Terahertz wave generation system, terahertz wave generation device, and terahertz wave generation method

Abstract

To generate a terahertz wave according to a use environment and also reduce costs.SOLUTION: A terahertz wave generation system includes an optical transmitting device and a terahertz wave generation device. The optical transmitting device includes a light source that transmits an optical signal including a wavelength serving as origin of a fundamental wave for generating a signal of a terahertz wave. The terahertz wave generation device includes: a wavelength selection unit that selects an optical signal of the wavelength serving as origin of the fundamental wave, included in the optical signal transmitted from the optical transmitting device; and a terahertz wave generation unit that generates the signal of the terahertz wave based on the selected optical signal.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a terahertz wave generation system, a terahertz wave generator, and a terahertz wave generation method.

Background Art

[0002] In recent years, research on the generation and application of electromagnetic waves in the frequency band called terahertz waves has been active. Terahertz waves indicate a frequency band from about 100 GHz to 10 THz. This frequency band has not been assigned a frequency by the Radio Law, and high-speed wireless communication can be expected from the high carrier frequency and wide frequency band. Terahertz waves have the properties of directivity, which is a property of light waves, and permeability, which is a property of radio waves. Furthermore, since terahertz waves have a shorter wavelength than radio waves, imaging inspection (non-destructive inspection without using X-rays) and substances having absorption spectra unique to this frequency band have been discovered in recent years, and the potential for application in various fields from the perspective of substance inspection is expanding.

[0003] Specific application fields of terahertz waves include high-speed wireless communication to replace radio waves, imaging inspection such as airport security checks, dangerous goods inspection of postal items, quality confirmation by internal defect inspection on production lines, and beauty diagnosis. In substance inspection, there are toxic gas detection in closed spaces, moisture content inspection, detection of impurities mixed in pharmaceuticals, etc. The application fields cover a wide range, including information communication, industry, bio-medical, and security.

[0004] So far, compared with the radio wave region (<100 GHz) and the optical wave region (>10 THz), the terahertz region has been an undeveloped area in terms of technology and applications. This can be attributed, in part, to the fact that technologies for efficiently generating terahertz waves have not been established. However, in recent years, many methods for efficiently generating terahertz waves have been reported due to technological advancements. The following methods have been reported for generating terahertz waves. As the first method, there is a method of generating terahertz waves in the electrical domain by inputting a local oscillation signal and a modulation signal in the intermediate frequency band into a mixer using an electronic circuit such as a CMOS (Complementary Metal Oxide Semiconductor) integrated circuit and performing frequency conversion. As the second method, there is a method of generating terahertz waves from difference frequency generation, which is one of the nonlinear optical effects, by inputting two wavelengths into a nonlinear optical crystal such as GaSe. As the third method, there is a method of generating terahertz waves in the optical domain by photoelectric conversion by irradiating a single-traveling carrier photodiode (UTC-PD: Uni-Traveling carrier Photodiode) with an optical beat signal generated by inputting two lights with different wavelengths (frequencies) into a 3 dB coupler.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] Methods for generating terahertz waves in the electrical domain have a simple structure and can be miniaturized by integrating them into a single chip. However, the terahertz waves that can be generated are limited by the bandwidth of the electronic device. For example, the range of terahertz waves that can be generated is 275 GHz to 305 GHz. On the other hand, methods for generating terahertz waves in the optical domain have low technical barriers because optical elements that can be used in optical communication can be diverted, but the structure becomes complex. Although many reports have been made on methods for generating terahertz waves, the range of terahertz waves that can be generated is limited, and it is difficult to realize an economical system because the devices for generating, detecting, and analyzing terahertz waves at the place of use are large and expensive. This problem will be described below.

[0007] As application fields of terahertz waves described in the prior art, high-speed wireless communication, imaging inspection, and substance inspection can be mentioned. However, the frequency bands of terahertz waves used vary depending on the application fields. For example, as described in Non-Patent Document 1, the terahertz wave frequency of the British company Thruvision used in the body scanner demonstration experiment at Narita International Airport was 250 GHz. As described in Non-Patent Document 2, the terahertz wave frequency of the portable terahertz scanner of Pioneer used in the non-destructive inspection of cultural properties was 0.1 THz to 1.7 THz. For application to high-speed wireless communication, it is also conceivable to effectively utilize frequency resources by changing the frequency of terahertz waves generated according to the required bandwidth. Furthermore, in substance inspection, in order to confirm the specific absorption spectrum of the substance, terahertz waves corresponding to the substance to be confirmed inside the inspection object must be generated.

[0008] Based on the above points, the range of terahertz waves is limited by the generation method, and it is necessary to develop a specific IC chip and change the light source each time. Since a dedicated terahertz device is required depending on the application, the existing methods are not economical in terms of cost. Furthermore, large devices in which the generation and detection functions are integrated are common at places where terahertz waves are used, and it is assumed that they may not be applicable depending on location restrictions.

[0009] In view of the above circumstances, an object of the present invention is to provide a technology capable of generating terahertz waves according to the usage environment and reducing costs.

Means for Solving the Problem

[0010] One aspect of the present invention is a terahertz wave generation system including an optical transmission device and a terahertz wave generation device. The optical transmission device includes a light source that transmits an optical signal including a wavelength that is a fundamental wave for generating a terahertz wave signal. The terahertz wave generation device includes a wavelength selection unit that selects an optical signal having a wavelength that is the fundamental wave included in the optical signal transmitted from the optical transmission device, and a terahertz wave generation unit that generates a terahertz wave signal based on the selected optical signal.

[0011] One aspect of the present invention is the terahertz wave generation device in a terahertz wave generation system including an optical transmission device and a terahertz wave generation device. The terahertz wave generation device includes a wavelength selection unit that selects an optical signal having a wavelength that is the fundamental wave included in the optical signal transmitted from the optical transmission device including a light source that transmits an optical signal including a wavelength that is a fundamental wave for generating a terahertz wave signal, and a terahertz wave generation unit that generates a terahertz wave signal based on the selected optical signal.

[0012] One aspect of the present invention is a terahertz wave generation method in a terahertz wave generation system including an optical transmission device and a terahertz wave generation device. The optical transmission device transmits an optical signal including a wavelength that is a fundamental wave for generating a terahertz wave signal, and the terahertz wave generation device selects an optical signal having a wavelength that is the fundamental wave included in the optical signal transmitted from the optical transmission device, and generates a terahertz wave signal based on the selected optical signal.

[0013] One aspect of the present invention is a terahertz wave generation method in a terahertz wave generation system including an optical transmission device and a terahertz wave generation device. The method includes selecting an optical signal having a wavelength that is the fundamental wave included in the optical signal transmitted from the optical transmission device including a light source that transmits an optical signal including a wavelength that is a fundamental wave for generating a terahertz wave signal, and generating a terahertz wave signal based on the selected optical signal.

Effects of the Invention

[0014] According to the present invention, it is possible to generate terahertz waves according to the usage environment and reduce costs.

Brief Description of the Drawings

[0015]

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Modes for Carrying Out the Invention

[0016] (First Embodiment) FIG. 1 is a diagram showing a configuration of a terahertz wave generating system 100 in the first embodiment. The terahertz wave generating system 100 includes an optical transmitting device 10 and terahertz wave generating devices 20-1 to 20-n (n is an integer equal to or greater than 1). The optical transmitting device 10 and the terahertz wave generating devices 20-1 to 20-n are connected via an optical transmission path such as an optical fiber. As shown in FIG. 1, the optical transmitting device 10 is provided on the center side that controls the system, and the terahertz wave generating devices 20-1 to 20-n are provided at a location (remote side) away from the optical transmitting device 10. In the following description, when there is no particular need to distinguish between the terahertz wave generating devices 20-1 to 20-n, they will simply be referred to as terahertz wave generating device 20.

[0017] The optical transmitting device 10 transmits a multi-wavelength optical signal to the terahertz wave generating devices 20-1 to 20-n by broadcasting as a fundamental wave for generating a terahertz wave signal in the terahertz wave generating device 20. The optical transmitting device 10 includes a light source 11. The light source 11 is a light source capable of outputting a multi-wavelength optical signal. For example, the light source 11 is an optical comb light source 111 or an LD array 112.

[0018] 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 the optical comb light source 111, the optical comb light source 111 outputs a multi-wavelength optical signal with wavelength spacing "Δλ" to all terahertz wave generators 20 connected via optical transmission paths. The output spectrum of the multi-wavelength optical signal output from the optical comb light source 111 is shown in FIG. 1.

[0019] The LD array 112 is composed of a plurality of LDs (Laser Diodes) arranged on an array. Each LD emits a different wavelength (for example, λ1 to λ m) outputs a laser beam. The LD array 112 outputs the multi-wavelength optical signals output from each LD to all the terahertz wave generation devices 20 connected via the optical transmission path. The output spectrum of the multi-wavelength optical signals output from the LD array 112 is shown in FIG. 1.

[0020] The terahertz wave generation device 20 generates a terahertz wave signal based on the multi-wavelength optical signal transmitted from the optical transmission device 10. More specifically, the terahertz wave generation device 20 extracts two wavelengths used to obtain a desired terahertz wave signal from the multi-wavelength optical signal, and generates a terahertz wave signal using the extracted two-wavelength optical signals. The desired terahertz wave signal is a signal having a frequency of terahertz required in the environment where the terahertz wave generation device 20 is installed. That is, the desired terahertz wave signal varies depending on the environment where the terahertz wave generation device 20 is installed. The terahertz wave generation device 20 in the present invention can generate a signal having a frequency of terahertz required depending on the environment where the terahertz wave generation device 20 is installed.

[0021] As shown in FIG. 1, in the present invention, in order to generate a terahertz wave, the function of the conventional terahertz device is separated into a transmission side (the optical transmission device 10 on the center side) and a reception side (the terahertz wave generation device 20 on the remote side). By separating the functions in this way, it becomes possible to share the transmission side among the reception sides (remote sides) installed at a plurality of bases from the conventional transmission-reception integrated terahertz device that was necessary for each application.

[0022] Next, with reference to FIGS. 2 and 3, the specific configuration of the terahertz wave generation device 20 will be described. FIG. 2 is a diagram showing a first configuration of the terahertz wave generation device 20 in the first embodiment. The terahertz wave generation device 20 shown in FIG. 2 includes a wavelength selection unit 21, an optical amplification unit 22, a polarizer 23, and a terahertz wave generation unit 24.

[0023] The wavelength selection unit 21 is a wavelength filter for extracting two wavelengths for generating a desired terahertz wave. Thereby, the wavelength selection unit 21 can select an optical signal of a predetermined wavelength from among multi-wavelength optical signals with a wavelength interval “Δλ”. The two-wavelength optical signal selected (transmitted through the wavelength selection unit 21) by the wavelength selection unit 21 is input to the optical amplification unit 22. For example, assume that the two-wavelength optical signal selected (transmitted through the wavelength selection unit 21) by the wavelength selection unit 21 is the optical signal of λ2 and the optical signal of λ6. Note that the combination of the optical signal of λ2 and the optical signal of λ6 is an example.

[0024] The optical amplification unit 22 amplifies the two-wavelength optical signal in order to efficiently generate a non-linear optical effect. Note that when the intensity of the optical signal output from the light source 11 included in the optical transmission device 10 is sufficiently high optical intensity in the terahertz wave generation device 20, the optical amplification unit 22 may not be provided.

[0025] The polarizer 23 transmits only an optical signal in a specific polarization state in the two-wavelength optical signal amplified by the optical amplification unit 22.

[0026] The terahertz wave generation unit 24 generates a terahertz wave optical signal using the two-wavelength optical signal transmitted through the polarizer 23. The terahertz wave generation unit 24 is, for example, a non-linear optical crystal. Inside the non-linear optical crystal, light (ω3 = |ω6 - ω2|) corresponding to the difference frequency of the optical frequencies (in FIG. 1, λ2 = ω2, λ6 = ω6) is generated by difference frequency generation of the second-order non-linear optical effect. By selecting the two wavelengths input to the non-linear optical crystal, it is possible to generate light (terahertz wave) in the terahertz region. Note that as the method for generating the terahertz wave in the first configuration, the method shown in Reference 1 can be used. (Reference 1: Zhiming Huang, Jinxing Lu, Jingguo Huang, Bingbing Wang, Yun Hou; Xuemin Shen, and Junhao Chu, “Terahertz generation from DFG and TPG configurations”, 2011 International Conference on Infrared, Millimeter, and Terahertz Waves, 2011.)

[0027] FIG. 3 is a diagram showing a second configuration of the terahertz wave generator 20 in the first embodiment. The terahertz wave generator 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 26.

[0028] The coupler 25 branches the optical signal transmitted from the optical transmission device 10. The coupler 25 is, for example, a 3dB optical coupler, and outputs the input optical signal to a first path and a second path. The wavelength selection unit 21-1 is connected to the first path, and the wavelength selection unit 21-2 is connected to the second path.

[0029] The wavelength selection unit 21-1 is a wavelength filter for extracting a wavelength for generating a desired terahertz wave. The optical signal having the wavelength selected (transmitted through the wavelength selection unit 21-1) by the wavelength selection unit 21-1 is input to the coupler 26. For example, assume that the optical signal having the wavelength selected (transmitted through the wavelength selection unit 21-1) by the wavelength selection unit 21-1 is an optical signal of λ2.

[0030] The wavelength selection unit 21-2 is a wavelength filter for extracting a wavelength for generating a desired terahertz wave. The optical signal having the wavelength selected (transmitted through the wavelength selection unit 21-2) by the wavelength selection unit 21-2 is input to the coupler 26. For example, assume that the optical signal having the wavelength selected (transmitted through the wavelength selection unit 21-2) by the wavelength selection unit 21-2 is an optical signal of λ6.

[0031] As described above, in the second configuration, the wavelength selection units 21-1 and 21-2 extract two wavelengths for generating a desired terahertz wave.

[0032] The coupler 26 multiplexes the optical signal output from the wavelength selection unit 21-1 (for example, the optical signal of λ2) and the optical signal output from the wavelength selection unit 21-2 (for example, the optical signal of λ6). The coupler 26 is, for example, a 3dB optical coupler. By multiplexing a plurality of optical signals with the coupler 26, an optical beat (f2 - f6) signal of the two input wavelengths (λ2 = f2, λ6 = f6, assuming f2 > f6) is generated.

[0033] The terahertz wave generation unit 24 generates an optical signal of terahertz wave using the optical beat signal generated by the coupler 26. The terahertz wave generation unit 24 is, for example, a UTC-PD. The terahertz wave generation unit 24 can generate light (terahertz wave) in the terahertz region by photoelectrically converting the input optical beat signal. Note that, as the method for generating the terahertz wave in the second configuration, the method shown in Reference 2 can be used. (Reference 2: H. Ito, T. Furuta, F. Nakajima, K. Yoshino, and T. Ishibashi: “Photonic Generation of Continuous THz Wave Using Uni-Traveling Carrier Photodiode”, J. Lightwave Technol., Vol.23, No.12, pp.4016-4021, 2005.)

[0034] Figure 4 is a sequence diagram showing the processing flow of the terahertz wave generation system 100 in the first embodiment. In the description of Figure 4, it is assumed that the terahertz wave generation device 20-1 has the first configuration shown in Figure 2, and the terahertz wave generation device 20-2 has the second configuration shown in Figure 3. The light source 11 of the optical transmission device 10 transmits an optical signal with multiple wavelengths to the terahertz wave generation devices 20-1 and 20-2 via an optical transmission line (step S101). Depending on the installation locations of the terahertz wave generation devices 20-1 and 20-2, there are differences in the arrival times of the optical signals transmitted from the optical transmission device 10. Here, for simplicity of explanation, after explaining the processing in the terahertz wave generation device 20-1, the processing in the terahertz wave generation device 20-2 will be explained.

[0035] In the wavelength selection unit 21 of the terahertz wave generation device 20-1, the wavelength is selected by transmitting two-wavelength optical signals for generating a desired terahertz wave (step S102). It is assumed that which wavelength optical signal is to be transmitted is preset in the wavelength selection unit 21. The two-wavelength optical signals that have passed through the wavelength selection unit 21 are input to the optical amplification unit 22. The optical amplification unit 22 amplifies the input optical signals (step S103). The optical amplification unit 22 outputs the amplified optical signals to the polarizer 23. The polarizer 23 transmits only the optical signals in a specific polarization state among the two-wavelength optical signals amplified by the optical amplification unit 22 (step S104). The two-wavelength optical signals that have passed through the polarizer 23 are input to the terahertz wave generation unit 24. The terahertz wave generation unit 24 generates a terahertz wave optical signal by utilizing a non-linear optical effect using the two-wavelength optical signals that have passed through the polarizer 23 (step S105).

[0036] In the coupler 25 of the terahertz wave generation device 20-2, the input optical signal is branched into a first path and a second path and output (step S106). The optical signal output from the coupler 25 is input to the wavelength selection units 21-1 and 21-2. In the wavelength selection units 21-1 and 21-2, the wavelength is selected by transmitting an optical signal having a wavelength for generating a desired terahertz wave (step S107). For example, the wavelength selection unit 21-1 selects the wavelength by transmitting an optical signal of one wavelength (for example, an optical signal of λ2), and the wavelength selection unit 21-2 selects the wavelength by transmitting an optical signal of one wavelength (for example, an optical signal of λ6). Note that which wavelength optical signal is to be transmitted is assumed to be preset in the wavelength selection units 21-1 and 21-2. The optical signal that has passed through the wavelength selection units 21-1 and 21-2 is input to the coupler 26. The coupler 26 multiplexes the optical signal output from the wavelength selection unit 21-1 (for example, an optical signal of λ2) and the optical signal output from the wavelength selection unit 21-2 (for example, an optical signal of λ6) (step S108). As a result, a two-wavelength optical beat signal input to the coupler 26 is generated. The generated beat signal is input to the terahertz wave generation unit 24. The terahertz wave generation unit 24 generates a terahertz wave optical signal using the optical beat signal generated by the coupler 26 (step S109).

[0037] According to the terahertz wave generation system 100 configured as described above, a light source 11 capable of outputting a multi-wavelength optical signal is mounted on the optical transmission device 10 installed on the center side, and a terahertz wave generation device 20 installed on the remote side selectively receives a two-wavelength optical signal via an optical fiber, and a terahertz wave optical signal corresponding to the usage environment is generated. In this way, by sharing the light source 11 installed on the center side among a plurality of terahertz wave generation devices 20, cost reduction can be expected, and a system having flexibility in selecting a desired terahertz wave on the remote side can be configured. Therefore, it is possible to generate a terahertz wave corresponding to the usage environment and reduce costs.

[0038] The terahertz wave generation device 20 only needs to have a configuration for generating terahertz waves and does not need to include a light source. This enables miniaturization of the device on the remote side. Therefore, the degree of freedom in the installation location of the terahertz wave generation device 20 increases, and it can be used in more places than before. As a result, convenience can be improved.

[0039] (Second Embodiment) In the second embodiment, a configuration will be described in which an optical transmission device on the center side transmits optical signals of two wavelengths requested from a terahertz wave generation device on the remote side. Hereinafter, the description will focus on the differences from the first embodiment.

[0040] FIG. 5 is a diagram showing the configuration of a terahertz wave generation system 100a in the second embodiment. The terahertz wave generation system 100a includes an optical transmission device 10a and terahertz wave generation devices 20a-1 to 20a-n. The optical transmission device 10a and the terahertz wave generation devices 20a-1 to 20a-n are connected via an optical transmission path such as an optical fiber.

[0041] The terahertz wave generation device 20a requests the optical transmission device 10a to transmit a fundamental wave used for generating a desired terahertz wave. In the second embodiment, the configuration for generating a terahertz wave signal is the same as that in the first embodiment. That is, the terahertz wave generation device 20a includes either the first configuration or the second configuration in the first embodiment. In FIG. 5, an example is shown in which the terahertz wave generation device 20a-1 has the first configuration in the first embodiment and the terahertz wave generation device 20a-n has the second configuration in the first embodiment.

[0042] Furthermore, the terahertz wave generating device 20a includes a circulator 27, a wavelength request unit 28, and a transmission unit 29. The circulator 27 is a component having a plurality of ports. In the example shown in FIG. 5, an example in which the circulator 27 has three ports (a first port to a third port) is shown. The first port of the circulator 27 is connected to the transmission unit 29, the second port is connected to an optical transmission line, and the third port is connected to the coupler 25. For example, an optical signal input to the first port is output to the optical transmission line, and an optical signal input to the second port is output to the coupler 25. Note that the terahertz wave generating device 20a may include a coupler instead of the circulator 27.

[0043] The wavelength request unit 28 generates a request including a transmission request for a fundamental wave for generating a signal of a desired terahertz wave. The wavelength request unit 28 in the second embodiment generates a request including a transmission request for an optical signal of two wavelengths. The transmission unit 29 includes an LD and a modulator. The transmission unit 29, the LD outputs an optical signal of a predetermined wavelength. The modulator generates a modulation signal by modulating the optical signal output from the LD using a request that is an electrical signal. The transmission unit 29 transmits the generated modulation signal to the optical transmission device 10a.

[0044] The optical transmission device 10a transmits the two-wavelength optical signal requested from the terahertz wave generating device 20a to the terahertz wave generating device 20a that is the requester. The optical transmission device 10a includes a light source 11a, a circulator 12, a reception unit 13, a request interpretation unit 14, and a wavelength control unit 15. The circulator 12 is a component having a plurality of ports. In the example shown in FIG. 5, an example in which the circulator 12 has three ports (a first port to a third port) is shown. The first port of the circulator 12 is connected to the optical transmission line, the second port is connected to the reception unit 13, and the third port is connected to the light source 11a. For example, an optical signal input to the first port is output to the reception unit 13, and an optical signal input to the third port is output to the optical transmission line. Note that the optical transmission device 10 may include a coupler instead of the circulator 12.

[0045] The receiving unit 13 converts the modulated signal (optical signal) transmitted from the terahertz wave generator 20a into an electrical signal. The request interpretation unit 14 interprets the request included in the electrical signal and acquires the information of the two wavelengths requested from the terahertz wave generator 20a. Specifically, the request interpretation unit 14 acquires the request for the requested wavelengths (for example, wavelengths λ2, λ6, etc.) from the photoelectrically converted bit string. The request interpretation unit 14 outputs the acquired request to the wavelength control unit 15.

[0046] The wavelength control unit 15 controls the light source 11a based on the request to transmit the optical signals of the two wavelengths requested from the terahertz wave generator 20a. The light source 11a is a light source capable of outputting multi-wavelength optical signals. For example, the light source 11a is composed of wavelength tunable light sources 113-1 and 113-2 and a coupler 114. The wavelength tunable light sources 113-1 and 113-2 output optical signals of wavelengths corresponding to the control of the wavelength control unit 15. The coupler 114 multiplexes the optical signals of each wavelength output from the wavelength tunable light sources 113-1 and 113-2.

[0047] FIG. 6 is a sequence diagram showing the processing flow of the terahertz wave generation system 100a in the second embodiment. In the description of FIG. 6, it is assumed that the terahertz wave generator 20a has the first configuration shown in FIG. 2. In FIG. 6, the same processes as those in FIG. 4 are denoted by the same reference numerals as in FIG. 4, and the description thereof is omitted. The wavelength request unit 28 of the terahertz wave generator 20a generates a request including a transmission request for optical signals of two desired wavelengths (step S201). The two desired wavelengths are assumed to be input by the user. The wavelength request unit 28 outputs the generated request to the transmission unit 29. The transmission unit 29 generates a modulated signal (optical signal) using the electrical signal of the request generated by the wavelength request unit 28. The transmission unit 29 transmits the generated modulated signal (optical signal) to the optical transmission device 10a via the optical transmission line (step S202).

[0048] The receiving unit 13 of the optical transmission device 10a receives the modulated signal (optical signal) transmitted from the terahertz wave generation device 20a (step S203). The receiving unit 13 converts the received modulated signal (optical signal) into an electrical signal and outputs it to the request interpretation unit 14. The request interpretation unit 14 interprets the request included in the electrical signal and acquires the information of the two wavelengths requested from the terahertz wave generation device 20a (step S204). The request interpretation unit 14 outputs the acquired two-wavelength information to the wavelength control unit 15. The wavelength control unit 15 controls the wavelength of the optical signal output from the light source 11a based on the two-wavelength information output from the request interpretation unit 14 (step S205). In the light source 11a, in response to the control of the wavelength control unit 15, the optical signals of the requested two wavelengths are multiplexed and the multiplexed optical signal is transmitted to the original optical transmission device 10a (step S206). Thereafter, the processes after step S102 are executed.

[0049] According to the terahertz wave generation system 100a configured as described above, the same effects as those of the first embodiment can be obtained. Furthermore, in the terahertz wave generation system 100a, it becomes possible to request the transmission of an optical signal of desired two wavelengths from the remote terahertz wave generation device 20a.

[0050] (Modification of the second embodiment) In the description of FIG. 6, the case where the terahertz wave generation device 20a has the first configuration in the first embodiment is described as an example. However, when the terahertz wave generation device 20a has the second configuration in the first embodiment, the processes of steps S102 to S105 in FIG. 6 may be changed to the processes of steps S106 to S109.

[0051] In the above description, an example in which the light source 11a is composed of the wavelength-variable light sources 113-1 and 113-2 and the coupler 114 was shown. The light source 11a may be a sweep light source that outputs wavelength-swept light whose wavelength is swept over time as shown in FIG. 7. FIG. 7 is a diagram showing another example of the light source 11a in the second embodiment. The light source 11a shown in FIG. 7 is composed of a plurality of wavelength-variable filters 115-1 and 115-2, a clock 116, an offset circuit 117, a plurality of wavelength-sweep light sources 118-1 and 118-2, and a coupler 119. The wavelength-variable filters 115-1 and 115-2 are filters capable of changing the wavelength to be transmitted. The wavelength-variable filters 115-1 and 115-2 transmit an optical signal having a wavelength set according to the control of the wavelength control unit 15.

[0052] The clock 116 outputs an operating frequency f0 that serves as an operating reference for the wavelength-sweep light sources 118-1 and 118-2. The offset circuit 117 gives a delay of Δf to the operating frequency f0 output from the clock 116. The wavelength-sweep light sources 118-1 and 118-2 generate laser light with a continuously changing wavelength. The wavelength-sweep light sources 118-1 and 118-2 generate laser light with a continuously changing wavelength based on the timing when the operating frequency f0 output from the clock 116 is input. FIG. 8 is a diagram showing the waveform of the optical signal output from the wavelength-sweep light sources 118-1 and 118-2. In FIG. 8, FIG. 8(A) shows the waveform of the optical signal output from the wavelength-sweep light source 118-1, and FIG. 8(B) shows the waveform of the optical signal output from the wavelength-sweep light source 118-2. The operating frequency f0 is input to the wavelength-sweep light source 118-2 with a delay of Δf time compared to the wavelength-sweep light source 118-1. In this way, by operating the wavelength-swept light at a certain operating frequency f0 and giving a frequency offset of Δf via the offset circuit 117, the wavelengths generated between the wavelength-sweep light sources 118-1 and 118-2 can be periodically shifted, and a desired terahertz fundamental wave can be generated.

[0053] From the wavelength sweep light sources 118-1 and 118-2, an optical signal with a wavelength that is swept over time is transmitted. Therefore, in order to obtain a desired wavelength, the wavelength variable filters 115-1 and 115-2 are controlled by the wavelength control unit 15 to obtain the desired wavelength based on the wavelength requested on the remote side. Here, controlling the wavelength variable filters 115-1 and 115-2 means setting the wavelength to be transmitted by the wavelength variable filters 115-1 and 115-2. The coupler 119 multiplexes the optical signals of each wavelength that have passed through the wavelength variable filters 115-1 and 115-2.

[0054] In the configuration shown in FIG. 7, the light source 11a is shown with an offset circuit 117. However, when the wavelength ranges of the wavelength sweep light source 118-1 and the wavelength sweep light source 118-2 are different, the light source 11a may not be provided with the offset circuit 117.

[0055] The optical transmission device 10a may include, as the light source 11a, the configuration shown in FIG. 5 (a configuration including the wavelength variable light sources 113-1 and 113-2 and the coupler 114) and the configuration shown in FIG. 7. When configured in this way, the wavelength request unit 28 of the terahertz wave generation device 20a generates a request including information indicating the type of light source in addition to the requested wavelength. In the second embodiment, the information indicating the type of light source is information indicating whether to use the light source 11a shown in FIG. 5 or the light source 11a shown in FIG. 7. The request interpretation unit 14 of the optical transmission device 10a interprets the request included in the electrical signal to obtain the information on the two wavelengths requested from the terahertz wave generation device 20a and the information indicating the type of light source. The wavelength control unit 15 controls the requested light source 11a based on the request to transmit the optical signals of the two wavelengths requested from the terahertz wave generation device 20a.

[0056] (Third Embodiment) In the second embodiment, a configuration in which an optical transmission device on the center side transmits optical signals of two wavelengths requested by a terahertz wave generation device on the remote side was described. In the third embodiment, a terahertz wave generation device on the remote side includes a wavelength-variable light source, and a configuration in which an optical transmission device on the center side transmits an optical signal of one wavelength requested by the terahertz wave generation device on the remote side will be described. Hereinafter, the description will focus on the differences from the second embodiment.

[0057] FIG. 9 is a diagram showing the configuration of a terahertz wave generation system 100b in the third embodiment. The terahertz wave generation system 100b includes an optical transmission device 10b and terahertz wave generation devices 20b-1 to 20b-n. The optical transmission device 10b and the terahertz wave generation devices 20b-1 to 20b-n are connected via an optical transmission path such as an optical fiber.

[0058] The terahertz wave generation device 20b requests the optical transmission device 10b to transmit a fundamental wave used to generate a desired terahertz wave. In the third embodiment, the configuration for generating a terahertz wave signal is the same as the first configuration of the first embodiment (the terahertz wave generation device 20a-1 in the second embodiment). That is, the terahertz wave generation device 20a includes the first configuration in the first embodiment. In FIG. 9, the terahertz wave generation device 20b-1 includes a wavelength-variable light source 30 in addition to the configuration of the terahertz wave generation device 20a-1 in the second embodiment.

[0059] The wavelength-variable light source 30 outputs an optical signal of a specific wavelength. For example, the wavelength-variable light source 30 outputs an optical signal of a specific wavelength to the optical amplification unit 22. Note that the output destination where the wavelength-variable light source 30 outputs the optical signal may be the polarizer 23 or the terahertz wave generation unit 24. The wavelength of the optical signal output by the wavelength-variable light source 30 may be predetermined. Thus, the terahertz wave generation device 20b in the third embodiment includes one light source that outputs an optical signal of a specific wavelength. Therefore, in the terahertz wave generation device 20b, in order to generate a terahertz wave signal, an optical signal of one wavelength is sufficient. Therefore, the wavelength request unit 28 of the terahertz wave generation device 20b generates a request including a transmission request for an optical signal of one wavelength that serves as a fundamental wave for generating a desired terahertz wave signal. At this time, the wavelength request unit 28 requests the transmission of an optical signal of one wavelength necessary for generating a desired terahertz wave signal based on the wavelength of the optical signal output by the wavelength-variable light source 30. Note that information on the requested wavelength may be input to the wavelength request unit 28 in advance.

[0060] The optical transmission device 10b transmits the optical signal of one wavelength requested from the terahertz wave generation device 20b to the terahertz wave generation device 20b that is the requester. The optical transmission device 10b includes a light source 11b, a circulator 12, a reception unit 13, a request interpretation unit 14, and a wavelength control unit 15b. The wavelength control unit 15b controls the light source 11b based on the request to transmit the optical signal of one wavelength requested from the terahertz wave generation device 20b. The light source 11b is a light source capable of outputting a multi-wavelength optical signal. For example, the light source 11b is composed of a wavelength-variable light source 113. The wavelength-variable light source 113 outputs an optical signal of one wavelength according to the control of the wavelength control unit 15b.

[0061] FIG. 10 is a sequence diagram showing the processing flow of the terahertz wave generation system 100b in the third embodiment. In the description of FIG. 10, it is assumed that the terahertz wave generation device 20b has the first configuration shown in FIG. 2. In the terahertz wave generation device 20b, it is assumed that an optical signal of a predetermined wavelength is output from the wavelength-variable light source 30.

[0062] The wavelength request unit 28 of the terahertz wave generation device 2010 generates a request including a transmission request for an optical signal of a desired single wavelength (step S301). Assume that the desired single wavelength is input by the user. The wavelength request unit 28 outputs the generated request to the transmission unit 29. The transmission unit 29 generates a modulation signal (optical signal) using the electrical signal of the request generated by the wavelength request unit 28. The transmission unit 29 transmits the generated modulation signal (optical signal) to the optical transmission device 10b via an optical transmission line (step S302).

[0063] The receiving unit 13 of the optical transmission device 10b receives the modulation signal (optical signal) transmitted from the terahertz wave generation device 20b (step S303). The receiving unit 13 converts the received modulation signal (optical signal) into an electrical signal and outputs it to the request interpretation unit 14. The request interpretation unit 14 interprets the request included in the electrical signal and acquires the information of the single wavelength requested from the terahertz wave generation device 20b (step S304). The request interpretation unit 14 outputs the acquired information of the single wavelength to the wavelength control unit 15b. The wavelength control unit 15b controls the wavelength of the optical signal output from the light source 11b based on the information of the single wavelength output from the request interpretation unit 14 (step S305). In the light source 11b, in response to the control of the wavelength control unit 15b, the optical signal of the requested single wavelength is transmitted to the optical transmission device 10b that is the request source (step S306).

[0064] In the wavelength selection unit 21 of the terahertz wave generation device 20b, the wavelength is selected by transmitting an optical signal of one wavelength for generating a desired terahertz wave (step S307). It is assumed that which optical signal wavelength is to be transmitted is preset in the wavelength selection unit 21. The optical signal of one wavelength that has passed through the wavelength selection unit 21 is input to the optical amplification unit 22. The optical signal of a predetermined wavelength output from the wavelength-variable light source 30 is also input to the optical amplification unit 22. The optical amplification unit 22 amplifies the input optical signal (step S308). The optical amplification unit 22 outputs the amplified optical signal to the polarizer 23. The polarizer 23 transmits only the optical signal in a specific polarization state among the optical signals of two wavelengths amplified by the optical amplification unit 22 (step S309). The optical signal of two wavelengths that has passed through the polarizer 23 is input to the terahertz wave generation unit 24. The terahertz wave generation unit 24 generates a terahertz wave optical signal using the optical signal of two wavelengths that has passed through the polarizer 23 (step S310).

[0065] According to the terahertz wave generation system 100b configured as described above, the same effects as those of the first and second embodiments can be obtained. Furthermore, in the terahertz wave generation system 100b, it is possible to reduce the wavelength resources required when sharing the center-side wavelength among a plurality of remote devices.

[0066] (Modification of the Third Embodiment) In the above description, an example in which the light source 11b is constituted by the wavelength-variable light source 113 has been shown. The light source 11b may be a sweep light source that outputs wavelength-swept light whose wavelength is swept over time as shown in FIG. 11. FIG. 11 is a diagram showing another example of the light source 11b in the third embodiment. The light source 11b shown in FIG. 11 is constituted by a wavelength-variable filter 115, a clock 116, and a wavelength sweep light source 118. The wavelength-variable filter 115 is a filter capable of changing the wavelength to be transmitted. The wavelength-variable filter 115 transmits an optical signal having a wavelength set according to the control of the wavelength control unit 15b. The clock 116 outputs an operating frequency f0 that serves as an operating reference for the wavelength sweep light source 118. The wavelength sweep light source 118 generates laser light with a continuously changing wavelength. The wavelength sweep light source 118 generates laser light with a continuously changing wavelength based on the timing at which the operating frequency f0 output from the clock 116 is input. Since an optical signal whose wavelength is swept over time is transmitted from the wavelength sweep light source 118, in order to obtain a desired wavelength, it is possible to obtain the desired wavelength by controlling the wavelength-variable filter 115 in the wavelength control unit 15b with the wavelength requested on the remote side.

[0067] The optical transmission device 10b may include, as the light source 11b, the configuration shown in FIG. 9 (the configuration including the wavelength-variable light source 113) and the configuration shown in FIG. 11. When configured in this way, the wavelength request unit 28 of the terahertz wave generation device 20b generates a request including information indicating the type of light source in addition to the requested wavelength. In the third embodiment, the information indicating the type of light source is information indicating whether to use the light source 11b shown in FIG. 9 or the light source 11b shown in FIG. 11. The request interpretation unit 14 of the optical transmission device 10b interprets the request included in the electrical signal and acquires the information of one wavelength requested from the terahertz wave generation device 20b and the information indicating the type of light source. The wavelength control unit 15b controls the requested light source 11b based on the request to transmit an optical signal of one wavelength requested from the terahertz wave generation device 20b.

[0068] (Fourth Embodiment) This is an embodiment that combines the first to third embodiments. Specifically, in the fourth embodiment, a fundamental wave is transmitted to a plurality of remote terahertz wave generation devices by any of the methods of the first to third embodiments.

[0069] FIG. 12 is a diagram showing the configuration of a terahertz wave generation system 100c in the fourth embodiment. The terahertz wave generation system 100c includes an optical transmission device 10c and terahertz wave generation devices 20c-1 to 20c-n. The optical transmission device 10c and the terahertz wave generation devices 20c-1 to 20c-n are connected via an optical transmission path such as an optical fiber. In the example shown in FIG. 12, the terahertz wave generation devices 20c-1 to 20c-n are installed at different sites. The configuration of the terahertz wave generation devices 20c-1 to 20c-n is any of the terahertz wave generation devices 20, 20a, 20b shown in the first to third embodiments.

[0070] The optical transmission device 10c transmits a multi-wavelength optical signal to the terahertz wave generation device 20c by broadcast as in the first embodiment, or transmits one or two wavelength optical signals requested from the terahertz wave generation device 20c to the terahertz wave generation device 20c as in the second and third embodiments.

[0071] The optical transmission device 10c includes a light source 11c, a receiving unit 13, a request interpretation unit 14c, a wavelength control unit 15c, and a wavelength selection unit 16. The light source 11c is composed of an optical communication light source 111, an LD array 112, a wavelength variable light source 113, and a wavelength sweep light source 118. The request interpretation unit 14c interprets the request included in the electrical signal and acquires the wavelength information requested from the terahertz wave generation device 20c. When the request includes information on the type of the light source 11c, the request interpretation unit 14c also acquires information on the type of the light source 11c in addition to the wavelength information.

[0072] The wavelength control unit 15c controls the light source 11c to cause the terahertz wave generation device 20c to transmit an optical signal having one or more wavelengths. For example, as in the first embodiment, the wavelength control unit 15c causes the terahertz wave generation devices 20c-1 to 20c-n to transmit a multi-wavelength optical signal by broadcast. For example, as in the second embodiment, the wavelength control unit 15c controls the light source 11c based on a request to cause the terahertz wave generation device 20c to transmit an optical signal having two wavelengths requested from the terahertz wave generation device 20c. For example, as in the third embodiment, the wavelength control unit 15c controls the light source 11c based on a request to cause the terahertz wave generation device 20c to transmit an optical signal having one wavelength requested from the terahertz wave generation device 20c. In this way, the wavelength control unit 15c causes the terahertz wave generation device 20c to transmit an optical signal having one or more wavelengths.

[0073] The wavelength selection unit 16 performs wavelength routing for multiplexing or demultiplexing an optical signal having one or more wavelengths output from the light source 11c and further transmitting it to the remote side. The wavelength selection unit 16 is, for example, an optical switch, a coupler, a WDM filter, or the like.

[0074] According to the terahertz wave generation system 100c configured as described above, the same effects as those of the first to third embodiments can be obtained.

[0075] (Modification common to the first to fourth embodiments) In each of the above embodiments, an optical signal for generating a terahertz wave signal is transmitted from the optical transmission devices 10, 10a, 10b, 10c on the center side and selectively received by the terahertz wave generation devices 20, 20a, 20b, 20c on the remote side, and then converted from one or two wavelengths to the terahertz region. However, applications other than terahertz generation are also conceivable and not dependent on this. For example, a method of transmitting information serving as a Clock source as an optical signal from the optical transmission devices 10, 10a, 10b, 10c on the center side and receiving it with the terahertz wave generation devices 20, 20a, 20b, 20c on the remote side, or a method of modulating an RF (Radio Frequency) outside the terahertz region with light and selectively receiving the light as needed in the terahertz wave generation devices 20, 20a, 20b, 20c on the remote side with the configuration of the present invention are conceivable.

[0076] In addition, in the above-described embodiments, the program implemented in the above manner does not depend on a single device. Instead, the program may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be read into a computer system and executed to perform image processing. Here, the "computer system" shall include hardware such as an OS and peripheral devices. Also, the "computer system" shall include a WWW system equipped with a homepage providing environment (or display environment). The "computer-readable recording medium" shall include, like the volatile memory (RAM) inside a computer system that becomes a server or a client when a program is transmitted via a network such as the Internet or a communication line such as a telephone line, those that hold a program for a certain period of time.

[0077] In addition, the above program may be transmitted from a computer system storing the program in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the "transmission medium" for transmitting the program refers to a medium having a function of transmitting information, such as a network (communication network) like the Internet or a communication line (communication wire) like a telephone line. Further, the above program may be for realizing a part of the functions described above. Furthermore, it may be a so-called differential file (differential program) that can realize the functions described above in combination with a program already recorded in a computer system.

[0078] As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and designs and the like within the scope not departing from the gist of the present invention are also included.

Industrial Applicability

[0079] The present invention is applicable to a system that generates and uses terahertz waves.

Explanation of Signs

[0080] 10, 10a, 10b, 10c... optical transmission devices, 11, 11a, 11b... light sources, 12... circulator, 13... receiving unit, 14, 14c... request interpretation units, 15, 15b, 15c... wavelength control units, 20, 20-1~20-n, 20a, 20a-1~20a-n, 20b, 20b-1~20b-n, 20c, 20c-1~20c-n... terahertz wave generation devices, 21... wavelength selection unit, 22... optical amplification unit, 23... polarizer, 24... terahertz wave generation unit, 25... coupler, 26... coupler, 27... circulator, 28... wavelength request unit, 29... transmission unit, 30... wavelength tunable light source, 111... optical communication light source, 112... LD array, 113... wavelength tunable light source, 114... coupler, 115, 115-1~115-2... wavelength tunable filters, 116... clock, 117... offset circuit, 118, 118-1~118-2... wavelength sweep light sources

Claims

1. A terahertz wave generation system comprising an optical transmission device and a terahertz wave generation device, wherein the optical transmission device comprises a light source that transmits an optical signal including a wavelength that is a fundamental wave for generating a terahertz wave signal, and the terahertz wave generation device comprises a wavelength selection unit that selects an optical signal having a wavelength that is the fundamental wave included in the optical signal transmitted from the optical transmission device, and a terahertz wave generation unit that generates a terahertz wave signal based on the selected optical signal, and the terahertz wave generation device further comprises a wavelength request unit that requests the optical transmission device to transmit a fundamental wave used for generating a desired terahertz wave, andthe optical transmission device further comprises a wavelength control unit that causes the light source to output an optical signal having a wavelength corresponding to the request from the terahertz wave generation device. A terahertz wave generation system.

2. The light source is a light source capable of outputting a multi-wavelength optical signal, the wavelength selection unit selects two optical signals having wavelengths that are the fundamental waves included in the optical signal transmitted from the optical transmission device, and the terahertz wave generation unit generates a terahertz wave signal based on the selected two optical signals. The terahertz wave generation system according to claim 1.

3. The terahertz wave generation device further comprises a wavelength tunable light source that outputs an optical signal having a wavelength used for generating a desired terahertz wave, and the wavelength request unit requests the optical transmission device to transmit an optical signal having a single wavelength as the fundamental wave used for generating the desired terahertz wave. The terahertz wave generation system according to claim 1 or claim 2.

4. The light source is composed of a combination of a plurality of types of light sources capable of outputting multi-wavelength optical signals, the wavelength request unit requests the optical transmission device while further including information indicating the type to be used as the light source, and the wavelength control unit causes a light source of the type requested by the wavelength request unit to output an optical signal having a wavelength corresponding to the request. The terahertz wave generation system according to any one of claims 1 to 3.

5. The terahertz wave generation device in a terahertz wave generation system comprising an optical transmission device and a terahertz wave generation device, ​ A wavelength selection unit that selects an optical signal having a wavelength that is a fundamental wave for generating a terahertz wave signal from the optical signal transmitted from the optical transmission device including a light source that transmits an optical signal including the wavelength of the fundamental wave; A terahertz wave generation unit that generates a terahertz wave signal based on the selected optical signal; A wavelength request unit that requests the optical transmission device to transmit a fundamental wave used to generate a desired terahertz wave, and causes the light source of the optical transmission device to output an optical signal having a wavelength corresponding to the request; A terahertz wave generation device comprising the above.

6. A terahertz wave generation method in a terahertz wave generation system including an optical transmission device and a terahertz wave generation device, comprising: The optical transmission device: Transmits an optical signal including a wavelength that is a fundamental wave for generating a terahertz wave signal from a light source; The terahertz wave generation device: Selects an optical signal having a wavelength that is the fundamental wave included in the optical signal transmitted from the optical transmission device; Generates a terahertz wave signal based on the selected optical signal; Requests the optical transmission device to transmit a fundamental wave used to generate a desired terahertz wave; The optical transmission device: Outputs an optical signal having a wavelength corresponding to the request from the light source in response to the request from the terahertz wave generation device. A terahertz wave generation method.

7. A terahertz wave generation method in a terahertz wave generation system including an optical transmission device and a terahertz wave generation device, comprising: Selecting an optical signal having a wavelength that is a fundamental wave included in the optical signal transmitted from the optical transmission device including a light source that transmits an optical signal including a wavelength that is a fundamental wave for generating a terahertz wave signal; Generating a terahertz wave signal based on the selected optical signal; Requesting the optical transmission device to transmit a fundamental wave used to generate a desired terahertz wave, and causing the light source of the optical transmission device to output an optical signal having a wavelength corresponding to the request; A terahertz wave generation method.

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