 and 15,
17 and a polarizer 18 for extracting wavelength-multiplexed data signal light having a specific polarization from the other branched light of the optical demultiplexer 12.
An optical demultiplexer 19 that splits the output light of the polarizer 18 into two, optical filters 20 and 21 that receive the respective branched lights of the optical demultiplexer 19 and extract the signal light of a specific wavelength (λm, λn), and PDs 22 and 23 that electrically convert the output light of the filters 20 and 21 are provided.

Next, the operation of the PMD detector configured as described above will be described. The optical transmission line 10 includes wavelength-multiplexed data signal light (λ1 ... λm ... λn ...) Including data signal light of two wavelengths (λn, λm) whose polarization relationship is known.
λz) is being transmitted. The optical tap 11 is the optical transmission line 10.
Wavelength multiplexed data signal light (λ1 ... λm ... λn)
(.Lambda.z) is branched into two by the optical demultiplexer 12, and the optical demultiplexer 13
And is input to the polarizer 18.

The optical filter 14 which receives one of the branched lights of the optical demultiplexer 13 extracts the data signal light of the wavelength λm from the branched light. As a result, the PD 16 outputs the intensity detection signal of the data signal light of the wavelength λm. Similarly, in the optical filter 15 that receives the other branched light of the optical demultiplexer 13,
Data signal light of wavelength λn is extracted from the branched light.
As a result, the PD 17 outputs the intensity detection signal of the data signal light of the wavelength λn.

In the polarizer 18, the wavelength-multiplexed data signal light having a specific polarization is extracted from the branched light input from the optical demultiplexer 12 and output to the optical demultiplexer 19. The optical filter 20 which receives one of the branched lights of the optical demultiplexer 19 extracts the data signal light of the wavelength λm from the branched light. As a result, the PD 22 outputs the intensity detection signal of the data signal light of the wavelength λm. Similarly, the optical filter 21 which receives the other branched light of the optical demultiplexer 19 extracts the data signal light of the wavelength λn from the branched light. As a result, P
An intensity detection signal of the data signal light of wavelength λn is output from D23.

Next, in a detection processing unit (not shown) that receives the outputs of the PDs 16, 17, 22, 23, the wavelength λm detected by the PDs 16, 17 when the polarizer 18 is not present,
The signal light intensity of λn and the PD when the polarizer 18 is interposed
From the relationship with the signal light intensities of the wavelengths λm and λn detected at 22 and 23, the polarization relationship at the time of output is calculated with respect to the polarization relationship at the time of input of the optical transmission path 10, and PM in the optical transmission path 10 is calculated.
The time variation of the D amount is analyzed.

Therefore, according to the first embodiment, since the PMD can be detected by specifying the wavelength, it becomes possible to detect the PMD amount with time change in the WDM optical transmission system. Further, since the PMD amount over the entire wavelength band can be detected by measuring the polarization relationship of a plurality of wavelengths, the PMD detector can be downsized.

Embodiment 2. 2 is a block diagram showing the configuration of a PMD detector that is Embodiment 2 of the present invention. In this second embodiment, as shown in FIG. 2, in the configuration shown in FIG.
Instead of 1, the variable optical filter 24 that can change the center wavelength
~ 27 are provided. Others are the same as the configuration shown in FIG. Here, the description will focus on the part related to the second embodiment.

By making the optical filter variable, it is possible to detect the light intensity of the data signal light of two or more wavelengths with and without the polarizer, so that more accurate PMD detection can be performed. It becomes possible to do.

Therefore, according to the second embodiment, since the PMD can be detected by specifying the wavelength, it becomes possible to detect the PMD amount with time in the WDM optical transmission system. Further, since the PMD amount over the entire wavelength band can be detected by measuring the polarization relationship of a plurality of wavelengths, the PMD detector can be downsized. Further, the PMD amount can be analyzed from the signal light of two or more waves, and the PMD amount can be detected with higher accuracy.

Embodiment 3. FIG. 3 is a block diagram showing the configuration of the PMD detector according to the first embodiment of the present invention. In FIG. 3, wavelength-multiplexed data signal light (λ1 ... λm ... λn ... λz) including two wavelengths (λn, λm) whose polarization relation is known is transmitted to the optical transmission line 10.

The PMD detector shown in FIG.
From wavelength-multiplexed data signal light (λ1 ... λm ... λn ... λz)
11 for extracting a part of the data, a polarizer 18 for receiving the output light of the optical tap 11, and each data signal of the wavelength multiplexed data signal light (λ1 ... λm ... λn ... λz) receiving the output light of the polarizer 18. And an optical spectrum analyzer 28 for simultaneously detecting the respective light intensities.

Next, the operation of the PMD detector configured as described above will be described. The optical transmission line 10 includes wavelength-multiplexed data signal lights (λ1 ... λm ... λn ...) Including data signal lights of two wavelengths (λn, λm) whose polarization relationship is known.
λz) is being transmitted.

The wavelength multiplexed data signal light (λ1 ... λm ... λn ... λz) extracted from the optical transmission line 10 by the optical tap 11 is
It is input to the optical spectrum analyzer 28 via the polarizer 18. The optical spectrum analyzer 28 simultaneously detects the optical intensities of the wavelength multiplexed data signal lights (λ1 ... λm ... λn ... λz).

Then, in the detection processing unit (not shown) which receives the output of the optical spectrum analyzer 28, based on the relationship between the signal light intensities after the polarizer detected by the optical spectrum analyzer 28, the polarization at the time of inputting the optical transmission line 10 is determined. The polarization relationship at the time of output is calculated for the relationship, and the PMD in the optical transmission line 10 is calculated.
The time variation of quantity is analyzed.

Therefore, according to the third embodiment, since the PMD can be detected by specifying the wavelength, it becomes possible to detect the time variation of the PMD amount in the WDM optical transmission system. Further, since the PMD amount over the entire wavelength band can be detected by measuring the polarization relationship of a plurality of wavelengths, the PMD detector can be downsized. Further, since it is possible to analyze the PMD amount over the entire wavelength band, it is possible to detect the PMD amount with higher accuracy.

Fourth Embodiment 4 is a block diagram showing the configuration of a PMD detector that is Embodiment 4 of the present invention. In the fourth embodiment, as shown in FIG. 4, a polarization beam splitter 29 is provided in place of the polarizer 18 and the optical demultiplexer 19 in the configuration shown in FIG. Others are the same as the configuration shown in FIG. Here, the description will focus on the part related to the fourth embodiment.

In FIG. 4, the polarization beam splitter 29
Demultiplexes the wavelength division multiplexed light input from the optical demultiplexer 12 into polarization components having an orthogonal relationship. Therefore, the optical filters 20, 21 and PDs 22, 23 can detect the light intensity as in the first embodiment, and the same effect as in the first embodiment can be obtained.

Therefore, according to the fourth embodiment, since the PMD can be detected by specifying the wavelength, it becomes possible to detect the time variation of the PMD amount by using the FA method in the WDM optical transmission system. Moreover, by sweeping the variable-length light source using the FA method, PM over the entire wavelength band can be obtained.
Since the D amount can be detected, the PMD detector can be downsized. The polarizer 18 in the third embodiment (FIG. 3) can be similarly replaced with a polarization beam splitter.

Embodiment 5. 5 is a block diagram showing a configuration of a wavelength division multiplexing optical transmission system having a PMD compensation function according to a fifth embodiment of the present invention. As shown in FIG. 5, in this wavelength division multiplexing optical transmission system, a PMD compensation optical circuit 34 is provided between the output end of the optical tap 11 and the input end of the optical demultiplexer 12 in the configuration shown in FIG. A PMD compensation optical circuit 35 is provided on the optical transmission line 10, and a control circuit 36 that electrically controls the PMD compensation optical circuits 34 and 35 is provided. The control circuit 36 includes PD1
The intensity signals detected from 6, 17, 22, and 23 are input.

Next, the PMD compensating operation in the wavelength division multiplexing optical transmission system having the PMD compensating function configured as above will be described. The optical transmission line 10 includes wavelength-multiplexed data signal light (λ1 ... λm ... λn ... λ) that contains data signal light of two wavelengths (λn, λm) whose polarization relationship is known.
z) has been transmitted.

The wavelength multiplexed data signal light (λ1 ... λm ... λn ... λz) extracted from the optical transmission line 10 by the optical tap 11 is
It is guided to the optical demultiplexer 12 via the PMD compensation optical circuit 34. The control circuit 36 analyzes the PMD amount of the data signal light of the wavelength λm and the wavelength λn based on the intensity signals from the PDs 16, 17, 22, and 23, and the PMD compensation optical circuit 34 is arranged to minimize the PMD amount. To control.

Then, the control circuit 36 applies to the PMD compensation optical circuit 35 the conditions of the PMD compensation optical circuit 34 that minimize the PMD amount obtained as a result of the control. This makes it possible to compensate for PMD in the optical transmission line 10.

As described above, according to the fifth embodiment, PM
The PMD in the optical transmission line 10 can be compensated by combining the D detector with the PMD compensation optical circuit and the control circuit. Therefore, in the WDM optical transmission system, it is possible to detect and compensate for the time variation of the PMD amount.

Although the configuration of the PMD detector in the first embodiment is used in the fifth embodiment, the second to second embodiments are used.
It goes without saying that the configuration of the PMD detector in 4 can be similarly used.

[0051]

As described above, according to the present invention, the wavelength division multiplexed data signal light including the data signal lights of arbitrary two wavelengths whose polarization relations are known is transmitted by the measurement light acquisition means. A part of the wavelength division multiplexed data signal light is extracted from the optical transmission line. When the first wavelength selecting means extracts each of the two wavelengths of the data signal light from the output light of the measuring light acquiring means, the first light intensity detecting means extracts the extracted two wavelengths of the data signal. The signal light intensity of each light is detected. On the other hand, when the polarizer extracts a predetermined polarization component from the output light of the measurement light acquiring unit, the second wavelength selecting unit outputs each of the two-wavelength data signal light from the output light of the polarizer. The extracted signal light intensities of the data signal lights of the two wavelengths in the predetermined polarization state are detected by the second light intensity detecting means. Therefore, it is possible to analyze and detect the time variation of the PMD amount in the optical transmission line based on the signal light intensity obtained in the state where the polarizer is not present and the state where the polarizer is present. This can be applied over the entire wavelength range, and the PMD amount can be detected following the time fluctuation. As a result, downsizing of the PMD detector can be realized.

According to the next invention, in the above invention, wavelength tunable selecting means is used as the first wavelength selecting means and the second wavelength selecting means. Therefore, the signal light intensity with and without the polarizer can be obtained from the signal light with two or more wavelengths, so that the PMD can be detected with higher accuracy.

According to the next invention, a part of the optical transmission line through which the wavelength multiplexed data signal light including the data signal lights of arbitrary two wavelengths whose polarization relations are known is transmitted by the measurement light acquisition means. When the wavelength-multiplexed data signal light is extracted, the polarizer extracts a predetermined polarization component from the output light of the measurement light acquisition means, and the light intensity detection means extracts the data signal of the two wavelengths from the output light of the polarizer. The signal light intensity of each of the wavelength-multiplexed data signal lights including light is detected. As a result, it is possible to obtain the signal light intensity in the case where the polarizer intervenes in all wavelength regions, so that it is possible to perform PMD detection with higher accuracy.

According to the next invention, a polarization beam splitter can be used instead of the polarizer. In the polarization beam splitter, the input wavelength-multiplexed data signal light is split into polarization components having an orthogonal relationship, and the light intensity is detected. Therefore, the same effect as the above invention can be obtained.

According to the next invention, the first PMD compensating means is arranged in the PMD detector so as to perform the PMD compensating operation on the output light of the measuring light acquiring means, and the second PMD compensating means is provided.
The D compensation means is arranged to perform a PMD compensation operation for the wavelength division multiplexed signal light on the optical transmission line. The control means controls the first PMD compensating means so that the PMD analyzed from the signal light intensity detected by the PMD detector is minimized, and the condition of the first PMD compensating means for minimizing the PMD is the second PMD compensating means. Given to. Therefore, a wavelength division multiplexing optical transmission system capable of detecting and compensating for PMD can be constructed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a PMD detector that is Embodiment 1 of the present invention.

FIG. 2 is a block diagram showing a configuration of a PMD detector that is Embodiment 2 of the present invention.

FIG. 3 is a block diagram showing a configuration of a PMD detector that is Embodiment 3 of the present invention.

FIG. 4 is a block diagram showing a configuration of a PMD detector that is Embodiment 4 of the present invention.

FIG. 5 is a configuration diagram of a wavelength division multiplexing transmission optical system having a PMD compensation function according to a fifth embodiment of the present invention.

FIG. 6 is a diagram showing a relationship between a bit rate of an optical signal and a PMD that causes a 1 dB power penalty.

FIG. 7 is a diagram for explaining a PMD detection method by a conventional FA method.

[Explanation of symbols]

10 optical transmission lines, 11 optical taps, 12, 13, 19
Optical demultiplexer, 14, 15, 20, 21 Optical filter, 1
6, 17, 22, 23 Photodiodes (PD), 1
8 polarizer, 24, 25, 26, 27 variable optical filter, 28 optical spectrum analyzer, 29 polarization beam splitter, 34, 35 PMD compensation optical circuit, 36 control circuit.

Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04J 14/02 (72) Inventor Katsuhiro Shimizu 2-3-3 Marunouchi, Chiyoda-ku, Tokyo Sanryo Electric Co., Ltd. (72 ) Inventor Ryuji Mizuochi 2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo Sanryu Electric Co., Ltd. F term (reference) 2G020 BA20 CA15 CC26 CC47 CD05 CD24 CD38 5K002 BA02 CA01 DA02 EA05 FA01

Claims (5)

[Claims] 1. A measurement light acquisition means for extracting a part of the wavelength-multiplexed data signal light from an optical transmission line through which the wavelength-multiplexed data signal light including the data signal lights of arbitrary two wavelengths whose polarization relations are known is transmitted. A first wavelength selecting means for extracting each of the two wavelengths of the data signal light from the output light of the measuring light acquiring means; and a first wavelength selecting means for receiving the output light of the first wavelength selecting means. First light intensity detecting means for detecting signal light intensity, a polarizer for passing a predetermined polarization component of the output light of the measuring light obtaining means, and data signal light of the two wavelengths from the output light of the polarizer. A second wavelength selecting means for extracting each of them, and a second light intensity detecting means for receiving the output light of the second wavelength selecting means and detecting the signal light intensity of each of the data signal lights of the two wavelengths. PM characterized by D detector. 2. The PMD detector according to claim 1, wherein the first wavelength selecting unit and the second wavelength selecting unit are wavelength tunable selecting units. 3. A measuring light acquisition means for extracting a part of the wavelength-multiplexed data signal light from an optical transmission line through which the wavelength-multiplexed data signal light including the data signal lights of arbitrary two wavelengths whose polarization relations are known is transmitted. A signal light intensity of each of the wavelength-multiplexed data signal lights including the data signal light of the two wavelengths from the output light of the polarizer, A PMD detector comprising: a light intensity detecting unit for detecting. 4. The PMD detector according to claim 1, wherein a polarization beam splitter is used instead of the polarizer. 5. A wavelength-division-multiplexed optical transmission system for transmitting a wavelength-division-multiplexed data signal light including data-signal light of arbitrary two wavelengths whose polarization relation is known, wherein an optical transmission line through which the wavelength-division-multiplexed data signal light is transmitted. 2. A part of wavelength-multiplexed data signal light is extracted from the optical fiber, and the signal light intensity of at least the two-wavelength data signal light is detected.
4. The PMD detector according to any one of claims 1 to 4, and a first P arranged to perform a PMD compensation operation on the output light of the measurement light acquisition means in the PMD detector.
MD compensating means, and a second PM arranged to perform a PMD compensating operation on the wavelength-multiplexed data signal light transmitted through the optical transmission line.
The condition of the D compensating means and the first PMD compensating means for controlling the first PMD compensating means to minimize the PMD analyzed from the signal light intensity detected by the PMD detector and minimizing the PMD is described above. A wavelength division multiplexing optical transmission system, comprising: a control unit provided to the second PMD compensation unit.