Communication system, optical communication device, and control signal transmission method

Abstract

To constitute an economical system using light and wireless means in combination.SOLUTION: In a communication system including an optical communication device and a terahertz wave generating device, the optical communication device includes a light source that outputs light having multiple wavelengths, a wavelength selection unit that selects, from the light having multiple wavelengths output from the light source, light of a plurality of wavelengths to be used to generate a desired terahertz wave signal and light having a wavelength for a control signal addressed to a subscriber device connected to the optical communication device, a control signal generation unit that generates a control signal by modulating the light having the wavelength for the control signal with the control signal addressed to the subscriber device, and a light distribution unit that transfers the light having the plurality of wavelengths selected by the wavelength selection unit to the terahertz wave generating device and transfers the control signal generated by the control signal generation unit to the subscriber device, and the terahertz wave generating device includes a terahertz wave generation unit that generates a terahertz wave signal based on the light of the plurality of wavelengths transferred from the light distribution unit.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a communication system, an optical communication device, and a control signal transmission method. [Background technology]

[0002] In recent years, there has been active research into the generation and application of electromagnetic waves in a frequency band called terahertz waves. Terahertz waves refer to a frequency band from approximately 100 GHz to 10 THz. This frequency band is not assigned to any frequencies under the Radio Law, and high-speed wireless communication is expected due to its high carrier frequency and wide frequency band. Terahertz waves have the directivity that is a characteristic of light waves, and the transparency that is a characteristic of radio waves. Furthermore, since terahertz waves have a shorter wavelength than radio waves, they can be used in imaging inspections (non-destructive inspections that do not use X-rays) and, in recent years, materials with absorption spectra specific to this frequency band have been discovered, and the possibility of applying terahertz waves to various fields from the perspective of material inspection is expanding.

[0003] Specific applications of terahertz waves include high-speed wireless communication replacing radio waves, imaging inspections such as airport security checks, hazardous material inspection of mail, quality assurance by internal defect inspection on production lines, and skin beauty diagnosis, as well as material inspections such as the detection of toxic gases in closed spaces, moisture content inspection, and detection of impurities in pharmaceuticals. Applications of terahertz waves are diverse, including information and communications, industry, biomedicine, and security.

[0004] On the other hand, serious issues such as further increase in communication volume, further complexity of the network, and increase in delay due to congestion are expected in the future. To address these issues, the Innovative Optical and Wireless Network (IOWN) concept, one of the next-generation information infrastructures, has been proposed. The IOWN concept is composed of the All-Photonics Network (APN), which introduces photonics technology to everything from the network to the terminals, Digital Twin Computing (DTC), which realizes future predictions by combining the real world and the digital world, and the Cognitive Foundation (CF), which connects everything and realizes its control. In particular, the APN relays the optical access network, including the optical backbone network and the wireless section, with optical nodes called Photonic Gateways (Ph-GWs), and provides optical paths End-to-End (E2E). To realize optical paths in E2E, it is necessary to specify and control the wavelength for each user, and to control and monitor the wavelength of the signal.

[0005] Remote wavelength control and monitoring functions are broadly divided into out-channel control and in-channel control. Out-channel control is control via a separate monitoring and control network, for example, and requires network reachability (provision of lines) for the control signals. On the other hand, in-channel control exchanges control signals over the same lines as data signals. The simplest method of in-channel control is to use the main signal (wavelength λ1) and control signal (wavelength λ2) on the same core wire using wavelength division multiplexing. In this case, a light source that generates an optical signal with wavelength λ1, which is the main signal, and a light source that generates an optical signal with wavelength λ2, which is the control signal, are required.

[0006] Patent Document 1 proposes a system that has the flexibility to select a desired terahertz wave on the remote side by installing a light source for generating terahertz waves on the center side, receiving light output from the light source installed on the center side on the remote side, and converting two selectively received wavelengths on the remote side into the terahertz range by difference frequency generation of a nonlinear optical effect or by optical beats. The configuration shown in Patent Document 1 is highly compatible with the APN described above, since it uses a wideband terahertz band to increase the speed of wireless sections and utilizes photonics technology to directly convert optical signals into wireless signals. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2023-20088 A Summary of the Invention [Problem to be solved by the invention]

[0008] The configuration shown in Patent Document 1 is a configuration in which a light source capable of outputting multiple wavelengths (e.g., an optical comb light source, an LD (Laser Diode) array) is mounted on the center side, a fundamental wave for generating terahertz waves is transmitted to the remote side via optical fiber, and the remote side selectively converts the two wavelengths received into the terahertz range. In this configuration, the light source installed on the center side outputs light of multiple optical wavelengths (e.g., n wavelengths) to generate desired terahertz waves depending on the application, and the remote side selects the desired two wavelengths from the light of n wavelengths, n This allows the generation of terahertz waves in two highly flexible ways. On the other hand, the wavelengths that are not used to generate terahertz waves become surplus. Therefore, with the conventional method, it was impossible to build an economical system that combined light and wireless technology.

[0009] In view of the above circumstances, an object of the present invention is to provide a technique that enables the construction of an economical system that combines optical and wireless communication. [Means for solving the problem]

[0010] One aspect of the present invention is a communication system comprising an optical communications device and a terahertz wave generating device, wherein the optical communications device comprises a light source that outputs multiple wavelengths of light, a wavelength selection unit that selects, from the multiple wavelengths of light output from the light source, light of multiple wavelengths to be used to generate a desired terahertz wave signal and light of a wavelength for a control signal addressed to a subscriber device connected to the optical communications device, a control signal generation unit that generates a control signal by modulating the light of the wavelength for the control signal with a control signal addressed to the subscriber device, and a light distribution unit that transfers the multiple wavelengths of light selected by the wavelength selection unit to the terahertz wave generating device and transfers the control signal generated by the control signal generation unit to the subscriber device, and the terahertz wave generating device comprises a terahertz wave generation unit that generates a terahertz wave signal based on the multiple wavelengths of light transferred from the light distribution unit.

[0011] One aspect of the present invention is an optical communications device in a communication system comprising an optical communications device and a terahertz wave generating device, the optical communications device comprising: a light source that outputs multi-wavelength light; a wavelength selection unit that selects, from the multi-wavelength light output from the light source, light of multiple wavelengths to be used to generate a desired terahertz wave signal and light of a wavelength for a control signal addressed to a subscriber device connected to the optical communications device; a control signal generation unit that generates a control signal by modulating the light of the wavelength for the control signal with a control signal addressed to the subscriber device; and an optical distribution unit that transfers the light of the multiple wavelengths selected by the wavelength selection unit to the terahertz wave generating device and transfers the control signal generated by the control signal generation unit to the subscriber device.

[0012] One aspect of the present invention is a control signal transmission method performed by an optical communication device in a communication system including the optical communication device and a terahertz wave generating device, the control signal transmission method selecting, from the multi-wavelength light output from a light source that outputs multi-wavelength light, light of multiple wavelengths to be used for generating a desired terahertz wave signal and light of a wavelength for a control signal addressed to a subscriber device connected to the optical communication device, generating a control signal by modulating the light of the wavelength for the control signal with a control signal addressed to the subscriber device, transferring the selected light of the multiple wavelengths to the terahertz wave generating device, and transferring the generated control signal to the subscriber device. Effect of the Invention

[0013] The present invention makes it possible to build an economical system that combines optical and wireless communication. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a communication system according to a first embodiment. [Diagram 2] 1 is a diagram showing a first configuration of a terahertz wave generating device in a first embodiment. [Diagram 3] 4 is a diagram showing a second configuration of the terahertz wave generating device in the first embodiment. FIG. [Figure 4] FIG. 4 is a sequence diagram showing a processing flow of the communication system in the first embodiment. [Diagram 5] FIG. 11 is a diagram illustrating a configuration of a communication system according to a second embodiment. [Figure 6] FIG. 11 is a diagram illustrating an example of the configuration of a subscriber device in the second embodiment. [Figure 7] FIG. 13 is a diagram illustrating an example of the configuration of a subscriber device in the third embodiment. [Figure 8] FIG. 13 is a diagram illustrating the relationship between the saturation characteristic of a reflective SOA and an input signal in the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. (First embodiment) FIG. 1 is a diagram showing a configuration of a communication system 100 in the first embodiment. The communication system 100 includes a plurality of optical communication devices 10, a management control device 15, and one or more terahertz wave generating devices 20. FIG. 1 shows an example in which the number of optical communication devices 10 is three and the number of terahertz wave generating devices 20 is one, but the number of optical communication devices 10 and terahertz wave generating devices 20 is not particularly limited. In FIG. 1, a plurality of subscriber devices 30-1 and 30-2 are connected to the optical communication device 10-1 via an optical transmission path such as an optical fiber. The optical communication devices 10 and the optical communication device 10-1 and the terahertz wave generating device 20-1 are connected to each other via an optical transmission path. The optical communication device 10-1 and the management control device 15 are connected to each other via an electric line for transmitting an electric signal.

[0016] 1, for convenience of explanation, a configuration is shown in which the management control device 15 is connected only to the optical communication device 10-1, but the management control device 15 is connected to each optical communication device 10. As shown in Fig. 1, the optical communication device 10-1 is provided on the center side that controls the system, and the terahertz wave generating device 20 is provided at a location (remote side) away from the installation position of the optical communication device 10.

[0017] The optical communication device 10 selects two wavelengths of light to be used to generate a desired terahertz wave signal in the terahertz wave generating device 20 from the multi-wavelength light output from a light source capable of outputting multi-wavelength light, and transmits the selected light to the terahertz wave generating device 20. The desired terahertz wave signal is a signal with a terahertz frequency required in the environment in which the terahertz wave generating device 20 is installed. That is, the desired terahertz wave signal differs depending on the environment in which the terahertz wave generating device 20 is installed. The optical communication device 10 may hold information on the two wavelengths of light to be used to generate a desired terahertz wave signal for each terahertz wave generating device 20, or may be notified by the terahertz wave generating device 20. In this way, the terahertz wave generating device 20 can generate a signal with a terahertz frequency required depending on the environment in which the terahertz wave generating device 20 is installed.

[0018] Furthermore, the optical communication device 10 generates a control signal addressed to the subscriber device 30 based on the light of the wavelengths assigned to the subscriber device 30 that is the destination of the control signal received from the management control device 15, out of the multi-wavelength light. The control signal is a signal for controlling the subscriber device 30. The optical communication device 10 transmits the generated control signal to the destination subscriber device 30. In this way, the optical communication device 10 assigns at least one wavelength output from a light source capable of outputting multi-wavelength light, as a wavelength for transmitting the control signal.

[0019] The management control device 15 controls the optical communication device 10 and the subscriber device 30. For example, the management control device 15 assigns a wavelength to be used for communication to the subscriber device 30 in response to a request from the subscriber device 30. For example, the management control device 15 instructs the optical communication device 10 to transmit a control signal to the destination subscriber device 30.

[0020] The terahertz wave generating device 20 generates a terahertz wave signal based on the light of two wavelengths transmitted from the optical communication device 10.

[0021] The subscriber device 30 communicates with other devices via the optical communication device 10. The subscriber device 30 communicates by using light of a wavelength assigned by the management control device 15. The subscriber devices 30-1 and 30-2 connected to the optical communication device 10-1 communicate by using light of different wavelengths.

[0022] Next, a specific configuration of the optical communication device 10 will be described. The optical communication device 10 includes a light source 11, a wavelength selection unit 12, a control signal generation unit 13, and a light distribution unit 14. The light source 11 is a light source capable of outputting optical signals of multiple wavelengths. For example, the light source 11 is an optical comb light source 111 or an LD array 112.

[0023] The optical comb light source 111 has a wavelength interval of Δλ=λ0 2 Multi-wavelength (e.g., λ1~λ m ) optical signal. Here, "λ0" represents an arbitrary reference wavelength. "f0" represents a frequency determined by the clock frequency of the optical comb light source 111. "C" represents the speed of light. "m" represents an integer equal to or greater than 2. When the light source 11 is an optical comb light source 111, the optical comb light source 111 outputs a multi-wavelength optical signal with wavelength spacing "Δλ" to the wavelength selection unit 12. The output spectrum of the multi-wavelength optical signal output from the optical comb light source 111 is shown in FIG. 1.

[0024] The LD array 112 is composed of multiple LDs arranged on an array. Each LD has a different wavelength (e.g., λ1 to λ m ) laser light. The LD array 112 outputs the multi-wavelength optical signals output from each LD to the wavelength selection unit 12. The output spectrum of the multi-wavelength optical signals output from the LD array 112 is shown in FIG.

[0025] The wavelength selection unit 12 is a wavelength filter for extracting a specific wavelength. The wavelength selection unit 12 extracts, for example, two wavelengths for generating a desired terahertz wave in the terahertz wave generating device 20. This allows the wavelength selection unit 12 to select light of a specific wavelength from a multi-wavelength optical signal with a wavelength interval of "Δλ". The two-wavelength light selected by the wavelength selection unit 12 (transmitted through the wavelength selection unit 12) is transferred to the terahertz wave generating device 20 via the light distribution unit 14. For example, it is assumed that the two-wavelength light selected by the wavelength selection unit 12 (transmitted through the wavelength selection unit 12) is light of λ2 and light of λ5. Note that the combination of light of λ2 and light of λ5 is just an example, and other combinations may be used.

[0026] Furthermore, the wavelength selection unit 12 extracts light of a wavelength (hereinafter referred to as the "control wavelength") for transmitting a control signal received from the management control device 15. For example, the wavelength selection unit 12 extracts light of a wavelength assigned to the subscriber device 30 that is the destination of the control signal received from the management control device 15 as the control wavelength. This allows the wavelength selection unit 12 to select light of a control wavelength for transmitting a control signal to the subscriber device 30 from among multi-wavelength optical signals with wavelength intervals of "Δλ". In FIG. 1, the light of the control wavelength is assumed to be light of λ1down. The light of the control wavelength selected by the wavelength selection unit 12 (transmitted through the wavelength selection unit 12) is output to the control signal generation unit 13.

[0027] The control signal generating unit 13 receives as input a control signal received from the management control device 15 and the light of the control wavelength output from the wavelength selecting unit 12. The control signal generating unit 13 generates a control signal (optical signal) by modulating the light of the control wavelength with the control signal.

[0028] The light distribution unit 14 has a plurality of first ports and a plurality of second ports. The light distribution unit 14 outputs an optical signal input from one port from another port. The wavelength selection unit 12 and the control signal generation unit 13 are connected to the first port of the light distribution unit 14, and the plurality of subscriber devices 30-1, 30-2 and the terahertz wave generation device 20 are connected to the second port of the light distribution unit 14. The light distribution unit 14 transfers the light of two wavelengths output from the wavelength selection unit 12 to the terahertz wave generation device 20 as the destination, and transfers the control signal (optical signal) output from the control signal generation unit 13 to the subscriber device 30 as the destination.

[0029] Next, a specific configuration of the terahertz wave generating device 20 will be described with reference to Fig. 2 and Fig. 3. Fig. 2 is a diagram showing a first configuration of the terahertz wave generating device 20 in the first embodiment. The terahertz wave generating device 20 shown in Fig. 2 includes an optical amplifier 22, a polarizer 23, and a terahertz wave generating unit 24.

[0030] The optical amplifier 22 receives the optical signals of two wavelengths output from the optical communication device 10-1. The optical amplifier 22 amplifies the input optical signals of two wavelengths. The amplification by the optical amplifier 22 is for efficiently generating a nonlinear optical effect. Note that if the intensity of the light of the two wavelengths transmitted from the optical communication device 10 is sufficiently high when received by the terahertz wave generating device 20, the optical amplifier 22 does not need to be provided.

[0031] The polarizer 23 transmits only light having a specific polarization state among the two wavelengths of light amplified by the optical amplifier 22 .

[0032] Terahertz wave generating unit 24 generates a terahertz wave optical signal using the light of two wavelengths transmitted through polarizer 23. Terahertz wave generating unit 24 is, for example, a nonlinear optical crystal. In the nonlinear optical crystal, light (ω3 = |ω5 - ω2|) equivalent to the difference frequency of the optical frequencies (in FIG. 2, λ2 = ω2, λ5 = ω5) is generated by difference frequency generation of the second-order nonlinear optical effect. By selecting the two wavelengths to be input to the nonlinear optical crystal, it is possible to generate light in the terahertz region (terahertz waves).

[0033] 3 is a diagram showing a second configuration of the terahertz wave generation device 20 in the first embodiment. The terahertz wave generation device 20 shown in FIG. 3 includes a plurality of wavelength selection units 21-1 and 21-2, a terahertz wave generation unit 24, a coupler 25, and a coupler .

[0034] The coupler 25 branches the light of two wavelengths transmitted from the optical communication device 10. The coupler 25 is, for example, a 3 dB optical coupler, and outputs the input light of two wavelengths to a first path and a second path. A wavelength selection unit 21-1 is connected to the first path, and a wavelength selection unit 21-2 is connected to the second path.

[0035] The wavelength selection unit 21-1 is a wavelength filter. The wavelength selection unit 21-1 extracts light of wavelength λ2, for example. The light of the wavelength extracted by the wavelength selection unit 21-1 is input to the coupler 26.

[0036] The wavelength selection unit 21-2 is a wavelength filter. The wavelength selection unit 21-2 extracts light of wavelength λ5, for example. The light of the wavelength extracted by the wavelength selection unit 21-2 is input to the coupler 26.

[0037] As described above, in the second configuration, the wavelength selection units 21-1 and 21-2 extract two wavelengths for generating desired terahertz waves.

[0038] The coupler 26 multiplexes the light of the wavelength output from the wavelength selection unit 21-1 (e.g., light of wavelength λ2) and the light of the wavelength output from the wavelength selection unit 21-2 (e.g., an optical signal of wavelength λ5). The coupler 26 is, for example, a 3 dB optical coupler. By multiplexing a plurality of optical signals by the coupler 26, an optical beat (f2-f5) signal of the two input wavelengths (λ2=f2, λ5=f5, assuming f2>f5) is generated.

[0039] The terahertz wave generating unit 24 generates a terahertz wave optical signal using the optical beat signal generated by the coupler 26. The terahertz wave generating unit 24 is, for example, a UTC-PD. The terahertz wave generating unit 24 is capable of generating light in the terahertz region (terahertz wave) by photoelectrically converting the input optical beat signal.

[0040] 4 is a sequence diagram showing a process flow of the communication system 100 in the first embodiment. In the explanation of FIG. 4, it is assumed that the terahertz wave generating device 20 has the first configuration shown in FIG. The optical communication device 10 receives a control signal transmitted from the management control device 15 (step S101). The control signal received by the optical communication device 10 is input to the control signal generating unit 13. The light source 11 outputs light of multiple wavelengths (step S102). The wavelength selecting unit 12 selects a wavelength by transmitting two wavelengths of light for generating a desired terahertz wave and light of a control wavelength of the control signal (step S103). The two wavelengths of light transmitted by the wavelength selecting unit 12 may be preset in the wavelength selecting unit 12, or may be notified from the terahertz wave generating device 20. The light of the control wavelength of the control signal transmitted by the wavelength selecting unit 12 may be notified from the management control device 15 at the same time as the control signal, or may be selected by referring to the information of the wavelengths held when the optical communication device 10 holds information of the wavelengths assigned to each subscriber device 30.

[0041] The wavelength selection unit 12 outputs the light of the selected control wavelength to the control signal generation unit 13. The control signal generation unit 13 generates a control signal (optical signal) by modulating the input light of the control wavelength based on the control signal (step S104). The wavelength selection unit 12 outputs the generated control signal (optical signal) to the optical distribution unit 14. The optical distribution unit 14 connects a first port to which the control signal generation unit 13 is connected and a second port to which the destination subscriber device 30 is connected, in response to an instruction from the management control device 15 or an instruction from a control unit (not shown) included in the optical communication device 10. Therefore, the optical distribution unit 14 outputs the control signal (optical signal) input from the first port to which the control signal generation unit 13 is connected from the second port to which the destination subscriber device 30 is connected. In this manner, the optical distribution unit 14 transfers the control signal (optical signal) (step S105). The control signal (optical signal) transferred from the optical distribution unit 14 is received by the subscriber device 30 (step S106). The subscriber device 30 performs setting based on the received control signal (optical signal) (step S107).

[0042] The wavelength selection unit 12 outputs the light of the two wavelengths selected in the process of step S103 to the light distribution unit 14. In the light distribution unit 14, a first port to which the wavelength selection unit 12 is connected is connected to a second port to which the terahertz wave generating device 20 is connected, according to an instruction from a control unit (not shown) included in the optical communication device 10. Therefore, the light distribution unit 14 outputs the light of the two wavelengths input from the first port to which the wavelength selection unit 12 is connected from the second port to which the terahertz wave generating device 20 is connected. In this manner, the light distribution unit 14 transfers the light of the two wavelengths (step S108). The light of the two wavelengths transferred from the light distribution unit 14 is received by the terahertz wave generating device 20.

[0043] The optical amplifier 22 of the terahertz wave generating device 20 amplifies the received light of the two wavelengths (step S109). The optical amplifier 22 outputs the amplified light of the two wavelengths to the polarizer 23. The polarizer 23 transmits only optical signals of a specific polarization state in the light of the two wavelengths amplified by the optical amplifier 22 (step S110). The light of the two wavelengths that has passed through the polarizer 23 is input to the terahertz wave generating unit 24. The terahertz wave generating unit 24 uses the light of the two wavelengths that has passed through the polarizer 23 to utilize the nonlinear optical effect, thereby generating an optical signal of a terahertz wave (step S111).

[0044] According to the communication system 100 configured as above, among the multi-wavelength light output from the light source 11 installed on the center side, some wavelengths (spectrum) are used as control wavelengths. This makes it unnecessary to provide a light source for the control signal, which was previously necessary. Therefore, it becomes possible to build an economical system that combines light and wireless.

[0045] Second embodiment In the second embodiment, a configuration will be described in which a wavelength (spectrum) output from a light source installed in an optical communication device is assigned to a wavelength for a control signal transmitted from a subscriber device to a management control device.

[0046] FIG. 5 is a diagram showing a configuration of a communication system 100a in the second embodiment. The communication system 100a includes a plurality of optical communication devices 10a, a management control device 15, and one or more terahertz wave generating devices 20. FIG. 5 shows an example in which the number of optical communication devices 10a is three and the number of terahertz wave generating devices 20 is one, but the number of optical communication devices 10a and terahertz wave generating devices 20 is not particularly limited. In FIG. 5, a plurality of subscriber devices 30a-1 and 30a-2 are connected to the optical communication device 10a-1 via an optical transmission path such as an optical fiber. The optical communication devices 10a and the optical communication device 10a-1 and the terahertz wave generating device 20-1 are connected to each other via an optical transmission path. The optical communication device 10-1 and the management control device 15 are connected to each other via an electric line for transmitting an electric signal.

[0047] The optical communication device 10a includes a light source 11, a wavelength selection unit 12a, a control signal generation unit 13a, and a light distribution unit 14. The wavelength selection unit 12a is a wavelength filter for extracting a specific wavelength. The wavelength selection unit 12a is similar to the first embodiment in that it extracts two wavelengths for generating desired terahertz waves in the terahertz wave generation device 20 and extracts light of a control wavelength.

[0048] Furthermore, the wavelength selection unit 12a extracts light of a wavelength (hereinafter referred to as the "upstream control wavelength") used for transmitting a control signal from the subscriber device 30a to the management and control device 15. In FIG. 5, the light of the upstream control wavelength is assumed to be light of λ1up. λ1down and λ1up are different wavelengths. For example, the wavelength λ1down is 1550 nm, and the wavelength λ1up is 1310 nm. Note that the values ​​of the wavelengths λ1down and λ1up are merely examples, and other wavelengths may also be used. The light of the control wavelength selected by the wavelength selection unit 12a (transmitted through the wavelength selection unit 12a) and the light of the upstream control wavelength are output to the control signal generation unit 13a.

[0049] The control signal generating unit 13a receives as input a control signal received from the management control device 15, the light of the control wavelength output from the wavelength selecting unit 12a, and the light of the upstream control wavelength. The control signal generating unit 13a generates a control signal (optical signal) by modulating the light of the control wavelength with the control signal. The control signal generating unit 13a multiplexes the generated control signal (optical signal) with the input light of the upstream control wavelength and outputs the multiplexed signal to the optical distribution unit 14 as a control signal. At this time, the control signal generating unit 13a multiplexes the input light of the upstream control wavelength with the control signal (optical signal) without modulating it. The light of the upstream control wavelength is unmodulated CW (Continuous wave) light. As a result, the control signal (optical signal) and the light of the upstream control wavelength are transferred to the destination subscriber device 30a.

[0050] Although FIG. 5 shows a configuration in which light of the upstream control wavelength is also input to the control signal generating unit 13a, the configuration may also be such that light of the upstream control wavelength is output from another port of the wavelength selecting unit 12a, and is multiplexed with the control signal (optical signal) output from the control signal generating unit 13a, and then transmitted to the subscriber device 30a via the optical distribution unit 14.

[0051] 6 is a diagram showing an example of the configuration of a subscriber device 30a in the second embodiment. The subscriber device 30a includes a main signal transceiver 31, a MAC 32, a WDM filter 33, a control signal receiver 34, a management and control unit 35, and a modulator 36.

[0052] The main signal transceiver 31 transmits the main signal output from the MAC 32 via the WDM filter 33 , or receives the main signal separated by the WDM filter 33 .

[0053] The MAC 32 performs processing in the MAC (Media Access Control) layer on the main signal received by the main signal transceiver 31. The MAC 32 outputs the processed main signal to the outside. The MAC 32 performs processing in the MAC layer on the main signal input from the outside and outputs it to the main signal transceiver 31.

[0054] The WDM filter 33 is a wavelength multiplexer / demultiplexer that multiplexes or demultiplexes input optical signals. The WDM filter 33 separates, for example, a main signal light of a certain wavelength from a control signal light. More specifically, the WDM filter 33 separates a main signal light of a certain wavelength from a control signal light of a control wavelength (wavelength λ1down in FIG. 6) and an upstream control wavelength light (wavelength λ1up in FIG. 6). The main signal light of a certain wavelength separated by the WDM filter 33 is input to the main signal transceiver 31, the separated control signal light of the control wavelength is input to the control signal receiver 34, and the separated upstream control wavelength light is folded back and input to the modulator 36.

[0055] The control signal receiver receives a control signal (optical signal). The control signal receiver converts the received control signal (optical signal) into a control signal (electrical signal), and outputs the control signal to the management control unit .

[0056] The management and control unit 35 interprets the content of the control signal based on the control signal (electrical signal) output from the control signal receiver 34. The management and control unit 35 outputs the control signal (electrical signal) to the outside. The management and control unit 35 inputs an upstream control signal addressed to the management control device 15 from the outside. The management and control unit 35 outputs the input upstream control signal to the modulator 36.

[0057] The modulator 36 receives as input the light of the upstream control wavelength output from the WDM filter 33 and the upstream control signal output from the management and control unit 35. The modulator 36 generates an upstream control signal (optical signal) by modulating the input light of the upstream control wavelength with the upstream control signal output from the management and control unit 35. The modulator 36 transmits the generated upstream control signal (optical signal) to the optical communication device 10 via the WDM filter 33.

[0058] According to the communication system 100a configured as above, the wavelength (spectrum) output from the light source 11 installed in the optical communication device 10a is assigned to the wavelength for the control signal transmitted from the subscriber device 30a to the management control device 15, thereby eliminating the need for a light source for the control signal of the optical communication device 10 and the subscriber device 30a. Therefore, it becomes possible to build an economical system combining optical and wireless.

[0059] (Third embodiment) In the third embodiment, a configuration will be described in which a wavelength (spectrum) output from a light source installed in an optical communication device is assigned as a control wavelength to be transmitted from the optical communication device to a subscriber device, and the light of the control wavelength is reused as a control signal light to be transmitted from the subscriber device to the optical communication device. The system configuration in the third embodiment is similar to that of the first embodiment. Below, the third embodiment will be described taking the differences from the first embodiment as an example.

[0060] 7 is a diagram showing an example of the configuration of a subscriber device 30b in the third embodiment. The subscriber device 30b includes a main signal transceiver 31, a MAC 32, a WDM filter 33, a control signal receiver 34, a management and control unit 35, a coupler 37, and a reflective SOA 38. The subscriber device 30b does not include a modulator 36, and is different from the subscriber device 30a in that it newly includes a coupler 37 and a reflective SOA 38. The other configurations of the subscriber device 30b are similar to those of the subscriber device 30a. The following description will focus on the differences from the subscriber device 30a.

[0061] The main signal transceiver 31 transmits the main signal output from the MAC 32 via the WDM filter 33 , or receives the main signal separated by the WDM filter 33 .

[0062] The MAC 32 performs processing in the MAC layer on the main signal received by the main signal transceiver 31. The MAC 32 outputs the processed main signal to the outside. The MAC 32 performs processing in the MAC layer on the main signal input from the outside and outputs it to the main signal transceiver 31.

[0063] The WDM filter 33 is a wavelength multiplexer / demultiplexer that multiplexes or demultiplexes input optical signals. The WDM filter 33 separates, for example, a main signal light of a certain wavelength from a control signal light. More specifically, the WDM filter 33 separates a main signal light of a certain wavelength from a control signal light of a control wavelength (wavelength λ1down in FIG. 7). The main signal light of a certain wavelength separated by the WDM filter 33 is input to the main signal transceiver 31, and the separated control signal light of the control wavelength is input to the coupler 37.

[0064] The control signal receiver receives a control signal (optical signal). The control signal receiver converts the received control signal (optical signal) into a control signal (electrical signal), and outputs the control signal to the management control unit .

[0065] The management and control unit 35 interprets the content of the control signal based on the control signal (electrical signal) output from the control signal receiver 34. The management and control unit 35 outputs the control signal (electrical signal) to the outside. The management and control unit 35 inputs an upstream control signal addressed to the management control device 15 from the outside. The management and control unit 35 outputs the input upstream control signal to the reflective SOA 38.

[0066] The coupler 37 branches the light of the control signal with the control wavelength output from the WDM filter 33. The light of the control signal with the control wavelength branched by the coupler 37 is output to the control signal receiver and the reflective SOA .

[0067] The reflective SOA 38 is an optical amplifier in which a reflective multilayer film is formed on the end face of an SOA (Semiconductor Optical Amplifier). The reflective SOA 38 has a characteristic that the output optical intensity is saturated with respect to the injection current as shown in FIG. 8. FIG. 8 is a diagram showing the relationship between the saturation characteristic of the reflective SOA 38 in the third embodiment and the input signal. When a modulated optical signal is input with the characteristic shown in FIG. 8, the output optical signal becomes a signal in which the modulated optical signal is saturated as shown in FIG. 8. When the reflective SOA 38 having such a characteristic is used, the modulated optical signal, which is a bit pattern of "1" and "0" input to the reflective SOA 38, is saturated (smoothed) and becomes a continuous signal that is not a bit pattern of "1" and "0". This continuous signal is the output optical signal. The reflective SOA 38 generates an upstream control signal (optical signal) by modulating the output optical signal with an upstream control signal. The reflective SOA 38 transmits the generated upstream control signal (optical signal) to the optical communication device 10 via the WDM filter 33.

[0068] According to the communication system 100 in the third embodiment configured as above, the wavelength (spectrum) output from the light source 11 installed in the optical communication device 10 is assigned as a control wavelength to be transmitted from the optical communication device 10 to the subscriber device 30b, and the light of the control wavelength is reused as a control signal light to be transmitted from the subscriber device 30b to the optical communication device 10. This makes it possible to reduce the number of wavelengths of the control signal assigned to the subscriber device 30b by half. Therefore, it becomes possible to improve the wavelength utilization efficiency. Furthermore, it becomes possible to eliminate the light source that is used as a control signal for the optical communication device 10a and the subscriber device 30b, which was previously necessary. Therefore, it becomes possible to build an economical system that combines light and wireless.

[0069] In the above-mentioned embodiment, the program implemented in the above-mentioned form does not depend on a single device, but may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read into a computer system and executed to perform image processing. Note that the term "computer system" here includes hardware such as an OS and peripheral devices. The term "computer system" also includes a WWW system equipped with a homepage providing environment (or display environment). The term "computer-readable recording medium" also includes a memory that holds a program for a certain period of time, such as a volatile memory (RAM) inside a computer system that becomes a server or client when a program is transmitted via a network such as the Internet or a communication line such as a telephone line.

[0070] The above program may also be transmitted from a computer system in which the program is stored in a storage device or the like to another computer system via a transmission medium, or by transmission waves in the transmission medium. Here, the "transmission medium" that transmits the program refers to a medium that has the function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. The above program may also be for realizing part of the above-mentioned functions. Furthermore, it may be a so-called difference file (difference program) that can realize the above-mentioned functions in combination with a program already recorded in the computer system. [Industrial Applicability]

[0071] The present invention is applicable to systems that generate and utilize terahertz waves.

[0072] Although an embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and designs that do not deviate from the gist of the present invention are also included. [Explanation of symbols]

[0073] 10, 10a...optical communication device, 11...light source, 12, 12a...wavelength selection unit, 13, 13a...control signal generation unit, 14...light distribution unit, 15...management control device, 20...terahertz wave generation device, 21, 21-1 to 21-2...wavelength selection unit, 22...optical amplification unit, 23...polarizer, 24...terahertz wave generation unit, 25, 26...coupler, 30, 30-1 to 30-2, 30a, 30a-1 to 30a-2...subscriber device, 31...main signal transceiver, 32...MAC, 33...WDM filter, 34...control signal receiver, 35...management control unit, 36...modulator, 37...coupler, 38...reflective SOA, 100, 100a...communication system, 111...optical comb light source, 112…LD array

Claims

1. A communication system including an optical communication device and a terahertz wave generating device, The optical communication device includes: A light source that outputs light of multiple wavelengths; a wavelength selection unit that selects, from the multi-wavelength light output from the light source, light of a plurality of wavelengths to be used for generating a desired terahertz wave signal and light of a wavelength for a control signal addressed to a subscriber device connected to the optical communication device; a control signal generating unit that generates a control signal by modulating light having a wavelength for the control signal with a control signal addressed to the subscriber device; a light distribution unit that transfers the light of the plurality of wavelengths selected by the wavelength selection unit to the terahertz wave generation device and transfers the control signal generated by the control signal generation unit to the subscriber device; Equipped with The terahertz wave generating device is a terahertz wave generating unit that generates a terahertz wave signal based on the light of the plurality of wavelengths transferred from the light distributing unit; A communication system comprising:

2. The wavelength selection unit is selecting, from the multi-wavelength light output from the light source, a wavelength of light for an upstream control signal to be used by a subscriber device connected to the optical communication device for transmitting a control signal; The subscriber device: a modulation unit that generates an upstream control signal by modulating light having a wavelength for the upstream control signal with the control signal; Equipped with The communication system according to claim 1 .

3. The light distribution unit includes: a wavelength selector for selecting a wavelength for the upstream control signal and transmitting the selected wavelength to the subscriber device together with the control signal without modulating the light; The communication system according to claim 2 .

4. The subscriber device: a wavelength multiplexer / demultiplexer for multiplexing or demultiplexing an input signal; a branching unit that branches the control signal input to the wavelength division multiplexer; a management control unit that converts the control signal branched by the branch unit into an electrical signal and outputs the electrical signal to an outside, and that receives a control signal to be transmitted from an outside; a reflective optical amplifier that generates an upstream control signal by modulating the control signal to be transmitted, which is input to the management and control unit, with a continuous signal based on the control signal branched by the branch unit; Further comprising: The communication system according to claim 1 .

5. the reflective optical amplifier has a characteristic of converting a modulated optical signal, when the modulated optical signal is input, into the continuous signal, which is a saturated signal, and generates the upstream control signal by modulating the control signal to be transmitted with the continuous signal; 5. The communication system according to claim 4.

6. An optical communication device in a communication system including an optical communication device and a terahertz wave generating device, A light source that outputs light of multiple wavelengths; a wavelength selection unit that selects, from the multi-wavelength light output from the light source, light of a plurality of wavelengths to be used for generating a desired terahertz wave signal and light of a wavelength for a control signal addressed to a subscriber device connected to the optical communication device; a control signal generating unit that generates a control signal by modulating light having a wavelength for the control signal with a control signal addressed to the subscriber device; a light distribution unit that transfers the light of the plurality of wavelengths selected by the wavelength selection unit to the terahertz wave generation device and transfers the control signal generated by the control signal generation unit to the subscriber device; An optical communication device comprising:

7. 1. A control signal transmission method performed by an optical communication device in a communication system including an optical communication device and a terahertz wave generating device, comprising: selecting light of a plurality of wavelengths to be used for generating a desired terahertz wave signal from a light source that outputs light of a plurality of wavelengths and light of a wavelength for a control signal addressed to a subscriber device connected to the optical communication device; generating a control signal by modulating light having a wavelength for the control signal with a control signal intended for the subscriber device; Transferring the selected light of the multiple wavelengths to the terahertz wave generating device; forwarding the generated control signal to the subscriber device; Control signal transmission method.

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