Optical communication device, control device, and control system

Abstract

Select a transmission wavelength suitable for light propagation in free space. [Solution] The optical communication device comprises an optical transmitting unit that transmits a main signal, which is an optical signal, into free space, and a control unit that controls the wavelength of the main signal transmitted by the optical transmitting unit.

Description

Technical Field

[0001] The present disclosure relates to an optical communication device, a control device, and a control system.

Background Art

[0002] Free Space Optical Communication (FSOC), which propagates optical signals in free space for communication, is known. Non-Patent Document 1 discloses a modular FSO transceiver used for FSOC. Here, "free space" refers to a space such as the atmosphere, outer space, or vacuum space that does not include a solid optical transmission medium such as an optical fiber cable.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] It has been considered to introduce FSOC into a transmission system including at least one of a wired electrical communication network, a wireless communication network, and an optical wired communication network. In order to appropriately transmit signals in a transmission system in which FSOC is introduced, it is necessary to select a transmission wavelength that allows light to propagate in free space. However, the modular FSO transceiver disclosed in Non-Patent Document 1 can only transmit light of a predetermined wavelength and cannot necessarily meet such requirements.

Means for Solving the Problems

[0005] An optical communication device according to one aspect of the present disclosure comprises an optical transmitting unit that transmits a main signal, which is an optical signal, into free space, and a control unit that controls the wavelength of the main signal transmitted by the optical transmitting unit. [Effects of the Invention]

[0006] According to this disclosure, it becomes possible to select a transmission wavelength suitable for the propagation of light in free space. [Brief explanation of the drawing]

[0007] [Figure 1A] Figure 1A is a diagram showing a first example of the configuration of a communication system according to an embodiment. [Figure 1B] Figure 1B shows a second example of the configuration of a communication system according to the embodiment. [Figure 2A] Figure 2A is a perspective view showing a first example of the external configuration of an FSOC device according to an embodiment. [Figure 2B] Figure 2B is a perspective view showing a second example of the external configuration of the FSOC apparatus according to the embodiment. [Figure 3] Figure 3 is a block diagram showing an example of the hardware configuration of an FSOC device according to this embodiment. [Figure 4] Figure 4 is a block diagram showing an example of the hardware configuration of a processing circuit. [Figure 5] Figure 5 is a functional block diagram showing an example of the functions of a processing circuit. [Figure 6] Figure 6 is a block diagram showing an example of the configuration of a control device according to this embodiment. [Figure 7] Figure 7 is a flowchart showing an example of the initialization process of the FSOC device according to the embodiment. [Figure 8] Figure 8 is a sequence diagram showing an example of the operation of the control system according to the embodiment. [Modes for carrying out the invention]

[0008] <Summary of the embodiments of this disclosure> The embodiments of this disclosure are outlined below.

[0009] (1) The optical communication device according to this embodiment includes an optical transmitting unit that transmits a main signal, which is an optical signal, to free space, and a control unit that controls the wavelength of the main signal transmitted by the optical transmitting unit. This makes it possible to select a transmission wavelength suitable for the propagation of light in free space.

[0010] (2) In (1) above, the optical transmitting unit includes a first transmitting unit that transmits an optical signal of a first wavelength and a second transmitting unit that transmits an optical signal of a second wavelength different from the first wavelength, and the control unit may select either the transmission of the main signal of the first wavelength by the first transmitting unit or the transmission of the main signal of the second wavelength by the second transmitting unit. This makes it possible to select the transmission wavelength of the main signal from the first wavelength and the second wavelength.

[0011] (3) In (2) above, the first transmitting unit transmits the main signal received from the outside without changing the wavelength of the main signal, and the optical communication device further comprises a wavelength conversion unit that converts the wavelength of the main signal received from the outside from the first wavelength to the second wavelength, and the second transmitting unit transmits the main signal of the second wavelength output from the wavelength conversion unit. This makes it possible to select the first wavelength as the transmission wavelength when the main signal can propagate in free space by the wavelength of the main signal received from the outside (first wavelength), and to select the second wavelength as the transmission wavelength when the main signal can propagate in free space by the second wavelength.

[0012] (4) In any one of (1) to (3) above, the optical transmitting unit includes a first optical transmitting unit capable of transmitting the main signal and a second optical transmitting unit capable of transmitting the main signal, and the control unit may select one of the first optical transmitting unit and the second optical transmitting unit as the source of the main signal. This allows the optical communication device to control the transmission wavelength of the main signal and to select the source of the main signal from the first optical transmitting unit and the second optical transmitting unit.

[0013] (5) In the above (4), the first optical transmission unit may be included in a first path in the communication network, and the second optical transmission unit may be included in a second path that is a redundant path of the first path in the communication network. Thereby, the transmission path of the optical signal can be controlled.

[0014] (6) In the above (4), when there is no abnormality in the first optical transmission unit, the control unit may select the first optical transmission unit as the transmission source, and when an abnormality has occurred in the first optical transmission unit, the control unit may select the second optical transmission unit as the transmission source. Thereby, even when an abnormality occurs in the first optical transmission unit, the transmission of the main signal can be continued.

[0015] (7) In any one of the above (1) to (6), the optical communication device includes a reception unit that receives a control signal including control information transmitted from a control device, and the control unit may control the wavelength of the main signal transmitted by the optical transmission unit based on the control information included in the control signal received by the reception unit. Thereby, the transmission wavelength of the main signal of the optical communication device can be remotely controlled by the control device.

[0016] (8) In the above (7), the control signal may be an optical control signal as an optical signal. Thereby, the control signal can be transmitted to the optical communication device using the optical communication network.

[0017] (9) In the above (8), the reception unit may be connected to an optical fiber cable and receive a multiplexed signal of the main signal and the optical control signal transmitted through the optical fiber cable. Thereby, the main signal and the optical control signal can be transmitted to the optical communication device through one optical transmission path.

[0018] (10) In the above (9), the control wavelength, which is the wavelength of the optical control signal, is different from the wavelength of the main signal, and the multiplexed signal may be a wavelength division multiplexed signal of the main signal and the optical control signal. Thereby, the main signal and the optical control signal can be multiplexed without sacrificing the transmission capacity of each channel of the main signal and the optical control signal.

[0019] (11) In the above (9), the control wavelength, which is the wavelength of the optical control signal, is the same as the wavelength of the main signal, and the multiplexed signal may be a time division multiplexed signal of the main signal and the optical control signal. By using time division multiplexing suitable for multiplexing digital signals, the main signal and the optical control signal, which are digital signals, can be efficiently multiplexed.

[0020] (12) In any one of the above (8) to (11), the control unit may function as a subscriber side optical line terminal device corresponding to the control device that functions as a local side optical line terminal device in a passive optical network (PON: Passive Optical Network). Thereby, an optical communication device can be controlled using PON.

[0021] (13) In any one of the above (1) to (12), the optical communication device may further include an abnormality detection unit that detects an abnormality related to transmission and reception of the optical signal via the free space, and a notification unit that notifies an external control device of the abnormality detected by the abnormality detection unit. Thereby, when an abnormality occurs in the optical communication device, the abnormality can be notified to the control device.

[0022] (14) In the above (13), the optical communication device may further include a tracking function unit that tracks an optical axis formed between the optical communication device and a counter device via the free space, and the abnormality detection unit may detect an abnormality in the tracking of the optical axis by the tracking function unit. Thereby, when the communication becomes impossible due to an optical axis deviation, an abnormality in the tracking of the optical axis can be notified to the control device.

[0023] (15) The control device according to this embodiment is a control device for controlling an optical communication device that transmits and receives a main signal, which is an optical signal, over free space, and comprises a determination unit that determines the wavelength of the main signal transmitted from the optical communication device to the free space, and a transmission unit that transmits a control signal indicating the wavelength of the main signal determined by the determination unit to the optical communication device. This makes it possible to select a transmission wavelength suitable for the propagation of light in free space.

[0024] (16) The control system according to this embodiment comprises an optical communication device that transmits and receives a main signal, which is an optical signal, over free space, and a control device that controls the optical communication device, wherein the optical communication device includes an optical transmitting unit that transmits the main signal to free space, and a control unit that controls the wavelength of the main signal transmitted by the optical transmitting unit, wherein the control device includes a determination unit that determines the wavelength of the main signal transmitted from the optical communication device to free space, and a transmission unit that transmits a control signal to the optical communication device indicating the wavelength of the main signal determined by the determination unit, wherein the control device sets the wavelength of the main signal to the wavelength indicated in the control signal received from the control device. This makes it possible to select a transmission wavelength suitable for the propagation of light in free space.

[0025] This disclosure can be implemented not only as an optical communication device having the characteristic configuration described above, a control device having the characteristic configuration, and a control system having the characteristic configuration, but also as a control method for the optical communication device or as a computer program for controlling the optical communication device. Furthermore, this disclosure can be implemented as a semiconductor integrated circuit for part or all of the optical communication device, or as a semiconductor integrated circuit for part or all of the control device.

[0026] <Details of the embodiments of this disclosure> The embodiments of the present invention will be described in detail below with reference to the drawings. At least some of the embodiments described below may be combined in any way.

[0027] [1. Communication Systems] Figure 1A is a diagram showing a first example of the configuration of a communication system according to an embodiment. The communication system 10A shown in Figure 1A includes optical wired communication networks 2A, 2B and artificial satellites 20_1A, 20_1B, 20_2A, 20_2B.

[0028] Optical wired communication network 2A includes multiple optical switches (hereinafter, switches are also referred to as "SW") 3_1A, 3_2A. Optical wired communication network 2A also includes multiple optical SWs 3_1B, 3_2B. For example, optical wired communication networks 2A and 2B are APNs (All Photonics Networks) that transmit optical signals end-to-end.

[0029] Optical SW3_1A and 3_2A can, for example, switch the direction to which an optical signal is transmitted. Optical SW3_1A and 3_2A can, for example, multiplex multiple optical signals and transmit them, or separate a multiplexed optical signal into multiple optical signals and transmit each separated optical signal. Optical SW3_1A and 3_2A are, for example, optical splitters, optical couplers, or ROADMs (Reconfigurable Optical Add / Drop Multiplexers). The configuration of optical SW3_1B and 3_2B is the same as that of optical SW3_1A and 3_2A. Hereinafter, optical SW3_1A, 3_2A, 3_1B, 3_2B and optical SW3_1C, which will be described later, will be collectively referred to as "Optical SW3".

[0030] Optical SW3_2A is connected to optical transmission device 4A via an optical fiber cable (optical transmission path). Similarly, optical SW3_2B is connected to optical transmission device 4B via an optical fiber cable. Optical transmission device 4A is connected to, for example, a user device and transmits the main signal from the user device to the optical wired communication network 2A, and transmits the main signal from the optical wired communication network 2A to the user device. Optical transmission device 4A is, for example, a media converter that converts between electrical signals and optical signals. In Figure 1A, only optical transmission device 4A is connected to the optical wired communication network 2A, but multiple optical transmission devices may be connected to the optical wired communication network 2A. The configuration of optical transmission device 4B is the same as that of optical transmission device 4A. Hereinafter, optical transmission devices 4A, 4B, and optical transmission device 4C, which will be described later, will be collectively referred to as "optical transmission device 4".

[0031] FSOC devices 100_1A and 100_2A are connected to the optical wired communication network 2A. Specifically, FSOC device 100_1A is connected to optical switch 3_1A, and FSOC device 100_2A is connected to optical switch 3_2A. Similarly, FSOC devices 100_1B and 100_2B are connected to the optical wired communication network 2B. Specifically, FSOC device 100_1B is connected to optical switch 3_1B, and FSOC device 100_2B is connected to optical switch 3_2B. Hereinafter, FSOC devices 100_1A, 100_2A, 100_1B, 100_2B, and FSOC device 100_1C (described later) will be collectively referred to as "FSOC device 100".

[0032] The FSOC device 100 transmits and receives a main signal, which is an optical signal, through free space. The FSOC device 100 is an example of an "optical communication device".

[0033] FSOC device 100_1A and FSOC device 100_1B transmit and receive optical signals from each other via free space. FSOC device 100_1A can also transmit and receive optical signals from satellite 20_1A via free space. FSOC device 100_1B can also transmit and receive optical signals from satellite 20_1B via free space. Satellites 20_1A and 20_1B transmit and receive optical signals from each other via free space.

[0034] FSOC device 100_2A transmits and receives optical signals to and from satellite 20_2A via free space. FSOC device 100_2B transmits and receives optical signals to and from satellite 20_2B via free space. Satellites 20_1A and 20_2A transmit and receive optical signals to and from each other via free space. Satellites 20_1B and 20_2B transmit and receive optical signals to and from each other via free space.

[0035] For example, the communication path through free space between FSOC device 100_1A and FSOC device 100_1B is the active path. The paths including the communication path through free space between FSOC device 100_1A and satellite 20_1A, the communication path through free space between satellite 20_1A and satellite 20_1B, and the communication path through free space between satellite 20_1B and FSOC device 100_1B are redundant paths. In Figure 1A, solid arrows indicate connected communication paths, and dashed arrows indicate connectable but disconnected communication paths.

[0036] A control device 30A is connected to the optical wired communication network 2A. Specifically, control device 30A is connected to optical switch 3_2A via an optical fiber cable. A control device 30B is connected to the optical wired communication network 2B. Specifically, control device 30B is connected to optical switch 3_2B via an optical fiber cable. Hereafter, control devices 30A and 30B will be collectively referred to as "control device 30". Optical wired communication network 2A is an example of a "control system".

[0037] The control device 30A remotely controls, for example, optical switches 3_1A and 3_2A, optical transmission device 4A, and FSOC devices 100_1A and 100_2A. For example, the control device 30A can send and receive optical control signals, which are optical signals. For example, the main signal and the optical control signal are multiplexed and transmitted in the optical wired communication network 2A. In one specific example, the main signal and the optical control signal are wavelength-division multiplexed. That is, in this case, the wavelength of the main signal and the wavelength of the optical control signal are different from each other. In another example, the main signal and the optical control signal are time-division multiplexed. In this case, the wavelength of the main signal and the wavelength of the optical control signal are the same. Here, "the same" means that when multiple signals are mixed, the wavelengths of each signal are within the range in which each signal interferes with each other. The following describes an example in which the main signal and the optical control signal are wavelength-division multiplexed. In Figure 1A, the thick solid arrows indicate the transmission path of the main signal, and the thin solid arrows indicate the transmission path of the optical control signal.

[0038] For example, optical SW3_1A receives an optical control signal from the control device 30A and wavelength-division multiplexes the received optical control signal and the received main signal. For example, optical SW3_2A separates the wavelength-division multiplexed signal (multiplexed optical signal) of the received main signal and optical control signal into the main signal and the optical control signal.

[0039] An example of remote control of the FSOC device 100_1A by the control device 30A is described. The control device 30A transmits an optical control signal to SW3_1A for controlling the FSOC device 100_1A. The optical transmission device 4A converts the uplink main signal, an electrical signal received from the user device, into an optical signal. The optical transmission device 4A transmits the uplink main signal, which is an optical signal, to optical SW3_1A. Optical SW3_1A wavelength-division multiplexes the uplink main signal received from optical transmission device 4A with the optical control signal received from the control device 30A, and transmits the uplink multiplexed optical signal to the FSOC device 100_1A. The FSOC device 100_1A separates the uplink main signal and the optical control signal from the received uplink multiplexed optical signal, and transmits the uplink main signal to the FSOC device 100_1B (or satellite 20_1A). The FSOC device 100_1A executes control processing based on the received optical control signal.

[0040] The FSOC device 100_1A wavelength-division multiplexes the downlink main signal received from the FSOC device 100_1B (or satellite 20_1A) and the optical control signal containing the result of the control processing, and transmits the downlink multiplexed optical signal to the optical SW3_1A. The optical SW3_1A separates the downlink main signal and the optical control signal from the received downlink multiplexed optical signal and transmits the optical control signal to the control device 30A. The control device 30A performs processing according to the result of the control processing based on the received optical control signal.

[0041] Optical SW3_1A transmits the downlink main signal, separated from the downlink multiplexed optical signal, to optical transmission device 4A. Optical transmission device 4A converts the received downlink main signal from an optical signal to an electrical signal and transmits the electrical downlink main signal to the user device.

[0042] An example of remote control of the optical transmission device 4A by the control device 30A is described. The control device 30A transmits an optical control signal to SW3_1A for controlling the optical transmission device 4A. The optical SW3_1A wavelength-division multiplexes the downlink main signal received from the FSOC device 100_1A and the optical control signal received from the control device 30A, and transmits the downlink optical multiplexed signal to the optical transmission device 4A. The optical transmission device 4A separates the downlink main signal and the optical control signal from the received downlink multiplexed optical signal. The optical transmission device 4A converts the downlink main signal from an optical signal to an electrical signal and transmits the electrical downlink main signal to the user device. The optical transmission device 4A executes control processing based on the received optical control signal.

[0043] The optical transmission device 4A converts the upstream main electrical signal received from the user device into an optical signal. The optical transmission device 4A wavelength-division multiplexes the upstream main signal and the optical control signal containing the result of the control processing, and transmits the upstream multiplexed optical signal to the optical SW3_1A. The optical SW3_1A separates the upstream main signal and the optical control signal from the received upstream multiplexed optical signal and transmits the optical control signal to the control device 30A. The control device 30A performs processing according to the result of the control processing based on the received optical control signal.

[0044] Optical SW3_1A transmits the uplink main signal, separated from the uplink multiplexed optical signal, to FSOC device 100_1A. FSOC device 100_1A transmits the uplink main signal to FSOC device 100_1B (or satellite 20_1A).

[0045] Figure 1B is a diagram showing a second example of the configuration of a communication system according to the embodiment. The communication system 10B shown in Figure 1B includes an optical wired communication network 2A, a communication network 2C, and artificial satellites 20_1A, 20_1B, and 20_2A.

[0046] Communication network 2C includes optical switch 3_1C, optical transmission device 4C, and network device 5. Optical transmission device 4C is connected to optical switch 3_1C via an optical fiber cable (optical transmission path). Optical transmission device 4C and network device 5 are connected in a communicable manner via an electrical transmission path (shown as a dashed line in the figure), such as an electrical signal line, wired network, or wireless network. Network device 5 is, for example, a router, Wi-Fi router, L2 switch, L3 switch, etc. Network device is an example of user equipment.

[0047] The FSOC device 100_1C is connected to communication network 2C. Specifically, the FSOC device 100_1C is connected to optical switch SW3_1C.

[0048] FSOC device 100_1C and FSOC device 100_1A transmit and receive optical signals from each other via free space. FSOC device 100_1C can also transmit and receive optical signals from satellite 20_1B via free space.

[0049] For example, the communication path through free space between FSOC device 100_1A and FSOC device 100_1C is the active path. The path including the communication path through free space between FSOC device 100_1A and satellite 20_1A, the communication path through free space between satellite 20_1A and satellite 20_1B, and the communication path through free space between satellite 20_1B and FSOC device 100_1C is a redundant path.

[0050] The control device 30C is connected to the communication network 2C. Specifically, the control device 30C is connected to the optical SW3_1C via an optical fiber cable. The communication network 2C is another example of a "control system".

[0051] The control device 30C remotely controls, for example, the optical SW3_1C, the optical transmission device 4C, and the FSOC device 100_1C.

[0052] An example of remote control of the FSOC device 100_1C by the control device 30C is described. The control device 30C transmits an optical control signal to SW3_1C for controlling the FSOC device 100_1C. The optical transmission device 4C converts the uplink main signal, an electrical signal received from the network device 5, into an optical signal. The optical transmission device 4C transmits the uplink main signal, which is an optical signal, to the optical SW3_1C. The optical SW3_1C wavelength-division multiplexes the uplink main signal received from the optical transmission device 4C with the optical control signal received from the control device 30C, and transmits the uplink multiplexed optical signal to the FSOC device 100_1C. The FSOC device 100_1C separates the uplink main signal and the optical control signal from the received uplink multiplexed optical signal, and transmits the uplink main signal to the FSOC device 100_1A (or satellite 20_1B). The FSOC device 100_1C executes control processing based on the received optical control signal.

[0053] The FSOC device 100_1C wavelength-division multiplexes the downlink main signal received from the FSOC device 100_1A (or satellite 20_1B) and the optical control signal including the result of the control processing, and transmits the downlink multiplexed optical signal to the optical SW3_1C. The optical SW3_1C separates the downlink main signal and the optical control signal from the received downlink multiplexed optical signal and transmits the optical control signal to the control device 30C. The control device 30C performs processing according to the result of the control processing based on the received optical control signal.

[0054] Optical SW3_1C transmits the downlink main signal, separated from the downlink multiplexed optical signal, to optical transmission device 4C. Optical transmission device 4C converts the received downlink main signal from an optical signal to an electrical signal and transmits the electrical downlink main signal to the user device.

[0055] An example of remote control of the optical transmission device 4C by the control device 30C is described. The control device 30C transmits an optical control signal to SW3_1C for controlling the optical transmission device 4C. The optical SW3_1C wavelength-division multiplexes the downlink main signal received from the FSOC device 100_1C and the optical control signal received from the control device 30C, and transmits the downlink optical multiplexed signal to the optical transmission device 4C. The optical transmission device 4C separates the downlink main signal and the optical control signal from the received downlink multiplexed optical signal. The optical transmission device 4C converts the downlink main signal from an optical signal to an electrical signal and transmits the electrical downlink main signal to the network device 5. The optical transmission device 4C executes control processing based on the received optical control signal.

[0056] The optical transmission device 4C converts the upstream main electrical signal received from the network device 5 into an optical signal. The optical transmission device 4C wavelength-division multiplexes the upstream main signal and the optical control signal containing the result of the control processing, and transmits the upstream multiplexed optical signal to the optical SW3_1C. The optical SW3_1C separates the upstream main signal and the optical control signal from the received upstream multiplexed optical signal and transmits the optical control signal to the control device 30C. The control device 30C performs processing according to the result of the control processing based on the received optical control signal.

[0057] Optical SW3_1C transmits the uplink main signal, separated from the uplink multiplexed optical signal, to FSOC device 100_1C. FSOC device 100_1C transmits the uplink main signal to FSOC device 100_1A (or satellite 20_1B).

[0058] [2. FSOC System Configuration] Figure 2A is a perspective view showing a first example of the external configuration of an FSOC device according to an embodiment. For example, the FSOC device 100 can switch the communication path for sending and receiving optical signals. In Figure 2A, the X1 and X2 directions are opposite to each other, the Y1 and Y2 directions are opposite to each other, and the Z1 and Z2 directions are opposite to each other. Each of the X1 and X2 directions is orthogonal to each of the Y1 and Y2 directions. Furthermore, each of the X1 and X2 directions is orthogonal to each of the Z1 and Z2 directions. Each of the Y1 and Y2 directions is orthogonal to each of the Z1 and Z2 directions. For example, the X1 direction is to the right and the X2 direction is to the left. The Y1 direction is forward and the Y2 direction is backward. The Z1 direction is upward and the Z2 direction is downward.

[0059] The FSOC device 100 in the first example is a hexahedron including two faces facing each other in the X1 direction (X2 direction) (hereinafter referred to as the "right side" and the "left side"), two faces facing each other in the Y1 direction (Y2 direction) (hereinafter referred to as the "front" and the "rear"), and two faces facing each other in the Z1 direction (Z2 direction) (hereinafter referred to as the "top" and the "bottom").

[0060] The front of the housing of the FSOC device 100 according to the first example includes an optical signal output section 110A and an optical signal input section 110C. The FSOC device 100 can emit (transmit) an optical signal A in the Y1 direction from the output section 110A and receive an optical signal C in the Y2 direction at the input section 110C.

[0061] The upper surface of the housing of the FSOC device 100 according to the first example includes an optical signal output section 110B and an optical signal input section 110D. The FSOC device 100 can emit (transmit) an optical signal B in the Z1 direction from the output section 110B and receive an optical signal D in the Z2 direction at the input section 110D.

[0062] For example, there is an FSOC device 100 (the first opposing device in the first example) located in the Y1 direction from FSOC device 100, and a satellite 20 (the second opposing device in the first example) located in the Z1 direction from FSOC device 100. That is, FSOC device 100 transmits optical signal A to FSOC device 100 as the first opposing device and receives optical signal C from FSOC device 100 as the first opposing device. FSOC device 100 transmits optical signal B to satellite 20 as the second opposing device and receives optical signal D from satellite 20 as the second opposing device. FSOC device 100 can select either a communication path along the Y1 direction from FSOC device 100 (first path) or a communication path along the Z1 direction from FSOC device 100 (second path).

[0063] Figure 2B is a perspective view showing a second example of the external configuration of the FSOC apparatus according to the embodiment.

[0064] The front of the housing of the FSOC device 100 in the second example includes an optical signal output section 110A and an optical signal input section 110C. The FSOC device 100 can emit (transmit) an optical signal A in the Y1 direction from the output section 110A and receive an optical signal C in the Y2 direction at the input section 110C.

[0065] The rear surface of the housing of the FSOC device 100 in the second example includes an optical signal output section 110B and an optical signal input section 110D. The FSOC device 100 can emit (transmit) an optical signal B in the Y2 direction from the output section 110B and receive an optical signal D in the Y1 direction at the input section 110D.

[0066] For example, a first FSOC device 100 (the first opposing device in the first example) exists in the direction of Y1 from FSOC device 100, and a second FSOC device 100 (the second opposing device in the second example) exists in the direction of Y2 from FSOC 100. That is, FSOC device 100 transmits optical signal A to the first opposing device and receives optical signal C from the first opposing device. FSOC device 100 transmits optical signal B to the second opposing device and receives optical signal D from the second opposing device. FSOC device 100 can select either a communication path along the Y1 direction from FSOC device 100 (first path) or a communication path along the Y2 direction from FSOC device 100 (second path).

[0067] Figure 3 is a block diagram showing an example of the hardware configuration of an FSOC device according to the embodiment. In Figure 3, solid arrows indicate the optical connection relationships between elements, and dashed arrows indicate the electrical connection relationships between elements.

[0068] The FSOC device 100 includes a processing circuit 120, a transmission wavelength selection unit 121T, transmission wavelength conversion units 122T_A, 122T_B, a transmission power monitor unit 123T, an optical transmission unit 124T, a reception wavelength selection unit 121R, reception wavelength conversion units 122R_C, 122R_D, a reception power monitor unit 123R, an optical reception unit 124R, and connectors 127_1, 127_2, 127_3.

[0069] Connectors 127_1, 127_2, and 127_3 are each connected to an optical fiber cable. In the example in Figure 3, optical signals are transmitted by a two-core optical fiber cable (the transmission directions of the two cores are opposite to each other). In Figure 3, each of the two cores of the optical fiber cable is indicated by a different arrow. Connector 127_1 is connected to the optical fiber cable that connects the control device 30 and the optical transmission device 4. For the sake of simplicity, the direction from the optical transmission device 4 to the FSOC device 100 will be referred to as the "upstream direction," and the direction from the FSOC device 100 to the optical transmission device 4 will be referred to as the "downstream direction." As a specific example, in Figure 1A, connector 127_1 (not shown) of the FSOC device 100_1A is connected to one of the two cores (upstream transmission path) of the optical fiber cable extending from optical SW3_1A to the FSOC device 100_1A. Connector 127_3 is connected to the optical fiber cable that connects the control device 30 and the optical transmission device 4. As a specific example, in Figure 1A, connector 127_3 (not shown) of FSOC device 100_1A is connected to one of the two cores (downstream transmission path) of the optical fiber cable extending from optical SW3_1A to FSOC device 100_1A.

[0070] An optical transmission path extends from connector 127_1 to the transmission wavelength selection unit 121T. A WDM coupler 128T is located along this optical transmission path, and an optical transmission path extends from the WDM coupler 128T to the processing circuit 120.

[0071] The uplink multiplexed optical signal, which is a multiplexed uplink main signal transmitted from the optical transmission device 4 and an optical control signal transmitted from the control device 30, is transmitted along the uplink optical transmission path and input to connector 127_1. Connector 127_1 is an example of a "reception unit". The uplink multiplexed optical signal output from connector 127_1 is input to WDM coupler 128T, which separates the uplink main signal and the optical control signal from the input multiplexed optical signal. The uplink main signal output from WDM coupler 128T is input to the optical wavelength selection unit. The optical control signal output from WDM coupler 128T is input to the processing circuit.

[0072] Figure 4 is a block diagram showing an example of the hardware configuration of a processing circuit.

[0073] The processing circuit 120 includes a processor 131, a non-volatile memory 132, a volatile memory 133, a communication circuit 134, an optical transceiver (optical TRx) 135, and an input / output interface (I / O) 136.

[0074] The volatile memory 133 is a semiconductor memory such as SRAM (Static Random Access Memory) or DRAM (Dynamic Random Access Memory). The non-volatile memory 132 is a flash memory, hard disk, or ROM (Read Only Memory). The non-volatile memory 132 stores the control program 140, which is a computer program, and the data used to execute the control program 140. The functions of the FSOC device 100, described later, are realized when the control program 140 is executed by the processor 131.

[0075] The processor 131 is, for example, a CPU (Central Processing Unit). However, the processor 131 is not limited to a CPU. The processor 131 may also be a GPU (Graphics Processing Unit). In a specific example, the processor 131 is a multi-core processor. The processor 131 may also be a single-core processor. The processor 131 is configured to execute computer programs. However, the processor 131 may also be, for example, an ASIC (Application Specific Integrated Circuit) or a programmable logic device such as an FPGA (Field Programmable Gate Array). In this case, the ASIC or programmable logic device is configured to execute the same functions as the control program 140.

[0076] The optical transmission path extending from the WDM coupler 128T is connected to the optical TRx135. The optical TRx135 receives the optical control signal and converts the optical control signal into an electrical control signal. The optical TRx135 outputs the control signal to the communication circuit 134.

[0077] A control signal contains control information. In a specific example, a control signal includes a control frame containing the control information. For example, the communication circuit 134 performs frame processing. Specifically, the communication circuit 134 extracts control information from the control frame. The communication circuit 134 outputs the extracted control information to the processor 131.

[0078] The processor 131 executes control processing using control information. The processor 131 outputs the result of the control processing to the communication circuit 134. The communication circuit 134 creates a control frame containing the result of the control processing. The communication circuit 134 generates a control signal including the created control frame and outputs the generated control signal to the optical TRx135. The optical TRx135 converts the input control signal including the control frame into an optical control signal and transmits the optical control signal to the optical transmission path.

[0079] I / O 136 performs data input and output. Referring to Figure 3, I / O 136 is connected via electrical signal lines to the transmit wavelength selection unit 121T, the transmit wavelength conversion unit 122T_A, the transmit wavelength conversion unit 122T_B, the transmit power monitor unit 123T, and the optical transmit unit 124T. More specifically, the optical transmit unit 124T includes a first optical transmit unit 124T_A and a second optical transmit unit 124T_B. The first optical transmit unit 124T_A includes an optical wired-to-wireless conversion unit 124T_A1 and an optical wired-to-wireless conversion unit 124T_A2. The second optical transmit unit 124T_B includes an optical wired-to-wireless conversion unit 124T_B1 and an optical wired-to-wireless conversion unit 124T_B2. If the optical wired-to-wireless converter 124T_A1 corresponds to the "first transmitter," then the optical wired-to-wireless converter 124T_A2 corresponds to the "second transmitter." If the optical wired-to-wireless converter 124T_B1 corresponds to the "first transmitter," then the optical wired-to-wireless converter 124T_B2 corresponds to the "second transmitter." I / O 136 is connected to each of the optical wired-to-wireless converters 124T_A1, 124T_A2, 124T_B1, and 124T_B2 via electrical signal lines.

[0080] I / O 136 is further connected via electrical signal lines to the receiving wavelength selection unit 121R, the receiving wavelength conversion unit 122R_C, the receiving wavelength conversion unit 122R_D, the receiving power monitor unit 123R, and the optical receiving unit 124R. More specifically, the optical receiving unit 124R includes a first optical receiving unit 124R_C and a second optical receiving unit 124R_D. The first optical receiving unit 124R_C includes an optical wireless-to-wired conversion unit 124R_C1 and an optical wireless-to-wired conversion unit 124R_C2. The second optical receiving unit 124R_D includes an optical wireless-to-wired conversion unit 124R_D1 and an optical wireless-to-wired conversion unit 124R_D2. If the optical wireless-to-wired conversion unit 124R_C1 corresponds to the "first receiving unit," then the optical wireless-to-wired conversion unit 124R_C2 corresponds to the "second receiving unit." If the optical wireless-to-wired conversion unit 124R_D1 corresponds to the "first receiving unit," then the optical wireless-to-wired conversion unit 124R_D2 corresponds to the "second receiving unit." I / O 136 is connected to each of the optical wireless-to-wired conversion units 124R_C1, 124R_C2, 124R_D1, and 124R_D2 via electrical signal lines.

[0081] I / O136 is further connected to the detection function unit 125 and the tracking function unit 126, respectively, via electrical signal lines.

[0082] The transmit wavelength selection unit 121T is connected to the optical wired-to-wireless conversion unit 124T_A1 via a single optical transmission line. The optical transmission line branches midway, and the branched end is connected to the transmit power monitor unit 123T. The transmit wavelength selection unit 121T is connected to the transmit wavelength conversion unit 122T_A via a single optical transmission line, and the transmit wavelength conversion unit 122T_A is connected to the optical wired-to-wireless conversion unit 124T_A2 via a single optical transmission line. The optical transmission line extending from the transmit wavelength conversion unit 122T_A to the optical wired-to-wireless conversion unit 124T_A2 branches midway, and the branched end is connected to the transmit power monitor unit 123T.

[0083] The transmit wavelength selection unit 121T is connected to the optical wired-to-wireless conversion unit 124T_B1 via a single optical transmission line. The optical transmission line branches midway, and the branched end is connected to the transmit power monitor unit 123T. The transmit wavelength selection unit 121T is connected to the transmit wavelength conversion unit 122T_B via a single optical transmission line, and the transmit wavelength conversion unit 122T_B is connected to the optical wired-to-wireless conversion unit 124T_B2 via a single optical transmission line. The optical transmission line extending from the transmit wavelength conversion unit 122T_B to the optical wired-to-wireless conversion unit 124T_B2 branches midway, and the branched end is connected to the transmit power monitor unit 123T.

[0084] The transmission wavelength selection unit 121T can select the output destination of the input optical signal (upstream main signal). Specifically, the transmission wavelength selection unit 121T selects one of the following as the output destination of the upstream main signal: optical wired-to-wireless conversion unit 124T_A1, transmission wavelength conversion unit 122T_A, optical wired-to-wireless conversion unit 124T_B1, and transmission wavelength conversion unit 122T_B, according to a command from the processing circuit 120.

[0085] The wavelength of the uplink main signal input to connector 127_1 is selected from, for example, the C-band (Conventional-band, a wavelength band from 1530nm to 1565nm). The transmit wavelength selection unit 121T outputs the uplink main signal to the selected output destination without converting the wavelength. Hereinafter, the C-band will also be referred to as the "first band".

[0086] Each of the optical wired-to-wireless conversion units 124T_A1, 124T_A2, 124T_B1, and 124T_B2 outputs (transmits) the upstream main signal input from the optical transmission path (optical fiber cable) to free space. In other words, the optical wired-to-wireless conversion units 124T_A1, 124T_A2, 124T_B1, and 124T_B2 are devices that convert the communication mode from optical wired communication to optical wireless communication.

[0087] For example, when an uplink main signal is output from the transmitting wavelength selection unit 121T to the optical wired-to-wireless conversion unit 124T_A1, the optical wired-to-wireless conversion unit 124T_A1 transmits the received uplink main signal to free space without converting the wavelength of the first band. The optical wired-to-wireless conversion unit 124T_A1 is facing the first opposing device and transmits the optical signal A of the first band to the first opposing device. Similarly, for example, when an uplink main signal is output from the transmitting wavelength selection unit 121T to the optical wired-to-wireless conversion unit 124T_B1, the optical wired-to-wireless conversion unit 124T_B1 transmits the received uplink main signal to free space without converting the wavelength of the first band. The optical wired-to-wireless converter 124T_B1 is oriented toward the second opposing device, and the optical wired-to-wireless converter 124T_B1 transmits the optical signal B of the first band to the second opposing device.

[0088] Connector 127_2 is connected to a single-core optical fiber cable extending from the light source device 6. The light source device 6 includes a tunable wavelength light source. The light source device 6 outputs excitation light (light used to convert the wavelength of an optical signal), and the excitation light output from the light source device 6 is transmitted through the optical fiber cable and input to connector 127_2.

[0089] A single-core optical transmission path extends from connector 127_2 to each of the transmitting wavelength conversion units 122T_A, 122T_B and receiving wavelength conversion units 122R_C, 122R_D. Excitation light is output from connector 127_2 to each of the transmitting wavelength conversion units 122T_A, 122T_B and receiving wavelength conversion units 122R_C, 122R_D via this optical transmission path.

[0090] Each of the transmission wavelength conversion units 122T_A and 122T_B converts the wavelength of the optical signal. Specifically, each of the transmission wavelength conversion units 122T_A and 122T_B converts the wavelength of the input uplink main signal according to the input excitation light. For example, each of the transmission wavelength conversion units 122T_A and 122T_B converts the wavelength of the main signal from the C-band to a wavelength suitable for light propagation in free space. In a more specific example, each of the transmission wavelength conversion units 122T_A and 122T_B converts the wavelength of the main signal from the C-band to a wavelength suitable for light propagation in air. For example, the wavelength band from 3.5 μm to 4.0 μm is suitable for light propagation in air. Hereinafter, the wavelength band from 3.5 μm to 4.0 μm will also be referred to as the "second band".

[0091] The transmit wavelength conversion units 122T_A and 122T_B each output the uplink main signal after wavelength conversion. The uplink main signal output from the transmit wavelength conversion unit 122T_A is input to the optical wired-to-wireless conversion unit 124T_A2. The uplink main signal output from the transmit wavelength conversion unit 122T_B is input to the optical wired-to-wireless conversion unit 124T_B2.

[0092] For example, when an uplink main signal is output from the transmission wavelength selection unit 121T to the transmission wavelength conversion unit 122T_A, the transmission wavelength conversion unit 122T_A converts the wavelength of the received uplink main signal to the wavelength of the second band and outputs the uplink main signal after wavelength conversion to the optical wired-to-wireless conversion unit 124T_A2. The optical wired-to-wireless conversion unit 124T_A2 transmits the input uplink main signal to free space at the converted wavelength. The optical wired-to-wireless conversion unit 124T_A2 is facing the first opposing device and transmits the optical signal A of the second band to the first opposing device. Similarly, for example, when an uplink main signal is output from the transmission wavelength selection unit 121T to the transmission wavelength conversion unit 122T_B, the transmission wavelength conversion unit 122T_B converts the wavelength of the received uplink main signal to the wavelength of the second band and outputs the uplink main signal after wavelength conversion to the optical wired-to-wireless conversion unit 124T_B2. The optical wired-to-wireless conversion unit 124T_B2 transmits the input uplink main signal to free space at the converted wavelength. The optical wired-to-wireless conversion unit 124T_B2 is facing the second opposing device and transmits the optical signal B of the second band to the second opposing device.

[0093] The transmit power monitor unit 123T monitors the intensity level of the optical signal transmitted into free space. For example, the transmit power monitor unit 123T includes a photodetector such as an APD (Avalanche PhotoDiode), and detects the intensity level of the optical signal by measuring the voltage output from the photodetector, which corresponds to the intensity level of the received light.

[0094] For example, when an uplink main signal is output from the transmission wavelength selection unit 121T to the optical wired-to-wireless conversion unit 124T_A1, the uplink main signal is input to the transmission power monitor unit 123T. The transmission power monitor unit 123T monitors the intensity level of the uplink main signal transmitted from the optical wired-to-wireless conversion unit 124T_A1 to free space. Similarly, for example, when an uplink main signal is output from the transmission wavelength selection unit 121T to the optical wired-to-wireless conversion unit 124T_B1, the uplink main signal is input to the transmission power monitor unit 123T. The transmission power monitor unit 123T monitors the intensity level of the uplink main signal transmitted from the optical wired-to-wireless conversion unit 124T_B1 to free space.

[0095] For example, if an uplink main signal is output from the transmission wavelength selection unit 121T to the transmission wavelength conversion unit 122T_A, the uplink main signal after wavelength conversion, output from the transmission wavelength conversion unit 122T_A, is input to the transmission power monitor unit 123T. The transmission power monitor unit 123T monitors the intensity level of the uplink main signal transmitted from the optical wired-to-wireless conversion unit 124T_A2 to free space. Similarly, for example, if an uplink main signal is output from the transmission wavelength selection unit 121T to the transmission wavelength conversion unit 122T_B, the uplink main signal after wavelength conversion, output from the transmission wavelength conversion unit 122T_B, is input to the transmission power monitor unit 123T. The transmission power monitor unit 123T monitors the intensity level of the uplink main signal transmitted from the optical wired-to-wireless conversion unit 124T_B2 to free space.

[0096] Each of the optical wireless-to-wired conversion units 124R_C1, 124R_C2, 124R_D1, and 124R_D2 receives an optical signal (downlink main signal) transmitted from the opposing device and transmitted in free space. For example, each of the optical wireless-to-wired conversion units 124R_C1, 124R_C2, 124R_D1, and 124R_D2 is capable of receiving optical signals in the corresponding wavelength band. In a specific example, the optical wireless-to-wired conversion units 124R_C1 and 124_D1 are capable of receiving C-band optical signals. The optical wireless-to-wired conversion units 124R_C2 and 124_D2 are capable of receiving optical signals in the 3.5 μm to 4.0 μm band.

[0097] The optical wireless-to-wired conversion unit 124R_C1 is connected to the wavelength selection unit 121R via a single optical transmission line. The optical transmission line branches midway, and the branched end is connected to the receiving power monitor unit 123R. The optical wireless-to-wired conversion unit 124R_C2 is connected to the receiving wavelength conversion unit 122R_C via a single optical transmission line. The optical transmission line branches midway, and the branched end is connected to the receiving power monitor unit 123R. The receiving wavelength conversion unit 122R_C is connected to the receiving wavelength selection unit 121R via a single optical transmission line.

[0098] The optical wireless-to-wired conversion unit 124R_D1 is connected to the wavelength selection unit 121R via a single optical transmission line. The optical transmission line branches midway, and the branched end is connected to the receiving power monitor unit 123R. The optical wireless-to-wired conversion unit 124R_D2 is connected to the receiving wavelength conversion unit 122R_D via a single optical transmission line. The optical transmission line branches midway, and the branched end is connected to the receiving power monitor unit 123R. The receiving wavelength conversion unit 122R_D is connected to the receiving wavelength selection unit 121R via a single optical transmission line.

[0099] The receiving wavelength selection unit 121R can select the input source for the optical signal (upstream main signal). Specifically, the transmitting wavelength selection unit 121T selects one of the following as the input source for the upstream main signal: the optical wireless-to-wired conversion unit 124R_C1, the receiving wavelength conversion unit 122R_C, the optical wireless-to-wired conversion unit 124R_D1, and the receiving wavelength conversion unit 122R_D, according to a command from the processing circuit 120.

[0100] For example, optical wireless-to-wired conversion units 124R_C1 and 124R_C2 are each directed toward the first opposing device, while optical wireless-to-wired conversion units 124R_D1 and 124R_D2 are each directed toward the second opposing device. When a downlink main signal of the first band is transmitted from the first opposing device to free space, the optical wireless-to-wired conversion unit 124R_C1 receives the downlink main signal of the first band (optical signal C of the first band) and outputs the received downlink main signal of the first band to the receiving wavelength selection unit 121R. On the other hand, the optical wireless-to-wired conversion unit 124R_C2, whose receivable wavelength band is the second band, does not substantially receive the downlink main signal of the first band from the first opposing device.

[0101] Each of the receiving wavelength conversion units 122R_C and 122R_D converts the wavelength of the optical signal. Specifically, each of the receiving wavelength conversion units 122R_C and 122R_D converts the wavelength of the input downlink main signal according to the input excitation light. For example, each of the receiving wavelength conversion units 122R_C and 122R_D converts the wavelength of the main signal from the wavelength of the second band to the wavelength of the first band.

[0102] For example, when a downlink main signal in the second band is transmitted from the first opposing device to free space, the optical wireless-to-wired conversion unit 124R_C2 receives the downlink main signal in the second band (optical signal C in the second band) and outputs the received downlink main signal in the second band to the receiving wavelength conversion unit 122R_C. The receiving wavelength conversion unit 122R_C converts the input downlink main signal from the wavelength of the second band to the wavelength of the first band and outputs the downlink main signal after wavelength conversion to the receiving wavelength selection unit 121R. On the other hand, the optical wireless-to-wired conversion unit 124R_C1, whose receivable wavelength band is the first band, does not substantially receive the downlink main signal in the second band from the first opposing device.

[0103] For example, when a downlink main signal in the first band is transmitted from the second opposing device to free space, the optical wireless-to-wired conversion unit 124R_D1 receives the downlink main signal in the first band (optical signal D in the first band) and outputs the received downlink main signal in the first band to the receiving wavelength selection unit 121R. On the other hand, the optical wireless-to-wired conversion unit 124R_D2, whose receivable wavelength band is the second band, does not substantially receive the downlink main signal in the first band from the second opposing device.

[0104] For example, when a second-band downstream main signal is transmitted to free space from the second opposing device, the optical wireless-to-wired conversion unit 124R_D2 receives the second-band downstream main signal (second-band optical signal D) and outputs the received second-band downstream main signal to the receiving wavelength conversion unit 122R_D. The receiving wavelength conversion unit 122R_D converts the input downstream main signal from the wavelength of the second band to the wavelength of the first band and outputs the wavelength-converted downstream main signal to the receiving wavelength selection unit 121R. On the other hand, the optical wireless-to-wired conversion unit 124R_D1, whose receivable wavelength band is the first band, does not substantially receive the second-band downstream main signal from the second opposing device.

[0105] The receiving power monitor unit 123R receives optical signals output from each of the optical wireless-to-wired conversion units 124R_C1, 124R_C2, 124R_D1, and 124R_D2, and compares the intensity level of each received optical signal with a threshold. If the intensity level of any of the optical signals output from each of the optical wireless-to-wired conversion units 124R_C1, 124R_C2, 124R_D1, and 124R_D2 exceeds the threshold, the receiving power monitor unit 123R outputs a notification signal to the processing circuit 120 that indicates the source of the optical signal whose intensity level exceeded the threshold.

[0106] For example, when a downlink main signal of the first band is transmitted from the first opposing device to free space, the intensity level of the optical signal received by the optical wireless-to-wired conversion unit 124R_C1 (hereinafter also referred to as the "received power level") is the highest and exceeds the threshold. The received power levels of the optical signals in each of the optical wireless-to-wired conversion units 124R_C2, 124R_D1, and 124R_D2 do not exceed the threshold. Therefore, the received power monitor unit 123R notifies the processing circuit 120 that the received power level of the optical wireless-to-wired conversion unit 124R_C1 has exceeded the threshold.

[0107] For example, when the downlink main signal of the second band is transmitted from the first opposing device to free space, the received power level in the optical wireless-to-wired conversion unit 124R_C2 is the highest and exceeds the threshold. The received power levels of the optical signals in each of the optical wireless-to-wired conversion units 124R_C1, 124R_D1, and 124R_D2 do not exceed the threshold. Therefore, the received power monitor unit 123R notifies the processing circuit 120 that the received power level of the optical wireless-to-wired conversion unit 124R_C2 has exceeded the threshold.

[0108] For example, when the downlink main signal of the first band is transmitted from the second opposing device to free space, the received power level in the optical wireless-to-wired conversion unit 124R_D1 is the highest and exceeds the threshold. The received power levels of the optical signals in each of the optical wireless-to-wired conversion units 124R_C1, 124R_C2, and 124R_D2 do not exceed the threshold. Therefore, the received power monitor unit 123R notifies the processing circuit 120 that the received power level of the optical wireless-to-wired conversion unit 124R_D1 has exceeded the threshold.

[0109] For example, when the second opposing device transmits the second bandwidth downlink main signal into free space, the received power level in the optical wireless-to-wired conversion unit 124R_D2 is the highest and exceeds the threshold. The received power levels of the optical signals in each of the optical wireless-to-wired conversion units 124R_C1, 124R_C2, and 124R_D1 do not exceed the threshold. Therefore, the received power monitor unit 123R notifies the processing circuit 120 that the received power level of the optical wireless-to-wired conversion unit 124R_D2 has exceeded the threshold.

[0110] An optical transmission path extends from the receiving wavelength selection unit 121R to the connector 127_3. A WDM coupler 128R is located along this optical transmission path, and an optical transmission path extends from the WDM coupler 128R to the processing circuit 120.

[0111] The receiving wavelength selection unit 121R can select the output source of the input optical signal (downlink main signal). Specifically, the receiving wavelength selection unit 121R selects one of the following as the output source of the downlink main signal according to the command from the processing circuit 120: optical wireless-to-wired conversion unit 124R_C1, optical wireless-to-wired conversion unit 124R_C2 (receiving wavelength conversion unit 122R_C), optical wireless-to-wired conversion unit 124R_D1, and optical wireless-to-wired conversion unit 124R_D2 (receiving wavelength conversion unit 122R_D).

[0112] The processing circuit 120 outputs a command to the receiving wavelength selection unit 121R, which is notified by the receiving power monitor unit 123R, to select an output source whose reception level exceeds a threshold.

[0113] For example, if the output source whose reception level exceeds a threshold is the optical wireless-to-wired conversion unit 124R_C1, the processing circuit 120 outputs a command to the receiving wavelength selection unit 121R to select the optical wireless-to-wired conversion unit 124R_C1. The receiving wavelength selection unit 121R selects the optical wireless-to-wired conversion unit 124R_C1 in response to the command from the processing circuit 120, and outputs the downlink main signal output from the selected optical wireless-to-wired conversion unit 124R_C1 to the WDM coupler 128R.

[0114] For example, if the output source whose reception level exceeds a threshold is the optical wireless-to-wired conversion unit 124R_C2, the processing circuit 120 outputs a command to the receiving wavelength selection unit 121R to select the optical wireless-to-wired conversion unit 124R_C2. The receiving wavelength selection unit 121R selects the optical wireless-to-wired conversion unit 124R_C2 in response to the command from the processing circuit 120, and outputs the downlink main signal output from the receiving wavelength conversion unit 122R_C connected to the selected optical wireless-to-wired conversion unit 124R_C2 to the WDM coupler 128R.

[0115] For example, if the output source whose reception level exceeds a threshold is the optical wireless-to-wired conversion unit 124R_D1, the processing circuit 120 outputs a command to the receiving wavelength selection unit 121R to select the optical wireless-to-wired conversion unit 124R_D1. The receiving wavelength selection unit 121R selects the optical wireless-to-wired conversion unit 124R_D1 in response to the command from the processing circuit 120, and outputs the downlink main signal output from the selected optical wireless-to-wired conversion unit 124R_D1 to the WDM coupler 128R.

[0116] For example, if the output source whose reception level exceeds a threshold is the optical wireless-to-wired conversion unit 124R_D2, the processing circuit 120 outputs a command to the receiving wavelength selection unit 121R to select the optical wireless-to-wired conversion unit 124R_D2. The receiving wavelength selection unit 121R selects the optical wireless-to-wired conversion unit 124R_D2 in response to the command from the processing circuit 120, and outputs the downlink main signal output from the receiving wavelength conversion unit 122R_D connected to the selected optical wireless-to-wired conversion unit 124R_D2 to the WDM coupler 128R.

[0117] The WDM coupler 128R wavelength-division multiplexes the downlink main signal output from the receiving wavelength selection unit 121R and the optical control signal output from the processing circuit 120, and outputs the downlink multiplexed optical signal to the connector 127_3. The downlink multiplexed optical signal input to the connector 127_3 is transmitted through a single optical transmission path extending from the connector 127_3 to the outside of the FSOC device 100. For example, the optical SW3 separates the downlink main signal and the optical control signal from the downlink multiplexed optical signal, the downlink main signal is received by the optical transmission device 4, and the optical control signal is received by the control device 30.

[0118] The detection function unit 125 detects the optical axis between itself and the opposing device in response to a command from the processing circuit 120. Specifically, the detection function unit 125 detects the beacon signal (laser light) emitted from the opposing device and also emits a beacon signal toward the opposing device. The tracking function unit 126 is equipped with a VCM (Voice Coil Motor) and has a known optical axis tracking function as disclosed in Non-Patent Literature 1. The tracking function unit 126 tracks the optical axis detected by the detection function unit 125 in response to a command from the processing circuit 120.

[0119] [3. Functions of the FSOC device] Figure 5 is a functional block diagram showing an example of the functions of a processing circuit.

[0120] When the processor 131 executes the control program 140, the processing circuit 120 performs the functions of the control unit 141, the anomaly detection unit 142, and the notification unit 143.

[0121] The control unit 141 controls the wavelength of the uplink main signal transmitted by the optical transmission unit 124T. For example, the control unit 141 selects either the transmission of the uplink main signal at the wavelength of the first band (first wavelength) by the optical wired-to-wireless conversion unit 124T_A1, or the transmission of the uplink main signal at the wavelength of the second band (second wavelength) by the optical wired-to-wireless conversion unit 124T_A2.

[0122] The control unit 141 selects one of the first optical transmitter 124T_A and the second optical transmitter 124T_B as the source of the uplink main signal.

[0123] The control unit 141 selects one of the first optical receiver 124R_C and the second optical receiver 124R_D as the target for receiving the downstream main signal.

[0124] For example, the first optical transmitter 124T_A and the first optical receiver 124R_C are included in the active path. In this case, the second optical transmitter 124T_B and the second optical receiver 124R_D are included in the redundant path. Therefore, the control unit 141 can select the active path by selecting the first optical transmitter 124T_A as the source of the uplink main signal and the first optical receiver 124R_C as the recipient of the downlink signal. The control unit 141 can select the redundant path by selecting the second optical transmitter 124T_B as the source of the uplink main signal and the second optical receiver 124R_D as the recipient of the downlink signal.

[0125] For example, the control unit 141 selects the first optical transmitter 124T_A as the source of the uplink main signal if there is no abnormality in the first optical transmitter 124T_A. Furthermore, the control unit 141 selects the first optical receiver 124R_C as the target for receiving the downlink main signal if there is no abnormality in the first optical receiver 124R_C. In a more specific example, the control unit 141 selects the first optical transmitter 124T_A as the source of the uplink main signal and the first optical receiver 124R_C as the target for receiving the downlink main signal if there are no abnormalities in both the first optical transmitter 124T_A and the first optical receiver 124R_C.

[0126] For example, if an abnormality occurs in the first optical transmitter 124T_A, the control unit 141 selects the second optical transmitter 124T_B as the source of the uplink main signal. Furthermore, if an abnormality occurs in the first optical receiver 124R_C, the control unit 141 selects the second optical receiver 124R_D as the recipient of the downlink main signal. In a more specific example, if an abnormality occurs in at least one of the first optical transmitter 124T_A and the first optical receiver 124R_C, the control unit 141 selects the second optical transmitter 124T_B as the source of the uplink main signal and the second optical receiver 124R_D as the recipient of the downlink main signal. This allows communication to continue via a redundant path if an abnormality occurs in the active path, thereby achieving fault tolerance.

[0127] As described later, the control device 30 transmits an optical control signal that includes control information specifying the transmission wavelength of the uplink main signal, the reception wavelength of the downlink signal, and the communication path (active path or redundant path) of the FSOC device 100. The optical control information transmitted from the control device 30 is received by the connector 127_1. The optical control signal received by the connector 127_1 is received by the optical TRx135 of the processing circuit 120.

[0128] The control unit 141 selects one of the optical wired-to-wireless converters 124T_A1, 124T_A2, 124T_B1, and 124T_B2 as the source of the uplink main signal, according to the transmission wavelength and communication path specified in the control information included in the received optical control signal. If optical wired-to-wireless converter 124T_A1 or 124T_B1 is selected as the source, the first band is selected as the transmission wavelength of the uplink main signal. If optical wired-to-wireless converter 124T_A2 or 124T_B2 is selected as the source, the second band is selected as the transmission wavelength of the uplink main signal. In other words, the transmission wavelength of the uplink main signal is controlled by selecting one of the optical wired-to-wireless converters 124T_A1, 124T_A2, 124T_B1, and 124T_B2 as the source of the uplink main signal.

[0129] The control unit 141 selects one of the optical wireless-to-wired conversion units 124R_C1, 124R_C2, 124R_D1, and 124R_D2 as the receiving target for the downlink main signal, according to the receiving wavelength and communication path specified in the control information included in the received optical control signal. If the optical wireless-to-wired conversion unit 124R_C1 or 124R_D1 is selected as the receiving target, the first band is selected as the receiving wavelength for the downlink main signal. If the optical wireless-to-wired conversion unit 124R_C2 or 124R_D2 is selected as the receiving target, the second band is selected as the receiving wavelength for the downlink main signal. In other words, the receiving wavelength of the downlink main signal is controlled by selecting one of the optical wireless-to-wired conversion units 124R_C1, 124R_C2, 124R_D1, and 124R_D2 as the receiving target for the downlink main signal.

[0130] The anomaly detection unit 142 detects anomalies in the FSOC device 100. For example, the transmit wavelength selection unit 121T, transmit wavelength conversion units 122T_A, 122T_B, transmit power monitor unit 123T, optical wired-to-wireless conversion units 124T_A1, 124T_A2, 124T_B1, 124T_B2, receive wavelength selection unit 121R, receive wavelength conversion units 122R_C, 122R_D, receive power monitor unit 123R, optical wireless-to-wired conversion units 124R_C1, 124R_C2, 124R_D1, 124R_D2, detection function unit 125, and tracking function unit 126 each output anomaly information to the processing circuit 120 when an anomaly occurs. The anomaly detection unit 142 detects an anomaly occurring in any of the following based on the received anomaly information: the transmission wavelength selection unit 121T, the transmission wavelength conversion units 122T_A, 122T_B, the transmission power monitor unit 123T, the optical wired-to-wireless conversion units 124T_A1, 124T_A2, 124T_B1, 124T_B2, the receiving wavelength selection unit 121R, the receiving wavelength conversion units 122R_C, 122R_D, the receiving power monitor unit 123R, the optical wireless-to-wired conversion units 124R_C1, 124R_C2, 124R_D1, 124R_D2, the detection function unit 125, and the tracking function unit 126.

[0131] The anomaly detection unit 142 detects anomalies related to the transmission and reception of optical signals over free space. For example, if the transmission power monitor unit 123T outputs anomaly information indicating an optical signal transmission anomaly when the intensity levels of the optical signals output to the optical wired-to-wireless conversion units 124T_A1, 124T_A2, 124T_B1, and 124T_B2 do not all exceed a threshold, the anomaly detection unit 142 detects an optical signal transmission anomaly based on the anomaly information received from the transmission power monitor unit 123T.

[0132] For example, if the receiving power monitor unit 123R outputs abnormal information indicating an abnormality in optical signal reception if the intensity levels of the optical signals output from the optical wireless-to-wired conversion units 124R_C1, 124R_C2, 124R_D1, and 124R_D2 do not all exceed a threshold, the abnormality detection unit 142 detects an abnormality in optical signal reception based on the abnormality information received from the receiving power monitor unit 123R.

[0133] For example, the tracking function unit 126 outputs abnormal information indicating a tracking abnormality when it becomes unable to track the optical axis. The abnormality detection unit 142 detects the optical axis tracking abnormality based on the abnormality information received from the tracking function unit 126.

[0134] The notification unit 143 notifies the control device 30 of any abnormalities detected by the abnormality detection unit 142. For example, if an abnormality is detected by the abnormality detection unit 142, the notification unit 143 generates control information indicating the nature of the detected abnormality. The processing circuit 120 creates a control frame containing the control information and transmits an optical control signal including the created control frame to the control device 30.

[0135] [4. Control device] Figure 6 is a block diagram showing an example of the configuration of a control device according to this embodiment.

[0136] The control device 30 includes a processing circuit 301, a communication circuit 302, and an optical TRx303.

[0137] The processing circuit 301 includes a processor 311 and a memory 312.

[0138] Memory 312 includes, for example, volatile memory and non-volatile memory. Memory 312 stores the remote control program 320 and the data used to execute the remote control program 320. The functions of the control device 30, described later, are realized when the remote control program 320 is executed by the processor 311.

[0139] The processor 311 is, for example, a CPU. However, the processor 311 is not limited to a CPU. The processor 311 may also be a GPU. In a specific example, the processor 311 is a multi-core processor. The processor 311 may also be a single-core processor. The processor 311 is configured to execute computer programs. However, the processor 311 may also be, for example, an ASIC or a programmable logic device such as an FPGA. In this case, the ASIC or programmable logic device is configured to execute the same functions as the remote control program 320.

[0140] The processor 311 executes the remote control program 320, thereby enabling the control device 30 to perform the functions of the determination unit 321.

[0141] The determination unit 321 determines the transmission wavelength of the uplink main signal transmitted from the subordinate FSOC device 100 to free space. The determination unit 321 further determines the reception wavelength of the downlink main signal that the subordinate FSOC device 100 receives from free space.

[0142] When FSOC device 100 and the first opposing device communicate (active path), the transmission wavelength of the uplink main signal from FSOC device must match the reception wavelength of the uplink main signal from the first opposing device, and the transmission wavelength of the downlink main signal from the first opposing device must match the reception wavelength of the downlink main signal from FSOC device. When FSOC device 100 and the second opposing device communicate (redundant path), the transmission wavelength of the uplink main signal from FSOC device must match the reception wavelength of the uplink main signal from the second opposing device, and the transmission wavelength of the downlink main signal from the second opposing device must match the reception wavelength of the downlink main signal from FSOC device.

[0143] For example, the decision unit 321 determines whether to use the active route or the redundant route for communication. If the active route is in use and the first optical transmitter 124T_A of the FSOC device 100 is functioning normally (i.e., no abnormality has been reported), then the communication status between the FSOC device 100 and the first opposing device is normal. In this case, the decision unit 321 determines the active route to be used. If the active route is in use and the first optical transmitter 124T_A of the FSOC device 100 is malfunctioning (i.e., an abnormality has been reported), then the communication status between the FSOC device 100 and the first opposing device is abnormal. In this case, the decision unit 321 determines the redundant route to be used.

[0144] For example, if the determination unit 321 determines the currently used path as the path to be used, it determines the transmission wavelength of the uplink main signal of the FSOC device 100 and the transmission wavelength of the downlink signal of the first opposing device. The determination unit 321 determines the reception wavelength of the uplink main signal of the first opposing device to be the same wavelength as the transmission wavelength of the uplink main signal of the FSOC device 100. The determination unit 321 determines the reception wavelength of the downlink main signal of the FSOC device 100 to be the same wavelength as the transmission wavelength of the downlink main signal of the first opposing device.

[0145] For example, if the determination unit 321 determines that a redundant path is the path to be used, it determines the transmission wavelength of the upstream main signal of the FSOC device 100 and the transmission wavelength of the downstream signal of the second opposing device. The determination unit 321 determines that the reception wavelength of the upstream main signal of the second opposing device is the same wavelength as the transmission wavelength of the upstream main signal of the FSOC device 100. The determination unit 321 determines that the reception wavelength of the downstream main signal of the FSOC device 100 is the same wavelength as the transmission wavelength of the downstream main signal of the second opposing device.

[0146] The determination unit 321 generates control information indicating the determined transmission wavelength, reception wavelength, and route used. The determination unit 321 outputs the generated control information to the communication circuit 302.

[0147] For example, the communication circuit 302 performs frame processing. In a specific example, the communication circuit 302 creates a control frame containing control information. The communication circuit 302 generates a control signal including the created control frame and outputs the generated control signal to the optical TRx303. The optical TRx303 converts the input control signal including the control frame into an optical control signal and transmits the optical control signal to the optical transmission path.

[0148] Optical TRx303 receives an optical control signal and converts it into an electrical control signal. Optical TRx303 outputs the control signal to the communication circuit 302.

[0149] The communication circuit 302 extracts the result of the control processing from the control frame. The communication circuit 302 outputs the extracted information to the processor 311.

[0150] For example, the control device 30 remotely controls the FSOC device 100 using TDM-PON (TDM: Time Division Multiplexing). The control device 30 functions as the central office-side optical line terminal (OLT) of the PON. The processing circuit 120 of the FSOC device 100 functions as the subscriber-side optical network unit (ONU) of the PON. In other words, in this case, the control frame is a PON frame.

[0151] In this case, the control device 30 remotely controls not only the FSOC device 100, but also, for example, the optical transmission device 4 and the light source device 6. Each of the optical transmission device 4 and the light source device 6 functions as an ONU. The control device 30 transmits optical control signals, which are TDM signals for PON frames, to the multiple ONUs under its control. Each of the multiple ONUs, including the FSOC device 100, transmits a PON frame. Multiple PON frames transmitted from the multiple ONUs are time-division multiplexed, and the optical control signals, which are TDM signals, are received by the control device 30.

[0152] [5. Operation of the FSOC device] The operation of the FSOC device will be described below. Figure 7 is a flowchart showing an example of the initialization process of the FSOC device according to this embodiment. The FSOC device 100 performs the initialization process immediately after startup or restart.

[0153] The detection function unit 125 emits a beacon signal and determines whether or not it has detected the beacon signal (optical axis) emitted from the first opposing device (step S101). If the detection function unit 125 has not detected the optical axis (NO in step S101), it repeats step S101. If the detection function unit 125 has detected the optical axis (YES in step S101), it notifies the processing circuit 120 that the optical axis has been successfully detected.

[0154] When the processor 131 of the processing circuit 120 receives notification of successful detection of the optical axis, it commands the tracking function unit 126 to start tracking the optical axis. The tracking function unit 126 starts tracking the optical axis in response to the command from the processing circuit 120 (step S102).

[0155] The received power monitor unit 123R monitors the received power in the optical wireless-to-wired conversion units 124R_C1, 124R_C2, 124R_D1, and 124R_D2. Specifically, the received power monitor unit 123R compares the received power levels of the optical wireless-to-wired conversion units 124R_C1, 124R_C2, 124R_D1, and 124R_D2 with a threshold, and if the received power level of one of the optical wireless-to-wired conversion units 124R_C1 and 124R_C2 exceeds the threshold, it confirms the optical input (reception of the downlink main signal) (step S103).

[0156] For example, if an optical input is detected, the processor 131 generates query information to inquire with the control device 30 about the transmission wavelength of the upstream main signal, the reception wavelength of the downstream main signal, and the path used. The processing circuit 120 transmits a control frame containing the query information to the control device 30.

[0157] When the control device 30 receives the inquiry information, it determines the transmission wavelength of the uplink main signal, the reception wavelength of the downlink main signal, and the path to be used by the FSOC device 100. The control device 30 transmits a control frame containing control information specifying the transmission wavelength of the uplink main signal, the reception wavelength of the downlink main signal, and the path to be used to the FSOC device 100.

[0158] The processor 131 of the FSOC device 100 receives control information (step S104). The processor 131 sets the transmission wavelength of the uplink main signal, the reception wavelength of the downlink main signal, and the path to be used as specified in the received control information (step S105). That is, the processor 131 determines the output destination of the uplink main signal to the transmission wavelength selection unit 121T and commands the transmission wavelength selection unit 121T to determine the output destination. The processor 131 determines the output source of the downlink main signal to the reception wavelength selection unit 121R and commands the reception wavelength selection unit 121R to determine the output source.

[0159] The processor 131 notifies the control device 30 of permission to emit light (transmit the main signal) to the optical transmission device 4 (step S106). That is, the processor 131 generates permission information to permit light emission to the optical transmission device 4. The processing circuit 120 transmits a control frame containing the permission information to the control device 30.

[0160] When the control device 30 receives permission information, it transmits a control frame containing the permission information to the optical transmission device 4. When the optical transmission device 4 receives permission information, it starts transmitting the uplink main signal.

[0161] The processor 131 commands the transmit wavelength selection unit 121T and the receive wavelength selection unit 121R to start operation, and begins transmitting the uplink signal and receiving the downlink signal (step S107). This completes the initialization process.

[0162] Figure 8 is a sequence diagram showing an example of the operation of the control system according to the embodiment. Here, we will describe an example in which the main signal is transmitted and received via the active path.

[0163] For example, if an abnormality occurs, such as the interruption of the currently used path, the processor 131 of the FSOC device 100 detects the abnormality of the used path (current path) based on the outputs of the transmit power monitor unit 123T and the receive power monitor unit 123R, respectively (step S201).

[0164] The processor 131, having detected an abnormality in the usage path, generates abnormality information indicating that an abnormality has occurred in the usage path. The FSOC device 100 transmits a control frame containing the abnormality information to the control device 30 (step S202).

[0165] When the processor 311 of the control device 30 receives abnormal information, it determines a redundant path as a new path to use, and determines the transmission wavelength of the upstream main signal and the reception wavelength of the downstream main signal in the redundant path (step S203). The processor 311 generates control information that specifies the path to use, the transmission wavelength of the upstream main signal, and the reception wavelength of the downstream main signal. The control device 30 transmits a control frame containing the control information to the FSOC device 100 (step S204).

[0166] When the processor 131 of the FSOC device 100 receives control information, it sets the usage path, the transmission wavelength of the uplink main signal, and the reception wavelength of the downlink main signal as specified in the received control information (step S205).

[0167] The transmit power monitor unit 123T checks whether the intensity level of the uplink main signal to be transmitted exceeds a threshold. If the intensity level of the uplink main signal exceeds the threshold, it determines that the transmit power is normal.

[0168] The processor 131 notifies the control device 30 of permission to emit light (transmit the main signal) to the optical transmission device 4. Upon receiving the permission information, the control device 30 transmits a control frame containing the permission information to the optical transmission device 4. Upon receiving the permission information, the optical transmission device 4 starts transmitting the uplink main signal.

[0169] The processor 131 commands the transmit wavelength selection unit 121T and the receive wavelength selection unit 121R to start operation, and begins transmitting the uplink signal and receiving the downlink signal (step S207).

[0170] [6. Variant] In the embodiment described above, the control device 30 controlled the FSOC device 100 using the PON function, but is not limited to this. For example, the control device 30 may control the FSOC device 100 using an OAM function such as Ethernet OAM.

[0171] In the embodiment described above, optical control signals were transmitted and received between the control device 30 and the FSOC device 100, but the embodiment is not limited to this. For example, the control device 30 and the FSOC device 100 may be connected to an Ethernet network configured with electrical signal lines, and control signals, which are electrical signals, may be transmitted and received between the control device 30 and the FSOC device 100.

[0172] [7. Supplementary Notes] The embodiments disclosed herein are illustrative in all respects and are not restrictive. The scope of the present invention is indicated by the claims rather than by the embodiments described above, and includes all modifications within the meaning and scope of the equivalents of the claims. [Explanation of symbols]

[0173] 10A, 10B communication system 2A, 2B Fiber Optic Wired Communication Network 2C communication network 3,3_1A,3_2A,3_1B,3_2B,3_1C Optical switch (optical SW) 4,4A,4B,4C Optical transmission device 5 Network Devices 6 Light source device 20,20_1A,20_1B,20_2A,20_2B Satellite 30, 30A, 30B, 30C control devices 100,100_1A,100_2A,100_1B,100_2B,100_1C FSOC device (optical communication device) 110A,110B Output part 110C,110D entrance part 120 Processing Circuits 121T Transmit Wavelength Selection Section 121R Receiving wavelength selection section 122T_A, 122T_B Transmit Wavelength Conversion Unit 122R_C, 122R_D Receiver Wavelength Conversion Unit 123T Transmitter Power Monitor Unit 123R Receiver Power Monitor Unit 124T Optical Transmitter 124T_A 1st optical transmitter 124T_B 2nd optical transmitter 124T_A1, 124T_A2, 124T_B1, 124T_B2 Optical Wired-to-Wireless Conversion Unit (First Transmitter, Second Transmitter) 124R Optical Receiver 124R_C First Optical Receiver 124R_D Second Optical Receiver 124R_C1, 124R_C2, 124R_D1, 124R_D2 Optical Wireless-to-Wired Conversion Unit (First Receiver, Second Receiver) 125 Detection function unit 126 Tracking function section 127_1, 127_2, 127_3 connectors 128T, 128R WDM coupler 131 processors 132 Non-volatile memory 133 Volatile memory 134 Communication Circuit 135 Optical TRx 136 Input / Output Interfaces (I / O) 140 Control Programs 141 Control Unit 142 Anomaly detection unit 143 Notification Department 301 Processing Circuit 302 Communication Circuit 303 Optical TRx 311 Processors 312 memory 320 Remote Control Programs 321 Decision Section

Claims

1. An optical transmission unit that transmits a main signal, which is an optical signal, into free space, A control unit that controls the wavelength of the main signal transmitted by the optical transmission unit, Equipped with, Optical communication device.

2. The aforementioned optical transmitting unit is A first transmitting unit that transmits an optical signal of a first wavelength, A second transmitting unit that transmits an optical signal of a second wavelength different from the first wavelength, Includes, The control unit selects either the transmission of the main signal at the first wavelength by the first transmitting unit, or the transmission of the main signal at the second wavelength by the second transmitting unit. The optical communication device according to claim 1.

3. The first transmitting unit transmits the main signal received from the outside without changing its wavelength. The optical communication device further includes a wavelength conversion unit that converts the wavelength of the main signal received from the outside from a first wavelength to a second wavelength, The second transmitting unit transmits the main signal of the second wavelength output from the wavelength conversion unit. The optical communication device according to claim 2.

4. The aforementioned optical transmitting unit is A first optical transmitting unit capable of transmitting the main signal, A second optical transmitting unit capable of transmitting the main signal, Includes, The control unit selects one of the first optical transmission unit and the second optical transmission unit as the source of the main signal. The optical communication device according to claim 1.

5. The first optical transmission unit is included in the first path in the communication network. The second optical transmission unit is included in the second path, which is a redundant path of the first path in the communication network. The optical communication device according to claim 4.

6. The control unit selects the first optical transmission unit as the source when no abnormality occurs in the first optical transmission unit, and selects the second optical transmission unit as the source when an abnormality occurs in the first optical transmission unit. The optical communication device according to claim 4.

7. It includes a receiving unit that receives control signals, including control information transmitted from a control device, The control unit controls the wavelength of the main signal transmitted by the optical transmission unit based on the control information included in the control signal received by the receiving unit. The optical communication device according to claim 1.

8. The aforementioned control signal is an optical control signal as an optical signal. The optical communication device according to claim 7.

9. The receiving unit is connected to the optical fiber cable and receives the multiplexed signal of the main signal and the optical control signal transmitted through the optical fiber cable. The optical communication device according to claim 8.

10. The control wavelength, which is the wavelength of the optical control signal, is different from the wavelength of the main signal. The aforementioned multiplexed signal is a wavelength division multiplexed signal of the main signal and the optical control signal. The optical communication device according to claim 9.

11. The control wavelength, which is the wavelength of the optical control signal, is the same as the wavelength of the main signal. The aforementioned multiplexed signal is a time-division multiplexed signal of the main signal and the optical control signal. The optical communication device according to claim 9.

12. The control unit functions as a subscriber-side optical line termination device corresponding to the control unit which functions as a central office-side optical line termination device in a passive optical network. The optical communication device according to claim 8.

13. An anomaly detection unit that detects anomalies related to the transmission and reception of the optical signal through the free space, A notification unit that notifies an external control device of the abnormality detected by the abnormality detection unit, Furthermore, The optical communication device according to any one of claims 1 to 12.

14. The system further includes a tracking function that tracks the optical axis formed between the system and the opposing device via the aforementioned free space, The abnormality detection unit detects an abnormality in the tracking of the optical axis by the tracking function unit. The optical communication device according to claim 13.

15. A control device for controlling an optical communication device that transmits and receives a main signal, which is an optical signal, via free space, A determination unit that determines the wavelength of the main signal transmitted from the optical communication device to the free space, A transmitting unit that transmits a control signal indicating the wavelength of the main signal determined by the determination unit to the optical communication device, Equipped with, Control device.

16. An optical communication device that transmits and receives a main signal, which is an optical signal, via free space, A control device for controlling the optical communication device, Equipped with, The optical communication device is An optical transmitting unit that transmits the main signal to the free space, A control unit that controls the wavelength of the main signal transmitted by the optical transmission unit, Includes, The control device is A determination unit that determines the wavelength of the main signal transmitted from the optical communication device to the free space, A transmitting unit that transmits a control signal indicating the wavelength of the main signal determined by the determination unit to the optical communication device, Includes, The control unit sets the wavelength of the main signal to the wavelength indicated in the control signal received from the control device. Control system.

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