JPWO2009144997A1 - Optical fiber dispersion detector and automatic dispersion compensation system using the same - Google Patents

Abstract

The dispersion detection apparatus of the present invention includes a waveform monitoring unit that monitors an eye opening shape of an eye pattern waveform representing a state of an optical signal based on a result of sampling an optical signal passing through an optical fiber, and the waveform monitoring unit. Based on information representing the monitored eye opening shape, eye opening calculating means for detecting the maximum opening length in the voltage direction and the maximum opening length in the phase direction of the eye pattern waveform, and detected by the eye opening calculating means Dispersion amount detection means for detecting the polarization dispersion amount and the chromatic dispersion amount of the optical signal based on information representing the maximum aperture length in the voltage direction and information representing the maximum aperture length in the phase direction.

Description

  The present invention relates to a technique for detecting chromatic dispersion or polarization dispersion of an optical fiber, which is a limiting factor of a transmission distance of a high-speed optical signal, in an ultrahigh-speed optical transmission system based on information representing an eye opening of the optical fiber.

  With the rapid increase in network capacity in recent years, there is a demand for an increase in capacity of optical transmission systems. Recently, replacement of a 10 Gbps wavelength division multiplexing (WDM) transmission system with a 40 Gbps WDM optical transmission system capable of transmitting a larger capacity has been promoted, and the development to increase the capacity of the optical transmission system has been at a rapid pace. Is progressing.

  In such a 40 Gbps optical transmission system, in addition to the waveform degradation caused by chromatic dispersion, which has been a problem with 10 Gbps systems, the influence of waveform degradation caused by polarization dispersion becomes very large. There is a problem in that the transmission distance is significantly limited.

  First, the influence of chromatic dispersion will be described.

  Chromatic dispersion is dispersion that occurs because the speed of an optical signal propagated in an optical fiber is not uniform over all wavelengths, but varies from wavelength to wavelength, and its tolerance (allowable amount of generation) is the square of the bit rate. Inversely proportional. Therefore, the chromatic dispersion is about 800 ps / nm in the existing 10 Gbps system, and is very severe at about 50 ps / nm (1/16 of 10 Gbps) in the 40 Gbps system.

  In addition, the chromatic dispersion value of the optical fiber transmission line changes with time according to environmental changes such as temperature and pressure. For example, when a temperature change occurs in the range of −50 ° C. to 100 ° C., the dispersion value change amount over 50 km of the single mode fiber is 16 ps / nm, which is a value that cannot be ignored on the system. Therefore, it is understood that not only the compensation amount for dispersion is optimized at the start of operation of the system, but also the dispersion compensation amount needs to be optimized in response to the temporal change of the dispersion value during operation of the system.

  Next, the influence of polarization dispersion will be described.

  Polarization dispersion is due to the effect of deviation from a perfect circle and the effect of stress on the optical fiber because the optical fiber is slightly elliptical (the two optical modes, TE mode and TM mode). This is a dispersion caused by different propagation delay times. In general, polarization dispersion increases as the transmission speed of an optical signal increases and as the transmission distance increases.

Some old optical fibers (mainly installed outside Japan) have large polarization dispersion exceeding 1 ps / km ^1/2 . For example, when an optical signal is transmitted 100 km through such an optical fiber, a group delay (DGD: Differential Group Delay) Δτ generated in two polarization components is about 10 ps, which is 2/5 of one time slot 25 ps of a 40 Gbps optical signal. Also reach. Therefore, the waveform deterioration of the optical signal becomes significant, and the transmission distance is greatly limited.

  Furthermore, polarization dispersion is caused by changes in the transmission path environment due to temperature changes and stress such as fiber touch (stress is applied to the optical fiber by touching the optical fiber or wind blowing on the optical fiber). Varies over time.

  For example, Non-Patent Document 1 discloses changes in polarization dispersion with respect to temperature changes. Non-Patent Document 1 points out the correlation between the polarization dispersion fluctuation amount of the single mode fiber in the underground pipe line over 48.8 km and the environmental temperature change. According to this result, it can be seen that the fluctuation of the polarization dispersion with respect to the temperature change is a relatively slow fluctuation that occurs in minutes.

  On the other hand, Non-Patent Document 2 reports the frequency of occurrence of polarization dispersion fluctuation due to mechanical vibrations (mechanical vibration). Non-Patent Document 2 reports that the speed of polarization dispersion fluctuation is generally kilohertz, that is, a speed in milliseconds. Therefore, in order to compensate the polarization dispersion with high accuracy, as well as the chromatic dispersion described above, not only the compensation operation is automatically performed according to the transmission path state at the time of starting the system (so-called no adjustment / adjustment). It is necessary to monitor the influence of polarization dispersion dynamically during system operation and to perform compensation operation following the polarization dispersion at high speed in milliseconds.

  To summarize the above, the following elemental technologies are required to realize the transmission distance extension in the 40 Gbps optical transmission system.

(1) Variable dispersion compensator (2) Method of monitoring transmission line dispersion (wavelength dispersion or polarization dispersion) In the case of polarization dispersion, it is necessary to monitor high-speed dispersion fluctuations in milliseconds.
(3) Feedback Optimization Control Method for Variable Dispersion Compensator Here, as a method for monitoring the amount of dispersion, for example, in chromatic dispersion, light of a plurality of different wavelengths is input to an optical fiber, and a group delay difference between output lights or A pulse method or a phase method for measuring a phase difference is used. However, in order to always perform dispersion measurement during system operation using these methods, a set of chromatic dispersion measuring devices is required for each relay section of the optical transmission system. Furthermore, in order to measure the dispersion amount without interrupting the transmission of the data signal light, it is necessary to use measurement light having a wavelength different from that of the data signal light.

  As described above, it is difficult to say that the pulse method and the phase method are executed in the optical transmission apparatus in terms of size and economy. Furthermore, when a wavelength different from the main signal light wavelength is used, there is a possibility of lack of strictness because of the process of estimating the dispersion value at the signal light wavelength based on the measurement value at the measurement light wavelength. Therefore, a method that can monitor the chromatic dispersion value directly from the main signal light is desirable. As this chromatic dispersion monitoring method, a method using 40 GHz component intensity in the baseband spectrum of a 40 Gb / s OTDM (optical time division multiplexing) signal and an NRZ (Non-Return-to-Zero) signal has been recently proposed.

  Next, related technologies for polarization dispersion monitoring and dispersion compensation will be described.

  For example, Patent Document 1 discloses a technique for optimally controlling the amount of compensation for waveform degradation based on information related to a code error of an optical signal. That is, the code error information of the optical signal serves as a dispersion monitor. Specifically, in the automatic dispersion compensation system disclosed in Patent Document 1, an optical signal is amplified by an optical amplifier 101 and then sent to a tunable dispersion compensator 102 as shown in FIG. The output signal of the tunable dispersion compensator 102 is amplified by the optical amplifier 103 and then converted into an electric signal by the light receiving element 104. The output signal of the light receiving element 104 is amplified by the amplifier circuit 105, the clock recovery / identification circuit 106 performs clock recovery and identification processing, and the serial / parallel conversion circuit 107 performs serial / parallel conversion. The error correction circuit 108 performs code processing on the output signal of the serial / parallel conversion circuit 107 to detect a code error, and feeds back information about the detected code error to the control circuit 109. The control circuit 109 optimally controls the tunable dispersion compensator 102 based on the information fed back from the error correction circuit 108.

  Patent Document 2 discloses a technique for separating two dispersions of chromatic dispersion and polarization dispersion, which are main causes of transmission quality degradation, using a general transmission quality monitor. Here, examples of the transmission quality monitor include an error measuring device and a transmission quality monitor for measuring the Q value. Specifically, in the first automatic dispersion compensation system disclosed in Patent Document 2, as shown in FIG. 2, an optical receiver 110 includes a photodiode (PD) 111 that converts an optical signal into an electrical signal, and The preamplifier 112 and the amplifier 113, an equalizing amplifier 114 for amplifying an electric signal and shaping the waveform, a clock extracting circuit 115 for extracting a clock signal from the output signal of the equalizing amplifier 114, and an equalizing amplifier 114 And an identification circuit 116 for identifying the state of the output signal. The status monitor 117 monitors the status of the PD 111, the equalizing amplifier 114, and the identification circuit 116. In the second automatic dispersion compensation system disclosed in Patent Document 2, the PMD compensator 118 is controlled according to the monitoring result of the PMD monitor 119 as shown in FIG. As a result, PMD compensation for the optical reception signal input to the dispersion compensator 120 is performed. Further, the dispersion compensator 120 is controlled according to the monitoring result of the dispersion monitor 122 that monitors the optical / electrical converter (O / E) 121.

  As specific techniques for chromatic dispersion compensation, for example, there are techniques disclosed in Patent Documents 4 to 6, Non-Patent Documents 3 and 4, and the like. Examples of the variable chromatic dispersion compensation device used for chromatic dispersion compensation include VIPA (Virtually-Imaged-Phased-Array) disclosed in Non-Patent Document 5, and FBG (Fiber-Bragg-Grating) disclosed in Non-Patent Document 6. ) And other optical devices.

  In addition, specific techniques for polarization dispersion compensation include, for example, methods such as an optical processing type, a photoelectric processing type, and an electric processing type disclosed in Non-Patent Document 7. Among these, the light processing type and the photoelectric processing type need to control the polarization state. Further, as a control method for polarization dispersion compensation, the frequency component of 1/2 of the clock signal included in the optical signal after polarization dispersion compensation, disclosed in Non-Patent Documents 8 and 9, or 1/4 There is a method for controlling the polarization state by monitoring frequency components.

  However, there are some problems in the dispersion monitoring technique and dispersion compensation technique of the related art as described above. The problems are described below.

  (1) The technique disclosed in Patent Document 1 is advantageous from the viewpoint of downsizing and cost reduction of the apparatus because the identification and control of dispersion are performed by electrical processing as shown in FIG. It has been attracting attention in recent years. However, in the case of this technique using the code error information for dispersion compensation control, generally, the coefficient adjustment of the variable dispersion compensator is performed so that the number of errors is minimized. However, since errors occur randomly, it is necessary to accumulate error counts for a certain period of time until the number of errors is accumulated to some extent. In addition, in this system, when a dispersion variation occurs due to some condition change and a code error occurs thereby, dispersion compensation is controlled excessively (to the + side) than the current state, or in a decreasing direction (to the − side). B) Does not have data for determining whether to control. In general, a dithering method that expresses gradation with dots generated randomly, as disclosed in Patent Document 7, or a next candidate from the current vertex as disclosed in Non-Patent Document 10 When the vertices are developed, an algorithm such as a hill-climbing technique that determines the next search course that is closest to the goal is used to find an optimal compensation point. However, since the technique disclosed in Patent Document 1 does not have the above data, it cannot be determined first whether the error rate decreases or increases when the dispersion compensation amount is increased. That is, when the dispersion compensation amount is controlled based on the error rate, the time required to reach the optimum value becomes long. Furthermore, if the step of the dispersion compensation amount control interval is rough, the convergence point of the system may not be found. Therefore, the dispersion compensation amount control interval must maintain a certain degree of accuracy. In this case, the time required for convergence and the number of repetitions further increase. Therefore, there is a problem that it is difficult to apply to a system that requires high-speed compensation in milliseconds.

  (2) Among the techniques disclosed in Patent Document 2, the automatic dispersion compensation system shown in FIG. 3 requires a monitor, a control device, and a dispersion compensator for each of chromatic dispersion and polarization dispersion. Become. Most of the dispersion compensator and its peripheral devices, which are these components, are composed of optical components, leading to an increase in the size and cost of the device due to an increase in the number of components. Therefore, there is a problem that it is difficult to generalize.

  (3) Other specific conventional techniques for polarization dispersion compensation include several techniques for performing optical processing, electrical processing, and the like. However, most of these polarization dispersion compensation techniques require control of the polarization state. In this case, there is a problem that it is difficult to realize polarization control with respect to polarization dispersion that changes with time at a high speed in milliseconds.

  From the above, the dispersion compensation technique in the ultrahigh-speed optical transmission technique requires the following two points to realize the high-speed dispersion compensation without stopping the system even during operation.

1) Increase / decrease direction of the amount of dispersion that cannot be obtained by using error correction information, and a dispersion monitoring mechanism that can estimate the amount 2) Even when high-speed dispersion changes occur, the amount of change is instantaneous Dispersion monitoring method using simple arithmetic processing, and dispersion compensation apparatus, which can estimate the dispersion compensation amount and change the dispersion compensation amount to an optimum value at high speed

Japanese Patent Laid-Open No. 7-221705 JP 2002-208992 A JP 2004-7150 A JP-A-8-321805 JP-A-9-326755 Japanese Patent Laid-Open No. 10-276172 JP 2002-337701 A “J. Cameron et al .: Time evolution of polarization-mode dispersion for aerial and buried cables, Proc. OFC98, pp240-241”. “H. Brown et al .: Measurement of the Maximum Speed of PMD Fluctuation in Installed Field Fiber, Proc. OFC'99, pp 83-85”. “G. Ishikawa et al.,“ DEMONSTRATION OF AUTOMATIC DISPERSION EQUALIZEN IN 40 Gbit / s OTDM TRANSMISSION ”, ECOC'98, pp. 519-520”. “Y. Akiyama et al.,“ AUTOMATIC DISPERSION EQUALIZATION IN 40 Gbit / s TRANSMISSION BY SEAMLESS-SWITCHING BETWEEN MULTIIPSIGNAL WAVEENP ”51-150. “M. Shirasaki et al.,“ Dispersion Compensation Using The Virtually Imaged Phased Array ”, APCC / OECC '99, pp. 1367-1370, 1999”. “M.M. Ohn et al.,“ Tunable Fiber Grading Dispersion Usagea Piezoelectric Stack ”, OFC'97 WJ3” “H. Bullow et al.,“ Optical and electronic PMD compensation ”, OFC’03, p.541” “H. Ooi et al.,“ Automatic Polarization-ModeDispersion Compensation in 40 Gbit / s Transmission, IOOC'99, WE5 ” “D. Sandel et al.,“ Automatic polarization mode dispersion compensation in 40 Gbit / s optical transmission system ”, Electron. Lett., 1998, pp 2258-2259. “Makoto Nagaoka: Software Science 14“ Knowledge and Reasoning ”, Iwanami Shoten, 1988, pp. 114-120 "

  Accordingly, an object of the present invention is to provide a high-speed and simple dispersion detector for compensating polarization dispersion at a high speed in milliseconds and an automatic dispersion compensation system using the same.

  In order to achieve the above object, the dispersion detection device of the present invention monitors a shape of an eye opening of an eye pattern waveform representing a state of an optical signal based on a result of sampling an optical signal passing through an optical fiber. An eye opening calculation unit that detects a maximum opening length in the voltage direction and a maximum opening length in the phase direction of the eye pattern waveform based on information representing the eye opening shape monitored by the waveform monitoring circuit; The dispersion for detecting the polarization dispersion amount and the chromatic dispersion amount of the optical signal based on the information indicating the maximum aperture length in the voltage direction and the information indicating the maximum aperture length in the phase direction detected by the eye aperture calculator And a quantity detection unit. Although the waveform monitor circuit has been described as an example here, the waveform monitor unit including the following may be used.

  In addition, the dispersion amount detection unit of the present invention calculates a division ratio when the maximum eye opening length in the phase direction is divided into two with the specific phase position where the maximum eye opening length in the voltage direction is obtained as a base point. Thus, a polarization dispersion amount detection unit that detects the power branching ratio of the slow wave component and the fast wave component of the optical waveform, which is information representing the polarization dispersion amount, is configured.

  Further, the polarization dispersion amount detection unit of the present invention calculates information indicating a ratio of the length of the eye opening maximum length in the voltage direction and the eye opening maximum length in the phase direction, and calculates the ratio of the calculated length. By multiplying the detected power branching ratio, the group delay amount which is information indicating the polarization dispersion amount is detected.

  In addition, the waveform monitor circuit of the present invention is a discriminator that samples data exceeding a discrimination threshold in the voltage direction set from the outside at a timing based on the discrimination clock inputted from the outside from the received waveform after passing through the optical fiber. And a circuit for setting a discrimination threshold of the discriminator, and a phase adjustment circuit for changing the phase of the discrimination clock input to the discriminator, changing the discrimination threshold of the discriminator in the voltage direction, and The eye opening shape of the eye pattern waveform is extracted by repeatedly sampling a plurality of data from the received waveform while changing the phase of the identification clock input to the discriminator.

  In addition, the dispersion amount detection unit of the present invention calculates a division ratio when the eye opening maximum length in the voltage direction is divided into upper and lower parts, starting from the specific voltage position where the eye opening maximum length in the phase direction is obtained. The wavelength for detecting the amount of chromatic dispersion by calculating the ratio of the maximum length of the eye opening in the voltage direction and the maximum length of the eye opening in the phase direction and multiplying the calculated ratio of the length by the calculated division ratio A dispersion amount detection unit is provided.

  As described above, according to the dispersion detection apparatus of the present invention, with respect to waveform deterioration due to polarization dispersion, a feature that the eye opening amount of the received eye pattern waveform is asymmetrical on the left and right is extracted by a high-speed monitor. Since the amount of polarization dispersion is detected by a simple calculation method, the effect that polarization dispersion can be compensated at a high speed in milliseconds can be obtained. The waveform degradation caused by chromatic dispersion is also characterized by the fact that the cross-point of the received eye pattern waveform fluctuates from the middle position to the upper side or lower side, and the amount of aperture in the phase direction of the eye pattern waveform decreases. Since the chromatic dispersion amount is detected by a simple calculation method after being extracted by the monitor, it is possible to obtain an effect that the dispersion can be compensated with a high-speed and small device.

It is a figure which shows the example of 1 structure of the conventional automatic dispersion compensation system. It is a figure which shows the other structural example of the conventional automatic dispersion compensation system. It is a figure which shows the further another structural example of the conventional automatic dispersion compensation system. It is a block diagram which shows the structure of the dispersion | distribution detection apparatus of one Embodiment of this invention. FIG. 5 is an explanatory diagram showing a specific method for detecting the amount of polarization dispersion in the dispersion detection apparatus shown in FIG. 4. FIG. 5 is a diagram showing an estimation result of polarization dispersion amount by the dispersion detection apparatus shown in FIG. 4. FIG. 5 is an explanatory diagram showing a specific method for detecting the amount of chromatic dispersion in the dispersion detection apparatus shown in FIG. 4. It is a figure which shows the estimation result of the amount of chromatic dispersion by the dispersion | distribution detection apparatus shown in FIG. It is a figure which shows the example of 1 structure of the automatic dispersion compensation system using the dispersion | distribution detection apparatus shown in FIG. 10 is a flowchart for explaining the schematic operation of the automatic dispersion compensation system shown in FIG. 9. It is a figure which shows the other structural example of the automatic dispersion compensation system using the dispersion | distribution detection apparatus shown in FIG. FIG. 10 is a diagram showing still another configuration example of an automatic dispersion compensation system using the dispersion detection apparatus shown in FIG. 4.

  The best mode for carrying out the present invention will be described below.

  First, a case will be described in which the amount of polarization dispersion is detected from a waveform degraded by the influence of polarization dispersion.

  As described above, polarization dispersion is waveform degradation caused by combining two waves of a slow wave component and a fast wave component of an optical waveform caused by group delay (DGD) with a power branching ratio γ. The transfer function z is expressed as Equation (1).

(1-γ) + γ × z- ^{DGD / 1UI} (1)
Here, z is the transfer function, γ is the energy ratio of the delayed wave to the input wave, DGD is the group delay, and UI is one symbol length.

  In the waveform deterioration caused by polarization dispersion, the eye opening amount of the received eye pattern waveform is asymmetrical at both the left and right sides in one symbol, except when the power branching ratio γ in the transfer function is 1: 1. It is.

  Therefore, first, the received waveform is sampled and extracted over a plurality of points, and the degree of asymmetry of the waveform is recognized by monitoring the eye opening shape of the eye pattern waveform based on the extracted data. The amount of polarization dispersion can be estimated from the degree of asymmetry.

  As described above, the dispersion detection apparatus according to the first aspect for detecting the polarization dispersion amount integrates the received signals passing through the optical fiber while sampling, and extracts the eye opening shape of the eye pattern waveform based on the result. A waveform monitor circuit, a voltage direction eye opening calculator that detects the maximum opening length in the voltage direction (height direction) of the waveform based on the information of the eye opening shape detected by the waveform monitor circuit, and the phase direction of the waveform The above-mentioned light is obtained by performing a predetermined calculation on the basis of information on the phase direction eye opening calculation unit that detects the maximum opening length in the (lateral direction) and the detected maximum opening length in the voltage direction and the maximum opening length in the phase direction. And a dispersion amount detection unit for detecting the polarization dispersion amount and the chromatic dispersion amount of the optical signal passing through the fiber.

  A specific method for detecting the amount of polarization dispersion is as follows. Polarization dispersion by calculating the division ratio when the maximum eye opening length in the phase direction is divided into two, based on the specific phase position where the maximum eye opening length in the voltage direction of the received eye pattern waveform is obtained The power branching ratio γ of the slow wave component and the fast wave component of the optical waveform, which is information representing the quantity, is detected. In addition, by calculating the information indicating the ratio of the length of the maximum eye opening in the voltage direction and the maximum length of the eye opening in the phase direction, the ratio of the calculated length is multiplied by the power branching ratio that has already been detected. The group delay amount which is information indicating the polarization dispersion amount is detected.

  Here, when the power branching ratio γ is 1: 1, that is, when the branching ratios are equal, the received eye pattern waveform is broken in the left-right symmetry only by collapsing the eye opening in the voltage direction, that is, in the height direction. There is no.

  Accordingly, the dispersion amount detection unit determines that γ = 0 or 50% when the eye opening amount in the voltage direction is not asymmetric when compared to the left and right of one symbol length. After that, when it is asymmetric, a specific γ value is estimated.

  Next, a case where the amount of chromatic dispersion is detected from a waveform deteriorated by the influence of chromatic dispersion will be described.

  In the case of waveform degradation due to chromatic dispersion, in contrast to waveform degradation due to polarization dispersion, the eye pattern cross-point of the received waveform varies from the middle position to the upper side or the lower side, and the eye pattern waveform The feature is that the phase direction margin is reduced.

  Therefore, it is possible to estimate the amount of chromatic dispersion by performing arithmetic processing after detecting the eye opening amount in the voltage direction, the eye opening amount in the phase direction, and the variation amount of the cross point of the received eye pattern waveform as described above. It becomes possible.

  A specific method for detecting chromatic dispersion is as follows. In the received eye pattern waveform, calculate the division ratio when dividing the maximum eye opening length in the voltage direction from the specific voltage position where the maximum eye opening length in the phase direction can be obtained, and at the same time, increase the eye opening maximum in the voltage direction. The ratio of the length to the length of the eye opening in the phase direction is calculated, and the chromatic dispersion amount is detected by multiplying the calculated length ratio by the division ratio calculated earlier.

  Next, an automatic dispersion compensation system using the above-described dispersion detection apparatus will be described.

  This automatic dispersion compensation system compensates for waveform deterioration due to the dispersion of the received signal converted into the electrical signal by the photoelectric conversion circuit and the photoelectric conversion circuit that converts the optical signal passing through the optical fiber from the optical signal to the electrical signal An electrical dispersion compensator, a dispersion detection device that detects the amount of dispersion based on a received waveform input to the electrical dispersion compensator, a clock signal reproduction and extraction from the signal that has passed through the electrical dispersion compensator, and data A clock data recovery circuit that recovers the signal and an adaptive compensation that controls the compensation coefficient of the electrical dispersion compensator and the identification threshold value of the clock data recovery circuit based on the detection result of the polarization dispersion amount detected by the dispersion detector A quantity control unit. In determining the compensation coefficient and the identification threshold, for example, a method of storing lookup data representing the correlation between the dispersion amount, the compensation coefficient, and the identification threshold in advance in the lookup data table and using the lookup data may be employed. it can.

  With the dispersion detection apparatus described above, it is possible to detect the amount of dispersion by estimating the amount of waveform deterioration due to polarization dispersion or wavelength dispersion in both cases of initial setting and service operation. Also, during service operation, not only relatively slow dispersion fluctuations due to temperature changes, but also high-speed dispersion fluctuations in milliseconds due to mechanical vibrations can be detected. It is.

  In addition, since it is configured to detect the amount of dispersion by simple calculation using information obtained by monitoring the received waveform at high speed, the number of repetitions of processing until detection is reduced compared to the case of using information such as a code error rate, This is sufficient to automatically compensate for polarization dispersion that fluctuates at a high speed in milliseconds.

  In addition, the routine of the automatic dispersion compensation system using these dispersion detection devices does not use the control of optical components such as polarization control, and everything can be performed by electrical processing. Therefore, compared to the case of using optical components. Small integration is possible, and the number of parts can be reduced and the cost can be reduced.

  Hereinafter, specific embodiments of the dispersion detection apparatus of the present invention will be described with reference to FIGS.

  FIG. 4 is a block diagram showing the configuration of the dispersion detection apparatus according to the embodiment of the present invention. The dispersion detection apparatus of this embodiment detects the amount of polarization dispersion or the amount of chromatic dispersion in an optical fiber that is a transmission path.

  Referring to FIG. 4, the dispersion detection apparatus of the present embodiment is based on a received waveform monitor unit 1 that monitors a signal received from an optical fiber, and a received eye pattern waveform monitored by the received waveform monitor unit 1. A voltage direction eye opening calculation module 4 that detects an eye opening amount in the voltage direction of the pattern, a phase direction eye opening calculation module 5 that detects an eye opening amount in the phase direction of the eye pattern, and a dispersion amount detection unit that detects the dispersion amount 6.

  The received waveform monitor unit 1 includes a waveform monitor module 2 and an eye pattern detection module 3.

  The waveform monitor module 2 samples the received optical fiber transmission signal in real time.

  The eye pattern detection module 3 controls the sampling points of the data sampled by the waveform monitor module 2 and at the same time integrates the sampling data and reproduces the eye pattern waveform using the calculation result. Specifically, the eye pattern detection module 3 performs control so that the identification threshold value and the clock phase of data input to the waveform monitor module 2 are gradually swept. As a result, the waveform monitor module 2 performs data sampling while sweeping both the amplitude direction and the phase direction, and this data is subjected to a multipoint integration process and an averaging process to obtain information representing an eye pattern waveform. (Data) is played back.

  Next, the voltage direction eye opening calculation module 4 detects the maximum opening length in the voltage direction (height direction) of the waveform based on information representing the eye opening shape of the eye pattern detected by the received waveform monitor unit 1. To do. On the other hand, the phase direction eye opening calculation module 5 detects the maximum opening length in the phase direction (lateral direction) of the waveform based on the information representing the eye opening shape of the eye pattern that is also detected.

  The dispersion amount detection unit 6 includes a polarization dispersion amount detection module 7 and a chromatic dispersion detection module 8, and is predetermined based on information on the maximum aperture length in the voltage direction and the maximum aperture length in the phase direction detected as described above. By performing this calculation, the polarization dispersion amount or the chromatic dispersion amount of the transmission signal is detected. Details of this dispersion amount estimation method will be described in detail with reference to FIGS. 5 and 6 in the case of polarization dispersion and FIGS. 7 and 8 in the case of chromatic dispersion. 5 and FIG. 7, the vertical axis represents the voltage direction of a standardized voltage (au: Arbitrary Unit) in the following description regarding the method of estimating the dispersion amount from the eye pattern waveform shown in FIGS. The voltage is converted with the lowest voltage portion of the waveform as 0 and the highest voltage portion as 1. On the other hand, the horizontal axis indicates the phase direction of the standardized phase, and the phase is converted with 1 unit interval length of the waveform as 1.

  First, a method for estimating polarization dispersion will be specifically described with reference to FIG.

  As described above, polarization dispersion is waveform degradation caused by combining two waves of a slow wave component and a fast wave component of an optical waveform caused by group delay (DGD) with a power branching ratio γ. Except for the case where γ is 1: 1, the feature is that the eye opening amount of the received eye pattern waveform is asymmetrical at both left and right ends in one symbol. For this reason, as shown in FIG. 5, the phase position where the maximum eye opening length A in the voltage direction is obtained is used as a base point (that is, based on the intersection of the maximum eye opening length A in the voltage direction and the maximum eye opening length B in the phase direction). When the left side of the eye opening in the phase direction is divided into a and the right side is divided into b, the branching ratio γ is expressed as shown in Expression (2).

γ = α × (a / (a + b)) (2)
Here, α is a constant, and a / (a + b) represents the left and right eye opening asymmetric ratio.

  On the other hand, the maximum voltage direction eye opening decreases as the group delay amount DGD increases, and varies depending on the asymmetry ratio a / (a + b).

DGD = β × (B / A) / (a / (a + b)) (3)
Here, β is a constant.

  As described above, it is possible to detect the amount of polarization dispersion by performing the predetermined calculation shown in Expression (2) and Expression (3) using the waveform monitor result.

  FIG. 6 shows the result of estimating the polarization dispersion amount in the actual optical fiber transmission system using the dispersion detection apparatus shown in the above equation (3). The horizontal axis indicates the DGD actually generated in the optical fiber, and the vertical axis indicates the DGD amount estimated using the equation (3). The oblique line indicates an ideal straight line when the actual numerical value and the estimated amount coincide with each other. The closer the actual estimation result shown in the plot is to the ideal straight line, the smaller the error in the estimated value. From the result of FIG. 6, it can be seen that the DGD estimation result is within ± 2 ps of error and the polarization dispersion amount can be detected with high accuracy.

  Next, a method for estimating chromatic dispersion will be specifically described with reference to FIG.

  In the case of waveform degradation due to chromatic dispersion, in contrast to the waveform degradation due to polarization dispersion described above, the cross-point of the received waveform eye pattern changes from the middle position to the upper side or the lower side, and the eye pattern The feature is that the opening amount in the phase direction of the waveform is reduced. Therefore, as shown in FIG. 7, the voltage position at which the maximum eye opening length B in the phase direction is obtained is a base point (that is, based on the intersection of the maximum eye opening length A in the voltage direction and the maximum eye opening length B in the phase direction). When the upper side of the eye opening in the voltage direction is divided into c and the lower side is divided into d, the CD dispersion shifts from the center of the cross-point position of the eye pattern as the dispersion amount increases. It is expressed as follows.

CD = α × (B / A) × (c / (c + d)) (4)
Here, α is a constant.

  As described above, it is possible to detect the amount of chromatic dispersion by performing a predetermined calculation shown in Expression (4) using the waveform monitor result.

  FIG. 8 shows the result of estimating the amount of chromatic dispersion in an actual optical fiber transmission system using the dispersion detector shown in the above equation (4). The horizontal axis represents the chromatic dispersion amount CD actually generated in the optical fiber, and the vertical axis represents the chromatic dispersion amount estimated using the equation (4). The oblique line indicates an ideal straight line when the actual numerical value and the estimated amount coincide with each other. The closer the actual estimation result shown in the plot is to the ideal straight line, the smaller the error in the estimated value. From the result of FIG. 8, it can be seen that the estimation result of chromatic dispersion can be accurately detected within an error of ± 3 ps.

  As described above, in this embodiment, the typical feature of waveform degradation caused by chromatic dispersion or polarization dispersion is a configuration in which the amount of dispersion is detected by simple calculation using information obtained by sampling and monitoring the received waveform at high speed. Therefore, it is possible to detect dispersion fluctuations at a higher speed compared to related monitoring techniques that use information such as the code error rate, etc., and at the same time, optical components and complicated control are not applied. It can also contribute to downsizing. Further, for example, a dispersion detection device that estimates the polarization dispersion amount or the chromatic dispersion amount by comparing the characteristic waveform degradation shape due to dispersion of the waveform received by the waveform monitor with a lookup data table stored in advance. In this case, in order to estimate the amount of dispersion with high accuracy, it is necessary to store a large amount of waveform-degraded shape data, which requires a huge memory device in hardware. On the other hand, the dispersion detection apparatus of this embodiment does not require these accumulated data and can estimate the amount of dispersion by a relatively simple calculation. This also contributes to the simplification and cost reduction of the apparatus. Is possible.

(First embodiment)
FIG. 9 is a diagram showing an embodiment of an automatic dispersion compensation system using the dispersion detection apparatus shown in FIG.

  Referring to FIG. 9, the automatic dispersion compensation system of this example calculates the eye opening amount in the voltage direction of the eye pattern from the received waveform monitor unit 1 and the received eye pattern waveform monitored by the received waveform monitor unit 1. A voltage direction eye opening calculation module 4 to detect, a phase direction eye opening calculation module 5 to detect an eye opening amount in the phase direction of the eye pattern, a dispersion amount detection unit 6 to detect the dispersion amount, a photoelectric conversion circuit 9, An electrical dispersion compensator 10, a clock data recovery circuit (CDR: clock data recovery) 11, an adaptive compensation amount control module 12, and a lookup data table module 13 are included.

  The photoelectric conversion circuit 9 converts the received signal transmitted through the optical fiber from an optical signal to an electrical signal.

  The electrical dispersion compensator 10 compensates for waveform deterioration due to polarization dispersion or wavelength dispersion of the reception signal converted into an electrical signal by the photoelectric conversion circuit 9.

  The clock data recovery circuit 11 regenerates and extracts the clock signal and further recovers the data signal based on the signal that has passed through the electrical dispersion compensator 10.

  The waveform monitor module 2 includes an identifier 14, a phase interpolator 16, and a counter 19.

  The eye pattern detection module 3 includes a fluctuation threshold control circuit 15, a phase controller 17, a timer circuit 18, and a time differentiation circuit 20.

  The discriminator 14 is adjusted by the fluctuation threshold control circuit 15 from the received waveform before passing through the electric dispersion compensator 10 at the timing based on the discriminating clock whose phase is adjusted by the phase interpolator 16 and the phase controller 17. Data discrimination sampling is performed using the discrimination threshold as a discrimination criterion. During this identification sampling, the identification threshold and the identification clock phase are gradually swept using a timer circuit. As a result, data sampling is performed while sweeping both the amplitude direction and the phase direction.

  The eye pattern waveform is reproduced by subjecting the sampling data obtained as described above to processing such as integration, differential value calculation, and averaging in the time differentiation circuit 20.

  Next, the voltage direction eye opening calculation module 4 detects the maximum opening length of the waveform in the voltage direction (height direction) based on the information on the eye opening shape of the eye pattern detected by the waveform monitor unit 1. On the other hand, the phase direction eye opening calculation module 5 detects the maximum opening length in the phase direction (lateral direction) of the waveform based on the information of the eye opening shape of the eye pattern that is also detected.

  The dispersion amount detection unit 6 detects the polarization dispersion amount or the chromatic dispersion amount of the transmission signal by performing a predetermined calculation based on the detected information about the maximum aperture length in the voltage direction and the maximum aperture length in the phase direction. . In this example, the case where the amount of polarization dispersion is estimated is described as an example. However, if this dispersion detection device is used, the amount of chromatic dispersion can also be estimated.

  Based on the detection result of the polarization dispersion amount detected by the dispersion amount detector 6, the adaptive compensation amount control module 12 optimizes the optimum compensation coefficient of the electrical dispersion compensator 10 and the identification threshold value of the clock data recovery circuit 11. Control to determine the value. Here, when determining the compensation coefficient and the identification threshold, for example, the lookup data indicating the correlation between the polarization dispersion amount and the compensation coefficient and the correlation between the polarization dispersion amount and the identification threshold are stored in the lookup data table module 13. It is possible to adopt a method of storing in advance and determining a compensation coefficient and an identification threshold using this lookup data.

  FIG. 10 is a flowchart for explaining the schematic operation of the automatic dispersion compensation system shown in FIG.

  Referring to FIG. 10, first, when a received waveform is input (step 701), the received waveform monitor unit 1 samples the received waveform while changing the discrimination threshold in the voltage direction (steps 702 and 703). Data extraction in the voltage direction at the clock phase point is performed (step 704). Further, the received waveform monitor unit 1 repeats steps 702 to 704 while changing the clock phase (step 705). As a result, information representing the received eye pattern is detected, and the eye pattern waveform is reproduced (step 706).

  Next, the dispersion amount detection unit 6 detects the maximum eye opening amount in the voltage direction by analyzing the reception eye pattern waveform extracted by the reception waveform monitor unit 1 (step 707), and the maximum eye in the phase direction. The opening amount is detected (step 708).

  Next, the dispersion amount detector 6 uses the obtained phase position of the maximum eye opening length A in the voltage direction as a base point (that is, based on the intersection of the maximum eye opening length A in the voltage direction and the maximum eye opening length B in the phase direction). When the left side of the eye opening in the phase direction is divided into a and the right side is divided into b, and the asymmetric ratio a / (a + b) is equal to 0.5, the power branching ratio γ is determined to be 0.5 or 0 (step) 709, 710). On the other hand, if the asymmetric ratio is other than 0.5, γ is estimated (step 711), and the DGD amount is detected (step 712).

  Thereafter, the adaptive compensation amount control module 12 determines the optimum compensation coefficient of the electrical dispersion compensator 10 and the clock data recovery based on the detection result of the power branching ratio γ and the group delay DGD amount obtained by the dispersion amount detection unit 6. The optimum value of the discrimination threshold of the circuit 11 is determined, and the determined value is set in the electric dispersion compensator 10 and the clock data recovery circuit 11 (step 713). In determining the compensation coefficient and the identification threshold, as described above, for example, the lookup data representing the correlation between the polarization dispersion amount and the compensation coefficient and the polarization dispersion amount and the identification threshold is stored in the lookup data table module 13. It is possible to adopt a method of storing in advance and obtaining the compensation coefficient and the identification threshold value from the lookup data using the estimated variance described above as a reference key.

  As described above, according to the present embodiment, the degree of left-right asymmetry of the received eye pattern waveform, which is a typical characteristic of waveform degradation due to polarization dispersion, is extracted based on the data detected by the high-speed monitor, and polarization dispersion Detect the amount. Therefore, since the amount of dispersion is detected with a simple calculation, the number of repetitions of processing until detection is reduced compared to the case where information such as a code error rate is used, and the polarization changes at a high speed in milliseconds. Dispersion can be automatically compensated. In addition, since a high-speed waveform monitor is used, it is possible to estimate the amount of waveform degradation due to polarization dispersion and detect the amount of dispersion in both cases of initial setting and service operation. Also, during service operation, not only relatively slow dispersion fluctuations due to temperature changes, but also high-speed dispersion fluctuations in milliseconds due to mechanical vibrations can be detected. It is. Furthermore, since all electrical processing is possible without using optical component control such as polarization control, it is possible to reduce the number of components and reduce costs compared to using optical components. Is possible.

(Second embodiment)
FIG. 11 is a diagram showing another configuration example of the automatic dispersion compensation system using the dispersion detection apparatus shown in FIG.

  Referring to FIG. 11, the automatic dispersion compensation system of the present embodiment includes the above-described received waveform monitor unit 1, voltage direction eye opening calculation module 4, phase direction eye opening calculation module 5, and dispersion amount detection as receiving units. A unit 6, a photoelectric conversion circuit 9, and a clock data recovery circuit 11 are included. Further, as a transmission unit, a multiplexer (MUX) 21, an electric equalizer circuit 22, an optical modulator driver circuit 23, an optical modulator 24, a laser diode 25, an adaptive compensation amount control module 12, and lookup data. And a table module 13.

  The photoelectric conversion circuit 9 converts the received signal transmitted through the optical fiber from an optical signal to an electrical signal.

  The clock data recovery circuit 11 performs reproduction and extraction of the clock signal and recovery of the data signal based on the received signal.

  The received waveform monitor unit 1 monitors the received waveform received from the optical fiber, and the dispersion amount detection unit 6 detects the polarization dispersion amount of the received waveform monitored by the received waveform monitor unit 1. In this embodiment, the case where the polarization dispersion amount is estimated is described as an example. However, if this dispersion detection device is used, it is also possible to estimate the chromatic dispersion amount. The configuration and operation of the reception waveform monitor processing unit 1 and the dispersion amount detection unit 6 are the same as those shown in FIG. 10, and thus detailed description thereof will be omitted.

  The multiplexer 21 performs parallel / serial conversion on the transmission signal transmitted to the transmission destination.

  The electric equalizer circuit 22 corrects the frequency characteristic of the transmission signal based on the detection result of the polarization dispersion amount detected by the dispersion amount detection unit 6.

  The optical modulator driver circuit 23 controls the optical modulator 24 based on the output signal of the electric equalizer circuit 22.

  The optical modulator 24 modulates the optical signal emitted from the laser diode 25 under the control of the optical modulator driver circuit 23.

  As described above, in this embodiment, the detection result of the polarization dispersion amount at the reception unit is fed back to the transmission unit, and a transmission signal subjected to dispersion compensation processing in advance in anticipation of the waveform deterioration amount is transmitted to the reception destination. This optimizes the compensation amount.

(Third embodiment)
FIG. 12 is a diagram showing still another configuration example of the automatic dispersion compensation system using the dispersion detection apparatus shown in FIG.

  Referring to FIG. 12, the automatic dispersion compensation system according to the present embodiment includes, as receiving units, the above-described received waveform monitor unit 1, voltage direction eye opening calculation module 4, phase direction eye opening calculation module 5, and dispersion amount detection. A unit 6, a photoelectric conversion circuit 9, and a clock data recovery circuit 11 are included. In addition, the transmission unit includes a multiplexer (MUX) 21, an electric equalizer circuit 22, an optical modulator driver circuit 23, an optical modulator 24, and a laser diode 25. Further, as external modules, an adaptive compensation amount control module 12 and a lookup data table module 13 are provided.

  The photoelectric conversion circuit 9 converts the received signal transmitted through the optical fiber from an optical signal to an electrical signal.

  The clock data recovery circuit 11 performs reproduction and extraction of the clock signal and recovery of the data signal based on the received signal.

  The received waveform monitor unit 1 monitors the received waveform received from the optical fiber, and the dispersion amount detection unit 6 detects the polarization dispersion amount of the received waveform monitored by the received waveform monitor unit 1. In this embodiment, the case where the polarization dispersion amount is estimated is described as an example. However, if this dispersion detection device is used, it is also possible to estimate the chromatic dispersion amount. The configuration and operation of the reception waveform monitor processing unit 1 and the dispersion amount detection unit 6 are the same as those shown in FIG. 10, and thus detailed description thereof will be omitted.

  The multiplexer 21 performs parallel / serial conversion on the transmission signal transmitted to the transmission destination.

  The electric equalizer circuit 22 corrects the frequency characteristic of the transmission signal based on the detection result of the polarization dispersion amount detected by the dispersion amount detection unit 6.

  The optical modulator driver circuit 23 controls the optical modulator 24 based on the output signal of the electric equalizer circuit 22.

  The optical modulator 24 modulates the optical signal emitted from the laser diode 25 under the control of the optical modulator driver circuit 23.

  In the present embodiment, the compensation coefficient input to the electric equalizer circuit 22 installed on the transmission side and the clock data recovery circuit 11 installed on the reception side based on the detection result of the polarization dispersion amount at the reception unit. The identification threshold value to be input is determined using the calculation in the adaptive compensation amount control module 12 installed as an external module and the lookup data table module 13. The determined compensation coefficient is fed back to the electric equalizer circuit 22 of the transmission unit, and the compensation amount is optimized by transmitting a transmission signal subjected to dispersion compensation processing in advance in anticipation of the waveform degradation amount to the reception destination. Further, the determined identification threshold is fed back to the clock data recovery circuit 11 of the reception unit, and the waveform still having a deteriorated state remains even though the compensation amount is adjusted by the equalizer processing on the transmission side described above. Therefore, it is possible to identify at an optimum identification point and to reduce transmission errors at the receiving unit.

  As described above, the present invention has been described with reference to the embodiments and examples, but the present invention is not limited to the above embodiments and examples. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

  This application claims the priority on the basis of Japanese application Japanese Patent Application No. 2008-138163 for which it applied on May 27, 2008, and takes in those the indications of all here.

Claims (9)

A dispersion detection device for detecting dispersion in an optical fiber,
Waveform monitoring means for monitoring the eye opening shape of the eye pattern waveform representing the state of the optical signal based on the result of sampling the optical signal passing through the optical fiber;
Based on information representing the eye opening shape monitored by the waveform monitoring means, eye opening calculating means for detecting the maximum opening length in the voltage direction and the maximum opening length in the phase direction of the eye pattern waveform;
A dispersion amount for detecting the polarization dispersion amount and the chromatic dispersion amount of the optical signal based on the information indicating the maximum aperture length in the voltage direction and the information indicating the maximum aperture length in the phase direction detected by the eye aperture calculation means Detection means;
A dispersion detection apparatus comprising: The dispersion amount detecting means includes
Information indicating the polarization dispersion amount by calculating the division ratio when the eye opening maximum length in the phase direction is divided into two with the specific phase position where the eye opening maximum length in the voltage direction is obtained as a base point. The dispersion detection apparatus according to claim 1, further comprising polarization dispersion amount detection means for detecting a power branching ratio of a slow wave component and a fast wave component of a certain optical waveform. The polarization dispersion amount detecting means includes
By calculating information representing the ratio of the length of the eye opening maximum length in the voltage direction and the maximum length of the eye opening in the phase direction, and multiplying the calculated ratio of the length with the detected power branching ratio, polarization is achieved. The dispersion detection apparatus according to claim 2, wherein a group delay amount that is information representing the dispersion amount is detected. The waveform monitoring means includes
From the received waveform after passing through the optical fiber, at a timing based on an identification clock input from the outside, a discriminator that samples data above an identification threshold value in the voltage direction set from the outside,
Means for setting an identification threshold of the classifier;
Means for changing the phase of an identification clock input to the discriminator;
With
The eye opening shape of the eye pattern waveform is obtained by repeatedly sampling a plurality of data from the received waveform while changing the discrimination threshold of the discriminator in the voltage direction and further changing the phase of the discrimination clock input to the discriminator. The dispersion detection apparatus according to claim 1, wherein extraction is performed. The dispersion amount detecting means includes
Based on the specific voltage position where the maximum eye opening length in the phase direction is obtained as a base point, the division ratio when the eye opening maximum length in the voltage direction is divided vertically is calculated, and at the same time, the eye opening maximum length and the phase direction 2. A chromatic dispersion amount detecting unit that detects a chromatic dispersion amount by calculating a ratio of the length to the maximum length of the eye opening and multiplying the calculated ratio of the length with the calculated division ratio. The dispersion detection apparatus described. The waveform monitoring means includes
From the received waveform after passing through the optical fiber, at a timing based on an identification clock input from the outside, a discriminator that samples data above an identification threshold value in the voltage direction set from the outside,
Means for setting an identification threshold of the classifier;
Means for changing the phase of an identification clock input to the discriminator;
With
The eye opening shape of the eye pattern waveform is obtained by repeatedly sampling a plurality of data from the received waveform while changing the discrimination threshold of the discriminator in the voltage direction and further changing the phase of the discrimination clock input to the discriminator. The dispersion detection apparatus according to claim 5, wherein extraction is performed. The dispersion detection apparatus according to claim 1;
Photoelectric conversion means for converting a received signal passing through the optical fiber from an optical signal into an electrical signal;
In the received signal converted into an electrical signal by the photoelectric conversion means, electrical dispersion compensation means for compensating for waveform degradation due to polarization mode dispersion and wavelength dispersion;
Clock data recovery means for performing recovery and extraction of the clock signal and recovery of the data signal from the signal that has passed through the electrical dispersion compensation means;
Based on the detection result of the polarization dispersion amount and the chromatic dispersion amount detected by the dispersion detection device, the compensation coefficient input to the electrical dispersion compensation means and the identification threshold value input to the clock data recovery circuit are controlled. Adaptive compensation amount control means;
With
After detecting the polarization dispersion amount and the chromatic dispersion amount based on the received signal before passing through the electrical dispersion compensation unit in the dispersion detection device, the adaptive compensation amount control unit includes the electrical dispersion compensation unit. An automatic dispersion compensation system for automatically controlling an optimum compensation control coefficient used in the above and an identification threshold used in the clock data recovery means. The dispersion detection apparatus according to claim 1;
Photoelectric conversion means for converting a received signal passing through the optical fiber from an optical signal into an electrical signal;
Clock data recovery means for recovering and extracting a clock signal and recovering a data signal from the signal that has passed through the photoelectric conversion means;
Receiving means including:
A laser diode;
Based on the detection result of the polarization dispersion amount and the chromatic dispersion amount fed back from the dispersion detection device, transmission side equalizer means for performing dispersion compensation in advance on the optical signal to be a transmission signal;
Based on the detection result of the polarization dispersion amount and the chromatic dispersion amount detected by the dispersion detection device, adaptive compensation amount control means for controlling a compensation coefficient input to the transmission side equalizer means;
A multiplexer that performs signal processing on data input to the transmission side equalizer means;
Driver means for amplifying an output signal from the transmission side equalizer means;
An optical modulation means for performing modulation control of an optical signal emitted from the laser diode based on a signal of the driver means;
A transmission means including:
An automatic dispersion compensation system comprising: The dispersion detection apparatus according to claim 1;
Photoelectric conversion means for converting a received signal passing through the optical fiber from an optical signal into an electrical signal;
Clock data recovery means for recovering and extracting a clock signal and recovering a data signal from the signal that has passed through the photoelectric conversion means;
Receiving means including:
A laser diode;
Based on the polarization dispersion amount fed back from the dispersion detection device and the detection result of the chromatic dispersion amount, transmission-side equalizer means that performs dispersion compensation in advance on the optical signal that becomes the transmission signal;
A multiplexer that performs signal processing on data input to the transmission side equalizer means;
Driver means for amplifying an output signal from the transmission side equalizer means;
An optical modulation means for performing modulation control of an optical signal emitted from the laser diode based on a signal of the driver means;
A transmission means including:
Based on the detection result of the polarization dispersion amount and the chromatic dispersion amount detected by the dispersion detection device, the compensation coefficient input to the transmission side equalizer means and the identification threshold value input to the clock data recovery circuit are controlled. Adaptive compensation amount control means;
An automatic dispersion compensation system comprising:

Images