OPTICAL COMMUNICATION APPARATUS, OPTICAL COMMUNICATION SYSTEM AND TRANSMISSION METHOD

Abstract

An optical communication device includes: a plurality of first distribution units that is connected to a plurality of optical transmission lines and outputs an optical signal input from any of first devices to any of the optical transmission lines; a plurality of second distribution units that is connected to a plurality of optical transmission lines and outputs an optical signal input from any of the optical transmission lines to any of second devices; and a transfer unit configured to transfer the optical signal transmitted from the first device connected to any of the plurality of first distribution units to any of the plurality of second distribution units connected to the specific second device.

Claims

1. An optical communication device comprising: a plurality of first distributors units that is connected to a plurality of optical transmission lines and outputs an optical signal input from any of first devices to any of the optical transmission lines; a plurality of second distributors units that is connected to a plurality of optical transmission lines and outputs an optical signal input from any of the optical transmission lines to any of second devices; and a transferer configured to transfer the optical signal transmitted from the first device connected to any of the plurality of first distributors units to any of the plurality of second distributors connected to the specific second device.

2. The optical communication device according to claim 1, wherein: each of the plurality of first distributors units includes a plurality of first optical switches and a plurality of signal multiplexers units; each of the plurality of second distributors units includes a plurality of second optical switches and a plurality of signal separators; each of the plurality of first optical switches includes one first port to which the first device is connected and a plurality of second ports to which each of the plurality of signal multiplexers is connected, at least one of the plurality of second ports being connected to the transferer unit; and each of the plurality of second optical switches includes one first port to which the second device is connected and a plurality of second ports to which each of the plurality of signal separators is connected, at least one of the plurality of second ports being connected to the transferer.

3. The optical communication device according to claim 1, wherein: each of the plurality of first distributors units includes a plurality of first optical switches and a plurality of signal multiplexers; each of the plurality of second distributors includes a plurality of second optical switches and a plurality of signal separators units; each of the plurality of first optical switches includes one first port to which the first device is connected and a plurality of second ports to which each of the plurality of signal multiplexers units is connected; each of the plurality of second optical switches includes one first port to which the second device is connected and a plurality of second ports to which each of the plurality of signal separators is connected; at least one of the plurality of signal multiplexers is connected to the transferer; and at least one of the plurality of signal separators units is connected to the transferer.

4. The optical communication device according to claim 1, wherein: each of the plurality of first distributors units includes one or more first wavelength selective optical switches; each of the plurality of second distributors includes one or more second wavelength selective optical switches; at least one port included in one of the one or more first wavelength selective optical switches is connected to the transferer unit; and at least one port included in one of the one or more second wavelength selective optical switches is connected to the transferer unit.

5. The optical communication device according to claim 4, wherein: the one or more first wavelength selective optical switches are N (N is an integer of 1 or more)M (M is an integer of 2 or more) wavelength selective optical switches; the one or more second wavelength selective optical switches are NM wavelength selective optical switches; and at least one of M ports of each NM wavelength selective optical switch is connected to the transferer.

6. The optical communication device according to claim 4, wherein: the one or more first wavelength selective optical switches are a 1N (N is an integer of 1 or more) wavelength selective optical switch and a 1M (M is an integer of 2 or more) wavelength selective optical switch; the one or more second wavelength selective optical switches are a 1N wavelength selective optical switch and a 1M wavelength selective optical switch; the 1N wavelength selective optical switch is connected to the 1M wavelength selective optical switch; and at least one of M ports of the 1M wavelength selective optical switch is connected to the transferer unit.

7. The optical communication device according to claim 4, wherein the transferer includes one or more first signal multiplexers units that multiplex optical signals output from the respective one or more first wavelength selective optical switches and output the multiplexed optical signal, and one or more second signal separators units that split the optical signal output from the one or more first signal multiplexers or an optical signal based on the optical signal output from the one or more first signal multiplexers units and output the split optical signals to an optical transmission line to which the one or more second wavelength selective optical switches are connected.

8. The optical communication device according to claim 7, wherein: the one or more first signal multiplexer are a plurality of first signal multiplexers units; the one or more second signal separators units are a plurality of second signal separators; and the optical communication device further includes one or more host first signal multiplexers that multiplex a plurality of optical signals output from the respective plurality of first signal multiplexers units and output the multiplexed optical signal, and one or more host second signal separators that split the optical signal output from the host first signal multiplex and output the split optical signals to the respective plurality of second signal units.

9. The optical communication device according to claim 7, wherein: the one or more first signal multiplexers are a plurality of first signal multiplexers; the one or more second signal separators are a plurality of second signal separators units; and the optical communication device further includes a plurality of host first signal separators splits the optical signal output from each of the plurality of first signal multiplexers and outputs the split optical signals, and a plurality of host second signal multiplexers that multiplexes the optical signals output from the plurality of host first signal separators and outputs the multiplexed optical signal to each of the plurality of second signal separators.

10. The optical communication device according to claim 1, wherein the transferer unit includes a plurality of wavelength selective optical switches that transfers optical signals having one or more preset wavelengths, and a transfer wavelength controller unit configured to set the one or more wavelengths to be transferred by the plurality of wavelength selective optical switches.

11. An optical communication system comprising: a plurality of first distributors units that is connected to a plurality of optical transmission lines and outputs an optical signal input from any of first devices to any of the optical transmission lines; a plurality of second distributors that is connected to a plurality of optical transmission lines and outputs an optical signal input from any of the optical transmission lines to any of second devices; and a transferer configured to transfer the optical signal transmitted from the first device connected to any of the plurality of first distributors units to any of the plurality of second distributors units connected to the specific second device.

12. A transfer method comprising: causing a plurality of first distributors units connected to a plurality of optical transmission lines to output an optical signal input from any of first devices to any of the optical transmission lines; causing a plurality of second distributors units connected to a plurality of optical transmission lines to output an optical signal input from any of the optical transmission lines to any of second devices; and transferring the optical signal transmitted from the first device connected to any of the plurality of first distributors units to any of the plurality of second distributors connected to the specific second device.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0018] FIG. 1 is a configuration diagram of an optical communication system according to a first embodiment.

[0019] FIG. 2 is a block diagram illustrating a specific example of a (first) functional configuration of a return transfer unit according to the first embodiment.

[0020] FIG. 3 is a sequence diagram showing a flow of processing of the optical communication system according to the first embodiment.

[0021] FIG. 4 is a block diagram illustrating a specific example of a (second) functional configuration of the return transfer unit according to the first embodiment.

[0022] FIG. 5 is a block diagram illustrating a specific example of a (third) functional configuration of the return transfer unit according to the first embodiment.

[0023] FIG. 6 is a block diagram illustrating a specific example of a (fourth) functional configuration of the return transfer unit according to the first embodiment.

[0024] FIG. 7 is a block diagram illustrating a specific example of a (fifth) functional configuration of the return transfer unit according to the first embodiment.

[0025] FIG. 8 is a block diagram illustrating a specific example of a (first) functional configuration of a return transfer unit according to a second embodiment.

[0026] FIG. 9 is a block diagram illustrating a specific example of a (second) functional configuration of the return transfer unit according to the second embodiment.

[0027] FIG. 10 is a block diagram illustrating a specific example of a (third) functional configuration of the return transfer unit according to the second embodiment.

[0028] FIG. 11 is a block diagram illustrating a specific example of a (first) functional configuration of a return transfer unit according to a third embodiment.

[0029] FIG. 12 is a block diagram illustrating a specific example of a (second) functional configuration of the return transfer unit according to the third embodiment.

[0030] FIG. 13 is a block diagram illustrating a specific example of a (third) functional configuration of the return transfer unit according to the third embodiment.

[0031] FIG. 14 is a configuration diagram of an optical communication system according to a fourth embodiment.

[0032] FIG. 15 is a sequence diagram showing a flow of processing of the optical communication system according to the fourth embodiment.

[0033] FIG. 16 is a configuration diagram of an optical communication system according to a modification example of the fourth embodiment.

[0034] FIG. 17 is a configuration diagram of an optical communication system according to a fifth embodiment.

[0035] FIG. 18 is a block diagram illustrating a specific example of a (first) functional configuration of a return transfer unit according to a modification example of the fifth embodiment.

[0036] FIG. 19 is a block diagram illustrating a specific example of a (second) functional configuration of the return transfer unit according to the modification example of the fifth embodiment.

[0037] FIG. 20 is a block diagram illustrating a specific example of a (third) functional configuration of the return transfer unit according to the modification example of the fifth embodiment.

[0038] FIG. 21 is a configuration diagram of an optical communication system according to a sixth embodiment.

[0039] FIG. 22 illustrates a configuration example of an optical communication system including a conventional optical communication device.

[0040] FIG. 23 is an explanatory diagram of a configuration in which a plurality of optical SWs is arranged in parallel.

DESCRIPTION OF EMBODIMENTS

[0041] Hereinafter, embodiments of the present invention will be described with reference to drawings.

First Embodiment

[0042] FIG. 1 is a configuration diagram of an optical communication system 1 according to a first embodiment. The optical communication system 1 includes P optical SWs 10-1 to 10-P (P is an integer of 2 or more), P optical SWs 11-1 to 11-P, a control unit 12, and a return transfer unit 14. Hereinafter, description will be made on the assumption that the optical SWs 10-1 to 10-P are used for transmitting optical signals in an uplink direction and that the optical SWs 11-1 to 11-P are used for transmitting optical signals in a downlink direction. In the following description, the optical SWs 10-1 to 10-P will be simply referred to as the optical SWs 10 when not distinguished, and the optical SWs 11-1 to 11-P will be simply referred to as the optical SWs 11 when not distinguished. The optical SWs 10, the optical SWs 11, the control unit 12, and the return transfer unit 14 are functional units forming one optical communication device.

[0043] The optical SW 10 is connected to a plurality of optical transmission lines and outputs an optical signal input from any of the optical transmission lines to another optical transmission line. The optical transmission lines are, for example, optical fibers. The optical SW 10 includes a plurality of first ports (e.g. n first ports) and a plurality of second ports (e.g. n or more second ports). Each first port of the optical SW 10 is connected to a subscriber device 16 via a transmission line 18. FIG. 1 illustrates an example where a subscriber device 16-1 is connected to the optical SW 10-1 via an optical transmission line 18-1. The optical SW 10 is one aspect of a first optical distribution unit.

[0044] Among the plurality of second ports of the optical SW 10, n second ports are connected to the return transfer unit 14 via n optical transmission lines. Remaining second ports of the plurality of second ports of the optical SW 10 may be connected to another device via optical transmission lines. In the following description, the number of first ports and the number of second ports in the optical SW 10 are assumed to be n for simplicity of description.

[0045] The optical SW 11 is connected to a plurality of optical transmission lines and outputs an optical signal input from any of the optical transmission lines to another optical transmission line. The optical SW 11 includes a plurality of first ports (e.g. n first ports) and a plurality of second ports (e.g. n or more second ports). Each first port of the optical SW 11 is connected to the subscriber device 16 via the transmission line 18. FIG. 1 illustrates an example where a subscriber device 16-2 is connected to the optical SW 11-1 via an optical transmission line 18-2, and a subscriber device 16-3 is connected to the optical SW 11-P via an optical transmission line 18-3. The optical SW 11 is one aspect of a second optical distribution unit.

[0046] Among the plurality of second ports of the optical SW 11, n second ports are connected to the return transfer unit 14 via n optical transmission lines. Remaining second ports of the plurality of second ports of the optical SW 11 may be connected to another device via optical transmission lines. In the following description, the number of first ports and the number of second ports in the optical SW 11 are assumed to be n for simplicity of description.

[0047] The subscriber device 16 is connected to the optical SW 10 or 11 via an optical access network such as a passive optical network (PON). The subscriber device 16 includes an optical transceiver. The optical transceiver is an example of an optical transmission unit and an optical reception unit in the subscriber device 16. The optical transceiver is a wavelength-tunable optical transmitter/receiver. In this case, the subscriber device 16 can perform communication at an arbitrary wavelength. The optical transceiver may be an optical transceiver having an auxiliary management and control channel (AMCC) function. In this case, a wavelength used in the subscriber device 16 is controlled via a control signal superimposed by the AMCC. The subscriber device 16 is one aspect of a first device and a second device.

[0048] The control unit 12 is connected to the second port of each of the optical SWs 10 and 11 via an optical transmission line. The control unit 12 includes a wavelength management control unit 121 and an optical SW control unit 122. The wavelength management control unit 121 allocates a wavelength to each subscriber device 16. In a case where the wavelength management control unit 121 allocates a wavelength to each subscriber device 16, the optical SW control unit 122 switches a path between the ports of the optical SW 10 or 11 so as to connect the subscriber device 16 and the wavelength management control unit 121.

[0049] The optical SW control unit 122 switches connection between the ports of the optical SW 10 and connection between the ports of the optical SW 11. For example, the optical SW control unit 122 switches the connection between the ports of each of the optical SWs 10 and 11 such that the subscriber device 16 can communicate with a desired subscriber device 16. The optical SW control unit 122 is one aspect of an optical distribution control unit.

[0050] The control unit 12 stores a management table. The management table includes information for identifying the subscriber devices 16, information regarding a wavelength allocated to each subscriber device 16, and information regarding the optical SW 10 or 11 to which the subscriber device 16 is connected (e.g. information regarding a port to which the subscriber device 16 is connected). The control unit 12 includes one or more processors.

[0051] The return transfer unit 14 receives an optical signal output from the optical SW 10 as an input and transfers the input optical signal to at least the optical SW 11 to which a destination subscriber device 16 is connected. The n optical transmission lines are connected from one optical SW 10 to the return transfer unit 14, and thus nP uplink optical transmission lines are connected to the return transfer unit 14. The n optical transmission lines are connected from one optical SW 11 to the return transfer unit 14, and thus nP downlink optical transmission lines are connected to the return transfer unit 14. The return transfer unit 14 is one aspect of a transfer unit.

[0052] In a case where return communication is performed across the optical SW 10, the optical SW control unit 122 switches a path between the ports of the optical SW 10 so as to connect an output destination of an optical signal from the optical SW 10 to the return transfer unit 14. The return transfer unit 14 performs control such that the input optical signal is output to a desired optical SW 11. With this configuration, return communication between arbitrary optical SWs is implemented while the number of wires required for return in each optical SW is suppressed to n.

[0053] In a case where the return transfer unit 14 is implemented by one device, for example, a wavelength selective switch (WSS), fiber cross connect (FXC), or cyclic arrayed waveguide gratings (AWG) having nPnP ports is used. However, in a case where nP is large, it is difficult to implement the WSS and fiber cross connect having nPnP ports, which also leads to an increase in price. Therefore, hereinafter, a case where the return transfer unit 14 includes a plurality of devices will also be described.

[0054] FIG. 2 is a block diagram illustrating a specific example of a (first) functional configuration of the return transfer unit 14 according to the first embodiment.

[0055] The return transfer unit 14 includes a WSS 141, a WSS 142, and a transfer wavelength control unit 143. The WSS 141 is connected to the n optical transmission lines connected to the second ports of each optical SW 10 (nP optical transmission lines in total) and outputs, to the WSS 142, an optical signal having a wavelength set by the transfer wavelength control unit 143 (hereinafter, referred to as a set wavelength) among optical signals transmitted via a certain optical transmission line. The WSS 141 is a wavelength selective optical switch. The number of ports required for the WSS 141 is nP. The WSS 141 is one aspect of a first multiplexing/demultiplexing unit.

[0056] The WSS 142 is connected to the n optical transmission lines connected to the second ports of each optical SW 11 (nP optical transmission lines in total) and outputs the optical signal having the set wavelength output from the WSS 141 to an optical transmission line serving as an output path of the set wavelength. The WSS 142 is a wavelength selective optical switch. The number of ports required for the WSS 142 is nP. The WSS 142 is one aspect of a second multiplexing/demultiplexing unit.

[0057] The transfer wavelength control unit 143 sets a wavelength to be output by the WSSs 141 and 142 in response to an instruction from the control unit 12. Specifically, in a case where the transfer wavelength control unit 143 receives, from the control unit 12, an instruction on a wavelength to be transferred at the time of return communication, the transfer wavelength control unit 143 sets a designated wavelength to the WSSs 141 and 142. Therefore, the WSSs 141 and 142 can output an optical signal having the set wavelength. The transfer wavelength control unit 143 may be mounted on the control unit 12.

[0058] FIG. 3 is a sequence diagram showing a flow of processing of the optical communication system 1 according to the first embodiment. FIG. 3 shows a case where the subscriber device 16-1 connected to the optical SW 10-1 and the subscriber device 16-2 connected to the optical SW 11-1 in FIG. 1 perform communication. Here, a wavelength Al is assumed to be allocated to the subscriber device 16-1 and the subscriber device 16-2.

[0059] The transfer wavelength control unit 143 performs setting so as to transfer the wavelength 1 between the ports used between the WSS 141 and the optical SW 10-1 and between the ports used between the WSS 142 and the optical SW 11-1 (step S101). The subscriber device 16-1 transmits an optical signal having the wavelength 1 (step S102). The optical signal having the wavelength 1 transmitted from the subscriber device 16-1 is input to the first port of the optical SW 10-1 via the optical transmission line 18-1.

[0060] The optical SW 10-1 is controlled by the optical SW control unit 122 so as to connect a path between the first port of the optical SW 10-1 to which the subscriber device 16-1 is connected and the second port of the optical SW 10-1 to which the return transfer unit 14 is connected. Therefore, the optical signal having the wavelength Al input to the first port of the optical SW 10-1 is output from the second port to the return transfer unit 14 (step S103).

[0061] The optical signal having the wavelength Al output from the optical SW 10-1 is input to the WSS 141 (step S104). The WSS 141 outputs the optical signal having the set wavelength set by the transfer wavelength control unit 143 to the WSS 142 (step S105). Here, because the wavelength 1 is set as the set wavelength, the optical signal having the wavelength Al is output from the WSS 141. The optical signal having the wavelength Al output from the WSS 141 is input to the WSS 142 (step $106).

[0062] The WSS 142 outputs the optical signal having the set wavelength set by the transfer wavelength control unit 143 to the optical transmission line to which the optical SW 11-1 is connected (step S107). Here, because the wavelength 1 is set as the set wavelength, the optical signal having the wavelength 1 is output from the WSS 142. The optical signal having the wavelength 1 output from the WSS 142 is input to the second port of the optical SW 11-1 via the optical transmission line.

[0063] The optical SW 11-1 is controlled by the optical SW control unit 122 so as to connect a path between the first port of the optical SW 11-1 to which the subscriber device 16-2 is connected and the second port of the optical SW 11-1 to which the return transfer unit 14 is connected. Therefore, the optical signal having the wavelength Al input to the second port of the optical SW 11-1 is output from the first port to the subscriber device 16-2 via the optical transmission line 18-2 (step S108). The subscriber device 16-2 receives the optical signal having the wavelength Al output from the optical SW 11-1 (step S109).

[0064] In a case where one or more return communications have already been performed and another return communication is newly performed, the same wavelength cannot be used between the WSS 141 and the WSS 142. Therefore, in a case where a wavelength to be used in the new return communication is the same wavelength, the transfer wavelength control unit 143 outputs a wavelength change command to the wavelength management control unit 121. The wavelength change command is an instruction for changing the wavelength to be used by the subscriber device 16. In response to the wavelength change command, the wavelength management control unit 121 notifies a target subscriber device 16 to perform communication with a wavelength (e.g. 2) different from the wavelength already used for the return communication in the subscriber device 16. Therefore, even in a case where a return communication is newly performed, return communication can be performed by using different wavelengths.

[0065] According to the optical communication system 1 configured as described above, in a case where return communication is performed in the optical communication system 1 including the plurality of optical SWs 10 and 11, the number of wires required for return in each optical SW can be suppressed to n. Therefore, each subscriber device can be connected to an arbitrary subscriber device at an arbitrary timing by using the number of return transmission lines smaller than before.

Modification Example of First Embodiment

[0066] An amplifier may be provided between the WSS 141 and the WSS 142.

[0067] The return transfer unit 14 may have configurations of FIG. 4 to 7.

[0068] FIG. 4 is a block diagram illustrating a specific example of a (second) functional configuration of the return transfer unit 14 according to the first embodiment. The return transfer unit 14 includes the WSS 141, the transfer wavelength control unit 143, and an AWG 144. The configuration of FIG. 4 is different from the configuration of FIG. 2 in that a target to be controlled by the transfer wavelength control unit 143 is the WSS 141 and that the AWG 144 is newly provided instead of the WSS 142.

[0069] In the configuration of FIG. 4, the transfer wavelength control unit 143 sets an output wavelength only to the WSS 141. The AWG 144 is connected to the n optical transmission lines connected to the second ports of each optical SW 11 (nP optical transmission lines in total) and outputs an optical signal output from the WSS 141 via a path corresponding to the wavelength. Here, the AWG is lower in cost than the WSS, but an output port and a wavelength that can be output from the port are fixed. Therefore, it is necessary to control the wavelength in accordance with the other party of the return communication. The AWG 144 is one aspect of the second multiplexing/demultiplexing unit.

[0070] For example, in a case where the subscriber device 16-1 connected to the optical SW 10-1 and the subscriber device 16-2 connected to the optical SW 11-1 perform return communication, a wavelength that can be transferred between ports used between the AWG 144 and the optical SW 11-1 is determined. The wavelength management control unit 121 sets a transmission wavelength of the subscriber device 16-1 to the wavelength that can be transferred between the ports used between the AWG 144 and the optical SW 11-1. Further, the transfer wavelength control unit 143 sets the WSS 141 such that the wavelength that can be transferred between the ports used between the AWG 144 and the optical SW 11-1 can be transferred between ports used between the WSS 141 and the optical SW 10-1. This makes it possible to implement return communication.

[0071] The AWG 144 may be newly provided instead of the WSS 141 in the configuration of FIG. 2. The transfer wavelength control unit 143 may set an output wavelength only to the WSS 142. In this case, the AWG 144 is connected to the n optical transmission lines connected to the second ports of each optical SW 10 (nP optical transmission lines in total) and inputs an optical signal output from each optical SW 10 via a path corresponding to the wavelength. For example, in a case where the subscriber device 16-1 connected to the optical SW 10-1 and the subscriber device 16-2 connected to the optical SW 11-1 perform return communication, a wavelength that can be transferred between ports used between the AWG 144 and the optical SW 10-1 is determined. The wavelength management control unit 121 sets a transmission wavelength of the subscriber device 16-1 to the wavelength that can be transferred between the ports used between the AWG 144 and the optical SW 10-1. Further, the transfer wavelength control unit 143 sets the WSS 142 such that the wavelength that can be transferred between the ports used between the AWG 144 and the optical SW 10-1 can be transferred between ports used between the WSS 142 and the optical SW 11-1. This makes it possible to implement return communication. An amplifier may be provided between the WSS 141 and the AWG 144.

[0072] Next, another example will be described with reference to FIG. 5. FIG. 5 is a block diagram illustrating a specific example of a (third) functional configuration of the return transfer unit 14 according to the first embodiment. The return transfer unit 14 includes the AWG 144, a coupler 145, and an amplifier 146. The coupler 145 is connected to the n optical transmission lines connected to the second ports of each optical SW 10 (nP optical transmission lines in total) and receives an optical signal transmitted via any of the nP optical transmission lines as an input. The coupler 145 multiplexes the input optical signals and outputs the multiplexed optical signal. The coupler 145 is one aspect of the first multiplexing/demultiplexing unit.

[0073] The amplifier 146 amplifies the optical signal output from the coupler 145. The AWG 144 is connected to the n optical transmission lines connected to the second ports of each optical SW 11 (nP optical transmission lines in total), demultiplexes the optical signal amplified by the amplifier 146, and outputs the demultiplexed optical signals to the optical transmission lines. The coupler is lower in cost than the WSS and does not need to be controlled by the transfer wavelength control unit 143. In a case where a branching loss is relatively small, the amplifier 146 may not be provided.

[0074] Next, another example will be described with reference to FIGS. 6 and 7. In the return transfer unit 14 of FIGS. 2, 4, and 5, simplex communication has been described as an example. In the configuration of FIGS. 6 and 7, a configuration that can be used for duplex communication will be described. FIG. 6 is a block diagram illustrating a specific example of a (fourth) functional configuration of the return transfer unit 14 according to the first embodiment. The return transfer unit 14 includes WSSs 141-1 and 141-2 and the transfer wavelength control unit 143. The WSS 141-1 is connected to the n optical transmission lines connected to the second ports of each optical SW 10 (nP optical transmission lines in total) and outputs, to the WSS 141-2, an optical signal having the set wavelength among optical signals transmitted via a certain optical transmission line. Further, the WSS 141-1 outputs the optical signal having the set wavelength output from the WSS 141-2 to an optical transmission line serving as an output path of the set wavelength. The WSS 141-1 is a wavelength selective optical switch. The number of ports required for the WSS 141-1 is nP.

[0075] The WSS 141-2 is connected to the n optical transmission lines connected to the second ports of each optical SW 11 (nP optical transmission lines in total) and outputs the optical signal having the set wavelength output from the WSS 141-1 to an optical transmission line serving as an output path of the set wavelength. Further, the WSS 141-2 outputs, to the WSS 141-1, an optical signal having the set wavelength among optical signals transmitted via a certain optical transmission line to which each optical SW 11 is connected. The WSS 141-2 is a wavelength selective optical switch. The number of ports required for the WSS 141-2 is n x P.

[0076] The transfer wavelength control unit 143 sets a wavelength to be output by the WSSs 141-1 and 141-2 in response to an instruction from the control unit 12. Specifically, in a case where the transfer wavelength control unit 143 receives, from the control unit 12, an instruction on a wavelength to be transferred at the time of return communication, the transfer wavelength control unit 143 sets a designated wavelength to the WSSs 141 and 142. In order to perform duplex communication, the transfer wavelength control unit 143 sets at least two different wavelengths as the set wavelengths to each of the WSSs 141-1 and 141-2.

[0077] The configuration of FIG. 6 accommodates optical signals in two directions, i.e., a direction 1 and a direction 2 in duplex communication in a mixed manner. This makes it possible to perform duplex communication with the same components as those used for simplex communication. Meanwhile, there is one optical transmission line between the WSS 141-1 and the WSS 141-2, and thus the same wavelength cannot be used in the direction 1 and the direction 2.

[0078] FIG. 7 is a block diagram illustrating a specific example of a (fifth) functional configuration of the return transfer unit 14 according to the first embodiment. The return transfer unit 14 includes WSSs 141-1, 141-2, 141-3, and 141-4 and the transfer wavelength control unit 143. The configuration of the return transfer unit 14 of FIG. 7 includes another set of the same components as those used for simplex communication (e.g. FIG. 2). The WSSs 141-1 and 141-2 are used for the direction 1, and the WSSs 141-3 and 141-4 are used for the direction 2. The WSSs 141-1, 141-2, 141-3, and 141-4 are wavelength selective optical switches. The number of ports required for the WSSs 141-1, 141-2, 141-3, and 141-4 is nP.

[0079] The transfer wavelength control unit 143 sets a wavelength to be output by the WSSs 141-1, 141-2, 141-3, and 141-4 in response to an instruction from the control unit 12. Specifically, the transfer wavelength control unit 143 sets different wavelengths between the WSSs 141-1 and 141-2 used for the direction 1 and the WSSs 141-3 and 141-4 used for the direction 2. For example, the transfer wavelength control unit 143 sets the wavelength Al to the WSSs 141-1 and 141-2 and sets the wavelength 2 to the WSSs 141-3 and 141-4. Therefore, the WSSs 141-1, 141-2, 141-3, and 141-4 can output an optical signal having the set wavelength.

[0080] The WSS 141-1 is connected to the n optical transmission lines connected to the second ports of each optical SW 10 (nP optical transmission lines in total) and outputs, to the WSS 141-2, an optical signal having the set wavelength (e.g. wavelength 1) among optical signals transmitted via a certain optical transmission line. The WSS 141-2 is connected to the n optical transmission lines connected to the second ports of each optical SW 11 (nP optical transmission lines in total) and outputs the optical signal having the set wavelength (e.g. wavelength 1) output from the WSS 141-1 to an optical transmission line serving as an output path of the set wavelength.

[0081] The WSS 141-4 is connected to the n optical transmission lines connected to the second ports of each optical SW 11 (nP optical transmission lines in total) and outputs, to the WSS 141-3, an optical signal having the set wavelength (e.g. wavelength 2) among optical signals transmitted via a certain optical transmission line. The WSS 141-3 is connected to n optical transmission lines connected to the second ports of each optical SW 10 (nP optical transmission lines in total) and outputs the optical signal having the set wavelength (e.g. wavelength 2) output from the WSS 141-4 to an optical transmission line serving as an output path of the set wavelength. In the configuration of FIG. 7, optical signals in the directions 1 and 2 do not pass through the same optical transmission line, and thus the same wavelength can be used in the directions 1 and 2.

Second Embodiment

[0082] A second embodiment is similar to the first embodiment in the system configuration of the optical communication system 1, except for the configuration of the return transfer unit 14. Therefore, hereinafter, differences from the first embodiment will be described.

[0083] FIG. 8 is a block diagram illustrating a specific example of a (first) functional configuration of a return transfer unit 14a according to the second embodiment.

[0084] The return transfer unit 14a includes a plurality of WSSs 141-1 to 141-X (X is an integer of 2 or more), a plurality of WSSs 142-1 to 142-X, a transfer wavelength control unit 143a, and a plurality of host WSSs 147-1 and 147-2. In the example of FIG. 8, a WSS 141-x (1xX) is connected to the host WSS 147-1, and a WSS 142-x is connected to the host WSS 147-2.

[0085] The WSS 141-x is connected to different nP/X optical transmission lines among the n optical transmission lines connected to the second ports of each optical SW 10 (nP optical transmission lines in total) and outputs, to the host WSS 147, an optical signal having a set wavelength among optical signals transmitted via a certain optical transmission line. In this manner, substantially the same number of optical transmission lines is connected to each WSS 141 on average. For example, in a case where the number of WSSs 141 is two (X=2), the number of optical SWs 10 is three (P=3), and the number of optical transmission lines connected to the second ports of each optical SW 10 is two (n=2), three different optical transmission lines are connected to each WSS 141. The number of ports required for the WSS 141 is nP/X. The WSS 142-x is connected to different nP/X optical transmission lines and outputs an optical signal having the set wavelength output from the host WSS 147-2 to an optical transmission line serving as an output path of the set wavelength. In this manner, substantially the same number of optical transmission lines is connected to each WSS 142 on average. The number of ports required for the WSS 142 is nP/X.

[0086] The host WSS 147-1 outputs, to the host WSS 147-2, an optical signal having the set wavelength among optical signals output from each WSS 141. The number of ports required for the host WSS 147-1 is X.

[0087] The host WSS 147-2 outputs, to each WSS 142, an optical signal having the set wavelength among optical signals output from the host WSS 147-1. The number of ports required for the host WSS 147-2 is X.

[0088] The transfer wavelength control unit 143a sets a wavelength to be output by the WSSs 141 and 142 and the host WSSs 147 in response to an instruction from the control unit 12. The transfer wavelength control unit 143a may be mounted on the control unit 12.

[0089] According to the optical communication system 1 of the second embodiment configured as described above, the X WSSs 141 and X WSSs 142 are arranged in parallel, and the host WSS 147 is arranged on the host side of each of the WSSs 141 and 142 arranged in parallel. With such a configuration, the required number of ports per WSS can be reduced, as compared with the first embodiment.

Modification Example of Second Embodiment

[0090] The amplifier may be provided between any or all of the WSS 141-x and the host WSS 147-1, the host WSS 147-1 and the host WSS 147-2, and the WSS 142-x and the host WSS 147-2.

[0091] The return transfer unit 14a may have a configuration of FIG. 9 or 10.

[0092] FIG. 9 is a block diagram illustrating a specific example of a (second) functional configuration of the return transfer unit 14a according to the second embodiment.

[0093] The return transfer unit 14a includes the plurality of WSSs 141-1 to 141-X, the transfer wavelength control unit 143a, a plurality of AWGs 144-1 to 144-X, and the plurality of host WSSs 147-1 and 147-2. In the example of FIG. 9, the WSSs 141-1 to 141-X are connected to the host WSS 147-1, and the AWGs 144-1 to 144-X are connected to the host WSS 147-2.

[0094] The configuration of FIG. 9 is different from the configuration of FIG. 8 in that targets to be controlled by the transfer wavelength control unit 143a are the WSSs 141 and 142 and the host WSS 147-1 and that the plurality of AWGs 144-1 to 144-X is newly provided instead of the plurality of WSSs 142-1 to 142-X. The WSSs 141 and the host WSSs 147 perform processing similar to that of the functional units having the same names of FIG. 8, and thus description thereof is omitted.

[0095] The AWG 144-x is connected to different nP/X optical transmission lines among the n optical transmission lines connected to the second ports of each optical SW 11 (nP optical transmission lines in total) and outputs an optical signal having the set wavelength output from the host WSS 147-2 via a path corresponding to the wavelength. The number of ports required for the AWG 144 is nP/X.

[0096] The amplifier may be provided between any or all of the WSS 141-x and the host WSS 147-1, the host WSS 147-1 and the host WSS 147-2, and the AWG 144-x and the host WSS 147-2.

[0097] In the configuration of FIG. 8, the AWGs 144-1 to 144-X may be newly provided instead of the WSSs 141-1 to 141-X.

[0098] Next, another example will be described with reference to FIG. 10. FIG. 10 is a block diagram illustrating a specific example of a (third) functional configuration of the return transfer unit 14a according to the second embodiment. The return transfer unit 14a includes the plurality of AWGs 144-1 to 144-X, a plurality of couplers 145-1 to 145-X, the amplifier 146, a plurality of amplifiers 148-1 to 148-X, a plurality of host couplers 149-1 to 149-2, and a plurality of amplifiers 150-1 to 150-X.

[0099] In the example of FIG. 10, a coupler 145-x is connected to the host coupler 149-1 via an amplifier 148-x, the AWG 144-x is connected to the host coupler 149-2 via an amplifier 150-x, and the host coupler 149-1 and the host coupler 149-2 are connected via the amplifier 146.

[0100] The coupler 145-x is connected to different nP/X optical transmission lines among the n optical transmission lines connected to the second ports of each optical SW 10 (nP optical transmission lines in total) and receives an optical signal transmitted via any of the nP/X optical transmission lines as an input. The coupler 145-x multiplexes the input optical signals and outputs the multiplexed optical signal.

[0101] The amplifier 148-x amplifies the optical signal output from the coupler 145-x.

[0102] The host coupler 149-1 multiplexes the optical signals amplified by the respective amplifiers 148 and outputs the multiplexed optical signal.

[0103] The host coupler 149-2 splits the optical signal output from the host coupler 149-1 and amplified by the amplifier 146.

[0104] The amplifier 150-x amplifies the optical signal output from the host coupler 149-2.

[0105] The AWG 144-x is connected to different nP/X optical transmission lines among the n optical transmission lines connected to the second ports of each optical SW 11 (nP optical transmission lines in total) and outputs the optical signal amplified by each amplifier 150 via a path corresponding to the wavelength. The number of ports required for the AWG 144-x is nP/X.

Third Embodiment

[0106] A third embodiment is similar to the first embodiment in the system configuration of the optical communication system 1, except for the configuration of the return transfer unit 14. Therefore, hereinafter, differences from the first embodiment will be described.

[0107] FIG. 11 is a block diagram illustrating a specific example of a (first) functional configuration of a return transfer unit 14b according to the third embodiment.

[0108] The return transfer unit 14b includes the plurality of WSSs 141-1 to 141-X, the plurality of WSSs 142-1 to 142-X, a transfer wavelength control unit 143b, a plurality of host WSSs 147-1-1 to 147-1-X, and a plurality of host WSSs 147-2-1 to 147-2-X. In the example of FIG. 11, the WSS 141-x is connected to the host WSS 147-1-x, and the WSS 142-x is connected to the host WSS 147-2-x.

[0109] The WSS 141-x is connected to different nP/X optical transmission lines among the n optical transmission lines connected to the second ports of each optical SW 10 (nP optical transmission lines in total) and outputs, to the host WSS 147-1-x, an optical signal having the set wavelength among optical signals transmitted via a certain optical transmission line.

[0110] The WSS 142-x is connected to different nP/X optical transmission lines and outputs an optical signal having the set wavelength output from the host WSS 147-2-x to an optical transmission line serving as an output path of the set wavelength.

[0111] The host WSS 147-1-x outputs, to the host WSS 147-2, an optical signal having the set wavelength among optical signals output from the WSS 141-x.

[0112] The host WSS 147-2-x outputs, to the WSS 142-x, an optical signal having the set wavelength among optical signals output from the host WSS 147-1.

[0113] The transfer wavelength control unit 143b sets a wavelength to be output by the WSSs 141 and 142 and the host WSSs 147 in response to an instruction from the control unit 12. The transfer wavelength control unit 143b may be mounted on the control unit 12.

[0114] According to the optical communication system 1 of the third embodiment configured as described above, not only the X WSSs 141 and the X WSSs 142 but also the X host WSSs 147-1 and the X host WSSs 147-2 are also arranged in parallel. In the second embodiment, a maximum of nP wavelengths need to be aggregated in the host WSS 147. Meanwhile, in the third embodiment, the maximum number of wavelengths accommodated in each WSS is nP/X. This makes it possible to reduce the number of wavelengths to be accommodated in one WSS.

Modification Example of Third Embodiment

[0115] The amplifier may be provided between any or all of the WSS 141-x and the host WSS 147-1-x, the host WSS 147-1 and the host WSS 147-2, and the WSS 142-x and the host WSS 147-2-x.

[0116] The return transfer unit 14b may have a configuration of FIG. 12 or 13.

[0117] FIG. 12 is a block diagram illustrating a specific example of a (second) functional configuration of the return transfer unit 14b according to the third embodiment.

[0118] The return transfer unit 14b includes the plurality of WSSs 141-1 to 141-X, the transfer wavelength control unit 143b, the plurality of AWGs 144-1 to 144-X, the plurality of host WSSs 147-1-1 to 147-1- X, and the plurality of host WSSs 147-2-1 to 147-2-X.

[0119] In the example of FIG. 12, the WSS 141-x is connected to the host WSS 147-1-x, and the AWG 144-x is connected to the host WSS 147-2-x. The configuration of FIG. 12 is different from the configuration of FIG. 11 in that targets to be controlled by the transfer wavelength control unit 143b are the WSSs 141 and the host WSSs 147 and that the plurality of AWGs 144-1 to 144-X is newly provided instead of the plurality of WSSs 142-1 to 142-X. The WSSs 141 and the host WSSs 147 perform processing similar to that of the functional units having the same names of FIG. 11, and thus description thereof is omitted.

[0120] The AWG 144-x is connected to different nP/X optical transmission lines among the n optical transmission lines connected to the second ports of each optical SW 11 (nP optical transmission lines in total) and outputs an optical signal having the set wavelength output from the host WSS 147-2-x via a path corresponding to the wavelength. The number of ports required for the AWG 144-x is nP/X.

[0121] The amplifier may be provided between any or all of the WSS 141-x and the host WSS 147-1-x, the host WSS 147-1 and the host WSS 147-2, and the AWG 144-x and the host WSS 147-2-x.

[0122] In the configuration of FIG. 11, the AWGs 144-1 to 144-X may be newly provided instead of the WSSs 141-1 to 141-X.

[0123] Next, another example will be described with reference to FIG. 13. FIG. 13 is a block diagram illustrating a specific example of a (third) functional configuration of the return transfer unit 14b according to the third embodiment.

[0124] The return transfer unit 14b includes the plurality of AWGs 144-1 to 144-X, the plurality of couplers 145-1 to 145-X, a plurality of amplifiers 146-1-1 to 146-X-X, the plurality of amplifiers 148-1 to 148-X, a plurality of host couplers 149-1-1 to 149-1-X, a plurality of host couplers 149-2-1 to 149-2-X, and the plurality of amplifiers 150-1 to 150-X.

[0125] In the example of FIG. 13, the coupler 145-x is connected to a host coupler 149-1-x via the amplifier 148-x, the AWG 144-x is connected to a host coupler 149-2-x via the amplifier 150-x, and the host couplers 149-1 and the host couplers 149-2 are connected via the amplifiers 146.

[0126] The coupler 145-x is connected to different nP/X optical transmission lines among the n optical transmission lines connected to the second ports of each optical SW 10 (nP optical transmission lines in total) and receives an optical signal transmitted via any of the nP/X optical transmission lines as an input. The coupler 145-x multiplexes the input optical signals and outputs the multiplexed optical signal.

[0127] The amplifier 148-x amplifies the optical signal output from the coupler 145-x.

[0128] The host coupler 149-1-x splits the optical signal amplified by the amplifier 148-x and outputs the split optical signals.

[0129] The host coupler 149-2-x multiplexes the optical signals output from the respective host couplers 149-1 and amplified by the connected amplifiers 146.

[0130] The amplifier 150-x amplifies the optical signal output from the host coupler 149-2-x.

[0131] The AWG 144-x is connected to different nP/X optical transmission lines among the n optical transmission lines connected to the second ports of each optical SW 11 (nP optical transmission lines in total) and outputs the optical signal amplified by the amplifier 150-x via a path corresponding to the wavelength. The number of ports required for the AWG 144-x is n x P/X.

Fourth Embodiment

[0132] In the above first to third embodiments, the configuration in which the optical SWs are used as the uplink optical distribution unit and the downlink optical distribution unit connected to the return transfer unit has been described. In a fourth embodiment, the uplink optical distribution unit and the downlink optical distribution unit different from those of the first to third embodiments will be described. The fourth embodiment is similar to the first embodiment in the system configuration of the optical communication system 1, except for the configuration of the optical distribution unit. Therefore, hereinafter, differences from the first embodiment will be described.

[0133] FIG. 14 is a configuration diagram of the optical communication system 1 according to the fourth embodiment. The optical communication system 1 according to the fourth embodiment includes P optical distribution units 30-1 to 30-P. P optical distribution units 40-1 to 40-P, the control unit 12 (not illustrated), and the return transfer unit 14. Hereinafter, description will be made on the assumption that the optical distribution units 30-1 to 30-P are used for transmitting optical signals in the uplink direction and that the optical distribution units 40-1 to 40-P are used for transmitting optical signals in the downlink direction.

[0134] The optical distribution units 30-1 to 30-P have the same configuration. The optical distribution units 40-1 to 40-P have the same configuration. In the following description, the optical distribution units 30-1 to 30-P will be simply referred to as the optical distribution units 30 when not distinguished, and the optical distribution units 40-1 to 40-P will be simply referred to as the optical distribution units 40 when not distinguished. The optical distribution units 30, the optical distribution units 40, the control unit 12, and the return transfer unit 14 are functional units forming one optical communication device. The optical distribution units 30 and the optical distribution units 40 are multicast switches (MCSs).

[0135] The optical distribution unit 30 includes a plurality of 1M optical switches 31 and a plurality of signal multiplexing units 32. The number of 1M optical switches 31 and the number of signal multiplexing units 32 may be the same or different. The optical distribution unit 30 is one aspect of the first optical distribution unit. Each 1M optical switch 31 is connected to a plurality of optical transmission lines and outputs an optical signal input from any of the optical transmission lines to another optical transmission line. Each 1M optical switch 31 has one first port and M second ports (M is an integer of 2 or more). The one first port included in each 1M optical switch 31 is connected to the edge node 15 or the subscriber device 16 via an optical transmission line.

[0136] One of the M second ports included in each 1M optical switch 31 is connected to the return transfer unit 14 via an optical transmission line. The remaining second ports (e.g. (M1) second ports) of the M second ports included in each 1M optical switch 31 are connected to different signal multiplexing units 32 via optical transmission lines, respectively. Some of the remaining second ports of the M second ports included in each 1M optical switch 31 may not be connected to the signal multiplexing unit 32.

[0137] The signal multiplexing unit 32 is any of an optical coupler, a wavelength selective switch, and an AWG. The signal multiplexing unit 32 multiplexes the optical signals output from each 1M optical switch 31 and outputs the multiplexed optical signal to another device via an optical transmission line.

[0138] The optical distribution unit 40 includes a plurality of signal separation units 41 and a plurality of 1M optical switches 42. The number of signal separation units 41 and the number of 1M optical switches 42 may be the same or different. The optical distribution unit 40 is one aspect of the second optical distribution unit. The signal separation unit 41 is any of an optical coupler, a wavelength selective switch, and an AWG. The signal separation unit 41 receives, as an input, an optical signal transmitted from another device connected via an optical transmission line. The signal separation unit 41 splits or demultiplexes the input optical signal and outputs the split or demultiplexed optical signals to the respective 1M optical switches 42. For example, in a case where the optical distribution unit 40 is an optical coupler, the optical coupler splits the input optical signal and outputs the split optical signals to the connected 1M optical switches 42, respectively. For example, in a case where the optical distribution unit 40 is a wavelength selective switch or AWG, the wavelength selective switch or AWG demultiplexes the input optical signal and outputs the demultiplexed optical signals to the 1M optical switches 42 connected to ports of the corresponding wavelength.

[0139] Each 1M optical switch 42 is connected to a plurality of optical transmission lines and outputs an optical signal input from any of the optical transmission lines to another optical transmission line. Each 1M optical switch 42 has one first port and M second ports. The one first port included in each 1M optical switch 42 is connected to the subscriber device 16 via an optical transmission line.

[0140] One of the M second ports included in each 1M optical switch 42 is connected to the return transfer unit 14 via an optical transmission line. The remaining second ports (e.g. (M1) second ports) of the M second ports included in each 1M optical switch 42 are connected to different signal separation units 41 via optical transmission lines, respectively. Some of the remaining second ports of the M second ports included in each 1M optical switch 42 may not be connected to the signal separation unit 41.

[0141] An amplifier may be installed to compensate for a signal loss. A place where the amplifier may be installed is any or all of the optical transmission line connected to the first port of each of the 1M optical switches 31 and 42, the optical transmission line between each 1M optical switch 31 and each signal multiplexing unit 32, the optical transmission line between each signal separation unit 41 and each 1M optical switch 42, the optical transmission line on the output side of each signal multiplexing unit 32 (the side opposite to the side to which the 1M optical switch 31 is connected), and the optical transmission line on the input side of each signal separation unit 41 (the side opposite to the side to which the 1M optical switch 42 is connected).

[0142] The return transfer unit 14 receives an optical signal output from the 1M optical switch 31 as an input and transfers the input optical signal to at least the 1M optical switch 42 to which a destination subscriber device 16 is connected. One optical transmission line is connected to the return transfer unit 14 from one 1M optical switch 31. Therefore, in a case where n 1M optical switches 31 are provided in one optical distribution unit 30, n optical transmission lines are connected from one optical distribution unit 30 to the return transfer unit 14, and the number of optical distribution units 30 is P, and thus nP uplink optical transmission lines are connected to the return transfer unit 14. Further, in a case where n 1M optical switches 42 are provided in one optical distribution unit 40, n optical transmission lines are connected from one optical distribution unit 40 to the return transfer unit 14, and the number of optical distribution units 40 is P, and thus nP downlink optical transmission lines are connected to the return transfer unit 14.

[0143] In a case where return communication is performed across the optical distribution unit 30, the optical SW control unit 122 switches a path between the ports of the 1M optical switch 31 so as to connect an output destination of an optical signal from the 1M optical switch 31 to the return transfer unit 14. The return transfer unit 14 performs control such that the input optical signal is output to a desired 1M optical switch 42. With this configuration, return communication between arbitrary 1M optical switches is implemented while the number of wires required for return in each 1M optical switch is suppressed to nP.

[0144] The configuration of the return transfer unit 14 may be any of the configurations described in the first to third embodiments. That is, the configuration of the return transfer unit 14 may be any of the configurations of FIGS. 2 and 4 to 13.

[0145] In the fourth embodiment, the optical SW control unit 122 switches connection between the ports of the 1M optical switch 31 and connection between the ports of the 1M optical switch 42. Specifically, in the fourth embodiment, the optical SW control unit 122 switches the connection between the ports for each 1M optical switch 31 included in each optical distribution unit 30 and the connection between the ports for each 1M optical switch 42 included in each optical distribution unit 40.

[0146] For example, the optical SW control unit 122 switches the connection between the ports so as to connect the first port of the 1M optical switch 31 to which the edge node 15 or the subscriber device 16 is connected and the second port to which the return transfer unit 14 is connected. The 1M optical switch 31 outputs an optical signal transmitted from the edge node 15 or subscriber device 16 connected to the first port from the second port to which the return transfer unit 14 is connected. Therefore, the optical signal input to the first port of the 1M optical switch 31 is directly input to the return transfer unit 14.

[0147] Similarly, the optical SW control unit 122 switches the connection between the ports so as to connect the first port of the 1M optical switch 42 to which a desired subscriber device 16 is connected and the second port to which the return transfer unit 14 is connected. The optical signal transferred from the return transfer unit 14 is input to the second port of the 1M optical switch 42. The 1M optical switch 42 receives, as an input, the optical signal transferred from the return transfer unit 14 connected to the second port and outputs the input optical signal from the first port. Therefore, the optical signal output from the return transfer unit 14 is transferred to the desired subscriber device 16.

[0148] FIG. 15 is a sequence diagram showing a flow of processing of the optical communication system 1 according to the fourth embodiment. FIG. 15 shows a case where the subscriber device 16-1 connected to the optical distribution unit 30-1 and the subscriber device 16-2 connected to the optical distribution unit 40-1 perform communication. Here, a wavelength 1 is assumed to be allocated to the subscriber device 16-1 and the subscriber device 16-2. The configuration of the return transfer unit 14 will be described by using the configuration of FIG. 2 as an example.

[0149] The transfer wavelength control unit 143 of the return transfer unit 14 performs setting so as to transfer the wavelength 1 between the ports used between the WSS 141 and the optical SW 10-1 and between the ports used between the WSS 142 and the optical SW 11-1 (step S201). The subscriber device 16-1 transmits an optical signal having the wavelength 1 (step S102). The optical signal having the wavelength 1 transmitted from the subscriber device 16-1 is input to one 1M optical switch 31 included in the optical distribution unit 30-1 via an optical transmission line.

[0150] The 1M optical switch 31 is controlled by the optical SW control unit 122 so as to connect a path between the first port of the 1M optical switch 31 to which the subscriber device 16-1 is connected and the second port of the 1M optical switch 31 to which the return transfer unit 14 is connected. Therefore, the optical signal having the wavelength 1 input to the first port of the 1M optical switch 31 is output to the return transfer unit 14 from the second port to which the return transfer unit 14 is connected (step S203).

[0151] The optical signal having the wavelength Al output from the 1M optical switch 31 is input to the WSS 141 included in the return transfer unit 14 (step S204). The WSS 141 outputs the optical signal having the set wavelength set by the transfer wavelength control unit 143 to the WSS 142 (step S205). Here, because the wavelength Al is set as the set wavelength, the optical signal having the wavelength Al is output from the WSS 141. The optical signal having the wavelength Al output from the WSS 141 is input to the WSS 142 (step S206).

[0152] The WSS 142 outputs the optical signal having the set wavelength set by the transfer wavelength control unit 143 to the optical transmission line to which the optical SW 11-1 is connected (step S207). Here, because the wavelength Al is set as the set wavelength, the optical signal having the wavelength 1 is output from the WSS 142. The optical signal having the wavelength Al output from the WSS 142 is input to the second ports of the plurality of 1M optical switches 42 included in the optical distribution unit 40-1 via optical transmission lines.

[0153] The optical SW control unit 122 performs control so as to connect a path between the first port of the 1M optical switch 42 to which the subscriber device 16-2 is connected among the plurality of 1M optical switches 42 included in the optical distribution unit 40-1 and the second port of the 1M optical switch 42 to which the return transfer unit 14 is connected. Therefore, the optical signal having the wavelength 1 input to the second port of the 1M optical switch 42 is output from the first port to the subscriber device 16-2 via the optical transmission line (step $208). The subscriber device 16-2 receives the optical signal having the wavelength Al output from the 1M optical switch 42 (step S209).

[0154] According to the optical communication system 1 of the fourth embodiment configured as described above, the number of wires required for return in each of the optical distribution units 30 and 40 can be suppressed even in the configuration including multicast switches instead of the optical SWs as the optical distribution units. Therefore, each subscriber device can be connected to an arbitrary subscriber device at an arbitrary timing by using the number of return transmission lines smaller than before.

First Modification Example of Fourth Embodiment

[0155] The optical distribution units 30 and the optical distribution units 40 may have a configuration of FIG. 16. FIG. 16 is a configuration diagram of the optical communication system 1 according to a modification example of the fourth embodiment. The optical communication system 1 according to the modification example of the fourth embodiment has a system configuration similar to that of the fourth embodiment. FIG. 16 is different from FIG. 14 in connection between the optical distribution units 30 and the return transfer unit 14 and connection between the optical distribution units 40 and the return transfer unit 14.

[0156] In the configuration of FIG. 14, one of the second ports of each 1M optical switch 31 is connected to the return transfer unit 14, and one of the second ports of each 1M optical switch 42 is connected to the return transfer unit 14. Meanwhile, in the configuration of FIG. 16, one of the plurality of signal multiplexing units 32 is connected to the return transfer unit 14, and one of the plurality of signal separation units 41 is connected to the return transfer unit 14. With such a configuration, one optical distribution unit 30 or 40 only needs to be connected to the return transfer unit 14 via one optical transmission line. Therefore, it is unnecessary to connect one optical distribution unit 30 or 40 to the return transfer unit 14 via optical transmission lines corresponding to the number of 1M optical switches 31, unlike the fourth embodiment. This makes it possible to reduce the number of optical transmission lines connected to the return transfer unit 14.

[0157] In a case where return communication is performed across the optical distribution unit 30 in the configuration of FIG. 16, the optical SW control unit 122 switches a path between the ports of each 1M optical switch 31 such that an optical signal input to each 1M optical switch 31 is input to the return transfer unit 14. Specifically, the optical SW control unit 122 switches the path between the ports of the 1M optical switch 31 so as to connect the second port of the 1M optical switch 31 connected to the signal multiplexing unit 32 connected to the return transfer unit 14 and the first port of the 1M optical switch 31. The 1M optical switch 31 outputs an optical signal transmitted from the edge node 15 or subscriber device 16 connected to the first port from the second port connected to the signal multiplexing unit 32 connected to the return transfer unit 14. The signal multiplexing unit 32 multiplexes the optical signals output from each 1M optical switch 31 and outputs the multiplexed optical signal to the return transfer unit 14. Therefore, the optical signals input to the first ports of the 1M optical switches 31 are input to the return transfer unit 14 via the signal multiplexing units 32.

[0158] Similarly, the optical SW control unit 122 switches the path between the ports of the 1M optical switch 42 so as to connect the second port of the 1M optical switch 42 connected to the signal separation unit 41 connected to the return transfer unit 14 and the first port of the 1M optical switch 42. The signal separation unit 41 splits or demultiplexes the optical signal transferred from the return transfer unit 14 and outputs the split or demultiplexed optical signals to the respective 1M optical switches 42. The 1M optical switch 42 receives, as an input, the optical signal output from the signal separation unit 41 connected to the second port and outputs the input optical signal from the first port. Therefore, the optical signal transferred from the return transfer unit 14 is input to the second port of the 1M optical switch 42 via the signal separation unit 41. The optical signal input to the second port of the 1M optical switch 42 is output from the first port and is input to the desired subscriber device 16.

Second Modification Example of Fourth Embodiment

[0159] In the above embodiment, the configuration in which one optical communication device includes the optical distribution units 30, the optical distribution units 40, and the return transfer unit 14 has been described. Any of the optical distribution units 30, the optical distribution units 40, and the return transfer unit 14 may be mounted on another device. The same applies to a case where the return transfer unit 14 is the return transfer unit 14a or 14b.

Fifth Embodiment

[0160] In a fifth embodiment, the uplink optical distribution unit and the downlink optical distribution unit different from those of the first to fourth embodiments will be described. The fifth embodiment is similar to the first embodiment in the system configuration of the optical communication system 1, except for the configuration of the optical distribution unit. Therefore, hereinafter, differences from the first embodiment will be described.

[0161] FIG. 17 is a configuration diagram of the optical communication system 1 according to the fifth embodiment. The optical communication system 1 according to the fifth embodiment includes P optical distribution units 30a-1 to 30a-P, P optical distribution units 40a-1 to 40a-P, the control unit 12 (not illustrated), and the return transfer unit 14. Hereinafter, description will be made on the assumption that the optical distribution units 30a-1 to 30a-P are used for transmitting optical signals in the uplink direction and that the optical distribution units 40a-1 to 40a-P are used for transmitting optical signals in the downlink direction.

[0162] The optical distribution units 30a-1 to 30a-P have the same configuration. The optical distribution units 40a-1 to 40a-P have the same configuration. In the following description, the optical distribution units 30a-1 to 30a-P will be simply referred to as the optical distribution units 30a when not distinguished, and the optical distribution units 40a-1 to 40a-P will be simply referred to as the optical distribution units 40a when not distinguished. The optical distribution units 30a, the optical distribution units 40a, the control unit 12, and the return transfer unit 14 are functional units forming one optical communication device.

[0163] The optical distribution unit 30a includes one or more N x M wavelength selective switches 33. The optical distribution unit 30a is one aspect of the first optical distribution unit. The NM wavelength selective switch 33 is connected to a plurality of optical transmission lines and outputs an optical signal input from any of the optical transmission lines to another optical transmission line. The NM wavelength selective switch 33 includes N (N is an integer of 1 or more) first ports and M second ports. The N first ports included in the NM wavelength selective switch 33 are connected to the edge node 15 or the subscriber device 16 via optical transmission lines. The NM wavelength selective switch 33 is a WSS.

[0164] One of the M second ports included in the NM wavelength selective switch 33 is connected to the return transfer unit 14 via an optical transmission line. The remaining second ports (e.g. (M1) second ports) of the M second ports included in the NM wavelength selective switch 33 are connected to another device via optical transmission lines, respectively.

[0165] The optical distribution unit 40a includes one or more NM wavelength selective switches 43. The optical distribution unit 40a is one aspect of the second optical distribution unit. The NM wavelength selective switch 43 is connected to a plurality of optical transmission lines and outputs an optical signal input from any of the optical transmission lines to another optical transmission line. The NM wavelength selective switch 43 has N first ports and M second ports. The N first ports included in the NM wavelength selective switch 43 are connected to the subscriber device 16 via optical transmission lines.

[0166] One of the M second ports included in the NM wavelength selective switch 43 is connected to the return transfer unit 14 via an optical transmission line. The remaining second ports (e.g. (M1) second ports) of the M second ports included in the NM wavelength selective switch 43 are connected to another device via optical transmission lines, respectively. The NM wavelength selective switch 43 is a WSS.

[0167] An amplifier may be installed to compensate for a signal loss. A place where the amplifier may be installed is any or all of the optical transmission line connected to the first port of each of the NM wavelength selective switches 33 and 43 and the optical transmission line connected to the second port of each of the NM wavelength selective switches 33 and 43.

[0168] The return transfer unit 14 receives an optical signal output from each the NM wavelength selective switch 33 as an input and transfers the input optical signal to at least the NM wavelength selective switch 43 to which a destination subscriber device 16 is connected. One optical transmission line is connected to the return transfer unit 14 from one the NM wavelength selective switch 33. Therefore, one optical transmission line is connected from one optical distribution unit 30a to the return transfer unit 14, and the number of optical distribution units 30a is P, and thus P uplink optical transmission lines are connected to the return transfer unit 14. Further, one optical transmission line is connected from one optical distribution unit 40a to the return transfer unit 14, and the number of optical distribution units 40a is P, and thus P downlink optical transmission lines are connected to the return transfer unit 14.

[0169] In a case where return communication is performed across the optical distribution unit 30a, the optical SW control unit 122 switches a path between the ports of each the NM wavelength selective switch 33 so as to connect an output destination of an optical signal from each the NM wavelength selective switch 33 to the return transfer unit 14. The return transfer unit 14 performs control such that the input optical signal is output to a desired the NM wavelength selective switch 43. With this configuration, return communication between arbitrary the NM optical switches is implemented while the number of wires required for return in each the NM wavelength selective switch is suppressed to nP.

[0170] The configuration of the return transfer unit 14 may be any of the configurations described in the first to third embodiments. That is, the configuration of the return transfer unit 14 may be any of the configurations of FIGS. 2 and 4 to 13.

[0171] In the fifth embodiment, the optical SW control unit 122 switches connection between the ports of the NM wavelength selective switch 33 and connection between the ports of the NM wavelength selective switch 43. Specifically, in the fifth embodiment, the optical SW control unit 122 switches the connection between the ports for each the NM wavelength selective switch 33 included in each optical distribution unit 30a and the connection between the ports for each the NM wavelength selective switch 43 included in each optical distribution unit 40a.

[0172] For example, the optical SW control unit 122 switches the connection between the ports so as to connect the first port of the NM wavelength selective switch 33 to which the edge node 15 or the subscriber device 16 serving as a transmission target is connected and the second port to which the return transfer unit 14 is connected. The NM wavelength selective switch 33 outputs an optical signal transmitted from the edge node 15 or subscriber device 16 connected to the first port from the second port to which the return transfer unit 14 is connected. Therefore, the optical signal input to the first port of the NM wavelength selective switch 33 is directly input to the return transfer unit 14.

[0173] Similarly, the connection between the ports is switched to connect the first port of the NM wavelength selective switch 43 to which a destination subscriber device 16 is connected and the second port to which the return transfer unit 14 is connected. The optical signal transferred from the return transfer unit 14 is input to the second port of the NM wavelength selective switch 43. The NM wavelength selective switch 43 outputs the optical signal transferred from the return transfer unit 14 and input to the second port from the first port to which the destination subscriber device 16 is connected. Therefore, the optical signal output from the return transfer unit 14 is transferred to the desired subscriber device 16.

[0174] According to the optical communication system 1 of the fifth embodiment configured as described above, the number of wires required for return in each of the optical distribution units 30a and 40a can be suppressed even in the configuration including the NM wavelength selective switches 33 and 43 instead of the optical SWs as the optical distribution units. Therefore, each subscriber device can be connected to an arbitrary subscriber device at an arbitrary timing by using the number of return transmission lines smaller than before.

First Modification Example of Fifth Embodiment

[0175] In a case where the optical distribution unit 30a includes the NM wavelength selective switch 33 and the optical distribution unit 40a includes the NM wavelength selective switch 43 as in the fifth embodiment, the return transfer unit 14 may have a configuration of any of FIGS. 18 to 20. The configurations of the return transfer unit 14 of FIGS. 18 to 20 include components having no wavelength dependency on the ports.

[0176] In a case where the optical distribution unit 30a includes the NM wavelength selective switch 33, a plurality of optical signals can be multiplexed in the optical distribution unit 30a and be then input to the return transfer unit 14. Therefore, each the NM wavelength selective switch 33 only needs to be connected to the return transfer unit 14 via one optical transmission line, and, in a case where P the NM wavelength selective switches 33 are provided, P optical transmission lines are connected to the return transfer unit 14.

[0177] FIG. 18 is a block diagram illustrating a specific example of a (first) functional configuration of a return transfer unit 14c according to a modification example of the fifth embodiment. The return transfer unit 14c includes a coupler 151, an amplifier 152, and a coupler 153. The coupler 151 is connected to the P optical transmission lines connected to the respective optical distribution units 30a and receives an optical signal transmitted via any of the P optical transmission lines as an input. The coupler 151 multiplexes the input optical signals and outputs the multiplexed optical signal. The number of ports required for the coupler 151 is P.

[0178] The amplifier 152 amplifies the optical signal output from the coupler 151.

[0179] The coupler 153 splits the optical signal amplified by the amplifier 152 and outputs the split optical signals. The number of ports required for the coupler 153 is P. The optical signals split and output by the coupler 153 are input to the NM wavelength selective switch 43 of each optical distribution unit 40a via the P optical transmission lines. Even in a case where the optical signals input from the return transfer unit 14 to each the NM wavelength selective switch 43 are wavelength multiplexed signals, the wavelength multiplexed signals can be separated by each the NM wavelength selective switch 43.

[0180] With such a configuration, even in a case where a component having wavelength selectivity such as WSS or AWG is not provided in the return transfer unit 14, return communication can be performed between arbitrary users.

[0181] FIG. 19 is a block diagram illustrating a specific example of a (second) functional configuration of the return transfer unit 14c according to the modification example of the fifth embodiment. The return transfer unit 14c includes a plurality of couplers 151-1 to 151-X, the amplifier 152, a plurality of couplers 153-1 to 153-X, a plurality of host couplers 156-1 and 156-2, a plurality of amplifiers 157-1 to 157-X, and a plurality of amplifiers 158-1 to 158-X.

[0182] In the example of FIG. 19, a coupler 151-x (1xX) is connected to the host coupler 156-1 via an amplifier 157-x, a coupler 153-x is connected to the host coupler 156-2 via an amplifier 158-x, and the host coupler 156-1 and the host coupler 156-2 are connected via the amplifier 152.

[0183] The coupler 151-x is connected to different P/X optical transmission lines among the P optical transmission lines connected to each optical distribution unit 30a and receives an optical signal transmitted via any of the P/X optical transmission lines as an input. The coupler 151-x multiplexes the input optical signals and outputs the multiplexed optical signal. In this manner, approximately the same number of optical transmission lines is connected to each coupler 151 on average. For example, in a case where the number of couplers 151 is two (X=2) and the number of optical distribution units 30a is four (P=4), two different optical transmission lines are connected to each coupler 151.

[0184] The amplifier 157-x amplifies the optical signal output from the coupler 151-x. The host coupler 156-1 multiplexes the optical signals amplified by the respective amplifiers 157 and outputs the multiplexed optical signal. The host coupler 156-2 splits the optical signal output from the host coupler 156-1 and amplified by the amplifier 152.

[0185] The amplifier 158-x amplifies the optical signal output from the host coupler 156-2. The coupler 153-x splits the optical signal amplified by the amplifier 158-x and outputs the split optical signals. The number of ports required for the coupler 153-x is P/X. The optical signals split and output by the coupler 153-x are input to the N x M wavelength selective switch 43 of each optical distribution unit 40a via the P/X optical transmission lines. Even in a case where the optical signals input from the return transfer unit 14 to each the NM wavelength selective switch 43 are wavelength multiplexed signals, the wavelength multiplexed signals can be separated by each the NM wavelength selective switch 43.

[0186] With such a configuration, even in a case where a component having wavelength selectivity such as WSS or AWG is not provided in the return transfer unit 14, return communication can be performed between arbitrary users.

[0187] FIG. 20 is a block diagram illustrating a specific example of a (third) functional configuration of the return transfer unit 14c according to the modification example of the fifth embodiment. The return transfer unit 14c includes the plurality of couplers 151-1 to 151-X, a plurality of amplifiers 152-1-1 to 152-X-X, the plurality of couplers 153-1 to 153-X, a plurality of host couplers 156-1-1 to 156-1-X, a plurality of host couplers 156-2-1 to 156-2-X, the plurality of amplifiers 157-1 to 157-X, and the plurality of amplifiers 158-1 to 158-X.

[0188] In the example of FIG. 20, the coupler 151-x is connected to a host coupler 156-1-x via the amplifier 157-x, the coupler 153-x is connected to a host coupler 156-2-x via the amplifier 158-x, and the host couplers 156-1 and the host couplers 156-2 are connected via the amplifiers 152.

[0189] The coupler 151-x is connected to different P/X optical transmission lines among the P optical transmission lines connected to each optical distribution unit 30a and receives an optical signal transmitted via any of the P/X optical transmission lines as an input. The coupler 151-x multiplexes the input optical signals and outputs the multiplexed optical signal.

[0190] The amplifier 157-x amplifies the optical signal output from the coupler 151-x. The host coupler 156-1-x splits the optical signal amplified by the amplifier 157-x and outputs the split optical signals. The host coupler 156-2-x multiplexes the optical signals output from the respective host couplers 156-1 and amplified by the connected amplifiers 152.

[0191] The amplifier 158-x amplifies the optical signal output from the host coupler 156-2-x. The coupler 153-x splits the optical signal amplified by the amplifier 158-x and outputs the split optical signals. The number of ports required for the coupler 153-x is P/X. The optical signals split and output by the coupler 153-x are input to the NM wavelength selective switch 43 of each optical distribution unit 40a via the P/X optical transmission lines. Even in a case where the optical signals input from the return transfer unit 14 to each the NM wavelength selective switch 43 are wavelength multiplexed signals, the wavelength multiplexed signals can be separated by each the NM wavelength selective switch 43.

[0192] With such a configuration, even in a case where a component having wavelength selectivity such as WSS or AWG is not provided in the return transfer unit 14, return communication can be performed between arbitrary users.

Second Modification Example of Fifth Embodiment

[0193] In the above embodiment, the configuration in which one optical communication device includes the optical distribution units 30a, the optical distribution units 40a, and the return transfer unit 14 has been described. Any of the optical distribution units 30a, the optical distribution units 40a, and the return transfer unit 14 may be mounted on another device. The same applies to a case where the return transfer unit 14 is the return transfer unit 14a or 14b.

Sixth Embodiment

[0194] In a sixth embodiment, the uplink optical distribution unit and the downlink optical distribution unit different from those of the first to fifth embodiments will be described. The sixth embodiment is similar to the first embodiment in the system configuration of the optical communication system 1, except for the configuration of the optical distribution unit. Therefore, hereinafter, differences from the first embodiment will be described.

[0195] FIG. 21 is a configuration diagram of the optical communication system 1 according to the sixth embodiment. The optical communication system 1 according to the sixth embodiment includes P optical distribution units 30b-1 to 30b-P, P optical distribution units 40b-1 to 40b-P, the control unit 12 (not illustrated), and the return transfer unit 14. Hereinafter, description will be made on the assumption that the optical distribution units 30b-1 to 30b-P are used for transmitting optical signals in the uplink direction and that the optical distribution units 40b-1 to 40b-P are used for transmitting optical signals in the downlink direction.

[0196] The optical distribution units 30b-1 to 30b-P have the same configuration. The optical distribution units 40b-1 to 40b-P have the same configuration. In the following description, the optical distribution units 30b-1 to 30b-P will be simply referred to as the optical distribution units 30b when not distinguished, and the optical distribution units 40b-1 to 40b-P will be simply referred to as the optical distribution units 40b when not distinguished. The optical distribution units 30b, the optical distribution units 40b, the control unit 12, and the return transfer unit 14 are functional units forming one optical communication device.

[0197] The optical distribution unit 30b includes one or more the 1M wavelength selective switches 34 and one or more 1M wavelength selective switches 35. The optical distribution unit 30b is one aspect of the first optical distribution unit. The 1N wavelength selective switch 34 and the 1M wavelength selective switch 35 are connected to a plurality of optical transmission lines and output an optical signal input from any of the optical transmission lines to another optical transmission line. The 1N wavelength selective switch 34 has N first ports and one second port. The N first ports included in the 1N wavelength selective switch 34 are connected to the edge node 15 or the subscriber device 16 via optical transmission lines. The one second port included in the 1N wavelength selective switch 34 is connected to the 1M wavelength selective switch 35 via an optical transmission line. The 1N wavelength selective switch 34 is a WSS.

[0198] The 1M wavelength selective switch 35 has one first port and M second ports. The one first port included in the 1M wavelength selective switch 35 is connected to the 1N wavelength selective switch 34 via the optical transmission line. One of the M second ports included in the 1M wavelength selective switch 35 is connected to the return transfer unit 14 via an optical transmission line. The remaining second ports (e.g. (M1) second ports) of the M second ports included in the 1M wavelength selective switch 35 are connected to another device via optical transmission lines, respectively. The 1M wavelength selective switch 35 is a WSS.

[0199] The optical distribution unit 40b includes one or more 1M wavelength selective switches 44 and one or more 1N wavelength selective switches 45. The optical distribution unit 40b is one aspect of the second optical distribution unit. The 1M wavelength selective switch 44 and the 1N wavelength selective switch 45 are connected to a plurality of optical transmission lines and output an optical signal input from any of the optical transmission lines to another optical transmission line. The 1M wavelength selective switch 44 has one first port and M second ports.

[0200] The one first port included in the 1M wavelength selective switch 44 is connected to the 1N wavelength selective switch 45 via an optical transmission line.

[0201] One of the M second ports included in each 1M wavelength selective switch 44 is connected to the return transfer unit 14 via an optical transmission line. The remaining second ports (e.g. (M1) second ports) of the M second ports included in the 1M wavelength selective switch 44 are connected to another device via optical transmission lines, respectively. The 1M wavelength selective switch 44 is a WSS.

[0202] The 1N wavelength selective switch 45 has N first ports and one second port. The N first ports included in the 1N wavelength selective switch 45 are connected to the subscriber device 16 via optical transmission lines. The one second port included in the 1N wavelength selective switch 45 is connected to the 1M wavelength selective switch 44 via the optical transmission line. The 1N wavelength selective switch 45 is a WSS.

[0203] An amplifier may be installed to compensate for a signal loss. A place where the amplifier may be installed is any or all of the transmission line of the first port of each of the 1N wavelength selective switches 34 and 45, the transmission line between the 1N wavelength selective switch 34 and the 1M wavelength selective switch 35, the transmission line between the 1M wavelength selective switch 44 and the 1N wavelength selective switch 45, and the transmission line of the second port of each of the 1M wavelength selective switches 35 and 44.

[0204] The return transfer unit 14 receives an optical signal output from each 1M wavelength selective switch 35 as an input and transfers the input optical signal to at least the 1M wavelength selective switch 44 to which a destination subscriber device 16 is connected. One optical transmission line is connected to the return transfer unit 14 from one 1M wavelength selective switch 35. Therefore, one optical transmission line is connected from one optical distribution unit 30b to the return transfer unit 14, and the number of optical distribution units 30b is P, and thus P uplink optical transmission lines are connected to the return transfer unit 14. Further, one optical transmission line is connected from one optical distribution unit 40b to the return transfer unit 14, and the number of optical distribution units 40b is P, and thus P downlink optical transmission lines are connected to the return transfer unit 14.

[0205] In a case where return communication is performed across the optical distribution unit 30b, the optical SW control unit 122 switches a path between the ports of the 1N wavelength selective switch 34 and the 1M wavelength selective switch 35 included in the optical distribution unit 30b so as to connect an output destination of an optical signal from the optical distribution unit 30b to the return transfer unit 14. The return transfer unit 14 performs control such that the input optical signal is output to a desired optical distribution unit 40b. With this configuration, return communication between arbitrary optical distribution units is implemented while the number of wires required for return in each optical distribution unit 40b is suppressed to P.

[0206] The configuration of the return transfer unit 14 may be any of the configurations described in the first to third embodiments. That is, the configuration of the return transfer unit 14 may be any of the configurations of FIGS. 2 and 4 to 13.

[0207] In the sixth embodiment, the optical SW control unit 122 switches connection between the ports of each of the 1N wavelength selective switches 34 and 45 and connection between the ports of each of the 1M wavelength selective switches 35 and 44. Specifically, in the sixth embodiment, the optical SW control unit 122 switches the connection between the ports for each of the 1N wavelength selective switch 34 and the 1M wavelength selective switch 35 included in each optical distribution unit 30b and the connection between the ports for each of the 1M wavelength selective switch 44 and the 1N wavelength selective switch 45 included in each optical distribution unit 40b.

[0208] For example, the optical SW control unit 122 switches the connection between the ports of the 1 x N wavelength selective switch 34 and the 1 x M wavelength selective switch 35 so as to connect the first port and the second port of the 1 x N wavelength selective switch 34 to which the edge node 15 or the subscriber device 16 serving as a transmission target is connected and connect the first port of the 1 x M wavelength selective switch 35 and the second port to which the return transfer unit 14 is connected. The 1N wavelength selective switch 34 outputs, from the second port, an optical signal transmitted from the edge node 15 or the subscriber device 16 connected to the first port. The optical signal output from the 1N wavelength selective switch 34 is input to the first port of the 1M wavelength selective switch 35. The 1M wavelength selective switch 35 outputs the optical signal input to the first port from the second port connected to the return transfer unit 14. Therefore, the optical signal input to the optical distribution unit 30b is transferred to the return transfer unit 14.

[0209] Further, the optical SW control unit 122 switches the connection between the ports of the 1M wavelength selective switch 44 and the 1N wavelength selective switch 45 so as to connect the first port of the 1M wavelength selective switch 44 and the second port of the 1M wavelength selective switch 44 to which the return transfer unit 14 is connected and connect the second port of the 1N wavelength selective switch 45 and the first port to which a destination subscriber device 16 is connected. The optical signal transferred from the return transfer unit 14 is input to the second port of the 1M wavelength selective switch 44. The 1M wavelength selective switch 44 outputs, from the first port, the optical signal transferred from the return transfer unit 14 and input to the second port. The optical signal output from the 1M wavelength selective switch 44 is input to the second port of the 1 x N wavelength selective switch 45. The 1N wavelength selective switch 45 outputs the optical signal input to the second port from the first port to which the destination subscriber device 16 is connected. Therefore, the optical signal output from the return transfer unit 14 is transferred to the destination subscriber device 16.

[0210] According to the optical communication system 1 of the sixth embodiment configured as described above, the number of wires required for return in each of the optical distribution units 30b and 40b can be suppressed even in the configuration including the 1N wavelength selective switch and the 1M wavelength selective switch in combination, instead of the optical SW as the optical distribution unit. Therefore, each subscriber device can be connected to an arbitrary subscriber device at an arbitrary timing by using the number of return transmission lines smaller than before.

First Modification Example of Sixth Embodiment

[0211] In a case where the optical distribution unit 30b includes the 1N wavelength selective switch 34 and the 1M wavelength selective switch 35 and the optical distribution unit 40b includes the 1M wavelength selective switch 44 and the 1N wavelength selective switch 45 as in the sixth embodiment, the return transfer unit 14 may have the configuration of any of FIGS. 12 to 14.

Second Modification Example of Sixth Embodiment

[0212] Any or all of the 1N wavelength selective switches 34 and 45 and the 1M wavelength selective switches 35 and 44 may be couplers.

Third Modification Example of Sixth Embodiment

[0213] In the above embodiment, the configuration in which one optical communication device includes the optical distribution units 30b, the optical distribution units 40b, and the return transfer unit 14 has been described. Any of the optical distribution units 30b, the optical distribution units 40b, and the return transfer unit 14 may be mounted on another device. The same applies to a case where the return transfer unit 14 is the return transfer unit 14a or 14b.

Modification Examples of First to Third Embodiments

[0214] In each of the above embodiments, the optical SWs are separately used in the uplink direction and in the downlink direction, but the same optical SWs may be used in the uplink direction and in the downlink direction.

[0215] In each of the above embodiments, the configuration in which the optical SWs 10, the optical SWs 11, and the return transfer unit 14, 14a, or 14b are provided in one optical communication device has been described. Any one of the optical SWs 10, the optical SWs 11, and the return transfer unit 14, 14a, or 14b may be mounted on another device.

[0216] Some functional units (e.g. the control unit 12 and the return transfer unit 14, 14a, 14b, or 14c) included in the optical communication device in the above embodiments may be implemented by a computer. In that case, a program for implementing this function may be recorded in a computer-readable recording medium, and the program recorded in the recording medium may be read and executed by a computer system to implement the function. Note that the computer system herein includes an OS and hardware such as peripheral devices.

[0217] The computer-readable recording medium refers to a portable medium such as a flexible disk, a magneto-optical disc, a ROM, or a CD-ROM or a storage device such as a hard disk included in the computer system. Further, the computer-readable recording medium may include a medium that dynamically holds the program for a short time, such as a communication line in a case where the program is transmitted via a network such as the Internet or a communication line such as a telephone line, and a medium that holds the program for a certain period of time, such as a volatile memory inside the computer system serving as a server or a client in that case. The above program may be for implementing some of the functions described above, may implement the functions described above by a combination with a program already recorded in the computer system, or may be implemented by using a programmable logic device such as an FPGA.

[0218] As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, specific configurations are not limited to the embodiments and include design and the like within the scope of the present invention.

INDUSTRIAL APPLICABILITY

[0219] The present invention is applicable to an optical communication system technique that performs return communication via an optical distribution unit.

REFERENCE SIGNS LIST

[0220] 10-1 to 10-P, 11-1 to 11-P Optical SW [0221] 12 Control unit [0222] 121 Wavelength management control unit [0223] 122 Optical SW control unit [0224] 14, 14a, 14b Return transfer unit [0225] 16-1 to 16-3 Subscriber device [0226] 30, 30-1 to 30-P, 30a, 30a-1 to 30a-P, 30b, 30b-1 to 30b-P, 40, 40-1 to 40-P, 40a, 40a-1 to 40a-P, 40b, 40b-1 to 40b-P Optical distribution unit [0227] 31, 42 1M optical switch [0228] 32 Signal multiplexing unit [0229] 33, 43 NM wavelength selective switch [0230] 34, 45 1N wavelength selective switch [0231] 35, 44 1M wavelength selective switch [0232] 41 Signal separation unit [0233] 141, 141-1 to 141-X, 141-1 to 141-4, 142, 142-1 to 142-X WSS [0234] 143, 143a, 143b Transfer wavelength control unit [0235] 144, 144-1 to 144-X AWG [0236] 145, 145-1 to 145-X, 151, 151-1 to 151-X, 153, 153-1 to 153-X Coupler [0237] 146, 146-1-1 to 146-X-X, 148-1 to 148-X, 150-1 to 150-X, 152, 152-1-1 to 152-X-X, 157-1 to 157-X, 158-1 to 158-X Amplifier [0238] 147-1, 147-2, 147-1-1 to 147-1-X, 147-2-1 to 147-2-X Host WSS [0239] 149-1, 149-2, 149-1-1 to 149-1-X, 149-2-1 to 149-2-X, 156-1 to 156-2, 156-1-1 to 156-1-X, 156-2-1 to 156-2-X Host coupler