Communication device and optical path opening method

Abstract

This communication device is a first communication device in an optical communication system comprising the first communication device, a second communication device, and a control device for controlling the opening of an optical path between the first communication device and the second communication device, and comprises a first reception unit which receives a downlink control signal that is an optical signal of a predetermined wavelength transmitted from the control device, and a second reception unit which receives a main signal that is an optical signal of a wavelength different from the predetermined wavelength transmitted from the second communication device.

Description

[Technical Field]

[0001] The present invention relates to a communication device and an optical path opening method. [Background technology]

[0002] Research into photonics technology-based APN (All Photonics Network) is underway with the aim of realizing a new network infrastructure that will enable higher speeds and larger capacities, as well as dramatically lower latency and lower power consumption than is possible with current networks (see, for example, Non-Patent Document 1). By providing end-to-end, full-mesh optical path connections that utilize wavelengths, APN can minimize latency and flexibly provide a high-speed, large-capacity network that uses dedicated wavelengths for each function.

[0003] In an APN, when a new subscriber device is connected to the network, the subscriber device management and control unit in the APN controller recognizes the connection, allocates a wavelength from among the unused wavelengths, and instructs the subscriber device to set the wavelength. At the same time, the optical distribution control unit in the APN controller selects the optimal optical route according to the subscriber device's communication partner, and sets the optical route using the optical distribution means in the Ph-GW (Photonic Gateway). In this way, automatic opening of end-to-end optical paths is realized.

[0004] In this way, in conventional optical communication systems, the optical distribution control unit sets the port-to-port connection by the optical distribution means so that the subscriber device can communicate with the subscriber device management and control unit at the time of initial connection. As soon as the registration, authentication, wavelength setting, etc. of the subscriber device are completed, the optical distribution control unit changes the port-to-port connection by the optical distribution unit and opens an optical path that directly connects to the subscriber device with which the communication is to be made. However, in the configuration of conventional optical communication systems, once the optical path is opened, the communication path between the subscriber device and the subscriber device management and control unit is cut off, so that if this is left as it is, there will be no control channel for transmitting control signals from the control unit to the subscriber device.

[0005] Therefore, a method can be considered in which an optical multiplexing / demultiplexing means is provided on the optical fiber transmission line to multiplex / demultiplex the optical signal carrying the main signal and the optical signal carrying the control signal, and a management and control port for communication with the subscriber device after the optical path is opened is provided in the subscriber device management and control unit.By connecting the management and control port for communication with the subscriber device after the optical path is opened to the optical multiplexing / demultiplexing means, the optical communication system can transmit upstream control signals from the subscriber device to the subscriber device management and control unit, and downstream control signals from the subscriber device management and control unit to the subscriber device, even after the optical path is opened. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Takuya Kanai, Kazuaki Honda, Yasunari Tanaka, Makoto Kaneko, Kazutaka Hara, Junichi Kani, Tomoaki Yoshida, “Photonic Gateway Supporting All-Photonics Networks”, Institute of Electronics, Information and Communication Engineers General Conference, B-8-20, March 2021 Summary of the Invention [Problem to be solved by the invention]

[0007] However, before the optical path is opened, the subscriber device cannot receive the downstream control signal unless the wavelength of the downstream control signal transmitted from the management and control port for communication with the subscriber device before the optical path is opened is within the transmission wavelength band of the wavelength filter installed in the subscriber device. Note that this wavelength filter is installed in the upstream stage of the receiver for receiving the control signal. Similarly, after the optical path is opened, the subscriber device cannot receive the downstream control signal unless the wavelength of the downstream control signal transmitted from the management and control port for communication with the subscriber device after the optical path is opened is within the transmission wavelength band of the wavelength filter installed in the subscriber device.

[0008] As such, in the past, there was a problem that before and after the optical path was opened, the subscriber device could not receive the downstream control signal unless the wavelength of the downstream control signal was within the transmission wavelength band of the wavelength filter installed in the subscriber device.

[0009] The present invention has been made in consideration of the above-mentioned technical background, and aims to provide a technology that enables subscriber devices to receive downstream control signals transmitted from a subscriber device management control unit before and after the opening of an optical path, thereby opening an optical path between subscriber devices. [Means for solving the problem]

[0010] One aspect of the present invention is a first communication device in an optical communication system having a first communication device, a second communication device, and a control device that controls the opening of an optical path between the first communication device and the second communication device, the first communication device comprising: a first receiving unit that receives a downstream control signal, which is an optical signal of a predetermined wavelength transmitted from the control device; and a second receiving unit that receives a main signal, which is an optical signal of a wavelength different from the predetermined wavelength transmitted from the second communication device.

[0011] One aspect of the present invention is an optical path opening method in an optical communication system having a first communication device, a second communication device, and a control device that controls the opening of an optical path between the first communication device and the second communication device, the optical path opening method comprising: a first control signal transmitting step in which the control device transmits a downstream control signal at a predetermined wavelength from a first communication port to the first communication device before the optical path is opened; a second control signal transmitting step in which the control device transmits the downstream control signal at a predetermined wavelength to the first communication device from a second port connected to an optical multiplexing means that multiplexes a main signal and the downstream control signal after the optical path is opened; a first receiving step in which the first communication device receives the downstream control signal by a first receiving means capable of receiving an optical signal of the predetermined wavelength; and a second receiving step in which the first communication device receives the main signal by a second receiving means capable of receiving an optical signal of a wavelength different from the predetermined wavelength. [Effects of the Invention]

[0012] The present invention enables subscriber devices to receive downstream control signals transmitted from the subscriber device management control unit before and after the opening of an optical path, thereby enabling the opening of an optical path between subscriber devices. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram for explaining a method for opening an optical path in a conventional optical communication system 1. [Figure 2] FIG. 1 is a diagram showing the overall configuration of a conventional optical communication system 1′. [Figure 3] FIG. 2 is a diagram for explaining an optical path opening method in the optical communication system 1a according to the first embodiment of the present invention. [Figure 4] 3 is a flowchart showing the operation of the optical communication system 1a in the first embodiment of the present invention. [Figure 5] FIG. 1 is a diagram illustrating the overall configuration of an optical communication system 1b according to a first modification of the first embodiment of the present invention. [Figure 6] FIG. 10 is a diagram illustrating the overall configuration of an optical communication system 1c according to a second modification of the first embodiment of the present invention. [Figure 7] FIG. 10 is a diagram illustrating the overall configuration of an optical communication system 1d according to a third modification of the first embodiment of the present invention. [Figure 8] FIG. 10 is a diagram for explaining an optical path opening method in an optical communication system 1e according to a second embodiment of the present invention. [Figure 9] 10 is a flowchart showing the operation of an optical communication system 1e according to the second embodiment of the present invention. [Figure 10] FIG. 10 is a diagram showing the overall configuration of an optical communication system 1f according to a modified example of the second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, a communication device and an optical path opening method according to an embodiment will be described with reference to the drawings.

[0015] For ease of understanding, the following will first describe the configuration of an optical communication system 1, which is an example of a conventional optical communication system. Fig. 1 is a diagram for explaining a method for opening an optical path in the conventional optical communication system 1.

[0016] 1, the conventional optical communication system 1 includes a plurality of subscriber devices #k_1 (k=1, 2, . . .), a plurality of subscriber devices #k_2 (k=1, 2, . . .), an optical distribution unit 10-1 and an optical distribution unit 10-2, a control unit 20-1 and a control unit 20-2, a wavelength multiplexing / demultiplexing unit 30-1 and a wavelength multiplexing / demultiplexing unit 30-2, a plurality of optical fiber transmission lines 50, and an optical communication network (NW) 60. The optical distribution unit 10-1 and the optical distribution unit 10-2 are configured using, for example, an optical switch or the like.

[0017] Hereinafter, as an example, an optical path opening method will be described in the case where subscriber device #k_1 is newly connected to the network and connects to subscriber device #k_2, which will be the communication partner, via the optical fiber transmission line 50, the optical distribution means 10-1, etc. Conversely, the optical path opening method in the case where subscriber device #k_2 is newly connected to the network and connects to subscriber device #k_1, which will be the communication partner, via the optical fiber transmission line 50, the optical distribution means 10-2, etc., is also similar to the configuration described below.

[0018] The light distribution means 10-1 has a plurality of ports. The light distribution means 10-1 is connected to a plurality of optical fiber transmission lines 50. The light distribution means 10-1 outputs an optical signal input from each port to a port that has a connection relationship set as a connection port for that port. The connection relationship between the plurality of ports can be changed and set as desired.

[0019] The subscriber device #k_1 is connected to the optical distribution unit 10-1 via the optical fiber transmission line 50. As shown in the upper diagram of Fig. 1, when the subscriber device #k_1 is initially connected to the network, the optical distribution control unit 22 changes the setting of the inter-port connection by the optical distribution unit 10-1 so that the subscriber device #k_1 and the subscriber device management control unit 21 can communicate with each other.

[0020] When the subscriber device #k_1 initially connects to the network, management and control information required for registering and authenticating the subscriber device #k_1 to the network is exchanged between the subscriber device #k_1 and the subscriber device management and control unit 21. Furthermore, when the subscriber device #k_1 initially connects to the network, management and control information for instructing the emission wavelength to be used by the subscriber device #k_1 is transmitted from the subscriber device management and control unit 21 to the subscriber device #k_1. As a channel for transmitting and receiving such management and control information, for example, an AMCC (Auxiliary Management and Control Channel) or the like can be used.

[0021] 1, as soon as the registration, authentication, wavelength setting, etc. of the subscriber device #k_1 to the network are completed, the optical distribution control unit 22 again changes the setting of the inter-port connection by the optical distribution means 10-1 so that the optical signal transmitted from the subscriber device #k_1 is forwarded to the subscriber device #k_2 with which it is communicating. As a result, the optical communication system 1 can open an optical path that directly connects the subscriber device #k_1 and the subscriber device #k_2.

[0022] However, in such a configuration of the conventional optical communication system 1, once the optical path is opened, the communication path between the subscriber device #k_1 and the subscriber device management and control unit 21 is cut off, and therefore, as shown in the lower diagram of Fig. 1, there is no control channel for transmitting a downstream control signal transmitted from the subscriber device management and control unit 21 to the subscriber device #k_1, or for transmitting an upstream control signal transmitted from the subscriber device #k_1 to the subscriber device management and control unit 21. In this case, the subscriber device management and control unit 21 cannot monitor the status of the optical path and the status of the subscriber device #k_1, or can not control switching of the optical path.

[0023] Therefore, a conceivable method is to provide an optical multiplexing / demultiplexing means 70 on the optical fiber transmission line 50 to multiplex / demultiplex an optical signal carrying a main signal and an optical signal carrying a control signal, and to provide a management and control port for communication with subscriber device #k_1 after the optical path is opened in the subscriber device management and control unit 21. By connecting the management and control port for communication with subscriber device #k_1 after the optical path is opened to the optical multiplexing / demultiplexing means 70, the optical communication system 1 becomes able to transmit upstream control signals from subscriber device #k_1 to the subscriber device management and control unit 21 and downstream control signals from the subscriber device management and control unit 21 to subscriber device #k_1 not only before the optical path is opened but also after the optical path is opened.

[0024] The overall configuration of an optical communication system 1', which is an example of a conventional optical communication system, will be described below. Fig. 2 is an overall configuration diagram of the conventional optical communication system 1'. As shown in Fig. 2, the conventional optical communication system 1' includes a plurality of subscriber devices #k_1 (k = 1, 2, ...), a plurality of subscriber devices #k_2 (k = 1, 2, ...), an optical distribution unit 10-1 and an optical distribution unit 10-2, a control unit 20-1 and a control unit 20-2, a wavelength multiplexing / demultiplexing unit 30-1 and a wavelength multiplexing / demultiplexing unit 30-2, a plurality of optical fiber transmission lines 50, an optical communication network (NW) 60, and a plurality of optical multiplexing / demultiplexing units 70.

[0025] In the following description, among the components of the conventional optical communication system 1' shown in Figure 2, those components having the same configuration as the components of the conventional optical communication system 1 shown in Figure 1 described above will be given the same symbols and will not be described again.

[0026] As shown in Fig. 2, an optical multiplexing / demultiplexing means 70 is provided for each of the multiple optical fiber transmission lines 50. The optical multiplexing / demultiplexing means 70 is configured using, for example, an optical demultiplexer / multiplexer. The subscriber device management and control unit 21 is provided with a management and control port a, which is a management and control port for communication with subscriber device #k_1 before the optical path is opened, and a management and control port b, which is a management and control port for communication with subscriber device #k_1 after the optical path is opened. By connecting the optical multiplexing / demultiplexing means 70 and the management and control port b, the conventional optical communication system 1' can transmit upstream control signals from subscriber device #k_1 to the subscriber device management and control unit 21 and downstream control signals from the subscriber device management and control unit 21 to subscriber device #k_1, respectively, even after the optical path is opened.

[0027] The conventional optical communication system 1' shown in FIG. 2 controls the wavelength of an optical signal carrying a downstream control signal and the wavelength of an optical signal carrying a main signal to be different from each other. As a result, even if the frequency band of the downstream control signal and the frequency band of the main signal overlap, the conventional optical communication system 1' can prevent interference between the main signal and the downstream control signal during reception. Specifically, in the conventional optical communication system 1', subscriber device #k_1 separates the downstream control signal and the main signal, which have different wavelengths, and detects and demodulates the downstream control signal and the main signal, respectively. As a result, subscriber device #k_1 can receive both the downstream control signal and the main signal.

[0028] Before and after the optical path is opened, the subscriber device management and control unit 21 transmits downstream control signals addressed to the same subscriber device #k_1 from different management and control ports. Specifically, as shown in Fig. 1, before the optical path is opened, the subscriber device management and control unit 21 transmits downstream control signals addressed to the subscriber device #k_1 from management and control port a, and after the optical path is opened, it transmits downstream control signals addressed to the subscriber device #k_1 from management and control port b.

[0029] The subscriber device #k_1 is equipped with a wavelength filter (not shown) and has a receiving wavelength selectivity that allows it to select a specific wavelength to receive an optical signal. However, before the optical path is opened, if the wavelength of the downstream control signal transmitted from the management control port a for communication with the subscriber device #k_1 before the optical path is opened is not within the transmission wavelength band of the wavelength filter (not shown) installed in the subscriber device #k_1 at the upstream stage of the receiver for the downstream control signal, the subscriber device #k_1 cannot receive the downstream control signal.

[0030] Similarly, after the optical path is opened, if the wavelength of the downstream control signal transmitted from the management control port b for communication with the subscriber device #k_1 after the optical path is opened is not within the transmission wavelength band of the wavelength filter installed in the front stage of the receiver for the downstream control signal in the subscriber device #k_1, the subscriber device #k_1 will not be able to receive the downstream control signal. An optical communication system in an embodiment of the present invention that can solve such problems will be described below.

[0031] First Embodiment The following describes the optical communication system 1a in the first embodiment. Fig. 3 is a diagram for explaining the optical path opening method in the optical communication system 1a in the first embodiment of the present invention.

[0032] As shown in Figure 3, the optical communication system 1a in the first embodiment is configured to include a plurality of subscriber devices #k_1 (k = 1, 2, ...), a plurality of subscriber devices #k_2 (k = 1, 2, ...), an optical distribution means 10-1 and an optical distribution means 10-2, a control unit 20-1 and a control unit 20-2, a wavelength multiplexing / demultiplexing means 30-1 and a wavelength multiplexing / demultiplexing means 30-2, a plurality of optical fiber transmission paths 50, an optical communication network (NW) 60, and a plurality of optical multiplexing / demultiplexing means 70.

[0033] In the following description, among the components of the optical communication system 1a in the first embodiment shown in Figure 3, those components having the same configuration as the components of the conventional optical communication system 1 shown in Figure 1 above and the components of the conventional optical communication system 1' shown in Figure 2 above will be given the same symbols and will not be described.

[0034] The wavelength λ of the downstream control signal transmitted by the management control port a for communication with the subscriber device #k_2 before the optical path is opened D_1 is set in advance as λ SET where λ SET is a wavelength different from the wavelength that can be assigned to the main signal after the optical path is opened. SET is the same wavelength as the wavelength assigned to the downstream control signal after the optical path is opened.

[0035] For example, a transmitter (not shown) provided in the subscriber equipment management control section 21 that transmits a downstream control signal from management control port a has an emission wavelength of λ SET Alternatively, for example, a wavelength-variable transmitter is used as a transmitter (not shown) provided in the subscriber equipment management and control unit 21 that transmits the downstream control signal from the management and control port a. When a wavelength-variable transmitter is used, the subscriber equipment management and control unit 21 sets the emission wavelength of the wavelength-variable transmitter that transmits the downstream control signal from the management and control port a to λ SET Set to.

[0036] In the optical communication system 1a, the wavelength λ of the downstream control signal is D_1It is not necessary to set a different wavelength for each subscriber device #k_2 (k=1, 2, . . .). That is, the wavelength λ of the downstream control signal transmitted from the management control port a for communication with the subscriber device #k_2 before the optical path is opened is D_1 is λ for all subscriber devices #k_2. SET It may be configured to be fixed at

[0037] The subscriber device #k_2 has a wavelength λ SET A receiver (not shown) for receiving a downstream control signal is set so as to selectively receive the optical signal. As shown in Fig. 3, subscriber device k_2 is provided with a wavelength filter 91-1 in the preceding stage of a receiver (not shown) for receiving a main signal, and a wavelength filter 91-2 in the preceding stage of the receiver for receiving a downstream control signal. As shown in Fig. 3, optical signals demultiplexed by an optical demultiplexing means 93 are input to the wavelength filter 91-1 and the wavelength filter 91-2, respectively. Also, as shown in Fig. 3, subscriber device k_2 is configured to perform direct detection using, for example, a photodiode (PD) 92-1 and a photodiode (PD) 92-2 as optical-to-electrical conversion means.

[0038] In the above configuration, for example, a wavelength filter 91-2 provided in the front stage of the receiver for receiving the downstream control signal is a wavelength λ SET Alternatively, for example, a wavelength-variable filter is used as the wavelength filter 91-2 provided in the front stage of the receiver for receiving the downstream control signal. When a wavelength-variable filter is used, the subscriber device #k_2 receives a signal of wavelength λ SET The wavelength tunable filter (wavelength filter 91-2) is set to transmit the optical signal.

[0039] When a wavelength tunable filter is used as the wavelength filter 91-2, the wavelength tunable filter is set to the wavelength λ SETAlternatively, if a wavelength tunable filter is used as the wavelength filter 91-2, the subscriber device #k_2 may sweep the transmission band of the wavelength tunable filter before the optical path is opened, so that the wavelength of the downstream control signal is set to the wavelength λ SET The configuration may be such that it is detected that the

[0040] In addition, when coherent reception is applied to the reception of the downstream control signal, the subscriber unit #k_2 does not need to be equipped with the wavelength filter 91-1 and the wavelength filter 91-2. In this case, the subscriber unit #k_2 does not need to use the wavelength λ SET and selectively demodulates the optical signal of the downstream control signal and the beat component of the local light.

[0041] In addition, after the optical path is opened, the wavelength λ of the downstream control signal transmitted by the management control port b for communication with the subscriber device #k_2 is D_2 The wavelength λ of the downstream control signal transmitted by the management control port a is D_1 Similarly, the wavelength λ SET Therefore, for example, a transmitter (not shown) that transmits a downstream control signal from management control port b has an emission wavelength of λ SET A wavelength-locked transmitter can be used where:

[0042] Alternatively, for example, a tunable wavelength transmitter is used as a transmitter (not shown) that transmits a downstream control signal from management control port b. When a tunable wavelength transmitter is used, the subscriber device management control section 21 sets the emission wavelength of the tunable wavelength transmitter that transmits the downstream control signal from management control port b to λ SET Set to.

[0043] It is also possible to configure an optical distribution means other than the optical distribution means 10-2 to be disposed between the management control port b of the subscriber device management control unit 21 and the optical multiplexing and demultiplexing means 70, so that the output of the management control port b is distributed to the optical multiplexing and demultiplexing means 70 according to the destination of the downstream control signal. In this case, the number of management control ports b can be reduced.

[0044] In addition, if the wavelength filter 91-2 provided in the front stage of the receiver (not shown) for receiving the downstream control signal in the subscriber device #k_2 has wavelength tunability, the subscriber device #k_2 continues to use the wavelength λ SET The setting of the transmission wavelength of the wavelength filter 91-2 may be maintained so as to transmit the signal.

[0045] When coherent reception is applied to the reception of the downstream control signal, the subscriber unit #k_2 continues to set the wavelength of the local light to the wavelength λ SET The settings are maintained so that they are close to each other, and the beat component of the optical signal of the downstream control signal and the local light can be selectively demodulated.

[0046] On the other hand, the subscriber device #k_1 (k=1, 2, 3, . . . ) transmits the upstream control signal to the subscriber device management and control unit 21 at a wavelength different from that of the main signal. Alternatively, the subscriber device #k_1 (k=1, 2, 3, . . . ) may frequency-multiplex the upstream control signal to be transmitted to the subscriber device management and control unit 21 onto the same wavelength as the main signal and transmit it.

[0047] In the case where the upstream control signal is transmitted at a wavelength different from that of the main signal (the former case), if the configuration is such that light of a wavelength different from that of the main signal transmitted from the subscriber device #k_1 does not reach the subscriber device #k_2, which is the communication partner, the subscriber device #k_1 transmits the upstream control signal at a wavelength λ D_2 It may be transmitted by

[0048] For example, as shown in Figure 3, if a wavelength multiplexing / demultiplexing means 30-1 is inserted in the optical fiber transmission line 50, an optical signal having a wavelength different from the wavelength of the main signal transmitted from subscriber device #k_1 cannot pass through the wavelength multiplexing / demultiplexing means 30-1 and does not reach the communicating subscriber device #k_2. Therefore, since the optical signal of the upstream control signal is not input to the communicating subscriber device #k_2, the wavelength of the optical signal of the upstream control signal is the same wavelength λ as the wavelength of the optical signal of the downstream control signal. D_2Even if this is the case, the communicating subscriber device #k_2 can receive the downstream control signal without interference with other signals.

[0049] 3, the optical multiplexing / demultiplexing unit 70 is disposed between the optical distribution unit 10-1 and the wavelength multiplexing / demultiplexing unit 30-1, and between the optical distribution unit 10-2 and the wavelength multiplexing / demultiplexing unit 30-2, but the present invention is not limited to this configuration. For example, the optical multiplexing / demultiplexing unit 70 may be disposed between the optical distribution unit 10-1 and the subscriber device #k_1, and between the optical distribution unit 10-2 and the subscriber device #k_2.

[0050] 3, it is assumed that rightward signals (from subscriber device #k_1 to subscriber device #k_2) and leftward signals (from subscriber device #k_2 to subscriber device #k_1) travel through the same optical fiber core, but the present invention is not limited to such a configuration. For example, the present invention may be configured such that there are sections in which rightward signals and leftward signals travel through different optical fiber cores.

[0051] 3, it is assumed that the optical communication system 1a in the first embodiment uses wavelength multiplexing means without wavelength selectivity, such as an optical coupler, as the optical multiplexing / demultiplexing means 70 to multiplex an optical signal carrying a downstream control signal and an optical signal carrying a main signal, but the present invention is not limited to this configuration. For example, it is also possible to use wavelength multiplexing means with wavelength selectivity, such as a wavelength filter, as the optical multiplexing / demultiplexing means 70.

[0052] 3, the optical distribution unit 10-1 and the optical distribution unit 10-2 are configured using, for example, a fiber cross connect (FXC) that outputs light input from each port to another port (which is set as a connection port corresponding to the input port) regardless of wavelength. For example, the optical distribution unit 10-1 and the optical distribution unit 10-2 may be a space optical switch using a micro electro mechanical system (MEMS) or a piezoelectric actuator.

[0053] [Operation of optical communication system] An example of the operation of the optical communication system 1a will be described below. Fig. 4 is a flowchart showing the operation of the optical communication system 1a in the first embodiment of the present invention.

[0054] Before the optical path between the subscriber device #k_1 and the subscriber device #k_2 is opened, the subscriber device management control unit 21 of the control unit 20-2 transmits a downstream control signal with a wavelength λ from a management control port a for communication with the subscriber device #k_2 before the optical path is opened. SET The subscriber device #k_2 transmits the signal at wavelength λ SET The downstream control signal is received by a receiver that can selectively receive the optical signal (step S002).

[0055] After the optical path between the subscriber device #k_1 and the subscriber device #k_2 is opened, the subscriber device management control unit 21 of the control unit 20-2 transmits the downstream control signal at wavelength λ from a management control port b for communication with the subscriber device #k_2 after the optical path is opened, which is connected to the optical multiplexing / demultiplexing means 70 that multiplexes the main signal and the downstream control signal. SET The subscriber device #k_2 transmits the signal at wavelength λ SET The downstream control signal is received by a receiver that can selectively receive the optical signal (step S004).

[0056] In addition, the subscriber device #k_2 has a wavelength λ SET different wavelength λS The main signal is received by a receiver that can selectively receive the optical signal (step S005). With this, the operation of the optical communication system 1a shown in the flowchart of FIG.

[0057] [Modification 1 of the First Embodiment] FIG. 5 is a diagram showing the overall configuration of an optical communication system 1b according to the first modification of the first embodiment of the present invention.

[0058] As shown in Figure 5, the optical communication system 1b in variant 1 of the first embodiment is configured to include a plurality of subscriber devices #k_1 (k = 1, 2, ...), a plurality of subscriber devices #k_2 (k = 1, 2, ...), optical distribution means 10-1 and optical distribution means 10-2, control units 20-1 and 20-2, a plurality of optical fiber transmission paths 50, an optical communication network (NW) 60, and a plurality of optical multiplexing / demultiplexing means 70.

[0059] In the following description, among the components of the optical communication system 1b in the first embodiment variation 1 shown in Figure 5, those components having the same configuration as the components of the optical communication system 1a of the first embodiment shown in Figure 3 above will be given the same symbols and will not be described.

[0060] As shown in Fig. 5, the optical communication system 1b in the first modification of the first embodiment is configured without the wavelength multiplexing / demultiplexing means 30-1 and the wavelength multiplexing / demultiplexing means 30-2, unlike the optical communication system 1a in the first embodiment shown in Fig. 3. Therefore, in the optical communication system 1b in the first modification of the first embodiment, an optical signal having a wavelength different from the wavelength of the main signal transmitted from the subscriber device #k_1 reaches the communicating subscriber device #k_2 without being blocked.

[0061] In such a configuration, the subscriber device #k_1 transmits an upstream control signal with a wavelength λ D_2 The wavelength filter 91-2 provided in the preceding stage of a receiver (not shown) for receiving downstream control signals in the subscriber device #k_2 of the communication partner transmits the signal at a wavelength other than λ D_2The downstream control signal with wavelength λ D_2 Therefore, the communicating subscriber device #k_2 can receive the downstream control signal without interference with other signals.

[0062] [Modification 2 of the First Embodiment] FIG. 6 is a diagram showing the overall configuration of an optical communication system 1c according to the second modification of the first embodiment of the present invention.

[0063] As shown in Figure 6, the optical communication system 1c in variant example 2 of the first embodiment is configured to include a plurality of subscriber devices #k_1 (k = 1, 2, ...), a plurality of subscriber devices #k_2 (k = 1, 2, ...), an optical distribution means 10-1 and an optical distribution means 10-2, a control unit 20-1 and a control unit 20-2, a wavelength multiplexing / demultiplexing means 30-1 and a wavelength multiplexing / demultiplexing means 30-2, a plurality of optical fiber transmission paths 50, and an optical communication network (NW) 60.

[0064] In the following description, among the components of the optical communication system 1c in the variant 2 of the first embodiment shown in Figure 6, those components having the same configuration as the components of the optical communication system 1a of the first embodiment shown in Figure 3 above will be given the same symbols and will not be described.

[0065] In the optical communication system 1c according to the second modification of the first embodiment, the optical distribution unit 10-1 and the optical distribution unit 10-2 can set a transmission path for each wavelength. In this case, as shown in Fig. 6, by inputting a downstream control signal from a port other than the port to which the main signal is input, it is possible to multiplex an optical signal carrying the main signal and an optical signal carrying the downstream control signal. For example, an arrayed waveguide grating (AWG) or a wavelength selective switch (WSS) is used as the optical distribution unit 10-1 and the optical distribution unit 10-2.

[0066] [Modification 3 of the First Embodiment] FIG. 7 is a diagram showing the overall configuration of an optical communication system 1d according to a third modification of the first embodiment of the present invention.

[0067] As shown in Figure 7, the optical communication system 1d in variant example 3 of the first embodiment is configured to include a plurality of subscriber devices #k_1 (k = 1, 2, ...), a plurality of subscriber devices #k_2 (k = 1, 2, ...), an optical distribution means 10-1 and an optical distribution means 10-2, a control unit 20-1 and a control unit 20-2, a plurality of optical fiber transmission paths 50, and an optical communication network (NW) 60.

[0068] In the following description, among the components of the optical communication system 1d in the variant 3 of the first embodiment shown in Figure 7, those components having the same configuration as the components of the optical communication system 1a of the first embodiment shown in Figure 3 above will be given the same symbols and will not be described.

[0069] The optical communication system 1c in the second modification of the first embodiment shown in Fig. 6 described above is configured to wavelength-multiplex each optical path by wavelength multiplexing / demultiplexing means 30-1 and wavelength multiplexing / demultiplexing means 30-2 configured by, for example, AWG or WSS, etc. However, because the optical distribution means 10-1 and the optical distribution means 10-2 can wavelength-multiplex each optical path, it is possible to omit the wavelength multiplexing / demultiplexing means 30-1 and wavelength multiplexing / demultiplexing means 30-2 as shown in Fig. 7.

[0070] In the configuration of the optical communication system 1d in the third modification of the first embodiment shown in FIG. 7, a multicast switch (MCS) can also be used as the light distribution unit 10-1 and the light distribution unit 10-2.

[0071] <Second embodiment> The optical communication system 1e according to the second embodiment will be described below. Fig. 8 is a diagram for explaining an optical path opening method in the optical communication system 1e according to the second embodiment of the present invention.

[0072] As shown in Figure 8, the optical communication system 1e in the second embodiment is configured to include a plurality of subscriber devices #k_1 (k = 1, 2, ...), a plurality of subscriber devices #k_2 (k = 1, 2, ...), an optical distribution means 10-1 and an optical distribution means 10-2, a control unit 20-1 and a control unit 20-2, a wavelength multiplexing / demultiplexing means 30-1 and a wavelength multiplexing / demultiplexing means 30-2, a plurality of optical fiber transmission paths 50, an optical communication network (NW) 60, and a plurality of optical multiplexing / demultiplexing means 70.

[0073] In the following description, among the components of the optical communication system 1e of the second embodiment shown in Figure 8, those components having the same configuration as the components of the optical communication system 1a of the first embodiment shown in Figure 3 above will be given the same symbols and will not be described again.

[0074] The configuration of the optical communication system 1e according to the second embodiment shown in FIG. 8 differs from the configuration of the optical communication system 1a according to the first embodiment shown in FIG. 3 in that the wavelength λ of the downstream control signal transmitted from the management control port a for communication with the subscriber device #k_2 before the optical path is opened is 1. D_1 and the wavelength λ of the downstream control signal transmitted by the management control port b for communication with the subscriber device #k_2 after the optical path is opened. D_2 However, these are not necessarily the same.

[0075] Therefore, in the optical communication system 1e according to the second embodiment, the wavelength λ of the downstream control signal transmitted from the management control port a for communication with the subscriber device #k_2 before the optical path is opened to the subscriber device #k_2 is set to λ . D_2 will be notified in advance.

[0076] In addition, the wavelength λ of the main signal assigned to the subscriber device #k_2 is transmitted from the management control port a for communication with the subscriber device #k_2 before the optical path is opened to the subscriber device #k_2. S The wavelength λ of the main signal is also notified. S The timing at which the wavelength λ of the downstream control signal is notified is D_2This may be at the same time as the notification of the above, or at different times.

[0077] The subscriber device #k_2 has a wavelength λ D_2 A receiver (not shown) for receiving downstream control signals is set so as to selectively receive the signals. As shown in Fig. 8, subscriber device k_2 is provided with a wavelength filter 91-1 in the preceding stage of a receiver (not shown) for receiving main signals, and a wavelength filter 91-2 in the preceding stage of the receiver for receiving downstream control signals. As shown in Fig. 8, optical signals demultiplexed by an optical demultiplexing means 93 are input to the wavelength filter 91-1 and the wavelength filter 91-2, respectively. As shown in Fig. 8, subscriber device k_2 is configured to perform direct detection using, for example, a photodiode (PD) 92-1 and a photodiode (PD) 92-2 as optical-to-electrical conversion means.

[0078] In the above configuration, for example, a wavelength tunable filter is used as the wavelength filter 91-2 provided in the front stage of the receiver for receiving the downstream control signal. D_2 The wavelength tunable filter (wavelength filter 91-2) is set to transmit the signal.

[0079] In addition, when coherent reception is applied to the reception of the downstream control signal, the subscriber unit #k_2 does not need to be equipped with the wavelength filter 91-1 and the wavelength filter 91-2. In this case, the subscriber unit #k_2 does not need to set the wavelength of the local light to the notified wavelength λ D_2 Set it to be close to .

[0080] [Operation of optical communication system] An example of the operation of the optical communication system 1e will be described below. Fig. 9 is a flowchart showing the operation of the optical communication system 1e in the second embodiment of the present invention.

[0081] Before the optical path between the subscriber device #k_1 and the subscriber device #k_2 is opened, the subscriber device management control unit 21 of the control unit 20-2 transmits a downstream control signal with a wavelength λ from a management control port a for communication with the subscriber device #k_2 before the optical path is opened. D_1 The subscriber device #k_2 transmits the signal at wavelength λ D_1 The downstream control signal is received by a receiver that can selectively receive the optical signal (step 1002).

[0082] Before the optical path between the subscriber device #k_1 and the subscriber device #k_2 is opened, the subscriber device management control unit 21 of the control unit 20-2 sends a signal of wavelength λ 1 to the management control port a for communication with the subscriber device #k_2 before the optical path is opened. D_1 The wavelength λ of the downstream control signal after the optical path is opened is D_2 to the subscriber device #k_2 (step S103).

[0083] After the optical path between the subscriber device #k_1 and the subscriber device #k_2 is opened, the subscriber device management control unit 21 of the control unit 20-2 transmits the downstream control signal at wavelength λ from a management control port b for communication with the subscriber device #k_2 after the optical path is opened, which is connected to the optical multiplexing / demultiplexing means 70 that multiplexes the main signal and the downstream control signal. D_2 The subscriber device #k_2 transmits the signal at wavelength λ D_2 The downstream control signal is received by a receiver that can selectively receive the optical signal (step S105).

[0084] In addition, the subscriber device #k_2 has a wavelength λ D_1 and wavelength λ D_2 different wavelength λ S The main signal is received by a receiver that can selectively receive the optical signal (step S106). With this, the operation of the optical communication system 1e shown in the flowchart of FIG.

[0085] [Modification of the second embodiment] FIG. 10 is a diagram showing the overall configuration of an optical communication system 1f according to a modified example of the second embodiment of the present invention.

[0086] As shown in Figure 10, the optical communication system 1f in the modified example of the second embodiment is configured to include a plurality of subscriber devices #k_1 (k = 1, 2, ...), a plurality of subscriber devices #k_2 (k = 1, 2, ...), an optical distribution means 10-1 and an optical distribution means 10-2, a control unit 20-1 and a control unit 20-2, a plurality of optical fiber transmission paths 50, an optical communication network (NW) 60, and a plurality of optical multiplexing / demultiplexing means 70.

[0087] In the following description, among the components of the optical communication system 1f in the modified example of the second embodiment shown in Figure 10, those components having the same configuration as the components of the optical communication system 1a of the first embodiment shown in Figure 3 above will be given the same symbols and will not be described.

[0088] In the optical communication system 1f according to the modification of the second embodiment, the management control port b for communication with the subscriber device #k_2 after the optical path is opened switches the wavelength of the optical signal output from the management control port b according to the destination of the downstream control signal. Here, the wavelength assigned to the optical path connecting the subscriber device #k_1 and the subscriber device #k_2 is λ S #k, and the FSR (Free Spectral Range) of the wavelength multiplexing / demultiplexing means 30-1 and the wavelength multiplexing / demultiplexing means 30-2 is Δλ FSR In this case, the management control port b has a wavelength λ of the downstream control signal to the subscriber device #k_1 and the subscriber device #k_2. D_2 #k is set as shown in the following equation (1).

[0089] λ D_2 #k=λ S #k±Δλ FSR ×h(h=1,2,3,...) (1)

[0090] By adopting such a configuration, the number of management control ports b can be reduced.

[0091] The subscriber device #k_1 and the subscriber device #k_2 have a wavelength λ of a downstream control signal transmitted from the management control port b for communication with the subscriber devices after the optical path is opened. D_2 #k is recognized by a notification sent in advance from a management control port a for communication with a subscriber device before the optical path is opened.

[0092] In addition, from the management control port a for communication with the subscriber device before the optical path is opened, the wavelength λ of the main signal is transmitted to the subscriber device #k_1 and the subscriber device #k_2. S #k, and the wavelength λ of the downstream control signal D_2 #k may be notified in advance.

[0093] Alternatively, the wavelength λ of the main signal is transmitted from the management control port a for communication with the subscriber device before the optical path is opened to the subscriber device #k_1 and the subscriber device #k_2. S The wavelength λ of the main signal may be notified in advance. S When only #k is notified in advance, the subscriber device #k_1 and the subscriber device #k_2 receive the wavelength λ 1 that satisfies the above equation (1). D_2 A receiver (not shown) for receiving downstream control signals may be set so as to selectively receive the #k optical signal.

[0094] As explained above, the optical communication system in each of the above-mentioned embodiments and modifications of each embodiment includes an optical multiplexing / demultiplexing means 70 on the optical fiber transmission line 50, and also includes management control ports for communication with subscriber devices before and after the opening of an optical path in the subscriber device management control section 21. The above-mentioned optical communication system also includes an optical demultiplexing means 93, wavelength filters 91-1 and 91-2 in front of a receiver (not shown) for receiving a main signal and a receiver (not shown) for receiving a downstream control signal provided in the subscriber device.

[0095] By providing such a configuration, according to the optical communication systems in the above-described embodiments and modifications of the embodiments, a subscriber device equipped with a receiver (not shown) having wavelength selectivity in receiving a downstream control signal can receive a downstream control signal transmitted from the subscriber device management and control unit 21 before an optical path is opened. This makes it possible to exchange control signals between the subscriber device and the management and control port a of the subscriber device management and control unit 21 before an optical path is opened, thereby enabling the opening of an optical path between subscriber devices.

[0096] Furthermore, by providing such a configuration, according to the optical communication systems in the above-described embodiments and modifications of the embodiments, a subscriber device equipped with a receiver (not shown) having wavelength selectivity in receiving a downstream control signal can receive the downstream control signal transmitted from the subscriber device management and control unit 21 without interfering with other signals after the optical path is opened. This makes it possible to exchange control signals between the subscriber device and the management and control port b of the subscriber device management and control unit 21 after the optical path is opened, and enables the subscriber device management and control unit 21 to monitor the status of the optical path and the subscriber device, and to control the switching of the optical path.

[0097] According to the above-described embodiment, the communication device is a first communication device in an optical communication system having a first communication device, a second communication device, and a control device that controls opening of an optical path between the first communication device and the second communication device. For example, the first communication device is subscriber device #k_2 in the embodiment, the second communication device is subscriber device #k_1 in the embodiment, the control device is control unit 20-2 in the embodiment, and the optical communication system is optical communication system 1a to optical communication system 1f in the embodiment.

[0098] The above communication device includes a first receiving unit and a second receiving unit. The first receiving unit receives a downstream control signal, which is an optical signal with a predetermined wavelength transmitted from a control device. The second receiving unit receives a main signal, which is an optical signal with a wavelength different from the predetermined wavelength transmitted from a second communication device. For example, the first receiving unit is a photodiode (PD) 92-2 in the embodiment, and the second receiving unit is a photodiode (PD) 92-1 in the embodiment. Also, for example, the predetermined wavelength is a wavelength λ in the embodiment. SET , wavelength λ D_1 or wavelength λ D_2 and the wavelength different from the predetermined wavelength is the wavelength λ in the embodiment. S is.

[0099] In the above communication device, the downstream control signal may be an optical signal transmitted from a first communication port of the control device before the optical path is opened, and may be an optical signal transmitted from a second communication port of the control device different from the first communication port after the optical path is opened, and demultiplexed from an optical signal multiplexed with a main signal and transmitted. For example, the first communication port is management control port a in the embodiment, and the second communication port is management control port b in the embodiment.

[0100] The communication device may further include a first wavelength filter and a second wavelength filter. For example, the first wavelength filter is wavelength filter 91-2 in the embodiment, and the second wavelength filter is wavelength filter 91-1 in the embodiment. The first wavelength filter is provided before the first receiving unit and can selectively receive an optical signal of a predetermined wavelength. The second wavelength filter is provided before the second receiving unit and can selectively receive an optical signal of a wavelength different from the predetermined wavelength.

[0101] The communication device may further include an optical demultiplexer. For example, the optical demultiplexer is the optical demultiplexing means 93 in the embodiment. The optical demultiplexer demultiplexes an optical signal obtained by combining the main signal transmitted from the second communication device and the downstream control signal transmitted from the control device, and distributes the demultiplexed optical signal to the first wavelength filter and the second wavelength filter.

[0102] In the above communication device, the first receiving unit may receive a downstream control signal including wavelength switching information indicating the wavelength of the downstream control signal to be received after the optical path is opened, transmitted from the control device before the optical path is opened, and may change the setting to receive a downstream control signal of a wavelength based on the wavelength switching information after the optical path is opened. For example, the wavelength of the downstream control signal to be received after the optical path is opened may be wavelength λ in the embodiment. D_2 is.

[0103] In the above communication device, the wavelengths included in the wavelength switching information may be wavelengths that are assigned to the plurality of first communication devices so as to be different from one another.

[0104] In the above communication device, the wavelengths allocated to each of the plurality of first communication devices so as to be different from one another may be wavelengths allocated so that the frequency difference between the wavelength of the main signal received by the first communication device and the wavelength of the main signal is an integer multiple of the resonant frequency spacing (FSR) in the wavelength multiplexing / demultiplexing means provided in the communication path between the first communication device and the second communication device. For example, the resonant frequency spacing in the wavelength multiplexing / demultiplexing means is an integer multiple of the FSR (Δλ) of the wavelength multiplexing / demultiplexing means 30-1 and the wavelength multiplexing / demultiplexing means 30-2 in the embodiment. FSR )

[0105] The above communication device may further include a first transmitter and a second transmitter. For example, the first transmitter is a transmitter (not shown) in the embodiment that transmits a main signal from subscriber device #k_2 to subscriber device #k_2, and the second transmitter is a transmitter (not shown) in the embodiment that transmits an upstream control signal from subscriber device #k_2 to control unit 20-2. The first transmitter transmits a main signal to the second communication device. The second transmitter transmits the upstream control signal to the control device at a wavelength different from the wavelength used for transmitting the main signal, or transmits the upstream control signal by frequency-multiplexing it with the same wavelength as the wavelength used for transmitting the main signal.

[0106] Furthermore, according to the above-described embodiment, the optical communication system includes a first communication device, a second communication device, and a control device that controls the opening of an optical path between the first communication device and the second communication device. For example, the optical communication system is optical communication system 1a to optical communication system 1f in the embodiment, the first communication device is subscriber device #k_2 in the embodiment, the second communication device is subscriber device #k_1 in the embodiment, and the control device is control unit 20-2 in the embodiment.

[0107] The control device transmits a downstream control signal at a predetermined wavelength from a first communication port to the first communication device before the optical path is opened. After the optical path is opened, the control device transmits a downstream control signal at a predetermined wavelength from a second port connected to an optical multiplexing means that multiplexes a main signal and the downstream control signal to the first communication device. For example, the first communication port is a management control port a in the embodiment, and the predetermined wavelength is wavelength λ in the embodiment. SET , wavelength λ D_1 or wavelength λ D_2 The second communication port is the management control port b in the embodiment, and the optical multiplexing means is the optical multiplexing / demultiplexing means 70 in the embodiment.

[0108] The first communication device receives a downstream control signal by a first receiving means capable of receiving an optical signal of a predetermined wavelength. The first communication device also receives a main signal by a second receiving means capable of receiving an optical signal of a wavelength different from the predetermined wavelength. For example, the first receiving means is a photodiode (PD) 92-2 in the embodiment, and the wavelength different from the predetermined wavelength is a wavelength λ in the embodiment. S and the second receiving means is a photodiode (PD) 92-1 in the embodiment.

[0109] The control device may transmit, before the optical path is opened, a downstream control signal including wavelength switching information indicating the wavelength of the downstream control signal to be received after the optical path is opened to the first communication device. For example, the wavelength of the downstream control signal to be received after the optical path is opened may be the wavelength λ D_2 is.

[0110] A part of the configuration of the optical communication systems 1a to 1f in the above-described embodiments may be implemented by a computer. In this case, a program for implementing the functions may be recorded on a computer-readable recording medium, and the program may be loaded into a computer system and executed. Note that the term "computer system" as used herein includes hardware such as an OS and peripheral devices. Furthermore, the term "computer-readable recording medium" 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, the term "computer-readable recording medium" may also include devices that dynamically store programs for a short period of time, such as communication lines used when transmitting programs via networks such as the Internet or communication lines such as telephone lines, or devices that store programs for a fixed period of time, such as volatile memory within a computer system that serves as a server or client. The program may be for implementing a part of the above-described functions, or may be capable of implementing the above-described functions in combination with a program already stored in the computer system, or may be implemented using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0111] Although an embodiment of the present invention has been described in detail above 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. [Explanation of symbols]

[0112] 1, 1', 1a to 1f... optical communication system, 10-1, 10-2... optical distribution means, 20-1, 20-2... control unit, 21... subscriber device management control unit, 22... optical distribution control unit, 30-1, 30-2... wavelength multiplexing / demultiplexing means, 50... optical fiber transmission line, 60... optical communication network (NW), 70... optical multiplexing / demultiplexing means, 91-1, 91-2... wavelength filter, 92-1, 92-2... photodiode (PD), 93... optical demultiplexing means

Claims

1. 1. A first communication device in an optical communication system including a first communication device, a second communication device, and a control device that controls opening of an optical path between the first communication device and the second communication device, a first receiving unit that receives a downstream control signal, which is an optical signal with a predetermined wavelength, transmitted from the control device; a second receiving unit that receives a main signal that is an optical signal having a wavelength different from the predetermined wavelength transmitted from the second communication device; Equipped with The downstream control signal is an optical signal transmitted from a first communication port of the control device before the optical path is opened, and is an optical signal transmitted from a second communication port of the control device that is different from the first communication port after the optical path is opened. Communication equipment.

2. After the optical path is opened, the downstream control signal is an optical signal demultiplexed from the optical signal that is multiplexed with the main signal and transmitted. The communication device according to claim 1 .

3. a first wavelength filter provided in front of the first receiving unit and capable of selectively receiving an optical signal of the predetermined wavelength; a second wavelength filter provided in front of the second receiving unit and capable of selectively receiving an optical signal having a wavelength different from the predetermined wavelength; Further equipped 3. The communication device according to claim 1 or 2.

4. an optical demultiplexer that demultiplexes an optical signal obtained by combining the main signal transmitted from the second communication device and the downstream control signal transmitted from the control device, and distributes the demultiplexed signal to the first wavelength filter and the second wavelength filter; Further equipped The communication device according to claim 3 .

5. A first communication device in an optical communication system having a second communication device, and a control device that controls opening of an optical path between the first communication device and the second communication device, a first receiving unit that receives a downstream control signal, which is an optical signal with a predetermined wavelength, transmitted from the control device; a second receiving unit that receives a main signal that is an optical signal having a wavelength different from the predetermined wavelength transmitted from the second communication device; Equipped with the first receiving unit receives the downstream control signal, which is transmitted from the control device before the optical path is opened, and which includes wavelength switching information indicating a wavelength of the downstream control signal to be received after the optical path is opened; After the optical path is opened, the setting is changed so that the downstream control signal of the wavelength based on the wavelength switching information is received. Communication equipment.

6. The wavelengths included in the wavelength switching information are wavelengths that are assigned differently to each of the plurality of first communication devices. The communication device according to claim 5 .

7. 1. An optical path opening method in an optical communication system having a first communication device, a second communication device, and a control device that controls opening of an optical path between the first communication device and the second communication device, comprising: a first control signal transmitting step in which the control device transmits a downstream control signal at a predetermined wavelength from a first communication port to the first communication device before the optical path is opened; a second control signal transmitting step in which, after the optical path is opened, the control device transmits the downstream control signal at a predetermined wavelength from a second port connected to an optical multiplexing means that multiplexes a main signal and the downstream control signal to the first communication device; a first receiving step in which the first communication device receives the downstream control signal by a first receiving means capable of receiving an optical signal of the predetermined wavelength; a second receiving step in which the first communication device receives the main signal by a second receiving means capable of receiving an optical signal having a wavelength different from the predetermined wavelength; An optical path opening method comprising:

8. a third control signal transmission step in which the control device transmits, before the optical path is opened, the downstream control signal including wavelength switching information indicating the wavelength of the downstream control signal to be received after the optical path is opened to the first communication device; The optical path establishing method according to claim 7, further comprising:

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