Control signal multiplexing device, control signal receiving device, control signal multiplexing method, and control signal receiving method

Abstract

This control signal multiplexer comprises a modulation unit that uses a control signal to polarize and modulate an optical signal for conveying a main signal.

Description

[Technical Field]

[0001] The present invention relates to a control signal multiplexing device, a control signal receiving device, a control signal multiplexing method, and a control signal receiving method. [Background technology]

[0002] In recent years, there has been a demand for the realization of low-latency optical access networks using Photonic Gateways (hereinafter referred to as "PGs") (see, for example, Non-Patent Document 1). A PG is connected to multiple user devices (CPE: Customer Premises Equipment), and wavelengths to be used for each user device are set. Since optical signals of various protocols are input to the PG, it is desirable to set wavelengths and optical paths for the user devices using control signals that are independent of the optical signal protocols. A method that uses AMCC (Auxiliary Management Control Channel) is known as a management control method that is independent of the communication protocol of the main signal. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] "New System Architecture for Realizing All-Photonics Networks", Journal of the Institute of Electronics, Information and Communication Engineers, Vol. 104, No. 5, pp. 471-477, 2021,<URL:https: / / www.journal.ieice.org / bin / pdf_link.php?fname=k104_5_471&lang=J&year=2021> Summary of the Invention [Problem to be solved by the invention]

[0004] In view of the above circumstances, an object of the present invention is to provide a technique that enables control signals to be transmitted and received using a method different from AMCC. [Means for solving the problem]

[0005] One aspect of the present invention is a multiplexing device that multiplexes a control signal onto a main signal by polarization modulation, or multiplexes the main signal onto an optical signal that has been polarization modulated by the control signal.

[0006] One aspect of the present invention is a control signal receiving device including a decoder that decodes a control signal based on the polarization state of an optical signal received from the control signal multiplexing device according to the above aspect.

[0007] One aspect of the present invention is a control signal multiplexing method that includes a step of polarization-modulating an optical signal for carrying a main signal with a control signal.

[0008] One aspect of the present invention is a control signal receiving method including the step of decoding a control signal based on the polarization state of an optical signal received from the control signal multiplexing device according to the above aspect. [Effects of the Invention]

[0009] According to the above aspect, it is possible to transmit and receive control signals using a method different from AMCC. [Brief explanation of the drawings]

[0010] [Figure 1A] 1 is a diagram illustrating a first configuration example of an optical communication system according to an embodiment. [Figure 1B] FIG. 2 is a diagram illustrating a second configuration example of the optical communication system according to the embodiment. [Figure 1C] FIG. 10 is a diagram illustrating a third configuration example of the optical communication system according to the embodiment. [Figure 2] 1 is a schematic block diagram illustrating the configuration of a relay device and a user device according to a first embodiment. [Figure 3] FIG. 2 is a diagram illustrating an example of the configuration of a detection unit according to the first embodiment. [Figure 4] FIG. 10 is a schematic block diagram illustrating the configuration of a relay device and a user device according to a second embodiment. [Figure 5]FIG. 10 is a schematic block diagram illustrating the configuration of a relay device and a user device according to a third embodiment. [Figure 6] FIG. 10 is a schematic block diagram illustrating the configuration of a relay device and a user device according to a fourth embodiment. [Figure 7] FIG. 10 is a diagram illustrating an example of the configuration of a DGD modulation unit according to a fourth embodiment. [Figure 8] FIG. 10 is a diagram illustrating an example of the configuration of a compensation amount derivation unit according to a fourth embodiment. [Figure 9] FIG. 10 is a diagram illustrating an example of the configuration of an optical communication system according to a fifth embodiment. [Figure 10] FIG. 10 is a schematic block diagram showing the configuration of a light distribution device according to a fifth embodiment. [Figure 11] FIG. 1 is a schematic block diagram illustrating the configuration of a computer according to at least one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, the embodiments will be described in detail with reference to the drawings. An optical communication system 1 described in the following embodiments includes a control signal multiplexer M that multiplexes an optical signal for carrying a main signal with a control signal, and a control signal receiver R that receives the control signal.

[0012] FIG. 1A is a diagram illustrating a first exemplary configuration of an optical communication system 1 according to an embodiment. As illustrated in FIG. 1A, the optical communication system 1 may include two user devices 40. The two user devices 40 are connected to each other via a path such as an optical fiber or a spatial transmission path. Examples of the spatial transmission path include FSO (Free Space Optics). In the example illustrated in FIG. 1A, one user device 40 functions as a control signal multiplexing device M, and the other user device 40 functions as a control signal receiving device R.

[0013] 1B is a diagram illustrating a second configuration example of the optical communication system 1 according to the embodiment. As illustrated in FIG. 1B, the optical communication system 1 may include two user devices 40 and a repeater device 50. The user devices 40 and the repeater device 50 are connected via a path such as an optical fiber or a spatial transmission path. In the example illustrated in FIG. 1B, one of the user devices 40 functions as a control signal multiplexer M, and the repeater device 50 functions as a control signal receiver R.

[0014] 1C is a diagram illustrating a third exemplary configuration of the optical communication system 1 according to the embodiment. As illustrated in FIG. 1C, the optical communication system 1 may include two user devices 40 and a repeater device 50. In the example illustrated in FIG. 1C, the repeater device 50 functions as a control signal multiplexer M, and one of the user devices 40 functions as a control signal receiver R.

[0015] The user equipment 40 may be, for example, a user terminal (UT), a CPE, or an optical network unit (ONU). The relay device 50 may be, for example, an optical line terminal (OLT), a gateway (GW), or an optical switch. In another embodiment, the user equipment 40 and the relay device 50 may each have the functions of a control signal multiplexer M and a control signal receiver R. In another embodiment, the user equipment 40 may not have the functions of a control signal multiplexer and a control signal receiver, and multiple relay devices 50 (for example, photonic gateways) provided on the path may have the functions of a control signal multiplexer M and a control signal receiver R.

[0016] First Embodiment The first embodiment will be described below. In the following description, an optical communication system 1 is described taking as an example a configuration in which the optical communication system 1 includes two user devices 40 and a relay device 50, as shown in FIG. 1B, one of the user devices functions as a control signal multiplexing device M, and the relay device 50 functions as a control signal receiving device R.

[0017] FIG. 2 is a schematic block diagram showing the configuration of the relay device 50 and the user device 40 according to the first embodiment. The user device 40 includes a main signal modulation unit 41, a control signal generation unit 42, and a polarization modulation unit 44.

[0018] The main signal modulator 41 generates an optical signal modulated by a main signal. The modulation method of the main signal may be any modulation method that is not affected by polarization modulation. For example, the main signal modulator 41 generates an optical signal modulated by a main signal using a direct modulation method or an external modulation method. The direct modulation method is a method of directly modulating the light by modulating the current applied to the light source. The external modulation method is a method of modulating the light output from the light source using an external modulator.

[0019] The control signal generator 42 generates a control signal indicating control information to be notified to the relay device 50 .

[0020] For example, the control signal generating unit 42 performs polarization modulation. For example, the polarization modulation may involve reading the control signal before modulation as a binary bit string, outputting a first modulation pattern when the bit of the control signal before modulation is "0", and outputting a second modulation pattern when the bit of the control signal before modulation is "1". Note that either the first modulation pattern or the second modulation pattern may be unmodulated. In other words, the control signal generating unit 42 may switch between performing and not performing polarization modulation based on the control signal.

[0021] Note that the control signal according to the first embodiment may be subject to polarization fluctuations due to external disturbances on the transmission line. Therefore, the control signal generator 42 selects a shift in polarization modulation, for example, a modulation pattern that is different enough to be distinguished from external disturbances. Furthermore, if the polarization state drifts due to external disturbances, the control signal generator 42 may modulate the amount of change from the previous polarization state in order to improve drift resistance. For example, in the case of binary modulation, modulation may be performed with or without change from the previous polarization state (continuation of the polarization state), or modulation may be performed with or without change from the previous polarization state. situationThe modulation may be based on a large or small amount of change from the previous code value, or on the direction of change. The control signal generator 42 may also perform modulation according to a differential encoding method that encodes the amount of change from the previous code value. For example, when the bit of the control signal does not change ("0" → "0" or "1" → "1"), the first modulation pattern may be output, and when the bit changes ("0" → "1" or "1" → "0"), the second modulation pattern may be output. Details of the modulation patterns will be described later. In another embodiment, the control signal generation unit 42 may switch the modulation pattern to be output when the bit of the control signal before modulation is 1, and may not switch the modulation pattern to be output when the bit of the control signal before modulation is 0. In another embodiment, the control signal generation unit 42 may switch the modulation pattern to be output when the bit of the control signal before modulation is 0, and may not switch the modulation pattern to be output when the bit of the control signal before modulation is 1.

[0022] The polarization modulation unit 44 polarization-modulates the optical signal output by the main signal modulation unit 41 using the modulation pattern output by the control signal generation unit 42 and outputs the resulting signal. The optical signal on which the main signal is superimposed is an example of an optical signal for carrying the main signal. Note that, although the polarization modulation unit 44 according to the present embodiment modulates the optical signal on which the main signal is superimposed using an external modulation method, other embodiments are not limited to this. For example, in other embodiments, the polarization modulation unit 44 may modulate the optical signal according to the main signal and the control signal using the same modulator as for the main signal. Also, in other embodiments, the output of the polarization modulation unit may be input to the main signal modulation unit. For example, the polarization modulation unit 44 may generate an optical signal modulated with the control signal using a direct modulation method using a light source in which the polarization of the output light changes depending on the applied current, etc. In this case, the polarization modulation unit 44 can be considered to serve as the light source of the main signal modulation unit 41. The main signal modulation unit 41 modulates the light from the polarization modulation unit 44, which is the light source, with the main signal using, for example, an external modulation method, to output an optical signal in which the control signal and the main signal are multiplexed. Therefore, the optical signal output from the polarization modulation unit 44 is later modulated with the main signal, and therefore can be said to be an optical signal for carrying the main signal.

[0023] The repeater 50 includes a splitter 11, a detector 12, a decoder 14, a controller 15, and a relay unit 16. Below, an example will be described in which the repeater relays signals transparently without OEO (Optical-Electrical-Optical) conversion. When relaying OE (Optical-Electrical) converted signals by electrically processing them and then converting them to EO (Electrical-Optical), the output of a receiver for receiving both the main signal and the control signal may be electrically split, without detecting the light split by an optical multiplexer / splitter to receive the control signal, and one of the signals may be input to the detector and the other to the repeater, which performs EO conversion and outputs the split signal.

[0024] The splitter 11 is an optical multiplexer / splitter that splits an optical signal received from the user device 40 and outputs the split signal to the detector 12 and the repeater 16 .

[0025] The detector 12 detects a control signal from the optical signal received from the user device 40 via the splitter 11. The detector 12 is a detector that can detect differences in polarization. Examples of the detector 12 include a polarization analyzer and a combination of a polarizer and a photoreceiver.

[0026] FIG. 3 is a diagram illustrating an example of the configuration of the detection unit 12 according to the first embodiment. For example, as shown in FIG. 3, the detection unit 12 may be a differential detection circuit including a PBS 121 (Polarization Beam Splitter), a first photodetector 122, and a second photodetector 123. The differential detection circuit detects the difference in intensity between two linearly polarized waves when a polarized wave incident on the PBS 121 is split into two linearly polarized waves. The first photodetector 122 and the second photodetector 123 are realized by, for example, a photodiode (PD) or an avalanche photodiode (APD). The first photodetector 122 and the second photodetector 123 have approximately the same light-receiving characteristics. If there is a difference between the light-receiving characteristics of the first photodetector 122 and the second photodetector 123, the difference may be canceled out by applying a gain corresponding to the reciprocal of the light-receiving characteristic in a stage subsequent to the photodetector. The first optical receiver 122 receives a polarization component, for example, a p-polarized component, of the optical signal separated from the PBS 121. The second optical receiver 123 receives a polarization component, for example, an s-polarized component, of the optical signal separated from the PBS 121. The first optical receiver 122 and the second optical receiver 123 constitute a balanced optical receiver connected in series in the same polarity direction.

[0027] As a result, the detector 12 shown in Fig. 3 can obtain a differential output of two orthogonal polarization components of the optical signal, for example, the p-polarized component and the s-polarized component. The detector 12 may also be configured with a photoreceiver that detects only one polarization component of the optical signal, for example, either the p-polarized component or the s-polarized component. In this case, however, the detection sensitivity will be roughly half that of the detector 12 shown in Fig. 3. For example, the detector 12 may be a polarization monitor that determines the amplitude and phase of the p-polarized component and the s-polarized component by measuring the power (Stokes parameters S0-S4) of four independent polarization states.

[0028] In this embodiment, the optical signal is orthogonally polarized and differentially detected using orthogonal polarization, but differential detection may be performed depending on the modulation value. For example, in another embodiment, the optical signal may be modulated using circular polarization, and circular polarizations in opposite directions may be received and detected using differential detection.

[0029] The decoder 14 decodes the signal output by the detector 12 into a bit string. If the user device 40 encodes the control signal using a differential encoding method, the decoder 14 decodes the bit string of the control signal based on the previous bit value. If the main signal is not polarization multiplexed or polarization modulated and the first modulation pattern and the second modulation pattern have different frequencies, the decoder 14 may perform pattern synchronization to detect an output of intensity locked in to the frequency associated with the modulation pattern before performing the above decoding.

[0030] The control unit 15 controls the relay device 50 based on the control signal decoded by the decoding unit 14. For example, when the control signal from the user device 40 indicates a wavelength request message, the control unit 15 allocates an available wavelength to the user device 40. Note that the control unit 15 may allocate or change the wavelength allocation even when there is no wavelength request message from the user device 40.

[0031] The repeater 16 outputs the optical signal output from the splitter 11 to the opposing user device 40 .

[0032] Modulation Pattern The control signal generator 42 of the user device 40 may switch the modulation pattern to be output between the first modulation pattern and the second modulation pattern based on the control signal. For example, the first modulation pattern may be p-polarized and the second modulation pattern may be s-polarized. For example, the first modulation pattern may be linearly polarized and the second modulation pattern may be circularly polarized. For example, the first modulation pattern and the second modulation pattern may be counter-rotating circular polarizations. For example, the first modulation pattern may be a pattern in which the polarization angle of the polarization plane of a linearly polarized optical signal is changed at a first frequency within a first variation range (amplitude). The state in which the polarization angle is changed at a first frequency within a first variation range is an example of a first polarization state. The second modulation pattern is a pattern in which the polarization angle of the polarization plane of a linearly polarized optical signal is changed at a second frequency within a second variation range. The state in which the polarization angle is changed at a second frequency within a second variation range is an example of a second polarization state. The second modulation pattern is a modulation pattern that differs from the first modulation pattern in at least one of the variation range of the polarization angle and the frequency.

[0033] Here, the variation range of each modulation pattern in the first embodiment is a range different from the range of polarization fluctuation due to external disturbances that may occur in the transmission path connecting the user device 40 and the relay device 50. That is, in terms of the variation width, the maximum value of the variation range of the modulation pattern is smaller than the minimum value of the range of polarization fluctuation due to external disturbances, or the minimum value of the variation range of the modulation pattern is larger than the maximum value of the range of polarization fluctuation due to external disturbances. In terms of frequency, the maximum value of the frequency of the variation of the modulation pattern is smaller than the minimum value of the frequency of the polarization fluctuation due to external disturbances, or the minimum value of the frequency of the variation range of the modulation pattern is larger than the maximum value of the frequency of the polarization fluctuation due to external disturbances. For example, if polarization fluctuation occurs in a maximum range of ±10 degrees in a transmission path, a range exceeding ±20 degrees (for example, ±90 degrees), which is twice that range, is determined as the fluctuation range of the first modulation pattern.In a transmission path where birefringence is uniformly distributed, the distribution of DGD (Differential Group Delay) fluctuations forms a Maxwellian distribution, so the fluctuation range is determined to be a range that is at least twice (2σ) the deviation of the DGD fluctuation distribution.

[0034] Furthermore, the frequency of each modulation pattern in the first embodiment is higher than the frequency of polarization fluctuation that may occur in the transmission path connecting the user device 40 and the relay device 50. For example, if polarization fluctuation occurs at a maximum frequency of 10 kHz in the transmission path, a frequency higher than 10 kHz (for example, 40 kHz) is determined as the frequency of the first modulation pattern.

[0035] In the first embodiment, both the range and frequency of the polarization fluctuation in the modulation pattern are significantly different from the polarization fluctuation caused by external disturbances, but this is not limiting. For example, in other embodiments, when the range of the polarization fluctuation in the modulation pattern is significantly different from the polarization fluctuation caused by external disturbances, the frequency of the polarization fluctuation in the modulation pattern may be approximately the same as the polarization fluctuation caused by external disturbances. Furthermore, when the frequency of the polarization fluctuation in the modulation pattern is significantly different from the polarization fluctuation caused by external disturbances, the range of the polarization fluctuation in the modulation pattern may be approximately the same as the polarization fluctuation caused by external disturbances. The modulation pattern may be a sine wave, a square wave, a sawtooth wave, a predetermined bit pattern, or any other arbitrary pattern.

[0036] For example, if the first modulation pattern has a fluctuation range of ±45 degrees and a frequency of 40 kHz, the second modulation pattern may have a fluctuation range of ±90 degrees and a frequency of 20 kHz.

[0037] The optical communication system 1 may include an optical amplifier in the transmission path connecting the user device 40 and the repeater device 50. The optical amplifier selected is one that does not modulate the signal light into unpolarized light. This is because the control signal disappears if the optical amplifier modulates the signal light into unpolarized light. Therefore, the optical amplifier may perform polarization modulation as long as the modulation does not interfere with the modulation of the control signal in the present device. For example, the optical amplifier may perform polarization modulation at a frequency that can be sufficiently distinguished from the modulation different from the modulation in the present device or the frequency associated with the modulation pattern of the control signal, such as a sufficiently low frequency (e.g., a frequency comparable to the polarization fluctuation that may occur in the transmission path) or a sufficiently high frequency. For example, if the modulation frequency of the control signal is several tens of kHz, the optical amplifier may perform polarization modulation at a frequency of several kHz or higher, corresponding to the excitation lifetime of erbium ions, approximately 10 ms, to address polarization-dependent loss.

[0038] Actions and Effects In this way, the user equipment 40 according to the first embodiment modulates the polarization state of an optical signal based on a control signal. When switching the modulation pattern between a first modulation pattern and a second modulation pattern, for example, the modulation pattern according to the first embodiment varies the polarization angle within a predetermined range at a predetermined frequency. According to the first embodiment, the range of the polarization angle and the frequency of the polarization fluctuation are significantly different from polarization fluctuations due to external disturbances that may occur in the transmission path of the optical signal. This allows the repeater 50 to distinguish and receive polarization fluctuations due to external disturbances from the control signal. Note that in other embodiments, either the range of the polarization angle or the frequency of the polarization fluctuation may be similar to the polarization fluctuations due to external disturbances.

[0039] The above describes an example in which the repeater device 50 transparently relays a signal without OEO conversion. However, if the OE-converted signal is electrically processed and then EO converted and relayed, the output of the receiver (user device 40) for receiving both the main signal and the control signal may be electrically branched without detecting the light branched by the optical multiplexer / branch to receive the control signal. In this case, the branch is an electrical multiplexer / branch that branches the optical signal that has been photoelectrically converted by the receiver and outputs it to a processing unit that decodes the control signal and a processing unit that performs 3R processing, etc., of the main signal. The processing in the decoding processing unit is similar.

[0040] Second Embodiment The optical communication system 1 according to the first embodiment polarization-modulates an optical signal with a control signal. The optical communication system 1 according to the second embodiment realizes transmission of a control signal by polarization modulation even when transmitting a main signal by polarization multiplexing or polarization modulation.

[0041] 4 is a schematic block diagram showing the configurations of a relay device 50 and a user device 40 according to the second embodiment. The user device 40 according to the second embodiment has the same configuration as that of the first embodiment.

[0042] The modulation deviation by the control signal generator 42 of the user equipment 40 according to the second embodiment is larger than the range of polarization fluctuation due to external disturbances that may occur in the transmission path connecting the user equipment 40. When the main signal is polarization compensated in the opposite equipment or the relay equipment 50, the fluctuation range of the modulation pattern only needs to be within the range in which the polarization compensation unit 13 can perform polarization compensation.

[0043] Furthermore, the polarization modulation frequency in the second embodiment, e.g., the frequency of each modulation pattern, is higher than the frequency of polarization fluctuation that may occur in the transmission path connecting the user device 40 and lower than the maximum frequency that can be guaranteed by the polarization compensation unit 13 of the opposite device or the relay device 50. For example, if polarization fluctuation occurs at a maximum frequency of 10 kHz in the transmission path and the polarization compensation unit 13 can compensate for polarization fluctuation of a maximum of 50 kHz, a frequency higher than 10 kHz and lower than 50 kHz (e.g., 40 kHz) is determined as the frequency of the first modulation pattern. When the primary signal is polarization modulated, the frequency of the modulation pattern may be such that the control signal and the primary signal can be distinguished. For example, the frequency of the modulation pattern may be frequency-multiplexed with the primary signal. Alternatively, for example, the frequency of the modulation pattern may be an integer multiple of the frequency of the primary signal, and the modulation pattern may be averaged during reception so as not to interfere with decoding of the primary signal.

[0044] In the second embodiment, both the range and frequency of the polarization fluctuation in the modulation pattern are significantly different from the polarization fluctuation caused by external disturbances, but this is not limiting. For example, in another embodiment, the range of the polarization fluctuation in the modulation pattern may be significantly different from the polarization fluctuation caused by external disturbances, and the frequency of the polarization fluctuation in the modulation pattern may be approximately the same as the polarization fluctuation caused by external disturbances. Alternatively, the frequency of the polarization fluctuation in the modulation pattern may be significantly different from the polarization fluctuation caused by external disturbances, and the range of the polarization fluctuation in the modulation pattern may be approximately the same as the polarization fluctuation caused by external disturbances. The modulation pattern may be a sine wave, a square wave, a sawtooth wave, a predetermined bit pattern, or any other arbitrary pattern.

[0045] The opposite device or repeater 50 according to the second embodiment further includes a polarization compensator 13 in addition to the configuration of the first embodiment. In the following, an example will be shown in which the polarization compensator 13 performs compensation based on a control signal received by a repeater assuming transparent transmission. The polarization compensator 13 compensates for the polarization of an optical signal received from a user device 40 via a splitter 11. The polarization compensation unit 13 may also be composed of, for example, a polarization controller, a polarization delay, and a polarization monitor. It is preferable to use a polarization controller that can continuously track any polarization fluctuations without saturating (an infinite tracking type). Examples of polarization controllers that can be used include a micro-optics type using a dielectric crystal, a fiber type that controls the tension on the fiber using a piezoelectric element, or a PLC (Planar Lightwave Circuit) type that uses LiNbO3 crystal or glass material. The polarization delay may be, for example, a polarization-maintaining fiber or a delay device with a variable delay time. The polarization monitor determines the amplitude and phase of the p-polarized and s-polarized components by measuring the power (Stokes parameters S0-S4) of four independent polarization states.

[0046] The decoder 14 according to the second embodiment decodes the signal output by the detector 12 into a bit string. If the user device 40 encodes the control signal using a differential encoding scheme, the decoder 14 decodes the bit string of the control signal based on the previous bit value. For example, if the code of a bit is represented by the differential intensity difference between polarized waves, the decoder 14 decodes the bit string of the control signal based on the previous intensity difference between polarized waves and the current intensity difference between polarized waves.

[0047] Actions and Effects As described above, according to the second embodiment, the polarization modulation of the control signal is limited to a level that can be compensated for by the opposite receiving device or repeater device. As a result, even if the protocol of the main signal involves polarization modulation or polarization multiplexing that may be affected by the polarization modulation of the control signal, the optical communication system 1 can compensate for the polarization modulation of the control signal and prevent the control signal from affecting the main signal.

[0048] Note that, although the polarization compensator 13 according to the second embodiment compensates for both the control signal and the polarization fluctuation, this is not limiting. For example, according to another embodiment, the polarization compensator 13 may compensate for only the control signal, leaving the polarization fluctuation. In this case, the configuration of the polarization compensator 13 can be simplified. Furthermore, the polarization compensator 13 according to another embodiment may compensate for only the polarization fluctuation without compensating for the control signal.

[0049] Furthermore, although the repeater device 50 according to the second embodiment performs polarization compensation of an optical signal in transparent transmission, this is not limited to this in other embodiments. For example, when the repeater device 50 relays using OEO or when the opposite device receives a control signal, polarization compensation may be performed when the main signal is received. For example, the polarization compensation unit 13 may perform PMD (Polarization Mode Dispersion) compensation using digital coherent transmission. As described above, the polarization modulation unit 44 performs polarization modulation only within the range that can be compensated by the polarization compensation unit 13, and therefore the polarization compensation unit 13 can suppress the influence of the control signal on the main signal.

[0050] Third Embodiment The repeater 50 according to the first and second embodiments detects a control signal from an optical signal using the detector 12. In contrast, the repeater 50 according to the third embodiment has the function of obtaining a control signal in the polarization compensator 13. The polarization compensator 13 of the third example detects a change in polarization and compensates according to information about the detected change, and is configured to be able to output information about the change itself or information about the compensation.

[0051] FIG. 5 is a schematic block diagram showing the configuration of a relay device 50 and a user device 40 according to the third embodiment. The repeater 50 according to the third embodiment does not include the branching unit 11 and the detection unit 12 of the second embodiment. The decoder 14 according to the third embodiment obtains a control signal superimposed on an optical signal by observing information related to polarization compensation by the polarization compensation unit 13. Specifically, the decoder 14 extracts a control signal corresponding to a unique polarization fluctuation that deviates from the normal polarization fluctuation value. When the polarization compensation unit 13 outputs a compensation signal, the decoder 14 extracts the inverted value of the compensation signal. In other words, the decoder 14 according to the third embodiment detects a bit pattern or the like that is inverted from that of the decoders 14 according to the first and second embodiments.

[0052] When the polarization compensation unit 13 outputs information on the polarization change itself, the decoding unit 14 extracts a control signal corresponding to a specific polarization fluctuation that deviates from the value of a normal polarization fluctuation. That is, the decoding unit 14 according to the third embodiment detects the same bit pattern as the decoding unit 14 according to the first and second embodiments.

[0053] The variation range of the modulation pattern by the control signal generator 42 of the user equipment 40 according to the third embodiment is larger than the range of polarization variation due to external disturbances that may occur in the transmission path connecting the user equipment 40. Note that if the polarization modulation of the control signal may affect the main signal, such as when the main signal is polarization modulated or polarization multiplexed, the range that can be compensated for by the polarization compensation unit 13 becomes the upper limit of the modulation of the control signal.

[0054] In other embodiments, the rate of change of the modulation pattern may be faster than the rate of change of polarization fluctuation due to external disturbances. In this case, if the main signal is polarization-modulated, the rate of change of the modulation pattern is set to a rate that can be distinguished from the polarization modulation of the main signal. In this case, the range of change of the modulation pattern may be approximately the same as the range of polarization fluctuation due to external disturbances, or may be set to a range greater than the range of polarization fluctuation due to external disturbances.

[0055] Furthermore, the frequency of each modulation pattern in the third embodiment is higher than the frequency of polarization fluctuation that may occur in the transmission path connecting the user device 40. Furthermore, the frequency of each modulation pattern is lower than the maximum frequency that can be guaranteed by the polarization compensation unit 13 of the corresponding device or relay device 50. For example, if polarization fluctuation occurs at a maximum frequency of 10 kHz in the transmission path and the polarization compensation unit 13 can compensate for polarization fluctuation of a maximum of 50 kHz, a frequency higher than 10 kHz and lower than 50 kHz (for example, 40 kHz) is determined as the frequency of the first modulation pattern.

[0056] In the third embodiment, both the range and frequency of the polarization fluctuation in the modulation pattern are significantly different from the polarization fluctuation caused by external disturbances, but this is not limiting. For example, in other embodiments, the range of the polarization fluctuation in the modulation pattern may be significantly different from the polarization fluctuation caused by external disturbances, and the frequency of the polarization fluctuation in the modulation pattern may be approximately the same as the polarization fluctuation caused by external disturbances. Alternatively, the frequency of the polarization fluctuation in the modulation pattern may be significantly different from the polarization fluctuation caused by external disturbances, and the range of the polarization fluctuation in the modulation pattern may be approximately the same as the polarization fluctuation caused by external disturbances. The modulation pattern may be a sine wave, or may be any waveform such as a square wave, a sawtooth wave, or a predetermined bit pattern.

[0057] As described above, according to the third embodiment, the repeater device 50 obtains a control signal superimposed on an optical signal by observing the amount of polarization compensation performed by the polarization compensation unit 13. This allows the repeater device 50 according to the third embodiment to obtain a control signal without detecting an optical signal using the detection unit 12.

[0058] Fourth Embodiment The modulation patterns according to the first to third embodiments are for changing the polarization state at a predetermined frequency, whereas the modulation pattern according to the fourth embodiment is for changing the DGD at a predetermined frequency.

[0059] FIG. 6 is a schematic block diagram showing the configuration of a relay device 50 and a user device 40 according to the fourth embodiment. A user device 40 according to the fourth embodiment includes a DGD modulation unit 45 instead of the polarization modulation unit 44 of the first embodiment. The DGD modulation unit 45 switches between a first modulation pattern and a second modulation pattern that change the DGD, which is the amount of deviation between the p-polarized component and the s-polarized component of an optical signal. Modulation using DGD is an example of polarization modulation.

[0060] The DGD modulation unit 45 may perform modulation by changing the amount of delay due to polarization. The modulation pattern may be, for example, a pattern that changes the DGD at a predetermined frequency within a predetermined fluctuation range. One of the multiple modulation patterns may be a modulation pattern that differs from the other in at least one of the DGD fluctuation range and frequency.

[0061] The variation range of the modulation pattern is equal to or less than the maximum DGD that can be guaranteed by the DGD compensation unit 18. Furthermore, the frequency of each modulation pattern is lower than the maximum frequency that can be guaranteed by the DGD compensation unit 18.

[0062] In the fourth embodiment, both the DGD variation range and the DGD frequency in the modulation pattern are significantly different from the DGD caused by external disturbances, but this is not limiting. For example, in other embodiments, the DGD range in the modulation pattern may be significantly different from the DGD caused by external disturbances, and the DGD frequency in the modulation pattern may be similar to the DGD caused by external disturbances. Alternatively, the DGD frequency in the modulation pattern may be significantly different from the DGD caused by external disturbances, and the DGD range in the modulation pattern may be similar to the DGD caused by external disturbances. The modulation pattern may be a sine wave, a square wave, a sawtooth wave, a predetermined bit pattern, or any other arbitrary pattern.

[0063] Fig. 7 is a diagram showing an example of the configuration of a DGD modulation unit 45 according to the fourth embodiment. In Fig. 7, optical signals are depicted by dashed lines. In Fig. 7, a symbol of a black circle within a white circle attached to the path of an optical signal indicates that the plane of polarization of the optical signal is oriented vertically. In Fig. 7, a symbol of an arrow within a white circle attached to the path of an optical signal indicates that the plane of polarization of the optical signal is oriented horizontally.

[0064] The DGD modulation unit 45 includes a PBS 441, a first quarter-wave plate 442, a first reflecting mirror 443, a second quarter-wave plate 444, a second reflecting mirror 445, and an actuator 446. Each component of the DGD modulation unit 45 is formed of, for example, an MEMS. The PBS 441 separates the light input to the DGD modulation unit 45 into a first polarized component and a second polarized component that are orthogonal to each other.

[0065] A first quarter-wave plate 442 and a first reflecting mirror 443 are provided on the optical path of the first polarized component separated by the PBS 441 so as to be perpendicular to the optical path. As a result, the polarization plane of the first polarized component is tilted by 45 degrees when it passes through the first quarter-wave plate 442, and after being reflected by the first reflecting mirror 443, it passes through the first quarter-wave plate 442 again, whereby the polarization plane is tilted another 45 degrees. The first polarized component is then incident on the PBS 441 again. In other words, the first polarized component travels a distance twice the distance between the PBS 441 and the first reflecting mirror 443 and is incident on the PBS 441 again in a state tilted by 90 degrees.

[0066] A second quarter-wave plate 444 and a second reflecting mirror 445 are provided on the optical path of the second polarized component separated by PBS 441 so as to be perpendicular to the optical path. As a result, the polarization plane of the second polarized component is tilted by 45 degrees when it passes through second quarter-wave plate 444, and after being reflected by second reflecting mirror 445, it passes through second quarter-wave plate 444 again, whereby the polarization plane is tilted another 45 degrees. The second polarized component is then incident on PBS 441 again. In other words, the second polarized component travels a distance twice the distance between PBS 441 and second reflecting mirror 445 and is incident on PBS 441 again in a state tilted by 90 degrees.

[0067] The first reflecting mirror 443 is configured so that the relative position with respect to the PBS 441 can be changed by the actuator 446. The actuator 446 moves the first reflecting mirror 443 in a direction along the optical path of the first polarized light component. On the other hand, second reflecting mirror 445 is fixed so as not to change its position relative to PBS 441. As a result, by driving actuator 446, the optical path length of the first polarized component changes relative to the optical path length of the second polarized component. The DGD modulation unit 45 drives the actuator 446 in accordance with the modulation pattern output by the control signal generation unit 42, thereby multiplexing the control signal onto the optical signal.

[0068] The DGD modulation unit 45 shown in Fig. 7 modulates the optical signal on which the main signal is superimposed by an external modulation method, but this is not limited to this in other embodiments. The DGD modulation unit 45 may use a combination of a light source whose output light polarization changes depending on the applied current or the like, and a polarization-dependent delay line. The DGD modulation unit 45 may also be a combination of a polarization modulator and a polarization-dependent delay line. When the DGD modulation unit 45 shown in Fig. 7 is used, a continuously changing pattern such as a sine wave is suitable as the modulation pattern.

[0069] As shown in FIG. 6, a compatible device or relay device 50 according to the fourth embodiment includes a compensation amount derivation unit 17 and a DGD compensation unit 18 instead of the detection unit 12 of the first embodiment. For example, when the repeater device 50 according to the fourth embodiment performs OEO conversion and the polarization compensation unit 13 electrically compensates for PMD after reception, such as in digital coherent transmission, the decoding unit 14 obtains a time series of the DGD of the optical signal by observing the magnitude of the DGD compensation (tap coefficients of the FIR filter) derived by the compensation amount derivation unit 17.

[0070] 8 is a diagram showing an example of the configuration of a compensation amount derivation unit 17 according to the fourth embodiment. The compensation amount derivation unit 17 according to the fourth embodiment has a butterfly filter that realizes polarization multiplexing transmission. Specifically, the compensation amount derivation unit 17 includes a first FIR filter Pxx, a second FIR filter Pxy, a third FIR filter Pyx, a fourth FIR filter Pyy, a first adder Ax, a second adder Ay, a first update unit Ux, and a second update unit Uy.

[0071] The first FIR filter Pxx multiplies the p-polarized component of the received optical signal by a predetermined gain. The tap coefficients of the first FIR filter Pxx are updated by the first update unit Ux. The second FIR filter Pxy multiplies the s-polarized component of the received optical signal by a predetermined gain. The tap coefficients of the second FIR filter Pxy are updated by the first update unit Ux. The third FIR filter Pyx multiplies the p-polarized component of the received optical signal by a predetermined gain. The tap coefficients of the third FIR filter Pyx are updated by the second update unit Uy. The fourth FIR filter Pyy multiplies the s-polarized component of the received optical signal by a predetermined gain. The tap coefficients of the fourth FIR filter Pyy are updated by the second update unit Uy.

[0072] The first adder Ax adds the output of the first FIR filter Pxx and the output of the second FIR filter Pxy. The second adder Ay adds the output of the third FIR filter Pyx and the output of the fourth FIR filter Pyy.

[0073] The first update unit Ux updates the tap coefficients of the first FIR filter Pxx and the second FIR filter Pxy so as to minimize the mean square error with respect to a predetermined reference signal. The second update unit Uy updates the tap coefficients of the third FIR filter Pyx and the fourth FIR filter Pyy so as to minimize the mean square error with respect to a predetermined reference signal. In the constant envelope modulation method, the first update unit Ux and the second update unit Uy may use a constant modulus algorithm (CMA) that uses a constant as a reference signal for minimum mean square error.

[0074] The output of such a circuit consisting of an FIR filter and an adder is expressed by equation (1).

[0075]

number

[0076] where o Xi is the value of the p-polarized component of the signal compensated by the compensation amount derivation unit 17. Yi is the value of the s-polarized component of the signal compensated by the compensation amount derivation unit 17. Xi is the value of the p-polarized component of the signal input to the compensation amount derivation unit 17. Yi is the value of the s-polarized component of the signal input to the compensation amount derivation unit 17. The first update unit Ux and the second update unit Uy set the tap coefficients of each FIR filter so that the matrix [Pxx, Pxy; Pyx, Pyy] in the above equation (1) normalizes the square matrix representing the polarization fluctuation in the transmission path. This allows the compensation amount derivation unit 17 to calculate the compensation amount for the polarization fluctuation in the transmission path.

[0077] The decoder 14 identifies the DGD of the received optical signal by observing each tap coefficient set by the first updater Ux and the second updater Uy of the compensation amount derivation unit 17. The decoder 14 decodes the control signal based on the time series of the identified DGD. Furthermore, the DGD compensator 18 compensates for the DGD of the optical signal output from the splitter 11 in accordance with the tap coefficients set by the first updater Ux and the second updater Uy of the compensation amount deriver 17. For example, the DGD compensator 18 may be realized with a configuration similar to that of the DGD modulator 45 shown in FIG.

[0078] In another embodiment, the repeater 50 may include an electro-optical converter at the rear of the compensation amount derivation unit 17, instead of the splitter 11 and the DGD compensation unit 18. That is, the repeater 50 according to the other embodiment may include an electro-optical converter at the rear of the compensation amount derivation unit 17. Xi and p-polarized component o Yi may be used to convert the signal into an optical signal.

[0079] Fifth Embodiment FIG. 9 is a diagram illustrating a configuration example of an optical communication system 1 according to a fifth embodiment. The optical communication system 1 according to the fifth embodiment includes multiple optical distribution devices 10, a control device 20, an optical communication network 30, and multiple user devices 40. That is, the fifth embodiment is configured such that the optical communication network 30 is provided between the user devices 40 functioning as the control signal multiplexing device M shown in FIG. 1A and the user devices 40 functioning as the control signal receiving device R. In FIG. 9, the optical communication system 1 includes an optical distribution device 10-1 and an optical distribution device 10-2, but the number of optical distribution devices 10 is not limited thereto. The optical distribution device 10 is connected to the control device 20. The optical distribution device 10 communicates with other optical distribution devices 10 via the optical communication network 30. The optical communication network 30 may be, for example, a WDM (Wavelength Division Multiplexing) network having various topologies. One or more user devices 40 are connected to the optical distribution device 10. The optical distribution device 10, the control device 20, and the optical communication network 30 constitute a relay system 2 that relays communications between user devices 40.

[0080] The control device 20 assigns wavelengths to be used by each user device 40 in response to connection requests from the user devices 40. The control device 20 transmits setting information such as the wavelengths to be used to each user device 40. The relay system 2 and the user devices 40 exchange control information including the setting information to transmit the main signals of the user devices 40.

[0081] In the optical communication systems 1 according to the first to fourth embodiments, a control signal is exchanged between a user device 40 and a repeater 50. On the other hand, an optical distribution device 10 according to the optical communication system 1 shown in FIG. 9 not only receives a control signal from a user device 40 but also transmits a control signal to another optical distribution device 10 to which the optical signal is to be transmitted. In the optical communication system 1 according to the fifth embodiment, a case will be described in which a control signal is deleted and overwritten along the path of the optical signal. Specifically, the optical distribution device 10-1 shown in FIG. 9 deletes the control signal received from the user device 40 from the optical signal and adds a control signal to the optical signal for transmission to the optical distribution device 10-2, which is the destination of the optical signal.

[0082] 10 is a schematic block diagram showing the configuration of an optical distribution device 10 according to the fifth embodiment. The optical distribution device 10 according to the fifth embodiment includes a splitter 11, a detector 12, a polarization compensation unit 13, a decoder 14, a controller 15, a control signal generator 21, a polarization modulator 22, and an optical SW 23. The following describes an example in which the optical distribution device 10 according to the fifth embodiment performs OEO conversion on an optical signal.

[0083] The splitter 11 splits the received optical signal and outputs it to the detector 12 and the polarization compensation unit 13. The detector 12 detects a control signal from the optical signal input from the splitter 11. The polarization compensation unit 13 compensates for the polarization of the optical signal input from the splitter 11. The polarization compensation unit 13 performs PMD compensation using, for example, digital coherent transmission. When performing PMD compensation using digital coherent transmission, the polarization compensation unit 13 is suitable for a configuration in which it performs opto-electrical conversion on the input signal to decode the control signal and main signal, and then performs electro-optical conversion on the decoded main signal to transmit it as an optical signal. The light split by the splitter 11 may be detected by the detector 12, and the PMD compensation value may be input to a compensator that performs polarization compensation as an optical signal. This allows the polarization compensator 13 to erase the control signal superimposed on the optical signal.

[0084] The decoding unit 14 decodes the signal output by the detection unit 12 into a bit string. The control unit 15 controls the light distribution device 10 based on the control signal decoded by the decoding unit 14.

[0085] Based on the control signal generated by the control unit 15, the control signal generation unit 21 performs reverse modulation of the modulation of the control signal to be deleted by the polarization modulation unit 22. Further polarization modulation may be performed with an additional control signal. This allows the optical distribution device 10 to delete the old control signal from the optical signal and superimpose a new control signal.

[0086] The optical SW 23 outputs the optical signal output from the polarization modulation unit 22 to the opposing optical distribution device 10 or the opposing device via the optical communication network 30. The optical SW 23 has a configuration equivalent to the repeater unit 16 shown in Figures 2, 4, 5, and 6. The optical SW 23 may be placed before the branching device 11, between the branching device 11 and the polarization compensation unit 13, or between the polarization compensation unit 13 and the polarization modulation unit 22. The polarization modulation unit 22 has a configuration equivalent to the polarization modulation unit 44 in Figures 2, 4, 5, and 6 in the configuration in which the repeater device 50 functions as the control signal multiplexer M as shown in Figure 1C. In the configuration shown in Figure 6, the polarization modulation unit 22 and the polarization compensation unit 13 are replaced with a DGD modulation unit 45 and a DGD compensation unit 18.

[0087] The light distribution device 10 according to the fifth embodiment includes a polarization compensation unit 13 and a polarization modulation unit 22, and multiplexes a new control signal after erasing an old control signal, but this is not limited to this. For example, in the light distribution device 10 according to other embodiments, the polarization compensation unit 13 or the polarization modulation unit 19 may simultaneously erase the old control signal and multiplex a new control signal. That is, the polarization compensation unit 13 or the polarization modulation unit 22 according to other embodiments modulates the polarization of the optical signal according to the difference between the old control signal and the new control signal, thereby simultaneously erasing the old control signal and multiplexing a new control signal.

[0088] Furthermore, the light distribution device 10 according to another embodiment may compensate only for the control signal and leave the polarization fluctuation in the polarization compensation unit 13. In this case, the configuration of the polarization compensation unit 13 can be simplified.

[0089] In another embodiment, the light distribution device 10 may retain the old control signal and multiplex a new control signal into the optical signal using a modulation pattern different from that of the old control signal by the polarization modulation unit 22. In this case, the light distribution device 10 may not include the polarization compensation unit 13, or may include a polarization compensation unit 13 that compensates only for polarization fluctuations without compensating for the control signal.

[0090] In another embodiment, the optical distribution device 10 may transmit the optical signal transparently without performing OEO conversion. In this case, the optical distribution device 10 may perform decoding by the decoder 14 not for decoding the main signal but for detecting PMD.

[0091] Other Embodiments Although one embodiment has been described in detail above with reference to the drawings, the specific configuration is not limited to that described above, and various design modifications and the like are possible.

[0092] In the optical communication system 1 according to the above-described embodiment, the user equipment 40 generates a control signal, and the repeater 50 or the optical distribution device 10 receives the control signal. However, this is not limited to this. For example, in other embodiments, the optical distribution device 10, the control device 20, the repeater 50, or the like may generate the control signal. In this case, the optical distribution device 10, the control device 20, or the repeater 50 has a configuration similar to that of the user equipment 40 in the above-described embodiment. In other embodiments, the control device 20 or the user equipment 40 may receive the control signal. For example, in other embodiments, control signals may be communicated between two user equipment devices 40 directly connected by optical fiber. For example, one user equipment device 40 may be an ONU, and the other user equipment device 40 may be an OLT. In this case, the control device 20 or the user equipment 40 has a configuration similar to that of the optical distribution device 10 or the repeater 50 in the above-described embodiment.

[0093] Although the light distribution device 10 according to the above-described embodiment includes the detection unit 12, this is not limiting. For example, the light distribution device 10 according to another embodiment may identify the polarization angle by detecting the intensity of one of the p-polarized component and the s-polarized component.

[0094] The modulation pattern of the optical communication system 1 according to the above-described embodiment changes the polarization angle or DGD at a predetermined frequency, but is not limited to this. For example, a modulation pattern according to another embodiment may change the polarization angle at a constant angular velocity, with the angular velocity or rotation direction being different between the first modulation pattern and the second modulation pattern.

[0095] Furthermore, for example, in other embodiments, if the main signal does not undergo polarization modulation or polarization multiplexing, a modulation pattern that maintains a constant polarization angle or a rotation direction of circular polarization may be used. In this case, the polarization angle or rotation direction differs between the first modulation pattern and the second modulation pattern. Furthermore, for example, the optical communication system 1 according to other embodiments may superimpose a control signal on an optical signal by combining a first modulation pattern that performs predetermined polarization modulation with a second modulation pattern that does not perform polarization modulation.

[0096] In another embodiment, the main signal for quantum cryptography key distribution, etc., is not polarization-modulated with the control signal. In this case, the user device 40 transmits the control signal via a separate transmission means (e.g., a different wavelength in the same core, a transmission path with a split core, or another transmission means such as wireless communication). In this case, the control unit 15 of the optical distribution device 10 switches the control signal to be acquired depending on whether the control signal is received via the separate transmission means. For example, when the control signal is received via the separate transmission means, the control unit 15 performs processing according to the control signal and ignores the control signal output from the decoding unit 14. In this case, the control unit 15 also turns off the control of the polarization compensation unit 13 and passes the optical signal without compensation. This prevents the polarization modulation of the main signal from being canceled and the quantum cryptography from being observed. Furthermore, when the control signal is not received via the separate transmission means, the control unit 15 performs processing according to the control signal output from the decoding unit 14. Note that the control unit 15 may not monitor the reception of the control signal and may preset whether to transmit the control signal by polarization modulation of the main signal or via a separate transmission means.

[0097] The control signal according to the above-described embodiment is superimposed on the optical signal using binary modulation, but is not limited to this. For example, the control signal according to other embodiments may be superimposed on the optical signal using multi-level modulation. Furthermore, the control signal according to the above-described embodiment is differentially encoded, but is not limited to this. For example, the control signal may be modulated using a first modulation pattern when the bit of the control signal is "0" and a second modulation pattern when the bit of the control signal is "1". Furthermore, the control signal according to other embodiments may be superimposed using analog modulation.

[0098] In the above-described embodiment, the optical communication system 1 has the configuration shown in Fig. 1B. However, the configuration of the optical communication system 1 is not limited to this. For example, if the optical communication system 1 according to another embodiment has the configuration shown in Fig. 1A, the user equipment 40 (receiving-side user equipment 40) functioning as the control signal receiving device R includes a main signal receiving unit instead of the repeater unit 16 of the repeater 50 in Figs. 2, 4, 5, and 6. Furthermore, the splitter 11 may split an electrical signal that has been photoelectrically converted instead of splitting an optical signal as it is with an optical multiplexer / splitter, or may share a processing circuit for the electrical signal as shown in Fig. 8.

[0099] For example, when the optical communication system 1 according to another embodiment has the configuration shown in FIG. 1C, the relay device 50 functioning as the control signal multiplexing device M is configured to input the optical signal from the preceding device to the polarization modulation unit instead of the main signal modulation unit 41 of the user device 40 in FIGS. 2, 4, 5, and 6.

[0100] <Computer Configuration> FIG. 11 is a schematic block diagram illustrating the configuration of a computer according to at least one embodiment. The computer 70 includes a processor 71 , a main memory 73 , a storage 75 , and an interface 77 . The above-described optical distribution device 10, user device 40, and relay device 50 are implemented in a computer 70. The operations of the above-described processing units are stored in the form of a program in a storage 75. A processor 71 reads the program from the storage 75, loads it into a main memory 73, and executes the above-described processing in accordance with the program. The processor 71 also allocates storage areas in the main memory 73 corresponding to the above-described storage units in accordance with the program. Examples of the processor 71 include a CPU (Central Processing Unit), a GPU (Graphic Processing Unit), and a microprocessor.

[0101] The program may be for realizing some of the functions to be performed by the computer 70. For example, the program may be combined with other programs already stored in storage or implemented in other devices to perform the functions. In other embodiments, the computer 70 may include a custom LSI (Large Scale Integrated Circuit) such as a PLD (Programmable Logic Device) in addition to or instead of the above configuration. Examples of PLDs include PAL (Programmable Array Logic), GAL (Generic Array Logic), CPLD (Complex Programmable Logic Device), and FPGA (Field Programmable Gate Array). In this case, some or all of the functions realized by the processor 71 may be realized by the integrated circuit. Such an integrated circuit is also an example of a processor.

[0102] Examples of storage 75 include a magnetic disk, a magneto-optical disk, an optical disk, and a semiconductor memory. Storage 75 may be an internal medium directly connected to the bus of computer 70, or an external medium connected to computer 70 via interface 77 or a communication line. Furthermore, when this program is distributed to computer 70 via a communication line, computer 70 that receives the program may load the program into main memory 73 and execute the above-described processing. In at least one embodiment, storage 75 is a non-transitory tangible storage medium.

[0103] The program may also be a program for realizing some of the above-described functions. Furthermore, the program may be a so-called differential file (differential program) that realizes the above-described functions in combination with another program already stored in storage 75. [Explanation of symbols]

[0104] REFERENCE SIGNS LIST 1...optical communication system 10...optical distribution device 11...branch 12...detector 121...PBS 122...first optical receiver 123...second optical receiver 13...polarization compensation unit 14...decoding unit 15...control unit 16...relay unit 17...compensation amount derivation unit 18...DGD compensation unit 21...control signal generation unit 22...polarization modulation unit 23...optical SW 20...control device 30...optical communication network 40...user equipment 41...main signal modulation unit 42...control signal generation unit 44...polarization modulation unit 441...PBS 442...first quarter-wave plate 443...first reflecting mirror 444...second quarter-wave plate 445...second reflecting mirror 446...actuator Ax...first adder Ay...second adder Pxx...first FIR filter Pxy...second FIR filter Pyx...third FIR filter Pyy...fourth FIR filter Ux...first update unit Uy...second update unit 70...computer 71...processor 73...main memory 75...storage 77...interface

Claims

1. A modulation unit that performs polarization modulation on the optical signal that carries the main signal based on the control signal. Equipped with A control signal multiplexing device, wherein the polarization modulation has a frequency or fluctuation range that allows polarization compensation in a device to which the optical signal is transmitted.

2. A decoding unit that decodes a control signal based on the polarization state of an optical signal received from the control signal multiplexing device according to claim 1. A control signal receiving device comprising:

3. A decoding unit that decodes the control signal based on the polarization state of the optical signal that has been polarization-modulated by the control signal; a compensation unit that compensates for polarization due to the polarization modulation of the optical signal; A control signal receiving device comprising:

4. A decoding unit that decodes the control signal based on the polarization state of the optical signal that has been polarization-modulated by the control signal; a compensation unit that compensates for the polarization of the optical signal; a modulation unit that performs polarization modulation on the polarization-compensated optical signal with a new control signal; A control signal receiving device comprising:

5. A decoding unit that decodes the control signal based on the polarization state of the optical signal that has been polarization-modulated with the control signal; a modulation unit that compensates for the polarization caused by the polarization modulation of the optical signal and performs polarization modulation with a new control signal; A control signal receiving device comprising:

6. A decoding unit that decodes the control signal based on the polarization state of the optical signal that has been polarization-modulated by the control signal; A modulation section that performs polarization modulation using a new control signal. A control signal receiving device comprising:

7. polarization-modulating an optical signal carrying a main signal based on a control signal; A control signal multiplexing method, wherein the polarization modulation has a frequency or fluctuation range that allows polarization compensation in a device to which the optical signal is transmitted.

8. 2. A control signal receiving method comprising the step of decoding a control signal based on the polarization state of an optical signal received from the control signal multiplexer according to claim 1.

9. A step of decoding the control signal based on the polarization state of the optical signal polarization-modulated by the control signal; compensating for the polarization due to the polarization modulation of the optical signal; A control signal receiving method comprising:

10. A step of decoding the control signal based on the polarization state of the optical signal polarization-modulated by the control signal; compensating for the polarization of the optical signal; polarization modulating the polarization-compensated optical signal with a new control signal; A control signal receiving method comprising:

11. A step of decoding the control signal based on the polarization state of the optical signal polarization-modulated by the control signal; compensating for the polarization caused by the polarization modulation of the optical signal and performing polarization modulation with a new control signal; A control signal receiving method comprising:

12. A step of decoding the control signal based on the polarization state of the optical signal polarization-modulated by the control signal; polarization modulation with a new control signal; A control signal receiving method comprising:

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