Optical communication system and optical communication method

Abstract

This optical communication system comprises: K (where K is an integer greater than 1) optical switches having a plurality of first ports and a plurality of second ports; and a plurality of wavelength multiplexers / demultiplexers connected to the second ports of the optical switches. The wavelength multiplexers / demultiplexers each have one third port connected to an optical switch and K fourth ports supporting different wavelengths. The K fourth ports of the wavelength multiplexer / demultiplexer are connected to the fourth ports of K other wavelength multiplexers / demultiplexers connected to the K optical switches. The connected fourth ports support the same wavelength. The optical switches each output, from the second port, an optical signal input from the first port, and output, from the first port, an optical signal input from the second port. The wavelength multiplexers / demultiplexers each output an optical signal input from the third port to a fourth port according to the wavelength, and outputs, from the third port, an optical signal input from a fourth port.

Description

Optical communication system and optical communication method

[0001] The present invention relates to an optical communication system and an optical communication method.

[0002] An optical communication system has been proposed in which an optical transceiver is located on the subscriber side and an optical switch and a control unit are located on the node side (see, for example, Patent Document 1). Figure 11 is a diagram showing an example of the configuration of an optical communication system using this technology. Optical signals transmitted and received by an optical transceiver are transmitted to the opposing optical transceiver via an optical switch without being converted to electrical signals. Optical signals are usually converted to electrical signals at the input and output of a line concentrator switch or router located at the node. This electrical processing results in a significant delay. The optical communication system shown in Figure 11 connects subscribers end-to-end without relying on such electrical processing. This enables communication with lower latency than conventional optical communication systems.

[0003] In the optical communication system shown in Figure 11, a control unit controls the connection of an optical switch to a destination path so that an optical transceiver connected to the optical switch can communicate with the opposing optical transceiver. Here, the upper surface of the optical switch in the drawing is referred to as surface 1, and the lower surface in the drawing is referred to as surface 2. Patent Document 1 presupposes a matrix optical switch in which, when a signal is input, the optical signal "enters from surface 2 and exits from surface 1," or the optical signal "enters from surface 1 and exits from surface 2," and the number of ports (L) on the surface 1 side is equal to the number of ports (L) on the surface 2 side. Figure 11 shows a case in which upstream and downstream signals are accommodated by the same optical switch, but they may also be accommodated by different optical switches.

[0004] Furthermore, the control unit dynamically controls the upstream and downstream wavelengths used by the optical transceiver. For simplicity, FIG. 11 illustrates a case in which the control signal is transmitted to the optical transceiver using a different optical path from that of the main signal. However, the control signal may be transmitted using the same optical path as that of the main signal. For example, the control signal may be inserted from the face 2 side of the optical switch using a coupler or the like, or the control signal may be inserted from a port on the face 1 side of the optical switch. In this case, the wavelength of the control signal may be set to the same wavelength band as that of the main signal wavelength division multiplexing (WDM) transmission, or may be set to a wavelength band different from that of the main signal.

[0005] On the side 1 of the optical switch, upstream signal ports and downstream signal ports connected to other nodes and in the return direction are assigned. On the side 2, upstream signal ports and downstream signal ports connected to each optical transceiver are assigned. Figure 11 illustrates a case in which optical transceiver #1 simultaneously communicates with the opposing optical transceiver on the other node side using wavelength λ1, optical transceiver #3 simultaneously communicates with the opposing optical transceiver on the other node side using wavelength λ3, and optical transceiver #2 and optical transceiver #4 simultaneously perform return communication using wavelength λ2.

[0006] FIG. 12 is a diagram showing a loopback communication configuration using two optical switches according to conventional technology (see, for example, Non-Patent Document 1 and Patent Document 2). Patent Document 2 describes a configuration with four optical switches and two WSSs (Wavelength Selective Switches) because the optical switches are separated into upstream and downstream signals. However, the functionality is equivalent to the configurations in FIG. 12 and Non-Patent Document 1. For simplicity, FIG. 12 does not show communication with other nodes. In addition to optical switches #1 and #2 and a control unit, the node is equipped with four 1xM WSSs. Of the four WSSs, two WSSs are for upstream (Upstream #1, Upstream #2), and the other two WSSs are for downstream (Downstream #1, Downstream #2). Half of the M ports of each WSS are connected to optical switch #1, and the other half are connected to optical switch #2. This configuration enables return communication between any two optical transceivers among the optical transceivers connected to optical switch #1 and all optical transceivers connected to optical switch #2. When N optical transceivers (two-core) are connected to one optical switch for return communication, the number of required ports per optical switch is 2N, and the number of WSS ports is M=N. Figure 12 illustrates the case where the number of subscribers that can be connected to each optical switch via return communication is N=4, the number of return ports of each optical switch is 2N=8, and the number of WSS ports is M=4.

[0007] Although the case where K is 3 or more is not shown, when there are K optical switches, of the M ports of each WSS, M / K (=N / K) ports are connected to each optical switch. The number of return ports of each optical switch is 2N × K = 2NK, which is an order of magnitude of K. In contrast, in return communications using multiple optical switches, if the top surface ports of the optical switches are connected to each other with individual optical paths without using a WSS, the number of return ports of all optical switches will be an order of magnitude of K. A configuration using a WSS can significantly reduce the number of return ports of the optical switches.

[0008] International Publication No. 2021 / 131202 International Publication No. 2023 / 062716

[0009] M. Yoshino, S. Kaneko, N. Shibata, R. Igarashi, J. Kani, and T. Yoshida, “New Photonic Gateway to Handle Digital-Coherent and IM-DD User Terminals and Enable Turn-back Connections in Metro / Access-Integrated All-Photonics Network,” OFC 2023, W3F.5, 2023.

[0010] The above-mentioned conventional technology is a configuration in which the return ports of optical switches are connected by a WSS when performing return communication across multiple optical switches. Using a WSS can significantly reduce the number of return ports on an optical switch. However, WSSs are expensive and have large insertion losses. Furthermore, the need to dynamically change the selected wavelength requires complex control by a control unit.

[0011] In view of the above circumstances, an object of the present invention is to provide an optical communication system and an optical communication method that are capable of performing loopback communication across optical switches at low cost and with low insertion loss.

[0012] One aspect of the present invention includes K (K is an integer of 2 or more) optical switches having a plurality of first ports and a plurality of second ports, each of which performs a process of outputting an optical signal input from the first port from the second port according to a setting, and a process of outputting an optical signal input from the second port from the first port according to a setting, and a plurality of wavelength multiplexers / demultiplexers connected to the second ports of the optical switch, respectively, wherein the wavelength multiplexer / demultiplexer has one third port connected to the second port of the optical switch and K fourth ports each corresponding to a different wavelength, and is an optical communication system in which each of the K wavelength multiplexers and demultiplexers is connected to the second port of each of the K optical switches, and the wavelength corresponding to the fourth port of the wavelength multiplexer and demultiplexer is the same as the wavelength corresponding to the fourth port of the other wavelength multiplexer and demultiplexer connected by the fourth port, and the wavelength multiplexer and demultiplexer perform one or both of the process of outputting an optical signal input from the third port to the fourth port corresponding to the wavelength of the optical signal and the process of outputting an optical signal input from the fourth port and having a wavelength corresponding to the fourth port from the third port.

[0013] One aspect of the present invention includes two optical switches having a plurality of first ports and a plurality of second ports, each of which performs a process of outputting an optical signal input from the first port from the second port according to a setting, and a process of outputting an optical signal input from the second port from the first port according to a setting, and a plurality of wavelength multiplexers / demultiplexers connected to the second ports of the optical switches, respectively, wherein the wavelength multiplexer / demultiplexer has one third port connected to the second port of the optical switch and two fourth ports corresponding to different wavelengths, and the fourth port of one of the wavelength multiplexers / demultiplexers is connected to the fourth port of the other wavelength multiplexer / demultiplexer connected to the optical switch to which the wavelength multiplexer / demultiplexer is connected. the other fourth port of the wavelength multiplexer / demultiplexer is connected to a fourth port of another wavelength multiplexer / demultiplexer that is connected to an optical switch different from the optical switch to which the wavelength multiplexer / demultiplexer is connected, the wavelength corresponding to the fourth port of the wavelength multiplexer / demultiplexer is the same as the wavelength corresponding to the fourth port of the other wavelength multiplexer / demultiplexer connected by the fourth port, and the wavelength multiplexer / demultiplexer performs one or both of the process of outputting an optical signal input from the third port to the fourth port corresponding to the wavelength of the optical signal and the process of outputting an optical signal input from the fourth port and having a wavelength corresponding to the fourth port from the third port.

[0014] One aspect of the present invention is an optical communication method executed by an optical communication system including K optical switches (K is an integer of 2 or more) each having a plurality of first ports and a plurality of second ports, and a plurality of wavelength multiplexers / demultiplexers connected to the second ports of the optical switches, respectively, wherein the wavelength multiplexer / demultiplexer has one third port connected to the second port of the optical switch and K fourth ports corresponding to different wavelengths, and the K fourth ports of the wavelength multiplexer / demultiplexer are connected to the second ports of the K optical switches, respectively, and the wavelength corresponding to the fourth port of the wavelength multiplexer / demultiplexer is the same as the wavelength corresponding to the fourth port of the other wavelength multiplexer / demultiplexer connected by the fourth port, and the optical switch is The optical signal input from one port is output from the second port according to the setting to a first wavelength multiplexer / demultiplexer, which is the wavelength multiplexer / demultiplexer connected to the second port; a demultiplexing step in which the first wavelength multiplexer / demultiplexer outputs the optical signal input from the third port from the fourth port among the plurality of fourth ports according to the wavelength of the optical signal to a second wavelength multiplexer / demultiplexer, which is another wavelength multiplexer / demultiplexer connected to the fourth port; an output step in which the second wavelength multiplexer / demultiplexer outputs the optical signal input from the fourth port connected to the first wavelength multiplexer / demultiplexer from the third port; and a second switching step in which the optical switch connected to the second wavelength multiplexer / demultiplexer outputs the optical signal input from the second port from the first port according to the setting.

[0015] One aspect of the present invention is an optical communication method executed by an optical communication system including two optical switches each having a plurality of first ports and a plurality of second ports, and a plurality of wavelength multiplexers / demultiplexers connected to the second ports of the optical switches, respectively, wherein the wavelength multiplexer / demultiplexer has one third port connected to the second port of the optical switch and two fourth ports corresponding to different wavelengths, the fourth port of one of the wavelength multiplexers / demultiplexers is connected to the fourth port of another wavelength multiplexer / demultiplexer connected to the optical switch to which the wavelength multiplexer / demultiplexer is connected, and the fourth port of the other wavelength multiplexer / demultiplexer is connected to the optical switch different from the optical switch to which the wavelength multiplexer / demultiplexer is connected, and the wavelength corresponding to the fourth port of the wavelength multiplexer / demultiplexer and the fourth port of the other wavelength multiplexer / demultiplexer connected by the fourth port are related to each other. a first switching step in which the optical switch outputs the optical signal input from the first port from the second port according to a setting to a first wavelength multiplexer / demultiplexer that is the wavelength multiplexer / demultiplexer connected to the second port; a demultiplexing step in which the first wavelength multiplexer / demultiplexer outputs the optical signal input from the third port from the fourth port of the two fourth ports that corresponds to the wavelength of the optical signal to a second wavelength multiplexer / demultiplexer that is the other of the wavelength multiplexers / demultiplexers connected to the fourth port; an output step in which the second wavelength multiplexer / demultiplexer outputs the optical signal input from the fourth port connected to the first wavelength multiplexer / demultiplexer from the third port; and a second switching step in which the optical switch connected to the second wavelength multiplexer / demultiplexer outputs the optical signal input from the second port from the first port according to a setting.

[0016] The present invention makes it possible to perform return communication across optical switches at low cost and with low insertion loss.

[0017] FIG. 1 is a diagram illustrating an example of the configuration of an optical communication system according to a first embodiment. FIG. 2 is a diagram illustrating the transmission characteristics of a wavelength multiplexer / demultiplexer according to the first embodiment. FIG. 3 is a diagram illustrating an example of the configuration of an optical communication system according to the first embodiment. FIG. 4 is a diagram illustrating the transmission characteristics of an interleaver according to the first embodiment. FIG. 5 is a diagram illustrating an example of the configuration of an optical communication system according to a second embodiment. FIG. 6 is a diagram illustrating the transmission characteristics of a wavelength multiplexer / demultiplexer according to the second embodiment. FIG. 7 is a diagram illustrating an example of the configuration of an optical communication system according to the second embodiment. FIG. 8 is a diagram illustrating the transmission characteristics of an interleaver according to the second embodiment. FIG. 9 is a diagram illustrating an example of the configuration of an optical communication system according to a third embodiment. FIG. 10 is a diagram illustrating wavelengths used for connecting between optical switches according to the third embodiment. FIG. 11 is a diagram illustrating an example of the configuration of an optical communication system according to the prior art. FIG. 12 is a diagram illustrating an example of the configuration of an optical communication system according to the prior art.

[0018] An embodiment of the present invention will be described in detail below with reference to the drawings. The optical communication system of this embodiment includes two optical switches and a plurality of wavelength multiplexers / demultiplexers connected to the top surface ports of each optical switch. The two output ports of the wavelength multiplexer / demultiplexer output optical signals of different wavelengths. These wavelengths are designated λa and λb. The output port for wavelength λa of the wavelength multiplexer / demultiplexer is connected to an output port for the same wavelength λa of another wavelength demultiplexer / multiplexer connected to another top surface port of the optical switch to which the input port of the wavelength multiplexer / demultiplexer is connected. The other output port for wavelength λb of the wavelength multiplexer / demultiplexer is connected to an output port for the same wavelength λb of yet another wavelength demultiplexer / demultiplexer connected to the top surface port of the other optical switch. The wavelength multiplexers / demultiplexers may be, for example, dielectric multilayer filters or arrayed waveguide gratings (AWGs), which are less expensive than WSSs.

[0019] According to this embodiment, by using a wavelength multiplexer / demultiplexer that is lower cost and has lower insertion loss than a WSS, the same number of optical switch ports as when a WSS is used are used, and optical transceivers connected to each of the two optical switches can perform return communication between any optical transceivers. Furthermore, there is no need for wavelength selection control, which is required when a WSS is used. Detailed embodiments are described below.

[0020] 1 is a configuration diagram of an optical communication system 10 according to a first embodiment of the present invention. The optical communication system 10 has N (N is an integer of 2 or more) optical transceivers 20, K (K is an integer of 2 or more) optical switches 30, and J (J is an integer of 2 or more) wavelength multiplexers / demultiplexers 40. For simplicity, a detailed description of the control mechanism of the optical switches 30 and the optical transceivers 20 by a control unit is omitted.

[0021] The optical transceiver 20 has a dual input / output port. The optical transceiver 20 includes an optical transmitter 21 and an optical receiver 22. The optical transmitter 21 transmits an optical signal from the input / output port to the optical switch 30. The optical receiver 22 receives the optical signal output by the optical switch from the input / output port. The nth (n is an integer between 1 and N) optical transceiver 20 is referred to as optical transceiver 20-n. The optical transceiver 20 transmits and receives an optical signal of a wavelength specified by the control unit.

[0022] The optical switch 30 is a matrix optical switch. The optical switch 30 has L first ports 31 and L second ports 32 (L is an integer equal to or greater than 2). The side of the optical switch 30 on which the first ports 31 are located is the bottom surface, and the side on which the second ports 32 are located is the top surface. The first ports 31 are also referred to as bottom ports, and the second ports are also referred to as top ports. FIG. 1 shows an example in which the number of optical switches is K=2 and the number of ports on each of the bottom and top surfaces is L=8. Below, the kth (k is an integer equal to or greater than 1 and equal to K) optical switch 30 is referred to as optical switch 30-k. The pth (p is an integer equal to or greater than 1 and equal to L) first port 31 of optical switch 30-k is referred to as first port 31-k-p, and the qth (q is an integer equal to or greater than 1 and equal to L) second port 32 of optical switch 30-k is referred to as second port 32-k-q.

[0023] A correspondence relationship between the first ports 31 and the second ports 32 is set in the optical switch 30 by a control unit (not shown). The optical switch 30 outputs light input from any of the first ports 31 from any of the second ports 32 in accordance with the correspondence between the first ports 31 and the second ports 32 specified by the control unit (not shown). The optical switch 30 also outputs light input from any of the second ports 32 to any of the first ports 31 in accordance with the correspondence between the first ports 31 and the second ports 32 specified by the control unit (not shown). The optical switch 30 is connected to the optical transmitter 21 and the optical receiver 22 of one optical transceiver 20, respectively, via the two first ports 31. Each of the second ports 32 of the optical switch 30 is connected to one wavelength multiplexer / demultiplexer 40.

[0024] A wavelength multiplexer / demultiplexer 40 is disposed at each second port 32 of the optical switch 30. In Fig. 1, the number J of wavelength multiplexers / demultiplexers 40 = the number K of optical switches 30 × the number L of second ports 32. A wavelength multiplexer / demultiplexer 40 connected to second port 32-q-k of optical switch 30-k is referred to as wavelength multiplexer / demultiplexer 40-q-k.

[0025] The wavelength multiplexer / demultiplexer 40 has (K+1) ports: a first port 41-0 and second ports 41-1 to 41-K. During wavelength demultiplexing, the first port 41-0 is an input port, and the second ports 41-1 to 41-K are output ports. The wavelength multiplexer / demultiplexer 40 demultiplexes an optical signal input from the first port 41-0, and outputs the demultiplexed optical signals from each of the second ports 41-1 to 41-K according to the wavelength. Furthermore, during wavelength multiplexing, the second ports 41-1 to 41-K are input ports, and the first port 41-0 is an output port. The wavelength multiplexer / demultiplexer 40 multiplexes optical signals of different wavelengths input from each of the second ports 41-1 to 41-K, and outputs the multiplexed optical signal from the first port 41-0.

[0026] The first port 41-0 of the wavelength multiplexer / demultiplexer 40-k-q is connected to the second port 32-k-q of the optical switch 30-k. The second port 41-1 of the wavelength multiplexer / demultiplexer 40-k-q is connected to the second port 41-1 of another wavelength multiplexer / demultiplexer 40-k-q' (q' ≠ q, q' is an integer between 1 and L) connected to the same optical switch 30-k as the wavelength multiplexer / demultiplexer 40-k-q. The second port 41-1 of the wavelength multiplexer / demultiplexer 40-k-q and the second port 41-1 of the wavelength multiplexer / demultiplexer 40-k-q' that are connected to each other are output ports of the same wavelength. The second port 41-2 of the wavelength multiplexer / demultiplexer 40-k-q is connected to the second port 41-2 of another wavelength multiplexer / demultiplexer 40-k'-q (q is an integer of 1 or more and L or less) that is connected to an optical switch 30-k' (k' ≠ k, k' is an integer of 1 or more and K or less) that is different from the optical switch 30-k to which the wavelength multiplexer / demultiplexer 40-k-q is connected. The second port 41-2 of the wavelength multiplexer / demultiplexer 40-k-q and the second port 41-2 of the wavelength multiplexer / demultiplexer 40-k'-q that are connected are output ports of the same wavelength.

[0027] For example, one of the two output ports (which become two input ports when multiplexing) of the wavelength multiplexer / demultiplexer 40-1-1 shown in FIG. 1 , a second port 41-1, is connected to a second port 41-1 of the wavelength multiplexer / demultiplexer 40-1-2. The wavelength multiplexer / demultiplexer 40-1-1 and the wavelength multiplexer / demultiplexer 40-1-2 are arranged on the same top surface port of the optical switch 30-1. The second port 41-1 of the wavelength multiplexer / demultiplexer 40-1-1 and the second port 41-1 of the wavelength multiplexer / demultiplexer 40-1-2 are output ports for the same wavelength λ1. The other output port, a second port 41-2, of the wavelength multiplexer / demultiplexer 40-1-1 when multiplexing is connected to a second port 41-2 of the wavelength multiplexer / demultiplexer 40-2-1. The wavelength multiplexer / demultiplexer 40-2-1 is arranged on a top surface port of the optical switch 30-2 different from the wavelength multiplexer / demultiplexer 40-1-1. The second port 41-2 of the wavelength division multiplexer 40-1-1 and the second port 41-2 of the wavelength division multiplexer 40-2-1 are output ports for the same wavelength λ3.

[0028] 1, one of the two output ports of the wavelength multiplexer / demultiplexer 40-2-5 when wavelength demultiplexing, the second port 41-1, is connected to the second port 41-1 of the wavelength multiplexer / demultiplexer 40-2-6. The wavelength multiplexer / demultiplexer 40-2-5 and the wavelength multiplexer / demultiplexer 40-2-6 are arranged on the top surface of the same optical switch 30-2. The second port 41-1 of the wavelength multiplexer / demultiplexer 40-2-5 and the second port 41-1 of the wavelength multiplexer / demultiplexer 40-2-6 are output ports for the same wavelength λ1. The other output port of the wavelength multiplexer / demultiplexer 40-2-5 when wavelength demultiplexing, the second port 41-2, is connected to the second port 41-2 of the wavelength multiplexer / demultiplexer 40-1-5. The wavelength multiplexer / demultiplexer 40-1-5 is arranged on the top surface of the optical switch 30-1 different from the wavelength multiplexer / demultiplexer 40-2-5. The second port 41-2 of the wavelength division multiplexer 40-2-5 and the second port 41-2 of the wavelength division multiplexer 40-1-5 are output ports for the same wavelength λ3.

[0029] 2 is a diagram showing the transmission characteristics of the wavelength multiplexer / demultiplexer 40. FIG. 2 shows a case where the wavelength multiplexer / demultiplexer 40 uses two output ports. As shown in FIG. 2, the second port 41-1 of the wavelength multiplexer / demultiplexer 40 transmits an optical signal with a wavelength of λ1 but does not transmit an optical signal with a wavelength of λ3. The second port 41-2 of the wavelength multiplexer / demultiplexer 40 transmits an optical signal with a wavelength of λ3 but does not transmit an optical signal with a wavelength of λ1.

[0030] 1 illustrates a case in which optical transceivers 20-1 and 20-2 simultaneously perform return communication across optical switches using wavelength λ3, and optical transceivers 20-3 and 20-4 simultaneously perform return communication between the same optical switches using wavelength λ1. The wavelength used for return communication may be set to a wavelength band different from the WDM wavelength band used for inter-node communication.

[0031] The operation of the optical communication system 10 during communication between the optical transceiver 20-1 and the optical transceiver 20-2 will be described. The optical transmitter 21 of the optical transceiver 20-1 outputs an optical signal with a wavelength of λ3. The optical switch 30-1 inputs the optical signal output by the optical transceiver 20-1 from a first port 31-1-1 and outputs it from a second port 32-1-5. The wavelength multiplexer / demultiplexer 40-1-5 inputs the optical signal output by the optical switch 30-1 from a first port 41-0. The wavelength multiplexer / demultiplexer 40-1-5 demultiplexes the input optical signal and outputs the demultiplexed optical signal with wavelength λ3 from a second port 41-2 that transmits the wavelength λ3. The wavelength multiplexer / demultiplexer 40-2-5 receives the optical signal output by the wavelength multiplexer / demultiplexer 40-1-5 from the second port 41-2, multiplexes it with the optical signal input from the second port 41-1, and outputs the combined optical signal from the first port 41-0. The optical switch 30-2 receives the optical signal output by the wavelength multiplexer / demultiplexer 40-2-5 from the second port 32-2-5 and outputs it from the first port 31-2-2. The optical receiver 22 of the optical transceiver 20-2 receives the optical signal with wavelength λ3 from the optical switch 30-2.

[0032] The optical transmitter 21 of the optical transceiver 20-2 outputs an optical signal with wavelength λ3. The optical switch 30-2 receives the optical signal output by the optical transceiver 20-2 from a first port 31-2-1 and outputs it from a second port 32-2-6. The wavelength multiplexer / demultiplexer 40-2-6 receives the optical signal output by the optical switch 30-2 from a first port 41-0. The wavelength multiplexer / demultiplexer 40-2-6 demultiplexes the input optical signal and outputs the demultiplexed optical signal with wavelength λ3 from a second port 41-2. The wavelength multiplexer / demultiplexer 40-1-6 receives the optical signal output by the wavelength multiplexer / demultiplexer 40-2-6 from a second port 41-2, multiplexes it with the optical signal input from the second port 41-1, and outputs the combined optical signal from the first port 41-0. The optical switch 30-1 receives the optical signal output by the wavelength multiplexer / demultiplexer 40-1-6 from the second port 32-1-6 and outputs it from the first port 31-1-2. The optical receiver 22 of the optical transceiver 20-1 receives the optical signal with wavelength λ3 from the optical switch 30-1.

[0033] Next, the operation of the optical communication system 10 during communication between the optical transceiver 20-3 and the optical transceiver 20-4 will be described. The optical transmitter 21 of the optical transceiver 20-3 outputs an optical signal with wavelength λ1. The optical switch 30-1 inputs the optical signal output by the optical transceiver 20-3 from a first port 31-1-3 and outputs it from a second port 32-1-1. The wavelength multiplexer / demultiplexer 40-1-1 inputs the optical signal output by the optical switch 30-1 from a first port 41-0. The wavelength multiplexer / demultiplexer 40-1-1 demultiplexes the input optical signal and outputs the demultiplexed optical signal with wavelength λ1 from a second port 41-1 that transmits wavelength λ1. The wavelength multiplexer / demultiplexer 40-1-2 receives the optical signal output by the wavelength multiplexer / demultiplexer 40-1-1 from the second port 41-1, multiplexes it with the optical signal input from the second port 41-2, and outputs the combined optical signal from the first port 41-0. The optical switch 30-1 receives the optical signal output by the wavelength multiplexer / demultiplexer 40-1-2 from the second port 32-1-2 and outputs it from the first port 31-1-6. The optical receiver 22 of the optical transceiver 20-4 receives the optical signal with wavelength λ1 from the optical switch 30-1.

[0034] The optical transmitter 21 of the optical transceiver 20-4 outputs an optical signal of wavelength λ1. The optical switch 30-1 receives the optical signal output by the optical transceiver 20-4 from a first port 31-1-5 and outputs it from a second port 32-1-4. The wavelength multiplexer / demultiplexer 40-1-4 receives the optical signal output by the optical switch 30-1 from a first port 41-0. The wavelength multiplexer / demultiplexer 40-1-4 demultiplexes the input optical signal and outputs the demultiplexed optical signal of wavelength λ1 from a second port 41-1. The wavelength multiplexer / demultiplexer 40-1-3 receives the optical signal output by the wavelength multiplexer / demultiplexer 40-1-4 from a second port 41-1, multiplexes it with the optical signal input from the second port 41-2, and outputs the combined optical signal from the first port 41-0. The optical switch 30-1 receives the optical signal output by the wavelength multiplexer / demultiplexer 40-1-3 from a second port 32-1-3 and outputs it from a first port 31-1-4. The optical receiver 22 of the optical transceiver 20-3 receives the optical signal with wavelength λ1 from the optical switch 30-1.

[0035] The configuration shown in Figure 1 enables return communication between any two optical transceivers among all the optical transceivers connected to each of the optical switches 30-1 to 30-K, using the same number of optical switch ports as when using WSS.

[0036] Furthermore, when K=2, an optical interleaver can be used instead of the wavelength multiplexer / demultiplexer. The optical interleaver has periodic transmission characteristics. Fig. 3 is a diagram showing the configuration of an optical communication system 11 according to the first embodiment. The optical communication system 11 shown in Fig. 3 differs from the optical communication system 10 shown in Fig. 1 in that an optical interleaver 50 is provided instead of the wavelength multiplexer / demultiplexer 40.

[0037] The optical interleaver 50 connected to the second port 32-q-k of the optical switch 30-k is referred to as the optical interleaver 50-q-k. The optical interleaver 50 has (K+1) ports, namely, a first port 51-0 and second ports 51-1 to 51-K. The optical interleaver 50 filters the optical signal input from the first port 51-0, and outputs the optical signals demultiplexed by the filtering from each of the second ports 51-1 to 51-K according to the wavelength. The optical interleaver 50 also multiplexes optical signals of different wavelengths input from each of the second ports 51-1 to 51-K, and outputs the multiplexed signal from the first port 51-0.

[0038] Fig. 4 is a diagram showing the transmission characteristics of the optical interleaver 50. Fig. 4 shows a case where the optical interleaver 50 uses two output ports. As shown in Fig. 4, the second port 51-1 of the optical interleaver 50 transmits an optical signal with wavelength λ2 but does not transmit an optical signal with wavelength λ3. The second port 51-2 of the optical interleaver 50 transmits an optical signal with wavelength λ3 but does not transmit an optical signal with wavelength λ2.

[0039] 3 illustrates a case in which optical transceivers 20-1 and 20-2 simultaneously perform return communication across optical switches using wavelength λ3, and optical transceivers 20-3 and 20-4 simultaneously perform return communication between the same optical switches using wavelength λ2. The wavelength used for return communication may be set to a wavelength band different from the WDM wavelength band used for inter-node communication.

[0040] The operation of the optical communication system 11 during communication between the optical transceiver 20-1 and the optical transceiver 20-2 will be described. The optical transmitter 21 of the optical transceiver 20-1 outputs an optical signal with wavelength λ3. The optical switch 30-1 inputs the optical signal output by the optical transceiver 20-1 from the first port 31-1-1 and outputs it from the second port 32-1-5. The optical interleaver 50-1-5 inputs the optical signal output by the optical switch 30-1 from the first port 51-0. The optical interleaver 50-1-5 demultiplexes the input optical signal and outputs an optical signal with wavelength λ3 from the second port 51-2. The optical interleaver 50-2-5 inputs the optical signal output by the optical interleaver 50-1-5 from the second port 51-2, multiplexes it with the optical signal input from the second port 51-1, and outputs the combined optical signal from the first port 51-0. The optical switch 30-2 receives the optical signal output by the optical interleaver 50-2-5 from the second port 32-2-5 and outputs it from the first port 31-2-2. The optical receiver 22 of the optical transceiver 20-2 receives the optical signal with wavelength λ3 from the optical switch 30-2.

[0041] The optical transmitter 21 of the optical transceiver 20-2 outputs an optical signal with wavelength λ3. The optical switch 30-2 inputs the optical signal output by the optical transceiver 20-2 from a first port 31-2-1 and outputs it from a second port 32-2-6. The optical interleaver 50-2-6 inputs the optical signal output by the optical switch 30-2 from a first port 51-0. The optical interleaver 50-2-6 demultiplexes the input optical signal and outputs the demultiplexed optical signal with wavelength λ3 from a second port 51-2. The optical interleaver 50-1-6 inputs the optical signal output by the optical interleaver 50-2-6 from a second port 51-2, multiplexes it with the optical signal input from the second port 51-1, and outputs the combined optical signal from a first port 51-0. The optical switch 30-1 receives the optical signal output by the optical interleaver 50-1-6 from the second port 32-1-6 and outputs it from the first port 31-1-2. The optical receiver 22 of the optical transceiver 20-1 receives the optical signal with wavelength λ3 from the optical switch 30-1.

[0042] Next, the operation of the optical communication system 11 during communication between the optical transceiver 20-3 and the optical transceiver 20-4 will be described. The optical transmitter 21 of the optical transceiver 20-3 outputs an optical signal with wavelength λ2. The optical switch 30-1 inputs the optical signal output by the optical transceiver 20-3 from the first port 31-1-3 and outputs it from the second port 32-1-1. The optical interleaver 50-1-1 inputs the optical signal output by the optical switch 30-1 from the first port 51-0. The optical interleaver 50-1-1 demultiplexes the input optical signal and outputs the demultiplexed optical signal with wavelength λ2 from the second port 51-1. The optical interleaver 50-1-2 inputs the optical signal output by the optical interleaver 50-1-1 from the second port 51-1, multiplexes it with the optical signal input from the second port 51-2, and outputs the combined optical signal from the first port 51-0. The optical switch 30-1 receives the optical signal output by the optical interleaver 50-1-2 from the second port 32-1-2 and outputs it from the first port 31-1-6. The optical receiver 22 of the optical transceiver 20-4 receives the optical signal with wavelength λ2 from the optical switch 30-1.

[0043] The optical transmitter 21 of the optical transceiver 20-4 outputs an optical signal of wavelength λ2. The optical switch 30-1 inputs the optical signal output by the optical transceiver 20-4 from a first port 31-1-5 and outputs it from a second port 32-1-4. The optical interleaver 50-1-4 inputs the optical signal output by the optical switch 30-1 from a first port 51-0. The optical interleaver 50-1-4 demultiplexes the input optical signal and outputs the demultiplexed optical signal of wavelength λ2 from a second port 51-1. The optical interleaver 50-1-3 inputs the optical signal output by the optical interleaver 50-1-4 from a second port 51-1, multiplexes it with the optical signal input from the second port 51-2, and outputs the combined optical signal from the first port 51-0. The optical switch 30-1 receives the optical signal output by the optical interleaver 50-1-3 from a second port 32-1-3 and outputs it from a first port 31-1-4. The optical receiver 22 of the optical transceiver 20-3 receives the optical signal with wavelength λ2 from the optical switch 30-1.

[0044] The wavelength used for the return communication may be set to a wavelength band different from the WDM wavelength band used for the inter-node communication.

[0045] Second Embodiment In this embodiment, optical transceivers having two input / output ports are connected to two bottom ports of an optical switch, and an optical transceiver having a single input / output port is connected to one bottom port of the optical switch. The second embodiment will be described focusing on the differences from the first embodiment.

[0046] 5 is a configuration diagram of an optical communication system 12 according to a second embodiment. In FIG. 5, the same components as those in the optical communication system 10 according to the first embodiment shown in FIG. 1 are designated by the same reference numerals, and their description will be omitted. The optical communication system 12 shown in FIG. 5 differs from the optical communication system 10 shown in FIG. 1 in that an optical transceiver 25 having a single input / output port is connected to the optical switch 30, instead of the optical transceivers 20-3 and 20-4 having two input / output ports. The optical transceiver 25 is connected to one first port 31 of the optical switch 30. The four optical transceivers 25 are referred to as optical transceivers 25-1 to 25-4, respectively. The optical transceiver 25-1 is connected to the first port 31-1-3 of the optical switch 30-1, the optical transceiver 25-2 is connected to the first port 31-1-6 of the optical switch 30-1, the optical transceiver 25-3 is connected to the first port 31-1-4 of the optical switch 30-1, and the optical transceiver 25-4 is connected to the first port 31-2-4 of the optical switch 30-2.

[0047] In the second embodiment, although the configurations of the optical switch 30 and wavelength multiplexer / demultiplexer 40 of the optical communication system 12 are the same as those of the optical switch 30 and wavelength multiplexer / demultiplexer 40 of the optical communication system 10 of the first embodiment, similar loopback communication is possible not only for the optical transceiver 20 having a two-fiber input / output port but also for the optical transceiver 25 having a single-fiber input / output port. However, in the case of the single-fiber optical transceiver 25, different wavelengths are used for the upstream optical signal and the downstream optical signal.

[0048] Fig. 6 is a diagram showing the transmission characteristics of the wavelength multiplexer / demultiplexer 40 included in the optical communication system 12. Fig. 6 shows a case where the wavelength multiplexer / demultiplexer 40 uses two output ports. As shown in Fig. 6, the second port 41-1 of the wavelength multiplexer / demultiplexer 40 transmits optical signals of wavelengths λ1 and λ2, but does not transmit optical signals of wavelengths λ3 and λ4. The second port 41-2 of the wavelength multiplexer / demultiplexer 40 transmits optical signals of wavelengths λ3 and λ4, but does not transmit optical signals of wavelengths λ1 and λ2.

[0049] Figure 5 shows a case in which optical transceivers 20-1 and 20-2 simultaneously perform return communication across an optical switch using wavelength λ3, optical transceivers 25-1 and 25-2 perform return communication between the same optical switches using wavelengths λ1 and λ2, and optical transceivers 25-3 and 25-4 perform return communication across an optical switch using wavelengths λ3 and λ4.

[0050] When the optical transceiver 25-1 transmits an optical signal using wavelength λ1, the optical transceiver 25-2 transmits an optical signal using wavelength λ2. Conversely, when the optical transceiver 25-1 transmits an optical signal using wavelength λ2, the optical transceiver 25-2 transmits an optical signal using wavelength λ1. When the optical transceiver 25-3 transmits an optical signal using wavelength λ3, the optical transceiver 25-4 transmits an optical signal using wavelength λ4. Conversely, when the optical transceiver 25-3 transmits an optical signal using wavelength λ4, the optical transceiver 25-4 transmits an optical signal using wavelength λ3. The wavelengths used in return communication may be set to a wavelength band different from the WDM wavelength band used in inter-node communication.

[0051] The operation of the optical communication system 12 in communication between the optical transceiver 20-1 and the optical transceiver 20-2 is the same as the operation of the optical communication system 10 of the first embodiment.

[0052] The operation of the optical communication system 12 during communication between the optical transceiver 25-1 and the optical transceiver 25-2 will be described. The optical transceiver 25-1 outputs an optical signal with wavelength λ1. The optical switch 30-1 inputs the optical signal output by the optical transceiver 25-1 from the first port 31-1-3 and outputs it from the second port 32-1-1. The wavelength multiplexer / demultiplexer 40-1-1 inputs the optical signal output by the optical switch 30-1 from the first port 41-0. The wavelength multiplexer / demultiplexer 40-1-1 demultiplexes the input optical signal and outputs the demultiplexed optical signals with wavelength λ1 from the second port 41-1 corresponding to wavelengths λ1 and λ2. The wavelength multiplexer / demultiplexer 40-1-2 inputs the optical signal output by the wavelength multiplexer / demultiplexer 40-1-1 from the second port 41-1, multiplexes it with the optical signal input from the second port 41-2, and outputs the combined optical signal from the first port 41-0. The optical switch 30-1 receives the optical signal output from the wavelength multiplexer / demultiplexer 40-1-2 from the second port 32-1-2 and outputs it from the first port 31-1-6. The optical transceiver 25-2 receives the optical signal with wavelength λ1 from the optical switch 30-1.

[0053] The optical transceiver 25-2 outputs an optical signal of wavelength λ2. The optical switch 30-1 receives the optical signal output by the optical transceiver 25-2 from a first port 31-1-6 and outputs it from a second port 32-1-2. The wavelength multiplexer / demultiplexer 40-1-2 receives the optical signal output by the optical switch 30-1 from a first port 41-0. The wavelength multiplexer / demultiplexer 40-1-2 demultiplexes the input optical signal and outputs the demultiplexed optical signals of wavelength λ2 from a second port 41-1 corresponding to wavelengths λ1 and λ2. The wavelength multiplexer / demultiplexer 40-1-1 receives the optical signal output by the wavelength multiplexer / demultiplexer 40-1-2 from a second port 41-1, multiplexes it with the optical signal input from the second port 41-2, and outputs the combined optical signal from the first port 41-0. The optical switch 30-1 receives the optical signal output from the wavelength multiplexer / demultiplexer 40-1-1 from the second port 32-1-1 and outputs it from the first port 31-1-3. The optical transceiver 25-1 receives the optical signal with wavelength λ2 from the optical switch 30-1.

[0054] Next, the operation of the optical communication system 12 during communication between the optical transceiver 25-3 and the optical transceiver 25-4 will be described. The optical transceiver 25-3 outputs an optical signal with a wavelength of λ3. The optical switch 30-1 inputs the optical signal output by the optical transceiver 25-3 from the first port 31-1-4 and outputs it from the second port 32-1-3. The wavelength multiplexer / demultiplexer 40-1-3 inputs the optical signal output by the optical switch 30-1 from the first port 41-0. The wavelength multiplexer / demultiplexer 40-1-3 demultiplexes the input optical signal and outputs the demultiplexed optical signals with wavelength λ3 from the second port 41-2 corresponding to wavelengths λ3 and λ4. The wavelength multiplexer / demultiplexer 40-2-3 inputs the optical signal output by the wavelength multiplexer / demultiplexer 40-1-3 from the second port 41-2, multiplexes it with the optical signal input from the second port 41-1, and outputs the combined optical signal from the first port 41-0. The optical switch 30-2 receives the optical signal output from the wavelength multiplexer / demultiplexer 40-2-3 from a second port 32-2-3 and outputs it from a first port 31-2-4. The optical transceiver 25-4 receives the optical signal with wavelength λ3 from the optical switch 30-2.

[0055] The optical transceiver 25-4 outputs an optical signal with a wavelength of λ4. The optical switch 30-2 receives the optical signal output by the optical transceiver 25-4 from a first port 31-2-4 and outputs it from a second port 32-2-3. The wavelength multiplexer / demultiplexer 40-2-3 receives the optical signal output by the optical switch 30-2 from a first port 41-0. The wavelength multiplexer / demultiplexer 40-2-3 demultiplexes the input optical signal and outputs the demultiplexed optical signals with wavelength λ4 from the second port 41-2 corresponding to wavelengths λ3 and λ4. The wavelength multiplexer / demultiplexer 40-1-3 receives the optical signal output by the wavelength multiplexer / demultiplexer 40-2-3 from a second port 41-2, multiplexes it with the optical signal input from the second port 41-1, and outputs the combined optical signal from the first port 41-0. The optical switch 30-1 receives the optical signal output from the wavelength multiplexer / demultiplexer 40-1-3 from a second port 32-1-3 and outputs it from a first port 31-1-4. The optical transceiver 25-3 receives the optical signal with wavelength λ4 from the optical switch 30-1.

[0056] Moreover, an optical interleaver can be used instead of the wavelength multiplexer / demultiplexer. Fig. 7 is a diagram showing the configuration of an optical communication system 13 according to the first embodiment. The optical communication system 13 shown in Fig. 7 differs from the optical communication system 12 shown in Fig. 5 in that it includes an optical interleaver 50 instead of the wavelength multiplexer / demultiplexer 40. The configurations of the optical switch 30 and the optical interleaver 50 of the optical communication system 13 are the same as the configurations of the optical switch 30 and the optical interleaver 50 of the optical communication system 11 of the first embodiment.

[0057] Fig. 8 is a diagram showing the transmission characteristics of the optical interleaver 50 included in the optical communication system 13. Fig. 8 shows a case where the optical interleaver 50 uses two output ports. As shown in Fig. 8, the second port 51-1 of the optical interleaver 50 transmits optical signals with wavelengths λ2 and λ4, but does not transmit optical signals with wavelengths λ1 and λ3. The second port 51-2 of the optical interleaver 50 transmits optical signals with wavelengths λ1 and λ3, but does not transmit optical signals with wavelengths λ2 and λ4.

[0058] The optical communication system 13 using the optical interleaver 50 operates in the same manner as the optical communication system 12. Fig. 7 shows a case in which the optical transceiver 20-1 and the optical transceiver 20-2 simultaneously perform return communication across the optical switch using wavelength λ3, the optical transceiver 25-1 and the optical transceiver 25-2 perform return communication between the same optical switches using wavelengths λ1 and λ3, and further the optical transceiver 25-3 and the optical transceiver 25-4 perform return communication across the optical switch using wavelengths λ2 and λ4.

[0059] When the optical transceiver 25-1 transmits an optical signal using wavelength λ1, the optical transceiver 25-2 transmits an optical signal using wavelength λ3. Conversely, when the optical transceiver 25-1 transmits an optical signal using wavelength λ3, the optical transceiver 25-2 transmits an optical signal using wavelength λ1. When the optical transceiver 25-3 transmits an optical signal using wavelength λ2, the optical transceiver 25-4 transmits an optical signal using wavelength λ4. Conversely, when the optical transceiver 25-3 transmits an optical signal using wavelength λ4, the optical transceiver 25-4 transmits an optical signal using wavelength λ2. The wavelengths used in return communication may be set to a wavelength band different from the WDM wavelength band used in inter-node communication.

[0060] The operation of the optical communication system 13 in communication between the optical transceiver 20-1 and the optical transceiver 20-2 is the same as the operation of the optical communication system 11 of the first embodiment.

[0061] The operation of the optical communication system 13 during communication between the optical transceiver 25-1 and the optical transceiver 25-2 will be described. The optical transceiver 25-1 outputs an optical signal with wavelength λ1. The optical switch 30-1 inputs the optical signal output by the optical transceiver 25-2 from the first port 31-1-3 and outputs it from the second port 32-1-1. The optical interleaver 50-1-1 inputs the optical signal output by the optical switch 30-1 from the first port 51-0. The optical interleaver 50-1-1 demultiplexes the input optical signal and outputs the demultiplexed optical signals with wavelength λ1 from the second port 51-1 corresponding to wavelengths λ1 and λ3. The optical interleaver 50-1-2 inputs the optical signal output by the optical interleaver 50-1-1 from the second port 51-1, multiplexes it with the optical signal input from the second port 51-2, and outputs the combined optical signal from the first port 51-0. The optical switch 30-1 receives the optical signal output from the wavelength multiplexer / demultiplexer 40-1-2 from the second port 32-1-2 and outputs it from the first port 31-1-6. The optical transceiver 25-2 receives the optical signal with wavelength λ1 from the optical switch 30-1.

[0062] The optical transceiver 25-2 outputs an optical signal with a wavelength of λ3. The optical switch 30-1 inputs the optical signal output by the optical transceiver 25-2 from a first port 31-1-6 and outputs it from a second port 32-1-2. The optical interleaver 50-1-2 inputs the optical signal output by the optical switch 30-1 from a first port 51-0. The optical interleaver 50-1-2 demultiplexes the input optical signal and outputs the demultiplexed optical signals with wavelength λ2 from a second port 51-1 corresponding to wavelengths λ1 and λ3. The optical interleaver 50-1-1 inputs the optical signal output by the optical interleaver 50-1-2 from a second port 51-1, multiplexes it with the optical signal input from the second port 51-2, and outputs the combined optical signal from the first port 51-0. The optical switch 30-1 receives the optical signal output from the wavelength division multiplexer 40-1-1 through a second port 32-1-1 and outputs it through a first port 31-1-3. The optical transceiver 25-1 receives the optical signal with wavelength λ3 from the optical switch 30-1.

[0063] Next, the operation of the optical communication system 13 during communication between the optical transceiver 25-3 and the optical transceiver 25-4 will be described. The optical transceiver 25-3 outputs an optical signal with wavelength λ2. The optical switch 30-1 inputs the optical signal output by the optical transceiver 25-3 from the first port 31-1-4 and outputs it from the second port 32-1-3. The optical interleaver 50-1-3 inputs the optical signal output by the optical switch 30-1 from the first port 51-0. The optical interleaver 50-1-3 demultiplexes the input optical signal and outputs the demultiplexed optical signals with wavelength λ2 from the second port 51-2 corresponding to wavelengths λ2 and λ4. The optical interleaver 50-2-3 inputs the optical signal output by the optical interleaver 50-1-3 from the second port 51-2, multiplexes it with the optical signal input from the second port 51-1, and outputs the combined optical signal from the first port 51-0. The optical switch 30-2 receives the optical signal output from the wavelength division multiplexer 40-2-3 from a second port 32-2-3 and outputs it from a first port 31-2-4. The optical transceiver 25-4 receives the optical signal with wavelength λ2 from the optical switch 30-2.

[0064] The optical transceiver 25-4 outputs an optical signal with a wavelength of λ4. The optical switch 30-2 inputs the optical signal output by the optical transceiver 25-4 from a first port 31-2-4 and outputs it from a second port 32-2-3. The optical interleaver 50-2-3 inputs the optical signal output by the optical switch 30-2 from a first port 51-0. The optical interleaver 50-2-3 demultiplexes the input optical signal and outputs the demultiplexed optical signals with wavelength λ4 from a second port 51-2 corresponding to wavelengths λ2 and λ4. The optical interleaver 50-1-3 inputs the optical signal output by the optical interleaver 50-2-3 from a second port 51-2, multiplexes it with the optical signal input from the second port 51-1, and outputs the combined optical signal from a first port 51-0. The optical switch 30-1 receives the optical signal output by the optical interleaver 50-1-3 from a second port 32-1-3 and outputs it from a first port 31-1-4. The optical transceiver 25-3 receives the optical signal with wavelength λ4 from the optical signals received from the optical switch 30-1.

[0065] (Third embodiment) When a wavelength multiplexer / demultiplexer is arranged at the top surface port of an optical switch, return communication between any optical transmitter / receivers connected to three or more optical switches is possible. The third embodiment will be described, focusing on the differences from the above-mentioned embodiments.

[0066] FIG. 9 is a diagram illustrating the connection configuration of wavelength multiplexers provided in a communication system according to the third embodiment. FIG. 9 illustrates a configuration example in which K=3 optical switches 30-1 to 30-3 are used. For simplicity, FIG. 9 illustrates a case in which the number of return ports of each optical switch 30 is L=2. There are a total of six wavelength multiplexers / demultiplexers 40 (=K×L). That is, wavelength multiplexers / demultiplexers 40-1-1 and 40-1-2 are connected to the second ports 32-1-1 and 32-1-2 of the optical switch 30-1, wavelength multiplexers / demultiplexers 40-2-1 and 40-2-2 are connected to the second ports 32-2-1 and 32-2-2 of the optical switch 30-2, and wavelength multiplexers / demultiplexers 40-3-1 and 40-3-2 are connected to the second ports 32-3-1 and 32-3-2 of the optical switch 30-3, respectively. The wavelength multiplexer / demultiplexer 40 multiplexes / demultiplexes optical signals of wavelengths λ1, λ2, and λ3. The optical transmitter / receiver 20 is connected to the bottom surface of the optical switches 30-1 to 30-3, but is not shown in FIG.

[0067] The wavelength multiplexer / demultiplexer 40 has four ports: a first port 41-0 and second ports 41-1 to 41-3. During wavelength demultiplexing, the first port 41-0 is an input port, and the second ports 41-1 to 41-3 are output ports. The wavelength multiplexer / demultiplexer 40 demultiplexes an optical signal input from the first port 41-0, and outputs the demultiplexed optical signals from each of the second ports 41-1 to 41-3 according to the wavelength. The second ports 41-1, 41-2, and 41-3 output optical signals of wavelengths λ1, λ2, and λ3, respectively. During wavelength multiplexing, the second ports 41-1 to 41-3 are input ports, and the first port 41-0 is an output port. The wavelength multiplexer / demultiplexer 40 multiplexes the optical signals of wavelengths λ1, λ2, and λ3 input from each of the second ports 41-1 to 41-3, and outputs the multiplexed optical signal from the first port 41-0.

[0068] 9, in all wavelength multiplexers / demultiplexers 40-k-q, one second port 41-m1 (m1 is an integer between 1 and K) of second ports 41-1 to 41-3, which are the three output ports when demultiplexing (the three input ports when multiplexing), is connected to second port 41-m1 of another wavelength multiplexer / demultiplexer 40-k-q' arranged in the same optical switch 30-k as wavelength multiplexer / demultiplexer 40-k-q. The second port 41-m1 of wavelength multiplexer / demultiplexer 40-k-q and the second port 41-m1 of wavelength multiplexer / demultiplexer 40-k-q' are output ports that output demultiplexed optical signals of the same wavelength. Then, another second port 41-m2 (m1 ≠ m2, m2 is an integer greater than or equal to 1 and less than or equal to K) of the second ports 41-1 to 41-3 of the wavelength multiplexer / demultiplexer 40-k-q is connected to a second port 41-m2 of a wavelength multiplexer / demultiplexer 40-k'-q arranged in another optical switch 30-k'. The second port 41-m2 of the wavelength multiplexer / demultiplexer 40-k-q and the second port 41-m2 of the wavelength multiplexer / demultiplexer 40-k'-q are output ports that output demultiplexed optical signals of the same wavelength. Furthermore, the remaining second port 41-m3 (m1 ≠ m3, m2 ≠ m3, m3 is an integer greater than or equal to 1 and less than or equal to K) of the second ports 41-1 to 41-3 of the wavelength multiplexer / demultiplexer 40-k-q is connected to a second port 41-m3 of a wavelength multiplexer / demultiplexer 40-k"-q arranged in yet another optical switch 30-k". The second port 41-m3 of the wavelength multiplexer / demultiplexer 40-k-q and the second port 41-m3 of the wavelength multiplexer / demultiplexer 40-k"-q are output ports that output demultiplexed optical signals of the same wavelength. In this way, the second ports 41-1 to 41-3 of the wavelength multiplexer / demultiplexer 40 are connected to three optical switches 30 via other wavelength multiplexers / demultiplexers 40 so as not to overlap with each other.

[0069] Fig. 10 is a diagram showing wavelengths used in the connections between the optical switches 30 of the optical communication system 14 shown in Fig. 9. The wavelength λ1 is used in the return communication of the optical switch 30-1, the wavelength λ2 is used in the return communication of the optical switch 30-2, and the wavelength λ3 is used in the return communication of the optical switch 30-3. Furthermore, the wavelength λ3 is used in the communication between the optical switches 30-1 and 30-2, the wavelength λ2 is used in the communication between the optical switches 30-1 and 30-3, and the wavelength λ1 is used in the communication between the optical switches 30-2 and 30-3.

[0070] When three optical switches 30-1 to 30-3 are used, the number of connections between wavelength multiplexers / demultiplexers 40 is 3^2 = 9. Generally, when the number of optical switches = K and the number of return ports of each optical switch 30 = 2, the number of connections is K^2. Also, the number of wavelengths = K and the number of wavelength multiplexers / demultiplexers = 2K. To increase the number of return ports by P times (= 2P), it is sufficient to provide P sets of this configuration.

[0071] If the number of optical switches to be crossed is two, an optical interleaver 50 can be used instead of the wavelength multiplexer / demultiplexer 40. Furthermore, if a single optical transmitter / receiver 25 is provided on the lower surface of the optical switch 30, multiple wavelengths are used for signals between the optical switches 30.

[0072] According to the embodiment described above, by appropriately connecting wavelength multiplexers and demultiplexers arranged on the same side of multiple matrix optical switches to each other, it is possible to realize return communication between any of the multiple optical transceivers connected to each of the multiple optical switches, utilizing the same number of optical switch ports as when a WSS is used.

[0073] According to the above-described embodiment, the optical communication system includes K optical switches (K is an integer equal to or greater than 1) each having a plurality of first ports and a plurality of second ports, and a plurality of wavelength multiplexers / demultiplexers connected to the second ports of each of the plurality of optical switches. Each wavelength multiplexer / demultiplexer has a third port connected to the second port of the optical switch and K fourth ports. For example, the third port corresponds to the first port 41-0 of the wavelength multiplexer / demultiplexer 40 of the embodiment, and the fourth port corresponds to the second ports 41-1 to 41-K of the wavelength multiplexer / demultiplexer 40 of the embodiment. The K fourth ports of each wavelength multiplexer / demultiplexer are connected to the fourth ports of K other wavelength multiplexers / demultiplexers connected to the second ports of the K optical switches. The wavelength corresponding to the fourth port of one wavelength multiplexer / demultiplexer is the same as the wavelength corresponding to the fourth port of the other wavelength multiplexer / demultiplexer connected to the fourth port. The optical switch has a configuration in which the first ports and second ports are configured, and this configuration is variable. Based on the settings, the optical switch performs a process of outputting an optical signal input from a first port from a second port corresponding to the first port, and a process of outputting an optical signal input from a second port from the first port corresponding to the second port. The wavelength multiplexer / demultiplexer performs one or both of a process of outputting an optical signal input from a third port to a fourth port corresponding to the wavelength of the optical signal, and a process of outputting an optical signal input from the fourth port with a wavelength corresponding to the fourth port from the third port.

[0074] For example, an optical communication system may include K (K is an integer of 2 or greater) optical switches, each having L (L is an integer of 2 or greater) first ports and L second ports, and L×K wavelength multiplexers / demultiplexers, each having one third port and K fourth ports. One of the K fourth ports of the wavelength multiplexer / demultiplexer is connected to the fourth port of another wavelength multiplexer / demultiplexer connected to the optical switch to which the third port of the wavelength multiplexer / demultiplexer is connected, and the remaining (K−1) fourth ports are respectively connected to the fourth ports of (K−1) other wavelength multiplexers / demultiplexers, each connected to (K−1) optical switches different from the optical switch to which the third port of the wavelength multiplexer / demultiplexer is connected.

[0075] The first port of the optical switch may either receive an optical signal transmitted from an optical transceiver or transmit an optical signal to the optical transceiver. The fourth port of the wavelength division multiplexer / demultiplexer passes a unidirectional optical signal.

[0076] The first port of the optical switch may input an optical signal transmitted from an optical transceiver and transmit an optical signal to the optical transceiver, provided that the wavelength of the optical signal transmitted from the optical transceiver is different from the wavelength of the optical signal transmitted to the optical transceiver. The fourth port of the wavelength division multiplexer / demultiplexer passes bidirectional optical signals of different wavelengths.

[0077] In the case of two optical switches, the wavelength multiplexer / demultiplexer may divide an optical signal input from a third port into two fourth ports based on the periodic wavelength transmission characteristics and output the divided optical signals. The wavelength multiplexer / demultiplexer may be a dielectric multilayer filter or an arrayed waveguide grating. Alternatively, an optical interleaver may be used instead of the wavelength multiplexer / demultiplexer.

[0078] Although the embodiments of the present invention have been described in detail above with reference to the drawings, the specific configurations are not limited to these embodiments, and include designs within the scope of the gist of the present invention.

[0079] 10, 11, 12, 13, 14 Optical communication system 20-1 to 20-4, 25-1 to 25-2 Optical transceiver 21 Optical transmitter 22 Optical receiver 30-1 to 30-3 Optical switch 31-1-1 to 31-1-8, 31-2-1 to 31-2-8 First port 32-1-1 to 32-1-8, 32-2-1 to 32-2-8, 32-3-1 to 32-3-2 Second port 40-1-1 to 40-1-8, 40-2-1 to 40-2-8, 40-3-1 to 40-3-2 Wavelength multiplexer / demultiplexer 41-0 First port 41-1 to 41-3 Second port 50-1-1 to 50-1-8, 50-2-1 to 50-2-8 Optical interleaver 51-0 First port 51-1 to 51-2 Second ports

Claims

1. K (K is an integer of 2 or more) optical switches each having a plurality of first ports and a plurality of second ports, each performing the process of outputting an optical signal input from the first port from the second port according to a setting, and outputting an optical signal input from the second port from the first port according to a setting; and a plurality of wavelength multiplexers / demultiplexers connected to the second ports of the optical switches, respectively; wherein the wavelength multiplexer / demultiplexer has one third port connected to the second port of the optical switch and K fourth ports corresponding to different wavelengths, and the K fourth ports of the wavelength multiplexer / demultiplexer are connected to the respective fourth ports of K other wavelength multiplexers / demultiplexers connected to the second ports of the K optical switches, and the wavelength corresponding to the fourth port of the wavelength multiplexer / demultiplexer is the same as the wavelength corresponding to the fourth port of the other wavelength multiplexer / demultiplexer connected by the fourth port; an optical communication system, wherein the wavelength multiplexer / demultiplexer performs one or both of a process of outputting an optical signal input from the third port to the fourth port corresponding to the wavelength of the optical signal, and a process of outputting an optical signal input from the fourth port and having a wavelength corresponding to the fourth port from the third port.

2. Two optical switches having a plurality of first ports and a plurality of second ports, each of which processes an optical signal input from the first port to be output from the second port according to a setting, and an optical signal input from the second port to be output from the first port according to a setting; and a plurality of wavelength multiplexers / demultiplexers connected to the second ports of the optical switches, respectively; wherein the wavelength multiplexer / demultiplexer has one third port connected to the second port of the optical switch and two fourth ports corresponding to different wavelengths; the fourth port of one of the wavelength multiplexers / demultiplexers is connected to the fourth port of another wavelength multiplexer / demultiplexer connected to the optical switch to which the wavelength multiplexer / demultiplexer is connected, and the fourth port of the other wavelength multiplexer / demultiplexer is connected to the fourth port of another wavelength multiplexer / demultiplexer connected to an optical switch different from the optical switch to which the wavelength multiplexer / demultiplexer is connected; the wavelength corresponding to the fourth port of the wavelength multiplexer / demultiplexer is the same as the wavelength corresponding to the fourth port of the other wavelength multiplexer / demultiplexer connected by the fourth port; an optical communication system, wherein the wavelength multiplexer / demultiplexer performs one or both of a process of outputting an optical signal input from the third port to the fourth port corresponding to the wavelength of the optical signal, and a process of outputting an optical signal input from the fourth port and having a wavelength corresponding to the fourth port from the third port.

3. An optical communication system according to claim 1 or 2, wherein the first port of the optical switch either inputs an optical signal transmitted from an optical transceiver or transmits an optical signal to the optical transceiver, and the fourth port passes a unidirectional optical signal.

4. An optical communication system according to claim 1 or claim 2, wherein the first port of the optical switch inputs an optical signal transmitted from an optical transceiver and transmits an optical signal to the optical transceiver, the wavelength of the optical signal transmitted from the optical transceiver is different from the wavelength of the optical signal transmitted to the optical transceiver, and the fourth port passes bidirectional optical signals of different wavelengths.

5. The optical communication system according to claim 2, wherein the wavelength multiplexer / demultiplexer divides the optical signal input from the third port into two of the fourth ports and outputs the divided optical signals according to the transmission characteristics of periodic wavelengths.

6. An optical communication method executed by an optical communication system having K (K is an integer of 2 or more) optical switches each having a plurality of first ports and a plurality of second ports, and a plurality of wavelength multiplexers / demultiplexers connected to the second ports of the optical switches, wherein the wavelength multiplexer / demultiplexer has one third port connected to the second port of the optical switch and K fourth ports corresponding to different wavelengths, the K fourth ports of the wavelength multiplexer / demultiplexer are connected to the fourth ports of K other wavelength multiplexers / demultiplexers connected to the second ports of the K optical switches, the wavelength corresponding to the fourth port of the wavelength multiplexer / demultiplexer is the same as the wavelength corresponding to the fourth port of the other wavelength multiplexer / demultiplexer connected by the fourth port, and a first switching step in which the optical switch outputs an optical signal input from the first port to a first wavelength multiplexer / demultiplexer that is the wavelength multiplexer / demultiplexer connected to the second port, from the second port according to a setting; an optical communication method comprising: a demultiplexing step in which the first wavelength multiplexer / demultiplexer outputs the optical signal input from the third port from a fourth port among the plurality of fourth ports that corresponds to the wavelength of the optical signal to a second wavelength multiplexer / demultiplexer that is another wavelength multiplexer / demultiplexer connected to the fourth port; an output step in which the second wavelength multiplexer / demultiplexer outputs the optical signal input from the fourth port connected to the first wavelength multiplexer / demultiplexer from the third port; and a second switching step in which the optical switch connected to the second wavelength multiplexer / demultiplexer outputs the optical signal input from the second port from the first port that corresponds to settings.

7. An optical communication method executed by an optical communication system comprising two optical switches each having a plurality of first ports and a plurality of second ports, and a plurality of wavelength multiplexers / demultiplexers connected to the second ports of the optical switches, wherein the wavelength multiplexers / demultiplexers have one third port connected to the second port of the optical switch and two fourth ports corresponding to different wavelengths, the fourth port of one of the wavelength multiplexers / demultiplexers is connected to the fourth port of another wavelength multiplexer / demultiplexer connected to the optical switch to which the wavelength multiplexer / demultiplexer is connected, and the fourth port of the other wavelength multiplexer / demultiplexer is connected to the fourth port of another wavelength multiplexer / demultiplexer connected to an optical switch different from the optical switch to which the wavelength multiplexer / demultiplexer is connected, the wavelength corresponding to the fourth port of the wavelength multiplexer / demultiplexer is the same as the wavelength corresponding to the fourth port of the other wavelength multiplexer / demultiplexer connected by the fourth port, an optical communication method comprising: a first switching step in which the optical switch outputs the optical signal input from the first port from the second port according to settings to a first wavelength multiplexer / demultiplexer, which is the wavelength multiplexer / demultiplexer connected to the second port; a demultiplexing step in which the first wavelength multiplexer / demultiplexer outputs the optical signal input from the third port from the fourth port of the two fourth ports according to the wavelength of the optical signal to a second wavelength multiplexer / demultiplexer, which is the other of the wavelength multiplexers / demultiplexers connected to the fourth port; an output step in which the second wavelength multiplexer / demultiplexer outputs the optical signal input from the fourth port connected to the first wavelength multiplexer / demultiplexer from the third port; and a second switching step in which the optical switch connected to the second wavelength multiplexer / demultiplexer outputs the optical signal input from the second port from the first port according to settings.

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