JP2010252204A - Optical reception device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical reception device capable of suitably adjusting a wavelength dispersion compensation value of polarization multiplex signal light. <P>SOLUTION: The optical reception device includes a variable wavelength dispersion compensator that inputs the polarization multiplex signal light generated by polarization-multiplexing two bit-synchronized signal light beams from a transmission line, and compensates for wavelength dispersion included in the polarization multiplex signal with the wavelength dispersion compensation value based upon a control signal, and a polarization separator that outputs separated signal light generated by polarization-separating the output of the variable wavelength dispersion compensator, generates the control signal depending upon the intensity of a clock signal included in the separated signal light, and adjusts the polarization separation based upon the control signal. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a variable chromatic dispersion compensator, an optical receiver and an optical transmission system in polarization multiplexing communication in which two signal lights that are bit-synchronized are polarization-multiplexed, and two signal lights that are bit-synchronized are polarized waves. The present invention relates to a chromatic dispersion compensation method, an optical reception method and an optical transmission method for multiplexed polarization multiplexing communication, and a chromatic dispersion compensation program and an optical reception program.

  In order to increase the total transmission capacity in a wavelength division multiplexing optical transmission system composed of a large number of channels, it is necessary to increase the transmission capacity per channel (one wavelength). As a result of vigorous progress in various technological developments aimed at increasing the channel speed, in addition to the mainstream 2.5 Gb / s and 10 Gb / s, 40 Gb / s has recently been put into practical use. In the near future, the practical use of 100 Gb / s is also expected.

  A problem in transmitting a high-speed signal such as 40 Gb / s is an extreme reduction in chromatic dispersion tolerance. In general, when the same transmission method is used, the improvement of the signal speed decreases the chromatic dispersion tolerance in inverse proportion to the square. For example, when the signal speed is quadrupled from 10 Gb / s to 40 Gb / s, the chromatic dispersion tolerance is 1/16.

  In long-distance transmission with a channel speed of 40 Gb / s or higher, it is impossible to accommodate the chromatic dispersion accumulated in the transmission line within this narrow chromatic dispersion tolerance only by managing and optimizing the dispersion compensating fiber in the transmission line. Is possible.

  Various attempts have been made to solve this problem. Among them, a variable chromatic dispersion compensator is arranged at the input of each receiver, and after compensating the chromatic dispersion remaining in the signal light with the chromatic dispersion compensation value by this variable chromatic dispersion compensator, the signal light is sent to the receiver. Is the most common solution (see, for example, Patent Document 1).

  FIG. 1 is a schematic configuration diagram of a related optical transmission system including a tunable dispersion compensator on the receiving side. The optical transmission system of FIG. 1 optimizes the chromatic dispersion compensation value using the code error rate detected by the receiver 21 as an index while passing the signal light from the transmitter 11 through the variable chromatic dispersion compensator 24. In the optical transmission system of FIG. 1, the chromatic dispersion compensation value is gradually changed within the variable range of the tunable dispersion compensator 24 to search for the chromatic dispersion compensation value that gives the best code error rate. .

  FIG. 8 is a flowchart for explaining optimization of the chromatic dispersion compensation value performed by the optical transmission system of FIG. After the optimization of the chromatic dispersion compensation value is started in step S11, the variable chromatic dispersion compensator 24 maximizes or minimizes the chromatic dispersion compensation value in step S12. The variable chromatic dispersion compensator 24 confirms whether or not the receiver 21 can measure the code error rate in step S13. If the measurement is impossible, the tunable dispersion compensator 24 changes the chromatic dispersion compensation value step by step in step S15. If measurement is possible, the variable chromatic dispersion compensator 24 compares the code error rate measured with the previous chromatic dispersion compensation value with the code error rate measured this time in step S14. If improved, the tunable dispersion compensator 24 changes the chromatic dispersion compensation value step by step in step S15. If it has deteriorated, the variable chromatic dispersion compensator 24 sweeps the vicinity of the current chromatic dispersion compensation value in step S16 and searches for and sets the chromatic dispersion compensation value that gives the best code error rate. After setting the optimum chromatic dispersion compensation value, the optimization of the chromatic dispersion compensation value is finished.

  On the other hand, there is a polarization multiplexing / demultiplexing transmission system as a technique that is attracting attention as a means for increasing the transmission capacity per channel (one wavelength). In a normal optical transmission system, the signal light of each channel uses only one of the two polarization axes of the optical fiber, whereas the polarization multiplexing system uses both. Specifically, two independent signal lights using the same signal wavelength are combined by a polarization multiplexer, propagated through the transmission line in that state, and then received again by the polarization separator at the receiver. And received by two independent receivers.

  FIG. 2 is a schematic configuration diagram of a related optical transmission system using the polarization multiplexing method. Two independent signal lights output from the two transmitters (11, 12) are multiplexed by the polarization multiplexer 13 and sent to the transmission line 401. At the receiving end, the signal light is again separated by the polarization separator 23, the signal light sent from the transmitter 11 is received by the receiver 21, and the signal light sent from the transmitter 12 is received by the receiver 22. . Since the chromatic dispersion has no polarization dependence, the chromatic dispersion accumulated in the transmission line 401 is collectively compensated by the variable chromatic dispersion compensator 24 in front of the polarization separator 23.

  FIG. 3 is a diagram for explaining an optical receiver in a related optical transmission system. The optical receiver of FIG. 3 includes a polarization separator 23, a variable dispersion compensator 24 disposed in front of the polarization separator 23, and a receiver (21, 22) disposed in the subsequent stage of the polarization separator 23. Prepare. The polarization separator 23 includes a polarization controller 31, a polarization beam splitter 32, an optical splitter 33, and a control signal extraction circuit 34.

  The polarization beam splitter 32 separates and outputs the signal light from the polarization controller 31 for each multiplexed polarization component. The optical splitter 33 branches one output of the polarization beam splitter 32. The control signal extraction circuit 34 outputs a control signal based on the signal light branched by the optical splitter 33. For example, the control signal extraction circuit 34 can measure the intensity of the clock component included in the signal light and output it as a control signal.

  Based on the input control signal, the polarization controller 31 changes the polarization state of the signal light so that the two polarization components of the signal light coincide with the two intrinsic polarization axes of the polarization beam splitter 32. Control. For example, the polarization controller 31 adjusts the polarization state of the signal light so as to maximize (or in some cases minimize) the intensity of the clock component included in one output of the polarization beam splitter 32.

JP 2002-208992 A

  However, when the polarization multiplexed signal light has chromatic dispersion, the polarization separator cannot completely separate the polarization. For this reason, the light input to each receiver becomes light in which the signal light from the two transmitters is mixed, and it is difficult to determine the chromatic dispersion compensation value using the code error rate as an index.

  For example, even if the chromatic dispersion compensation value is gradually changed with the variable chromatic dispersion compensator and the chromatic dispersion compensation value is found to be zero, the polarization multiplexing / demultiplexing process is symmetric, The receiver may receive signal light from different transmitters. As illustrated in FIG. 2, there is a possibility that the receiver 22 receives the signal light from the transmitter 11 and the receiver 21 receives the signal light from the transmitter 12. In this case, the receiver cannot detect a normal code error rate and cannot determine the chromatic dispersion compensation value. Thus, there is a problem that it is difficult to optimally adjust the chromatic dispersion compensation value for the polarization multiplexed signal light only by using the code error rate of the receiver as an index.

  The objective of this invention is providing the technique for solving the said subject. That is, an object of the present invention is to provide an optical receiver capable of optimally adjusting the chromatic dispersion compensation value of polarization multiplexed signal light.

  Specifically, in the optical receiver according to the present invention, polarization multiplexed signal light in which two signal lights that are bit-synchronized are polarization multiplexed is input from a transmission line, and a chromatic dispersion compensation value based on a control signal is obtained. A variable chromatic dispersion compensator that compensates for chromatic dispersion included in the polarization multiplexed signal light, and a separated signal light obtained by polarization-separating the output of the variable chromatic dispersion compensator, and included in the separated signal light A polarization separator that generates the control signal depending on the intensity of the clock component and adjusts polarization separation based on the control signal.

  The present invention can provide an optical receiver capable of optimally adjusting the chromatic dispersion compensation value of polarization multiplexed signal light.

It is a schematic block diagram of a related optical transmission system. It is a schematic block diagram of a related optical transmission system. It is a figure explaining the optical receiver in a related optical transmission system. It is a schematic block diagram of the optical receiver which concerns on this invention. It is the figure which showed the relationship between a chromatic dispersion compensation value and the intensity | strength of a clock component. It is a schematic block diagram of the optical receiver which concerns on this invention. It is the figure which showed the relationship between a chromatic dispersion compensation value and the intensity | strength of a clock component. It is a flowchart explaining optimization of the chromatic dispersion compensation value which a related optical receiver performs. It is a flowchart explaining the optimization of the chromatic dispersion compensation value which the optical receiver which concerns on this invention performs. It is a flowchart explaining the optimization of the chromatic dispersion compensation value which the optical receiver which concerns on this invention performs.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiment described below is an example of the configuration of the present invention, and the present invention is not limited to the following embodiment. In the present specification and drawings, the same reference numerals denote the same components.

(First embodiment)
FIG. 4 is a schematic configuration diagram of the optical transmission system of the present embodiment. This optical transmission system includes an optical transmission device 301 and an optical reception device 302 that output multiplexed signal light of polarization multiplexing communication in which two signal lights that are bit-synchronized are polarization multiplexed to the transmission line 401.

  In the optical receiver 302, polarization multiplexed signal light in which two bit-synchronized signal lights are polarization multiplexed is input from the transmission line 401, and is included in the polarization multiplexed signal light with a chromatic dispersion compensation value based on the control signal. The chromatic dispersion compensator 24 for compensating the chromatic dispersion, and the separated signal light obtained by polarization-separating the output (compensation signal light) of the variable chromatic dispersion compensator 24, and the clock component included in the separated signal light A polarization separator 23 that generates a control signal depending on intensity and adjusts polarization separation based on the control signal.

  A feature of the optical receiver 302 is that the polarization separator 23 generates a control signal including a value depending on chromatic dispersion, and the variable chromatic dispersion compensator 24 uses this as an index. The control signal generated by the polarization separator 23 depends on the intensity of the clock component of the separated signal light obtained by polarization-separating the polarization multiplexed signal light, and the intensity changes due to the chromatic dispersion included in the polarization multiplexed signal light. To do. For this reason, the variable chromatic dispersion compensator 24 compensates the chromatic dispersion so as to increase the intensity of the clock component of the separated signal light.

  The polarization separator 23 also performs polarization separation based on the control signal. In the polarization separation, the polarization angle for separation is adjusted so that interference between two orthogonal signal lights is minimized. Here, since the polarization multiplexed signal light input to the optical receiver 302 is two signal lights that are bit-synchronized, the polarization separator 23 has a predetermined value for the intensity of the clock component of the separated signal light. The polarization separation is adjusted as follows. For example, when the phase of the two signal lights is shifted by 150 °, the polarization separator 23 adjusts the polarization separation so that the intensity of the clock component of the separated signal light becomes a predetermined value lower than the maximum value. When the two signal lights are 180 ° out of phase, that is, in the case of bit interleaving, the polarization separator 23 adjusts the polarization separation so that the intensity of the clock component of the separated signal light is maximized. When the phase and amplitude of the two signal lights match, the polarization separator 23 adjusts the polarization separation so that the intensity of the clock component of the separated signal light is minimized.

  Hereinafter, the case where the polarization multiplexed signal light is bit interleaved will be described in more detail. The optical receiver 302 receives the multiplexed signal light of the polarization multiplexing communication that has been bit-interleaved multiplexed from the transmission path 401, and changes the chromatic dispersion accumulated in the transmission path 401 included in the multiplexed signal light with a variable chromatic dispersion compensation value. From the variable chromatic dispersion compensator 24 that compensates and outputs as a compensation signal light, the chromatic dispersion compensation amount controller 41 that instructs the chromatic dispersion compensation value to the variable chromatic dispersion compensator 24, A polarization separator 23 that separates the compensation signal light and outputs it as separated signal light, and a plurality of receivers (21, 22) that receive the separated signal light from the polarization separator 23, respectively.

  The chromatic dispersion compensation amount controller 41 uses the intensity of the clock component included in the separated signal light as an index for determining the chromatic dispersion compensation value. The polarization separator 23 uses the intensity of the clock component included in the separated signal light as an index for adjusting the polarization separation of the compensation signal light.

  The optical receiving apparatus 302 performs chromatic dispersion compensation and optimization of polarization separation, using the intensity of the clock component included in the polarization separated signal light as an index. The signal light format of the optical transmission system in which the optical receiver 302 is used is that each polarization component having the same signal speed is converted to RZ (Return to Zero), and the relative positions of the RZ pulses of both components are shifted by a half cycle and polarized. Wave-multiplexed bit interleave multiplexing.

  Because of bit interleave multiplexing, the intensity of the clock component is maximized when both polarization components are completely polarization separated. In the state where chromatic dispersion remains, the intensity of the clock component decreases due to the pulse spread of the signal light. The intensity of the clock component also increases / decreases depending on the magnitude of chromatic dispersion. For example, the intensity of the clock component is maximized when the chromatic dispersion is zero. Therefore, by using the intensity of the clock component as an index, not only the polarization separation but also the chromatic dispersion compensation value can be optimized.

  Since the optical receiver 302 does not use the code error rate at the receiver as an index of the chromatic dispersion compensation value, it can optimally adjust the chromatic dispersion compensation value of the polarization multiplexed signal light.

  Subsequently, a means for optimizing the chromatic dispersion compensation value will be described. The means in the first embodiment is always means for performing polarization control.

  The polarization separator 23 includes a polarization controller 31, a polarization beam splitter 32, an optical splitter 33, and a control signal extraction circuit 34. The polarization beam splitter 32 polarization-separates the compensation signal light and outputs it as a separated signal. The optical branching device 33 branches the signal light from one of the separated signals output from the polarization beam splitter 32. The control signal extraction circuit 34 measures the intensity of the clock component included in the signal light branched by the optical splitter 33 and outputs a control signal. Based on the control signal from the control signal extraction circuit 34, the polarization controller 31 always adjusts the polarization state of the compensation signal light from the variable wavelength dispersion compensator 24 and outputs it to the polarization beam splitter 32. Further, the polarization separator 23 adjusts the polarization state of the compensation signal light so that the intensity of the clock component included in the separation signal light is maximized when the compensation signal light is polarization separated.

  Based on the control signal input from the control signal extraction circuit 34, the chromatic dispersion compensation amount controller 41 determines the chromatic dispersion compensation value so that the intensity of the clock component included in the separated signal light is equal to or greater than a threshold value. More specifically, the chromatic dispersion compensation amount controller 41 gradually changes the chromatic dispersion compensation value of the variable chromatic dispersion compensator 24 and monitors the intensity of the clock component included in the separated signal light, thereby chromatic dispersion compensation. Investigate the relationship between the value and the intensity of the clock component.

  FIG. 5 shows an embodiment in which the chromatic dispersion compensation amount controller 41 monitors the intensity of the clock component contained in the separated signal light by gradually changing the chromatic dispersion compensation value of the variable chromatic dispersion compensator 24. When the maximum value of the intensity of the clock component appears within the variable range of the chromatic dispersion compensation value as shown in FIG. 5, this is the optimum chromatic dispersion compensation value.

  After the investigation, the chromatic dispersion compensation amount controller 41 notifies the variable chromatic dispersion compensator 24 of a chromatic dispersion compensation value that maximizes the intensity of the clock component. When the time for determining the chromatic dispersion compensation value is shortened, a threshold value may be provided, and the chromatic dispersion compensation value when the clock component intensity exceeds the threshold value may be notified to the variable chromatic dispersion compensator 24. The variable chromatic dispersion compensator 24 compensates the chromatic dispersion of the multiplexed signal light with the chromatic dispersion compensation value determined by the chromatic dispersion compensation amount controller 41. Thereby, the optical receiver 302 can optimally adjust the chromatic dispersion compensation value of the polarization multiplexed signal light.

  The optical receiving apparatus 302 may finely adjust the chromatic dispersion compensation value using the code error rate of the receiver as an index after completing the compensation of chromatic dispersion using the intensity of the clock component as an index. Specifically, the variable chromatic dispersion compensator 24 first compensates the chromatic dispersion included in the multiplexed signal with the intensity of the clock component included in the separated signal light, and then the code error detection function of the receiver (21, 22). To further compensate the chromatic dispersion included in the multiplexed signal so as to minimize the code error rate.

  Next, an optical reception method of the optical reception device 302 will be described. The optical receiver 302 includes a chromatic dispersion compensation value control procedure in which the chromatic dispersion compensation amount controller 41 determines a chromatic dispersion compensation value using the intensity of the clock component included in the separated signal light as an index, and the polarization separator 23 receives the separated signal. A polarization separation adjustment procedure for adjusting the polarization separation of the compensation signal light using the intensity of the clock component included in the light as an index is performed. In other words, the optical receiving method of the optical receiving apparatus 302 is that the polarization multiplexed signal light in which two bit-synchronized signal lights are polarization multiplexed is converted into the polarization multiplexed signal light with a chromatic dispersion compensation value based on the control signal. A variable chromatic dispersion compensation procedure for compensating for the included chromatic dispersion, and a separated signal light obtained by polarization-separating the polarization multiplexed signal light for which the chromatic dispersion compensation has been performed, and a clock component included in the separated signal light And a polarization separation procedure for generating the control signal depending on the intensity of the signal and adjusting the polarization separation based on the control signal. The polarization separation adjustment procedure performed by the polarization separator 23 is the same as that described with reference to FIG.

  FIG. 9 is a flowchart for explaining a chromatic dispersion compensation value control procedure and a chromatic dispersion compensation value adjustment procedure performed by the chromatic dispersion compensation amount controller 41. The chromatic dispersion compensation value control procedure includes steps S21 to S24. The chromatic dispersion compensation value adjustment procedure includes steps S25 to S29.

  After starting the chromatic dispersion compensation value control procedure in step S21, the chromatic dispersion compensation amount controller 41 maximizes or minimizes the chromatic dispersion compensation value of the variable chromatic dispersion compensator 24 in step S22. The chromatic dispersion compensation amount controller 41 determines whether or not the intensity of the clock component included in the separated signal light is greater than the threshold based on the control signal output from the control signal extraction circuit 34 in step S23. If it is smaller, the chromatic dispersion compensation amount controller 41 causes the tunable chromatic dispersion compensator 24 to change the chromatic dispersion compensation value step by step in step S24. If it is larger, the chromatic dispersion compensation amount controller 41 confirms whether or not the receiver (21, 22) can measure the code error rate in step S25. If measurement is impossible, the chromatic dispersion compensation amount controller 41 resets the polarization controller 31 in step S26 and confirms whether the code error rate can be measured again. If measurement is possible, the chromatic dispersion compensation amount controller 41 compares the code error rate measured with the previous chromatic dispersion compensation value with the code error rate measured this time in step S27. If it is improved, the chromatic dispersion compensation amount controller 41 changes the chromatic dispersion compensation value of the tunable chromatic dispersion compensator 24 step by step in step S24. If so, the chromatic dispersion compensation amount controller 41 searches for a chromatic dispersion compensation value that gives the best code error rate by sweeping the vicinity of the chromatic dispersion compensation value of the current variable chromatic dispersion compensator 24 in step S28. Set. The chromatic dispersion compensation amount controller 41 sets the optimum chromatic dispersion compensation value in the variable chromatic dispersion compensator 24 in step S29, and then ends the chromatic dispersion compensation value control procedure.

  The optical receiver 302 can simultaneously perform the polarization separation adjustment procedure and the chromatic dispersion compensation value control procedure, but after the polarization separator 23 performs the polarization separation adjustment procedure, the chromatic dispersion compensation amount controller 41. Can also perform a chromatic dispersion compensation value control procedure. The time for determining the chromatic dispersion compensation value can be shortened.

(Second Embodiment)
FIG. 6 is a schematic configuration diagram of another optical transmission system according to this embodiment. This optical transmission system is obtained by replacing the optical receiver 302 in the optical transmission system of FIG. Similar to the optical receiver 302, the optical receiver 303 also includes a tunable dispersion compensator 24 and a polarization separator 23. The optical receiver 303 compensates the chromatic dispersion so that the variable chromatic dispersion compensator 24 increases the intensity of the clock component of the separated signal light, and the polarization separator 23 sets the intensity of the clock component of the separated signal light to a predetermined value. The polarization adjustment is adjusted so that Hereinafter, the case where the polarization multiplexed signal light is bit interleaved will be described in more detail.

  The means for optimizing the chromatic dispersion compensation value of the optical receiver 303 is means for using the polarization controller as a scrambler during chromatic dispersion optimization. The difference between the optical receiver 303 and the optical receiver 302 of FIG. 4 is that the optical receiver 303 includes a polarization separator 23 a as an alternative to the polarization separator 23. The polarization separator 23 a includes a polarization controller 31, a polarization beam splitter 32, an optical splitter 33, a control signal extraction circuit 34, a random signal transmitter 35, and a switch 36.

  The difference between the polarization separator 23 a and the polarization separator 23 in FIG. 4 is that the polarization separator 23 a includes a random signal transmitter 35 and a switch 36. Since the polarization separator 23a includes the random signal transmitter 35 and the switch 36, the optical receiver 303 operates as follows. Only portions different from the polarization separator 23a and the polarization separator 23 will be described.

  The random signal transmitter 35 outputs a random signal. The switch 36 selects a random signal from the random signal transmitter 35 or a control signal from the control signal extraction circuit 34 and inputs the selected signal to the polarization controller 31. When a random signal is input, the polarization controller 31 changes the polarization state of the compensation signal light from the variable wavelength dispersion compensator 24 and outputs it to the polarization beam splitter 32, and when the control signal is input. Adjusts the polarization state of the compensation signal light from the tunable dispersion compensator 24 based on the control signal and outputs it to the polarization beam splitter 32.

  The polarization controller 31 operates as a polarization scrambler that randomly changes the output polarization state at a predetermined speed when a random signal is input. When the polarization controller 31 operates as a scrambler, the intensity of the clock component included in the separated signal light varies greatly. The maximum value of the intensity of the clock component appears at the moment when the two polarization components and the intrinsic polarization of the polarization beam splitter 32 coincide. On the other hand, when the control signal is input, the polarization controller 31 adjusts the polarization state of the compensation signal light so that the intensity of the clock component included in the separated signal light is maximized.

  While monitoring the maximum value, the chromatic dispersion compensation amount controller 41 gradually changes the chromatic dispersion compensation value and examines the relationship between the two. Specifically, the chromatic dispersion compensation amount controller 41 receives the control signal from the control signal extraction circuit 34, and when the random signal is input to the polarization controller 31, the variable chromatic dispersion compensator 24. The chromatic dispersion compensation value is instructed to be changed every predetermined period, the maximum value within the period in which the intensity of the clock component included in the separated signal light is maximum within the predetermined period, and the period for each predetermined period The maximum chromatic dispersion values are compared, and the chromatic dispersion compensation value for a predetermined period in which the maximum maximum value within the period is obtained is detected.

  FIG. 7 shows the relationship between the chromatic dispersion compensation value and the intensity of the clock component when the chromatic dispersion compensation amount controller 41 instructs the variable chromatic dispersion compensator 24 to change the chromatic dispersion compensation value every predetermined period. It is the Example which showed. FIG. 7 shows that the maximum value in the period in which the chromatic dispersion compensation value D [k + 1] is given is larger than the other periods, and the chromatic dispersion compensation value D [k + 1] is the optimum chromatic dispersion compensation value. .

  Regardless of the polarization state of the multiplexed signal light, the chromatic dispersion compensation amount controller 41 can find the optimum value of the chromatic dispersion compensation value. Thereafter, the variable chromatic dispersion compensator 24 compensates the chromatic dispersion of the multiplexed signal light with the optimum chromatic dispersion compensation value detected by the chromatic dispersion compensation amount controller 41. In addition, after the tunable dispersion compensator 24 compensates the chromatic dispersion of the multiplexed signal, the polarization separator 23a performs polarization separation of the compensation signal light. Specifically, the switch 36 switches from the random signal from the random signal transmitter 35 to the control signal from the control signal extraction circuit 34. As a result, the polarization controller 31 stops polarization scrambling and starts polarization control. As a result, the optical receiver 303 can reliably optimize both the chromatic dispersion compensation of the polarization multiplexed signal light and the polarization separation of the polarization multiplexed signal light.

  Similarly to the optical receiver 302 in FIG. 4, the optical receiver 303 also completes the chromatic dispersion compensation using the intensity of the clock component as an index, and then fine-tunes the chromatic dispersion compensation value with the code error rate of the receiver. Also good.

  Next, an optical reception method of the optical reception device 303 will be described. The optical receiving device 303 performs the polarization separation adjustment procedure and the chromatic dispersion compensation value control procedure as in the optical receiving device 302 of FIG.

  FIG. 10 is a flowchart for explaining the chromatic dispersion compensation value control procedure and the chromatic dispersion compensation value adjustment procedure performed by the chromatic dispersion compensation amount controller 41. The chromatic dispersion compensation value control procedure includes steps S31 to S34. The chromatic dispersion compensation value adjustment procedure includes steps S35 to S39. The polarization separation adjustment procedure can be performed after step S35 and before step S36. Further, the polarization separation adjustment procedure may be performed after step S39.

  After starting the chromatic dispersion compensation value control procedure in step S31, the chromatic dispersion compensation amount controller 41 switches the switch 36 to the random signal transmitter 35 and inputs a random signal to the polarization controller 31 in step S32. Thus, the polarization controller 31 functions as a polarization scrambler. In step S33, the chromatic dispersion compensation amount controller 41 changes the chromatic dispersion compensation value every predetermined period and instructs the tunable chromatic dispersion compensator 24. Then, the chromatic dispersion compensation amount controller 41 compares the maximum values in the period for each predetermined period as shown in FIG. 7, and finds the chromatic dispersion compensation value in the predetermined period that gives the largest maximum value in the period. Further, the chromatic dispersion compensation amount controller 41 sets the chromatic dispersion compensation value found in step S34 in the variable chromatic dispersion compensator 24. Thereafter, the chromatic dispersion compensation amount controller 41 switches the switch 36 in step S <b> 35 and inputs a control signal to the polarization controller 31. Thus, the polarization controller 31 can adjust the polarization state of the compensation signal light. Subsequently, the chromatic dispersion compensation amount controller 41 confirms whether or not the receiver (21, 22) can measure the code error rate in step S36. If measurement is impossible, the chromatic dispersion compensation amount controller 41 resets the polarization controller 31 in step S37 and confirms whether the code error rate can be measured again. If measurement is possible, the chromatic dispersion compensation amount controller 41 searches for and sets a chromatic dispersion compensation value that gives the best code error rate by sweeping the vicinity of the current chromatic dispersion compensation value in step S38. After setting the optimum chromatic dispersion compensation value, the optimization of the chromatic dispersion compensation value is finished.

  In the optical receiving device 303, since the variable chromatic dispersion compensator first provides an optimum amount of chromatic dispersion compensation, the polarization controller can always perform the polarization control accurately and improve the reliability of the optical transmission system. Can do.

  For example, the optical reception method of the optical reception device 302 and the optical reception device 303 can be realized by creating a computer-readable optical reception program and causing the computer to execute it. When the computer executes the optical reception program, the optical reception device 302 and the optical reception device 303 can optimally adjust the chromatic dispersion compensation value of the polarization multiplexed signal light.

11, 12: Transmitter 13: Polarization multiplexer 21, 22: Receiver 23, 23a: Polarization separator 24: Variable chromatic dispersion compensator 31: Polarization controller 32: Polarization beam splitter 33: Optical splitter 34: Control signal extraction circuit 35: Random signal transmitter 36: Switch 41: Chromatic dispersion compensation amount controller 301: Optical transmission device 302, 303: Optical reception device 401: Transmission paths S11 to S17, S21 to S29, S31 to S39 : Step

Claims (32)

A polarization multiplexed signal light in which two signal lights that are bit-synchronized are polarization multiplexed is input from a transmission line, and the chromatic dispersion included in the polarization multiplexed signal light is compensated with a chromatic dispersion compensation value based on the control signal. A tunable dispersion compensator to perform,
Outputs the separated signal light obtained by polarization-separating the output of the variable wavelength dispersion compensator, generates the control signal that depends on the intensity of the clock component included in the separated signal light, and polarizes based on the control signal A polarization separator for adjusting the separation;
An optical receiver comprising: The polarization separator is
A polarization beam splitter that polarization-separates the output of the variable chromatic dispersion compensator and outputs the separated signal; and
A control signal extraction circuit that measures the intensity of a clock component included in the separated signal light from the polarization beam splitter and outputs the control signal;
The optical receiver according to claim 1, comprising: The polarization separator is
Based on the control signal from the control signal extraction circuit, the polarization state of the output of the tunable dispersion compensator is adjusted by adjusting the polarization state of the variable chromatic dispersion compensator so that the intensity of the clock component included in the separated signal light becomes a predetermined value. The optical receiver according to claim 2, further comprising a polarization controller that outputs the beam to the beam splitter. The chromatic dispersion compensation amount controller is
4. The chromatic dispersion compensation value is determined such that the control signal from the control signal extraction circuit is input and the intensity of a clock component included in the separated signal light is equal to or greater than a threshold value. The optical receiver described in 1.   2. The chromatic dispersion compensation amount controller determines the chromatic dispersion compensation value after the polarization separator completes the adjustment of polarization separation of the output of the variable chromatic dispersion compensator. 5. The optical receiver according to any one of 4 above. The polarization separator is
A random signal transmitter that outputs a random signal;
When the random signal from the random signal transmitter or the control signal from the control signal extraction circuit is input and the random signal is input, the polarization state of the output of the variable chromatic dispersion compensator is randomly selected A polarization controller for varying and outputting to the polarization beam splitter;
The optical receiver according to claim 2, further comprising: The chromatic dispersion compensation amount controller is
The control signal from the control signal extraction circuit is input,
When the random signal is input to the polarization controller, the variable chromatic dispersion compensator is instructed to change the chromatic dispersion compensation value every predetermined period, and the separation is performed within the predetermined period. The maximum value within the period in which the intensity of the clock component included in the signal light is maximum is detected, the maximum value within the period for each predetermined period is compared, and the maximum value within the period is output in the predetermined period. The optical receiver according to claim 6, wherein the chromatic dispersion compensation value is found and determined. After the chromatic dispersion compensation amount controller determines the chromatic dispersion compensation value,
The polarization separator receives the control signal, and based on the control signal, the polarization state of the output of the tunable dispersion compensator so that the intensity of the clock component included in the separated signal light becomes a predetermined value The optical receiver according to claim 7, wherein the optical signal is adjusted and output to the polarization beam splitter to complete polarization separation of the output of the variable wavelength dispersion compensator.   The chromatic dispersion compensation amount controller further adjusts the chromatic dispersion compensation value so as to minimize a code error rate by using a code error detection function of a receiver that receives the separated signal light, respectively. The optical receiver according to claim 1. The bit phases of the two signal lights in bit synchronization are shifted by approximately 180 °,
10. The optical receiver according to claim 1, wherein the polarization separator adjusts polarization separation so that an intensity of a clock component included in the separated signal is maximized. 11.   11. An optical transmission device that outputs a polarization multiplexed signal light in which two signal lights that are bit-synchronized are polarization multiplexed to the transmission line, and the optical reception device according to claim 1. An optical transmission system characterized by Variable chromatic dispersion compensation that compensates for chromatic dispersion included in the polarization multiplexed signal light by using the chromatic dispersion compensation value based on the control signal for the polarization multiplexed signal light in which two signal lights that are bit-synchronized are polarization multiplexed. Procedure and
Outputting a separated signal light obtained by polarization-separating the polarization multiplexed signal light that has been compensated for the chromatic dispersion, generating the control signal depending on the intensity of a clock component included in the separated signal light, and the control signal Polarization separation procedure for adjusting polarization separation based on
Including an optical receiving method. The polarization separation adjustment procedure includes:
13. The optical receiving method according to claim 12, wherein the control signal is output by measuring an intensity of a clock component included in the separated signal light. The polarization separation adjustment procedure includes:
The polarization state of the output of the tunable dispersion compensator is adjusted based on the control signal so that the intensity of the clock component included in the separated signal light becomes a predetermined value. The optical receiving method as described. The chromatic dispersion compensation amount control procedure includes:
15. The optical reception according to claim 12, wherein the chromatic dispersion compensation value is determined based on the control signal so that an intensity of a clock component included in the separated signal light is equal to or higher than a threshold value. Method.   16. The optical reception method according to claim 12, wherein the chromatic dispersion compensation value control procedure is performed after the polarization separation adjustment procedure. The chromatic dispersion compensation amount control procedure includes:
The output of the variable wavelength dispersion compensator is randomly changed using a random signal, and then the output of the variable wavelength dispersion compensator is polarized and separated to obtain the separated signal light. Item 14. The optical receiving method according to Item 12 or 13. The chromatic dispersion compensation amount control procedure includes:
When the polarization state of the output of the variable chromatic dispersion compensator changes randomly, the variable chromatic dispersion compensator is instructed to change the chromatic dispersion compensation value every predetermined period, and the control signal Based on this, the maximum value within the period in which the intensity of the clock component included in the separated signal light is maximum within the predetermined period is detected, the maximum value within the period for each predetermined period is compared, and the largest maximum value within the period The optical reception method according to claim 17, wherein the chromatic dispersion compensation value in the predetermined period of time is determined and determined. After the chromatic dispersion compensation value control procedure,
The polarization separation adjustment procedure adjusts the polarization state of the output of the tunable dispersion compensator so that the intensity of the clock component included in the separated signal light becomes a predetermined value based on the control signal. The optical receiving method according to claim 18. After the chromatic dispersion compensation value control procedure and the polarization separation adjustment procedure,
20. The chromatic dispersion compensation value adjustment procedure for further adjusting the chromatic dispersion compensation value so as to minimize a code error rate when receiving the separated signal light is performed. Optical reception method. The bit phases of the two signal lights in bit synchronization are shifted by approximately 180 °,
21. The optical receiving method according to claim 12, wherein in the polarization separation procedure, the polarization separation is adjusted so that the intensity of the clock component included in the separated signal is maximized.   20. An optical transmission method for outputting a polarization multiplexed signal light in which two bit-synchronized signal lights are polarization multiplexed, and an optical reception method according to any one of claims 11 to 19. An optical transmission method characterized by the above. A variable chromatic dispersion compensator converts a polarization multiplexed signal light obtained by polarization multiplexing two signal lights that are bit-synchronized with a wavelength dispersion compensation value based on a control signal. Perform variable chromatic dispersion compensation procedure to compensate,
A polarization separator that outputs separated signal light obtained by polarization-separating the output of the variable wavelength dispersion compensator, and generates the control signal that depends on the intensity of a clock component included in the separated signal light, and the control An optical reception program for causing a computer to execute an optical reception method for performing a polarization separation procedure for adjusting polarization separation based on a signal. In the polarization separation adjustment procedure,
The control signal extraction circuit of the polarization separator causes a computer to execute an optical reception method of measuring the intensity of a clock component included in the separated signal light and outputting the control signal. The optical receiving program described. In the polarization separation adjustment procedure,
Based on the control signal, the polarization controller of the polarization separator adjusts the polarization state of the output of the tunable dispersion compensator so that the intensity of the clock component included in the separated signal light is maximized. 25. The optical reception program according to claim 23, wherein the optical reception method is executed by a computer. In the chromatic dispersion compensation amount control procedure,
The chromatic dispersion compensation amount controller causes the computer to execute an optical reception method for determining the chromatic dispersion compensation value based on the control signal so that the intensity of the clock component included in the separated signal light is equal to or greater than a threshold value. The optical reception program according to any one of claims 23 to 25.   27. The optical reception program according to claim 23, further causing a computer to execute an optical reception method for performing the chromatic dispersion compensation value control procedure after the polarization separation adjustment procedure. In the chromatic dispersion compensation amount control procedure,
The polarization controller of the polarization separator randomly varies the polarization state of the output of the variable chromatic dispersion compensator using a random signal, and the polarization beam splitter of the polarization separator includes the variable wavelength 25. The optical reception program according to claim 23 or 24, causing a computer to execute an optical reception method in which an output of a dispersion compensator is subjected to polarization separation to obtain the separated signal light. In the chromatic dispersion compensation amount control procedure,
When the polarization state of the output of the tunable dispersion compensator changes randomly, the chromatic dispersion compensation amount controller changes the chromatic dispersion compensation value for each predetermined period with respect to the tunable dispersion compensator. Based on the control signal, the maximum value within the period in which the intensity of the clock component included in the separated signal light is maximum within the predetermined period is detected, and the maximum value within the period for each predetermined period is compared. 29. The optical reception program according to claim 28, further causing a computer to execute an optical reception method for finding and determining the chromatic dispersion compensation value in the predetermined period when the largest maximum value in the period is output. After the chromatic dispersion compensation value control procedure, in the polarization separation adjustment procedure,
Based on the control signal, the polarization controller of the polarization separator adjusts the polarization state of the output of the tunable dispersion compensator so that the intensity of the clock component included in the separated signal light is maximized. 30. The optical reception program according to claim 29, which causes a computer to execute the optical reception method. In the chromatic dispersion compensation value adjustment procedure after the chromatic dispersion compensation value control procedure and the polarization separation adjustment procedure,
The polarization controller of the polarization separator causes a computer to execute an optical reception method for further adjusting the chromatic dispersion compensation value so as to minimize a code error rate when the separated signal light is received. The optical reception program according to any one of claims 23 to 30. The bit phases of the two signal lights in bit synchronization are shifted by approximately 180 °,
32. The method according to claim 23, wherein the polarization separator causes the computer to execute an optical reception method for adjusting polarization separation so as to maximize the intensity of the clock component included in the separated signal. The light receiving program according to the above.

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