Signal processing device, optical communication system, and optical communication method

Abstract

A signal processing device according to the present invention comprises: an adjustment unit to which can be connected an optical module that converts an optical signal received via an optical fiber into an electric signal, and which amplifies and / or attenuates a communication signal included in the electric signal output from the optical module connected to the signal processing device; and a control unit that acquires, from the optical module, reception level information indicating the reception strength of the optical signal received by the optical module, and that adjusts the gain of the adjustment unit on the basis of the acquired reception level information and the set value of the gain of the communication signal in an optical communication system.

Description

Signal processing device, optical communication system, and optical communication method

[0001] This application claims priority based on Japanese Patent Application No. 2023-15954, filed February 6, 2023, the disclosure of which is incorporated herein in its entirety by reference.

[0002] Patent Document 1 (JP-A-7-264139) discloses the following optical receiving device: That is, the optical receiving device includes an optical / electrical converter that receives an optical output of a constant level on which a high-frequency signal is superimposed via an optical cable of an unspecified length and converts the optical output into a high-frequency signal, and a variable gain amplifier that amplifies the output of the optical / electrical converter and outputs a high-frequency output signal of a specified level, a current detector that detects a current value of the optical / electrical converter that changes linearly in response to changes in the level of the received light of an unspecified level that is input to the optical / electrical converter, and a control circuit that provides a gain control signal to the variable gain amplifier such that the high-frequency output signal becomes a specified level for the detected current value obtained from the current detector, and is configured to compensate for loss proportional to the length of the optical cable so that the high-frequency output signal becomes the specified level regardless of the length of the optical cable.

[0003] Furthermore, Patent Document 2 (JP 2004-153758 A) discloses the following optical receiving device: That is, the optical receiving device converts an optical signal input via an optical fiber into an electrical signal, and includes photoelectric conversion means for converting the optical signal input via the optical fiber into an electrical signal, intensity detection means for detecting the intensity of the electrical signal converted by the photoelectric conversion means, and optical signal intensity adjustment means for adjusting the intensity of the optical signal input via the optical fiber so that the intensity of the electrical signal detected by the intensity detection means is constant.

[0004] Japanese Patent Laid-Open No. 7-264139 Japanese Patent Laid-Open No. 2004-153758

[0005] The signal processing device of the present disclosure is a signal processing device used in an optical communication system, and is connectable to an optical module that converts an optical signal received via an optical fiber into an electrical signal, and is equipped with an adjustment unit that performs at least one of amplifying and attenuating a communication signal included in the electrical signal output from the optical module connected to the signal processing device, and a control unit that acquires reception level information from the optical module that indicates the reception intensity of the optical signal received by the optical module connected to the signal processing device, and adjusts the gain of the adjustment unit based on the acquired reception level information and a set value of the gain of the communication signal in the optical communication system.

[0006] One aspect of the present disclosure may be realized not only as a signal processing device having such a characteristic processing unit, but also as a program for causing a computer to execute the steps of such a characteristic processing. Furthermore, one aspect of the present disclosure may be realized as a semiconductor integrated circuit that realizes part or all of the signal processing device, or as a system including the signal processing device.

[0007] FIG. 1 is a diagram illustrating a configuration of an optical communication system according to a first embodiment of the present disclosure. FIG. 2 is a diagram illustrating configurations of a master station device and a slave station device in the optical communication system according to the first embodiment of the present disclosure. FIG. 3 is a diagram illustrating an example of a sequence of gain adjustment of a variable ATT in the optical communication system according to the first embodiment of the present disclosure. FIG. 4 is a diagram illustrating configurations of a master station device and a slave station device in the optical communication system according to a second embodiment of the present disclosure. FIG. 5 is a diagram illustrating an example of a sequence of gain adjustment of a variable amplifier in a subsequent stage of an optical module in the optical communication system according to the second embodiment of the present disclosure. FIG. 6 is a diagram illustrating configurations of a master station device and a slave station device in the optical communication system according to a third embodiment of the present disclosure. FIG. 7 is a diagram illustrating an example of a sequence of gain adjustment of a variable amplifier in a previous stage of an optical module in the optical communication system according to the third embodiment of the present disclosure. FIG. 8 is a diagram illustrating configurations of a master station device and a slave station device in the optical communication system according to a fourth embodiment of the present disclosure. FIG. 9 is a diagram illustrating an example of distortion correction of an electrical signal in the optical communication system according to the fourth embodiment of the present disclosure. Fig. 10 is a diagram illustrating an example of a sequence of distortion correction in an optical communication system according to a fourth embodiment of the present disclosure. Fig. 11 is a diagram illustrating configurations of a master station device and a slave station device in an optical communication system according to a fifth embodiment of the present disclosure. Fig. 12 is a diagram illustrating an example of distortion correction of an electrical signal in the optical communication system according to the fifth embodiment of the present disclosure. Fig. 13 is a diagram illustrating an example of a sequence of distortion correction in the optical communication system according to the fifth embodiment of the present disclosure.

[0008] Conventionally, techniques have been developed to improve communication performance in optical communication systems.

[0009] [Problem to be Solved by the Present Disclosure] There is a need for a technology that goes beyond the technology described in Patent Documents 1 and 2 and enables the construction of an excellent optical communication system that compensates for optical loss according to the length of the optical fiber.

[0010] The present disclosure has been made to solve the above-mentioned problems, and its purpose is to provide a signal processing device, an optical communication system, and an optical communication method that are capable of constructing an excellent optical communication system that compensates for optical loss according to the length of the optical fiber.

[0011] Effect of the Present Disclosure According to the present disclosure, it is possible to construct an excellent optical communication system that compensates for optical loss according to the length of the optical fiber.

[0012] [Description of Embodiments of the Present Disclosure] First, the contents of the embodiments of the present disclosure will be listed and described.

[0013] (1) A signal processing device according to an embodiment of the present disclosure is a signal processing device used in an optical communication system, and is connectable to an optical module that converts an optical signal received via an optical fiber into an electrical signal. The signal processing device includes: an adjustment unit that performs at least one of amplification and attenuation of a communication signal included in the electrical signal output from the optical module connected to the signal processing device; and a control unit that acquires, from the optical module, reception level information indicating the reception intensity of the optical signal received by the optical module connected to the signal processing device, and adjusts the gain of the adjustment unit based on the acquired reception level information and a set value of the gain of the communication signal in the optical communication system.

[0014] In this way, the signal processing device is configured to acquire reception level information from the optical module and adjust the gain for amplifying or attenuating the communication signal contained in the electrical signal output from the optical module based on the reception level information and the set value of the gain of the communication signal. As a result, the signal processing device compensates for optical loss according to the length of the optical fiber while expanding the dynamic range of the communication signal without complicating the configuration of the optical module, compared to a configuration in which an adjustment unit and a control unit are located in the optical module, for example. Therefore, an excellent optical communication system that compensates for optical loss according to the length of the optical fiber can be constructed.

[0015] (2) In the above (1), the control unit may acquire transmission level information indicating the transmission strength of the optical signal in a device that transmits the optical signal to the optical fiber, and adjust the gain of the adjustment unit further based on the acquired transmission level information.

[0016] Such a configuration allows for more accurate compensation for optical losses in the optical fiber.

[0017] (3) In the above (2), the control unit may obtain the transmission level information from the electrical signal.

[0018] With this configuration, it is possible to obtain the transmission level information with a simple configuration without requiring a dedicated line for transmitting the transmission level information from the optical signal transmitter to the signal processor.

[0019] (4) In any of (1) to (3) above, the control unit may adjust the gain of the adjustment unit based on correspondence information that indicates the correspondence between the reception strength and the gain of the adjustment unit, the correspondence information being created based on the set value.

[0020] With this configuration, the gain of the adjustment unit can be easily adjusted according to the received intensity of the optical signal.

[0021] (5) An optical communication system according to an embodiment of the present disclosure includes a first optical communication device and a second optical communication device connected to the first optical communication device via an optical fiber, wherein the first optical communication device transmits a first optical signal including a communication signal to the second optical communication device, the second optical communication device converts the first optical signal received from the first optical communication device into an electrical signal and amplifies or attenuates the communication signal included in the electrical signal, and the second optical communication device adjusts the gain in amplifying or attenuating the communication signal based on the reception intensity of the first optical signal and a set value of the gain of the communication signal in the optical communication system.

[0022] In this manner, in the optical communication system, the second optical communication device adjusts the gain for amplifying or attenuating the communication signal included in the first optical signal based on the reception intensity of the first optical signal received from the first optical communication device and the set value of the gain of the communication signal in the optical communication system. This allows the optical communication system to compensate for optical loss according to the length of the optical fiber. Therefore, it is possible to construct an excellent optical communication system that compensates for optical loss according to the length of the optical fiber.

[0023] (6) In the above (5), the first optical communication device may generate a first control signal including transmission level information indicating the transmission intensity of the first optical signal, and transmit the first optical signal further including the generated first control signal to the second optical communication device, and the second optical communication device may acquire the transmission level information from the first control signal included in the received first optical signal, and adjust the gain in amplifying or attenuating the communication signal further based on the acquired transmission level information.

[0024] Such a configuration allows for more accurate compensation for optical losses in the optical fiber.

[0025] (7) In the above (5) or (6), the first optical communication device may generate the first optical signal by modulating the amplified or attenuated communication signal, the second optical communication device may generate a second control signal including OMI (Optical Modulation Index) information indicating an OMI of the received first optical signal, and transmit the generated second optical signal including the second control signal to the first optical communication device, and the first optical communication device may acquire the OMI information from the second control signal included in the received second optical signal, and adjust a gain in amplifying or attenuating the communication signal based on the acquired OMI information.

[0026] With this configuration, it is possible to compensate for individual variations in the EO conversion curve of the EO element that generates the first optical signal.

[0027] (8) In any of (5) to (7) above, the second optical communication device may acquire characteristic information indicating optical modulation characteristics in the first optical communication device, and correct the communication signal based on the acquired characteristic information.

[0028] With this configuration, in the second optical communication device, it is possible to compensate for the nonlinearity of the EO conversion curve in the EO element that generates the first optical signal.

[0029] (9) In any of (5) to (7) above, the first optical communication device may acquire characteristic information indicating optical modulation characteristics in the first optical communication device, correct the communication signal based on the acquired characteristic information, and generate the first optical signal by modulating the corrected communication signal.

[0030] With this configuration, in the first optical communication device, it is possible to compensate for the nonlinearity of the EO conversion curve in the EO element that generates the first optical signal.

[0031] (10) An optical communication method according to an embodiment of the present disclosure is an optical communication method in an optical communication system including a first optical communication device and a second optical communication device connected to the first optical communication device via an optical fiber, and includes the steps of: the first optical communication device transmitting a first optical signal including a communication signal to the second optical communication device; and the second optical communication device converting the first optical signal received from the first optical communication device into an electrical signal and amplifying or attenuating the communication signal included in the electrical signal, wherein in the step of the second optical communication device amplifying or attenuating the communication signal, the gain in amplifying or attenuating the communication signal is adjusted based on the reception intensity of the first optical signal and a set value of the gain of the communication signal in the optical communication system.

[0032] In this manner, the optical communication method is a method in which the second optical communication device adjusts the gain for amplifying or attenuating the communication signal contained in the first optical signal based on the reception intensity of the first optical signal received from the first optical communication device and the set value of the gain of the communication signal in the optical communication system. This compensates for optical loss according to the length of the optical fiber in the optical communication method. Therefore, it is possible to construct an excellent optical communication system that compensates for optical loss according to the length of the optical fiber.

[0033] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the drawings, identical or corresponding parts are designated by the same reference numerals, and their description will not be repeated. Furthermore, at least some of the embodiments described below may be combined in any manner.

[0034] First Embodiment [Configuration and Basic Operation] Fig. 1 is a diagram illustrating a configuration of an optical communication system according to a first embodiment of the present disclosure. Referring to Fig. 1, the optical communication system 301 includes a master station 111 and a slave station 211. The master station 111 and the slave station 211 are examples of a first optical communication device and an example of a second optical communication device. The master station 111 and the slave station 211 are connected to each other via an optical fiber 191. The optical communication system 301 may also include multiple slave station devices 211. In this case, for example, the multiple slave station devices 211 are connected to the master station 111 via a single optical fiber 191 and an optical coupler. For example, the optical communication system 301 is an analog Radio over Fiber (RoF) system.

[0035] The master station device 111 and the slave station device 211 transmit and receive optical signals including communication data via the optical fiber 191. Hereinafter, an optical signal transmitted from the slave station device 211 to the master station device 111 will also be referred to as an upstream optical signal, and an optical signal transmitted from the master station device 111 to the slave station device 211 will also be referred to as a downstream optical signal. The upstream optical signal and the downstream optical signal are examples of a first optical signal and an example of a second optical signal. The master station device 111 and the slave station device 211 may be connected to each other via two optical fibers 191. In this case, the master station device 111 and the slave station device 211 transmit and receive upstream optical signals via the first optical fiber 191 and downstream optical signals via the second optical fiber 191.

[0036] When the optical communication system 301 is applied to mobile wireless communication, for example, a TDD (Time Division Duplex) system is adopted for the mobile wireless communication. In this case, in the optical communication system 301, an upstream transmission period for transmitting communication data from the slave station device 211 to the master station device 111 and a downstream transmission period for transmitting communication data from the master station device 111 to the slave station device 211 are switched and alternately repeated.

[0037] More specifically, the master station device 111 receives an Orthogonal Frequency Division Multiplexing (OFDM) modulated analog signal including communication data from a base station device (not shown). The master station device 111 generates an RF (Radio Frequency) signal Srd by frequency converting the received analog signal. During a downstream transmission period, the master station device 111 transmits a downstream optical signal including the generated RF signal Srd to the slave station device 211 via the optical fiber 191. Note that the master station device 111 may be configured to receive the RF signal Srd from the base station device. The RF signal Srd is an example of a communication signal.

[0038] The slave station device 211 receives a downstream optical signal from the master station device 111 via the optical fiber 191. The slave station device 211 acquires an RF signal Srd from the received downstream optical signal and transmits the acquired RF signal Srd via an antenna (not shown). Note that the slave station device 211 may be configured to transmit a signal based on the acquired RF signal Srd to another device via a wired connection.

[0039] The slave station device 211 also receives an OFDM-modulated millimeter-wave RF signal Sru containing communication data via an antenna (not shown). During an upstream transmission period, the slave station device 211 transmits an upstream optical signal containing the received RF signal Sru to the master station device 111 via the optical fiber 191. Note that instead of receiving the RF signal Sru via an antenna, the slave station device 211 may be configured to receive a signal containing communication data via a wired line and generate the RF signal Sru based on the received signal. The RF signal Sru is an example of a communication signal.

[0040] The master station 111 receives an upstream optical signal from the slave station 211 via the optical fiber 191. The master station 111 acquires an RF signal Sru from the received upstream optical signal, and transmits a signal based on the acquired RF signal Sru to the base station.

[0041] 2 is a diagram illustrating the configurations of a master station device and a slave station device in an optical communication system according to a first embodiment of the present disclosure. Referring to FIG. 2, the master station device 111 includes a host board 101A, an optical module 201A, and a signal processing unit 121. The slave station device 211 includes a host board 101B, an optical module 201B, and an RF transceiver unit 221. Hereinafter, each of the host boards 101A and 101B will also be referred to as a host board 101, and each of the optical modules 201A and 201B will also be referred to as an optical module 201. The host board 101 is an example of a signal processing device used in the optical communication system 301.

[0042] The host board 101A includes an input connector 11A, an output connector 12A, a control unit 13A, a variable ATT (attenuator) 14A, an amplifier 15A, and a storage unit 16A. The host board 101B includes an input connector 11B, an output connector 12B, a control unit 13B, a variable ATT 14B, an amplifier 15B, and a storage unit 16B. Note that the host board 101A may not include the amplifier 15A, and the host board 101B may not include the amplifier 15B.

[0043] Hereinafter, each of the input connectors 11A and 11B will also be referred to as an input connector 11, each of the output connectors 12A and 12B will also be referred to as an output connector 12, each of the control units 13A and 13B will also be referred to as a control unit 13, each of the variable ATTs 14A and 14B will also be referred to as a variable ATT 14, each of the amplifiers 15A and 15B will also be referred to as an amplifier 15, and each of the storage units 16A and 16B will also be referred to as a storage unit 16. The variable ATT 14 is an example of an adjustment unit. The variable ATT 14 and the amplifier 15 may be differentially driven or single-ended driven. Part or all of the control unit 13 is realized, for example, by a processing circuit including one or more processors. The storage unit 16 is, for example, a non-volatile memory included in the processing circuit.

[0044] The optical module 201 includes an EO element that converts an electrical signal into an optical signal and an OE element that converts an optical signal into an electrical signal. The optical modules 201A and 201B are connected to each other via an optical fiber 191. For example, the optical module 201 is a small pluggable type module, such as an SFP (Small Form-Factor Pluggable). Note that the optical module 201 is not limited to an SFP, and may be a QSFP (Quad Small Form-Factor Pluggable) or an XFP (10 Gigabit Small Form-Factor Pluggable).

[0045] The optical module 201 receives an electrical signal via the input connector 11 on the host board 101 and converts the received electrical signal into an optical signal. The optical module 201 transmits the converted optical signal to the optical fiber 191. The optical module 201 also receives an optical signal via the optical fiber 191 and converts the received optical signal into an electrical signal.

[0046] The host board 101 can be connected to an optical module 201. In the optical communication system 301, an optical module 201A is connected to the host board 101A, and an optical module 201B is connected to the host board 101B. Note that a plurality of optical modules 201 may be connected to one host board 101.

[0047] In optical communication system 301, the optical module 201 can be made smaller by arranging the variable ATT 14 and amplifier 15 outside the optical module 201. Furthermore, since the thermal coupling between the EO element and the OE element and the variable ATT 14 and amplifier 15 can be reduced, the temperature rise of the variable ATT 14 and amplifier 15 can be suppressed.

[0048] (Downstream Communication) In the master station 111, the signal processing unit 121 receives an OFDM-modulated analog signal containing communication data from a base station (not shown). The signal processing unit 121 generates an RF signal Srd by frequency-converting the received analog signal. The signal processing unit 121 outputs the generated RF signal Srd to the host board 101A during a downstream transmission period. The signal processing unit 121 may be configured to receive the RF signal Srd from the base station and output the received RF signal Srd to the host board 101A. The signal processing unit 121 may also be configured to adjust the level of the signal received from the base station when the level of the signal received from the base station does not match the input level of the optical module 201A.

[0049] The optical module 201A receives the RF signal Srd from the signal processing unit 121 via the input connector 11A on the host board 101A, and generates a downstream optical signal with a wavelength λ1 by optically modulating the RF signal Srd, which is an electrical signal. The optical module 201A transmits the generated downstream optical signal to the optical fiber 191.

[0050] The optical module 201B in the slave station device 211 receives the downstream optical signal via the optical fiber 191, generates an electrical signal at a level corresponding to the intensity of the received downstream optical signal, and outputs the generated electrical signal, that is, an RF signal Srd, to the variable ATT 14B.

[0051] The variable ATT 14B attenuates the electrical signal output from the optical module 201B. More specifically, the variable ATT 14B attenuates the RF signal Srd received from the optical module 201B and outputs the attenuated RF signal Srd to the amplifier 15B.

[0052] The amplifier 15B amplifies the RF signal Srd received from the variable ATTB at a predetermined amplification factor, and outputs the amplified RF signal Srd to the RF transceiver unit 221 via the output connector 12B.

[0053] The RF transceiver 221 receives the RF signal Srd from the optical module 201B, amplifies the received RF signal Srd, and transmits the amplified RF signal Srd via an antenna (not shown).

[0054] In the slave station device 211, the RF transceiver 221 receives an OFDM-modulated millimeter-wave RF signal Sru containing communication data via an antenna (not shown). During an upstream transmission period, the RF transceiver 221 amplifies the received RF signal Sru and outputs the amplified RF signal Sru to the host board 101B.

[0055] The optical module 201B receives the RF signal Sru from the RF transceiver 221 via the input connector 11B on the host board 101B, and generates an upstream optical signal with a wavelength λ2 by optically modulating the RF signal Sru, which is an electrical signal. The optical module 201B transmits the generated upstream optical signal to the optical fiber 191.

[0056] The optical module 201A in the parent station 111 receives an upstream optical signal via the optical fiber 191, generates an electrical signal at a level corresponding to the intensity of the received upstream optical signal, and outputs the generated electrical signal, an RF signal Sru, to the variable ATT 14A.

[0057] The variable ATT 14A attenuates the electrical signal output from the optical module 201A. More specifically, the variable ATT 14A attenuates the RF signal Sru received from the optical module 201A, and outputs the attenuated RF signal Sru to the amplifier 15A.

[0058] The amplifier 15A amplifies the RF signal Sru received from the variable ATTA at a predetermined amplification factor, and outputs the amplified RF signal Sru to the signal processing unit 121 via the output connector 12A.

[0059] The signal processing unit 121 receives the RF signal Sru from the optical module 201A and transmits to the base station an analog signal obtained by frequency-converting, e.g., down-converting, the received RF signal Sru. The signal processing unit 121 may be configured to transmit the RF signal Sru received from the optical module 201A to the base station without frequency-converting it. The signal processing unit 121 may also be configured to adjust the level of the RF signal Sru received from the optical module 201A and transmit to the base station a signal obtained by frequency-converting the level-adjusted RF signal Sru or the level-adjusted RF signal Sru.

[0060] (Gain Adjustment of Variable ATT 14B) The slave station device 211 adjusts the gain for attenuation of the RF signal Srd based on the received intensity of the downstream optical signal and a set value SVd of the gain of the RF signal Srd in the optical communication system 301. Here, the set value SVd is a set value of the gain of the RF signal Srd received by the host board 101A and the RF signal Srd output by the host board 101B.

[0061] More specifically, the control unit 13B in the host board 101B acquires a current value C1d indicating the reception strength of a downstream optical signal received by the optical module 201B from the optical module 201B. The control unit 13B adjusts the gain of the variable ATT 14B based on the acquired current value C1d and the set value SVd, for example, at an adjustment timing according to a predetermined cycle. The current value C1d is an example of reception level information.

[0062] As an example, the optical module 201B includes a PD (Photodiode) that receives a downstream optical signal and outputs a current corresponding to the received intensity of the downstream optical signal. The optical module 201A holds a current value C1d that indicates the magnitude of the current output by the PD.

[0063] When the adjustment timing arrives, the control unit 13B in the host board 101B acquires the current value C1d from the optical module 201B.

[0064] For example, the storage unit 16B stores a gain setting table TS1d that is created based on a predetermined setting value SVd and indicates the correspondence relationship between the current value C1d and the gain of the variable ATT 14B. The gain setting table TS1d is an example of correspondence information.

[0065] The control unit 13B adjusts the gain of the variable ATT 14B based on the gain setting table TS1d in the storage unit 16B. More specifically, when the control unit 13B acquires the current value C1d, the control unit 13B refers to the gain setting table TS1d in the storage unit 16B to acquire the gain corresponding to the acquired current value C1d. Then, the control unit 13B sets the gain of the variable ATT 14B to the acquired gain.

[0066] (Gain Adjustment of Variable ATT 14A) The master station 111 adjusts the gain for attenuation of the RF signal Sru based on the received strength of the upstream optical signal and a set value SVu of the gain of the RF signal Sru in the optical communication system 301. Here, the set value SVu is a set value of the gain of the RF signal Sru received by the host board 101B and the RF signal Sru output by the host board 101A. The set value SVu may be the same as or different from the set value SVd.

[0067] More specifically, the control unit 13A in the host board 101A acquires a current value C1u indicating the reception strength of an upstream optical signal received by the optical module 201A from the optical module 201A. The control unit 13A adjusts the gain of the variable ATT 14A based on the acquired current value C1u and the set value SVu, for example, at an adjustment timing according to a predetermined cycle. The current value C1u is an example of reception level information.

[0068] As an example, the optical module 201A includes a PD that receives an upstream optical signal and outputs a current corresponding to the received intensity of the upstream optical signal. The optical module 201A holds a current value C1u that indicates the magnitude of the current output by the PD.

[0069] When the adjustment timing arrives, the control unit 13A on the host board 101A acquires the current value C1u from the optical module 201A.

[0070] For example, the storage unit 16A stores a gain setting table TS1u that is created based on a predetermined setting value SVu and indicates the correspondence relationship between the current value C1u and the gain of the variable ATT 14A. The gain setting table TS1u is an example of correspondence information.

[0071] The control unit 13A adjusts the gain of the variable ATT 14A based on the gain setting table TS1u in the storage unit 16A. More specifically, when the control unit 13A acquires the current value C1u, the control unit 13A refers to the gain setting table TS1u in the storage unit 16A to acquire the gain corresponding to the acquired current value C1u. Then, the control unit 13A sets the gain of the variable ATT 14A to the acquired gain.

[0072] [Operation Flow] FIG. 3 is a diagram illustrating an example of a sequence of gain adjustment of a variable ATT in the optical communication system according to the first embodiment of the present disclosure.

[0073] 3, first, during a downstream transmission period, the master station device 111 transmits a downstream optical signal including an RF signal Srd to the slave station device 211 via the optical fiber 191 (step S11).

[0074] Next, the slave station device 211 acquires a current value C1d indicating the reception intensity of the downstream optical signal received by the optical module 201B (step S12).

[0075] Next, the slave station device 211 adjusts the gain of the variable ATT 14B based on the acquired current value C1d and setting value SVd. More specifically, the control unit 13B in the host board 101B refers to the gain setting table TS1d in the storage unit 16B to acquire the gain corresponding to the current value C1d. Then, the control unit 13B sets the gain of the variable ATT 14B to the acquired gain (step S13).

[0076] Next, during the upstream transmission period, the slave station device 211 transmits an upstream optical signal including the RF signal Sru to the master station device 111 via the optical fiber 191 (step S14).

[0077] Next, the parent station 111 acquires a current value C1u indicating the reception intensity of the upstream optical signal received by the optical module 201A (step S15).

[0078] Next, the master station device 111 adjusts the gain of the variable ATT 14A based on the acquired current value C1u and setting value SVu. More specifically, the control unit 13A in the host board 101A refers to the gain setting table TS1u in the storage unit 16A to acquire the gain corresponding to the current value C1u. Then, the control unit 13A sets the gain of the variable ATT 14A to the acquired gain (step S16).

[0079] The order of steps S12 and S13 and steps S15 and S16 is not limited to the above, and they may be reversed or performed in parallel.

[0080] In the master station device 111 according to the first embodiment of the present disclosure, the control unit 13A in the host board 101A is configured to adjust the gain of the variable ATT 14A based on the gain setting table TS1u in the storage unit 16A, but this is not limiting. The control unit 13A may be configured to acquire a setting value SVu from the optical module 201A, calculate a target value for the gain of the variable ATT 14A based on the acquired setting value SVu and current value C1u, and set the gain of the variable ATT 14A to the calculated target value.

[0081] Similarly, the control unit 13B in the host board 101B of the slave station device 211 may be configured to acquire the setting value SVd from the optical module 201B, calculate a target value for the gain of the variable ATT 14B based on the acquired setting value SVd and the current value C1d, and set the gain of the variable ATT 14B to the calculated target value.

[0082] Furthermore, in the master station device 111 according to the first embodiment of the present disclosure, the host board 101A is configured to include the variable ATT 14A and the amplifier 15A, but this is not limited to this. The host board 101A may be configured to include a variable amplifier that amplifies the RF signal Sru, but not to include the variable ATT 14A or the amplifier 15A. In this case, the control unit 13A adjusts the gain of the variable amplifier based on the current value C1u and the set value SVu.

[0083] Similarly, the host board 101B of the slave station device 211 may be configured to include a variable amplifier that amplifies the RF signal Srd, but not include the variable ATT 14B or the amplifier 15B. In this case, the control unit 13A adjusts the gain of the variable amplifier based on the current value C1d and the set value SVd.

[0084] Although the optical communication system 301 according to the first embodiment of the present disclosure is an analog RoF system, the present disclosure is not limited to this. For example, the optical communication system 301 may be an IFoF (Intermediate Frequency over Fiber) system.

[0085] In this case, the signal processing unit 121 outputs an IF signal Srdif of, for example, several GHz to the host board 101A instead of the RF signal Srd. The optical module 201A receives the IF signal Srdif from the signal processing unit 121 via the input connector 11A on the host board 101A, generates a downstream optical signal with a wavelength λ1 obtained by optically modulating the IF signal Srdif, and transmits the generated downstream optical signal to the optical fiber 191. The IF signal Srdif is an example of a communication signal.

[0086] The optical module 201B in the slave station device 211 receives a downstream optical signal via the optical fiber 191, generates an IF signal Srdif at a level corresponding to the intensity of the received downstream optical signal, and outputs the generated IF signal Srdif to the variable ATT 14B. The variable ATT 14B attenuates the IF signal Srdif received from the optical module 201B and outputs the attenuated IF signal Srdif to the amplifier 15B. The amplifier 15B amplifies the IF signal Srdif received from the variable ATT 14B by a predetermined gain and outputs the amplified IF signal Srdif to the RF transceiver 221 via the output connector 12B. The RF transceiver 221 receives the IF signal Srdif from the optical module 201B, up-converts the received IF signal Srdif to generate an RF signal Srd in the millimeter wave band, and amplifies the generated RF signal Srd to transmit it via an antenna (not shown). The control unit 13B in the slave station device 211 adjusts the gain for attenuating the IF signal Srdif based on the reception intensity of the downstream optical signal and the set value SVd of the gain of the IF signal Srdif in the optical communication system 301 .

[0087] The RF transceiver 221 also down-converts the RF signal Sru to generate an IF signal Sruif of, for example, several GHz, and outputs the generated IF signal Sruif to the host board 101B. The optical module 201B receives the IF signal Sruif from the RF transceiver 221 via the input connector 11B on the host board 101B, generates an upstream optical signal with a wavelength λ2 by optically modulating the received IF signal Sruif, and transmits the generated upstream optical signal to the optical fiber 191. The IF signal Sruif is an example of a communication signal.

[0088] The optical module 201A in the parent station 111 receives an upstream optical signal via the optical fiber 191, generates an IF signal Sruif at a level corresponding to the intensity of the received upstream optical signal, and outputs the generated IF signal Sruif to the variable ATT 14A. The variable ATT 14A attenuates the IF signal Sruif received from the optical module 201A and outputs the attenuated IF signal Sruif to the amplifier 15A. The amplifier 15A amplifies the IF signal Sruif received from the variable ATT 14A by a predetermined gain and outputs the amplified IF signal Sruif to the signal processing unit 121 via the output connector 12A. The signal processing unit 121 receives the IF signal Sruif from the optical module 201A and transmits the received IF signal Sruif to the base station device. The control unit 13A in the master station 111 adjusts the gain in attenuation of the IF signal Sruif based on the received intensity of the upstream optical signal and the set value SVu of the gain of the IF signal Sruif in the optical communication system 301 .

[0089] Next, other embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals and their description will not be repeated.

[0090] Second Embodiment [Configuration and Basic Operation] This embodiment relates to an optical communication system 302 that adjusts the gain of an adjustment unit based additionally on the transmission intensity of an optical signal, as compared with the optical communication system 301 according to the first embodiment. Except for the contents described below, the optical communication system 302 is the same as the optical communication system 301 according to the first embodiment.

[0091] 4 is a diagram illustrating the configurations of a master station device and a slave station device in an optical communication system according to a second embodiment of the present disclosure. Compared to the optical communication system 301, the optical communication system 302 includes a master station device 112 instead of the master station device 111 and a slave station device 212 instead of the slave station device 211.

[0092] Compared to the master station device 111, the master station device 112 has a host board 102A instead of the host board 101A. Compared to the slave station device 211, the slave station device 212 has a host board 102B instead of the host board 101B. Hereinafter, each of the host boards 102A and 102B will also be referred to as a host board 102. The host board 102 is an example of a signal processing device used in the optical communication system 302.

[0093] Compared to host board 101A, host board 102A has a control unit 21A and a memory unit 25A instead of control unit 13A and memory unit 16A. Also, compared to host board 101A, host board 102A does not have variable ATT 14A and amplifier 15A, but has a multiplexing unit 22A, variable amplifier 23A, and separation unit 24A. Compared to host board 101B, host board 102B has a control unit 21B and a memory unit 25B instead of control unit 13B and memory unit 16B. Also, compared to host board 101B, host board 102B does not have variable ATT 14B and amplifier 15B, but has a multiplexing unit 22B, variable amplifier 23B, and separation unit 24B.

[0094] Hereinafter, each of the control units 21A and 21B will also be referred to as a control unit 21, each of the multiplexing units 22A and 22B will also be referred to as a multiplexing unit 22, each of the variable amplifiers 23A and 23B will also be referred to as a variable amplifier 23, each of the separation units 24A and 24B will also be referred to as a separation unit 24, and each of the storage units 25A and 25B will also be referred to as a storage unit 25. The variable amplifier 23 is an example of an adjustment unit. For example, the multiplexing unit 22 and the separation unit 24 are diplexers. Part or all of the control unit 21 is realized, for example, by a processing circuit including one or more processors. The storage unit 25 is, for example, a non-volatile memory included in the processing circuit.

[0095] Variable amplifier 23 amplifies the electrical signal output from optical module 201. More specifically, variable amplifier 23 amplifies the electrical signal received from optical module 201, and outputs the amplified electrical signal to separator 24. Controller 21 adjusts the gain of variable amplifier 23.

[0096] (Gain Adjustment of Variable Amplifier 23B) The master station device 112 generates a digital signal Sdd1 including a current value C2d indicating the transmission intensity of the downstream optical signal, and transmits a downstream optical signal further including the generated digital signal Sdd1 to the slave station device 212. For example, the master station device 112 transmits a downstream optical signal including the RF signal Srd and the digital signal Sdd1 to the slave station device 212 in accordance with AMCC (Auxiliary Management and Control Channel) technology. The current value C2d is an example of transmission level information. The digital signal Sdd1 is an example of a first control signal.

[0097] As an example, the optical module 201A includes a PD that outputs a current corresponding to the transmission intensity of the generated downstream optical signal. The optical module 201A holds a current value C2d that indicates the magnitude of the current output by the PD.

[0098] The control unit 21A in the host board 102A acquires the current value C2d from the optical module 201A when an adjustment timing according to a predetermined cycle arrives, for example, and generates a digital signal Sdd1 including the acquired current value C2d and outputs the generated digital signal Sdd1 to the multiplexing unit 22A.

[0099] The multiplexing unit 22A frequency-multiplexes the RF signal Srd received from the signal processing unit 121 via the input connector 11A and the digital signal Sdd1 received from the control unit 21A. The multiplexing unit 22A generates an electrical signal in which the RF signal Srd and the digital signal Sdd1 are frequency-multiplexed, and outputs the electrical signal to the optical module 201A.

[0100] The optical module 201 A generates a downstream optical signal with a wavelength of λ 1 by optically modulating the electrical signal received from the multiplexing section 22 A, and transmits the generated downstream optical signal to the optical fiber 191 .

[0101] The optical module 201B in the slave station 212 receives the downstream optical signal via the optical fiber 191, generates an electrical signal at a level corresponding to the intensity of the received downstream optical signal, and outputs the generated electrical signal to the variable amplifier 23B.

[0102] Variable amplifier 23B amplifies the electrical signal received from optical module 201B and outputs the amplified signal to demultiplexer 24B.

[0103] The separator 24B separates the RF signal Srd and the digital signal Sdd1 contained in the electrical signal received from the variable amplifier 23B, outputs the RF signal Srd to the RF transceiver 221 via the output connector 12B, and outputs the digital signal Sdd1 to the control unit 21B.

[0104] The slave station device 212 acquires the current value C2d from the digital signal Sdd1 included in the received downstream optical signal, and adjusts the gain in amplifying the RF signal Srd based on the acquired current value C2d. That is, the slave station device 212 receives a downstream optical signal including the RF signal Srd and the digital signal Sdd1, and adjusts the gain in amplifying the RF signal Srd based on the current value C2d acquired from the digital signal Sdd1.

[0105] More specifically, the control unit 21B in the host board 102B acquires the current value C2d from, for example, an electrical signal output from the optical module 201B. The control unit 21B adjusts the gain of the variable amplifier 23B further based on the acquired current value C2d.

[0106] Specifically, the control unit 21B obtains a current value C2d from the digital signal Sdd1 received from the demultiplexer 24B. The control unit 21B also obtains a current value C1d from the optical module 201B. The control unit 21B then calculates a differential current value Dd by subtracting the current value C1d indicating the reception strength of the downstream optical signal from the current value C2d indicating the transmission strength of the downstream optical signal.

[0107] For example, storage unit 25B stores a gain setting table TS2d that is created based on a predetermined setting value SVd and indicates the correspondence relationship between the differential current value Dd and the gain of variable amplifier 23B. Gain setting table TS2d is an example of correspondence information.

[0108] After calculating the differential current value Dd, the control unit 21B refers to the gain setting table TS2d in the storage unit 25B to obtain the gain corresponding to the calculated differential current value Dd. Then, the control unit 21B sets the gain of the variable amplifier 23B to the obtained gain.

[0109] (Gain Adjustment of Variable Amplifier 23A) The slave station device 212 generates a digital signal Sdu1 including a current value C2u indicating the transmission intensity of the upstream optical signal, and transmits an upstream optical signal further including the generated digital signal Sdu1 to the master station device 112. For example, the slave station device 212 transmits an upstream optical signal including the RF signal Sru and the digital signal Sdu1 to the master station device 112 according to the AMCC technique. The current value C2u is an example of transmission level information. The digital signal Sdu1 is an example of a first control signal.

[0110] As an example, the optical module 201B includes a PD that outputs a current corresponding to the transmission intensity of the generated upstream optical signal. The optical module 201B holds a current value C2u that indicates the magnitude of the current output by the PD.

[0111] The control unit 21B in the host board 102B acquires the current value C2u from the optical module 201B when an adjustment timing according to a predetermined cycle arrives, for example, and generates a digital signal Sdu1 including the acquired current value C2u and outputs the generated digital signal Sdu1 to the multiplexing unit 22B.

[0112] The multiplexing unit 22B frequency-multiplexes the RF signal Sru received from the RF transceiver unit 221 via the input connector 11B and the digital signal Sdu1 received from the control unit 21B. The multiplexing unit 22B generates an electrical signal in which the RF signal Sru and the digital signal Sdu1 are frequency-multiplexed, and outputs the electrical signal to the optical module 201B.

[0113] The optical module 201B generates an upstream optical signal with wavelength λ2 by optically modulating the electrical signal received from the multiplexing unit 22B, and transmits the generated upstream optical signal to the optical fiber 191.

[0114] The optical module 201A in the parent station 112 receives an upstream optical signal via the optical fiber 191, generates an electrical signal at a level corresponding to the intensity of the received upstream optical signal, and outputs the generated electrical signal to the variable amplifier 23A.

[0115] Variable amplifier 23A amplifies the electrical signal received from optical module 201A and outputs the amplified signal to demultiplexer 24A.

[0116] The separation unit 24A separates the RF signal Sru and the digital signal Sdu1 contained in the electrical signal received from the variable amplifier 23A, outputs the RF signal Sru to the signal processing unit 121 via the output connector 12A, and outputs the digital signal Sdu1 to the control unit 21A.

[0117] The master station device 112 acquires a current value C2u from the digital signal Sdu1 included in the received upstream optical signal, and adjusts the gain in amplifying the RF signal Sru based on the acquired current value C2u. That is, the master station device 112 receives an upstream optical signal including the RF signal Sru and the digital signal Sdu1, and adjusts the gain in amplifying the RF signal Sru based on the current value C2u acquired from the digital signal Sdu1.

[0118] More specifically, the control unit 21A in the host board 102A acquires the current value C2u from, for example, an electrical signal output from the optical module 201A. The control unit 21A adjusts the gain of the variable amplifier 23A further based on the acquired current value C2u.

[0119] Specifically, the control unit 21A obtains a current value C2u from the digital signal Sdu1 received from the demultiplexer 24A. The control unit 21A also obtains a current value C1u from the optical module 201A. The control unit 21A then calculates a differential current value Du by subtracting the current value C1u indicating the reception strength of the upstream optical signal from the current value C2u indicating the transmission strength of the upstream optical signal.

[0120] For example, the storage unit 25A stores a gain setting table TS2u that is created based on a predetermined setting value SVu and indicates the correspondence relationship between the differential current value Du and the gain of the variable amplifier 23A. The gain setting table TS2u is an example of correspondence information.

[0121] After calculating the differential current value Du, the control unit 21A refers to the gain setting table TS2u in the storage unit 25A to obtain a gain corresponding to the calculated differential current value Du. Then, the control unit 21A sets the gain of the variable amplifier 23A to the obtained gain.

[0122] [Operation Flow] FIG. 5 is a diagram illustrating an example of a sequence of gain adjustment of a variable amplifier at a subsequent stage of an optical module in an optical communication system according to the second embodiment of the present disclosure.

[0123] 5, first, during the downstream transmission period, the master station device 112 transmits a downstream optical signal including the RF signal Srd to the slave station device 212 via the optical fiber 191 (step S21).

[0124] During the upstream transmission period, the slave station device 212 transmits an upstream optical signal including the RF signal Sru to the master station device 112 via the optical fiber 191 (step S22).

[0125] Next, when the adjustment timing according to the predetermined cycle arrives, the master station 112 acquires a current value C2d indicating the transmission intensity of the downstream optical signal transmitted during the downstream transmission period (step S23).

[0126] Next, for example, in the next downstream transmission period, the parent station device 112 generates a digital signal Sdd1 including the current value C2d and transmits a downstream optical signal including the generated digital signal Sdd1 and the RF signal Srd to the child station device 212 via the optical fiber 191 (step S24).

[0127] Next, the slave station device 212 acquires the current value C2d from the digital signal Sdd1 included in the received downstream optical signal (step S25).

[0128] Next, the slave station device 212 acquires a current value C1d indicating the reception intensity of the downstream optical signal received by the optical module 201B (step S26).

[0129] Next, the slave station device 212 adjusts the gain of the variable amplifier 23B based on the current value C2d, the current value C1d, and the set value SVd. More specifically, the control unit 21B in the host board 102B calculates a differential current value Dd by subtracting the current value C1d from the current value C2d. The control unit 21B references the gain setting table TS2d in the storage unit 25B to obtain a gain corresponding to the calculated differential current value Dd. The control unit 21B then sets the gain of the variable amplifier 23B to the obtained gain (step S27).

[0130] Next, the slave station device 212 acquires a current value C2u indicating the transmission intensity of the upstream optical signal transmitted during the upstream transmission period (step S28).

[0131] Next, for example, in the next upstream transmission period, the slave station device 212 generates a digital signal Sdu1 including the current value C2u and transmits an upstream optical signal including the generated digital signal Sdu1 and the RF signal Sru to the master station device 112 via the optical fiber 191 (step S29).

[0132] Next, the parent station 112 obtains the current value C2u from the digital signal Sdu1 included in the received upstream optical signal (step S30).

[0133] Next, the parent station 112 acquires a current value C1u indicating the reception intensity of the upstream optical signal received by the optical module 201A (step S31).

[0134] Next, the master station equipment 112 adjusts the gain of the variable amplifier 23A based on the current values ​​C2u, C1u, and the setting value SVu. More specifically, the control unit 21A in the host board 102A calculates a differential current value Du by subtracting the current value C1u from the current value C2u. The control unit 21A references the gain setting table TS2u in the storage unit 25A to obtain a gain corresponding to the calculated differential current value Du. The control unit 21A then sets the gain of the variable amplifier 23A to the obtained gain (step S32).

[0135] The order of steps S23, S24, S25, S26, and S27 and steps S28, S29, S30, S31, and S32 is not limited to the above, and they may be reversed or performed in parallel.

[0136] In the master station device 112 according to the second embodiment of the present disclosure, the control unit 21A on the host board 101A is configured to obtain the current value C2u from the electrical signal output from the optical module 201B, but this is not limiting. For example, the control unit 21A may be configured to receive the digital signal Sdu1 from the slave station device 212 via a dedicated communication line and obtain the current value C2u from the received digital signal Sdu1.

[0137] Similarly, the control unit 21B on the host board 101B of the slave station equipment 212 may be configured to receive the digital signal Sdd1 from the master station equipment 112 via a dedicated communication line and obtain the current value C2d from the received digital signal Sdd1.

[0138] Furthermore, in the optical communication system 302 according to the second embodiment of the present disclosure, the master station device 112 is configured to generate a digital signal Sdd1 including a current value C2d, but this is not limiting. The master station device 112 may be configured to generate an analog signal Sad1 indicating the current value C2d instead of the digital signal Sdd1 and transmit a downstream optical signal including the RF signal Srd and the analog signal Sad1 to the slave station device 212. In this case, the slave station device 212 obtains the current value C2d from the analog signal Sad1 included in the received downstream optical signal and adjusts the gain in amplifying the RF signal Srd based on the obtained current value C2d. The analog signal Sad1 is an example of a first control signal.

[0139] Furthermore, in the optical communication system 302 according to the second embodiment of the present disclosure, the slave station device 212 is configured to generate a digital signal Sdu1 including a current value C2u, but this is not limiting. The slave station device 212 may be configured to generate an analog signal Sau1 indicating the current value C2u instead of the digital signal Sdu1 and transmit an upstream optical signal including the RF signal Sru and the analog signal Sau1 to the master station device 112. In this case, the master station device 112 obtains the current value C2u from the analog signal Sau1 included in the received upstream optical signal and adjusts the gain in amplifying the RF signal Sru based on the obtained current value C2u. The analog signal Sau1 is an example of a first control signal.

[0140] Next, other embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals and their description will not be repeated.

[0141] Third Embodiment [Configuration and Basic Operation] This embodiment relates to an optical communication system 303 that adjusts the gain in amplifying or attenuating an RF signal before optical modulation, as compared to the optical communication system 301 according to the first embodiment. Except for the contents described below, the optical communication system 303 is the same as the optical communication system 301 according to the first embodiment and the optical communication system 302 according to the second embodiment.

[0142] 6 is a diagram illustrating the configuration of a master station device and a slave station device in an optical communication system according to a third embodiment of the present disclosure. Compared to the optical communication system 302, the optical communication system 303 includes a master station device 113 instead of the master station device 112 and a slave station device 213 instead of the slave station device 212.

[0143] Compared to the master station device 112, the master station device 113 has a host board 103A instead of the host board 102A. Compared to the slave station device 212, the slave station device 213 has a host board 103B instead of the host board 102B. Hereinafter, each of the host boards 103A and 103B will also be referred to as a host board 103. The host board 103 is an example of a signal processing device used in the optical communication system 303.

[0144] Compared to host board 102A, host board 103A includes a control unit 31A and a storage unit 33A instead of control unit 21A and storage unit 25A, and further includes a variable amplifier 32A. Compared to host board 102B, host board 103B includes a control unit 31B and a storage unit 33B instead of control unit 21B and storage unit 25B, and further includes a variable amplifier 32B.

[0145] Hereinafter, each of control units 31A and 31B will also be referred to as control unit 31, each of variable amplifiers 32A and 32B will also be referred to as variable amplifier 32, and each of storage units 33A and 33B will also be referred to as storage unit 33. Part or all of control unit 31 is realized, for example, by a processing circuit including one or more processors. Storage unit 33 is, for example, a non-volatile memory included in the processing circuit.

[0146] The variable amplifier 32 receives the electrical signal from the multiplexer 22, amplifies the received electrical signal, and outputs the amplified electrical signal to the optical module 201. The controller 31 adjusts the gain of the variable amplifier 32.

[0147] (Gain Adjustment of Variable Amplifier 32A) When an adjustment timing according to a predetermined cycle arrives, for example, the control unit 31A on the host board 103A of the master station device 113 sets the gain of the variable amplifier 32A to a predetermined value.

[0148] Variable amplifier 32A amplifies the electrical signal received from multiplexer 22A at a predetermined amplification factor set by controller 31A, and outputs the amplified electrical signal to optical module 201A.

[0149] Optical module 201 A generates a downstream optical signal with wavelength λ 1 by optically modulating the electrical signal received from variable amplifier 32 A, and transmits the generated downstream optical signal to optical fiber 191 .

[0150] The slave station device 213 generates a digital signal Sdu2 including an OMI value Vd indicating the OMI of the received downstream optical signal, and transmits an upstream optical signal further including the generated digital signal Sdu2 to the master station device 113. The OMI value Vd is an example of OMI information. The digital signal Sdu2 is an example of a second control signal.

[0151] More specifically, the control unit 31B in the host board 103B acquires a current value C1d from the optical module 201B during a predetermined monitoring period, and calculates the optical power PWd of the downstream optical signal based on the acquired current value C1d and a predetermined conversion formula. Then, the control unit 31B calculates the OMI value Vd expressed by the following formula (1): Vd=(Pdmax-Pdave) / Pdave (1)

[0152] Here, Pdmax is the maximum value of the optical power PWd during the monitoring period, Pdave is the average value of the optical power PWd during the monitoring period, and the OMI value Vd is a value indicating the slope of the electrical-optical conversion curve of the optical module 201A in the master station 113.

[0153] The control unit 31B generates a digital signal Sdu2 including the calculated OMI value Vd, and outputs the generated digital signal Sdu2 to the multiplexing unit 22B.

[0154] The multiplexing unit 22B frequency-multiplexes the RF signal Sru received from the RF transceiver unit 221 via the input connector 11B and the digital signal Sdu2 received from the control unit 31B. The multiplexing unit 22B generates an electrical signal in which the RF signal Sru and the digital signal Sdu2 are frequency-multiplexed, and outputs the electrical signal to the variable amplifier 32B.

[0155] Variable amplifier 32B receives the electrical signal from multiplexer 22B, amplifies the received electrical signal, and outputs the amplified signal to optical module 201B.

[0156] Optical module 201B generates an upstream optical signal with wavelength λ2 by optically modulating the electrical signal received from variable amplifier 32B, and transmits the generated upstream optical signal to optical fiber 191.

[0157] The optical module 201A in the parent station 113 receives an upstream optical signal via the optical fiber 191, generates an electrical signal at a level corresponding to the intensity of the received upstream optical signal, and outputs the generated electrical signal to the variable amplifier 23A.

[0158] Variable amplifier 23A amplifies the electrical signal received from optical module 201A and outputs the amplified signal to demultiplexer 24A.

[0159] The separation unit 24A separates the RF signal Sru and the digital signal Sdu2 contained in the electrical signal received from the variable amplifier 23A, outputs the RF signal Sru to the signal processing unit 121 via the output connector 12A, and outputs the digital signal Sdu2 to the control unit 31A.

[0160] The master station 113 acquires the OMI value Vd from the digital signal Sdu2 included in the received upstream optical signal, and adjusts the gain in amplifying the RF signal Srd based on the acquired OMI value Vd.

[0161] More specifically, the control unit 31A acquires the OMI value Vd from the digital signal Sdu2 received from the demultiplexer 24A. The control unit 31A calculates a differential OMI value Vdd by subtracting the OMI value Vd from a preset target value Vtd of the downstream optical signal OMI.

[0162] For example, the storage unit 33A stores a gain setting table TS3d that indicates the correspondence between the differential OMI value Vdd and the gain of the variable amplifier 32A.

[0163] After calculating the differential OMI value Vdd, the control unit 31A refers to the gain setting table TS3d in the storage unit 33A to obtain a gain corresponding to the calculated differential OMI value Vdd, and then sets the gain of the variable amplifier 32A to the obtained gain.

[0164] For example, in optical communication system 303, gain adjustment of variable amplifier 32A is repeated until the differential OMI value Vdd calculated by control unit 31A becomes equal to or less than a predetermined value, and when the differential OMI value Vdd calculated by control unit 31A becomes equal to or less than the predetermined value, gain adjustment of variable amplifier 23A is performed using the procedure described above.

[0165] (Gain Adjustment of Variable Amplifier 32B) When an adjustment timing according to a predetermined cycle arrives, for example, the control unit 31B on the host board 103B of the slave station equipment unit 213 sets the gain of the variable amplifier 32B to a predetermined value.

[0166] Variable amplifier 32B amplifies the electrical signal received from multiplexer 22B at a predetermined amplification factor set by controller 31B, and outputs the amplified electrical signal to optical module 201B.

[0167] Optical module 201B generates an upstream optical signal with wavelength λ2 by optically modulating the electrical signal received from variable amplifier 32B, and transmits the generated upstream optical signal to optical fiber 191.

[0168] The parent station device 113 generates a digital signal Sdd2 including an OMI value Vu indicating the OMI of the received upstream optical signal, and transmits a downstream optical signal including the generated digital signal Sdd2 to the child station device 213. The OMI value Vu is an example of OMI information. The digital signal Sdd2 is an example of a second control signal.

[0169] More specifically, the control unit 31A in the host board 103A acquires a current value C1u from the optical module 201A during a predetermined monitoring period, and calculates the optical power PWu of the downstream optical signal based on the acquired current value C1u and a predetermined conversion formula. Then, the control unit 31A calculates the OMI value Vu expressed by the following formula (2): Vu=(Pumax-Puave) / Puave (2)

[0170] Here, Pumax is the maximum value of the optical power PWu during the monitoring period, Puave is the average value of the optical power PWu during the monitoring period, and the OMI value Vu is a value indicating the slope of the electrical-optical conversion curve of the optical module 201B in the slave station equipment 213.

[0171] The control unit 31A generates a digital signal Sdd2 including the calculated OMI value Vu, and outputs the generated digital signal Sdd2 to the multiplexing unit 22A.

[0172] The multiplexing unit 22A frequency-multiplexes the RF signal Srd received from the signal processing unit 121 via the input connector 11A and the digital signal Sdd2 received from the control unit 31A. The multiplexing unit 22A generates an electrical signal in which the RF signal Srd and the digital signal Sdd2 are frequency-multiplexed, and outputs the electrical signal to the variable amplifier 32A.

[0173] Variable amplifier 32A receives the electrical signal from multiplexing section 22A, amplifies the received electrical signal, and outputs the amplified signal to optical module 201A.

[0174] The optical module 201 A generates a downstream optical signal with a wavelength of λ 1 by optically modulating the electrical signal received from the multiplexing section 22 A, and transmits the generated downstream optical signal to the optical fiber 191 .

[0175] The optical module 201B in the slave station 213 receives the downstream optical signal via the optical fiber 191, generates an electrical signal at a level corresponding to the intensity of the received downstream optical signal, and outputs the generated electrical signal to the variable amplifier 23B.

[0176] Variable amplifier 23B amplifies the electrical signal received from optical module 201B and outputs the amplified signal to demultiplexer 24B.

[0177] The separator 24B separates the RF signal Srd and the digital signal Sdd2 contained in the electrical signal received from the variable amplifier 23B, outputs the RF signal Srd to the RF transceiver 221 via the output connector 12B, and outputs the digital signal Sdd2 to the control unit 31B.

[0178] The slave station device 213 acquires the OMI value Vu from the digital signal Sdd2 included in the received downstream optical signal, and adjusts the gain in amplifying the RF signal Sru based on the acquired OMI value Vu.

[0179] More specifically, the control unit 31B acquires the OMI value Vu from the digital signal Sdd2 received from the demultiplexer 24B. The control unit 31B calculates a differential OMI value Vdu by subtracting the OMI value Vu from a preset target value Vtu of the OMI of the upstream optical signal.

[0180] For example, the storage unit 33B stores a gain setting table TS3u that indicates the correspondence between the difference OMI value Vdu and the gain of the variable amplifier 32B.

[0181] After calculating the differential OMI value Vdu, the control unit 31B refers to the gain setting table TS3u in the storage unit 33B to obtain a gain corresponding to the calculated differential OMI value Vdu, and then sets the gain of the variable amplifier 32B to the obtained gain.

[0182] For example, in optical communication system 303, gain adjustment of variable amplifier 32B is repeated until the differential OMI value Vdu calculated by control unit 31B becomes equal to or less than a predetermined value, and when the differential OMI value Vdu calculated by control unit 31B becomes equal to or less than the predetermined value, gain adjustment of variable amplifier 23B is performed using the procedure described above.

[0183] [Operation Flow] FIG. 7 is a diagram illustrating an example of a sequence of gain adjustment of a variable amplifier in a front stage of an optical module in an optical communication system according to the third embodiment of the present disclosure.

[0184] 7, first, the master station device 113 transmits a downstream optical signal to the slave station device 213 via the optical fiber 191 during a downstream transmission period (step S41).

[0185] Next, the slave station device 213 calculates an OMI value Vd indicating the OMI of the received downstream optical signal (step S42).

[0186] Next, during the upstream transmission period, the slave station device 213 generates a digital signal Sdu2 including the OMI value Vd, and transmits an upstream optical signal including the generated digital signal Sdu2 and the RF signal Sru to the master station device 113 via the optical fiber 191 (step S43).

[0187] Next, the parent station 113 acquires the OMI value Vd from the digital signal Sdu2 included in the received upstream optical signal (step S44).

[0188] Next, the master station equipment 113 adjusts the gain of the variable amplifier 32A based on the OMI value Vd. More specifically, the control unit 31A in the host board 103A calculates a differential OMI value Vdd by subtracting the OMI value Vd from the target value Vtd. The control unit 31A references the gain setting table TS3d in the storage unit 33A to obtain a gain corresponding to the calculated differential OMI value Vdd. The control unit 31A then sets the gain of the variable amplifier 32A to the obtained gain (step S45).

[0189] Next, the parent station 113 calculates an OMI value Vu indicating the OMI of the received upstream optical signal (step S46).

[0190] Next, during the downstream transmission period, the parent station device 113 generates a digital signal Sdd2 including the OMI value Vu, and transmits a downstream optical signal including the generated digital signal Sdd2 and the RF signal Srd to the child station device 213 via the optical fiber 191 (step S47).

[0191] Next, the slave station device 213 acquires the OMI value Vu from the digital signal Sdd2 included in the received downstream optical signal (step S48).

[0192] Next, the slave station equipment 213 adjusts the gain of the variable amplifier 32B based on the OMI value Vu. More specifically, the control unit 31B in the host board 103B calculates a differential OMI value Vdu by subtracting the OMI value Vu from the target value Vtu. The control unit 31B references the gain setting table TS3u in the storage unit 33B to obtain a gain corresponding to the calculated differential OMI value Vdu. The control unit 31B then sets the gain of the variable amplifier 32B to the obtained gain (step S49).

[0193] The order of steps S42, S43, S44, and S45 and steps S46, S47, S48, and S49 is not limited to the above, and they may be reversed or performed in parallel.

[0194] Furthermore, in the optical communication system 303 according to the third embodiment of the present disclosure, the slave station device 213 is configured to generate the digital signal Sdu2 including the OMI value Vd, but this is not limited thereto. The slave station device 213 may be configured to generate an analog signal Sau2 indicating the OMI value Vd instead of the digital signal Sdu2 and transmit an upstream optical signal including the RF signal Sru and the analog signal Sau2 to the master station device 113. In this case, the master station device 113 obtains the OMI value Vd from the analog signal Sau2 included in the received upstream optical signal and adjusts the gain in amplifying the RF signal Srd based on the obtained OMI value Vd. The analog signal Sau2 is an example of a second control signal.

[0195] Furthermore, in the optical communication system 303 according to the third embodiment of the present disclosure, the master station 113 is configured to generate the digital signal Sdd2 including the OMI value Vu, but this is not limiting. The master station 113 may be configured to generate an analog signal Sad2 indicating the OMI value Vu instead of the digital signal Sdd2 and transmit a downstream optical signal including the RF signal Srd and the analog signal Sad2 to the slave station 213. In this case, the slave station 213 obtains the OMI value Vu from the analog signal Sad2 included in the received downstream optical signal and adjusts the gain in amplifying the RF signal Sru based on the obtained OMI value Vu. The analog signal Sad2 is an example of a second control signal.

[0196] Next, other embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals and their description will not be repeated.

[0197] Fourth Embodiment [Configuration and Basic Operation] This embodiment relates to an optical communication system 304 that corrects an electrical signal output from an optical module 201, as compared with the optical communication system 301 according to the first embodiment. Except for the contents described below, the optical communication system 304 is the same as the optical communication system 301 according to the first embodiment, the optical communication system 302 according to the second embodiment, and the optical communication system 303 according to the third embodiment.

[0198] 8 is a diagram illustrating the configurations of a master station device and a slave station device in an optical communication system according to a fourth embodiment of the present disclosure. Compared to the optical communication system 302, the optical communication system 304 includes a master station device 114 instead of the master station device 112 and a slave station device 214 instead of the slave station device 212.

[0199] Compared to the master station device 112, the master station device 114 has a host board 104A instead of the host board 102A. Compared to the slave station device 212, the slave station device 214 has a host board 104B instead of the host board 102B. Hereinafter, each of the host boards 104A and 104B will also be referred to as a host board 104. The host board 104 is an example of a signal processing device used in the optical communication system 304.

[0200] Compared to host board 102A, host board 104A includes a control unit 41A and a storage unit 43A instead of control unit 21A and storage unit 25A, and further includes a correction unit 42A. Compared to host board 102B, host board 104B includes a control unit 41B and a storage unit 43B instead of control unit 21B and storage unit 25B, and further includes a correction unit 42B.

[0201] Hereinafter, each of the control units 41A and 41B will also be referred to as a control unit 41, each of the correction units 42A and 42B will also be referred to as a correction unit 42, and each of the storage units 43A and 43B will also be referred to as a storage unit 43. Part or all of the control unit 41 is realized, for example, by a processing circuit including one or more processors. The storage unit 43 is, for example, a non-volatile memory included in the processing circuit.

[0202] Correction unit 42 corrects the analog electrical signal received from variable amplifier 23. For example, in an initial state, correction unit 42 outputs the electrical signal received from variable amplifier 23 to separation unit 24 without correcting it. When correction unit 42 receives a correction start instruction from control unit 41, it starts correcting the electrical signal received from variable amplifier 23 and outputs the corrected electrical signal to separation unit 24.

[0203] (Correction of RF Signal Srd) The slave station device 214 acquires harmonic distortion HDd that indicates the optical modulation characteristics of the master station device 114, and corrects the RF signal Srd based on the acquired harmonic distortion HDd.

[0204] More specifically, the control unit 41B in the host board 104B calculates the harmonic distortion HDd of the electrical signal output from the optical module 201B. The harmonic distortion HDd is a value that indicates the nonlinearity of the electrical-to-optical conversion curve of the optical module 201A in the master station 114. The harmonic distortion HDd is an example of characteristic information.

[0205] For example, the storage unit 43B stores a correction table TCd that indicates the correspondence between harmonic distortion HDd and correction coefficient Cd.

[0206] After calculating the harmonic distortion HDd, the control unit 41B refers to the correction table TCd in the storage unit 43B to obtain a correction coefficient Cd corresponding to the calculated harmonic distortion HDd, and then outputs a correction start instruction including the obtained correction coefficient Cd to the correction unit 42B.

[0207] Correction unit 42B receives a correction start instruction from control unit 41B and stores correction coefficient Cd included in the received correction start instruction. Correction unit 42B uses this correction coefficient Cd to correct distortion in the electrical signal received from variable amplifier 23B.

[0208] 9 is a diagram illustrating an example of distortion correction of an electrical signal in an optical communication system according to a fourth embodiment of the present disclosure. In FIG. 9, the vertical axis represents the amplitude [V] of the electrical signal, and the horizontal axis represents time [t]. The dashed line in FIG. 9 indicates the waveform of the electrical signal output from variable amplifier 23B to correction unit 42B. The solid line in FIG. 9 indicates the waveform of the electrical signal after correction by correction unit 42B.

[0209] Referring to FIG. 9, the electrical signal output from optical module 201B has a waveform with a lower amplitude peak due to the nonlinearity of the electrical-to-optical conversion curve of optical module 201A.

[0210] Correction unit 42B corrects distortion of the electrical signal received from variable amplifier 23A by multiplying amplitude values ​​that are greater than predetermined threshold value THV2 and amplitude values ​​that are less than predetermined threshold value THV1 by a correction coefficient Cd that is equal to or greater than 1. Correction unit 42B outputs the distortion-corrected electrical signal to separation unit 24B.

[0211] For example, in the optical communication system 304, after the correction unit 42B starts the distortion correction, the gain of the variable amplifier 23B is adjusted according to the above-described procedure.

[0212] (Correction of RF Signal Sru) Referring again to FIG. 8, the master station device 114 acquires harmonic distortion HDu indicating the optical modulation characteristics of the slave station device 214, and corrects the RF signal Sru based on the acquired harmonic distortion HDu.

[0213] More specifically, the control unit 41A on the host board 104A calculates the harmonic distortion HDu of the electrical signal output from the optical module 201A. The harmonic distortion HDu is a value that indicates the nonlinearity of the electrical-to-optical conversion curve of the optical module 201B in the slave station equipment 214. The harmonic distortion HDu is an example of characteristic information.

[0214] For example, the storage unit 43A stores a correction table TCu that indicates the correspondence between harmonic distortion HDu and correction coefficient Cu.

[0215] After calculating the harmonic distortion HDu, the control unit 41A refers to the correction table TCu in the storage unit 43A to obtain a correction coefficient Cu corresponding to the calculated harmonic distortion HDu, and then outputs a correction start instruction including the obtained correction coefficient Cu to the correction unit 42A.

[0216] Correction unit 42A receives a correction start instruction from control unit 41A and stores the correction coefficient Cu included in the received correction start instruction. Correction unit 42A uses the correction coefficient Cu to correct distortion in the electrical signal received from variable amplifier 23A.

[0217] More specifically, corrector 42A corrects distortion of the electrical signal received from variable amplifier 23A by multiplying amplitude values ​​greater than threshold value THV2 and amplitude values ​​less than threshold value THV1 by a correction coefficient Cu, which is equal to or greater than 1. Corrector 42A outputs the distortion-corrected electrical signal to separator 24A.

[0218] For example, in the optical communication system 304, after the correction unit 42A starts the distortion correction, the gain of the variable amplifier 23A is adjusted according to the procedure described above.

[0219] [Operation Flow] FIG. 10 is a diagram illustrating an example of a sequence of distortion correction in the optical communication system according to the fourth embodiment of the present disclosure.

[0220] 10, first, the master station device 114 transmits a downstream optical signal to the slave station device 214 via the optical fiber 191 during a downstream transmission period (step S51).

[0221] Next, the slave station device 214 calculates the harmonic distortion HDd of the electrical signal output from the optical module 201B (step S52).

[0222] Next, the slave station device 214 refers to the correction table TCd in the storage unit 43B to obtain the correction coefficient Cd corresponding to the calculated harmonic distortion HDd (step S53).

[0223] Next, the slave station device 214 starts distortion correction using the correction coefficient Cd. More specifically, the correction unit 42B on the host board 104B starts distortion correction of the electrical signal received from the variable amplifier 23B using the correction coefficient Cd (step S54).

[0224] Next, during the upstream transmission period, the slave station device 214 transmits the upstream optical signal to the master station device 114 via the optical fiber 191 (step S55).

[0225] Next, the master station 114 calculates the harmonic distortion HDu of the electrical signal output from the optical module 201A (step S56).

[0226] Next, the master station device 114 refers to the correction table TCu in the storage unit 43A to obtain the correction coefficient Cu corresponding to the calculated harmonic distortion HDu (step S57).

[0227] Next, the master station 114 starts distortion correction using the correction coefficient Cu. More specifically, the correction unit 42A on the host board 104A starts distortion correction of the electrical signal received from the variable amplifier 23A using the correction coefficient Cu (step S58).

[0228] The order of steps S52, S53, S54 and steps S56, S57, S58 is not limited to the above, and they may be reversed or performed in parallel.

[0229] In the master station device 114 according to the fourth embodiment of the present disclosure, the correction unit 42A on the host board 104A is configured to correct distortion of the analog electrical signal received from the variable amplifier 23A, but this is not limiting. The correction unit 42A may also be configured to correct distortion of the waveform indicated by the electrical signal output from the variable amplifier 23A and converted into a digital signal.

[0230] Similarly, the correction unit 42B on the host board 104B of the slave station equipment unit 214 may be configured to correct distortion in the waveform indicated by the electrical signal output from the variable amplifier 23B and converted into a digital signal.

[0231] Fifth Embodiment [Configuration and Basic Operation] This embodiment relates to an optical communication system 305 that corrects an electrical signal output to an optical module 201, as compared with the optical communication system 301 according to the first embodiment. Except for the contents described below, the optical communication system 305 is the same as the optical communication system 301 according to the first embodiment, the optical communication system 302 according to the second embodiment, the optical communication system 303 according to the third embodiment, and the optical communication system 304 according to the fourth embodiment.

[0232] 11 is a diagram illustrating the configurations of a master station device and a slave station device in an optical communication system according to a fifth embodiment of the present disclosure. Compared to the optical communication system 304, the optical communication system 305 includes a master station device 115 instead of the master station device 114 and a slave station device 215 instead of the slave station device 214.

[0233] Compared to the master station device 114, the master station device 115 has a host board 105A instead of the host board 104A. Compared to the slave station device 214, the slave station device 215 has a host board 105B instead of the host board 104B. Hereinafter, each of the host boards 105A and 105B will also be referred to as a host board 105. The host board 105 is an example of a signal processing device used in the optical communication system 305.

[0234] Compared to the host board 104A, the host board 105A includes a control unit 51A and a correction unit 52A instead of the control unit 41A and the correction unit 42A. Compared to the host board 104B, the host board 105B includes a control unit 51B and a correction unit 52B instead of the control unit 41B and the correction unit 42B.

[0235] Hereinafter, each of the control units 51A and 51B will also be referred to as a control unit 51, and each of the correction units 52A and 52B will also be referred to as a correction unit 52. Part or all of the control unit 51 is realized, for example, by a processing circuit including one or more processors.

[0236] The correcting unit 52 corrects the electrical signal received from the multiplexing unit 22. For example, in an initial state, the correcting unit 52 outputs the electrical signal received from the multiplexing unit 22 to the optical module 201 without correcting it. When the correcting unit 52 receives a correction start instruction from the control unit 51, it starts correcting the electrical signal received from the multiplexing unit 22 and outputs the corrected electrical signal to the optical module 201.

[0237] (Correction of RF signal Srd) The master station 115 acquires harmonic distortion HDd that indicates the optical modulation characteristics of the master station 115, and corrects the RF signal Srd based on the acquired harmonic distortion HDd. The master station 115 generates a downstream optical signal by modulating the corrected RF signal Srd.

[0238] More specifically, the control unit 51B in the host board 105B acquires the correction coefficient Cd according to the procedure described above, generates a digital signal Sdu3 including the acquired correction coefficient Cd, and outputs the generated digital signal Sdu3 to the multiplexing unit 22B.

[0239] The multiplexing unit 22B frequency-multiplexes the RF signal Sru received from the RF transceiver unit 221 via the input connector 11B and the digital signal Sdu3 received from the control unit 51B. The multiplexing unit 22B generates an electrical signal in which the RF signal Sru and the digital signal Sdu3 are frequency-multiplexed, and outputs the electrical signal to the correction unit 52B.

[0240] The correcting section 52B receives the electrical signal from the multiplexing section 22B and outputs the received electrical signal to the optical module 201B without correcting it.

[0241] The optical module 201B generates an upstream optical signal with wavelength λ2 by optically modulating the electrical signal received from the correcting unit 52B, and transmits the generated upstream optical signal to the optical fiber 191.

[0242] The optical module 201A in the parent station 115 receives an upstream optical signal via the optical fiber 191, generates an electrical signal at a level corresponding to the intensity of the received upstream optical signal, and outputs the generated electrical signal to the variable amplifier 23A.

[0243] Variable amplifier 23A amplifies the electrical signal received from optical module 201A and outputs the amplified signal to demultiplexer 24A.

[0244] The separation unit 24A separates the RF signal Sru and the digital signal Sdu3 contained in the electrical signal received from the variable amplifier 23A, outputs the RF signal Sru to the signal processing unit 121 via the output connector 12A, and outputs the digital signal Sdu3 to the control unit 51A.

[0245] The control unit 51A obtains the correction coefficient Cd from the digital signal Sdu3 received from the separation unit 24A, and then outputs a correction start instruction including the obtained correction coefficient Cd to the correction unit 52A.

[0246] The corrector 52A receives a correction start instruction from the controller 51A and stores the correction coefficient Cd included in the received correction start instruction. The corrector 52A uses the correction coefficient Cd to correct distortion in the electrical signal received from the multiplexer 22A.

[0247] Fig. 12 is a diagram illustrating an example of distortion correction of an electrical signal in an optical communication system according to a fifth embodiment of the present disclosure. In Fig. 12, the vertical axis represents the amplitude [V] of the electrical signal, and the horizontal axis represents time [t]. The dashed line in Fig. 12 indicates the waveform of the electrical signal output from the multiplexing unit 22A to the correcting unit 52A. The solid line in Fig. 12 indicates the waveform of the electrical signal after correction by the correcting unit 52A.

[0248] 12 , the corrector 52A corrects distortion of the electrical signal received from the multiplexer 22A by multiplying amplitude values ​​greater than a predetermined threshold THV4 and amplitude values ​​less than a predetermined threshold THV3 by a correction coefficient Cd, which is equal to or greater than 1. The corrector 52A outputs the distortion-corrected electrical signal to the optical module 201A.

[0249] For example, in the optical communication system 305, after the correction unit 52A starts the distortion correction, the gain of the variable amplifier 23A is adjusted according to the above-described procedure.

[0250] 11 , the slave station device 215 acquires harmonic distortion HDu, which indicates the optical modulation characteristics of the slave station device 215, and corrects the RF signal Sru based on the acquired harmonic distortion HDu. The slave station device 215 generates an upstream optical signal by modulating the corrected RF signal Sru.

[0251] More specifically, the control unit 51A in the host board 105A acquires the correction coefficient Cu according to the above-described procedure, generates a digital signal Sdd3 including the acquired correction coefficient Cu, and outputs the generated digital signal Sdd3 to the multiplexing unit 22A.

[0252] The multiplexing unit 22A frequency-multiplexes the RF signal Srd received from the signal processing unit 121 via the input connector 11A and the digital signal Sdd3 received from the control unit 51A. The multiplexing unit 22A generates an electrical signal in which the RF signal Srd and the digital signal Sdd3 are frequency-multiplexed, and outputs the electrical signal to the correction unit 52A.

[0253] The correcting section 52A receives the electrical signal from the multiplexing section 22A, corrects distortion of the received electrical signal, and outputs the corrected electrical signal to the optical module 201B.

[0254] The optical module 201 A generates a downstream optical signal with a wavelength of λ 1 by optically modulating the electrical signal received from the correcting unit 52 A, and transmits the generated downstream optical signal to the optical fiber 191 .

[0255] The optical module 201B in the slave station 215 receives the downstream optical signal via the optical fiber 191, generates an electrical signal at a level corresponding to the intensity of the received downstream optical signal, and outputs the generated electrical signal to the variable amplifier 23B.

[0256] Variable amplifier 23B amplifies the electrical signal received from optical module 201B and outputs the amplified signal to demultiplexer 24B.

[0257] The separator 24B separates the RF signal Srd and the digital signal Sdd3 contained in the electrical signal received from the variable amplifier 23B, outputs the RF signal Srd to the RF transceiver 221 via the output connector 12A, and outputs the digital signal Sdd3 to the control unit 51B.

[0258] The control unit 51B acquires the correction coefficient Cu from the digital signal Sdd3 received from the separation unit 24B, and then outputs a correction start instruction including the acquired correction coefficient Cu to the correction unit 52B.

[0259] The corrector 52B receives a correction start instruction from the controller 51B and stores the correction coefficient Cu included in the received correction start instruction. The corrector 52B uses the correction coefficient Cu to correct distortion in the electrical signal received from the multiplexer 22B.

[0260] More specifically, the corrector 52B corrects distortion of the electrical signal received from the multiplexer 22B by multiplying amplitude values ​​greater than the threshold THV4 and amplitude values ​​less than the threshold THV3 by a correction coefficient Cu, which is equal to or greater than 1. The corrector 52B outputs the distortion-corrected electrical signal to the optical module 201B.

[0261] For example, in the optical communication system 305, after the correction unit 52A starts the distortion correction, the gain of the variable amplifier 23B is adjusted according to the procedure described above.

[0262] [Operation Flow] FIG. 13 is a diagram illustrating an example of a sequence of distortion correction in the optical communication system according to the fifth embodiment of the present disclosure.

[0263] 13, first, the master station device 115 transmits a downstream optical signal to the slave station device 215 via the optical fiber 191 during a downstream transmission period (step S61).

[0264] Next, the slave station device 215 calculates the harmonic distortion HDd of the electrical signal output from the optical module 201B (step S62).

[0265] Next, the slave station device 215 refers to the correction table TCd in the storage unit 43B to obtain the correction coefficient Cd corresponding to the calculated harmonic distortion HDd (step S63).

[0266] Next, during the upstream transmission period, the slave station device 215 generates a digital signal Sdu3 including the correction coefficient Cd, and transmits an upstream optical signal including the generated digital signal Sdu3 and the RF signal Sru to the master station device 115 via the optical fiber 191 (step S64).

[0267] Next, the parent station 115 obtains the correction coefficient Cd from the digital signal Sdu3 included in the received upstream optical signal (step S65).

[0268] Next, the master station 115 starts distortion correction using the correction coefficient Cd. More specifically, the correction unit 52A on the host board 105A starts distortion correction of the electrical signal received from the multiplexing unit 22A using the correction coefficient Cd (step S66).

[0269] Next, the master station 115 calculates the harmonic distortion HDu of the electrical signal output from the optical module 201A (step S67).

[0270] Next, the master station device 115 refers to the correction table TCu in the storage unit 43A to obtain the correction coefficient Cu corresponding to the calculated harmonic distortion HDu (step S68).

[0271] Next, during the downstream transmission period, the parent station device 115 generates a digital signal Sdd3 including the correction coefficient Cu, and transmits a downstream optical signal including the generated digital signal Sdd3 and the RF signal Srd to the child station device 215 via the optical fiber 191 (step S69).

[0272] Next, the slave station device 215 acquires the correction coefficient Cu from the digital signal Sdd3 included in the received downstream optical signal (step S70).

[0273] Next, the slave station equipment 215 starts distortion correction using the correction coefficient Cu. More specifically, the correction unit 52B on the host board 105B starts distortion correction of the electrical signal received from the multiplexing unit 22B using the correction coefficient Cu (step S71).

[0274] The order of steps S62, S63, S64, S65, and S66 and steps S67, S68, S69, S70, and S71 is not limited to the above, and they may be reversed or performed in parallel.

[0275] The above-described embodiments should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0276] Each process (each function) in the above-described embodiments is realized by a processing circuit (circuitry) including one or more processors. The processing circuit may be configured as an integrated circuit or the like that combines one or more memories, various analog circuits, and various digital circuits in addition to the one or more processors. The one or more memories store programs (instructions) that cause the one or more processors to execute each of the processes. The one or more processors may execute each of the processes according to the program read from the one or more memories, or may execute each of the processes according to a logic circuit designed in advance to execute each of the processes. The processor may be any of various processors suitable for computer control, such as a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), and an ASIC (Application Specific Integrated Circuit). Note that the physically separated processors may cooperate with each other to execute the processes. For example, the processors installed in the physically separated computers may cooperate with each other via a network such as a LAN (Local Area Network), a WAN (Wide Area Network), or the Internet to execute the processes. The program may be installed into the memory from an external server device or the like via the network, or may be distributed in a state stored on a recording medium such as a CD-ROM (Compact Disc Read Only Memory), a DVD-ROM (Digital Versatile Disc Read Only Memory), or a semiconductor memory, and then installed into the memory from the recording medium.

[0277] 11, 11A, 11B Input connector 12, 12A, 12B Output connector 13, 13A, 13B, 21, 21A, 21B, 31, 31A, 31B, 41, 41A, 41B, 51, 51A, 51B Control unit 14, 14A, 14B Variable ATT 15, 15A, 15B Amplifier 16, 16A, 16B, 25, 25A, 25B, 33, 33A, 33B, 43, 43A, 43B Storage unit 22, 22A, 22B Multiplexing unit 23, 23A, 23B, 32, 32A, 32B Variable amplifier 24, 24A, 24B Separation unit 42, 42A, 42B, 52, 52A, 52B Correction unit 101, 101A, 101B, 102, 102A, 102B, 103, 103A, 103B, 104, 104A, 104B, 105, 105A, 105B host board 111, 112, 113, 114, 115 master station device 121 signal processing unit 191 optical fiber 201, 201A, 201B optical module 221 RF transceiver unit 211, 212, 213, 214, 215 slave station device 301, 302, 303, 304, 305 optical communication system

Claims

1. A signal processing device for use in an optical communication system, comprising: An optical module that converts optical signals received via optical fiber into electrical signals can be connected. an adjustment unit that amplifies and / or attenuates a communication signal included in the electrical signal output from the optical module connected to the signal processing device; a control unit that acquires, from the optical module connected to the signal processing device, reception level information indicating the reception intensity of the optical signal received at the optical module, and adjusts the gain of the adjustment unit based on the acquired reception level information and a setting value of the gain of the communication signal in the optical communication system.

2. 2. The signal processing device according to claim 1, wherein the control unit acquires transmission level information indicating a transmission intensity of the optical signal in a device that transmits the optical signal to the optical fiber, and adjusts the gain of the adjustment unit further based on the acquired transmission level information.

3. The signal processing device according to claim 2 , wherein the control unit acquires the transmission level information from the electrical signal.

4. 4. The signal processing device according to claim 1, wherein the control unit adjusts the gain of the adjustment unit based on correspondence information that indicates a correspondence relationship between the reception strength and the gain of the adjustment unit, the correspondence information being created based on the set value.

5. 1. An optical communication system, comprising: a first optical communication device; a second optical communication device connected to the first optical communication device via an optical fiber; the first optical communication device transmits a first optical signal including a communication signal to the second optical communication device; the second optical communication device converts the first optical signal received from the first optical communication device into an electrical signal, and amplifies or attenuates the communication signal included in the electrical signal; The second optical communication device adjusts a gain in amplifying or attenuating the communication signal based on the received intensity of the first optical signal and a set value of the gain of the communication signal in the optical communication system.

6. the first optical communication device generates a first control signal including transmission level information indicating a transmission intensity of the first optical signal, and transmits the first optical signal further including the generated first control signal to the second optical communication device; 6. The optical communication system according to claim 5, wherein the second optical communication device acquires the transmission level information from the first control signal included in the received first optical signal, and adjusts a gain in amplifying or attenuating the communication signal based on the acquired transmission level information.

7. the first optical communication device generates the first optical signal by modulating the amplified or attenuated communication signal; the second optical communication device generates a second control signal including OMI information indicating an OMI (Optical Modulation Index) of the received first optical signal, and transmits the generated second optical signal including the second control signal to the first optical communication device; The optical communication system described in claim 5 or claim 6, wherein the first optical communication device acquires the OMI information from the second control signal contained in the received second optical signal, and adjusts the gain in amplifying or attenuating the communication signal based on the acquired OMI information.

8. 7. The optical communication system according to claim 5, wherein the second optical communication device acquires characteristic information indicating optical modulation characteristics in the first optical communication device, and corrects the communication signal based on the acquired characteristic information.

9. The optical communication system described in Claim 8, wherein the second optical communication device acquires harmonic distortion of the electrical signal as the characteristic information and corrects the communication signal based on the acquired harmonic distortion.

10. 7. The optical communication system according to claim 5, wherein the first optical communication device acquires characteristic information indicating optical modulation characteristics in the first optical communication device, corrects the communication signal based on the acquired characteristic information, and modulates the corrected communication signal to generate the first optical signal.

11. The optical communication system described in Claim 10, wherein the first optical communication device acquires harmonic distortion of the electrical signal as the characteristic information, corrects the communication signal based on the acquired harmonic distortion, and generates the first optical signal by modulating the corrected communication signal.

12. 1. An optical communication method in an optical communication system including a first optical communication device and a second optical communication device connected to the first optical communication device via an optical fiber, comprising: transmitting a first optical signal including a communication signal from the first optical communication device to the second optical communication device; the second optical communication device converting the first optical signal received from the first optical communication device into an electrical signal, and amplifying or attenuating the communication signal included in the electrical signal; an optical communication method, in which, in the step of the second optical communication device amplifying or attenuating the communication signal, a gain in amplifying or attenuating the communication signal is adjusted based on the reception intensity of the first optical signal and a set value of a gain of the communication signal in the optical communication system.