Optical communication device, optical communication system, and transfer method

Abstract

Provided are an optical communication device, a communication system, and a transfer method that, when performing return communication in an optical communication system having a plurality of optical distribution units, allows each subscriber device to connect to any other subscriber device at any timing using a smaller number of return transmission paths than conventionally. [Solution] The optical communication system includes a transfer unit 14 that forwards an optical signal output from one of a plurality of second ports of the first optical distribution units 10-1 to 10-P back to one of a plurality of second ports of the second optical distribution units 11-1 to 11-P, and some of the plurality of second ports of the first optical distribution units 10-1 to 10-P are connected to the transfer unit 14, and the remaining second ports of the first optical distribution units 10-1 to 10-P are connected to other devices, and some of the plurality of second ports of the second optical distribution units 11-1 to 11-P are connected to the transfer unit 14, and the remaining second ports of the second optical distribution units 11-1 to 11-P are connected to other devices.

Description

[Technical Field]

[0001] The present invention relates to an optical communication device, an optical communication system, and a transfer method. This application claims priority based on PCT / JP2021 / 037731, filed in Japan on October 12, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] Conventionally, optical communication devices have been proposed that can relay optical signals according to their destinations while reducing delay (see, for example, Patent Document 1). Fig. 22 is a diagram showing an example of the configuration of an optical communication system 100 that includes a conventional optical communication device. The optical communication system 100 includes an optical SW 110 that configures the optical communication device, and a control unit 115. Subscriber devices 140-1 to 140-3 are connected to the optical SW 110.

[0003] The optical SW 110 is connected to a plurality of optical transmission lines, and outputs an optical signal input from one of the optical transmission lines to another optical transmission line. The optical SW 110 shown in Fig. 22 has first ports 111-1 to 111-6 and second ports 112-1 to 112-6. Each of the first ports 111 is connected to one of the subscriber devices 140-1 to 140-3 via one of the optical transmission lines 135-1 to 135-3. Each of the second ports 112 is connected to one of the optical transmission lines 136-1 to 136-4 and a return transmission line 137.

[0004] The return transmission line 137 is an optical transmission line for inputting an optical signal output from one port to another port. For example, in the example shown in Fig. 22, the return transmission line 137 is connected to the second port 112-4 and the second port 112-5. This allows, for example, an optical signal output from the second port 112-4 to be input to the second port 112-5.

[0005] The control unit 115 is connected to the second port 112-6 of the optical SW 110 via an optical transmission path 136-4. The control unit 115 includes a wavelength management control unit 120 and an optical SW control unit 130. The wavelength management control unit 120 assigns wavelengths to the optical subscriber devices 140. The optical SW control unit 130 switches the path of the optical SW 110. In the example shown in FIG. 22 , the optical SW control unit 130 switches the path of the optical SW 110 so that the first port 111-2 to which the optical subscriber device 140-1 is connected is connected to the second port 112-2, the first port 111-4 to which the optical subscriber device 140-2 is connected is connected to the second port 112-4, and the first port 111-5 to which the optical subscriber device 140-3 is connected is connected to the second port 112-5.

[0006] As a result, the optical signal transmitted from the subscriber device 140-1 is input to the first port 111-2 of the optical SW 110 via the optical transmission path 135-1 and is output from the second port 112-2 of the optical SW 110 to the optical transmission path 136-2. Furthermore, the optical signal transmitted from the subscriber device 140-2 is input to the first port 111-4 of the optical SW 110 via the optical transmission path 135-2 and is output from the second port 112-4 of the optical SW 110 to the return transmission path 137. The optical signal output to the return transmission path 137 is input to the second port 112-5 of the optical SW 110 and is output from the first port 111-5 of the optical SW 110 to the optical transmission path 135-3. The optical signal output to the optical transmission path 135-3 is transmitted to the subscriber device 140-3.

[0007] As described above, low-delay communication can be achieved by using the return transmission path 137 for a port (e.g., the second port 112) different from the port (e.g., the first port 111) to which the subscriber device 140 is connected. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2021 / 131202 Summary of the Invention [Problem to be solved by the invention]

[0009] In the optical communication system 100 shown in Fig. 22, by arranging multiple optical SWs 110-1 to 110-P (P is an integer equal to or greater than 2) in parallel at one point, the maximum number of users that can transmit to each direction can be increased. Fig. 23 is a diagram for explaining a configuration in which multiple optical SWs 110 are arranged in parallel. The example shown in Fig. 23 shows a configuration in which optical SWs 110-1 to 110-P are arranged in parallel, and a subscriber device 140 is connected to each optical SW 110.

[0010] In order to perform loopback communication between the optical subscriber device 140-1 connected to the optical SW 110-1 and the optical subscriber device 140-2 connected to the optical SW 110-2, it is necessary to connect the second port 112-1 of the optical SW 110-1 and the second port 112-1 of the optical SW 110-2 with a loopback transmission line 137. When there are P optical SWs 110 and one optical SW 110 accommodates n (n is an integer equal to or greater than 1) optical subscriber devices 140, in order for each optical SW 110 to connect with an arbitrary optical subscriber device 140 at an arbitrary timing, it is necessary to connect the loopback transmission lines 137 using n×(p−1) ports from one optical SW 110.

[0011] Within the optical SW 110, n lines are required to communicate with any subscriber device 140, so a total of np ports are required for connections between SWs and within the SW. While it is conceivable to reduce the number of return transmission lines 137 and physically change the wiring each time a connection request is received, this is undesirable because it increases on-site operation. Therefore, there is a need for technology that eliminates the need for physical wiring and enables each subscriber device to connect to any subscriber device at any time using fewer return transmission lines than before. This problem is not limited to optical SWs, but is a common problem when performing return communication in optical communication systems equipped with an optical distribution unit that has the function of distributing input optical signals to other devices.

[0012] In view of the above circumstances, the present invention aims to provide a technology that enables each subscriber device to connect to any other subscriber device at any timing using a smaller number of return transmission paths than conventional methods when performing return communication in an optical communication system equipped with multiple optical distribution units. [Means for solving the problem]

[0013] One aspect of the present invention is an optical communication device comprising: a plurality of first distribution units connected to a plurality of optical transmission paths and outputting an optical signal input from any of the first devices to any of the optical transmission paths; a plurality of second distribution units connected to a plurality of optical transmission paths and outputting an optical signal input from any of the optical transmission paths to any of the second devices; and a transfer unit that transfers an 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 to which a specific of the second devices is connected.

[0014] One aspect of the present invention is an optical communication system comprising a plurality of first distribution units connected to a plurality of optical transmission paths and outputting an optical signal input from any of the first devices to any of the optical transmission paths, a plurality of second distribution units connected to a plurality of optical transmission paths and outputting an optical signal input from any of the optical transmission paths to any of the second devices, and a transfer unit that transfers an 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 to which a specific of the second devices is connected.

[0015] One aspect of the present invention is a transfer method in which a plurality of first distribution units are connected to a plurality of optical transmission paths and output an optical signal input from any of the first devices to any of the optical transmission paths, and a plurality of second distribution units are connected to a plurality of optical transmission paths and output an optical signal input from any of the optical transmission paths to any of the second devices, and an optical signal transmitted from a first device connected to any of the plurality of first distribution units is transferred to any of the plurality of second distribution units to which a specific second device is connected. [Effects of the Invention]

[0016] According to the present invention, when performing return communication in an optical communication system having multiple optical distribution units, it becomes possible for each subscriber device to connect to any subscriber device at any timing using a smaller number of return transmission paths than in the past. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a configuration diagram of an optical communication system according to a first embodiment. [Figure 2] FIG. 2 is a block diagram showing a specific example of a functional configuration (part 1) of a return transfer unit in the first embodiment. [Figure 3] FIG. 3 is a sequence diagram illustrating a processing flow of the optical communication system according to the first embodiment. [Figure 4] FIG. 10 is a block diagram showing a specific example of a functional configuration (part 2) of the return transfer unit in the first embodiment. [Figure 5] FIG. 10 is a block diagram showing a specific example of a functional configuration (part 3) of the return transfer unit in the first embodiment. [Figure 6] FIG. 10 is a block diagram showing a specific example of a functional configuration (part 4) of the return transfer unit in the first embodiment. [Figure 7] FIG. 10 is a block diagram showing a specific example of a functional configuration (part 5) of the return transfer unit in the first embodiment. [Figure 8] FIG. 10 is a block diagram showing a specific example of a functional configuration (part 1) of a return transfer unit in the second embodiment. [Figure 9] FIG. 10 is a block diagram showing a specific example of a functional configuration (part 2) of the return transfer unit in the second embodiment. [Figure 10] FIG. 10 is a block diagram showing a specific example of a functional configuration (part 3) of the return transfer unit in the second embodiment. [Figure 11] FIG. 13 is a block diagram showing a specific example of a functional configuration (part 1) of a return transfer unit in the third embodiment. [Figure 12] FIG. 13 is a block diagram showing a specific example of a functional configuration (part 2) of a return transfer unit in the third embodiment. [Figure 13] FIG. 13 is a block diagram showing a specific example of a functional configuration (part 3) of a return transfer unit in the third embodiment. [Figure 14] FIG. 10 is a configuration diagram of an optical communication system according to a fourth embodiment. [Figure 15] FIG. 10 is a sequence diagram illustrating a processing flow of an optical communication system according to a fourth embodiment. [Figure 16] FIG. 11 is a configuration diagram of an optical communication system according to a modified example of the fourth embodiment. [Figure 17] FIG. 10 is a configuration diagram of an optical communication system according to a fifth embodiment. [Figure 18] FIG. 13 is a block diagram showing a specific example of a functional configuration (part 1) of a return transfer unit in a modified example of the fifth embodiment. [Figure 19] FIG. 13 is a block diagram showing a specific example of a functional configuration (part 2) of a return transfer unit in a modified example of the fifth embodiment. [Figure 20] FIG. 13 is a block diagram showing a specific example of a functional configuration (part 3) of a return transfer unit in a modified example of the fifth embodiment. [Figure 21] FIG. 10 is a configuration diagram of an optical communication system according to a sixth embodiment. [Figure 22] FIG. 1 is a diagram illustrating an example of the configuration of an optical communication system including a conventional optical communication device. [Figure 23] FIG. 10 is a diagram for explaining a configuration in which a plurality of optical switches are arranged in parallel. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. (First embodiment) 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 equal to or greater than 2), P optical SWs 11-1 to 11-P, a control unit 12, and a turn-back transfer unit 14. In the following description, it is assumed that the optical SWs 10-1 to 10-P are used to transmit optical signals in the upstream direction, and the optical SWs 11-1 to 11-P are used to transmit optical signals in the downstream direction. In the following description, when the optical SWs 10-1 to 10-P are not distinguished, they will simply be referred to as optical SW10, and when the optical SWs 11-1 to 11-P are not distinguished, they will simply be referred to as optical SW11. The optical SWs 10, 11, control unit 12, and turn-back transfer unit 14 are functional units that constitute one optical communication device.

[0019] The optical SW10 is connected to a plurality of optical transmission lines, and outputs an optical signal input from one of the optical transmission lines to another optical transmission line. The optical transmission line is, for example, an optical fiber. The optical SW10 has a plurality of first ports (for example, n first ports) and a plurality of second ports (for example, n or more second ports). Each first port of the optical SW10 is connected to a subscriber device 16 via a transmission line 18. FIG. 1 shows an example in which a subscriber device 16-1 is connected to the optical SW10-1 via an optical transmission line 18-1. The optical SW10 is one aspect of a first optical distribution unit.

[0020] Of the multiple second ports of the optical SW10, n second ports are connected to the turn-back forwarding unit 14 via n optical transmission lines. The remaining second ports of the multiple second ports of the optical SW10 may be connected to other devices via optical transmission lines. In the following explanation, for simplicity, it is assumed that the number of first ports and second ports of the optical SW10 is n.

[0021] The optical SW11 is connected to a plurality of optical transmission lines and outputs an optical signal input from one of the optical transmission lines to another optical transmission line. The optical SW11 has 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 SW11 is connected to a subscriber device 16 via a transmission line 18. FIG. 1 shows an example in which a subscriber device 16-2 is connected to the optical SW11-1 via the optical transmission line 18-2, and a subscriber device 16-3 is connected to the optical SW11-P via the optical transmission line 18-3. The optical SW11 is one aspect of a second optical distribution unit.

[0022] Of the multiple second ports of the optical SW11, n second ports are connected to the turn-back forwarding unit 14 via n optical transmission lines. The remaining second ports of the multiple second ports of the optical SW11 may be connected to other devices via optical transmission lines. In the following explanation, for simplicity, it is assumed that the number of first ports and second ports of the optical SW11 is n.

[0023] The subscriber device 16 is connected to the optical SW 10 or 11 via an optical access network such as a PON (Passive Optical Network). The subscriber device 16 includes an optical transceiver. The optical transceiver is an example of an optical transmitter and an optical receiver in the subscriber device 16. The optical transceiver is a wavelength-tunable optical transmitter / receiver. In this case, the subscriber device 16 can communicate at any wavelength. The optical transceiver may be an optical transceiver with an AMCC (Auxiliary Management and Control Channel) function. In this case, the wavelength used by the subscriber device 16 is controlled via a control signal superimposed by the AMCC. The subscriber device 16 is one aspect of the first device and the second device.

[0024] The control unit 12 is connected to the second ports of the optical SWs 10 and 11 via optical transmission paths. The control unit 12 includes a wavelength management control unit 121 and an optical SW control unit 122. The wavelength management control unit 121 assigns wavelengths to each subscriber device 16. When the wavelength management control unit 121 assigns wavelengths to each subscriber device 16, the optical SW control unit 122 switches the path between the ports of the optical SW 10 or 11 so that the subscriber device 16 and the wavelength management control unit 121 are connected.

[0025] The optical SW control unit 122 switches the connection between ports of the optical SW 10 and the connection between ports of the optical SW 11. For example, the optical SW control unit 122 switches the connection between ports of the optical SW 10 and the optical SW 11 so 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.

[0026] The control unit 12 stores a management table. The management table includes information for identifying the subscriber device 16, information on the wavelength assigned to each subscriber device 16, and information on the optical SW 10 or 11 to which the subscriber device 16 is connected (for example, information on the port to which the subscriber device 16 is connected). The control unit 12 is composed of one or more processors.

[0027] The turn-back transfer unit 14 receives an optical signal output from the optical SW 10 and forwards the input optical signal to the optical SW 11 connected to at least the destination subscriber device 16. Since n optical transmission paths are connected from one optical SW 10 to the turn-back transfer unit 14, nP upstream optical transmission paths are connected to the turn-back transfer unit 14. Furthermore, since n optical transmission paths are connected from one optical SW 11 to the turn-back transfer unit 14, nP downstream optical transmission paths are connected to the turn-back transfer unit 14. The turn-back transfer unit 14 is one aspect of a forwarding unit.

[0028] When performing return communication across the optical SW 10, the optical SW control unit 122 switches the path between the ports of the optical SW 10 so that the output destination of the optical signal from the optical SW 10 is connected to the return forwarding unit 14. The return forwarding unit 14 controls so that the input optical signal is output to the desired optical SW 11. This configuration realizes return communication between any optical SWs while limiting the number of wirings required for return at each optical SW to n.

[0029] When the turn-back transfer unit 14 is realized by a single device, a WSS (Wavelength Selective Switch) with nP x nP ports, a fiber cross connect (FXC), or a circular AWG (Arrayed Waveguide Gratings) is used. However, when nP is large, it is difficult to realize a WSS or a fiber cross connect with nP x nP ports, and this leads to an increase in cost. For this reason, the following explanation also covers the case where the turn-back transfer unit 14 is configured by multiple devices.

[0030] FIG. 2 is a block diagram showing a specific example of a functional configuration (part 1) of the return transfer unit 14 in the first embodiment. The return forwarding unit 14 includes a WSS 141, a WSS 142, and a forwarding wavelength control unit 143. The WSS 141 is connected to n optical transmission lines (a total of nP optical transmission lines) connected to the second port of each optical SW10, and outputs an optical signal having a wavelength (hereinafter referred to as the "set wavelength") set by the forwarding wavelength control unit 143, among optical signals transmitted via a certain optical transmission line, to the WSS 142. The WSS 141 is a wavelength selective optical switch. The number of ports required for the WSS 141 is n×P. The WSS 141 is one aspect of the first demultiplexing unit.

[0031] The WSS 142 is connected to n optical transmission lines (a total of nP optical transmission lines) connected to the second ports of each optical SW11, and outputs the optical signal of the set wavelength output from the WSS 141 to the optical transmission line that serves as the 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 n×P. The WSS 142 is one aspect of the second demultiplexing unit.

[0032] The transfer wavelength control unit 143 sets the wavelengths to be output from the WSSs 141 and 142 in accordance with instructions from the control unit 12. Specifically, when the control unit 12 instructs the transfer wavelength control unit 143 on the wavelengths to be transferred during return communication, the transfer wavelength control unit 143 sets the specified wavelengths to the WSSs 141 and 142. This allows the WSSs 141 and 142 to output optical signals with the set wavelengths. The transfer wavelength control unit 143 may be implemented in the control unit 12.

[0033] Fig. 3 is a sequence diagram for explaining the processing flow of the optical communication system 1 in the first embodiment. Fig. 3 explains a case where a subscriber device 16-1 connected to the optical SW10-1 shown in Fig. 1 communicates with a subscriber device 16-2 connected to the optical SW11-1. Here, it is assumed that a wavelength λ1 is assigned to the subscriber devices 16-1 and 16-2.

[0034] The forwarding wavelength control unit 143 sets the port used between the WSS 141 and the optical SW10-1 and the port used between the WSS 142 and the optical SW11-1 to forward the wavelength λ1 (step S101). The optical subscriber device 16-1 transmits an optical signal with wavelength λ1 (step S102). The optical signal with wavelength λ1 transmitted from the optical subscriber device 16-1 is input to the first port of the optical SW10-1 via the optical transmission line 18-1.

[0035] The optical SW10-1 is controlled by the optical SW control unit 122 so as to connect the path between the first port of the optical SW10-1, to which the subscriber device 16-1 is connected, and the second port of the optical SW10-1, to which the turn-back transfer unit 14 is connected. As a result, the optical signal of wavelength λ1 input to the first port of the optical SW10-1 is output from the second port to the turn-back transfer unit 14 (step S103).

[0036] The optical signal with wavelength λ1 output from optical SW10-1 is input to WSS 141 (step S104). WSS 141 outputs an optical signal with a set wavelength set by transfer wavelength control unit 143 to WSS 142 (step S105). Here, since wavelength λ1 is set as the set wavelength, an optical signal with wavelength λ1 is output from WSS 141. The optical signal with wavelength λ1 output from WSS 141 is input to WSS 142 (step S106).

[0037] The WSS 142 outputs an optical signal of the set wavelength set by the transfer wavelength control unit 143 to the optical transmission line to which the optical SW11-1 is connected (step S107). Here, since the wavelength λ1 is set as the set wavelength, the optical signal of wavelength λ1 is output from the WSS 142. The optical signal of wavelength λ1 output from the WSS 142 is input to the second port of the optical SW11-1 via the optical transmission line.

[0038] The optical SW11-1 is controlled by the optical SW control unit 122 so that the path between the first port of the optical SW11-1 to which the optical subscriber device 16-2 is connected and the second port of the optical SW11-1 to which the return forwarding unit 14 is connected is connected. As a result, the optical signal of wavelength λ1 input to the second port of the optical SW11-1 is output from the first port to the optical subscriber device 16-2 via the optical transmission line 18-2 (step S108). The optical subscriber device 16-2 receives the optical signal of wavelength λ1 output from the optical SW11-1 (step S109).

[0039] Note that if one or more return communications have already been performed and a new return communication is to be performed, the same wavelength cannot be used between WSS 141 and WSS 142. Therefore, if the wavelength to be used in the new return communication is the same wavelength, the forwarding wavelength control unit 143 outputs a wavelength change command to the wavelength management control unit 121. The wavelength change command is an instruction to change the wavelength used by the subscriber device 16. In response to the wavelength change command, the wavelength management control unit 121 notifies the target subscriber device 16 to perform communication using a wavelength (e.g., λ2) different from the wavelength already being used by the subscriber device 16 for the return communication. This makes it possible to perform the return communication using a different wavelength even when a new return communication is to be performed.

[0040] According to the optical communication system 1 configured as above, when performing return communication in the optical communication system 1 including the multiple optical SWs 10 and 11, the number of wirings required for return communication in each optical SW can be reduced to n. Therefore, it becomes possible to connect each subscriber device to any other subscriber device at any timing using a smaller number of return transmission paths than conventionally.

[0041] (Modification of the first embodiment) An amplifier may be provided between WSS 141 and WSS 142.

[0042] The return transfer unit 14 may have the configuration shown in FIGS. 4 is a block diagram showing a specific example of a functional configuration (part 2) of the turn-back forwarding unit 14 in the first embodiment. The turn-back forwarding unit 14 includes a WSS 141, a forwarding wavelength control unit 143, and an AWG 144. The configuration shown in FIG. 4 differs from the configuration shown in FIG. 2 in that the WSS 141 is controlled by the forwarding wavelength control unit 143, and that an AWG 144 is newly provided instead of the WSS 142.

[0043] In the configuration shown in FIG. 4, the forwarding wavelength control unit 143 sets the wavelength to be output only to the WSS 141. The AWG 144 is connected to n optical transmission lines (a total of nP optical transmission lines) connected to the second port of each optical SW 11, and outputs the optical signal output from the WSS 141 from a path according to the wavelength. Here, while the AWG is less expensive than the WSS, the output port and the wavelength that can be output from that port are fixed. Therefore, it is necessary to control the wavelength according to the other party of the return communication. The AWG 144 is one aspect of the second demultiplexing unit.

[0044] For example, when a subscriber device 10-1 connected to optical SW10-1 and a subscriber device 16-2 connected to optical SW11-1 perform loopback communication, the wavelengths that can be transferred at the port used between the AWG 144 and optical SW11-1 are determined. The wavelength management control unit 121 sets the transmission wavelength of the subscriber device 16-1 to a wavelength that can be transferred at the port used between the AWG 144 and optical SW11-1. Furthermore, the transfer wavelength control unit 143 sets the WSS 141 so that the port used between the WSS 141 and optical SW10-1 can transfer the wavelength that can be transferred at the port used between the AWG 144 and optical SW11-1. This makes it possible to realize loopback communication.

[0045] 2, an AWG 144 may be newly provided instead of the WSS 141. The forwarding wavelength control unit 143 may set wavelengths to be output only to the WSS 142. In this case, the AWG 144 is connected to n optical transmission lines (a total of nP optical transmission lines) connected to the second ports of the optical SWs 10, and inputs optical signals output from each optical SW 10 through a route corresponding to the wavelength. For example, when a subscriber device 10-1 connected to the optical SW 10-1 and a subscriber device 16-2 connected to the optical SW 11-1 perform loopback communication, the wavelengths that can be forwarded at the port used between the AWG 144 and the optical SW 10-1 are determined. The wavelength management control unit 121 sets the transmission wavelength of the subscriber device 16-1 to a wavelength that can be forwarded at the port used between the AWG 144 and the optical SW 10-1. Furthermore, the forwarding wavelength control unit 143 sets the WSS 142 so that the wavelengths that can be forwarded at the port used between the WSS 142 and the optical SW11-1 can be forwarded at the port used between the AWG 144 and the optical SW10-1. This makes it possible to realize loopback communication. An amplifier may be provided between the WSS 141 and the AWG 144.

[0046] Next, another example will be described with reference to Fig. 5. Fig. 5 is a block diagram showing a specific example of a functional configuration (part 3) of the turn-back transfer unit 14 in the first embodiment. The turn-back transfer unit 14 includes an AWG 144, a coupler 145, and an amplifier 146. The coupler 145 is connected to n optical transmission lines (a total of nP optical transmission lines) connected to the second ports of each optical SW10, and receives as input an optical signal transmitted through any of the nP optical transmission lines. The coupler 145 multiplexes the input optical signals and outputs the multiplexed signal. The coupler 145 is one aspect of the first demultiplexing unit.

[0047] The amplifier 146 amplifies the optical signal output from the coupler 145. The AWG 144 is connected to n optical transmission lines (a total of nP optical transmission lines) connected to the second port of each optical SW11, and demultiplexes the optical signal amplified by the amplifier 146 and outputs it to the optical transmission lines. A coupler is less expensive than a WSS, and does not require control by the forwarding wavelength control unit 143. Note that if the branching loss is relatively small, the amplifier 146 may not be provided.

[0048] Next, another example will be described using FIGS. 6 and 7. The turn-back transfer unit 14 shown in FIGS. 2, 4, and 5 has been described using an example of unidirectional communication. The configuration shown in FIGS. 6 and 7 will be described as being capable of supporting bidirectional communication. FIG. 6 is a block diagram showing a specific example of a functional configuration (part 4) of the turn-back transfer unit 14 in the first embodiment. The turn-back transfer unit 14 includes WSSs 141-1 and 141-2 and a forwarding wavelength control unit 143. The WSS 141-1 is connected to n optical transmission lines (a total of nP optical transmission lines) connected to the second ports of each optical SW10, and outputs an optical signal of a set wavelength among optical signals transmitted via a certain optical transmission line to the WSS 141-2. Furthermore, the WSS 141-1 outputs the optical signal of the set wavelength output from the WSS 141-2 to an optical transmission line that serves as an output path for the set wavelength. The WSS 141-1 is a wavelength selective optical switch. The number of ports required for the WSS 141-1 is n×P.

[0049] WSS 141-2 is connected to n optical transmission lines (a total of nP optical transmission lines) connected to the second ports of each optical SW11, and outputs the optical signal of the set wavelength output from WSS 141-1 to the optical transmission line that serves as the output path for the set wavelength. Furthermore, WSS 141-2 outputs the optical signal of the set wavelength to WSS 141-1 from the optical signals transmitted via an optical transmission line to which each optical SW11 is connected. WSS 141-2 is a wavelength-selective optical switch. The number of ports required for WSS 141-2 is n×P.

[0050] The transfer wavelength control unit 143 sets wavelengths to be output by the WSSs 141-1 and 141-2 in accordance with instructions from the control unit 12. Specifically, when the control unit 12 instructs the transfer wavelength control unit 143 on wavelengths to be transferred during return communication, the transfer wavelength control unit 143 sets the specified wavelengths to the WSSs 141 and 142. To enable bidirectional communication, the transfer wavelength control unit 143 sets at least two different wavelengths as set wavelengths to each of the WSSs 141-1 and 141-2.

[0051] The configuration shown in Figure 6 accommodates a mixture of two bidirectional optical signals, direction 1 and direction 2. This allows bidirectional communication to be supported using the same components as for unidirectional communication. However, because there is only one optical transmission path between WSS141-1 and WSS141-2, the same wavelength cannot be used in direction 1 and direction 2.

[0052] 7 is a block diagram showing a specific example of a functional configuration (part 5) of the turn-back transfer unit 14 in the first embodiment. The turn-back transfer unit 14 includes WSSs 141-1, 141-2, 141-3, and 141-4, and a forwarding wavelength control unit 143. The configuration of the turn-back transfer unit 14 shown in FIG. 7 includes another set of the same components as those used for one-way communication (for example, FIG. 2). WSSs 141-1 and 141-2 are used for direction 1, and WSSs 141-3 and 141-4 are used for direction 2. WSSs 141-1, 141-2, 141-3, and 141-4 are wavelength selective optical switches. The number of ports required for WSSs 141-1, 141-2, 141-3, and 141-4 is n×P.

[0053] The transfer wavelength control unit 143 sets wavelengths to be output from the WSSs 141-1, 141-2, 141-3, and 141-4 in accordance with instructions from the control unit 12. Specifically, the transfer wavelength control unit 143 sets different wavelengths for the WSSs 141-1 and 141-2 used for direction 1 and the WSSs 141-3 and 141-4 used for direction 2. For example, the transfer wavelength control unit 143 sets a wavelength λ1 for the WSSs 141-1 and 141-2, and a wavelength λ2 for the WSSs 141-3 and 141-4. This allows the WSSs 141-1, 141-2, 141-3, and 141-4 to output optical signals with the set wavelengths.

[0054] WSS 141-1 is connected to n optical transmission lines (a total of nP optical transmission lines) connected to the second ports of each optical SW10, and outputs an optical signal of a set wavelength (for example, wavelength λ1) among the optical signals transmitted via a certain optical transmission line to WSS 141-2. WSS 141-2 is connected to n optical transmission lines (a total of nP optical transmission lines) connected to the second ports of each optical SW11, and outputs the optical signal of a set wavelength (for example, wavelength λ1) output from WSS 141-1 to an optical transmission line that serves as an output path for the set wavelength.

[0055] WSS 141-4 is connected to n optical transmission lines (a total of nP optical transmission lines) connected to the second ports of each optical SW11, and outputs an optical signal of a set wavelength (for example, wavelength λ2) among the optical signals transmitted via a certain optical transmission line to WSS 141-3. WSS 141-3 is connected to n optical transmission lines (a total of nP optical transmission lines) connected to the second ports of each optical SW10, and outputs an optical signal of a set wavelength (for example, wavelength λ1) output from WSS 141-4 to an optical transmission line that serves as an output path for the set wavelength.

[0056] The configuration shown in FIG. 7 does not allow optical signals in directions 1 and 2 to pass through the same optical transmission line, making it possible to use the same wavelength in directions 1 and 2.

[0057] (Second embodiment) In the second embodiment, the system configuration of the optical communication system 1 is the same as that of the first embodiment, but differs only in the configuration of the return forwarding unit 14. Therefore, the differences from the first embodiment will be described below.

[0058] FIG. 8 is a block diagram showing a specific example of a functional configuration (part 1) of the return transfer unit 14a in the second embodiment. The return forwarding unit 14a includes multiple WSSs 141-1 to 141-X (X is an integer equal to or greater than 2), multiple WSSs 142-1 to 142-X, a forwarding wavelength control unit 143a, and multiple upper WSSs 147-1 to 147-2. In the example shown in Fig. 8, WSS 141-x (1 < x < X) is connected to upper WSS 147-1, and WSS 142-x is connected to upper WSS 147-2.

[0059] Each WSS 141-x is connected to different nP / X optical transmission lines among the n optical transmission lines (a total of nP optical transmission lines) connected to the second port of each optical SW 10, and outputs an optical signal of a set wavelength among the optical signals transmitted through a certain optical transmission line to the upper WSS 147. In this way, on average, approximately the same number of optical transmission lines are connected to each WSS 141. For example, if there are two WSSs 141 (X=2), three optical SWs 10 (P=3), and the number of optical transmission lines connected to the second port 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 n×P / X.

[0060] WSS 142-x is connected to nP / X different optical transmission lines and outputs the optical signal of the set wavelength output from the upper WSS 147-2 to the optical transmission line that serves as the output path for the set wavelength. In this way, on average, approximately the same number of optical transmission lines are connected to each WSS 142. The number of ports required for WSS 142 is n×P / X.

[0061] The upper WSS 147-1 outputs to the upper WSS 147-2 an optical signal of a set wavelength among the optical signals output from each WSS 141. The upper WSS 147-1 requires X ports.

[0062] The upper WSS 147-2 outputs optical signals of a set wavelength among the optical signals output from the upper WSS 147-1 to each WSS 142. The upper WSS 147-2 requires X ports.

[0063] The transfer wavelength control unit 143a sets wavelengths to be output from the WSSs 141 and 142 and the upper WSS 147 in accordance with instructions from the control unit 12. The transfer wavelength control unit 143a may be implemented in the control unit 12.

[0064] In the optical communication system 1 of the second embodiment configured as described above, X WSSs 141 and 142 are arranged in parallel, and an upper WSS 147 is arranged above each of the parallel WSSs 141 and 142. This configuration makes it possible to reduce the number of ports required per WSS compared to the first embodiment.

[0065] (Modification of the second embodiment) Amplifiers may be provided between WSS 141-x and upper WSS 147-1, between upper WSS 147-1 and upper WSS 147-2, and between WSS 142-x and upper WSS 147-2, or in all of these.

[0066] The return transfer unit 14a may have the configuration shown in FIG. 9 or FIG. FIG. 9 is a block diagram showing a specific example of a functional configuration (part 2) of the return transfer unit 14a in the second embodiment. The return forwarding unit 14a includes a plurality of WSSs 141-1 to 141-X, a forwarding wavelength control unit 143a, a plurality of AWGs 144-1 to 144-X, and a plurality of upper WSSs 147-1 to 147-2. In the example shown in Fig. 9, the WSSs 141-1 to 141-X are connected to the upper WSS 147-1, and the AWGs 144-1 to 144-X are connected to the upper WSS 147-2.

[0067] 9 differs from the configuration shown in Fig. 8 in that the control targets of the transfer wavelength control unit 143a are WSSs 141 and 142 and an upper WSS 147-1, and in that a plurality of AWGs 144-1 to 144-X are newly provided instead of a plurality of WSSs 142-1 to 142-X. The WSS 141 and the upper WSS 147 perform the same processes as the functional units with the same names shown in Fig. 8, and therefore a description thereof will be omitted.

[0068] The AWG 144-x is connected to nP / X different optical transmission lines among the n optical transmission lines (a total of nP optical transmission lines) connected to the second port of each optical SW 11, and outputs the optical signal of the set wavelength output from the upper WSS 147-2 through a route according to the wavelength. The number of ports required for the AWG 144 is n × P / X.

[0069] An amplifier may be provided between the WSS 141-x and the upper WSS 147-1, between the upper WSS 147-1 and the upper WSS 147-2, or between the AWG 144-x and the upper WSS 147-2, or all of these.

[0070] In the configuration shown in FIG. 8, AWGs 144-1 to 144-X may be newly provided in place of the WSSs 141-1 to 141-X.

[0071] Next, another example will be described with reference to Fig. 10. Fig. 10 is a block diagram showing a specific example of the functional configuration (part 3) of the return transfer unit 14a in the second embodiment. The return transfer unit 14a includes a plurality of AWGs 144-1 to 144-X, a plurality of couplers 145-1 to 145-X, an amplifier 146, a plurality of amplifiers 148-1 to 148-X, a plurality of upper couplers 149-1 to 149-2, and a plurality of amplifiers 150-1 to 150-X.

[0072] In the example shown in FIG. 10, coupler 145-x is connected to upper coupler 149-1 via amplifier 148-x, AWG 144-x is connected to upper coupler 149-2 via amplifier 150-x, and upper couplers 149-1 and 149-2 are connected via amplifier 146.

[0073] The coupler 145-x is connected to different nP / X optical transmission lines among the n optical transmission lines (a total of nP optical transmission lines) connected to the second port of each optical SW10, and receives an optical signal transmitted through any of the nP / X optical transmission lines as input. The coupler 145-x multiplexes the input optical signals and outputs the combined signal.

[0074] The amplifier 148-x amplifies the optical signal output from the coupler 145-x.

[0075] The upstream coupler 149-1 multiplexes the optical signals amplified by the amplifiers 148 and outputs the multiplexed signals.

[0076] The upstream coupler 149-2 branches the optical signal output from the upstream coupler 149-1 and amplified by the amplifier 146.

[0077] The amplifier 150-x amplifies the optical signal output from the upstream coupler 149-2.

[0078] The AWG 144-x is connected to different nP / X optical transmission lines out of the n optical transmission lines (a total of nP optical transmission lines) connected to the second port of each optical SW11, and outputs the optical signals amplified by each amplifier 146 from a path according to the wavelength. The number of ports required for the AWG 144-x is n×P / X.

[0079] (Third embodiment) In the third embodiment, the system configuration of the optical communication system 1 is the same as that of the first embodiment, but differs only in the configuration of the return transfer unit 14. Therefore, the differences from the first embodiment will be described below.

[0080] FIG. 11 is a block diagram showing a specific example of a functional configuration (part 1) of the return transfer unit 14b in the third embodiment. The return forwarding unit 14b includes multiple WSSs 141-1 to 141-X, multiple WSSs 142-1 to 142-X, a forwarding wavelength control unit 143b, multiple upstream WSSs 147-1-1 to 147-1-X, and multiple upstream WSSs 147-2-1 to 147-2-X. In the example shown in Fig. 11, WSS 141-x is connected to upstream WSS 147-1-x, and WSS 142-x is connected to upstream WSS 147-2-x.

[0081] WSS141-x is connected to different nP / X optical transmission paths out of the n optical transmission paths (a total of nP optical transmission paths) connected to the second port of each optical SW10, and outputs an optical signal of a set wavelength out of the optical signals transmitted through a certain optical transmission path to upper WSS147-x.

[0082] The WSS 142-x is connected to different nP / X optical transmission lines, and outputs an optical signal of a set wavelength output from the upper WSS 147-2-x to an optical transmission line that serves as an output path for the set wavelength.

[0083] The upper WSS 147-1-x outputs the optical signal of the set wavelength among the optical signals output from the WSS 141-x to the upper WSS 147-2.

[0084] The upper WSS 147-2-x outputs the optical signal of the set wavelength among the optical signals output from the upper WSS 147-1 to the WSS 142-x.

[0085] The transfer wavelength control unit 143b sets wavelengths to be output from the WSSs 141 and 142 and the upper WSS 147 in accordance with instructions from the control unit 12. The transfer wavelength control unit 143b may be implemented in the control unit 12.

[0086] In the optical communication system 1 of the third embodiment configured as described above, in addition to X WSSs 141 and 142, X upper WSSs 147-1 and 147-2 are also arranged in parallel. In the second embodiment, it was necessary to aggregate a maximum of nP wavelengths in the upper WSS 147. In contrast, in the third embodiment, the maximum number of wavelengths that can be accommodated by all WSSs is nP / X, making it possible to reduce the number of wavelengths that must be accommodated by a single WSS.

[0087] (Modification of the third embodiment) Amplifiers may be provided between WSS 141-x and upper WSS 147-1-x, between upper WSS 147-1 and upper WSS 147-2, and between WSS 142-x and upper WSS 147-2-x, or in all of these.

[0088] The return transfer unit 14b may have the configuration shown in FIG. 12 or FIG. FIG. 12 is a block diagram showing a specific example of a functional configuration (part 2) of the return transfer unit 14b in the third embodiment. The return transfer unit 14b includes a plurality of WSSs 141-1 to 141-X, a transfer wavelength control unit 143b, a plurality of AWGs 144-1 to 144-X, a plurality of upper WSSs 147-1-1 to 147-1-X, and a plurality of upper WSSs 147-2-1 to 147-2-X.

[0089] In the example shown in Fig. 12, WSS 141-x is connected to upper WSS 147-1-x, and AWG 144-x is connected to upper WSS 147-2-x. The configuration shown in Fig. 12 differs from the configuration shown in Fig. 11 in that the control targets of the forwarding wavelength control unit 143b are WSS 141 and upper WSS 147, and in that multiple AWGs 144-1 to 144-X are newly provided instead of multiple WSSs 142-1 to 142-X. The WSS 141, upper WSS 147, and upper WSS 147 perform the same processes as the functional units with the same names shown in Fig. 11, and therefore their explanations will be omitted.

[0090] The AWG 144-x is connected to nP / X different optical transmission lines among the n optical transmission lines (a total of nP optical transmission lines) connected to the second port of each optical SW 11, and outputs the optical signal of the set wavelength output from the upper WSS 147-2-x through a route according to the wavelength. The number of ports required for the AWG 144-x is n × P / X.

[0091] Amplifiers may be provided between the WSS 141-x and the upper WSS 147-1-x, between the upper WSS 147-1 and the upper WSS 147-2, and between the AWG 144-x and the upper WSS 147-2-x, or in all of these.

[0092] In the configuration shown in FIG. 11, AWGs 144-1 to 144-X may be newly provided in place of the WSSs 141-1 to 141-X.

[0093] Next, another example will be described with reference to Fig. 13. Fig. 13 is a block diagram showing a specific example of a functional configuration (part 3) of the return transfer unit 14b in the third embodiment. The return transfer unit 14b includes a plurality of AWGs 144-1 to 144-X, a plurality of couplers 145-1 to 145-X, a plurality of amplifiers 146-1-1 to 146-XX, a plurality of amplifiers 148-1 to 148-X, a plurality of upper couplers 149-1-1 to 149-1-X, a plurality of upper couplers 149-2-1 to 149-2-X, and a plurality of amplifiers 150-1 to 150-X.

[0094] In the example shown in FIG. 13, coupler 145-x is connected to upstream coupler 149-1-x via amplifier 148-x, AWG 144-x is connected to upstream coupler 149-2-x via amplifier 150-x, and upstream couplers 149-1 and 149-2 are connected via amplifier 146.

[0095] The coupler 145-x is connected to different nP / X optical transmission lines among the n optical transmission lines (a total of nP optical transmission lines) connected to the second port of each optical SW10, and receives an optical signal transmitted through any of the nP / X optical transmission lines as input. The coupler 145-x multiplexes the input optical signals and outputs the combined signal.

[0096] The amplifier 148-x amplifies the optical signal output from the coupler 145-x.

[0097] The upstream coupler 149-1-x branches and outputs the optical signal amplified by the amplifier 148-x.

[0098] The upstream coupler 149-2-x multiplexes the optical signals output from the upstream couplers 149-1 and amplified by the amplifiers 146 connected thereto.

[0099] The amplifier 150-x amplifies the optical signal output from the upstream coupler 149-2-x.

[0100] The AWG 144-x is connected to different nP / X optical transmission lines among the n optical transmission lines (a total of nP optical transmission lines) connected to the second port of each optical SW 11, and outputs the optical signal amplified by the amplifier 146-x from a path according to the wavelength. The number of ports required for the AWG 144-x is n×P / X.

[0101] (Fourth embodiment) In the first to third embodiments described above, a configuration using optical SWs has been described as an upstream light distribution unit and a downstream light distribution unit connected to a return transfer unit. In the fourth embodiment, an upstream light distribution unit and a downstream light distribution unit different from those in the first to third embodiments will be described. In the fourth embodiment, the system configuration of the optical communication system 1 is the same as in the first embodiment, but the configuration of the light distribution unit is different. Therefore, the differences from the first embodiment will be described below.

[0102] 14 is a configuration diagram of an optical communication system 1 in the fourth embodiment. The optical communication system 1 in the fourth embodiment includes P optical distribution units 30-1 to 30-P, P optical distribution units 40-1 to 40-P, a control unit 12 (not shown), and a return transfer unit 14. In the following description, it is assumed that the optical distribution units 30-1 to 30-P are used for transmitting optical signals in the upstream direction, and the optical distribution units 40-1 to 40-P are used for transmitting optical signals in the downstream direction.

[0103] 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, when the optical distribution units 30-1 to 30-P do not need to be distinguished from one another, they will simply be referred to as the optical distribution unit 30, and when the optical distribution units 40-1 to 40-P do not need to be distinguished from one another, they will simply be referred to as the optical distribution unit 40. The optical distribution units 30, 40, control unit 12, and return transfer unit 14 are functional units that constitute one optical communication device. The optical distribution units 30 and 40 are multicast switches (MCS).

[0104] The optical distribution unit 30 includes a plurality of 1×M optical switches 31 and a plurality of signal multiplexing units 32. The number of 1×M 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 a first optical distribution unit. Each 1×M optical switch 31 is connected to a plurality of optical transmission paths and outputs an optical signal input from one of the optical transmission paths to another optical transmission path. Each 1×M optical switch 31 has one first port and M second ports (M is an integer equal to or greater than 2). The one first port of each 1×M optical switch 31 is connected to an edge node 15 or a subscriber device 16 via an optical transmission path.

[0105] One second port out of the M second ports that each 1×M optical switch 31 has is connected to the turn-back transfer unit 14 via an optical transmission line. The remaining second ports (for example, (M−1) second ports) of the M second ports that each 1×M optical switch 31 has are connected to different signal multiplexing units 32 via optical transmission lines. Note that some of the remaining second ports out of the M second ports that each 1×M optical switch 31 has may not be connected to the signal multiplexing unit 32.

[0106] The signal multiplexing unit 32 is either an optical coupler, a wavelength selective switch, or an AWG. The signal multiplexing unit 32 multiplexes the optical signals output from each 1×M optical switch 31, and outputs the multiplexed signals to another device via an optical transmission line.

[0107] The optical distribution unit 40 includes a plurality of signal separation units 41 and a plurality of 1×M optical switches 42. The number of signal separation units 41 and the number of 1×M optical switches 42 may be the same or different. The optical distribution unit 40 is one aspect of a second optical distribution unit. The signal separation unit 41 is either an optical coupler, a wavelength selective switch, or an AWG. The signal separation unit 41 receives an optical signal transmitted from another device connected via an optical transmission line. The signal separation unit 41 branches or demultiplexes the input optical signal and outputs it to each 1×M optical switch 42. For example, if the optical distribution unit 40 is an optical coupler, the optical coupler branches the input optical signal and outputs it to each connected 1×M optical switch 42. For example, if the optical distribution unit 40 is a wavelength selective switch or an AWG, the wavelength selective switch or AWG demultiplexes the input optical signal and outputs it to the 1×M optical switch 42 connected to the port of the corresponding wavelength.

[0108] Each 1×M optical switch 42 is connected to multiple optical transmission lines and outputs an optical signal input from one of the optical transmission lines to another optical transmission line. Each 1×M optical switch 42 has one first port and M second ports. The one first port of each 1×M optical switch 42 is connected to a subscriber device 16 via an optical transmission line.

[0109] One second port out of the M second ports that each 1×M optical switch 42 has is connected to the turn-back transfer unit 14 via an optical transmission line. The remaining second ports (for example, (M−1) second ports) of the M second ports that each 1×M optical switch 42 has are connected to different signal separation units 41 via optical transmission lines. Note that some of the remaining second ports out of the M second ports that each 1×M optical switch 42 has may not be connected to the signal separation unit 41.

[0110] An amplifier may be installed to compensate for signal loss. The amplifier may be installed in any or all of the following locations: on the optical transmission line connected to the first port of each of the 1×M optical switches 31 and 42; on the optical transmission line between each of the 1×M optical switches 31 and each of the signal multiplexing units 32; on the optical transmission line between each of the signal demultiplexing units 41 and each of the 1×M optical switches 42; on the optical transmission line on the output side of each of the signal multiplexing units 32 (the side opposite to the side connected to the 1×M optical switch 31); and on the optical transmission line on the input side of each of the signal demultiplexing units 41 (the side opposite to the side connected to the 1×M optical switch 42).

[0111] The turn-back transfer unit 14 receives an optical signal output from the 1×M optical switch 31 as input and forwards the input optical signal to at least the 1×M optical switch 42 to which the destination subscriber device 16 is connected. One optical transmission path is connected from one 1×M optical switch 31 to the turn-back transfer unit 14. Therefore, if one optical distribution unit 30 is provided with n 1×M optical switches 31, n optical transmission paths are connected from one optical distribution unit 30 to the turn-back transfer unit 14, and since there are P optical distribution units 30, nP upstream optical transmission paths are connected to the turn-back transfer unit 14. Furthermore, if one optical distribution unit 40 is provided with n 1×M optical switches 42, n optical transmission paths are connected from one optical distribution unit 40 to the turn-back transfer unit 14, and since there are P optical distribution units 40, nP downstream optical transmission paths are connected to the turn-back transfer unit 14.

[0112] When performing return communication across the optical distribution unit 30, the optical SW control unit 122 switches the path between the ports of the 1×M optical switch 31 so that the output destination of the optical signal from the 1×M optical switch 31 is connected to the return transfer unit 14. The return transfer unit 14 controls so that the input optical signal is output to the desired 1×M optical switch 42. With this configuration, return communication between any 1×M optical switches is realized while limiting the number of wirings required for return at each 1×M optical switch to nP.

[0113] The configuration of the return transfer unit 14 may be any of the configurations shown in the first to third embodiments. That is, the configuration of the return transfer unit 14 may be any of the configurations shown in FIG. 2 and FIG. 4 to FIG. 13.

[0114] In the fourth embodiment, the optical SW control unit 122 switches the connection between ports of the 1×M optical switch 31 and the connection between ports of the 1×M optical switch 42. Specifically, in the fourth embodiment, the optical SW control unit 122 switches the connection between ports for each 1×M optical switch 31 included in each light distribution unit 30, and switches the connection between ports for each 1×M optical switch 42 included in each light distribution unit 40.

[0115] For example, the optical SW control unit 122 switches the connection between ports so as to connect the first port of the 1×M optical switch 31, to which the edge node 15 or the subscriber device 16 is connected, with the second port, to which the turn-back forwarding unit 14 is connected. The 1×M optical switch 31 outputs an optical signal transmitted from the edge node 15 or the subscriber device 16 connected to the first port, from the second port, to which the turn-back forwarding unit 14 is connected. As a result, the optical signal input to the first port of the 1×M optical switch 31 is directly input to the turn-back forwarding unit 14.

[0116] Similarly, the optical SW control unit 122 switches the connection between the ports so as to connect the first port of the 1×M optical switch 42 to which the 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 1×M optical switch 42. The 1×M optical switch 42 receives 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. As a result, the optical signal output from the return transfer unit 14 is transferred to the desired subscriber device 16.

[0117] Fig. 15 is a sequence diagram for explaining the processing flow of the optical communication system 1 in the fourth embodiment. Fig. 15 explains a case where a subscriber device 16-1 connected to the optical distribution unit 30-1 communicates with a subscriber device 16-2 connected to the optical distribution unit 40-1. Here, it is assumed that a wavelength λ1 is assigned to the subscriber devices 16-1 and 16-2. Furthermore, the configuration of the return forwarding unit 14 will be explained using the configuration shown in Fig. 2 as an example.

[0118] The forwarding wavelength control unit 143 of the return forwarding unit 14 sets the port used between the WSS 141 and the optical SW10-1 and the port used between the WSS 142 and the optical SW11-1 to forward the wavelength λ1 (step S201). The subscriber device 16-1 transmits an optical signal with wavelength λ1 (step S102). The optical signal with wavelength λ1 transmitted from the subscriber device 16-1 is input to one 1×M optical switch 31 provided in the optical distribution unit 30-1 via an optical transmission path.

[0119] The 1×M optical switch 31 is controlled by the optical SW control unit 122 so as to connect a path between the first port of the 1×M optical switch 31 to which the subscriber device 16-1 is connected and the second port of the 1×M optical switch 31 to which the turn-back transfer unit 14 is connected. As a result, the optical signal of wavelength λ1 input to the first port of the 1×M optical switch 31 is output to the turn-back transfer unit 14 from the second port to which the turn-back transfer unit 14 is connected (step S203).

[0120] The optical signal with wavelength λ1 output from the 1×M optical switch 31 is input to the WSS 141 included in the return transfer unit 14 (step S204). The WSS 141 outputs an optical signal with the set wavelength set by the transfer wavelength control unit 143 to the WSS 142 (step S205). Here, since the wavelength λ1 is set as the set wavelength, the optical signal with wavelength λ1 is output from the WSS 141. The optical signal with wavelength λ1 output from the WSS 141 is input to the WSS 142 (step S206).

[0121] The WSS 142 outputs an optical signal of the set wavelength set by the forwarding wavelength control unit 143 to the optical transmission path to which the optical SW11-1 is connected (step S207). Here, since the wavelength λ1 is set as the set wavelength, an optical signal of wavelength λ1 is output from the WSS 142. The optical signal of wavelength λ1 output from the WSS 142 is input to second ports of the multiple 1×M optical switches 42 included in the optical distribution unit 40-1 via the optical transmission path.

[0122] Of the multiple 1×M optical switches 42 included in the optical distribution unit 40-1, the optical SW control unit 122 controls so that a path between the first port of the 1×M optical switch 42 to which the subscriber device 16-2 is connected and the second port of the 1×M optical switch 42 to which the return forwarding unit 14 is connected is connected. As a result, the optical signal of wavelength λ1 input to the second port of the 1×M optical switch 42 is output from the first port to the subscriber device 16-2 via the optical transmission line (step S208). The subscriber device 16-2 receives the optical signal of wavelength λ1 output from the 1×M optical switch 42 (step S209).

[0123] According to the optical communication system 1 of the fourth embodiment configured as described above, even in a configuration in which a multicast switch is used instead of an optical SW as an optical distribution unit, it is possible to reduce the number of wirings required for return in each of the optical distribution units 30 and 40. Therefore, it becomes possible to connect each subscriber device to any other subscriber device at any timing using a smaller number of return transmission paths than conventionally.

[0124] (Modification 1 of the fourth embodiment) The light distribution unit 30 and the light distribution unit 40 may have the configuration shown in Fig. 16. Fig. 16 is a configuration diagram of an optical communication system 1 in a modified example of the fourth embodiment. The system configuration of the optical communication system 1 in the modified example of the fourth embodiment is the same as that of the fourth embodiment. In Fig. 16, what differs from Fig. 14 is the connection between the light distribution unit 30 and the turn-back transfer unit 14, and the connection between the light distribution unit 40 and the turn-back transfer unit 14.

[0125] In the configuration shown in FIG. 14 , one of the second ports of each 1×M optical switch 31 is connected to the turn-back transfer unit 14, and one of the second ports of each 1×M optical switch 42 is connected to the turn-back transfer unit 14. In contrast, in the configuration shown in FIG. 16 , one signal multiplexing unit 32 out of the multiple signal multiplexing units 32 is connected to the turn-back transfer unit 14, and one signal demultiplexing unit 41 out of the multiple signal demultiplexing units 41 is connected to the turn-back transfer unit 14. With this configuration, it is sufficient to connect one optical distribution unit 30, 40 to the turn-back transfer unit 14 via one optical transmission line. Therefore, unlike the fourth embodiment, it is not necessary to connect one optical distribution unit 30, 40 to the turn-back transfer unit 14 via optical transmission lines equal to the number of 1×M optical switches 31. This allows the number of optical transmission lines connected to the turn-back transfer unit 14 to be reduced.

[0126] 16 , when loopback communication across the optical distribution unit 30 is performed, the optical SW control unit 122 switches the paths between the ports of each 1×M optical switch 31 so that the optical signal input to each 1×M optical switch 31 is input to the loopback forwarding unit 14. Specifically, the optical SW control unit 122 switches the paths between the ports of the 1×M optical switch 31 so that the second port of the 1×M optical switch 31 connected to the signal multiplexing unit 32 connected to the loopback forwarding unit 14 is connected to the first port of the 1×M optical switch 31. The 1×M optical switch 31 outputs the optical signal transmitted from the edge node 15 or the subscriber device 16 connected to the first port from the second port connected to the signal multiplexing unit 32 connected to the loopback forwarding unit 14. The signal multiplexing unit 32 multiplexes the optical signals output from each 1×M optical switch 31 and outputs the multiplexed signals to the loopback forwarding unit 14. As a result, the optical signal input to the first port of the 1×M optical switch 31 is input to the return transfer unit 14 via the signal multiplexing unit 32 .

[0127] Similarly, the optical SW control unit 122 switches the path between the ports of the 1×M optical switch 42 so as to connect the second port of the 1×M optical switch 42 connected to the signal separation unit 41 connected to the return transfer unit 14 with the first port of the 1×M optical switch 42. The signal separation unit 41 branches or demultiplexes the optical signal transferred from the return transfer unit 14 and outputs it to each 1×M optical switch 42. The 1×M optical switch 42 receives the optical signal output from the signal separation unit 41 connected to its second port and outputs the input optical signal from its first port. As a result, the optical signal transferred from the return transfer unit 14 is input to the second port of the 1×M optical switch 42 via the signal separation unit 41. The optical signal input to the second port of the 1×M optical switch 42 is output from the first port and input to the desired subscriber device 16.

[0128] (Modification 2 of the fourth embodiment) In the above embodiment, the optical distribution unit 30, the optical distribution unit 40, and the turn-back forwarding unit 14 are provided in one optical communication device. However, any one of the optical distribution unit 30, the optical distribution unit 40, and the turn-back forwarding unit 14 may be implemented in another device. The same applies when the turn-back forwarding unit 14 is the turn-back forwarding unit 14a or 14b.

[0129] (Fifth embodiment) In the fifth embodiment, an upstream light distribution unit and a downstream light distribution unit that are different from the first to fourth embodiments will be described. In the fifth embodiment, the system configuration of the optical communication system 1 is the same as in the first embodiment, but the configuration of the light distribution unit is different. Therefore, the differences from the first embodiment will be described below.

[0130] 17 is a configuration diagram of an 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, a control unit 12 (not shown), and a return transfer unit 14. In the following description, it is assumed that the optical distribution units 30a-1 to 30a-P are used for transmitting optical signals in the upstream direction, and the optical distribution units 40a-1 to 40a-P are used for transmitting optical signals in the downstream direction.

[0131] The light distribution units 30a-1 to 30a-P have the same configuration. The light distribution units 40a-1 to 40a-P have the same configuration. In the following description, when there is no need to distinguish between the light distribution units 30a-1 to 30a-P, they will simply be referred to as light distribution unit 30a, and when there is no need to distinguish between the light distribution units 40a-1 to 40a-P, they will simply be referred to as light distribution unit 40a. The light distribution unit 30a, the light distribution unit 40a, the control unit 12, and the return transfer unit 14 are functional units that make up one optical communication device.

[0132] The optical distribution unit 30a is configured to include one or more N×M wavelength selective switches 33. The optical distribution unit 30a is one aspect of a first optical distribution unit. The N×M wavelength selective switch 33 is connected to a plurality of optical transmission paths, and outputs an optical signal input from one of the optical transmission paths to another optical transmission path. The N×M wavelength selective switch 33 has N (N is an integer equal to or greater than 1) first ports and M second ports. The N first ports of the N×M wavelength selective switch 33 are connected to the edge node 15 or the subscriber device 16 via the optical transmission paths. The N×M wavelength selective switch 33 is a WSS.

[0133] One second port out of the M second ports of the N×M wavelength selective switch 33 is connected to the return transfer unit 14 via an optical transmission line. The remaining second ports (for example, (M−1) second ports) of the M second ports of the N×M wavelength selective switch 33 are connected to other devices via optical transmission lines, respectively.

[0134] The optical distribution unit 40a includes one or more N×M wavelength selective switches 43. The optical distribution unit 40a is one aspect of a second optical distribution unit. The N×M wavelength selective switch 43 is connected to a plurality of optical transmission paths and outputs an optical signal input from one of the optical transmission paths to another optical transmission path. The N×M wavelength selective switch 43 has N first ports and M second ports. The N first ports of the N×M wavelength selective switch 43 are connected to the subscriber device 16 via the optical transmission paths.

[0135] One second port of the M second ports of the N×M wavelength selective switch 43 is connected to the return transfer unit 14 via an optical transmission line. The remaining second ports of the M second ports of the N×M wavelength selective switch 43 (for example, (M−1) second ports) are each connected to another device via an optical transmission line. The N×M wavelength selective switch 43 is a WSS.

[0136] To compensate for signal loss, an amplifier may be installed on either or all of the optical transmission lines connected to the first ports of the N×M wavelength selective switches 33 and 43 or the optical transmission lines connected to the second ports of the N×M wavelength selective switches 33 and 43.

[0137] The turn-back transfer unit 14 receives as input the optical signals output from each N×M wavelength selective switch 33 and forwards the input optical signals to at least the N×M wavelength selective switch 43 connected to the destination subscriber device 16. One optical transmission path is connected from one N×M wavelength selective switch 33 to the turn-back transfer unit 14. Therefore, one optical transmission path is connected from one optical distribution unit 30a to the turn-back transfer unit 14, and since there are P optical distribution units 30a, P upstream optical transmission paths are connected to the turn-back transfer unit 14. Furthermore, one optical transmission path is connected from one optical distribution unit 40a to the turn-back transfer unit 14, and since there are P optical distribution units 40a, P downstream optical transmission paths are connected to the turn-back transfer unit 14.

[0138] When performing return communication across the optical distribution unit 30a, the optical SW control unit 122 switches the paths between the ports of each N×M wavelength selective switch 33 so that the output destination of the optical signal from each N×M wavelength selective switch 33 is connected to the return transfer unit 14. The return transfer unit 14 controls so that the input optical signal is output to the desired N×M wavelength selective switch 43. This configuration realizes return communication between any N×M wavelength selective switches while limiting the number of wirings required for return at each N×M wavelength selective switch to P.

[0139] The configuration of the return transfer unit 14 may be any of the configurations shown in the first to third embodiments. That is, the configuration of the return transfer unit 14 may be any of the configurations shown in FIG. 2 and FIG. 4 to FIG. 13.

[0140] In the fifth embodiment, the optical SW control unit 122 switches the connection between ports of the N×M wavelength selective switches 33 and the connection between ports of the N×M wavelength selective switches 43. Specifically, in the fourth embodiment, the optical SW control unit 122 switches the connection between ports for each N×M wavelength selective switch 33 included in each light distribution unit 30a, and the connection between ports for each N×M wavelength selective switch 43 included in each light distribution unit 40a.

[0141] For example, the optical SW control unit 122 switches the connection between ports so as to connect a first port of the N×M wavelength selective switch 33 to which the edge node 15 or subscriber device 16 to be transmitted is connected and a second port to which the turn-back forwarding unit 14 is connected. The N×M 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 turn-back forwarding unit 14 is connected. As a result, the optical signal input to the first port of the N×M wavelength selective switch 33 is directly input to the turn-back forwarding unit 14.

[0142] Similarly, the connection between ports is switched so that the first port of the N×M wavelength selective switch 43, to which the destination subscriber device 16 is connected, is connected to the second port to which the return forwarding unit 14 is connected. The optical signal forwarded from the return forwarding unit 14 is input to the second port of the N×M wavelength selective switch 43. The N×M wavelength selective switch 43 outputs the optical signal forwarded from the return forwarding unit 14 and input to the second port from the first port to which the destination subscriber device 16 is connected. In this way, the optical signal output from the return forwarding unit 14 is forwarded to the desired subscriber device 16.

[0143] According to the optical communication system 1 of the fifth embodiment configured as described above, even in a configuration in which the N×M wavelength selective switches 33, 43 are used as the optical distribution units instead of the optical SW, the number of wirings required for return in each of the optical distribution units 30 a, 40 a can be reduced. Therefore, it becomes possible to connect each subscriber device to any subscriber device at any timing using a smaller number of return transmission lines than conventionally.

[0144] (Modification 1 of the fifth embodiment) As shown in the fifth embodiment, when the light distribution unit 30a is configured with an N×M wavelength selective switch 33 and the light distribution unit 40a is configured with an N×M wavelength selective switch 43, the turn-back transfer unit 14 may have the configuration shown in any one of Figures 18 to 20. The configuration of the turn-back transfer unit 14 shown in Figures 18 to 20 is configured with components that are not wavelength-dependent for the ports.

[0145] When the light distribution unit 30a is configured with an N×M wavelength selective switch 33, a plurality of optical signals can be multiplexed in the light distribution unit 30a and then input to the turn-back transfer unit 14. Therefore, it is sufficient that each N×M wavelength selective switch 33 is connected to the turn-back transfer unit 14 by one optical transmission line, and when there are P N×M wavelength selective switches 33, P optical transmission lines are connected to the turn-back transfer unit 14.

[0146] 18 is a block diagram showing a specific example of a functional configuration (part 1) of the turn-back transfer unit 14c in a modified example of the fifth embodiment. The turn-back transfer unit 14c includes a coupler 151, an amplifier 152, and a coupler 153. The coupler 151 is connected to P optical transmission lines connected to each optical distribution unit 30a, and receives an optical signal transmitted through any of the P optical transmission lines. The coupler 151 multiplexes the input optical signals and outputs the multiplexed signals. The number of ports required for the coupler 151 is P.

[0147] The amplifier 152 amplifies the optical signal output from the coupler 151 .

[0148] The coupler 153 branches and outputs the optical signal amplified by the amplifier 152. The number of ports required for the coupler 153 is P. The optical signals branched and output by the coupler 153 are input to the N×M wavelength selective switches 43 of each optical distribution unit 40a via P optical transmission paths. Even if the optical signal input from the return transfer unit 14 to each N×M wavelength selective switch 43 is a wavelength multiplexed signal, it can be separated by each N×M wavelength selective switch 43.

[0149] With this configuration, even if the return transfer unit 14 is not provided with a component having wavelength selectivity such as a WSS or AWG, return communication between any users is possible.

[0150] 19 is a block diagram showing a specific example of a functional configuration (part 2) of the loopback transfer unit 14c in a modification of the fifth embodiment. The loopback transfer unit 14c includes a plurality of couplers 151-1 to 151-X, an amplifier 152, a plurality of couplers 153-1 to 153-X, a plurality of upper-level couplers 156-1 to 156-2, a plurality of amplifiers 157-1 to 157-X, and a plurality of amplifiers 158-1 to 158-X.

[0151] In the example shown in FIG. 19, coupler 151-x (1≦x≦X) is connected to upstream coupler 156-1 via amplifier 157-x, coupler 153-x is connected to upstream coupler 156-2 via amplifier 158-x, and upstream couplers 156-1 and 156-2 are connected via amplifier 152.

[0152] The coupler 151-x is connected to different P / X optical transmission paths out of the P optical transmission paths connected to each optical distribution unit 30a, and receives as input an optical signal transmitted through any of the P / X optical transmission paths. The coupler 151-x multiplexes the input optical signals and outputs the multiplexed optical signals. In this way, on average, approximately the same number of optical transmission paths are connected to each coupler 151. For example, if there are two couplers 151 (X=2) and four optical distribution units 30a (P=4), two different optical transmission paths are connected to each coupler 151.

[0153] The amplifier 157-x amplifies the optical signal output from the coupler 151-x. The upstream coupler 156-1 multiplexes and outputs the optical signals amplified by the amplifiers 157. The upstream coupler 156-2 branches the optical signal output from the upstream coupler 156-1 and amplified by the amplifier 152.

[0154] The amplifier 158-x amplifies the optical signal output from the upstream coupler 156-2. The coupler 153-x branches and outputs the optical signal amplified by the amplifier 158-x. The number of ports required for the coupler 153-x is P / X. The optical signals branched and output by the coupler 153-x are input to the N×M wavelength selective switches 43 of each optical distribution unit 40a via P / X optical transmission paths. Even if the optical signals input from the return transfer unit 14 to each N×M wavelength selective switch 43 are wavelength multiplexed signals, they can be separated by each N×M wavelength selective switch 43.

[0155] With this configuration, even if the return transfer unit 14 is not provided with a component having wavelength selectivity such as a WSS or AWG, return communication between any users is possible.

[0156] 20 is a block diagram showing a specific example of a functional configuration (part 3) of the loopback transfer unit 14c in a modification of the fifth embodiment. The loopback transfer unit 14c includes a plurality of couplers 151-1 to 151-X, a plurality of amplifiers 152-1-1 to 152-XX, a plurality of couplers 153-1 to 153-X, a plurality of upper level couplers 156-1-1 to 156-1-X, a plurality of upper level couplers 156-2-1 to 156-2-X, a plurality of amplifiers 157-1 to 157-X, and a plurality of amplifiers 158-1 to 158-X.

[0157] In the example shown in Figure 20, coupler 151-x is connected to upstream coupler 156-1-x via amplifier 157-x, coupler 153-x is connected to upstream coupler 156-2-x via amplifier 158-x, and upstream couplers 156-1 and 156-2 are connected via amplifier 152.

[0158] 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 through any of the P / X optical transmission lines as input. The coupler 151-x multiplexes the input optical signals and outputs the multiplexed signal.

[0159] The amplifier 157-x amplifies the optical signal output from the coupler 151-x. The upstream coupler 156-1-x branches and outputs the optical signal amplified by the amplifier 157-x. The upstream coupler 156-2-x multiplexes the optical signals output from the upstream couplers 156-1 and amplified by the amplifiers 152 connected thereto.

[0160] The amplifier 158-x amplifies the optical signal output from the upstream coupler 156-2-x. The coupler 153-x branches and outputs the optical signal amplified by the amplifier 158-x. The number of ports required for the coupler 153-x is P / X. The optical signals branched and output by the coupler 153-x are input to the N×M wavelength selective switches 43 of each optical distribution unit 40a via P / X optical transmission paths. Even if the optical signals input from the return transfer unit 14 to each N×M wavelength selective switch 43 are wavelength multiplexed signals, they can be separated by each N×M wavelength selective switch 43.

[0161] With this configuration, even if the return transfer unit 14 is not provided with a component having wavelength selectivity such as a WSS or AWG, return communication between any users is possible.

[0162] (Modification 2 of the fifth embodiment) In the above embodiment, the optical distribution unit 30a, the optical distribution unit 40a, and the turn-back forwarding unit 14 are provided in one optical communication device. However, any one of the optical distribution unit 30a, the optical distribution unit 40a, and the turn-back forwarding unit 14 may be implemented in another device. The same applies when the turn-back forwarding unit 14 is the turn-back forwarding unit 14a or 14b.

[0163] (Sixth embodiment) In the sixth embodiment, an upstream light distribution unit and a downstream light distribution unit that are different from the first to fifth embodiments will be described. In the sixth embodiment, the system configuration of the optical communication system 1 is the same as in the first embodiment, but the configuration of the light distribution unit is different. Therefore, the differences from the first embodiment will be described below.

[0164] 21 is a configuration diagram of an 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, a control unit 12 (not shown), and a return transfer unit 14. In the following description, it is assumed that the optical distribution units 30b-1 to 30b-P are used for transmitting optical signals in the upstream direction, and the optical distribution units 40b-1 to 40b-P are used for transmitting optical signals in the downstream direction.

[0165] The light distribution units 30b-1 to 30b-P have the same configuration. The light distribution units 40b-1 to 40b-P have the same configuration. In the following description, when there is no need to distinguish between the light distribution units 30b-1 to 30b-P, they will simply be referred to as light distribution unit 30b, and when there is no need to distinguish between the light distribution units 40b-1 to 40b-P, they will simply be referred to as light distribution unit 40b. The light distribution units 30b, 40b, control unit 12, and return transfer unit 14 are functional units that constitute a single optical communication device.

[0166] The optical distribution unit 30b includes one or more 1×N wavelength selective switches 34 and one or more 1×M wavelength selective switches 35. The optical distribution unit 30b is one aspect of a first optical distribution unit. The 1×N wavelength selective switches 34 and the 1×M wavelength selective switches 35 are connected to multiple optical transmission paths and output an optical signal input from one of the optical transmission paths to another optical transmission path. The 1×N wavelength selective switch 34 has N first ports and one second port. The N first ports of the 1×N wavelength selective switch 34 are connected to the edge node 15 or the subscriber device 16 via the optical transmission paths. The one second port of the 1×N wavelength selective switch 34 is connected to the 1×M wavelength selective switch 35 via the optical transmission path. The 1×N wavelength selective switch 34 is a WSS.

[0167] The 1×M wavelength selective switch 35 has one first port and M second ports. The one first port of the 1×M wavelength selective switch 35 is connected to the 1×N wavelength selective switch 34 via an optical transmission line. One second port of the M second ports of the 1×M wavelength selective switch 35 is connected to the turn-back forwarding unit 14 via an optical transmission line. The remaining second ports of the M second ports of the 1×M wavelength selective switch 35 (for example, (M−1) second ports) are each connected to other devices via optical transmission lines. The 1×M wavelength selective switch 35 is a WSS.

[0168] The optical distribution unit 40b is configured to include one or more 1×M wavelength selective switches 44 and one or more 1×N wavelength selective switches 45. The optical distribution unit 40b is one aspect of a second optical distribution unit. The 1×M wavelength selective switches 44 and the 1×N wavelength selective switches 45 are connected to multiple optical transmission paths and output an optical signal input from one of the optical transmission paths to another optical transmission path. The 1×M wavelength selective switch 44 has one first port and M second ports. The one first port of the 1×M wavelength selective switch 44 is connected to the 1×N wavelength selective switch 45 via an optical transmission path.

[0169] One of the M second ports of the 1×M wavelength selective switch 44 is connected to the return forwarding unit 14 via an optical transmission line. The remaining M second ports of the 1×M wavelength selective switch 44 (for example, (M−1) second ports) are connected to other devices via optical transmission lines. The 1×M wavelength selective switch 44 is a WSS.

[0170] The 1×N wavelength selective switch 45 has N first ports and one second port. The N first ports of the 1×N wavelength selective switch 45 are connected to the subscriber device 16 via optical transmission lines. The one second port of the 1×N wavelength selective switch 45 is connected to the 1×M wavelength selective switch 44 via an optical transmission line. The 1×N wavelength selective switch 45 is a WSS.

[0171] Amplifiers may be installed to compensate for signal loss, and may be installed in any or all of the following locations: on the transmission line of the first port of each of the 1×N wavelength selective switches 34 and 45; on the transmission line between the 1×N wavelength selective switch 34 and the 1×M wavelength selective switch 35; on the transmission line between the 1×M wavelength selective switch 44 and the 1×N wavelength selective switch 45; and on the transmission line of the second port of each of the 1×M wavelength selective switches 35 and 44.

[0172] The turn-back transfer unit 14 receives as input the optical signals output from each 1×M wavelength selective switch 35 and forwards the input optical signals to at least the 1×M wavelength selective switch 44 connected to the destination subscriber device 16. One optical transmission path is connected from one 1×M wavelength selective switch 35 to the turn-back transfer unit 14. Therefore, one optical transmission path is connected from one optical distribution unit 30b to the turn-back transfer unit 14, and since there are P optical distribution units 30b, P upstream optical transmission paths are connected to the turn-back transfer unit 14. Furthermore, one optical transmission path is connected from one optical distribution unit 40b to the turn-back transfer unit 14, and since there are P optical distribution units 40b, P downstream optical transmission paths are connected to the turn-back transfer unit 14.

[0173] When performing return communication across the optical distribution unit 30b, the optical SW control unit 122 switches the paths between the ports of the 1×N wavelength selective switch 34 and the 1×M wavelength selective switch 35 provided in the optical distribution unit 30b so that the output destination of the optical signal from the optical distribution unit 30b is connected to the return transfer unit 14. The return transfer unit 14 controls so that the input optical signal is output to the desired optical distribution unit 40b. With this configuration, return communication between any optical distribution units is realized while limiting the number of wirings required for return at each optical distribution unit 40b to P.

[0174] The configuration of the return transfer unit 14 may be any of the configurations shown in the first to third embodiments. That is, the configuration of the return transfer unit 14 may be any of the configurations shown in FIG. 2 and FIG. 4 to FIG. 13.

[0175] In the sixth embodiment, the optical SW control unit 122 switches the connection between ports of the 1×N wavelength selective switches 34 and 45 and the connection between ports of the 1×M wavelength selective switches 35 and 44. Specifically, in the sixth embodiment, the optical SW control unit 122 switches the connection between ports for each of the 1×N wavelength selective switches 34 and 35 included in each light distribution unit 30b, and the connection between ports for each of the 1×M wavelength selective switches 44 and 45 included in each light distribution unit 40b.

[0176] For example, the optical SW control unit 122 switches the connections between the ports of the 1×N wavelength selective switch 34 and the 1×M wavelength selective switch 35 so as to connect the first port of the 1×N wavelength selective switch 34, to which the edge node 15 or subscriber device 16 to be transmitted is connected, to the second port, and to connect the first port of the 1×M wavelength selective switch 35 to the second port to which the turn-back forwarding unit 14 is connected. The 1×N wavelength selective switch 34 outputs the optical signal transmitted from the edge node 15 or subscriber device 16 connected to the first port from the second port. The optical signal output from the 1×N wavelength selective switch 34 is input to the first port of the 1×M wavelength selective switch 35. The 1×M wavelength selective switch 35 outputs the optical signal input to the first port from the second port connected to the turn-back forwarding unit 14. As a result, the optical signal input to the optical distribution unit 30b is forwarded to the turn-back forwarding unit 14.

[0177] Furthermore, the optical SW control unit 122 switches the connection between the ports of the 1×M wavelength selective switch 44 and the 1×N wavelength selective switch 45 so as to connect the first port of the 1×M wavelength selective switch 44 to the second port of the 1×M wavelength selective switch 44 to which the return forwarding unit 14 is connected, and to connect the second port of the 1×N wavelength selective switch 45 to the first port to which the destination subscriber device 16 is connected. The optical signal forwarded from the return forwarding unit 14 is input to the second port of the 1×M wavelength selective switch 44. The 1×M wavelength selective switch 44 outputs the optical signal forwarded from the return forwarding unit 14 and input to the second port from its first port. The optical signal output from the 1×M wavelength selective switch 44 is input to the second port of the 1×N wavelength selective switch 45. The 1×N 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. As a result, the optical signal output from the return forwarding unit 14 is forwarded to the destination subscriber device 16 .

[0178] According to the optical communication system 1 of the sixth embodiment configured as described above, even in a configuration in which a 1×N wavelength selective switch and a 1×M wavelength selective switch are combined as an optical distribution unit instead of an optical SW, the number of wirings required for return in each optical distribution unit 30 b, 40 b can be reduced. Therefore, it becomes possible to connect each subscriber device to any subscriber device at any timing using a smaller number of return transmission lines than conventionally.

[0179] (Modification 1 of the sixth embodiment) As shown in the sixth embodiment, when the optical distribution unit 30b is composed of a 1×N wavelength selective switch 34 and a 1×M wavelength selective switch 35, and the optical distribution unit 40b is composed of a 1×M wavelength selective switch 44 and a 1×N wavelength selective switch 45, the return transfer unit 14 may have the configuration shown in any of Figures 12 to 14.

[0180] (Modification 2 of the sixth embodiment) Either or both of the 1×N wavelength selective switches 34 and 45 and the 1×M wavelength selective switches 35 and 44 may be couplers.

[0181] (Modification 3 of the sixth embodiment) In the above embodiment, the optical distribution unit 30b, the optical distribution unit 40b, and the turn-back forwarding unit 14 are provided in one optical communication device. However, any one of the optical distribution unit 30b, the optical distribution unit 40b, and the turn-back forwarding unit 14 may be implemented in another device. The same applies when the turn-back forwarding unit 14 is the turn-back forwarding unit 14a or 14b.

[0182] (Modifications common to the first to sixth embodiments) In each of the above embodiments, the optical SW is divided into the upstream and downstream directions, but the same optical SW may be used for both the upstream and downstream directions.

[0183] In each of the above embodiments, the optical SW10, the optical SW11, or the turn-back forwarding units 14, 14a, and 14b are provided in one optical communication device. However, any of the optical SW10, the optical SW11, and the turn-back forwarding units 14, 14a, and 14b may be implemented in another device.

[0184] Some of the functional units (e.g., the control unit 12, the return transfer units 14, 14a, 14b, and 14c) of the optical communication device in the above-described embodiment may be realized by a computer. In this case, a program for realizing this function may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be read into a computer system and executed to realize the function. Note that the term "computer system" here includes hardware such as an OS and peripheral devices.

[0185] Furthermore, "computer-readable recording media" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into computer systems. Furthermore, "computer-readable recording media" may also include devices that dynamically store programs for a short period of time, such as communication lines used when transmitting programs over networks like the Internet or over communication lines like telephone lines, or devices that store programs for a fixed period of time, such as volatile memory within the computer systems that serve as servers or clients. Furthermore, the programs may be programs that implement some of the aforementioned functions, or may be programs that can realize the aforementioned functions in combination with programs already stored in the computer system, or may be programs that are implemented using programmable logic devices such as FPGAs.

[0186] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention. [Industrial Applicability]

[0187] The present invention can be applied to optical communication system technology that performs return communication via an optical distribution unit. [Explanation of symbols]

[0188] 10-1 to 10-P, 11-1 to 11-P...optical switches, 12...control unit, 121...wavelength management and control unit, 122...optical switch control unit, 14, 14a, 14b...loopback and forwarding unit, 16-1 to 16-3...substation equipment, 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, 31, 42...1×M optical switch, 32...signal multiplexing unit, 33, 43...N×M wavelength selective switch, 34, 45...1×N wavelength selective switch, 35, 44...1×M wavelength selective switch, 41...signal demultiplexing unit, 141, 141-1 to 141-X, 141-1 to 141-4, 142, 142-1 to 142-X...WSS, 143, 143a, 143b...Transfer wavelength control unit, 144, 144-1 to 144-X...AWG, 145, 145-1 to 145-X, 151, 151-1 to 151-X, 153, 153-1 to 153-X...Coupler, 146, 146-1-1 to 146-XX, 148-1 to 148-X, 150-1 to 150-X, 152, 152-1-1 to 152-XX, 157-1 to 157-X, 158-1 to 158-X...Amplifier, 147-1, 147-2, 147-1-1 to 147-1-X, 147-2-1 to 147-2-X...Upper WSS, 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...Upper coupler

Claims

1. a first optical distribution unit having a plurality of first ports and a plurality of second ports, and configured to output an optical signal input from any one of the plurality of first ports from any one of the plurality of second ports; a second optical distribution unit having a plurality of first ports and a plurality of second ports, and outputting an optical signal input from any one of the plurality of second ports from any one of the plurality of first ports; a transfer unit that returns and transfers an optical signal output from any one of the plurality of second ports of the first optical distribution unit to any one of the plurality of second ports of the second optical distribution unit; Equipped with some of the second ports of the first light distribution unit are connected to the transfer unit, and the remaining second ports of the first light distribution unit are connected to another device; An optical communication device, wherein some of the plurality of second ports of the second optical distribution unit are connected to the transfer unit, and the remaining second ports of the second optical distribution unit are connected to another device.

2. communication between subscriber devices connected under the own device is performed by return communication using a second port connected to the forwarding unit among the plurality of second ports of the first optical distribution unit and a second port connected to the forwarding unit among the plurality of second ports of the second optical distribution unit; 2. The optical communication device according to claim 1.

3. The transfer unit a first wavelength-selective optical switch that outputs an optical signal of a set wavelength from among optical signals output from any of the plurality of second ports of the first optical distribution unit; a second wavelength selective optical switch that outputs an optical signal having a set wavelength among the optical signals output from the first wavelength selective optical switch to any one of the plurality of second ports of the second optical distribution unit; Equipped with 3. The optical communication device according to claim 1 or 2.

4. The first light distribution unit and the second light distribution unit are different light distribution units or the same light distribution unit.

3. The optical communication device according to claim 1 or 2.

5. The first light distribution unit and the second light distribution unit are different light distribution units or the same light distribution unit.

4. The optical communication device according to claim 3.

6. the plurality of first ports of the first optical distribution unit and the plurality of first ports of the second optical distribution unit are connected to different subscriber devices via optical transmission paths; 3. The optical communication device according to claim 1 or 2.

7. the plurality of first ports of the first optical distribution unit and the plurality of first ports of the second optical distribution unit are connected to different subscriber devices via optical transmission paths; 4. The optical communication device according to claim 3.

8. the plurality of first ports of the first optical distribution unit and the plurality of first ports of the second optical distribution unit are connected to different subscriber devices via optical transmission paths; 5. The optical communication device according to claim 4.

9. the plurality of first ports of the first optical distribution unit and the plurality of first ports of the second optical distribution unit are connected to different subscriber devices via optical transmission paths; 6. The optical communication device according to claim 5.

10. a first optical distribution unit having a plurality of first ports and a plurality of second ports, and configured to output an optical signal input from any one of the plurality of first ports from any one of the plurality of second ports; a second optical distribution unit having a plurality of first ports and a plurality of second ports, and outputting an optical signal input from any one of the plurality of second ports from any one of the plurality of first ports; a transfer unit that returns and transfers an optical signal output from any one of the plurality of second ports of the first optical distribution unit to any one of the plurality of second ports of the second optical distribution unit; an optical communication device comprising: a control unit that, when performing the return transfer, controls to connect any one of the second ports of the first optical distribution unit to the transfer unit in order to transfer an optical signal transmitted from a source subscriber device, and to connect the transfer unit to any one of the second ports of the second optical distribution unit to which the optical signal is to be transferred; Equipped with some of the second ports of the first light distribution unit are connected to the transfer unit, and the remaining second ports of the first light distribution unit are connected to another device; An optical communication system, wherein some of the plurality of second ports of the second optical distribution unit are connected to the transfer unit, and the remaining second ports of the second optical distribution unit are connected to other devices.

11. The control unit switching connections between the plurality of first ports and the plurality of second ports of the first optical distribution unit and connections between the plurality of first ports and the plurality of second ports of the second optical distribution unit so as to enable communication between a subscriber device connected to the first optical distribution unit and a subscriber device connected to the second optical distribution unit; 11. The optical communication system according to claim 10.

12. a first optical distribution unit having a plurality of first ports and a plurality of second ports, and outputting an optical signal input from any one of the plurality of first ports from any one of the plurality of second ports; the second optical distribution unit has a plurality of first ports and a plurality of second ports, and outputs an optical signal input from any one of the plurality of second ports from any one of the plurality of first ports; a transfer unit that transfers the optical signal output from any one of the plurality of second ports of the first optical distribution unit back to any one of the plurality of second ports of the second optical distribution unit; some of the second ports of the first light distribution unit are connected to the transfer unit, and the remaining second ports of the first light distribution unit are connected to another device; A transfer method in which some of the multiple second ports of the second optical distribution unit are connected to the transfer unit, and the remaining second ports of the second optical distribution unit are connected to other devices.

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