Optical relay device, optical transmission system, and optical relay method

Abstract

An optical relay device (2) comprises: a coherent reception front end unit (110) that coherently detects an input optical signal to be inputted on the basis of locally emitted light; a coherent transmission front end unit (120) that coherently modulates the coherently detected signal on the basis of transmission light, and outputs a coherently modulated output optical signal; a light source (21) that outputs first light having a first wavelength; a light source (22) that outputs second light having a second wavelength; and a selection unit (130) that selects one of the first light and the second light, and outputs the selected light as locally emitted light or transmission light.

Description

Optical repeater, optical transmission system, and optical repeater method

[0001] The present disclosure relates to an optical repeater, an optical transmission system, and an optical repeating method.

[0002] In recent years, in the post-5G era, not only wireless communications but also optical communications are expected to be utilized for a variety of communication services. In particular, research is being conducted to enhance the functionality of reconfigurable optical add / drop multiplexer (ROADM) networks, and wavelength conversion technology, which is necessary when changing routes, is attracting particular attention. In increasingly complex wavelength division multiplexing (WDM) networks, wavelength conflicts with other signals make it impossible to establish the shortest path end-to-end using a single wavelength. Therefore, a path must be established while converting the wavelength to an available wavelength slot.

[0003] As a related technique, for example, Patent Document 1 discloses a wavelength converter that converts the wavelength of an optical signal at a receiving end and a transmitting end using a coherent system.

[0004] Special table 2017-511036 publication

[0005] In the wavelength converter disclosed in Patent Document 1, a receiving end including a coherent detection front-end module converts a received optical signal into an analog electrical signal, and a transmitting end including an optical modulation module converts the analog electrical signal into a transmitted optical signal. However, Patent Document 1 does not take into consideration, for example, the wavelength switching time of a tunable light source that outputs a local light source or a transmitting light source when switching the wavelength to be converted (the wavelength before or after conversion by the wavelength converter), resulting in a problem that it takes a long time to switch the wavelength to be converted.

[0006] In view of the above-described problems, the present disclosure aims to provide an optical repeater, an optical transmission system, and an optical repeating method that can reduce the time required to switch the wavelength to be converted.

[0007] The optical repeater according to the present disclosure comprises a coherent optical receiving front-end means for coherently detecting an input optical signal based on local light, a coherent optical transmitting front-end means for coherently modulating the coherently detected signal based on transmitted light and outputting the coherently modulated output optical signal, a first light source for outputting first light of a first wavelength, a second light source for outputting second light of a second wavelength, and a selecting means for selecting either the first light or the second light and outputting the selected light as the local light or the transmitted light.

[0008] The optical transmission system according to the present disclosure is an optical transmission system including a plurality of optical repeaters, each of which includes a coherent optical receiving front-end means for coherently detecting an input optical signal input from a previous optical repeater based on local light, a coherent optical transmitting front-end means for coherently modulating the coherently detected signal based on transmitted light and outputting the coherently modulated output optical signal to the next optical repeater, a first light source for outputting first light of a first wavelength, a second light source for outputting second light of a second wavelength, and a selection means for selecting either the first light or the second light and outputting the selected light as the local light or the transmitted light.

[0009] The optical relay method according to the present disclosure coherently detects an input optical signal based on local light, coherently modulates the coherently detected signal based on transmitted light, outputs the coherently modulated output optical signal, selects either a first light having a first wavelength output from a first light source or a second light having a second wavelength output from a second light source, and outputs the selected light as the local light or the transmitted light.

[0010] According to the present disclosure, it is possible to provide an optical repeater, an optical transmission system, and an optical repeating method that can reduce the time required to switch the wavelength to be converted.

[0011] 1 is a configuration diagram showing an example of a configuration of an optical transmission system according to an embodiment. FIG. 2 is a configuration diagram showing an example of a configuration of a related optical repeater. FIG. 3 is a configuration diagram showing another example of a configuration of a related optical repeater. FIG. 4 is a configuration diagram showing an example of a schematic configuration of an optical repeater according to an embodiment. FIG. 5 is a configuration diagram showing another example of a schematic configuration of an optical repeater according to an embodiment. FIG. 6 is a configuration diagram showing an example of a configuration of an optical repeater according to a first embodiment. FIG. 7 is a configuration diagram showing an example of a configuration of a coherent reception front-end unit according to the first embodiment. FIG. 8 is a configuration diagram showing an example of a configuration of a coherent transmission front-end unit according to the first embodiment. FIG. 9 is a configuration diagram showing an example of a configuration of a local light selection unit according to a specific example 1 of the first embodiment. FIG. 10 is a sequence diagram showing an example of an operation of an optical repeater according to a specific example 1 of the first embodiment. FIG. 11 is a configuration diagram showing an example of a configuration of a local light selection unit according to a specific example 2 of the first embodiment. FIG. 12 is a sequence diagram showing an example of an operation of an optical repeater according to a specific example 2 of the first embodiment. FIG. 13 is a configuration diagram showing an example of a configuration of a local light selection unit according to a specific example 3 of the first embodiment. FIG. 14 is a sequence diagram showing an example of an operation of an optical repeater according to a specific example 3 of the first embodiment. FIG. 15 is a configuration diagram showing an example of a configuration of an optical repeater according to a second embodiment. FIG. 16 is a configuration diagram showing another example of a configuration of an optical repeater according to a second embodiment. 10 is a configuration diagram showing a configuration example of a transmission light selection unit according to specific example 1 of embodiment 2. FIG. 11 is a sequence diagram showing an operation example of an optical repeater according to specific example 1 of embodiment 2. FIG. 12 is a configuration diagram showing a configuration example of a transmission light selection unit according to specific example 2 of embodiment 2. FIG. 13 is a sequence diagram showing an operation example of an optical repeater according to specific example 2 of embodiment 2. FIG. 14 is a configuration diagram showing a configuration example of a transmission light selection unit according to specific example 3 of embodiment 2. FIG. 15 is a sequence diagram showing an operation example of an optical repeater according to specific example 3 of embodiment 2. FIG. 16 is a configuration diagram showing another configuration example of an optical repeater according to embodiment 3. FIG. 17 is a sequence diagram showing an operation example of an optical repeater according to embodiment 4. FIG. 18 is a sequence diagram showing another operation example of an optical repeater according to embodiment 4. FIG. 19 is a sequence diagram showing another operation example of an optical repeater according to embodiment 4.

[0012] Hereinafter, embodiments will be described with reference to the drawings. In each drawing, the same or corresponding elements are designated by the same reference numerals, and for clarity of explanation, duplicate explanations will be omitted as necessary. Note that arrows shown in each drawing are for illustrative purposes only and do not limit the type or direction of signals.

[0013] (Outline of the embodiment) First, an outline of the embodiment will be described. FIG. 1 shows an example of the configuration of an optical transmission system 1 according to the embodiment. The optical transmission system 1 according to the embodiment is, for example, a backbone wavelength multiplexing optical transmission system, and performs wavelength multiplexing and digital coherent transmission using optical signals of each wavelength, thereby achieving high-capacity communications of over 100 Gbps or even 1 Tbps. Wavelength multiplexing makes it possible to improve the efficiency of optical frequency utilization and accommodate mobile traffic and wavelength defragmentation. Furthermore, wavelength multiplexing allows for flexible switching of transmission paths or wavelength paths while retaining the optical signal, thereby enabling infrastructure maintenance by switching and detouring transmission paths during transmission congestion or failures.

[0014] 1, the optical transmission system 1 includes a plurality of optical repeaters 2 (e.g., 2-1 to 2-10) connected to each other so as to be capable of optical communication via an optical fiber transmission line 3. The optical repeaters 2 are photonic nodes capable of relaying wavelength-multiplexed optical signals, such as ROADM devices. In this example, the optical repeaters 2-1 to 2-10 form a ring network including three rings, but may also form networks of other topologies.

[0015] Each optical repeater 2 is assigned a wavelength path, and forwards traffic of the local network it accommodates and traffic of other optical repeaters 2 via the assigned wavelength path. For example, optical repeater 2-1 accommodates the network of data center 4, and optical repeater 2-2 accommodates the network of data center 5, and forwards high-volume traffic such as a video distribution service that delivers high-quality video (4k / 8k). For example, when optical repeater 2-1 and optical repeater 2-2 are forwarding traffic between data center 4 and data center 5 via wavelength path P1, if a failure occurs in wavelength path P1, wavelength path P1 is switched to wavelength path P2. This allows traffic forwarding between data center 4 and data center 5 to be maintained via a detour route including optical repeater 2-3 and optical repeater 2-4.

[0016] However, when wavelength path P1 is switched to wavelength path P2, there is a possibility that wavelength collision will occur at the optical repeater to which the path is switched. For example, suppose that wavelength λ1 is set for wavelength path P1 between optical repeaters 2-1 and 2-2, and wavelength λ1 is also set for wavelength path P3 between optical repeaters 2-5 and 2-10. In this case, when wavelength path P1 is switched to wavelength path P2, the wavelength λ1 of wavelength path P3 being forwarded by optical repeater 2-4 will collide with the wavelength λ1 of wavelength path P2 to which the path is switched. In this case, a method of avoiding collision could be considered by switching wavelength path P3 to another route, but there is not necessarily an available wavelength slot on the other route. For this reason, it is necessary to convert the wavelength of the wavelength path relayed by optical repeater 2-4. For example, optical repeater 2-4 converts an optical signal of wavelength λ1 received from optical repeater 2-3 on wavelength path P2 to an optical signal of wavelength λ2 and transmits the converted signal to optical repeater 2-2. This makes it possible to avoid wavelength collision when switching a wavelength path to a detour route.

[0017] Furthermore, for example, optical repeater 2-5 accommodates the IoT sensor network of IT service provider 6, optical repeater 2-7 accommodates the IoT sensor network of IT service provider 7, and optical repeater 2-8 accommodates the mobile network of event venue 8. Mobile network traffic is traffic due to spot demand from moving users. For example, when optical repeater 2-5 and optical repeater 2-10 are forwarding traffic between IT service provider 6 and event venue 8 via wavelength path P3 including optical repeater 2-7 and optical repeater 2-4, if new traffic due to spot demand occurs at event venue 8, a new wavelength path P4 is set up. This allows traffic generated at event venue 8 to be forwarded via optical repeater 2-6, optical repeater 2-7, optical repeater 2-8, and optical repeater 2-9.

[0018] However, in this case, as in the case of switching the wavelength path route, there is a possibility of wavelength collisions at the optical repeater where a new wavelength path is set. For example, suppose that wavelength λ1 is set for wavelength path P3 between optical repeater 2-5 and optical repeater 2-10. Then, if wavelength λ1 is also set for wavelength path P4 newly assigned between optical repeater 2-5 and optical repeater 2-10, a collision will occur between the wavelength λ1 of wavelength path P3 being transferred by optical repeater 2-7 and the wavelength λ1 of the new wavelength path P4. Therefore, in this case as well, it is necessary to convert the wavelength of the wavelength path relayed by optical repeater 2-7. For example, optical repeater 2-7 converts the optical signal of wavelength λ1 received from optical repeater 2-6 on wavelength path P4 to an optical signal of wavelength λ2 and transmits it to optical repeater 2-8. This makes it possible to avoid wavelength collisions when setting up a new wavelength path.

[0019] In this way, when a failure occurs in a wavelength path and a detour route is set up, wavelength conversion is required if there is a path of the same wavelength in the detour route, and when a new route is set up and there is a path of the same wavelength in an existing route, wavelength conversion is also required. Therefore, the inventors studied wavelength conversion methods in optical repeater devices and found a problem that, in both of the above cases, rapid wavelength conversion switching is required, but with related technologies, it takes several seconds to several tens of seconds to switch the wavelength to be converted, depending on the wavelength switching time of the light source and the time required for automatic bias voltage control of the optical modulator.

[0020] 2 shows an example of the configuration of a related optical repeater device 9. In this example, a wavelength conversion method that suppresses an increase in latency that occurs when converting the wavelength of an optical signal is realized by optically modulating an optical signal detected by a coherent receiving front end with another wavelength by a coherent transmitting front end.

[0021] 2, the related optical repeater 9 includes a coherent receiver front end 110 and a coherent transmitter front end 120. The coherent receiver front end 110 coherently detects an input optical signal SO1 received from a previous optical repeater using a local oscillator light (locally oscillated light) LO of a predetermined wavelength from a local light source A1, which is a wavelength-tunable light source, and outputs the detected analog electrical signal SA to the coherent transmitter front end 120.

[0022] The coherent transmitter front end 120 optically modulates (coherently modulates) the analog electrical signal SA coherently detected by the coherent receiver front end 110 with transmission light PO of a predetermined wavelength from a transmission light source B1, which is a wavelength-tunable light source, and transmits the generated output optical signal SO2 to the next-stage optical repeater. The related optical repeater 9 is configured with analog circuits that do not perform digital processing, so wavelength conversion can be achieved with low delay and at low cost.

[0023] However, in the related technology, when switching the wavelength to be converted (the wavelength before conversion or the wavelength after conversion of the optical repeater), it is necessary to switch the wavelength of the local light LO of the local light source A1 or the wavelength of the transmitted light PO of the transmitted light source B1, and there is an issue in that it takes several seconds to several tens of seconds to switch the wavelength of a wavelength-tunable light source.

[0024] 3, in the related optical repeater 9, an automatic bias control circuit (ABC circuit; Automatic Bias Control circuit) 140 controls the bias voltage of the modulator in the coherent transmission front-end unit 120. However, since the automatic bias control circuit 140 monitors the monitor signal MO from the modulator in the coherent transmission front-end unit 120 and sets the optimal bias voltage BS based on the monitoring results, it becomes unable to properly control the bias voltage if the optical power input to the modulator fluctuates or becomes non-existent, or if the electrical signal driving the modulator becomes non-existent. Therefore, after the wavelength is switched and the optical power and electrical signal return to normal, it takes several seconds to a maximum of several tens of seconds for proper control to be performed and the optimal bias voltage to be achieved, which is a problem.

[0025] Therefore, the present embodiment is intended to solve at least one of these problems. Fig. 4 shows an example of a schematic configuration of an optical repeater 2 according to the embodiment. In the example of Fig. 4, the optical repeater 2 according to the embodiment includes a coherent receiver front-end unit 110, a coherent transmitter front-end unit 120, a light source 21, a light source 22, and a selector 130.

[0026] The coherent receiver front-end unit 110 and the coherent transmitter front-end unit 120 have the same configuration as in Fig. 2. That is, the coherent receiver front-end unit 110 is an optical / electrical converter that converts an optical signal into an electrical signal, and a coherent detector that performs coherent detection. The coherent receiver front-end unit 110 coherently detects the input optical signal SO1 based on the local oscillator light LO, and outputs the generated analog electrical signal SA.

[0027] The coherent transmission front-end unit 120 is an electrical-to-optical converter that converts an electrical signal into an optical signal and a coherent modulator that performs coherent modulation. The coherent transmission front-end unit 120 coherently modulates the analog electrical signal SA generated by the coherent reception front-end unit 110 based on the transmitted light PO, and outputs the generated output optical signal SO2. Note that a signal based on the analog electrical signal SA generated by the coherent reception front-end unit 110 may also be input to the coherent transmission front-end unit 120. For example, a signal obtained by performing signal processing such as predetermined compensation processing on the analog electrical signal SA using an analog circuit or a digital circuit may also be input to the coherent transmission front-end unit 120.

[0028] The frequency (wavelength) of the local light LO is the frequency (wavelength) of the input optical signal SO1 to be received, and the frequency of the transmitted light PO is the frequency of the output optical signal SO2 to be transmitted. Note that, although the "frequency" or "wavelength" of the signal is described, "frequency" and "wavelength" can be interpreted interchangeably. For example, the local light LO and the transmitted light PO have different frequencies, but they may also have the same frequency. By changing the frequencies of the local light LO and the transmitted light PO, the wavelength of the optical signal can be switched. In other words, the input optical signal SO1 can be converted into an output optical signal SO2 with a different wavelength.

[0029] The light source 21 (first light source) outputs a first light having a first wavelength. The light source 22 (second light source) outputs a second light having a second wavelength. The light sources 21 and 22 are local light sources that output local light, or transmission light sources that output transmission light. For example, the light sources 21 and 22 are tunable light sources that can change the wavelength of the light they output, but they may also be fixed-wavelength light sources that fix the wavelength of the light they output. The number of light sources is not limited to two, 21 and 22, and multiple light sources may be provided.

[0030] The selection unit 130 selects either the first light having a first wavelength output from the light source 21 or the second light having a second wavelength output from the light source 22, and outputs the selected light as a local optical fiber LO or a transmission optical fiber PO. The selection unit 130 may output either the local optical fiber LO or the transmission optical fiber PO, or may output both the local optical fiber LO and the transmission optical fiber PO. For example, the selection unit 130 may output either the first light or the second light as the local optical fiber LO to the coherent receiver front-end unit 110, or may output either the first light or the second light as the transmission optical fiber PO to the coherent transmitter front-end unit 120. For example, the selection unit 130 may be configured with an optical switch, or may be configured with a variable attenuator and an optical coupler.

[0031] In the example of Fig. 4, the light output from the two light sources is selected by a selector such as an optical switch to switch the wavelength of the local light or the transmitted light. This makes it possible to shorten the time required to switch the wavelength to be converted and speed up wavelength switching compared to when the wavelength of the local light or the transmitted light is switched by a single wavelength-tunable light source as in Fig. 2.

[0032] 5 shows another example of the schematic configuration of the optical repeater 2 according to the embodiment. In the example of FIG. 5, the optical repeater 2 according to the embodiment includes a coherent receiver front-end unit 110, a coherent transmitter front-end unit 120, an automatic bias control circuit 140, and a bias voltage storage unit 141. The optical repeater 2 according to the embodiment may include the configuration of FIG. 4 and the configuration of FIG. 5. For example, the optical repeater 2 may further include the bias voltage storage unit 141 in addition to the configuration of FIG. 4.

[0033] The automatic bias control circuit 140 has a configuration similar to that shown in FIG. 3 and automatically controls the bias voltage BS for the modulator in the coherent transmitter front-end 120. The automatic bias control circuit 140 monitors the monitor signal MO of the modulator in the coherent transmitter front-end 120 and, based on the monitoring results, performs optimization control (automatic bias control processing) of the bias voltage BS set for the modulator in the coherent transmitter front-end 120. For example, the automatic bias control circuit 140 stops (temporarily stops) the automatic bias control processing before switching the wavelength of the local light LO or the transmission light PO, and resumes the automatic bias control processing after the wavelength switching of the local light LO or the transmission light PO is completed. For example, when the selector 130 in FIG. 4 switches the wavelength of the local light LO or the transmission light PO, the automatic bias control circuit 140 may stop the automatic bias control processing before switching the light selected by the selector 130, and resume the automatic bias control processing after switching the light selected by the selector 130.

[0034] The bias voltage storage unit 141 stores the bias voltage BS (bias voltage optimized by automatic bias control) before (just before) switching the wavelength of the local light LO or the transmitted light PO. After completing the wavelength switching of the local light LO or the transmitted light PO, the automatic bias control circuit 140 resumes the automatic bias control process using the bias voltage BS stored in the bias voltage storage unit 141. For example, when the selection unit 130 in FIG. 4 switches the wavelength of the local light LO or the transmitted light PO, the automatic bias control circuit 140 may store the bias voltage BS before (just before) switching the light selected by the selection unit 130, and after switching the light selected by the selection unit 130, resume the automatic bias control process using the bias voltage BS stored in the bias voltage storage unit 141.

[0035] In the example of Fig. 5, the bias voltage of the automatic bias control circuit is stored before switching the wavelength to be converted, and after the wavelength switching is completed, the automatic bias control is resumed using the stored bias voltage, thereby shortening the time from switching the wavelength to optimizing the bias voltage.

[0036] (First Embodiment) Next, a first embodiment will be described. In this embodiment, an example will be described in which one of a plurality of local light sources is selected and the wavelength of the local light is switched. The configuration of an optical transmission system 1 according to this embodiment is the same as that shown in FIG.

[0037] Fig. 6 shows an example of the configuration of an optical repeater 2 according to this embodiment. As shown in Fig. 6, the optical repeater 2 according to this embodiment includes a wavelength conversion unit 100, a control unit 210, a wavelength selective switch 220, and a user interface unit 300. For example, the wavelength conversion unit 100, the control unit 210, and the wavelength selective switch 220 configure an optical signal repeater unit 200 that converts and repeats a predetermined wavelength. The optical repeater 2 may include a plurality of optical signal repeater units 200.

[0038] In this example, the wavelength multiplexed signal WO is input to the optical signal repeater unit 200 from the upstream optical repeater device 2 via the optical fiber transmission line 3. For example, the wavelength multiplexed signal WO may be input to the optical signal repeater unit 200 after being wavelength-demultiplexed from the optical fiber transmission line 3 via a coupler (demultiplexer) or other wavelength selective switch.

[0039] The wavelength selective switch 220 is a switch that selects and outputs an optical signal of a predetermined wavelength from the input optical signal. The wavelength selective switch 220 selects an optical signal of a wavelength set by the control unit 210. For example, the wavelength selective switch 220 selects and extracts one predetermined wavelength from the input wavelength-multiplexed signal WO, and outputs the extracted single-channel optical signal as the input optical signal SO1.

[0040] The wavelength conversion unit 100 converts the wavelength of the input optical signal SO1 input from the wavelength selective switch 220, and outputs the wavelength-converted output optical signal SO2 to the downstream optical repeater 2 via the optical fiber transmission line 3. For example, the output optical signal SO2 may be wavelength-multiplexed via a coupler (multiplexer) or another wavelength selective switch, and then output to the optical fiber transmission line 3.

[0041] The wavelength conversion unit 100 includes a coherent receiver front end unit 110 , a coherent transmitter front end unit 120 , local light sources A 1 and A 2 , a local light selector 131 , a transmitter light source B 1 , an automatic bias control circuit 140 , and a compensation unit 150 .

[0042] The local light source A1 (e.g., a first light source) generates a local light LO1 of a first wavelength and outputs the generated local light LO1 to the local light selection unit 131. The local light source A2 (e.g., a second light source) generates a local light LO2 of a second wavelength and outputs the generated local light LO2 to the local light selection unit 131. For example, the local light sources A1 and A2 are wavelength-tunable light sources that generate and output local light LO1 and LO2 of wavelengths set by the control unit 210. The local light sources A1 and A2 are not limited to wavelength-tunable light sources, and may each generate local light LO1 and LO2 of a preset fixed wavelength. For example, two or more fixed-wavelength light sources may be provided as the local light sources.

[0043] The local light selector 131 (e.g., a first selector) selects one of the local light sources LO1 and LO2 input from the local light sources A1 and A2, and outputs the selected light as the local light source LO to the coherent receiver front-end 110. The local light selector 131 selects the local light of one of the local light sources in accordance with control from the control unit 210. When the local light sources A1 and A2 are wavelength-tunable light sources and switching is to be made from the local light source A1 to the local light source A2, the local light selector 131 may select and output the local light LO2 of the local light source A2 after the wavelength switching of the local light source A2 is completed. For example, the local light selector 131 may be configured with an optical switch, a variable optical attenuator and an optical coupler, or some other configuration.

[0044] The transmission light source B1 generates transmission light PO of a predetermined wavelength and outputs the generated transmission light PO to the coherent transmission front-end unit 120. For example, the transmission light source B1 is a wavelength-tunable light source, and generates and outputs transmission light PO of a wavelength set by the control unit 210.

[0045] 4, the coherent receiver front end unit 110 coherently detects the input optical signal SO1 using the local optical signal LO from the local optical signal selector 131, converts it into an analog electrical signal SA1, and outputs it. For example, the coherent receiver front end unit 110 is configured by an integrated coherent receiver C1.

[0046] The coherent transmission front end unit 120 coherently modulates the analog electrical signal SA2 converted by the coherent reception front end unit 110 and signal processed by the compensation unit 150 with the transmission light PO from the transmission light source B1, converts it into an output optical signal SO2, and outputs it. For example, the coherent transmission front end unit 120 is composed of a driver amplifier C2 and an IQ modulator C3.

[0047] For example, the input optical signal SO1 and the output optical signal SO2 are phase-modulated and polarization-multiplexed optical signals. The analog electrical signals SA1 and SA2 are four-lane (4-channel) signals including an XI signal, which is the I component (in-phase component) of the X polarization, an XQ signal, which is the Q component (quadrature component) of the X polarization, a YI signal, which is the I component of the Y polarization, and a YQ signal, which is the Q component of the Y polarization.

[0048] The compensator 150 is a circuit that performs compensation processing to compensate for signal distortion of the analog electrical signal SA1 between the coherent receiver front-end 110 and the coherent transmitter front-end 120, and generates a compensated analog electrical signal SA2. The compensation processing may be analog signal processing by an analog circuit, or may include digital signal processing by a digital circuit. The compensation processing is processing that compensates for distortion (quality) of the signal to be transmitted, and includes, for example, frequency compensation, skew compensation, amplitude compensation, etc.

[0049] 5 , the automatic bias control circuit 140 monitors the monitor signal MO of the IQ modulator C3 of the coherent transmission front end unit 120, and performs optimization control (automatic bias control processing) of the bias voltage BS set in the IQ modulator C3 according to the monitoring results. For example, the automatic bias control circuit 140 starts, stops, pauses, etc. the automatic bias control processing according to control from the control unit 210.

[0050] The control unit 210 collectively controls each unit constituting the optical signal relay unit 200. The control unit 210 includes a setting information acquisition unit that acquires setting information from the user interface unit 300. The control unit 210 also includes a setting unit or instruction unit that sets or instructs the wavelength selective switch 220, the local light sources A1 and A2, the local light selection unit 131, the transmission light source B1, etc., in accordance with the setting information or instructions from the user interface unit 300.

[0051] For example, when setting or switching the wavelength of the input optical signal SO1, the control unit 210 controls the operations of the wavelength selective switch 220, the local light sources A1 and A2, and the local light selector 131. In controlling the wavelength selective switch 220, the control unit 210 sets the wavelength of the optical signal to be selected by the wavelength selective switch 220 based on setting information and a wavelength change instruction acquired from the user interface unit 300. The control unit 210 may set the wavelength of the optical signal to be selected based on setting information registered in advance in the optical signal repeater unit 200, rather than being limited to setting information acquired from the user interface unit 300.

[0052] In controlling the local light sources A1 and A2, if the local light sources A1 and A2 are wavelength-tunable light sources, the control unit 210 sets the wavelengths of the local light sources LO1 and LO2 output by the local light sources A1 and A2 based on setting information and a wavelength change instruction acquired from the user interface unit 300. The control unit 210 may set the wavelengths of the local light sources LO1 and LO2 based on setting information registered in advance in the optical signal repeater unit 200, rather than on setting information acquired from the user interface unit 300. Note that the wavelengths of the local light sources LO1 and LO2 output from the local light sources A1 and A2 may be monitored by a wavemeter or the like, and it may be determined whether or not wavelength control for the local light sources A1 and A2 has been completed based on the monitoring results of the wavelengths of the local light sources LO1 and LO2.

[0053] In controlling the local light selector 131 , the controller 210 controls the local light selected by the local light selector 131 based on setting information and wavelength change instructions acquired from the user interface 300 .

[0054] For example, when setting or switching the wavelength of the output optical signal SO2, the control unit 210 controls the operation of the transmission light source B1. In controlling the transmission light source B1, the control unit 210 sets the wavelength of the transmission light PO output by the transmission light source B1 based on setting information and a wavelength change instruction acquired from the user interface unit 300. The control unit 210 may set the wavelength of the transmission light PO based on setting information registered in advance in the optical signal repeater unit 200, rather than on setting information acquired from the user interface unit 300. Note that the wavelength of the transmission light PO output from the transmission light source B1 may be monitored by a wavemeter or the like, and whether or not wavelength control for the transmission light source B1 has been completed may be determined based on the monitoring result of the wavelength of the transmission light PO.

[0055] The user interface unit 300 is an interface for a user (operator) who configures and manages the optical repeater device 2 and the optical signal repeater unit 200. The user interface unit 300 may include, as necessary, an operation unit operated by the user and a display unit that displays information to the user. For example, the user interface unit 300 transmits setting information, wavelength change instructions, etc. for each unit of the optical signal repeater unit 200 to the control unit 210. The user interface unit 300 may transmit setting information, wavelength change instructions, etc. in response to input from the user, or may transmit setting information, wavelength change instructions, etc. based on information stored in advance in a database, etc.

[0056] The user interface unit 300 may be disposed inside the optical repeater 2 or outside the optical repeater 2. The user interface unit 300 may be realized, for example, as one function of a network control device that controls the entire optical transmission system 1 including the optical repeater 2. An example of the network control device may be an NMS (Network Management System) that controls and manages paths and wavelengths of the optical transmission system 1.

[0057] 7 shows an example of the configuration of the coherent receiving front-end unit 110 according to this embodiment. As shown in FIG. 7, the coherent receiving front-end unit 110 includes a polarization separation unit 111, 90-degree hybrid circuits 112-1 to 112-2, O / E conversion units 113-1 to 113-4, and amplifiers 114-1 to 114-4. For example, the polarization separation unit 111, the 90-degree hybrid circuits 112-1 to 112-2, the O / E conversion units 113-1 to 113-4, and the amplifiers 114-1 to 114-4 form an integrated coherent receiver C1.

[0058] The polarization separation unit 111 separates the input optical signal SO1, which is a polarization multiplexed signal input from the wavelength selective switch 220, into X-polarized and Y-polarized waves. 90-degree hybrid circuits (coherent optical detectors) 112-1 to 112-2 perform coherent detection by causing interference between the optical signal polarization-separated by the polarization separation unit 111 and the local optical light LO selected by the local optical light selection unit 131. O / E conversion units 113-1 to 113-4, which are configured with photodiodes and the like, convert the coherently detected signals into four-lane analog electrical signals.

[0059] The 90-degree hybrid circuit 112-1 separates the X-polarized wave of the input optical signal SO1 into an I component and a Q component, and then performs photoelectric conversion using O / E converters 113-1 and 113-2 to generate an XI signal and an XQ signal. The 90-degree hybrid circuit 112-2 separates the Y-polarized wave of the input optical signal SO1 into an I component and a Q component, and then performs photoelectric conversion using O / E converters 113-3 and 113-4 to generate a YI signal and a YQ signal. The amplifiers 114-1 to 114-4 respectively amplify the generated XI signal, XQ signal, YI signal, and YQ signal, and output them to the compensation unit 150 as a four-lane analog electrical signal SA1.

[0060] 8 shows an example of the configuration of the coherent transmission front-end unit 120 according to this embodiment. As shown in FIG. 8, the coherent transmission front-end unit 120 includes amplifiers 121-1 to 121-4, MZ modulators (Mach-Zehnder Modulators) 122-1 to 122-4, and a polarization multiplexing unit 123. For example, the amplifiers 121-1 to 121-4 form a driver amplifier C2. The MZ modulators 122-1 to 122-4 and the polarization multiplexing unit 123 form an IQ modulator C3.

[0061] The amplifiers 121-1 to 121-4 respectively amplify the XI signal, XQ signal, YI signal, and YQ signal of the analog electrical signal SA2 output from the compensation unit 150 and drive the MZ modulators 122-1 to 122-4. The MZ modulators (IQ optical modulators) 122-1 to 122-4 apply IQ modulation to the transmission light PO from the transmission light source B1 in accordance with the XI signal, XQ signal, YI signal, and YQ signal respectively applied to them. A bias voltage BS from the automatic bias control circuit 140 is applied to the MZ modulators 122-1 to 122-2.

[0062] MZ modulators 122-1 to 122-2 generate X-polarized IQ-modulated optical signals based on the XI signal and XQ signal transmitted through amplifiers 121-1 to 121-2. MZ modulators 122-3 to 122-4 generate Y-polarized IQ-modulated optical signals based on the YI signal and YQ signal transmitted through amplifiers 121-3 to 121-4. A monitor signal MO that monitors the power of the generated X-polarized IQ-modulated optical signal and Y-polarized IQ-modulated optical signal is output to automatic bias control circuit 140. Polarization multiplexing unit 123 polarization-multiplexes the generated X-polarized IQ-modulated optical signal and Y-polarized IQ-modulated optical signal, and outputs the combined optical signal as output optical signal SO2.

[0063] <Specific Example 1 of Embodiment 1> Next, a description will be given of specific example 1 of embodiment 1. In this specific example 1, an optical switch is used as the local light selector 131.

[0064] Fig. 9 shows a configuration example of the local light selecting unit 131 according to this specific example 1. As shown in Fig. 9, in this specific example 1, the local light selecting unit 131 is configured with an optical switch SW1. Also, in this specific example 1, the local light sources A1 and A2 are wavelength-tunable light sources.

[0065] The optical switch SW1 is a local light selection switch and is a 2×1 optical switch (two input, one output optical switch). The optical switch SW1 selects either the local light LO1 or LO2 input from the local light sources A1 and A2, and outputs the selected light as the local light LO to the coherent receiver front end unit 110. The optical switch SW1 switches the local light LO to be output from the input light in response to an instruction from the control unit 210.

[0066] 10 shows an example of operation of this specific example 1. Fig. 10 shows an example of operation when switching the wavelength of input optical signal SO1 from λ1 to λ2. Note that Fig. 10 is merely an example, and steps S102-S106 may be omitted if local light source A1 outputs local light LO1 with wavelength λ1 and local light source A2 outputs local light LO2 with wavelength λ2. In this case, the user interface unit 300 sets wavelength information (λ2) of the next input optical signal SO1 to the control unit 210 (S101), and the control unit 210 may instruct the optical switch SW1 to change the selection of the input signal to the local light source A2 side (S107).

[0067] 10, first, the wavelength of the input optical signal SO1 is λ1. Specifically, λ1 is set as the selected wavelength of the wavelength selective switch 220, and the wavelength selective switch 220 selects an optical signal with wavelength λ1 from the wavelength-multiplexed signal WO and outputs the selected optical signal with wavelength λ1 as the input optical signal SO1.

[0068] Furthermore, the wavelengths of the local light sources A1 and A2 are set to λ1, and a local light LO1 of wavelength λ1 and a local light LO1 of wavelength λ1 are output from the local light sources A1 and A2. The optical switch SW1 is set to select the local light LO1 on the local light source A1 side, and the local light LO1 of wavelength λ1 is output from the optical switch SW1. The coherent receiver front end unit 110 coherently detects the input optical signal SO1 of wavelength λ1 input from the wavelength selective switch 220 using the local light LO1 of wavelength λ1 from the optical switch SW1.

[0069] In this state, the user interface unit 300 sets wavelength information (λ2) of the next input optical signal SO1 to the control unit 210 (S101). For example, before switching the wavelength of the input optical signal SO1, the user inputs the next wavelength λ2 to the user interface unit 300, and the user interface unit 300 sets the wavelength information of the input wavelength λ2.

[0070] When the control unit 210 receives wavelength information (λ2) of the next input optical signal SO1 from the user interface unit 300, it instructs the local light source A2 (a local light source not currently selected by the optical switch) to change the optical output wavelength to λ2 (S102). When the local light source A2 receives the instruction to change the wavelength to λ2 from the control unit 210, it changes the wavelength of the local light LO2 it outputs to the instructed wavelength λ2 (S103) and notifies the control unit 210 of the completion of the wavelength change (S104).

[0071] When the control unit 210 receives the notification that the wavelength change has been completed from the local light source A2, it notifies the user interface unit 300 that the standby is OK (S105). For example, the user interface unit 300 receives the notification that the standby is OK from the control unit 210 and outputs (displays) to the user that the standby for switching the wavelength of the input optical signal SO1 has been completed.

[0072] Thereafter, the user interface unit 300 instructs the control unit 210 to change the wavelength of the input optical signal SO1 (S106). For example, after receiving standby OK, the user inputs a wavelength change instruction to the user interface unit 300 at any timing (timing to switch the wavelength of the input optical signal SO1), and the user interface unit 300 instructs the control unit 210 to change the wavelength.

[0073] When the control unit 210 receives an instruction to change the wavelength of the input optical signal SO1 from the user interface unit 300, it instructs the optical switch SW1 to change the selection of the input signal to the local light source A2 (S107).The control unit 210 also instructs the wavelength selective switch 220 to change the selected wavelength to wavelength λ2 (S108).

[0074] When the optical switch SW1 receives an instruction from the control unit 210 to change the selection of the input signal, it switches to select and output the local light LO2 from the local light source A2 (S109) and notifies the control unit 210 of the completion of the change (S110). Furthermore, when the wavelength selective switch 220 receives an instruction from the control unit 210 to change the selected wavelength, it switches to select and output the wavelength λ2 (S111) and notifies the control unit 210 of the completion of the change (S112).

[0075] As a result, the wavelength selective switch 220 selects an optical signal of wavelength λ2 from the wavelength multiplexed signal WO and outputs the selected optical signal of wavelength λ2 as the input optical signal SO1. In addition, the optical switch SW1 outputs a local light LO2 of wavelength λ2, and the coherent receiver front end unit 110 coherently detects the input optical signal SO1 of wavelength λ2 input from the wavelength selective switch 220 using the local light LO2 of wavelength λ2 from the optical switch SW1.

[0076] When the control unit 210 receives a notification of completion of the change of the input signal selection from the optical switch SW1 and a notification of completion of the change from the wavelength selective switch 220, it notifies the user interface unit 300 of the completion of the wavelength change of the input optical signal SO1 (S113). For example, the user interface unit 300 receives a notification of the completion of the wavelength change from the control unit 210 and outputs (displays) to the user that the wavelength change of the input optical signal SO1 has been completed.

[0077] <Specific Example 2 of Embodiment 1> Next, a description will be given of specific example 2 of embodiment 1. In this specific example 2, a variable optical attenuator and an optical coupler are used as the local light selector 131.

[0078] Fig. 11 shows a configuration example of the local light selecting unit 131 according to this specific example 2. As shown in Fig. 11, in this specific example 2, the local light selecting unit 131 includes variable optical attenuators VOA1 and VOA2 and an optical coupler CP1. In this specific example 2, the local light sources A1 and A2 are wavelength-tunable light sources.

[0079] The variable optical attenuator VOA1 (e.g., a first variable attenuator) attenuates the optical power of the local optical signal LO1 input from the local light source A1 and outputs the attenuated optical signal to the optical coupler CP1. The variable optical attenuator VOA1 attenuates the optical power of the local optical signal LO1 by an attenuation amount set by the control unit 210. For example, when the attenuation amount is ∞ (infinity), the local optical signal LO1 is not output from the variable optical attenuator VOA1.

[0080] The variable optical attenuator VOA2 (e.g., a second variable attenuator), like the variable optical attenuator VOA1, attenuates the optical power of the local light LO2 input from the local light source A2 and outputs the attenuated optical signal to the optical coupler CP1. The variable optical attenuator VOA2 attenuates the optical power of the local light LO2 by an attenuation amount set by the control unit 210. For example, when the attenuation amount is ∞, the local light LO2 is not output from the variable optical attenuator VOA2.

[0081] The optical coupler (multiplexer) CP1 is a 1x2 optical coupler (one input, two output optical coupler) that multiplexes local light LO1 and LO2 input via variable optical attenuators VOA1 and VOA2 and outputs the multiplexed light as a local light LO to the coherent receiver front end 110. By controlling the attenuation of the variable optical attenuators VOA1 and VOA2, either the local light LO1 or the local light LO2 is output from the optical coupler CP1. For example, when the local light LO1 is output from the variable optical attenuator VOA1 but the local light LO2 is not output from the variable optical attenuator VOA2, the optical coupler CP1 outputs the local light LO1. When the local light LO2 is output from the variable optical attenuator VOA2 but the local light LO1 is not output from the variable optical attenuator VOA1, the optical coupler CP1 outputs the local light LO2.

[0082] FIG. 12 shows an example of operation of this specific example 2. Similar to FIG. 10, FIG. 12 shows an example of operation when switching the wavelength of the input optical signal SO1 from λ1 to λ2. Note that FIG. 12 is merely an example, and steps S102 to S106 may be omitted if the local light source A1 outputs a local light source LO1 with a wavelength λ1 and the local light source A2 outputs a local light source LO2 with a wavelength λ2. In this case, the user interface unit 300 sets wavelength information (λ2) of the next input optical signal SO1 to the control unit 210 (S101), and the control unit 210 may instruct the variable optical attenuator VOA1 to change the attenuation to ∞ (S121) and instruct the variable optical attenuator VOA2 to change the attenuation to 0 (S122).

[0083] In the example of Fig. 12, first, the wavelength of the input optical signal SO1 is operated at λ1, as in Fig. 10. Specifically, λ1 is set as the selected wavelength of the wavelength selective switch 220, and the wavelength selective switch 220 selects an optical signal with wavelength λ1 from the wavelength-multiplexed signal WO and outputs the selected optical signal with wavelength λ1 as the input optical signal SO1.

[0084] Furthermore, the wavelengths of the local light sources A1 and A2 are set to λ1, and a local light LO1 of wavelength λ1 and a local light LO2 of wavelength λ1 are output from the local light sources A1 and A2. The attenuation (ATT) of the variable optical attenuator VOA1 is set to 0, and the attenuation of the variable optical attenuator VOA2 is set to ∞. As a result, the optical coupler CP1 outputs the local light LO1 of wavelength λ1 via the variable optical attenuator VOA1 to the coherent receiver front end unit 110. The coherent receiver front end unit 110 coherently detects the input optical signal SO1 of wavelength λ1 input from the wavelength selective switch 220 using the local light LO1 of wavelength λ1 from the optical coupler CP1.

[0085] 10 , the user interface unit 300 sets wavelength information (λ2) of the next input optical signal SO1 to the control unit 210 (S101). The control unit 210 instructs the local light source A2 to change the optical output wavelength to λ2 (S102), the local light source A2 changes the wavelength of the local light LO2 it outputs to the instructed wavelength λ2 (S103), and notifies the control unit 210 that the wavelength change is complete (S104). The control unit 210 then notifies the user interface unit 300 that standby is OK (S105).

[0086] Thereafter, the user interface unit 300 instructs the control unit 210 to change the wavelength of the input optical signal SO1 (S106).

[0087] When the control unit 210 receives an instruction to change the input optical signal SO1 from the user interface unit 300, it instructs the variable optical attenuator VOA1 to change the attenuation to ∞ (S121) and instructs the variable optical attenuator VOA2 to change the attenuation to 0 (S122). In addition, the control unit 210 instructs the wavelength selective switch 220 to change the selected wavelength to wavelength λ2 (S108).

[0088] When the variable optical attenuator VOA1 receives an instruction to change the attenuation from the user interface unit 300, it changes the attenuation of the local optical light LO1 to infinity, stops output of the local optical light LO1 with wavelength λ1 (S123), and notifies the control unit 210 of the completion of the change (S124). When the variable optical attenuator VOA2 receives an instruction to change the attenuation from the user interface unit 300, it changes the attenuation of the local optical light LO2 to zero, starts output of the local optical light LO2 with wavelength λ2 (S125), and notifies the control unit 210 of the completion of the change (S126). When the wavelength selective switch 220 receives an instruction to change the selected wavelength from the user interface unit 300, it switches to select and output wavelength λ2 (S111), and notifies the control unit 210 of the completion of the change (S112).

[0089] As a result, the wavelength selective switch 220 selects an optical signal of wavelength λ2 from the wavelength multiplexed signal WO and outputs the selected optical signal of wavelength λ2 as the input optical signal SO1. In addition, the optical coupler CP1 outputs a local light LO2 of wavelength λ2, and the coherent receiver front end unit 110 coherently detects the input optical signal SO1 of wavelength λ2 input from the wavelength selective switch 220 using the local light LO2 of wavelength λ2 from the optical coupler CP1.

[0090] When the control unit 210 receives notification of completion of attenuation change from the variable optical attenuators VOA1 and VOA2 and change completion from the wavelength selective switch 220, it notifies the user interface unit 300 of completion of wavelength change of the input optical signal SO1 (S113).

[0091] <Specific Example 3 of Embodiment 1> Next, a description will be given of specific example 3 of embodiment 1. In this specific example 3, the optical switch of the local light selector 131 further switches between local light from a plurality of local light sources.

[0092] 13 shows an example of the configuration of the local light source selection unit 131 according to this specific example 3. As shown in FIG. 13, in this specific example 3, like in specific example 1, the local light source selection unit 131 is configured with an optical switch SW2. Also, in this specific example 3, the optical repeater 2 includes a plurality of local light sources A1-AN. ​​The local light sources A1-AN each output local light of a different fixed wavelength. The local light sources A1-AN are light sources with wavelengths that can be used in the optical transmission system 1. The wavelengths of the local light sources A1-AN correspond to the wavelengths used in the optical transmission system 1, and are λ1-λN.

[0093] The optical switch SW2 is a switch for selecting a local light source and is an N×1 optical switch (N input-1 output optical switch). The optical switch SW3 selects one of the local light sources LO1-LON input from the local light sources A1-AN, and outputs the selected light to the coherent receiver front-end unit 110 as the local light source LO. The optical switch SW2 switches the local light source LO to be output from the input light in response to an instruction from the control unit 210. Note that the same function as the optical switch SW2 may be realized by an optical variable attenuator and an optical coupler, as in the second specific example.

[0094] Fig. 14 shows an example of operation of this specific example 3. Like Fig. 10, Fig. 14 shows an example of operation when the wavelength of the input optical signal SO1 is switched from λ1 to λ2.

[0095] In the example of Fig. 14, first, the wavelength of the input optical signal SO1 is operated at λ1, as in Fig. 10. Specifically, λ1 is set as the selected wavelength of the wavelength selective switch 220, and the wavelength selective switch 220 selects an optical signal with wavelength λ1 from the wavelength-multiplexed signal WO and outputs the selected optical signal with wavelength λ1 as the input optical signal SO1.

[0096] Furthermore, local light sources A1-AN output local light of wavelengths λ1-λN, and optical switch SW2 is set to select local light LO1 of local light source A1, and local light LO1 of wavelength λ1 is output from optical switch SW2. The coherent receiver front end unit 110 coherently detects the input optical signal SO1 of wavelength λ1 input from the wavelength selective switch 220 using the local light LO1 of wavelength λ1 from optical switch SW2.

[0097] In this state, the user interface unit 300 sets wavelength information (λ2) of the next input optical signal SO1 to the control unit 210 (S101). For example, at the timing when the wavelength of the input optical signal SO1 is to be switched, the user inputs the next wavelength λ2 to the user interface unit 300, and the user interface unit 300 sets the wavelength information of the input wavelength λ2.

[0098] When the control unit 210 receives the wavelength information (λ2) of the next input optical signal SO1 from the user interface unit 300, it instructs the optical switch SW2 to change the selection of the input signal to the local light source A2 (S131).The control unit 210 also instructs the wavelength selective switch 220 to change the selected wavelength to the wavelength λ2 (S108).

[0099] When the optical switch SW2 receives an instruction to change the selection of the input signal from the user interface unit 300, it switches to select and output the local light LO2 from the local light source A2 (S132) and notifies the control unit 210 of the completion of the change (S133). Also, when the wavelength selective switch 220 receives an instruction to change the selected wavelength from the user interface unit 300, it switches to select and output the wavelength λ2 (S111) and notifies the control unit 210 of the completion of the change (S112).

[0100] As a result, the wavelength selective switch 220 selects an optical signal of wavelength λ2 from the wavelength multiplexed signal WO and outputs the selected optical signal of wavelength λ2 as the input optical signal SO1. The optical switch SW2 outputs a local light LO2 of wavelength λ2, and the coherent receiver front end unit 110 coherently detects the input optical signal SO1 of wavelength λ2 input from the wavelength selective switch 220 using the local light LO2 of wavelength λ2 from the optical switch SW2.

[0101] When the control unit 210 receives a notification of completion of change of input signal selection from the optical switch SW2 and a notification of change completion from the wavelength selective switch 220, it notifies the user interface unit 300 of the completion of wavelength change of the input optical signal SO1 (S113).

[0102] As described above, in this embodiment, local light from multiple local light sources is selected by a selection unit such as an optical switch and output to a coherent receiver front-end unit. This makes it possible to shorten the time required to change the wavelength of the local light source when the wavelength of the input optical signal input to the optical repeater is changed. Although it takes several seconds to several tens of seconds to change the wavelength of the output light from a wavelength-tunable light source used as a local light source, this embodiment makes it possible to respond to rapid wavelength switching.

[0103] For example, as in Example 1, by switching the local light source with an optical switch, the wavelength switching time can be reduced to about several tens of milliseconds. Also, as in Example 2, by realizing the same function as an optical switch with an optical variable attenuator and an optical coupler, the wavelength switching time can be further reduced to about several milliseconds. Also, as in Example 3, by preparing local light sources for the number of wavelengths that can be used and switching the local light sources, the wavelength can be switched immediately without having to change the wavelength of the wavelength-tunable light source in advance.

[0104] (Embodiment 2) Next, embodiment 2 will be described. In this embodiment, an example will be described in which one of a plurality of transmission light sources is selected and the wavelength of the transmission light is switched. This embodiment is an example in which the configuration of the local light source side of embodiment 1 is applied to the transmission light source side. Note that this embodiment can be implemented in combination with embodiment 1, and each configuration shown in embodiment 1 may be used as appropriate.

[0105] Fig. 15 shows a configuration example of an optical repeater 2 according to this embodiment. As shown in Fig. 15, the optical repeater 2 according to this embodiment further includes a transmission light source B2 and a transmission light selection unit 132, compared to Fig. 6 of the first embodiment, for example.

[0106] In this embodiment, the transmission light source B1 (e.g., a third light source) generates transmission light PO1 of a third wavelength and outputs the generated transmission light PO1 to the transmission light selection unit 132. The transmission light source B2 (e.g., a fourth light source) generates transmission light PO2 of a fourth wavelength and outputs the generated transmission light PO2 to the transmission light selection unit 132. For example, the transmission light sources B1 and B2 are wavelength-tunable light sources that generate and output transmission light PO1 and PO2 of wavelengths set by the control unit 210. The transmission light sources B1 and B2 are not limited to wavelength-tunable light sources, and may each generate transmission light PO1 and PO2 of a preset fixed wavelength. For example, two or more fixed-wavelength light sources may be provided as the transmission light sources.

[0107] The transmission light selector 132 (e.g., a second selector) selects one of the transmission light beams PO1 and PO2 input from the transmission light sources B1 and B2, and outputs the selected light beam as the transmission light beam PO to the coherent transmission front-end 120. The transmission light selector 132 selects the transmission light beam from one of the transmission light sources in accordance with control from the control unit 210. When the transmission light sources B1 and B2 are wavelength-tunable light sources and switching is performed from the transmission light source B1 to the transmission light source B2, the transmission light selector 132 may select and output the transmission light beam PO2 from the transmission light source B2 after the wavelength switching of the transmission light source B2 is completed. For example, the transmission light selector 132 may be configured with an optical switch, similar to the local light selector 131, or may be configured with a variable optical attenuator and an optical coupler, or may have other configurations. The other configurations are the same as those in the first embodiment.

[0108] In the example of FIG. 15 , when switching the wavelength of the input optical signal SO1, the local light selector 131 switches between the local light of the local light source A1 or A2, and when switching the wavelength of the output optical signal SO2, the transmission light selector 132 switches between the transmission light of the transmission light source B1 or B2. The wavelength of either the input optical signal SO1 or the output optical signal SO2 may be switched, or both wavelengths may be switched. When switching the wavelengths of both the input optical signal SO1 and the output optical signal SO2, the wavelength switching of the input optical signal SO1 and the wavelength switching of the output optical signal SO2 may be performed in parallel, or one may be performed first. For example, when setting or switching the wavelength of the output optical signal SO2, the control unit 210 controls the operation of the transmission light sources B1 and B2 and the transmission light selector 132. When controlling the transmission light sources B1 and B2, if the transmission light sources B1 and B2 are wavelength-tunable light sources, the control unit 210 sets the wavelengths of the transmission light sources PO1 and PO2 output by the transmission light sources B1 and B2 based on setting information and wavelength change instructions acquired from the user interface unit 300. In controlling the transmission light selection unit 132 , the control unit 210 controls the transmission light selected by the transmission light selection unit 132 based on setting information and wavelength change instructions acquired from the user interface unit 300 .

[0109] Note that the optical repeater 2 is not limited to the configuration example of Fig. 15 , and may be configured to include only one light source on the local light source side, as shown in Fig. 16 . In the example of Fig. 16 , the local light source A1 generates a local light LO1 of a predetermined wavelength and outputs the generated local light LO to the coherent receiver front end unit 110. In this case, the local light source A1 is a wavelength-tunable light source, and generates and outputs a local light LO of a wavelength set by the control unit 210.

[0110] <Specific Example 1 of Embodiment 2> Next, specific example 1 of embodiment 2 will be described. In this specific example 1, an optical switch is used as the transmission light selection unit 132. This specific example 1 is an example in which the configuration of specific example 1 of embodiment 1 is applied to the transmission light source side.

[0111] Fig. 17 shows a configuration example of the transmission light selecting unit 132 according to this specific example 1. As shown in Fig. 17, in this specific example 1, the transmission light selecting unit 132 is configured with an optical switch SW3. Also, in this specific example 1, the transmission light sources B1 and B2 are wavelength-tunable light sources.

[0112] The optical switch SW3 is an optical switch for selecting transmitted light and is a 2×1 optical switch (2 input-1 output optical switch). The optical switch SW3 selects either transmitted light PO1 or PO2 input from the transmitted light sources B1 and B2, and outputs the selected light as transmitted light PO to the coherent transmission front end unit 120. The optical switch SW3 switches the transmitted light PO to be output from the input light in response to an instruction from the control unit 210.

[0113] FIG. 18 shows an example of operation of this specific example 1. FIG. 18 shows an example of operation when the wavelength of output optical signal SO2 is switched from λ3 to λ4. Note that FIG. 18 is just one example, and if transmission light source B1 outputs transmission light PO1 with wavelength λ3 and transmission light source B2 outputs transmission light source PO2 with wavelength λ4, steps S202 to S206 may be omitted. In this case, the user interface unit 300 sets wavelength information (λ4) of the next output optical signal SO2 to the control unit 210 (S201), and the control unit 210 may instruct the optical switch SW3 to change the selection of the input signal to the transmission light source B2 side (S207).

[0114] 18, first, the wavelength of output optical signal SO2 is operated at λ3. Specifically, the wavelengths of transmission light sources B1 and B2 are set to λ3, and transmission light PO1 of wavelength λ3 and transmission light PO2 of wavelength λ3 are output from transmission light sources B1 and B2. Optical switch SW3 is set to select transmission light PO1 on the transmission light source B1 side, and transmission light PO1 of wavelength λ3 is output from optical switch SW3. The coherent transmission front-end unit 120 coherently modulates the analog electrical signal SA2 input from the compensation unit 150 with transmission light PO1 of wavelength λ3 from optical switch SW3.

[0115] In this state, the user interface unit 300 sets wavelength information (λ4) of the next output optical signal SO2 to the control unit 210 (S201). For example, before switching the wavelength of the output optical signal SO2, the user inputs the next wavelength λ4 to the user interface unit 300, and the user interface unit 300 sets the wavelength information of the input wavelength λ4.

[0116] When the control unit 210 receives wavelength information (λ4) of the next output optical signal SO2 from the user interface unit 300, it instructs the transmission light source B2 (a transmission light source not currently selected by the optical switch) to change the optical output wavelength to λ4 (S202). When the transmission light source B2 receives the instruction to change the wavelength to λ4 from the control unit 210, it changes the wavelength of the output transmission light PO2 to the instructed wavelength λ4 (S203) and notifies the control unit 210 of the completion of the wavelength change (S204).

[0117] When the control unit 210 receives the notification that the wavelength change has been completed from the transmission light source B2, it notifies the user interface unit 300 that the standby is OK (S205). For example, the user interface unit 300 receives the notification that the standby is OK from the control unit 210 and outputs (displays) to the user that the standby for switching the wavelength of the output optical signal SO2 has been completed.

[0118] Thereafter, the user interface unit 300 instructs the control unit 210 to change the wavelength of the output optical signal SO2 (S206). For example, after receiving standby OK, the user inputs a wavelength change instruction to the user interface unit 300 at any timing (timing to switch the wavelength of the output optical signal SO2), and the user interface unit 300 instructs the control unit 210 to change the wavelength.

[0119] When the control unit 210 receives an instruction to change the wavelength of the output optical signal SO2 from the user interface unit 300, it instructs the optical switch SW3 to change the selection of the input signal to the transmission light source B2 side (S207).

[0120] When the optical switch SW3 receives an instruction from the control unit 210 to change the selection of the input signal, it switches to select and output the transmission light PO2 from the transmission light source B2 (S208), and notifies the control unit 210 of the completion of the change (S209).

[0121] As a result, the optical switch SW3 outputs the transmission light PO2 of wavelength λ4, and the coherent transmission front end unit 120 coherently modulates the analog electrical signal SA2 input from the compensation unit 150 with the transmission light PO2 of wavelength λ4 from the optical switch SW3.

[0122] When the control unit 210 receives a notification from the optical switch SW3 indicating that the change in the input signal selection has been completed, the control unit 210 notifies the user interface unit 300 that the wavelength change of the output optical signal SO2 has been completed (S210). For example, the user interface unit 300 receives a notification from the control unit 210 indicating that the wavelength change has been completed, and outputs (displays) the completion of the wavelength change of the output optical signal SO2 to the user.

[0123] <Specific Example 2 of Embodiment 2> Next, specific example 2 of embodiment 2 will be described. In this specific example 2, an optical variable attenuator and an optical coupler are used as the transmission light selection unit 132. This specific example 2 is an example in which the configuration of specific example 2 of embodiment 1 is applied to the transmission light source side.

[0124] Fig. 19 shows a configuration example of the transmission light selecting unit 132 according to this specific example 2. As shown in Fig. 19, in this specific example 2, the transmission light selecting unit 132 includes variable optical attenuators VOA3 and VOA4 and an optical coupler CP2. In addition, in specific example 1, the transmission light sources B1 and B2 are wavelength-tunable light sources.

[0125] The variable optical attenuator VOA3 attenuates the optical power of the transmission light PO1 input from the transmission light source B1 and outputs the attenuated optical signal to the optical coupler CP2. The variable optical attenuator VOA3 attenuates the optical power of the transmission light PO1 by an attenuation amount set by the control unit 210. For example, when the attenuation amount is ∞ (infinity), the transmission light PO1 is not output from the variable optical attenuator VOA3.

[0126] Similar to the variable optical attenuator VOA3, the variable optical attenuator VOA4 attenuates the optical power of the transmission light PO2 input from the transmission light source B2 and outputs the attenuated optical signal to the optical coupler CP2. The variable optical attenuator VOA4 attenuates the optical power of the transmission light PO2 by an attenuation amount set by the control unit 210. For example, when the attenuation amount is ∞, the variable optical attenuator VOA4 does not output the transmission light PO2.

[0127] The optical coupler (multiplexer) CP2 is a 1x2 optical coupler (one input, two output optical coupler) that multiplexes the transmission light PO1 and PO2 input via the variable optical attenuators VOA3 and VOA4 and outputs the multiplexed light as transmission light PO to the coherent transmission front end unit 120. By controlling the attenuation of the variable optical attenuators VOA3 and VOA4, either transmission light PO1 or transmission light PO2 is output from the optical coupler CP2. For example, when transmission light PO1 is output from the variable optical attenuator VOA3 but transmission light PO2 is not output from the variable optical attenuator VOA4, the optical coupler CP2 outputs transmission light PO1. When transmission light PO2 is output from the variable optical attenuator VOA4 but transmission light PO1 is not output from the variable optical attenuator VOA3, the optical coupler CP2 outputs transmission light PO2.

[0128] FIG. 20 shows an example of operation of this specific example 2. Similar to FIG. 18, FIG. 20 shows an example of operation when switching the wavelength of output optical signal SO2 from λ3 to λ4. Note that FIG. 20 is merely an example, and if transmission light source B1 outputs transmission light PO1 with wavelength λ3 and transmission light source B2 outputs transmission light source PO2 with wavelength λ4, steps S202-S206 may be omitted. In this case, the user interface unit 300 sets wavelength information (λ4) of the next output optical signal SO2 to the control unit 210 (S201), and the control unit 210 instructs the variable optical attenuator VOA3 to change the attenuation to ∞ (S211) and instructs the variable optical attenuator VOA4 to change the attenuation to 0 (S212).

[0129] In the example of Figure 20, first, as in Figure 18, the wavelength of the output optical signal SO2 is operated at λ3. Specifically, the wavelengths of the transmission light sources B1 and B2 are set to λ3, and transmission light PO1 and transmission light PO2 having wavelengths λ3 are output from the transmission light sources B1 and B2. The attenuation (ATT) of the variable optical attenuator VOA3 is set to 0, and the attenuation of the variable optical attenuator VOA4 is set to ∞. As a result, the optical coupler CP2 outputs the transmission light PO1 having wavelength λ3 via the variable optical attenuator VOA3 to the coherent transmission front end unit 120. The coherent transmission front end unit 120 coherently modulates the analog electrical signal SA2 input from the compensation unit 150 with the transmission light PO1 having wavelength λ3 from the optical coupler CP2.

[0130] 18 , the user interface unit 300 sets wavelength information (λ4) of the next output optical signal SO2 to the control unit 210 (S201). The control unit 210 instructs the transmission light source B2 to change the optical output wavelength to λ4 (S202), the transmission light source B2 changes the wavelength of the output transmission light PO2 to the instructed wavelength λ4 (S203), and notifies the control unit 210 that the wavelength change is complete (S204). The control unit 210 then notifies the user interface unit 300 that standby is OK (S205).

[0131] Thereafter, the user interface unit 300 instructs the control unit 210 to change the wavelength of the output optical signal SO2 (S206).

[0132] When the control unit 210 receives an instruction to change the wavelength of the output optical signal SO2 from the user interface unit 300, it instructs the optical variable attenuator VOA3 to change the attenuation to infinity (S211) and instructs the optical variable attenuator VOA4 to change the attenuation to zero (S212).

[0133] When the variable optical attenuator VOA3 receives an instruction to change the attenuation from the user interface unit 300, it changes the attenuation of the transmission light PO1 to infinity, stops output of the transmission light PO1 with wavelength λ3 (S213), and notifies the control unit 210 of the completion of the change (S214). When the variable optical attenuator VOA4 receives an instruction to change the attenuation from the user interface unit 300, it changes the attenuation of the transmission light PO2 to 0, starts output of the transmission light PO2 with wavelength λ4 (S215), and notifies the control unit 210 of the completion of the change (S216).

[0134] As a result, the optical coupler CP2 outputs the transmission light PO2 of wavelength λ4, and the coherent transmission front end unit 120 coherently modulates the analog electrical signal SA2 input from the compensation unit 150 with the transmission light PO2 of wavelength λ4 from the optical coupler CP2.

[0135] When the control unit 210 receives notification of the completion of the change in the attenuation amount from the variable optical attenuators VOA3 and VOA4, it notifies the user interface unit 300 of the completion of the change in the wavelength of the output optical signal SO2 (S210).

[0136] <Specific Example 3 of Embodiment 2> Next, specific example 3 of embodiment 2 will be described. In this specific example 3, the transmitted light from a plurality of transmitted light sources is further switched by an optical switch in the transmitted light selection unit 132. This specific example 3 is an example in which the configuration of specific example 3 of embodiment 1 is applied to the transmitted light source side.

[0137] 21 shows an example of the configuration of the transmission light selection unit 132 according to this specific example 3. As shown in FIG. 21, in this specific example 3, like in specific example 1, the transmission light selection unit 132 is configured with an optical switch SW4. Also in specific example 3, the optical repeater 2 is equipped with a plurality of transmission light sources B1-BN. The transmission light sources B1-BN each output transmission light of a different fixed wavelength. The transmission light sources B1-BN are light sources with wavelengths that can be used in the optical transmission system 1. The wavelengths of the transmission light sources B1-BN correspond to the wavelengths used in the optical transmission system 1, and are λ1-λN.

[0138] The optical switch SW4 is a switch for selecting transmitted light and is an N×1 optical switch (N input-1 output optical switch). The optical switch SW4 selects one of the transmitted light PO1-PON input from the transmitted light sources B1-BN, and outputs the selected light as the transmitted light PO to the coherent transmission front end unit 120. The optical switch SW4 switches the transmitted light PO to be output from the input light in response to an instruction from the control unit 210. Note that the same function as the optical switch SW4 may be realized by an optical variable attenuator and an optical coupler, as in specific example 2.

[0139] In addition, when the optical repeater 2 includes local light sources A1-AN and transmitting light sources B1-BN, the local light sources and transmitting light source may be a common light source. For example, the optical repeater 2 may include N light sources that output optical signals of wavelengths λ1-λN, and the optical signals of wavelengths λ1-λN may be output from the N light sources to an optical switch SW2 on the local light source side and an optical switch SW4 on the transmitting light source side to switch between the local light and transmitting light. In this case, the N light sources output optical signals of the power required for the local light and transmitting light.

[0140] Fig. 22 shows an example of operation of this specific example 3. Like Fig. 18, Fig. 22 shows an example of operation when the wavelength of the output optical signal SO2 is switched from λ3 to λ4.

[0141] In the example of Fig. 22, first, as in Fig. 18, the wavelength of output optical signal SO2 is λ3. Specifically, transmission light sources B1-BN output transmission light of wavelengths λ1-λN, optical switch SW4 is set to select transmission light PO3 from transmission light source B3, and transmission light PO3 of wavelength λ3 is output from optical switch SW4. The coherent transmission front-end unit 120 coherently modulates the analog electrical signal SA2 input from the compensation unit 150 with the transmission light PO3 of wavelength λ3 from optical switch SW4.

[0142] In this state, the user interface unit 300 sets wavelength information (λ4) of the next output optical signal SO2 to the control unit 210 (S201). For example, at the timing when the wavelength of the output optical signal SO2 is to be switched, the user inputs the next wavelength λ4 to the user interface unit 300, and the user interface unit 300 sets the wavelength information of the input wavelength λ4.

[0143] When the control unit 210 receives the wavelength information (λ4) of the next output optical signal SO2 from the user interface unit 300, it instructs the optical switch SW4 to change the selection of the input signal to the transmitting light source B4 side (S221).

[0144] When the optical switch SW4 receives an instruction to change the selection of the input signal from the user interface unit 300, it switches to select and output the transmission light PO4 from the transmission light source B4 (S222), and notifies the control unit 210 of the completion of the change (S223).

[0145] As a result, the optical switch SW4 outputs transmission light PO4 of wavelength λ4, and the coherent transmission front end unit 120 coherently modulates the analog electrical signal SA2 input from the compensation unit 150 with the transmission light PO4 of wavelength λ4 from the optical switch SW4.

[0146] When the control unit 210 receives a notification from the optical switch SW3 that the change in the input signal selection has been completed, it notifies the user interface unit 300 that the wavelength change of the output optical signal SO2 has been completed (S210).

[0147] As described above, in this embodiment, transmission light from a plurality of transmission light sources is selected by a selection unit such as an optical switch and output to a coherent transmission front-end unit. As a result, similar to the first embodiment, when the wavelength of the output optical signal output from the optical repeater is changed, the time required to change the wavelength of the transmission light source can be shortened. Although it takes several seconds to several tens of seconds to change the output light wavelength of a wavelength-tunable light source used as a transmission light source, this embodiment makes it possible to accommodate rapid wavelength switching. As with the first embodiment, specific example 1-3 can also shorten the wavelength switching time.

[0148] (Embodiment 3) Next, embodiment 3 will be described. In this embodiment, an example will be described in which the automatic bias control circuit resumes automatic bias control after wavelength switching using the bias voltage immediately before wavelength switching. Note that this embodiment can be implemented in combination with embodiment 1 or 2, and the configurations shown in embodiment 1 or 2 may be used as appropriate.

[0149] Fig. 23 shows a configuration example of the optical repeater 2 according to this embodiment. As shown in Fig. 23, the optical repeater 2 according to this embodiment further includes a bias voltage storage unit 141, for example, compared to Fig. 15 of the second embodiment.

[0150] In this embodiment, the automatic bias control circuit 140 temporarily suspends (interrupts) and resumes (starts) the automatic bias control process in accordance with control from the control unit 210. When the automatic bias control circuit 140 temporarily suspends the automatic bias control process, it notifies the control unit 210 of the bias voltage BS (the current optimal value of the bias voltage) that is set in the IQ modulator C3 of the coherent transmission front end unit 120 at that time.

[0151] Furthermore, the control unit 210 controls the operation of the automatic bias control circuit 140 when switching the wavelength of the input optical signal SO1 or the output optical signal SO2. Before switching the wavelength, the control unit 210 instructs the automatic bias control circuit 140 to temporarily suspend the automatic bias control process, and acquires the bias voltage BS at the time of the temporary suspension. The bias voltage memory unit 141 stores the bias voltage BS acquired from the automatic bias control circuit 140. After the wavelength switching is completed, the control unit 210 instructs the automatic bias control circuit 140 to resume the automatic bias control process. When resuming the automatic bias control process, the control unit 210 resumes the automatic bias control process using the bias voltage BS stored in the bias voltage memory unit 141. The other configurations are the same as those of the first and second embodiments.

[0152] Note that the optical repeater 2 is not limited to the configuration example of FIG. 23 , and may be configured to include only one light source on either the local light source side or the transmission light source side, or both. For example, in the example of FIG. 24 , only one light source is provided on each of the local light source side and the transmission light source side. In the example of FIG. 24 , the local light source A1 generates a local light LO1 of a predetermined wavelength and outputs the generated local light LO to the coherent receiver front end 110. In this case, the local light source A1 is a wavelength-tunable light source that generates and outputs the local light LO of a wavelength set by the control unit 210. Furthermore, the transmission light source B1 generates a transmission light PO1 of a predetermined wavelength and outputs the generated transmission light PO to the coherent transmitter front end 120. In this case, the transmission light source B1 is a wavelength-tunable light source that generates and outputs the transmission light PO of a wavelength set by the control unit 210.

[0153] 25A and 25B show an example of the operation of this embodiment. FIGS. 25A and 25B show an example in which this embodiment is applied to the operation of Specific Example 1 of Embodiment 1 in FIG. 10. In this example, as in Specific Example 1 of Embodiment 1, the local light selector 131 is configured with an optical switch SW1. This embodiment may also be applied to Specific Examples 2 and 3 of Embodiment 1. For example, when this embodiment is applied to the operation of Specific Example 2 of Embodiment 1 in FIG. 12, in response to an instruction from the user interface unit 300 to change the wavelength of the input optical signal SO1 (S106), S301-S304 may be executed, the attenuation amounts of the variable optical attenuators VOA1 and VOA2 may be changed (S121-S126), the wavelength selective switch 220 may be switched (S108, S111-S112), and then S305-S306 may be executed. When this embodiment is applied to the operation of specific example 3 of embodiment 1 in Figure 14, S301-S304 may be executed according to the setting of wavelength information (λ2) of the next input optical signal SO1 from the user interface unit 300 (S101), the optical switch SW2 may be switched (S131-S133), and after switching the wavelength selective switch 220 (S108, S111-S112), S305-S306 may be executed.

[0154] 25A and 25B show an example of operation when the wavelength of the input optical signal SO1 is switched from λ1 to λ2, similar to Fig. 10. In the example of Fig. 25A and 25B, the wavelength of the input optical signal SO1 is first operated at λ1. As in Fig. 10, λ1 is set as the selected wavelength of the wavelength selective switch 220, the wavelengths of the local light sources A1 and A2 are set to λ1, and the optical switch SW1 is set to select the local light source LO1 on the local light source A1 side.

[0155] 10 , the user interface unit 300 sets wavelength information (λ2) of the next input optical signal SO1 to the control unit 210 (S101). The control unit 210 instructs the local light source A2 to change the optical output wavelength to λ2 (S102), the local light source A2 changes the wavelength of the local light LO2 it outputs to the instructed wavelength λ2 (S103), and notifies the control unit 210 that the wavelength change is complete (S104). The control unit 210 then notifies the user interface unit 300 that standby is OK (S105).

[0156] Thereafter, the user interface unit 300 instructs the control unit 210 to change the wavelength of the input optical signal SO1 (S106).

[0157] When the control unit 210 receives an instruction to change the wavelength of the input optical signal SO1 from the user interface unit 300, it instructs the automatic bias control circuit 140 to temporarily suspend the automatic bias control process (fix the output bias voltage) (S301). When the automatic bias control circuit 140 receives the instruction to suspend from the control unit 210, it temporarily suspends the automatic bias control process (S302) and transmits the bias voltage BS at that time to the control unit 210 (S303). When the control unit 210 receives the bias voltage BS from the automatic bias control circuit 140, it stores the voltage value in the bias voltage storage unit 141 (S304).

[0158] Next, the control unit 210 instructs the optical switch SW1 to change the selection of the input signal to the local light source A2 (S107), and instructs the wavelength selective switch 220 to change the selected wavelength to wavelength λ2 (S108). The optical switch SW1 switches to select and output the local light LO2 from the local light source A2 (S109), and notifies the control unit 210 of the completion of the change (S110). The wavelength selective switch 220 switches to select and output the wavelength λ2 (S111), and notifies the control unit 210 of the completion of the change (S112).

[0159] When the control unit 210 receives a notification that the input signal selection has been changed from the optical switch SW1 and a notification that the change has been completed from the wavelength selective switch 220, it instructs the automatic bias control circuit 140 to resume the automatic bias control process at the bias voltage BS stored in the bias voltage storage unit 141 (S305). The automatic bias control circuit 140 resumes the automatic bias control process at the instructed bias voltage BS (S306). Next, the control unit 210 notifies the user interface unit 300 that the wavelength change of the input optical signal SO1 has been completed (S113).

[0160] 26A and 26B show another example of the operation of this embodiment. FIGS. 26A and 26B show an example in which this embodiment is applied to the operation of Specific Example 1 of Embodiment 2 in FIG. 18 . In this example, as in Specific Example 1 of Embodiment 2, the transmission light selection unit 132 is configured with the optical switch SW3. This embodiment may also be applied to Specific Examples 2 and 3 of Embodiment 2. For example, when this embodiment is applied to the operation of Specific Example 2 of Embodiment 2 in FIG. 20 , S301-S304 may be executed in response to an instruction from the user interface unit 300 to change the wavelength of the output optical signal SO2 (S206), and the attenuation amounts of the variable optical attenuators VOA3 and VOA4 may be changed (S211-S216), and then S305-S306 may be executed. When this embodiment is applied to the operation of specific example 3 of embodiment 2 of Figure 22, S301-S304 may be executed in accordance with the setting of wavelength information (λ4) of the next output optical signal SO2 from the user interface unit 300 (S201), and after switching the optical switch SW3 (S221-S223), S305-S306 may be executed.

[0161] 26A and 26B show an example of operation when the wavelength of output optical signal SO2 is switched from λ3 to λ4, similar to Fig. 18. In the example of Fig. 26A and 26B, the wavelength of output optical signal SO2 is first operated at λ3. As in Fig. 18, the wavelengths of transmitting light sources B1 and B2 are set to λ3, and optical switch SW3 is set to select transmitting light PO1 on the transmitting light source B1 side.

[0162] 18 , the user interface unit 300 sets wavelength information (λ4) of the next output optical signal SO2 to the control unit 210 (S201). The control unit 210 instructs the transmission light source B2 to change the optical output wavelength to λ4 (S202), the transmission light source B2 changes the wavelength of the output transmission light PO2 to the instructed wavelength λ4 (S203), and notifies the control unit 210 that the wavelength change is complete (S204). The control unit 210 then notifies the user interface unit 300 that standby is OK (S205).

[0163] Thereafter, the user interface unit 300 instructs the control unit 210 to change the wavelength of the output optical signal SO2 (S206).

[0164] When the control unit 210 receives an instruction to change the wavelength of the output optical signal SO2 from the user interface unit 300, it instructs the automatic bias control circuit 140 to temporarily suspend the automatic bias control process (S301). When the automatic bias control circuit 140 receives the instruction to suspend from the control unit 210, it temporarily suspends the automatic bias control process (S302) and transmits the bias voltage BS at that time to the control unit 210 (S303). When the control unit 210 receives the bias voltage BS from the automatic bias control circuit 140, it stores the voltage value in the bias voltage storage unit 141 (S304).

[0165] Next, the control unit 210 instructs the optical switch SW3 to change the input signal selection to the transmission light source B2 side (S207). The optical switch SW3 switches to select and output the transmission light PO2 from the transmission light source B2 (S208), and notifies the control unit 210 of the completion of the change (S209).

[0166] When the control unit 210 receives a notification from the optical switch SW3 indicating that the change in the input signal selection has been completed, it instructs the automatic bias control circuit 140 to resume control processing at the bias voltage BS stored in the bias voltage storage unit 141 (S305). The automatic bias control circuit 140 resumes the automatic bias control processing at the instructed bias voltage BS (S306). Next, the control unit 210 notifies the user interface unit 300 that the wavelength change of the output optical signal SO2 has been completed (S210).

[0167] As described above, in this embodiment, when switching the wavelength of an input optical signal input to an optical repeater or an output optical signal output from an optical repeater, the automatic bias control process of the automatic bias control circuit is temporarily stopped, the bias voltage at that time is stored, and after the wavelength switching is completed, the automatic bias control process is resumed with the stored bias voltage. This reduces the time required to optimize the bias voltage of the modulator in the coherent transmission front end when the wavelength of the input optical signal or the output optical signal is changed.

[0168] When the wavelength input to the modulator in the coherent transmitter front end is changed, if the optical power temporarily fluctuates, the optical input is lost, or the modulated signal becomes non-existent, the bias voltage controlled by the automatic bias control circuit deviates from the optimal value and takes time to return to its original value. However, according to this embodiment, the bias voltage immediately before the wavelength is switched is used to resume the automatic bias control process after the wavelength is switched, thereby shortening the time it takes for the bias voltage to return to its optimal value. Because the optimal bias voltage value tends to fluctuate over time, using the bias voltage immediately before the wavelength is switched makes it possible to return to the optimal bias value in a short time.

[0169] It should be noted that the present disclosure is not limited to the above-described embodiments and can be modified as appropriate without departing from the spirit of the present disclosure. For example, in the above-described embodiments, an example in which a single wavelength (single channel) is input and converted into another wavelength is described, but multiple wavelengths may be input and the multiple wavelengths may be collectively converted into multiple other wavelengths.

[0170] Each component in the above-described embodiments may be configured with hardware or software, or both, and may be configured with a single piece of hardware or software, or may be configured with multiple pieces of hardware or software. For example, the functions (processing) of the control unit 210, the user interface unit 300, etc. may be realized by a computer having a processor such as a CPU (Central Processing Unit) and a memory serving as a storage device. For example, a program for performing the method in the embodiment (optical relay method) may be stored in the memory, and each function may be realized by executing the program stored in the memory with a processor.

[0171] These programs include instructions (or software code) that, when loaded into a computer, cause the computer to perform one or more functions described in the embodiments. The programs may be stored on a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, computer-readable media or tangible storage media include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technology, CD-ROM, digital versatile disc (DVD), Blu-ray disc or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage device. The programs may also be transmitted on a transitory computer-readable medium or communication medium. By way of example and not limitation, transitory computer-readable media or communication media include electrical, optical, acoustic, or other forms of propagated signals.

[0172] Although the present disclosure has been described above with reference to the embodiments, the present disclosure is not limited to the above-described embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present disclosure within the scope of the present disclosure.

[0173] Some or all of the above embodiments can be described as, but are not limited to, the following supplementary notes. (Supplementary Note 1) An optical repeater comprising: coherent optical receiving front-end means for coherently detecting an input optical signal based on local light; coherent optical transmitting front-end means for coherently modulating the coherently detected signal based on transmitted light and outputting the coherently modulated output optical signal; a first light source for outputting first light of a first wavelength; a second light source for outputting second light of a second wavelength; and selection means for selecting either the first light or the second light and outputting the selected light as the local light or the transmitted light. (Supplementary Note 2) The optical repeater according to Supplementary Note 1, wherein the selection means includes an optical switch that receives the first light and the second light and switches between the input lights to be output. (Supplementary Note 3) The optical repeater according to Supplementary Note 1, wherein the selection means includes: a first variable attenuator that attenuates the power of the first light by a set attenuation amount, a second variable attenuator that attenuates the power of the second light by a set attenuation amount, and an optical coupler that multiplexes the first light passed through the first variable attenuator and the second light passed through the second variable attenuator. (Supplementary Note 4) The optical repeater according to Supplementary Note 3, wherein either the first light or the second light is output from the optical coupler by controlling the attenuation amounts of the first variable attenuator and the second variable attenuator. (Supplementary Note 5) The optical repeater according to any one of Supplementary Notes 1 to 4, wherein the first light source and the second light source are wavelength-tunable light sources, and when switching the light to be selected from the first light to the second light, the selection means switches the selected light to the second light after completing wavelength switching of the second light source. (Supplementary Note 6) The optical repeater according to any one of Supplementary Notes 1 to 4, wherein the first light source and the second light source are fixed-wavelength light sources. (Supplementary Note 7) The optical repeater according to Supplementary Note 6, further comprising a plurality of light sources including the first light source and the second light source, wherein the wavelengths of the plurality of light sources correspond to wavelengths usable in an optical transmission system including the optical repeater, and the selection means selects one of the light beams from the plurality of light sources and outputs the selected light as the local light beam or the transmission light.(Supplementary Note 8) The optical repeater according to Supplementary Note 7, wherein the selection means includes: a first selection means that selects one of the light beams from the plurality of light sources and outputs the selected light as the local light, and a second selection means that selects one of the light beams from the plurality of light sources and outputs the selected light as the transmission light. (Supplementary Note 9) The optical repeater according to any one of Supplements 1 to 6, comprising: a third light source that outputs third light of a third wavelength, and a fourth light source that outputs fourth light of a fourth wavelength, wherein the selection means includes: a first selection means that selects one of the first light and the second light and outputs the selected light as the local light, and a second selection means that selects one of the third light and the fourth light and outputs the selected light as the transmission light. (Supplementary Note 10) The optical repeater according to any one of Supplementary Notes 1 to 9, further comprising: automatic bias control means that controls a bias voltage for coherent modulation of the coherent optical transmission front-end means. (Supplementary Note 11) The optical repeater according to Supplementary Note 10, wherein the automatic bias control means stops automatic bias control processing before switching the light selected by the selection means, and resumes the automatic bias control processing after switching the light selected by the selection means. (Supplementary Note 12) The optical repeater according to Supplementary Note 11, further comprising storage means for storing the bias voltage before switching the light selected by the selection means, and the automatic bias control means resumes the automatic bias control processing using the stored bias voltage after switching the light selected by the selection means. (Supplementary Note 13) The optical repeater according to any one of Supplementary Notes 1 to 12, further comprising compensation means for compensating for distortion of a signal coherently detected by the coherent optical receiving front-end means, and the coherent optical transmitting front-end means coherently modulates the signal compensated by the compensation means.(Supplementary Note 14) An optical transmission system including a plurality of optical repeaters, wherein the plurality of optical repeaters include: coherent optical receiving front-end means for coherently detecting an input optical signal input from the optical repeater of a previous stage based on local light; coherent optical transmitting front-end means for coherently modulating the coherently detected signal based on transmitted light, and outputting the coherently modulated output optical signal to the optical repeater of a next stage; a first light source for outputting first light of a first wavelength; a second light source for outputting second light of a second wavelength; and selection means for selecting either the first light or the second light, and outputting the selected light as the local light or the transmitted light. (Supplementary Note 15) An optical relay method comprising: coherently detecting an input optical signal based on local light; coherently modulating the coherently detected signal based on transmitted light; outputting the coherently modulated output optical signal; selecting either a first light having a first wavelength output from a first light source or a second light having a second wavelength output from a second light source; and outputting the selected light as the local light or the transmitted light.

[0174] 1 Optical transmission system 2, 2-1 to 2-10, 9 Optical repeater 3 Optical fiber transmission path 4, 5 Data center 6, 7 IT service provider 8 Event venue 21, 22 Light source 100 Wavelength conversion unit 110 Coherent receiving front end unit 111 Polarization separation unit 112-1, 112-2 90-degree hybrid circuit 113-1 to 113-4 O / E conversion unit 114-1 to 114-4 Amplifier 120 Coherent transmitting front end unit 121-1 to 121-4 Amplifier 122-1 to 122-4 MZ modulator 123 Polarization multiplexing unit 130 Selection unit 131 Local light selection unit 132 Transmission light selection unit 140 Automatic bias control circuit 141 Bias voltage memory unit 150 Compensation unit 200 Optical signal repeater 210 Control unit 220 Wavelength selection switch 300 User interface unit A1 to AN Local light source B1 to BN Transmission light source C1 Integrated coherent receiver C2 Driver amplifier C3 IQ modulator CP1, CP2 Optical coupler SW1 to SW4 Optical switch VOA1 to VOA4 Optical variable attenuator

Claims

1. a coherent optical receiving front-end means for coherently detecting an input optical signal based on a local oscillator light; a coherent optical transmission front-end means for coherently modulating the coherently detected signal based on a transmission light and outputting the coherently modulated output optical signal; a first light source that outputs a first light having a first wavelength; a second light source that outputs second light of a second wavelength; a selection means for selecting either the first light or the second light and outputting the selected light as the local light or the transmission light; An optical repeater device comprising:

2. the selecting means includes an optical switch that receives the first light and the second light and switches between the input lights to be output; 2. The optical repeater according to claim 1.

3. The selection means a first variable attenuator that attenuates the power of the first light by a set attenuation amount; a second variable attenuator that attenuates the power of the second light by a set attenuation amount; an optical coupler that combines the first light passed through the first variable attenuator and the second light passed through the second variable attenuator, 2. The optical repeater according to claim 1.

4. outputting either the first light or the second light from the optical coupler by controlling the attenuation of the first variable attenuator and the attenuation of the second variable attenuator; 4. The optical repeater according to claim 3.

5. the first light source and the second light source are wavelength-tunable light sources, when switching the light to be selected from the first light to the second light, the selecting unit switches the selected light to the second light after the wavelength switching of the second light source is completed.

5. The optical repeater according to claim 1.

6. the first light source and the second light source are fixed wavelength light sources; 5. The optical repeater according to claim 1.

7. a plurality of light sources including the first light source and the second light source; the wavelengths of the plurality of light sources correspond to wavelengths that can be used in an optical transmission system including the optical repeater; the selection means selects one of the lights from the plurality of light sources and outputs the selected light as the local light or the transmission light.

7. The optical repeater according to claim 6.

8. The selection means a first selection means for selecting one of the light beams from the plurality of light sources and outputting the selected light beam as the local light beam; a second selection means for selecting one of the light beams from the plurality of light sources and outputting the selected light beam as the transmission light; 8. The optical repeater according to claim 7.

9. An optical transmission system including a plurality of optical repeaters, the plurality of optical repeaters, a coherent optical receiving front-end means for coherently detecting an input optical signal input from the optical repeater at a previous stage based on local light; a coherent optical transmission front-end means for coherently modulating the coherently detected signal based on a transmission light and outputting the coherently modulated output optical signal to the optical repeater at the next stage; a first light source that outputs a first light having a first wavelength; a second light source that outputs second light of a second wavelength; a selection means for selecting either the first light or the second light and outputting the selected light as the local light or the transmission light; An optical transmission system comprising:

10. Coherently detecting an input optical signal based on local light; coherently modulating the coherently detected signal based on a transmitted light, and outputting the coherently modulated output optical signal; selecting either a first light having a first wavelength output from a first light source or a second light having a second wavelength output from a second light source, and outputting the selected light as the local light or the transmission light; Optical relay method.

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