JP2010078775A - Polarization mode dispersion compensation apparatus and polarization mode dispersion compensation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To keep the state of polarization (SOP) of output light output from a polarization mode dispersion (PMD) compensator always constant even when the PMD compensation is in operation. <P>SOLUTION: The polarization mode dispersion compensation apparatus is configured by including: a first polarization face controller 210; a variable differential group delay (DGD) controlling part 220; a second polarization face controller 232; a polarization analyzer 236; and a control signal generator 240. The first polarization face controller adjusts the state of polarization of an input received PMD compensation signal 209 and generates a polarization face control signal 211. The variable DGD controlling part gives DGD to one of a rectangular cross peculiar polarization mode of polarization of the polarized face control signal to generate a PMD compensation signal 215. The second polarization face controller adjusts the state of polarization of the PMD compensation signal, and generates and outputs an output signal 233. The output signal is partially tapped by an optical splitter 234 and a monitor signal 235 is picked up, and output outside as an output signal 251. The first polarization face controller, the variable DGD controlling part and the second polarization face controller are respectively controlled by the polarization analyzer and the control signal generator. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention eliminates distortion of a time waveform of an optical pulse caused by polarization mode dispersion of an optical fiber (hereinafter also referred to as an optical fiber transmission line) constituting an optical transmission line in an optical transmission system. The present invention relates to a polarization mode dispersion compensation method and a polarization mode dispersion compensation apparatus.

  Factors that affect transmission quality in optical transmission systems include optical signal-to-noise ratio (OSNR), chromatic dispersion of optical fiber transmission lines, nonlinear optical effects, and polarization mode dispersion (PMD). : Polarization Mode Dispersion). Among these, PMD has characteristics that vary with time, and the higher the transmission speed, the greater the effect of distortion of the optical pulse time waveform caused by PMD on the transmission quality. The need to do increases.

  Birefringence develops in the optical fiber due to the fact that the cross-sectional shape of the core becomes slightly elliptical in the manufacturing process of the optical fiber. This birefringence varies depending on the bending stress applied to the optical fiber transmission line or the influence of temperature change. Further, the change in the birefringence of the optical fiber also occurs due to, for example, a situation in which the optical fiber transmission line is touched during the maintenance work of the system, or due to vibration of the bridge portion of the optical fiber transmission line.

  When an optical pulse composing an optical pulse signal propagates through an optical fiber transmission line, due to the birefringence of the optical fiber transmission line, a propagation time difference, that is, a group delay (DGD) between orthogonal polarization components of the optical pulse. : Differential Group Delay) occurs. This phenomenon is PMD. Note that the PMD here is sometimes referred to as a primary PMD in order to distinguish it from a higher-order PMD described later. However, in the following description, the primary PMD may be simply referred to as PMD unless it is necessary to distinguish between them in order to avoid complications.

The degree of the size of PMD expressed in the optical fiber constituting the optical transmission line is given by the PMD coefficient (unit: ps / (km ^1/2 )). It is known that when a DGD of 30% of the period of one bit of a transmission optical pulse signal occurs due to PMD, a large influence is exerted on a bit error rate in optical communication.

  As an example, the effect of PMD on an optical time division multiplexing (OTDM) signal with a transmission bit rate of 160 Gbit / s is examined.

The time width of one bit of an OTDM signal with a transmission bit rate of 160 Gbit / s is 6.25 ps. Here, it is assumed that the optical fiber transmission line is a single mode fiber (SMF) having a PMD coefficient of 0.2 ps / (km ^1/2 ). When an optical pulse propagates through this SMF for 88 km, the DGD value reaches 1.9 ps. In other words, the DGD value of 1.9 ps reaches 30% (1.9 / 6.25 ≒ 0.30) for the time width of 6.25 ps of 1 bit of this OTDM signal, and the effective transmission distance in this case is limited to 88 km. I understand that.

  Conventionally, two methods, an optical stage compensation method and an electrical stage compensation method, are known as a PMD compensation device that compensates for distortion of a time waveform of an optical pulse caused by polarization mode dispersion. In the electrical stage compensation method, it becomes difficult to perform PMD compensation of an optical path signal whose transmission speed exceeds 40 Gbit / s due to the upper limit of the operating speed of the electronic device. Therefore, an optical stage compensation method is required.

  As an optical stage compensation method, there is known a method of compensating for DGD by monitoring the degree of polarization (DOP: Degree of Polarization) of an optical pulse constituting an optical signal (see, for example, Non-Patent Document 1). The method of monitoring DOP and compensating for DGD can be performed without depending on the transmission bit rate of the optical signal that is the object of waveform distortion compensation, and for any RZ (Return to Zero) format optical signal Is also applicable.

  A PMD compensator for carrying out this method includes a polarization plane controller, a polarization degree compensator (hereinafter also referred to as a DGD compensator), a polarization analyzer, and a controller for controlling them. Composed. The PMD compensation method using this PMD compensator uses an algorithm that adaptively controls the polarization controller and DGD compensator so that the DOP value is maximized, and compensates for the temporal waveform distortion of the optical pulse due to PMD. Has been.

  The configuration and operation of a conventional PMD compensation device will be described with reference to FIG. FIG. 1 is a schematic block diagram of a conventional PMD compensation device. The optical signal path is indicated by a thick line, and the electrical signal path is indicated by a thin line.

  The PMD compensation apparatus 100 includes a polarization plane controller 102, a DGD compensator 104, a control signal generator 106, an optical splitter 108, and a polarization analyzer 110. The polarization plane controller 102 can arbitrarily convert the polarization state of the input optical signal 101 in accordance with the control signal 107a supplied from the control signal generator 106.

  The DGD compensator 104 has a DGD value for one polarization mode component of the intrinsic polarization mode of the optical signal 103 output from the polarization plane controller 102 in response to the control signal 107b supplied from the control signal generator 106. Can be adjusted arbitrarily. That is, the DGD compensator 104 has a function of reducing the DGD value of the optical signal 103 output from the polarization plane controller 102 and performing DGD compensation of the optical signal 103.

  In the PMD compensation apparatus 100, the PMD compensation method including the following first to third steps is performed on the input optical signal 101.

  The first step is for the input optical signal 101, the polarization direction of the intrinsic polarization mode component that has reached the PMD compensation device 100 first of the two intrinsic polarization modes of the input optical signal 101, and the DGD compensator In this step, the polarization plane controller 102 is controlled so that the direction of the slow axis coincides with the direction of the slow axis.

  The optical signal 105 output from the DGD compensator 104 is branched by the optical splitter 108 into a received optical pulse signal 109a and a received optical pulse signal 109b. The received optical pulse signal 109b is input to the polarization analyzer 110. The second step is a step in which the polarization analyzer 110 extracts the Stokes parameters of the received optical pulse signal 109b and calculates the DOP. The received optical pulse signal 109a is input to a reception processing unit (not shown) provided at a subsequent stage of the PMD compensation apparatus 100, and reception processing such as conversion into an electric signal form is performed.

  The third step is to control the polarization plane controller in the control signal generator 106 so that the DOP calculated by the polarization analyzer 110 is maximized based on the DOP signal 111 output from the polarization analyzer 110. 102 and control signals 107a and 107b to be supplied to the DGD compensator 104. It is known that the time waveform distortion of an optical pulse caused by PMD is minimized when DOP is maximal (see, for example, Non-Patent Document 2).

  By performing the feedback control by repeating the first to third steps described above, the PMD compensation apparatus 100 performs compensation for the time waveform distortion of the optical pulse.

  Due to the birefringence of the optical fiber, the direction dependence of the polarization plane of the propagation speed occurs. At this time, the axis that defines the direction of the polarization plane where the phase speed of light is slow is the slow axis. The axis that defines the direction of the plane of polarization where the phase velocity of the propagating light is fast is called the fast axis. The difference in propagation time between the slow axis and the fast axis is the PMD amount.

  When the length of the optical fiber as the optical transmission line is short, the fast axis and the slow axis exist in a state where the directions are preserved with respect to the light propagation direction (z-axis direction). To do. However, when the length of the optical fiber as the optical transmission line is increased, the fast axis and the slow axis do not exist in a state in which the direction is preserved with respect to the light propagation direction (z-axis direction). In other words, the phenomenon that the direction of the fast axis and the slow axis changes corresponding to the position of the z axis cannot be ignored.

  When an optical pulse propagates through this optical fiber, the direction of the fast axis and the slow axis differs between the long wavelength component and the short wavelength component of the wavelength spectral components of the optical pulse. That is, the z-axis dependency of the direction of the fast axis and the slow axis differs for each wavelength component, and the time waveform of the optical pulse is complicatedly deformed unlike the first-order PMD. Thus, the PMD generated due to the change of the direction of the fast axis and the slow axis corresponding to the position of the z axis is referred to as a high order PMD.

  As the transmission speed becomes higher in the optical transmission system, it is necessary to narrow the half width of the time waveform of the optical pulse constituting the transmitted optical pulse signal. That is, the wavelength spectrum width of the optical pulse becomes wider as the transmission speed becomes higher. Therefore, the long-wavelength component and the short-wavelength component of the wavelength spectrum component of the optical pulse are different in the direction of the fast axis and the slow axis as described above. Therefore, the wider the wavelength spectrum width of the optical pulse, the faster the fast axis. And the difference in the direction of the slow axis becomes large. As a result, the higher the transmission speed in the optical transmission system, the more likely the influence of higher-order PMD appears. In other words, the higher the transmission rate in the optical transmission system, the greater the need for higher-order PMD suppression.

  As an apparatus for realizing an optical stage compensation method for suppressing high-order PMD, an apparatus in which primary PMD compensators each including a polarization controller and a DGD compensator are connected in series is disclosed (for example, Non-Patent Document 3). reference). In addition, a method of removing higher-order PMD components and non-polarized components with a polarizer is disclosed (for example, see Non-Patent Document 4).

  On the other hand, there is known a polarization stabilizing circuit that inputs light whose polarization state (SOP: State of Polarization) changes every moment and outputs it in a constant SOP state (see, for example, Patent Document 1). It is used by being disposed in the previous stage of an optical circuit having polarization dependency.

  This polarization stabilization circuit separates the input light into P-polarization component and S-polarization component by polarization separation means, and the polarization plane of either the P-polarization component or the S-polarization component Is rotated 90 ° with a half-wave plate and then combined with the other polarization component to achieve polarization independence.

Further, a polarization stabilization circuit having a configuration different from the above-described polarization stabilization circuit is also known as a polarization stabilization circuit. This polarization stabilization circuit is a commercially available auto-tracking polarization plane controller that combines a quarter-wave plate and a half-wave plate, converts them into DOP Stokes parameters of the input light, and keeps the SOP constant. (For example, Opt-Quest Inc., model number: ALP 05A).
Japanese Unexamined Patent Publication No. 9-90299 Lianshan Yan, et al., "Practical Solutions to Polarization -Mode-Dispersion Emulation and Compensation", Journal of Lightwave Technology, vol. 24, No. 11 pp. 3992-4005 (2006). Akihiko Tsujimura, Shoji Ishikawa “Current Status and Issues of Automatic Polarization Mode Dispersion Compensation Technology” OPTRONICS, 2003, No. 10, pp. 126-129. C. Xie, et al., "Mitigation of Higher Order PMD by distributing PMD Compensators in the Transmission Line", ECOC 2002, 7.1.1. K. Ikeda, "Simple PMD Compensator with Higher Order PMD Mitigation", OFC 2003, MF90.

  However, changing the value of DGD by the DGD compensator corresponds to changing the phase difference between orthogonal polarization modes, and the SOP of the output light output from the DGD compensator changes. Since the DGD value of the optical signal that propagates through the optical fiber transmission line and reaches the receiving device in optical communication varies with time, the DGD compensator used in the PMD compensator in optical communication is a variable DGD compensator. Is used. When a variable DGD compensator is used as the DGD compensator that constitutes the PMD compensator, the SOP of the output light output from the DGD compensator is large due to the change in the compensation DGD amount and changes instantaneously. Therefore, it becomes difficult to arrange a device having an optical device having polarization dependency as a constituent element in the subsequent stage of the PMD compensation device.

  Accordingly, an object of the present invention is to input an PMD compensated optical pulse signal composed of an optical pulse whose time waveform is distorted by PMD of an optical fiber transmission line, and to perform an operation for shaping the time waveform of the optical pulse. A PMD compensation device that generates and outputs a PMD compensated optical pulse signal that is always kept constant and does not vary in time even when the optical pulse is in a state, and a PMD compensation method using this PMD compensation device There is to do.

  The inventor of the present invention arranges a polarization stabilizing circuit configured by combining a half-wave plate and a quarter-wave plate after the DGD compensator included in the conventional PMD compensation device. The above problem is solved by controlling the polarization stabilization circuit so that the Stokes parameter of the PMD-compensated output light output from the wave stabilization circuit always becomes a preset value. It came. In general, the polarization analyzer is an expensive device, but the number of parts can be reduced by using the same polarization analyzer used for the PMD compensation means and polarization analyzer used for the polarization stabilization means. Can be reduced. In other words, by controlling the Stokes parameter of the output light output from the polarization stabilization circuit to be constant over time, SOP fluctuations can be eliminated, and polarization dependency is added to the latter stage of the PMD compensator. It is possible to dispose an apparatus that includes an optical device having the constituent elements.

  According to the gist of the present invention based on the above philosophy, the following PMD compensation apparatus and PMD compensation method are provided.

  The PMD compensation device of the present invention is a device that shapes the time waveform of an optical pulse generated by PMD in an optical fiber transmission line, and includes a polarization mode adjustment unit and a polarization plane determination adjustment unit. The polarization mode adjustment unit receives the PMD compensated signal as an input signal, adjusts the polarization state of this input signal, and adjusts the DGD between the polarization modes of this input signal to generate a PMD compensation signal To do. The polarization plane determination adjustment unit receives the PMD compensation signal, generates a signal with the polarization direction of the PMD compensation signal fixed and the PMD compensated as an output signal, and outputs it.

  The PMD compensation device of the present invention is preferably configured as follows. That is, the PMD compensation apparatus of the present invention includes a first polarization plane controller, a variable DGD adjustment unit, a second polarization plane controller, a polarization analyzer, and a control signal generator.

  The first polarization plane controller adjusts the polarization state of the input signal according to the first parameter signal that indicates the amount of rotation of the polarization plane of the input signal for the PMD compensated signal input as the input signal. Thus, a polarization plane adjustment signal is generated.

  The variable DGD adjustment unit responds to a polarization plane adjustment signal supplied from the first polarization plane controller according to a second parameter signal instructing the DGD of the polarization plane adjustment signal. A PMD compensation signal is generated by applying DGD to one polarization mode component of the wave mode.

  The second polarization plane controller responds to the PMD compensation signal supplied from the variable DGD adjustment unit according to the third parameter signal indicating the amount of rotation of the polarization plane of the PMD compensation signal. It functions as a polarization stabilization circuit that determines the direction and generates and outputs an output signal.

  The polarization analyzer calculates the Stokes parameter of the tapped monitor signal from the output signal, converts the Stokes parameter into a Stokes parameter signal that is an electrical signal, and outputs the signal.

  The control signal generator generates a first parameter signal, a second parameter signal, and a third parameter signal from the Stokes parameter signal, supplies the first parameter signal to the first polarization plane controller, and supplies the second parameter signal. The third parameter signal is supplied to the second polarization plane controller by supplying the variable DGD adjustment unit.

  The variable DGD adjustment unit is preferably configured as follows. That is, the variable DGD adjustment unit includes a polarization demultiplexer, a polarization multiplexer, a movable arm, a stepping motor, and a stepping motor driver.

  The polarization demultiplexer branches the polarization plane adjustment signal into the first polarization mode component and the second polarization mode component of the orthogonal eigenpolarization mode of the polarization plane adjustment signal. The first polarization mode component is input to the polarization multiplexer, and the second polarization mode component is input to the movable arm, added with DGD, and input to the polarization multiplexer.

  Polarization demultiplexer, movable arm so that the PMD compensation signal is generated by combining the first polarization mode component and the second polarization mode component with DGD added by the polarization multiplexer And a polarization multiplexer.

  The stepping motor moves the movable arm to a position necessary for adding DGD to the second polarization mode component. The stepping motor driver performs control for moving the movable arm with respect to the stepping motor.

  The PMD compensation method of the present invention is a method of shaping the time waveform of an optical pulse generated by PMD in an optical fiber transmission line, and includes a polarization mode adjustment step and a polarization plane determination step.

  The polarization mode adjustment step adjusts the polarization state of this input signal for the PMD compensated signal input as the input signal, and adjusts the DGD between the polarization modes of this input signal to adjust the PMD compensation signal. Is a step of generating.

  The polarization plane determination step is a step in which a PMD compensation signal is input, the polarization direction of the PMD compensation signal is determined, and a signal in which PMD is compensated is generated and output as an output signal.

  The PMD compensation method of the present invention preferably includes the following steps. That is, it includes a first polarization plane control step, a DGD adjustment step, a second polarization plane control step, a polarization analysis step, and a control signal generation step.

  In the first polarization plane control step, for the PMD compensated signal input as an input signal, the polarization state of this input signal is determined according to the first parameter signal that indicates the amount of rotation of the polarization plane of this input signal. This is a control step for adjusting and generating a polarization plane adjustment signal.

  In the DGD adjustment step, one polarization mode of the orthogonal eigenpolarization mode of this polarization plane adjustment signal is determined in response to the second parameter signal indicating the DGD value of this polarization plane adjustment signal. This is a step of generating a PMD compensation signal by applying DGD to the component.

  The second polarization plane control step determines the polarization direction of the PMD compensation signal according to the third parameter signal that indicates the rotation amount of the polarization plane of the PMD compensation signal, and outputs the PMD compensation signal. A step of generating a signal;

  In the polarization analysis step, the monitor signal is branched by tapping the output signal, the Stokes parameter of the monitor signal is calculated, and the Stokes parameter is converted into a Stokes parameter signal that is an electrical signal and output.

  The control signal generation step generates a first parameter signal, a second parameter signal, and a third parameter signal from the Stokes parameter signal, supplies the first parameter signal to the first polarization plane controller, and supplies the second parameter signal. This is a step of supplying the third parameter signal to the second polarization plane controller by supplying the variable DGD adjustment unit.

  According to the PMD compensation device of the present invention, the PMD compensation signal output by changing the SOP of the input signal by adjusting the DGD between the polarization modes in the polarization mode adjustment unit is the polarization plane definite adjustment. Is input to the unit and fixed in a preset SOP and output. Therefore, the PMD compensation apparatus of the present invention outputs an output signal in which PMD is compensated and the polarization direction is fixed.

  Thus, according to the PMD compensation apparatus of the present invention, the PMD compensated optical pulse signal composed of the optical pulse whose time waveform is distorted by the PMD of the optical fiber transmission line is input and the time waveform of the optical pulse is shaped Even when the operation is being performed, it is possible to generate and output the SOP of the optical pulse as a PMD compensation optical pulse signal with no time fluctuation and always being constant. Accordingly, it becomes possible to connect an optical processing apparatus including an optical device having polarization dependency as a constituent element in the subsequent stage of the PMD compensation apparatus of the present invention.

  The polarization mode adjustment unit can be configured to include a first polarization plane controller and a variable DGD adjustment unit. When configured in this way, the first polarization plane controller functions to adjust the polarization state of the input signal and generate a polarization plane adjustment signal. In addition, the variable DGD adjustment unit adds DGD to one polarization mode component of the orthogonal eigenpolarization mode of the polarization plane adjustment signal supplied from the first polarization plane controller, and generates a PMD compensation signal. Therefore, the SOP of the input signal changes in this variable DGD adjustment unit.

  The polarization plane determining and adjusting unit can be configured by a second polarization plane controller having the same configuration as the first polarization plane controller described above. In this case, the PMD compensation signal is input to the second polarization plane controller, the polarization direction is determined so as to be a preset polarization direction, and an output signal is generated and output.

  According to the PMD compensation method of the present invention, the Stokes parameter of the output signal is calculated in the polarization analysis step. Since the DOP value is calculated from the Stokes parameter, the first polarization plane controller and the DGD compensator described above are controlled so that the DOP value is maximized. For this control, a known PSO (Particle Swarm Optimization) algorithm or the like can be used as appropriate.

  Control signals for controlling the first polarization plane controller and the variable DGD adjustment unit are the first parameter signal and the second parameter signal, respectively, so that the DOP of the output signal is maximized. In the control signal generator, based on the reference DOP value calculated based on the Stokes parameter obtained by observing the monitor signal tapped from the output signal, the DOP value is controlled to be maximized. A measured DOP value is determined according to an algorithm, and a first parameter signal and a second parameter signal are calculated from the measured DOP value.

  In the polarization analysis step, it is also obtained by observing the monitor signal tapped from the output signal in the control signal generator described above for the second polarization plane controller that performs the function of the polarization stabilization circuit. Stokes parameters are commonly used. Since the output signal output from the second polarization plane controller is controlled to be a preset SOP, a control signal is adaptively generated from this Stokes parameter. This control signal is the third parameter signal.

  For example, when the polarization analyzer observes that the DOP value has decreased due to the PMD change of the input signal, the first polarization plane controller and the variable DGD adjustment unit are controlled so that the DOP value increases. While the first polarization plane controller is under such control, the second polarization plane controller is always controlled such that the output signal is a preset SOP.

  As a result, the operation of shaping the time waveform of the input signal is performed without fluctuation of the intensity of the output light output from the second polarization plane controller that functions as a polarization stabilization circuit. However, it is possible to generate and output the SOP of the optical pulse as a PMD compensation optical pulse signal with no time variation and always being constant.

  That is, the PMD compensation device and the PMD compensation method of the present invention are characterized in that the first polarization plane controller and the variable DGD adjustment are commonly used by using the Stokes parameters obtained by observing the monitor signal tapped from the output signal. And controlling the second polarization plane controller.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. Note that FIG. 2 illustrates an example of the configuration according to the present invention, and merely schematically shows the arrangement relationship of each component to the extent that the present invention can be understood. It is not limited. In the following description, specific elements and operating conditions may be taken up. However, these elements and operating conditions are only one of preferred examples, and thus are not limited to these.

<PMD Compensator of Embodiment>
With reference to FIG. 2 and FIG. 3 (A) to FIG. 3 (C), the configuration and operation of the PMD compensation apparatus according to the embodiment of the present invention will be described. FIG. 2 is a schematic block diagram of the PMD compensation device according to the embodiment of the present invention. The optical signal path is indicated by a thick line, and the electrical signal path is indicated by a thin line.

  The PMD compensation device 250 according to the embodiment of the present invention includes a first polarization plane controller 210, a variable DGD adjustment unit 220, a second polarization plane controller 232, a polarization analyzer 236, and a control signal generator 240. .

  In response to the PMD compensated signal input as the input signal 209, the first polarization plane controller 210 responds to the first parameter signal 241a that indicates the amount of rotation of the polarization plane of the input signal 209, and the polarization of the input signal The polarization plane adjustment signal 211 is generated by adjusting the state.

  The variable DGD adjustment unit 220 responds to the polarization plane adjustment signal 211 supplied from the first polarization plane controller 210 according to the second parameter signal 241b instructing the DGD of the polarization plane adjustment signal 211. A PMD compensation signal 215 is generated by adding DGD to one polarization mode component of the orthogonal eigenpolarization mode 211.

  In response to the PMD compensation signal 215 supplied from the variable DGD adjustment unit 220, the second polarization plane controller 232 responds to the PMD compensation signal 215c according to the third parameter 241c signal that indicates the amount of rotation of the polarization plane of the PMD compensation signal 215. It functions as a polarization stabilization circuit that determines the polarization direction of the signal 215 and generates and outputs the output signal 233. The output signal 233 is partially tapped by the optical branching device 234, and the monitor signal 235 is taken out and output to the outside as the output signal 251.

  The polarization analyzer 236 calculates the Stokes parameter of the tapped monitor signal 235 from the output signal 233, converts this Stokes parameter into a Stokes parameter signal 237, which is an electrical signal, and outputs it.

  The control signal generator 240 generates a first parameter signal 241a, a second parameter signal 241b, and a third parameter signal 241c from the Stokes parameter signal 237, and supplies the first parameter signal 241a to the first polarization plane controller 210. Then, the second parameter signal 241b is supplied to the variable DGD adjustment unit 220, and the third parameter signal 241c is supplied to the second polarization plane controller 232.

  The variable DGD adjustment unit 220 includes a polarization demultiplexer 212, a polarization multiplexer 214, a movable arm 216, a stepping motor 218, and a stepping motor driver 222.

  The polarization demultiplexer 212 branches the polarization plane adjustment signal 211 into a first polarization mode component 213a and a second polarization mode component 213b of the orthogonal eigenpolarization mode of the polarization plane adjustment signal 211. The first polarization mode component 213a is input to the polarization multiplexer 214, and the second polarization mode component 213b is input to the movable arm 216 and added with DGD to form the second polarization mode component 213c. Input to the polarization multiplexer 214.

  The movable arm 216 has a reflecting mirror 216-1 and a reflecting mirror 216-2 fixed to both ends of the arm, and the reflecting mirror 216-1 and the reflecting mirror 216-2 are driven by a stepping motor 218, so that the second It has a function of adjusting the optical path length through which the polarization mode component 213b propagates.

  The polarization demultiplexer 214 multiplexes the first polarization mode component 213a and the second polarization mode component 213c to which DGD is added, and generates the PMD compensation signal 215 so that the PMD compensation signal 215 is generated. A device 212, a movable arm 216, and a polarization beam combiner 214 are disposed.

  The stepping motor 218 moves the movable arm 216 to a position necessary for adding DGD to the second polarization mode component 213b. The stepping motor driver 222 performs control for moving the movable arm 216 with respect to the stepping motor 218.

  In principle, the first polarization plane controller 210 and the second polarization plane controller 232 can be configured by combining a half-wave plate and a quarter-wave plate, and are commercially available under the name of the polarization plane controller or the like. It is possible to use the device as appropriate. In addition, a device that applies stress to the core of the optical fiber according to a control signal such as a voltage to control the plane of polarization can also be used. The variable DGD adjustment unit 220 can appropriately use a device that changes the optical path difference between orthogonal polarization modes by a motor or the like in accordance with a control signal such as a voltage. A polarization switch type DGD compensator in which a polarization rotator is arranged between a plurality of birefringent crystals can also be used.

  Here, the polarization plane controller PMP-3000 manufactured by General Photonics Corporation can be used as the first polarization plane controller 210 and the second polarization plane controller 232, and the variable DGD adjustment unit 220 or the like corresponds to the DGD compensation. As a generator, a DGD generator having a variable step sufficiently smaller than the optical carrier wavelength can be used. According to this polarization plane controller, it is possible to rotationally control the change plane in accordance with an external control signal with respect to the input light. Similarly, the DGD compensator can arbitrarily generate DGD in accordance with an external control signal.

  Specifically, with respect to the polarization plane controller PMP-3000, the input light is transmitted to the I / O connection terminal of the polarization plane controller PMP-3000 via RS-232 communication via a logic control circuit such as a personal computer. The direction of the polarization plane can be adjusted and output. Similarly, the DGD compensator can arbitrarily generate DGD by RS-232 communication from the outside.

  For the polarization analyzer 236, a DOP measuring instrument POD-101A of General Photonics was used. The Stokes parameter signal 237 output from the DOP measuring instrument POD-101A is supplied to the control signal generator 240 via the USB interface (not shown). As the control signal generator 240, a personal computer in which a program for calculating DOP from Stokes parameters is installed is used. That is, the DOP was calculated from the Stokes parameter signal 237 output from the DOP measuring instrument POD-101A by this personal computer.

  The configuration of the PMD compensator described above, the DOP measuring instrument POD-101A, and the personal computer in which the program for calculating the DOP from the Stokes parameters is installed, the configuration of the PMD compensation method of the embodiment of the present invention to be described later is configured It is possible to execute the step to be performed manually. Of course, it is needless to say that these steps can be appropriately automated using a general-purpose computer or the like.

  When an input signal including a time waveform distortion caused by PMD is input to the PMD compensation apparatus 250 according to the embodiment of the present invention, each of the first polarization plane controller 210 and the variable DGD adjustment unit 220 includes a control signal generator. Based on the first parameter signal 241a and the second parameter signal 241b supplied from 240, the PMD compensator operates so that the DOP of the output signal output from the PMD compensation device 250 is maximized.

  The third parameter signal 241c supplied from the control signal generator 240 is also supplied to the second polarization plane controller 232. Based on the third parameter signal 241c, the second polarization plane controller 232 operates so that the polarization direction of the output signal 233 is determined in a preset SOP.

For example, when the propagation direction is set in the z-axis direction and the polarization in the y-axis direction is set as SOP, the Stokes parameters (S ₀ , S ₁ , S ₂ , S ₃ ) = (1, 1, 0, 0 The second polarization plane controller 232 may be controlled so that The SOP can be set in the control signal generator 240 in advance.

Since DOP is a value defined as the ratio of the light intensity of the polarization component to the total light intensity of the light pulse, the following equation (1) is obtained by the Stokes parameters (S ₀ , S ₁ , S ₂ , S ₃ ) Given.
DOP = {S ₁ ² + S ₂ ² + S ₃ ² } ^1/2 / S ₀ (1)
Therefore, if the Stokes parameter is calculated, DOP is calculated using equation (1).

  When the polarization analyzer 236 observes that the DOP has decreased due to the PMD variation of the input signal propagating through the optical fiber transmission line and input to the PMD compensator 250 of the embodiment of the present invention, the first polarization The wavefront controller 210 and the variable DGD adjustment unit 220 are controlled to increase the DOP of the output signal 233. While the first polarization plane controller 210 and the variable DGD adjustment unit 220 perform the above-described operation, the second polarization plane controller 232 cooperates with the operations of the first polarization plane controller 210 and the variable DGD adjustment unit 220. Operates so that the output signal 233 is fixed to the preset SOP.

  When the first polarization plane controller 210, the variable DGD adjustment unit 220, and the second polarization plane controller 232 described above cooperate to control the SOP of the output signal 233, the minimum unit of the DGD adjustment value of the variable DGD adjustment unit 220 is When the wavelength is not sufficiently smaller than the wavelength of the input signal, the DGD value of the PMD compensation signal 215 input to the second polarization plane controller 232 output from the variable DGD adjustment unit 220 varies greatly. That is, in this case, the following operation of the second polarization plane controller 232 may not be in time.

  Therefore, it is preferable that the minimum unit of the DGD adjustment value of the variable DGD adjustment unit 220 is set to be sufficiently smaller than the wavelength of the input signal. As described above, as the stepping motor 218 constituting the variable DGD adjustment unit 220 in which the minimum unit of the DGD adjustment value can be set sufficiently smaller than the wavelength of the input signal, a stepping motor manufactured by Sigma Koki Co., Ltd. (model number: SGSP15-10, TS3682N5 ) Etc. can be used as appropriate. According to this, the minimum unit of the DGD adjustment value can be set to 0.008 μm.

  When the variable DGD adjustment unit 220 having the shape shown in FIG. 2 is constructed using the above stepping motor, the minimum unit of the DGD adjustment value that can be adjusted by the variable DGD adjustment unit 220 is 0.016 μm (= 0.008 μm × 2 The minimum unit value of the DGD adjustment value is 1/90 of the wavelength when the wavelength of the input signal is 1.55 μm. If the minimum unit value of the DGD adjustment value is small to this extent, the second polarization plane controller 232 can sufficiently follow the DGD value adjusted by the variable DGD adjustment unit 220 and operate.

Referring to FIG. 3 (A) to FIG. 3 (C), the relationship between the value of the Stokes parameter calculated with respect to the value of DGD adjusted by the variable DGD adjustment unit 220 is the minimum unit value of the DGD adjustment value. It will be explained how it changes depending on the difference. 3 (A) to 3 (C) are diagrams for explaining the relationship between the value of the Stokes parameter calculated with respect to the value of DGD adjusted by the variable DGD adjustment unit 220, and FIG. , (B) and (C) are diagrams showing cases where the minimum unit value of the DGD adjustment value is 0.053 femtosecond (fs), 0.2 fs, and 2 fs, respectively. The respective values of the Stokes parameters (S ₁ , S ₂ , S ₃ ) are indicated by square marks (S ₁ value), circle marks (S ₂ value), and triangle marks (S ₃ value).

  As shown in FIG. 3A, when the minimum unit value of the DGD adjustment value is 0.053 fs, it can be considered that the value of the Stokes parameter changes continuously with respect to the fluctuation of the DGD adjustment value. Further, as shown in FIG. 3B, even when the minimum unit value of the DGD adjustment value is 0.2 fs, it can be considered that the value of the Stokes parameter continuously changes with respect to the fluctuation of the DGD adjustment value. However, as shown in FIG. 3C, it can be seen that when the minimum unit value of the DGD adjustment value is 2 fs, the value of the Stokes parameter changes rapidly with respect to the fluctuation of the DGD adjustment value.

Since the frequency of visible to near-infrared light is about 10 ¹⁴ Hz, the period is about 10 ^-14 s. That is, about 10 fs. The minimum unit value of the DGD adjustment value shown in Fig. 3 (B) and Fig. 3 (C) is 0.2 fs and 2 fs, which corresponds to about 1/50 and 1/5 of the frequency of visible to near infrared light, respectively. To do. Therefore, in order to set the minimum unit of the DGD adjustment value of the variable DGD adjustment unit 220 to be sufficiently smaller than the wavelength of the input signal, it is necessary to set it to 1 or less, which is a few tenths of the frequency of the input signal. desirable.

  Next, an experimental system for verifying the operating principle of the PMD compensation apparatus according to the embodiment of the present invention will be described with reference to FIG. FIG. 4 is a schematic block configuration diagram of an experimental system for verifying the operation principle of the PMD compensation apparatus according to the embodiment of the present invention.

  This experimental system includes a transmitter 260, a first polarization plane controller 262, a variable DGD adjustment unit 264, a second polarization plane controller 266, a polarizer 268, and an optical power meter 270. The transmitter 260 outputs an optical time division multiplexed signal 261 (hereinafter abbreviated as OTDM signal 261) having a bit rate of 160 Gbit / s. The first polarization plane controller 262 receives the OTDM signal 261 and adjusts the polarization state of the OTDM signal 261 to generate the polarization plane adjustment signal 263. The variable DGD adjustment unit 264 adds DGD to one polarization mode component of the orthogonal eigenpolarization mode of the polarization plane adjustment signal 263 to generate a PMD compensation signal 265. The second polarization plane controller 266 determines the polarization direction of the PMD compensation signal 265 and generates and outputs an output signal 267. The output signal 267 passes through the polarizer 268 and is output as the monitoring output signal 269, and the light intensity is measured by the optical power meter 270.

  The PMD compensation signal 265 output from the variable DGD adjustment unit 264 is a commercially available polarization stabilizing device configured to include a 1/2 wavelength plate, a 1/4 wavelength plate, and a Stokes parameter monitor as the second polarization plane controller 266. An experiment was conducted in which a circuit (Opt Quest Co., Ltd .: model number ALP 05A) was input and generated and output as an output signal 267. That is, the above-described commercially available polarization stabilization circuit was used as the second polarization plane controller 266, and the polarization stabilization function of the PMD compensation device of the present invention was verified.

In the polarization stabilization circuit, the Stokes parameters (S ₁ , S ₂ , S ₃ ) are always set to (1, 0, 0). That is, the set Stokes parameters are (S ₁ , S ₂ , S ₃ ) = (1, 0, 0). Further, the rotational speeds of the half-wave plate and the quarter-wave plate constituting the first polarization plane controller 262 and the second polarization plane controller 266 were set to π radians / s. If the polarization plane of the output signal 267 is stabilized, the intensity of the monitoring output signal 269 output from the polarizer 268 should not change.

  The above experimental results will be described with reference to FIG. FIG. 5 is a diagram showing the minimum unit value dependency of the SOP DGD adjustment value of the output signal 267 output from the second polarization plane controller 266. In FIG. 5, the abscissa indicates the DGD value added by the variable DGD adjustment unit 264 in units of picoseconds (ps), and the abscissa indicates the monitor output signal 269 that is output light from the polarizer 268. The intensity is scaled in dBm.

  In FIG. 5, when the minimum unit value of the DGD adjustment value is 0.053 fs, 0.1 fs, and 0.5 fs, the values of the intensity of the monitoring output signal 269 are circled (when 0.053 fs ), Square marks (in the case of 0.1 fs), and triangle marks (in the case of 0.5 fs). As shown in FIG. 5, when the minimum unit value of the DGD adjustment value is 0.053 fs and 0.1 fs, the intensity of the monitoring output signal 269 output from the polarizer 268 may not change. I understand.

  In other words, if the minimum unit value of the DGD adjustment value is set to be smaller than at least 0.1 fs, the SOP of the PMD compensated optical pulse signal output from the polarization stabilization circuit (second polarization plane controller 266) does not change with time, and It can be seen that it remains constant. This result also shows that the Stokes parameters used during the PMD compensation operation of the polarization mode adjustment unit and the Stokes parameters used during the polarization stabilization operation of the wavefront determination adjustment unit can be shared. ing.

  Therefore, according to the PMD compensation apparatus of the embodiment of the present invention, the PMD compensated optical pulse signal composed of the optical pulse whose time waveform is distorted by the PMD of the fiber transmission line is input and the time waveform of the optical pulse is shaped. It was confirmed that it is possible to generate and output the SOP of the optical pulse as a PMD compensated optical pulse signal while keeping the SOP of the optical pulse constant at all times even when the operation is performed. .

  The PMD compensation device of the present invention can be set in front of the receiving device in the optical communication system, or can be installed in the middle of the optical fiber transmission line. In either case, the PMD compensation operation is effective. To work.

  According to the PMD compensation device of the present invention, PMD compensation is performed in a state where there is no time variation of the SOP. Therefore, the higher-order PMD component and the non-polarization component disclosed in Non-Patent Document 4 are removed by the polarizer. The method can also be used effectively.

<PMD Compensation Method of Embodiment>
According to the PMD compensation apparatus of the present invention described above, the PMD compensation method of the embodiment of the present invention described below can be implemented. In the following description, it is assumed that the above-described polarization mode adjustment step and polarization plane determination step are manually operated, and these steps can be appropriately automated using a general-purpose computer or the like.

  With reference to FIGS. 6 and 7, an embodiment of a PMD compensation method executed using the PMD compensation apparatus of the present invention will be described. FIG. 6 is a flowchart for explaining steps related to the initial PMD compensation operation, and FIG. 5 is a flowchart for explaining steps related to the end of the initial PMD compensation operation.

  In the flowchart shown in FIG. 6, in step S10, an initialization flag indicating whether or not initialization is completed is set to i = 0 when initialization is not completed, and then the PMD compensation device operates. Assumes to start. Therefore, when the PMD compensator starts operation, continuous observation of the output signal 233, that is, the DOP of the monitor signal 235 is started. The constant observation of the monitor signal 235 is executed by step S16 shown below.

  Step S12 is a step of setting a reference DOP value. The following steps are executed so as to be equal to or less than the value of the reference DOP.

  Step S14 is a step of setting a Stokes parameter that specifies the SOP of the output signal 251 that is PMD compensated and output from the PMD compensation device 250. The SOP of the output signal 251 is adjusted so that it always becomes the SOP given by the Stokes parameter set at this time. The designation of this SOP is made in consideration of the polarization plane dependency of the optical processing device installed at the subsequent stage of the PMD compensation device of the embodiment of the present invention.

  Step S16 is a step of measuring the polarization state of the output signal 233 output from the PMD compensation device 250 by the polarization analyzer 236, calculating the Stokes parameter of the output light, and generating the first to third parameter signals It is. The optical signal to be measured by the polarization analyzer 236 is a monitor signal 235 obtained by tapping a part of the output light 233 by the optical splitter 234. The output signal 233 and the monitor signal 235 are only different in strength, and the SOPs are the same. Step S16 corresponds to a polarization analysis step and a control signal generation step.

  Step S18 compares the measured DOP value determined from the Stokes parameter calculated in Step S16 with the reference DOP value set in Step S12, and the measured DOP value determined from the Stokes parameter calculated in Step S16 is If it is equal to or greater than the reference DOP value set in S12, the initialization flag is set to i = 1, and if it is the following value, the initialization flag remains at i = 0. This step can be performed by appropriately using the aforementioned polarization plane controller PMP-3000, DGD compensator, etc. manufactured by General Photonics. Step S18 corresponds to a polarization analysis step.

  However, if it is determined in step S18 that the measured DOP value is greater than or equal to the reference DOP value, the process proceeds to step S32. If it is determined that the measured DOP value does not exceed the reference DOP value, the process proceeds to step S22. .

  Step S22 is a step in which the first polarization plane controller 210 is controlled based on the first parameter signal 241a, and the polarization plane of the PMD compensated signal 209 is rotationally controlled so that the DOP value is maximized. This step can also be performed by appropriately using the PMD compensator described above. Step S22 corresponds to a first polarization plane control step.

  Step S24 is a step of controlling the variable DGD adjustment unit 220 based on the second parameter signal 241b to adjust and output the DGD of the output light 211 from the first polarization plane controller 210 so as to decrease. Step S24 corresponds to a DGD adjustment step.

  Step S32 is a step in which the first polarization plane controller 210 performs minute rotation control on the polarization plane of the PMD compensated signal 209 so that the DOP value becomes maximum. In this step, as described above, in step S18, the measured DOP value determined from the Stokes parameter calculated in step S16 is compared with the reference DOP value set in step S12, and the Stokes parameter calculated in step S16 is compared. This is the step after the initialization flag is set to i = 1, assuming that the measured DOP value determined from is equal to or greater than the reference DOP value set in step S12. Therefore, it is not necessary to significantly change the polarization plane of the PMD compensated signal 209, but it is preferable to finely adjust it. Step S32 corresponds to a first polarization plane control step.

  Step S34 is a step in which the variable DGD adjustment unit 220 finely adjusts and outputs the DGD of the output light 211 from the first polarization plane controller 210 so as to decrease. Similarly to step S32, this step is also a step after the initialization flag is set to i = 1. Therefore, fine adjustment is preferably performed in the variable DGD adjustment unit 220. Step S34 corresponds to a DGD adjustment step.

  Step S36 is a step in which the second polarization plane controller 232 is controlled based on the third parameter signal 241c to control the rotation of the polarization plane of the PMD compensation signal 215 so that the DOP value is maximized. Similarly to step S32, this step is also a step after the initialization flag is set to i = 1. Therefore, it is preferable that the second polarization plane controller 232 performs fine adjustment. Step S36 corresponds to a second polarization plane control step.

  Step S40 is a step of comparing the set Stokes parameter set in Step S14 with the measured Stokes parameter of the output signal (monitor signal 235). Step S40 can also be performed by appropriately using the above-described configuration of the PMD compensator as in step S18. Step S40 corresponds to a polarization analysis step.

  If it is determined in step S40 that the set Stokes parameter is equal to the measured Stokes parameter, the process proceeds to step S16. If it is determined that the set Stokes parameter is not equal to the measured Stokes parameter, the process proceeds to step S36. When step S24 is completed, the process returns to step S16, and step S18, step S22, and step S24 are repeatedly executed.

  The measured DOP value determined from the Stokes parameter calculated in step S16 is compared with the reference DOP value determined in step S12, and the measured DOP value determined in step S16 is set in step S12. When the initialization flag i is set to i = 1 because it is greater than or equal to the reference DOP value, step S32 is executed as shown in FIG. Steps from step S32 to step S40 are steps executed after the initial PMD compensation operation is completed.

  As long as the DOP measured in step S18 is greater than or equal to the reference DOP, the steps from step S32 to step S40 are executed, and the DOP of the output signal 251 is constantly monitored by using the monitor signal 235.

It is a schematic block diagram of a conventional PMD compensation device. 1 is a schematic block configuration diagram of a PMD compensation apparatus according to an embodiment of the present invention. (A), (B) and (C) are diagrams for explaining the relationship between the DGD value and the Stokes parameter value, 0.2 fs when the minimum unit value of the DGD adjustment value is 0.053 fs, And 2 fs. 1 is a schematic block configuration diagram of an experimental system for verifying an operation principle of a PMD compensation apparatus according to an embodiment of the present invention. It is a figure which shows the value dependence of the minimum unit of the DGD adjustment value of SOP of the output signal output from a 2nd polarization plane controller. It is a flowchart with which it uses for description of the step which concerns on initial PMD compensation operation | movement. It is a flowchart with which description of the step concerned after completion | finish of an initial PMD compensation operation | movement is provided.

Explanation of symbols

100, 250: PMD compensator
102: Polarization plane controller
104: DGD compensator
106, 240: Control signal generator
108, 234: Optical splitter
110, 236: Polarization analyzer
210, 262: First polarization plane controller
212: Polarization demultiplexer
214: Polarization multiplexer
216: Movable arm
216-1, 216-2: Reflector
218: Stepping motor
220, 264: Variable DGD adjustment unit
222: Stepping motor driver
232, 266: Second polarization plane controller
260: Transmitter
268: Polarizer
270: Optical power meter

Claims (6)

A polarization mode dispersion compensation signal is generated by inputting the polarization mode dispersion compensation signal as an input signal, adjusting the polarization state of the input signal, and adjusting the group delay between the polarization modes of the input signal. A polarization mode adjustment unit,
Polarization plane deterministic adjustment in which the polarization mode dispersion compensation signal is input, the polarization direction of the polarization mode dispersion compensation signal is determined, and the polarization mode dispersion compensated signal is generated and output as an output signal A polarization mode dispersion compensator. Comprising a first polarization plane controller, a variable group delay adjustment unit, a second polarization plane controller, a polarization analyzer, and a control signal generator,
The first polarization plane controller demodulates the input signal in response to a first parameter signal that indicates the amount of rotation of the polarization plane of the input signal with respect to the polarization mode dispersion compensation signal input as an input signal. Adjust the wave state to generate the polarization adjustment signal,
The variable group delay adjustment unit, according to a second parameter signal instructing a group delay of the polarization plane adjustment signal supplied from the first polarization plane controller, one of the orthogonal eigenpolarization modes of the polarization plane adjustment signal A polarization mode dispersion compensation signal is generated by adding a group delay to the polarization mode component of
The second polarization plane controller, in response to a third parameter signal instructing a rotation amount of the polarization plane of the polarization mode dispersion compensation signal supplied from the variable group delay adjustment unit, of the polarization mode dispersion compensation signal Determine the polarization direction, generate and output an output signal,
The polarization analyzer calculates the Stokes parameter of the tapped monitor signal from the output signal, converts the Stokes parameter to a Stokes parameter signal that is an electrical signal, and outputs the Stokes parameter signal.
The control signal generator generates the first parameter signal, the second parameter signal, and the third parameter signal from the Stokes parameter signal, and supplies the first parameter signal to the first polarization plane controller And supplying the second parameter signal to the variable group delay adjusting unit and supplying the third parameter signal to the second polarization plane controller. The variable group delay adjustment unit includes a polarization demultiplexer, a polarization multiplexer, a movable arm, a stepping motor, and a stepping motor driver.
The polarization demultiplexer branches the polarization plane adjustment signal into a first polarization mode component and a second polarization mode component of the orthogonal eigenpolarization mode of the polarization plane adjustment signal,
The first polarization mode component is input to the polarization multiplexer,
The second polarization mode component is input to the movable arm and added to the group delay to be input to the polarization multiplexer,
The polarization multiplexer combines the first polarization mode component and the second polarization mode component to which the group delay is added, so that the polarization mode dispersion compensation signal is generated. The polarization splitter, the movable arm, and the polarization multiplexer are arranged,
The stepping motor moves the movable arm to a position necessary for adding the group delay to the second polarization mode component,
3. The polarization mode dispersion compensator according to claim 2, wherein the stepping motor driver controls the stepping motor to move the movable arm. For a polarization mode dispersion compensation signal input as an input signal, the polarization mode dispersion compensation signal is adjusted by adjusting the polarization state of the input signal and adjusting the group delay between the polarization modes of the input signal. A polarization mode adjustment step for generating
Polarization plane determining step of receiving the polarization mode dispersion compensation signal, determining a polarization direction of the polarization mode dispersion compensation signal, and generating and outputting a signal compensated for polarization mode dispersion as an output signal And a polarization mode dispersion compensation method. For the polarization-mode dispersion compensation signal input as an input signal, the polarization state of the input signal is adjusted by adjusting the polarization state of the input signal according to the first parameter signal that indicates the amount of rotation of the polarization plane of the input signal. A first polarization plane control step for generating an adjustment signal;
In response to the second parameter signal instructing the group delay of the polarization plane adjustment signal, a group delay is given to one polarization mode component of the orthogonal eigenpolarization mode of the polarization plane adjustment signal, and the polarization mode A variable group delay adjustment step for generating a dispersion compensation signal;
Second polarization plane control for generating an output signal by determining the polarization direction of the polarization mode dispersion compensation signal according to the third parameter signal indicating the rotation amount of the polarization plane of the polarization mode dispersion compensation signal. Steps,
A polarization analysis step of tapping the output signal to branch the monitor signal, calculating a Stokes parameter of the monitor signal, converting the Stokes parameter to a Stokes parameter signal that is an electrical signal, and outputting the Stokes parameter signal,
Generating the first parameter signal, the second parameter signal, and the third parameter signal from the Stokes parameter signal, supplying the first parameter signal to a first polarization plane controller, and supplying the second parameter signal A polarization mode dispersion compensation method comprising: a control signal generation step of supplying the third parameter signal to a second polarization plane controller by supplying the variable group delay adjustment unit to the variable parameter delay adjustment unit. Comprising a first polarization plane controller, a variable group delay adjustment unit, a second polarization plane controller, a polarization analyzer, and a control signal generator,
The first polarization plane controller responds to the input polarization mode dispersion compensation signal according to the first parameter signal that indicates the amount of rotation of the polarization plane of the polarization mode dispersion compensation signal. The polarization mode adjustment signal is generated by adjusting the polarization state of the wave mode dispersion compensation signal,
The variable group delay adjustment unit is configured to adjust the polarization plane according to a second parameter signal instructing a group delay of the polarization plane adjustment signal with respect to the polarization plane adjustment signal supplied from the first polarization plane controller. Giving a group delay to one polarization mode component of the orthogonal eigenpolarization mode of the signal to generate a polarization mode dispersion compensation signal,
The second polarization plane controller, with respect to the polarization mode dispersion compensation signal supplied from the variable group delay adjustment unit, a third parameter signal that indicates the amount of rotation of the polarization plane of the polarization mode dispersion compensation signal Accordingly, the polarization direction of the polarization mode dispersion compensation signal is determined, and an output signal is generated.
The polarization analyzer calculates the Stokes parameter of the tapped monitor signal from the output signal, converts the Stokes parameter to a Stokes parameter signal that is an electrical signal, and outputs the Stokes parameter signal.
The control signal generator generates the first parameter signal, the second parameter signal, and the third parameter signal from the Stokes parameter signal, and supplies the first parameter signal to the first polarization plane controller And supplying the second parameter signal to the variable group delay adjustment unit, supplying the third parameter signal to the second polarization plane controller,
The variable group delay adjustment unit includes a polarization demultiplexer, a polarization multiplexer, a movable arm, a stepping motor, and a stepping motor driver.
The polarization demultiplexer branches the polarization plane adjustment signal into a first polarization mode component and a second polarization mode component of the orthogonal eigenpolarization mode of the polarization plane adjustment signal,
The first polarization mode component is input to the polarization multiplexer,
The second polarization mode component is input to the movable arm and added to the group delay to be input to the polarization multiplexer,
The polarization multiplexer combines the first polarization mode component and the second polarization mode component to which the group delay is added, so that the polarization mode dispersion compensation signal is generated. The polarization splitter, the movable arm, and the polarization multiplexer are arranged,
The stepping motor moves the movable arm to a position necessary for adding the group delay to the second polarization mode component,
The stepping motor driver is a polarization mode dispersion compensation method used for a polarization mode dispersion compensation apparatus, wherein the stepping motor performs control for moving the movable arm with respect to the stepping motor.
A step (step S10) of setting an initialization flag indicating whether or not the initialization is completed to i = 0 when the initialization is not completed and setting i = 1 when the initialization is completed; ,
Setting a reference polarization degree value (step S12);
Setting a Stokes parameter that specifies the polarization state of the output light that is polarization mode dispersion compensated and output from the polarization mode dispersion compensation device (step S14);
Measuring a polarization state of output light output from the polarization mode dispersion compensation device, calculating a Stokes parameter of the output light by the polarization analyzer, and generating first to third parameter signals (step) S16)
The measured polarization degree value determined from the Stokes parameter calculated in step S16 is compared with the reference polarization degree value set in step S12, and the measurement determined from the Stokes parameter calculated in step S16. When the polarization degree value is equal to or greater than the reference polarization degree value set in step S12, the initialization flag is set to i = 1, and the measured polarization degree value is equal to or less than the reference polarization degree value. If it is, the step of leaving the initialization flag i = 0 (step S18),
Controlling the first polarization plane controller based on the first parameter signal to rotate and control the polarization plane of the polarization-mode dispersion compensation signal so that the value of polarization degree is maximized (step S22); ,
Controlling the variable group delay adjustment unit based on the second parameter signal to adjust and output the group delay of the output light from the first polarization plane controller to be reduced (step S24);
Performing a minute rotation control on the polarization plane of the polarization-mode dispersion compensation signal so that the value of the degree of polarization is maximized by the first polarization plane controller (step S32);
Finely adjusting the variable group delay adjustment unit so that the group delay of the output light from the first polarization plane controller is reduced (step S34);
Controlling the second polarization plane controller based on the third parameter signal and performing rotation control of the polarization plane of the polarization mode dispersion compensation signal so that the value of the polarization degree is maximized (step S36); ,
Comparing the set Stokes parameter set in step S14 with the measured Stokes parameter of the output signal (step S40),
If it is determined in step S18 that the measured polarization degree value is greater than or equal to the reference polarization degree value, the process proceeds to step S32, and the measured polarization degree value exceeds the reference polarization degree value. If it is determined that there is not, the process proceeds to step S22.
If it is determined in step S40 that the set Stokes parameter is equal to the measured Stokes parameter, the process proceeds to step S16. If it is determined that the set Stokes parameter is not equal to the measured Stokes parameter, the step is performed. Proceed to S36
When step S24 is completed, the process returns to step S16, and step S18, step S22, and step S24 are repeatedly executed.

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