Terahertz system

Abstract

This terahertz system includes: a first oscillation element capable of generating a first terahertz wave by oscillation; and a second oscillation element capable of generating a second terahertz wave by oscillation. The terahertz system includes a detection element disposed at a position where the first terahertz wave and the second terahertz wave are detected. The terahertz system includes: a superimposing circuit that applies, to the first oscillation element, a first drive signal on which a first modulation signal having a first modulation frequency is superimposed; and a superimposing circuit that applies a second drive signal on which a second modulation signal having a second modulation frequency is superimposed.

Description

Terahertz System

[0001] The present disclosure relates to terahertz systems.

[0002] In recent years, as electronic devices such as transistors have become increasingly miniaturized and their size has reached nanoscale, a phenomenon known as the quantum effect has been observed. Development is underway to realize ultrafast devices and devices with new functionalities that utilize this quantum effect. In this environment, as shown in Patent Document 1, for example, attempts are being made to perform high-capacity communication, information processing, imaging, measurement, and the like using electromagnetic waves in a frequency range known as the terahertz band, which has a frequency of 0.1 THz to 10 THz. Electromagnetic waves in this frequency range possess properties of both light and radio waves. Devices operating in this frequency range can be used for a wide range of applications, including the aforementioned imaging, high-capacity communication, and information processing, as well as measurements in various fields such as physical property analysis, astronomy, and biology.

[0003] Japanese Patent Application Laid-Open No. 2020-115500

[0004] [Summary] In a system that uses terahertz waves to detect an object to be detected, it is sometimes required to easily perform detection using a plurality of terahertz waves.

[0005] A terahertz system according to one aspect of the present disclosure includes a first oscillation element capable of oscillating a first terahertz wave, a first application circuit that applies to the first oscillation element a first drive signal having a modulated signal of a first modulation frequency superimposed thereon, a second oscillation element capable of oscillating a second terahertz wave, a second application circuit that applies to the second oscillation element a second drive signal having a modulated signal of a second modulation frequency different from the first modulation frequency superimposed thereon, and a first detection element arranged at a position to detect the first terahertz wave and the second terahertz wave.

[0006] FIG. 1 is a block circuit diagram showing an outline of an exemplary terahertz system according to an embodiment. FIG. 2 is a block circuit diagram showing an example of the configuration of a transmitting device and a receiving device. FIG. 3 is a schematic perspective view showing an example of a terahertz element. FIG. 4 is a schematic plan view of the terahertz element of FIG. 3. FIG. 5 is a schematic cross-sectional view of the terahertz element taken along line F5-F5 of FIG. 4. FIG. 6 is a schematic cross-sectional view of the active element of FIG. 5. FIG. 7 is a schematic plan view showing an example of an arrangement of transmitting elements and receiving elements. FIG. 8 is an explanatory diagram showing the frequency-signal strength characteristics of a signal received by a receiving element. FIG. 9 is a schematic plan view showing an arrangement of transmitting elements and receiving elements according to a modified example. FIG. 10 is a schematic plan view showing an arrangement of transmitting elements and receiving elements according to a modified example. FIG. 11 is a schematic plan view showing an arrangement of transmitting elements and receiving elements according to a modified example. FIG. 12 is a block circuit diagram of a terahertz system according to a modified example. FIG. 13 is a schematic plan view showing an arrangement of transmitting elements and receiving elements of the terahertz system of FIG. 12. Fig. 14 is a block circuit diagram showing an outline of a terahertz system according to a modified example. Fig. 15 is a block circuit diagram showing an outline of a terahertz system according to a modified example. Fig. 16 is a block circuit diagram showing an outline of a terahertz system according to a modified example. Fig. 17 is a block circuit diagram showing an outline of a terahertz system according to a modified example. Fig. 18 is an explanatory diagram showing the frequency-signal strength characteristics of a received signal of the terahertz system of Fig. 17. Fig. 19 is an explanatory diagram showing the frequency-signal strength characteristics of a received signal of the terahertz system of Fig. 17. Fig. 20 is a block circuit diagram showing an outline of a terahertz system according to a modified example.

[0007] DETAILED DESCRIPTION Hereinafter, several embodiments of the terahertz system of the present disclosure will be described with reference to the accompanying drawings. Note that for simplicity and clarity of description, components shown in the drawings are not necessarily drawn to scale. Also, for ease of understanding, hatching lines may be omitted in cross-sectional views. The accompanying drawings merely illustrate embodiments of the present disclosure and should not be considered to limit the present disclosure. Terms such as "first," "second," and "third" in the present disclosure are used merely to distinguish between objects and do not rank the objects.

[0008] The following detailed description includes devices, systems, and methods embodying exemplary embodiments of the present disclosure. This detailed description is merely illustrative in nature and is not intended to limit the embodiments of the present disclosure or the application and uses of such embodiments.

[0009] (Embodiment) (Outline of Terahertz System) A terahertz system 10 according to an embodiment will be described with reference to FIGS. 1 and 2. FIG.

[0010] Fig. 1 is a block circuit diagram showing an outline of a terahertz system 10. Fig. 2 is a block circuit diagram showing an example of the configuration of transmitters 11 and 12 and a receiver 41.

[0011] The terahertz system 10 shown in Figures 1 and 2 may be used to detect a detection object 81, for example, for physical property analysis, non-destructive imaging, chemical composition analysis, etc. The detection object 81 may be a solid, for example. The detection object 81 may be a liquid or a gas. The detection object 81 may include a container containing a liquid or a gas.

[0012] 1, the terahertz system 10 includes a control device 70, two transmitting devices 11 and 12, and one receiving device 41. The terahertz system 10 may include two or more transmitting devices. The terahertz system 10 may also include one or more receiving devices.

[0013] The control device 70 controls the first transmitting device 11, the second transmitting device 12, and the receiving device 41. The first transmitting device 11 includes a first oscillator 21. The first oscillator 21 is configured to oscillate a first terahertz wave W1. The first oscillator 21 may be referred to as a terahertz element that oscillates the first terahertz wave W1. The first transmitting device 11 is disposed so as to radiate the first terahertz wave W1 oscillated by the first oscillator 21 toward the detection object 81.

[0014] For example, the first oscillation element 21 may include a resonant tunneling diode (RTD). The first oscillation element 21 may also include, for example, a tunnel injection transit time (TUNNETT) diode, an impact ionization avalanche transit time (IMPATT) diode, a GaAs-based field effect transistor (FET), a GaN-based FET, a high electron mobility transistor (HEMT), or a heterojunction bipolar transistor (HBT).

[0015] The first transmitting device 11 is configured to generate a first modulated signal having a first modulation frequency fm1 and apply a first drive signal Sd1 including the first modulated signal to the first oscillator 21. The first oscillator 21 oscillates a first terahertz wave W1 in response to the first drive signal Sd1. The first terahertz wave W1 is an electromagnetic wave with a frequency in the terahertz band. For example, the frequency in the terahertz band may be equal to or greater than 0.1 THz and equal to or less than 10 THz.

[0016] In FIG. 1, the first oscillator element 21 is shown as being built into the first transmitter 11, but it may also be configured to be connected to the first transmitter 11 by, for example, a high-frequency cable.

[0017] The second transmitting device 12 includes a second oscillator 22. The second oscillator 22 is configured to oscillate a second terahertz wave W2. The second oscillator 22 may be referred to as a terahertz element that oscillates the second terahertz wave W2. The second transmitting device 12 is disposed so as to radiate the second terahertz wave W2 oscillated by the second oscillator 22 toward the detection object 81.

[0018] The second oscillation element 22 is, for example, a resonant tunneling diode (RTD). The second oscillation element 22 may include, for example, a TUNNET diode, an IMPATT diode, a GaAs-based FET, a GaN-based FET, a HEMT, or an HBT.

[0019] The second transmitting device 12 is configured to generate a second modulation signal with a second modulation frequency fm2 different from the first modulation frequency fm1, and apply a second drive signal Sd2 including the second modulation signal to the second oscillation element 22. The second oscillation element 22 oscillates a second terahertz wave W2 in response to the second drive signal Sd2. The second terahertz wave W2 is an electromagnetic wave with a frequency in the terahertz band.

[0020] In FIG. 1, the second oscillator element 22 is shown as being built into the second transmitter 12, but it may also be configured to be connected to the second transmitter 12 by, for example, a high-frequency cable.

[0021] The receiving device 41 includes a detecting element 51. The detecting element 51 is disposed at a position where it detects the first terahertz wave W1 and the second terahertz wave W2. In the embodiment shown in FIG. 1 , the detecting element 51 is disposed at a position where it detects reflected waves W1r and W2r that are the first terahertz wave W1 and the second terahertz wave W2 reflected by the detection object 81.

[0022] Although the detecting element 51 is shown in FIG. 1 as being built into the receiving device 41, it may be configured to be connected to the receiving device 41 by, for example, a high-frequency cable.

[0023] 7 shows an example of the arrangement of the first oscillation element 21, the second oscillation element 22, and the detection element 51. The first oscillation element 21, the second oscillation element 22, and the detection element 51 are mounted on a surface 201 of a support substrate 200. In one example, the support substrate 200 has a rectangular shape in which the length in the second direction Ys is longer than the length in the first direction Xs. The first direction Xs may be referred to as the width direction of the support substrate 200, and the second direction Ys may be referred to as the length direction of the support substrate 200. In one example, the first oscillation element 21, the second oscillation element 22, and the detection element 51 are arranged in a single row. The detection element 51 is arranged between the first oscillation element 21 and the second oscillation element 22.

[0024] The first oscillation element 21, the second oscillation element 22, and the detection element 51 include an antenna 140. In one example, the antenna 140 may be a dipole antenna. The first oscillation element 21 and the second oscillation element 22 are arranged so that the directions of the antennas 140 are the same. In one example, the first oscillation element 21 and the second oscillation element 22 are arranged so that the antenna 140 extends in the length direction (second direction Ys) of the support substrate 200. The detection element 51, like the first oscillation element 21 and the second oscillation element 22, is arranged so that the antenna 140 extends in the length direction (second direction Ys) of the support substrate 200.

[0025] The detection element 51 may include, for example, a resonant tunneling diode (RTD). The detection element 51 may also include, for example, a TUNNET diode, an IMPATT diode, a GaAs-based FET, a GaN-based FET, a HEMT, an HBT, or a Schottky barrier diode (SBD). The detection element 51 may also be a calorimeter or a microbolometer (thermal detection).

[0026] Note that, when detecting a detection item for the detection object 81, for example, the transmittance of the detection object 81, a reflecting member 82 may be used. In this case, the detecting element 51 of the receiving device 41 may be disposed at a position where it detects reflected waves W1r and W2r that are formed when the first terahertz wave W1 and the second terahertz wave W2 that have passed through the detection object 81 are reflected by the reflecting member 82. Note that the detecting element 51 of the receiving device 41 may be disposed at a position where it detects the first terahertz wave W1 and the second terahertz wave W2 that have passed through the detection object 81.

[0027] The detection element 51 detects the first terahertz wave W1 and the second terahertz wave W2. The receiving device 41 outputs a reception signal S23 according to the detection result of the detection element 51. The reception signal S23 includes information related to the electromagnetic waves detected by the detection element 51, that is, information related to the first terahertz wave W1 and information related to the second terahertz wave W2.

[0028] The control device 70 derives the signal strength at the first modulation frequency fm1 and the second modulation frequency fm2 based on the received signal S23 obtained by the detection element 51 of the receiving device 41. The control device 70 may include a derivation unit that derives the signal strength at the first modulation frequency fm1 and the second modulation frequency fm2 based on the received signal S23. For example, the control device 70 acquires frequency data by performing a fast Fourier transform (FFT) on the time-series data of the received signal S23 obtained by the detection element 51. The frequency data is data on the signal strength relative to the frequency. The frequencies of the frequency data include the first modulation frequency fm1 and the second modulation frequency fm2. Therefore, the control device 70 can derive the signal strength at the first modulation frequency fm1 and the signal strength at the second modulation frequency fm2 based on the received signal S23.

[0029] The control device 70 estimates the state of the detection object 81 based on the received signal S23 obtained by the receiving device 41. The state of the detection object 81 may be, for example, reflectance. The control device 70 can be said to include an estimation unit that estimates the reflectance of the detection object 81 based on the received signal S23. The control device 70 can be said to be an estimation unit that estimates the reflectance of the detection object 81 based on the received signal S23. The terahertz system 10 can be said to include an estimation unit that estimates the reflectance of the detection object 81 based on the received signal S23.

[0030] The estimated state of the detection object 81 may be the presence or absence of the detection object 81. In this case, the control device 70 can be said to include an estimation unit that estimates the presence or absence of the detection object 81 based on the reception signal S23. The control device 70 can be said to be an estimation unit that estimates the presence or absence of the detection object 81 based on the reception signal S23. The terahertz system 10 can be said to include an estimation unit that estimates the presence or absence of the detection object 81 based on the reception signal S23.

[0031] The estimated state of the detection object 81 may be the reflectance of the detection object 81. In this case, the control device 70 can be said to include an estimation unit that estimates the reflectance of the detection object 81 based on the received signal S23. The control device 70 can be said to be an estimation unit that estimates the reflectance of the detection object 81 based on the received signal S23. The terahertz system 10 can be said to include an estimation unit that estimates the reflectance of the detection object 81 based on the received signal S23.

[0032] The estimated state of the detection object 81 may be the transmittance of the detection object 81. In this case, the control device 70 can be said to include an estimation unit that estimates the transmittance of the detection object 81 based on the received signal S23. The control device 70 can be said to be an estimation unit that estimates the transmittance of the detection object 81 based on the received signal S23. The terahertz system 10 can be said to include an estimation unit that estimates the transmittance of the detection object 81 based on the received signal S23.

[0033] The estimated state of the detection object 81 may be the polarization state of the detection object 81. In this case, the control device 70 can be said to include an estimation unit that estimates the polarization state of the detection object 81 based on the received signal S23. The control device 70 can be said to estimate the polarization state of the detection object 81 based on the received signal S23. The terahertz system 10 can be said to include an estimation unit that estimates the polarization state of the detection object 81 based on the received signal S23.

[0034] For example, the presence or absence of the detection object 81 indicates the presence or absence of the detection object 81 in the optical path of at least one of the first terahertz wave W1 and the second terahertz wave W2 detected by the detection element 51. In one example, the detection object 81 reflects the first terahertz wave W1 and the second terahertz wave W2. In this case, the detection element 51 detects a reflected wave W1r formed when the first terahertz wave W1 emitted from the first oscillation element 21 is reflected by the detection object 81. The path along which the first terahertz wave W1 and the reflected wave W1r propagate from the first oscillation element 21 to the detection element 51 is defined as a first optical light path L1. Furthermore, the detection element 51 detects a reflected wave W2r formed when the second terahertz wave W2 emitted from the second oscillation element 22 is reflected by the detection object 81. The path along which the second terahertz wave W2 and the reflected wave W2r propagate from the second oscillation element 22 to the detection element 51 is defined as a second optical light path L2.

[0035] The receiving device 41 generates a reception signal S23 including the detection result of the detection element 51. The control device 70 derives the signal strength of the first modulation frequency fm1 and the signal strength of the second modulation frequency fm2 from the reception signal S23. These signal strengths indicate the intensities of the reflected waves W1r and W2r reflected by the detection element 51. For example, if the detection target 81 is not on the first optical path L1, the reflected wave W1r of the first terahertz wave W1 is not detected by the detection element 51. Therefore, the signal strength of the first modulation frequency fm1 is lower than when the detection target 81 is present. In this way, the presence or absence of the detection target 81 can be estimated from the signal strength of the first modulation frequency fm1 and the signal strength of the second modulation frequency fm2.

[0036] The reflectivity of the detection object 81 can be obtained by using a reflecting member 82 that reflects the first terahertz wave W1 and the second terahertz wave W2. The control device 70 detects, using the detecting element 51, reflected waves W1r, W2r resulting from the first terahertz wave W1 and the second terahertz wave W2 reflected by the reflecting member 82. The control device 70 detects, using the detecting element 51, reflected waves W1r, W2r resulting from the first terahertz wave W1 and the second terahertz wave W2 reflected by the detection object 81. The control device 70 can then obtain the reflectivity of the first terahertz wave W1 and the reflectivity of the second terahertz wave W2 at the detection object 81 based on the signal strength of each modulation frequency in the reception signal S23 received by the reflecting member 82 and the signal strength of each modulation frequency in the reception signal S23 received by the detection object 81. The control device 70 may include a storage unit that stores the signal strength of each modulation frequency in the received signal S23 by the reflecting member 82. From these reflectivities, the transmittance of the first terahertz wave W1 and the transmittance of the second terahertz wave W2 in the detection object 81 can be obtained. In addition, from the reflectivities, the dielectric constant (refractive index) of the detection object 81 can be estimated.

[0037] (Circuit Configuration) The configurations of the first transmitting device 11, the second transmitting device 12, and the receiving device 41 will be described with reference to Fig. 2. Note that the circuit configuration shown in Fig. 2 illustrates a case in which oscillator elements 21 and 22 including RTDs as active elements and a detector element 51 are used. The circuit configuration may be changed depending on the configurations of the oscillator elements 21 and 22 and the detector element 51.

[0038] 2, the first transmission device 11 includes a first application circuit 30A that applies a first drive signal to the first oscillation element 21. The first application circuit 30A may include a signal generation circuit 31A, a bias circuit 32A, and a superposition circuit 33A.

[0039] The signal generating circuit 31A generates a first modulation signal Sm1 having a first modulation frequency fm1. The first modulation signal Sm1 may be, for example, an AC signal. The first modulation signal Sm1 may be, for example, a rectangular wave (square wave). The first modulation signal Sm1 may be a sine wave, a triangular wave, or the like. The first modulation frequency fm1 may be lower than the oscillation wavelength of the first oscillation element 21.

[0040] The bias circuit 32A generates a first bias voltage VB11 for the first oscillation element 21. The first bias voltage VB11 may be, for example, a DC voltage. The superimposing circuit 33A generates a first drive signal Sd1 by superimposing the first modulation signal Sm1 on the bias voltage VB11. The first drive signal Sd1 is applied to the first oscillation element 21. For example, the superimposing circuit 33A may include a bias-T. The first superimposing circuit 33A may include an amplifier, a noise filter, etc.

[0041] The first drive signal Sd1 is applied to the first oscillation element 21. When the first drive signal Sd1 is applied, the first oscillation element 21 oscillates a first terahertz wave W1. The first bias voltage VB11 is set by the first drive signal Sd1 so that the operating point of the first oscillation element 21 changes between an oscillation state and a non-oscillation state. As a result, the first oscillation element 21 alternates between the oscillation state and the non-oscillation state at the first modulation frequency fm1. Therefore, it can be said that the first terahertz wave W1 includes a component of the oscillation frequency of the first oscillation element 21 and a component of the first modulation frequency fm1 of the first modulation signal Sm1.

[0042] (Second Transmission Device) The second transmission device 12 includes the same components as the first transmission device 11. For convenience, the components of the second transmission device 12 will be described below with the letter "B" attached.

[0043] The second transmission device 12 includes a second application circuit 30B that applies a second drive signal to the second oscillation element 22. The second application circuit 30B may include a signal generation circuit 31B, a bias circuit 32B, and a superposition circuit 33B.

[0044] The signal generating circuit 31B generates a second modulation signal Sm2 having a second modulation frequency fm2. The second modulation signal Sm2 may be, for example, an AC signal. The signal waveform of the second modulation signal Sm2 may be, for example, a rectangular wave (square wave). The signal waveform of the second modulation signal Sm2 may be a sine wave, a triangular wave, or the like. The second modulation signal Sm2 may have a signal waveform different from that of the first modulation signal Sm1. The second modulation frequency fm2 is different from the first modulation frequency fm1. In one example, the first modulation frequency fm1 is 0.98 MHz, and the second modulation frequency fm2 is 1.00 MHz. The second modulation frequency fm2 may be lower than the oscillation wavelength of the second oscillation element 22.

[0045] The bias circuit 32B generates a second bias voltage VB12 for the second oscillation element 22. The second bias voltage VB12 may be, for example, a DC voltage. The superimposing circuit 33B generates a second drive signal Sd2 by superimposing the second modulation signal Sm2 on the bias voltage VB12. The second drive signal Sd2 is applied to the second oscillation element 22. For example, the superimposing circuit 33B may include a bias-T. The second superimposing circuit 33B may include an amplifier, a noise filter, etc.

[0046] The second drive signal Sd2 is applied to the second oscillation element 22. When the second drive signal Sd2 is applied, the second oscillation element 22 oscillates a second terahertz wave W2. The second bias voltage VB12 is set by the second drive signal Sd2 so that the operating point of the second oscillation element 22 changes between an oscillation state and a non-oscillation state. As a result, the second oscillation element 22 alternates between the oscillation state and the non-oscillation state at the second modulation frequency fm2. Therefore, it can be said that the second terahertz wave W2 includes a component of the oscillation frequency of the second oscillation element 22 and a component of the second modulation frequency fm2 of the second modulation signal Sm2.

[0047] (Receiving Device) The first transmitting device 11 includes a receiving circuit 60 that outputs a receiving signal S23 according to the detection result of the detecting element 51. The receiving circuit 60 may include a bias circuit 61, an extraction circuit 62, and a signal processing circuit 63.

[0048] The bias circuit 61 generates a bias voltage VB21 for the detection element 51. The bias voltage VB21 may be, for example, a DC voltage. The extraction circuit 62 applies the bias voltage VB21 to the detection element 51. For example, the extraction circuit 62 may include a bias-T. The extraction circuit 62 may also include a noise filter for the bias voltage VB21.

[0049] The bias voltage VB21 enables the detection element 51 to detect electromagnetic waves in the terahertz band with good sensitivity, that is, the detection element 51 can detect the first terahertz wave W1 and the second terahertz wave W2.

[0050] The detection element 51 generates a detection signal S21 corresponding to the detected first terahertz wave W1 and second terahertz wave W2. The extraction circuit 62 extracts an alternating current component (AC component) included in the detection signal S21 of the detection element 51, and outputs a signal S22 including the extracted AC component.

[0051] The signal processing circuit 63 outputs a received signal S23 based on the signal S22 output from the extraction circuit 62. The signal processing circuit 63 may include circuits such as an amplifier and a noise filter. The signal processing circuit 63 may include an AD converter. The signal processing circuit 63 outputs a received signal S23 including digital data obtained by converting the signal S22 output from the extraction circuit 62 by the AD converter.

[0052] 3 to 6, an example of the terahertz element 100 will be described. The terahertz element 100 may be used as the first oscillator 21, the second oscillator 22, and the detector 51 shown in FIGS.

[0053] Fig. 3 is a schematic perspective view showing an example of terahertz element 100. Fig. 4 is a schematic plan view of terahertz element 100 of Fig. 3. Fig. 5 is a schematic cross-sectional view of terahertz element 100 taken along line F5-F5 of Fig. 4. Fig. 6 is a schematic cross-sectional view of active element 130 of Fig. 5. In the explanations shown in Figs. 3 to 6, the thickness direction of terahertz element 100 is defined as the Z-axis direction, and directions orthogonal to the Z-axis direction and orthogonal to each other are defined as the X-axis direction and the Y-axis direction.

[0054] 3 and 4, the terahertz element 100 has a rectangular parallelepiped shape. In one example, the terahertz element 100 has a square shape when viewed from the Z-axis direction. Note that the shape of the terahertz element 100 is not limited to a square shape, and may be any of a circle, an ellipse, and a polygon.

[0055] The terahertz element 100 includes an element front surface 101 and an element back surface 102 opposite to the element front surface 101. The terahertz element 100 also includes a plurality of element side surfaces 103, 104, 105, and 106 connecting the element front surface 101 and the element back surface 102. The element side surfaces 103 to 106 face either the X-axis direction or the Y-axis direction. The element side surfaces 103 and 104 extend along the XZ plane. The element side surfaces 103 and 104 constitute both end surfaces in the Y-axis direction. The element side surfaces 105 and 105 extend along the YZ plane. The element side surfaces 105 and 106 constitute both end surfaces in the X-axis direction.

[0056] The terahertz element 100 includes a substrate 110. The substrate 110 has a rectangular parallelepiped shape. The substrate 110 includes a substrate front surface 111 and a substrate back surface 112 opposite the substrate front surface 111. The substrate 110 includes substrate side surfaces that form part of each of the element side surfaces 103 to 106. The substrate side surfaces connect the substrate front surface 111 and the substrate back surface 112.

[0057] The substrate 110 may include a semiconductor substrate. The substrate 110 may be made of at least one semiconductor material selected from the group consisting of InP (indium phosphide), GaAs (gallium arsenide), AlGaAs (aluminum gallium arsenide), InGaAs (indium gallium arsenide), InGaAsP (indium gallium arsenide phosphide), Si (silicon), SiC (silicon carbide), GaN (gallium nitride), and single-crystal AlN (aluminum nitride). In one example, the substrate 110 may be made of a material including InP.

[0058] The terahertz device 100 includes an insulating layer 120. The insulating layer 120 is provided on the substrate 110. The insulating layer 120 may cover at least a portion of the substrate surface 111 of the substrate 110. In one example, the insulating layer 120 may cover the entire substrate surface 111 of the substrate 110. The insulating layer 120 is made of an insulating material. The insulating layer 120 may be made of, for example, silicon oxide (SiO ２ ), silicon nitride (SiN), silicon oxynitride (SiON), hafnium oxide (HfO ２ ), aluminum oxide (Al ２ O ３ In one example, the insulating layer 120 may be made of at least one semiconductor material selected from the group consisting of SiO ２ The insulating film may be made of a material containing

[0059] The insulating layer 120 includes an insulating front surface 121 and an insulating back surface 122 opposite to the insulating front surface 121. The insulating back surface 122 of the insulating layer 120 is in contact with the substrate front surface 111 of the substrate 110. The insulating layer 120 includes insulating side surfaces that form part of each of the element side surfaces 103 to 106. The insulating side surfaces connect the insulating front surface 121 and the insulating back surface 122.

[0060] The terahertz device 100 includes an active element 130 and an antenna 140. The active element 130 is disposed on a substrate surface 111 of a substrate 110. In one example, the active element 130 has a rectangular shape when viewed from the Z-axis direction. Note that the shape of the active element 130 is not limited to a rectangular shape, and may be any of a circular shape, an elliptical shape, and a polygonal shape.

[0061] The active element 130 is an element that converts electromagnetic waves to electrical energy. The active element 130 converts supplied electrical energy into electromagnetic waves by oscillating with the supplied electrical energy. The active element 130 oscillates electromagnetic waves in a desired frequency band.

[0062] The antenna 140 is disposed on the element surface 101 of the substrate 110. In one example, the antenna 140 is configured as a dipole antenna. The antenna 140 includes a first antenna member 141 and a second antenna member 142. The first antenna member 141 and the second antenna member 142 extend in the X-axis direction. The first antenna member 141 and the second antenna member 142 are disposed so as to sandwich the active element 130 in the X-axis direction. The first antenna member 141 and the second antenna member 142 may be disposed at the center of the substrate 110 in the Y-axis direction.

[0063] The length of the antenna 140 is indicated as the distance from the tip of the first antenna member 141 to the tip of the second antenna member 142. The length of the antenna 140 may be set according to the wavelength λ of the electromagnetic wave generated by the active element 130. In one example, the length of the antenna 140 may be set to ½ wavelength (λ / 2) where λ is the wavelength of the electromagnetic wave generated by the active element 130. Note that the antenna 140 is not limited to a dipole antenna, and may be other antennas such as a bowtie antenna, a slot antenna, a patch antenna, or a ring antenna. The length of the antenna 140 may be changed depending on the antenna configuration.

[0064] The active element 130 is connected between the first antenna member 141 and the second antenna member 142. The antenna 140 has a radiation pattern in the Z-axis direction, which is a direction perpendicular to the element surface 101, due to the first antenna member 141 and the second antenna member 142. Therefore, the terahertz element 100 has the active element 130 that oscillates electromagnetic waves with a frequency in the terahertz band, and the antenna 140 that radiates electromagnetic waves with a radiation pattern in a direction perpendicular to the element surface 101.

[0065] The active element 130 is provided on the substrate 110. In one example, the active element 130 is provided at the center of the element surface 101. The terahertz element 100 emits electromagnetic waves via the antenna 140. Therefore, the active element 130 can be referred to as an oscillation point P1 that oscillates terahertz waves, and the antenna 140 can be referred to as a radiation point P2 that radiates terahertz waves. The terahertz element 100 has the radiation point P2 at the center of the element surface 101 when viewed from the Z-axis direction. In one example, the terahertz element 100 has the radiation point P2 and the oscillation point P1 at the same position. Note that the position of the oscillation point P1 is not limited to the same position as the radiation point P2 and can be changed arbitrarily. Furthermore, the position of the oscillation point P1 can be changed to any position on the element surface 101 when viewed from the Z-axis direction.

[0066] Additionally, active element 130 receives electromagnetic waves and converts the electromagnetic waves into electrical energy. Terahertz element 100 receives electromagnetic waves at antenna 140 and detects them at active element 130. Terahertz element 100 has antenna 140, which receives electromagnetic waves with a radiation pattern perpendicular to element surface 101, and active element 130, which detects the electromagnetic waves.

[0067] The antenna 140 can be referred to as a reception point P3 that receives electromagnetic waves. The antenna 140 can also be referred to as a resonance point that resonates with electromagnetic waves. The active element 130 can be referred to as a detection point P4 that detects electromagnetic waves. Therefore, the terahertz element 100 has the reception point P3 at the center of the element surface 101 when viewed from the Z-axis direction. In one example, the terahertz element 100 has the reception point P3 and the detection point P4 at the same position. Note that the position of the detection point P4 is not limited to the same position as the reception point P3 and can be changed arbitrarily. Note that the position of the detection point P4 can be changed arbitrarily on the element surface 101 when viewed from the Z-axis direction.

[0068] 5, the active element 130 is provided between a first antenna member 141 and the substrate 110. The first antenna member 141 includes a first antenna body 141B provided on the insulating layer 120 and a first connection portion 141C connected to the active element 130. The second antenna member 142 includes a second antenna body 142B provided on the insulating layer 120 and a second connection portion 142C connected to the semiconductor layer 131A.

[0069] 5 and 6, a semiconductor layer 131A is disposed on the substrate 110. The semiconductor layer 131A is made of, for example, GaInAs and is doped with a high concentration of n-type impurities.

[0070] 6, a GaInAs layer 132A is stacked on a semiconductor layer 131A. The GaInAs layer 132A is doped with n-type impurities. For example, the impurity concentration of the GaInAs layer 132A is lower than the impurity concentration of the semiconductor layer 131A.

[0071] A GaInAs layer 133A is stacked on the GaInAs layer 132A. The GaInAs layer 133A is not doped with impurities. An AlAs layer 134A is stacked on the GaInAs layer 133A, an InGaAs layer 135 is stacked on the AlAs layer 134A, and an AlAs layer 134B is stacked on the InGaAs layer 135. The AlAs layer 134A, the InGaAs layer 135, and the AlAs layer 134B form a resonant tunnel section.

[0072] A GaInAs layer 133B, which is not doped with impurities, is stacked on the AlAs layer 134B. A GaInAs layer 132B, which is doped with n-type impurities, is stacked on the GaInAs layer 133B. A GaInAs layer 131B is stacked on the GaInAs layer 132B. The GaInAs layer 131B is doped with a high concentration of n-type impurities. For example, the impurity concentration of the GaInAs layer 131B is higher than the impurity concentration of the GaInAs layer 132B. A first connection portion 141C of the first antenna member 141 is connected to the GaInAs layer 131B.

[0073] The specific configuration of the active element 130 is arbitrary as long as it can generate (or detect, or both) electromagnetic waves. In other words, the active element 130 may be any element that can perform at least one of oscillation and detection of electromagnetic waves in the terahertz band.

[0074] Although not shown, a GaInAs layer doped with a high concentration of n-type impurities may be interposed between the GaInAs layer 131B and the first connecting portion 141C shown in Fig. 6. This can improve contact between the first antenna member 141 (first connecting portion 141C) and the GaInAs layer 131B.

[0075] As shown in FIGS. 3 and 4 , the terahertz device 100 includes a first conductive layer 150 and a second conductive layer 160. The first conductive layer 150 and the second conductive layer 160 are each disposed on the device surface 101. The first conductive layer 150 and the second conductive layer 160 are insulated from each other. The first conductive layer 150 and the second conductive layer 160 each have a metal laminate structure. The laminate structure of each of the first conductive layer 150 and the second conductive layer 160 is, for example, a laminate structure of Au (gold), Pd (palladium), and Ti (titanium). Alternatively, the laminate structure of each of the first conductive layer 150 and the second conductive layer 160 is a laminate structure of Au and Ti. Both the first conductive layer 150 and the second conductive layer 160 are formed by vacuum deposition, sputtering, or the like.

[0076] 4 , the first conductive layer 150 includes a first antenna member 141, a first connection portion 151, and a first pad electrode 152. The second conductive layer 160 includes a second antenna member 142, a second connection portion 161, and a second pad electrode 162.

[0077] The first connection portion 151 extends in the Y-axis direction and connects the first antenna member 141 and the first pad electrode 152. The second connection portion 161 extends in the Y-axis direction and connects the second antenna member 142 and the second pad electrode 162. The first pad electrode 152 and the second pad electrode 162 are spaced apart from each other in the X-axis direction and are insulated from each other.

[0078] The terahertz element 100 of this embodiment also includes a metal-insulator-metal (MIM) reflector 170. The MIM reflector 170 has a layered structure made of metal / insulator / metal. For example, the MIM reflector 170 is configured by sandwiching an insulating layer 120 between a part of the first pad electrode 152 and a part of the second pad electrode 162 in the thickness direction of the terahertz element 100.

[0079] The MIM reflector 170 short-circuits the first conductive layer 150 and the second conductive layer 160 at high frequencies. The MIM reflector 170 can reflect high-frequency electromagnetic waves. The MIM reflector 170 functions as a low-pass filter. However, the MIM reflector 170 is not essential and may be omitted.

[0080] 2 , the terahertz system 10 includes a first oscillation element 21 capable of oscillating a first terahertz wave W1 and a second oscillation element 22 capable of oscillating a second terahertz wave W2. The terahertz system 10 includes a detection element 51 disposed at a position for detecting the first terahertz wave W1 and the second terahertz wave W2. The terahertz system 10 includes a superposition circuit 33A that applies, to the first oscillation element 21, a first drive signal Sd1 on which a first modulation signal Sm1 having a first modulation frequency fm1 is superimposed, and a superposition circuit 33B that applies, to the second oscillation element 22, a second drive signal Sd2 on which a second modulation signal Sm2 having a second modulation frequency fm2 is superimposed.

[0081] This terahertz system 10 can simultaneously detect the first terahertz wave W1 oscillated by the first oscillator 21 and the second terahertz wave W2 oscillated by the second oscillator 22 using one detector element 51. Therefore, the system configuration can be simplified compared to a system including detector elements that individually detect the first terahertz wave W1 and the second terahertz wave W2.

[0082] The receiving device 41 only needs to generate the receiving signal S23 based on the detection result from one detecting element 51, and therefore the configuration of the receiving device 41 can be simplified compared to when individual detecting elements are included.

[0083] 7 shows an example of the arrangement of the first oscillation element 21, the second oscillation element 22, and the detection element 51. The first oscillation element 21, the second oscillation element 22, and the detection element 51 are mounted on the surface 201 of the support substrate 200. In one example, the first oscillation element 21, the second oscillation element 22, and the detection element 51 are arranged in a row. The detection element 51 is disposed between the first oscillation element 21 and the second oscillation element 22. The detection element 51 can detect the first terahertz wave W1 radiated from the first oscillation element 21 and the second terahertz wave W2 radiated from the second oscillation element 22.

[0084] Here, detection of the first terahertz wave W1 and the second terahertz wave W2 in the terahertz system 10 of the embodiment will be described. The first terahertz wave W1 includes a first modulation frequency fm1 of a first modulation signal Sm1 used to generate the first terahertz wave W1. The second terahertz wave W2 includes a second modulation frequency fm2 of a second modulation signal Sm2 used to generate the second terahertz wave W2.

[0085] FIG. 8 shows an example of signal strength at a frequency obtained by demodulating terahertz-band electromagnetic waves detected by the detection element 51. In FIG. 8, the horizontal axis represents frequency, and the vertical axis represents signal strength. In FIG. 8, the first waveform WF1 shown by a solid line represents the signal S23 received by the detection element 51 when both the first oscillator 21 and the second oscillator 22 are driven. In FIG. 8, the second waveform WF2 shown by a dashed line represents the signal S23 received by the detection element 51 when the first oscillator 21 is driven and the second oscillator 22 is not driven. FIG. 8 also shows a range including the first modulation frequency fm1 and the second modulation frequency fm2. Note that the first waveform WF1 and the second waveform WF2 shown in FIG. 8 are drawn so that the signal strength at a predetermined frequency, for example, the signal strength at the first modulation frequency fm1, is equal.

[0086] 8, when the first waveform WF1 and the second waveform WF2 are compared, it is found that there is a difference in signal strength at the second modulation frequency fm2. That is, it is found that in the detection element 51, at the second modulation frequency fm2, the second terahertz wave W2 is detected in the first waveform WF1, but not in the second waveform WF2. Furthermore, the signal strength of the second terahertz wave W2 can be estimated from the signal strength at the second modulation frequency fm2.

[0087] In this way, one detection element 51 can simultaneously detect the first terahertz wave W1 oscillated by the first oscillation element 21 and the second terahertz wave W2 oscillated by the second oscillation element 22. The first modulation frequency fm1 and the second modulation frequency fm2 can be used to individually determine the first terahertz wave W1 and the second terahertz wave W2. That is, the states of the first terahertz wave W1 and the second terahertz wave W2 at the detection object 81 can be obtained from the frequency components of the reception signal S23 from the detection element 51 and the signal intensities at the frequency components. In the terahertz system 10 shown in FIG. 1 , the reflectivity of the detection object 81 with respect to the first terahertz wave W1 and the reflectivity of the detection object 81 with respect to the second terahertz wave W2 can be obtained. Furthermore, the dielectric constant (refractive index) of the detection object 81 can be derived from the reflectivity of the first terahertz wave W1 and the reflectivity of the second terahertz wave W2.

[0088] The signal intensity of the first modulation frequency fm1 in the received signal S23 corresponds to the signal intensity of the first modulation signal Sm1, i.e., the first terahertz wave W1. Similarly, the signal intensity of the second modulation frequency fm2 in the received signal S23 corresponds to the signal intensity of the second modulation signal Sm2, i.e., the second terahertz wave W2. Therefore, it can be said that the control device 70 converts the frequency information of the modulated signal in the received signal S23 into information corresponding to terahertz waves. It can be said that the control device 70 includes a conversion unit that converts the frequency information of the modulated signal in the received signal S23 into information corresponding to terahertz waves. It can also be said that the control device 70 is a conversion unit that converts the frequency information of the modulated signal in the received signal S23 into information corresponding to terahertz waves.

[0089] To obtain spectral information of the detection object 81, there are methods for detecting the detection light while changing the frequency of the detection light irradiated onto the detection object 81, and methods for detecting the detection light by dispersing it into predetermined frequency bands and individually detecting each frequency. However, these methods require large equipment and require a long time for detection. In contrast, the terahertz system of this embodiment detects both the first terahertz wave W1 and the second terahertz wave W2 using a single detection element 51. This simplifies the system configuration. Furthermore, the detection element 51 can simultaneously detect both the first terahertz wave W1 and the second terahertz wave W2. This enables detection in a short time.

[0090] (Effects of the embodiment) As described above, the terahertz system 10 of the embodiment provides the following effects.

[0091] (1) The terahertz system 10 includes a first oscillation element 21 capable of oscillating a first terahertz wave W1 and a second oscillation element 22 capable of oscillating a second terahertz wave W2. The terahertz system 10 includes a detection element 51 disposed at a position for detecting the first terahertz wave W1 and the second terahertz wave W2. The terahertz system 10 includes a superposition circuit 33A that applies, to the first oscillation element 21, a first drive signal Sd1 superimposed with a first modulation signal Sm1 having a first modulation frequency fm1, and a superposition circuit 33B that applies, to the second oscillation element 22, a second drive signal Sd2 superimposed with a second modulation signal Sm2 having a second modulation frequency fm2.

[0092] This terahertz system 10 uses one detection element 51 to detect both the first terahertz wave W1 oscillated by the first oscillation element 21 and the second terahertz wave W2 oscillated by the second oscillation element 22. Therefore, the system configuration can be simplified compared to a system including detection elements that individually detect the first terahertz wave W1 and the second terahertz wave W2.

[0093] (2) The terahertz system 10 includes a first oscillator 21 that oscillates a first terahertz wave W1 and a second oscillator 22 that oscillates a second terahertz wave W2. Therefore, the system configuration can be simplified compared to systems that change the frequency of electromagnetic waves for detection or separate them into wavelengths.

[0094] (3) The detection element 51 can detect both the first terahertz wave W1 and the second terahertz wave W2 simultaneously. This enables detection in a short time. (Modifications) The above embodiment can be modified, for example, as follows. The above embodiment and each of the following modifications can be combined with each other as long as no technical contradiction occurs. Note that in the following modifications, parts that are common to the above embodiment are assigned the same reference numerals as in the above embodiment, and their description will be omitted.

[0095] 9 shows a modified example of the arrangement of the first oscillation element 21, the second oscillation element 22, and the detection element 51. The first oscillation element 21, the second oscillation element 22, and the detection element 51 are arranged on the surface 211 of the support substrate 210.

[0096] The first oscillation element 21 and the second oscillation element 22 are arranged adjacent to each other in a row. The detection element 51 is arranged in a direction perpendicular to the arrangement direction of the first oscillation element 21 and the second oscillation element 22. The detection element 51 is arranged adjacent to the first oscillation element 21 and the second oscillation element 22 in the first direction Xs when viewed from a direction perpendicular to the surface 211 of the support substrate 210. In this way, by arranging the detection element 51 adjacent to the first oscillation element 21 and the second oscillation element 22, the first terahertz wave W1 of the first oscillation element 21 and the second terahertz wave W2 of the second oscillation element 22 can be detected.

[0097] 10 shows a modified example of the arrangement of the first oscillation element 21, the second oscillation element 22, and the detection element 51. The first oscillation element 21 and the second oscillation element 22 are arranged so that the directions of their antennas 140 are different. In one example, the first oscillation element 21 is arranged so that its antenna 140 extends in the second direction Ys, and the second oscillation element 22 is arranged so that its antenna 140 extends in the first direction Xs. By arranging the first oscillation element 21 and the second oscillation element 22 in this manner, the polarization direction of the first terahertz wave W1 generated by the first oscillation element 21 and the polarization direction of the second terahertz wave W2 generated by the second oscillation element 22 can be made different from each other.

[0098] 2 , the first oscillation element 21 is driven by a first drive signal Sd1 having a first modulation signal Sm1 superimposed thereon, and the second oscillation element 22 is driven by a second drive signal Sd2 having a second modulation signal Sm2 superimposed thereon. Therefore, the first modulation frequency fm1 of the first modulation signal Sm1 corresponds to the polarization direction of the first terahertz wave W1 emitted from the first oscillation element 21. Furthermore, the second modulation frequency fm2 of the second modulation signal Sm2 corresponds to the polarization direction of the second terahertz wave W2 emitted from the second oscillation element 22. Therefore, in the reception signal S23 obtained by the detection element 51, the first modulation frequency fm1 corresponds to the polarization direction of the first terahertz wave W1, and the second modulation frequency fm2 corresponds to the polarization direction of the second terahertz wave W2. Therefore, the control device 70 can simultaneously detect the state of the detection object 81 in mutually different polarization directions. The control device 70 can estimate the polarization state of the detection object 81 based on the received signal S23 obtained by the detection element 51. The control device 70 can be said to include an estimation unit that estimates the polarization state of the detection object 81. The control device 70 can be said to be an estimation unit that estimates the polarization state of the detection object 81.

[0099] In one example, the detection element 51 is arranged so that the antenna 140 extends in the same direction as the antenna 140 of the first oscillation element 21. The detection element 51 is arranged so that the antenna 140 of the detection element 51 is parallel to the antenna 140 of the first oscillation element 21. The detection element 51 is arranged so that the antenna 140 of the detection element 51 extends in a direction intersecting with the antenna 140 of the second oscillation element 22. Note that the detection element 51 may be arranged so that the antenna 140 of the detection element 51 is parallel to the antenna 140 of the second oscillation element 22 and extends in a direction intersecting with the antenna 140 of the first oscillation element 21.

[0100] As shown in FIG. 11 , the detection element 51 may be arranged so that the antenna 140 of the detection element 51 extends in a direction intersecting the antenna 140 of the first oscillation element 21 and the antenna 140 of the second oscillation element 22 .

[0101] 12 shows a schematic configuration of a modified terahertz system 301. This terahertz system 301 includes a first transmitting device 11, a second transmitting device 12, a first receiving device 41, and a second receiving device 42. The first transmitting device 11 includes a first oscillator 21, and the second transmitting device 12 includes a second oscillator 22. The first receiving device 41 includes a first detector 51, and the second receiving device 42 includes a second detector 52. The second receiving device 42 includes a receiving circuit configured similarly to the receiving circuit 60 of the first receiving device 41.

[0102] The first detection element 51 is disposed at a position where it detects the first terahertz wave W1 radiated from the first oscillation element 21 and the second terahertz wave W2 radiated from the second oscillation element 22. The second detection element 52 is disposed at a position where it detects the first terahertz wave W1 radiated from the first oscillation element 21 and the second terahertz wave W2 radiated from the second oscillation element 22.

[0103] 13 shows an example of the arrangement of the first oscillation element 21, the second oscillation element 22, the first detection element 51, and the second detection element 52. The first oscillation element 21, the second oscillation element 22, the first detection element 51, and the second detection element 52 are mounted on a surface 211 of a support substrate 210. The support substrate 210 has a rectangular shape when viewed from a direction perpendicular to the surface 211. In one example, the first oscillation element 21 and the second oscillation element 22 are arranged side by side in the second direction Ys. The first detection element 51 and the second detection element 52 are arranged at a distance from the first oscillation element 21 and the second oscillation element 22 in the first direction Xs. The first detection element 51 and the second detection element 52 are arranged side by side in the second direction Ys.

[0104] The first oscillation element 21 and the second oscillation element 22 may be arranged in a diagonal direction of the support substrate 210. The first detection element 51 and the second detection element 52 may be arranged in a diagonal direction different from that of the first oscillation element 21 and the second oscillation element 22 on the surface 211 of the support substrate 210.

[0105] The first oscillation element 21 and the second oscillation element 22 are arranged so that their respective antennas 140 extend in different directions. The first detection element 51 and the second detection element 52 are arranged so that their respective antennas 140 extend in different directions. The first oscillation element 21 and the second oscillation element 22 may be arranged so that their respective antennas 140 extend in the same direction. The first detection element 51 and the second detection element 52 may be arranged so that their respective antennas 140 extend in the same direction.

[0106] The control device 70 detects the detection target 81 based on the first reception signal S23 output from the first receiving device 41 by the first detecting element 51 and the second reception signal S23 output from the second receiving device 42 by the second detecting element 52. In this case, the same effects as those of the terahertz system of the above-described embodiment can be obtained. Furthermore, for example, by deriving the average value of the signal strengths of the modulation frequencies fm1 and fm2 obtained by the first reception signal S23 and the signal strengths of the modulation frequencies fm1 and fm2 obtained by the second reception signal S23, it is possible to stabilize the detection of the detection target 81.

[0107] 14 shows the configuration of a modified terahertz system 302. This terahertz system 302 includes a first transmitter 11, a second transmitter 12, and a receiver 41. The receiver 41 is disposed on the opposite side of the object to be detected 81 from the first transmitter 11 and the second transmitter 12. The detector 51 is disposed in a position to detect both the first terahertz wave W1 emitted from the first oscillator 21 of the first transmitter 11 and the second terahertz wave W2 emitted from the second oscillator 22 of the second transmitter 12. The detector 51 is disposed in a position sandwiching the object to be detected 81 between the first oscillator 21 and the second oscillator 22. The detector 51 detects the first terahertz wave W1 and the second terahertz wave W2 that have passed through the object to be detected 81.

[0108] 15 shows the configuration of a modified terahertz system 303. This terahertz system 303 includes a first transmitting device 11, a second transmitting device 12, and a receiving device 41. The first transmitting device 11 and the second transmitting device 12 are arranged to sandwich a detection object 81. In one example, the detecting element 51 of the receiving device 41 is arranged at a position where it detects a reflected wave W1r that is formed when a first terahertz wave W1 emitted from the first oscillator 21 of the first transmitting device 11 is reflected by the detection object 81. The detecting element 51 is also arranged at a position where it detects a second terahertz wave W2 emitted from the second oscillator 22 of the second transmitting device 12. The detecting element 51 detects the second terahertz wave W2 that has passed through the detection object 81. The first modulation frequency fm1 corresponds to the first terahertz wave W1 (reflected wave W1r) reflected by the detection object 81, and the second modulation frequency fm2 corresponds to the second terahertz wave W2 transmitted through the detection object 81. In this terahertz system 303, the reflectance and transmittance of the detection object 81 can be easily estimated.

[0109] 16 shows the configuration of a modified terahertz system 304. This terahertz system 304 includes a first transmitting device 11, a second transmitting device 12, and a receiving device 41. The detecting element 51 of the receiving device 41 is disposed at a position where it detects reflected waves W1r and W2r that are formed when the first terahertz wave W1 emitted from the first oscillator 21 of the first transmitting device 11 and the second terahertz wave W2 emitted from the second oscillator 22 of the second transmitting device 12 are reflected by the detection object 81. Furthermore, in this terahertz system 304, the second oscillator 22 is disposed closer to the detection object 81 than the first oscillator 21. That is, the length of the first optical light path L1 (first optical path length) of the first terahertz wave W1 and the length of the second optical light path L2 (second optical path length) of the second terahertz wave W2 are different from each other. Therefore, the first modulation frequency fm1 corresponds to the length (first optical path length) of the first optical path L1 of the first terahertz wave W1, and the second modulation frequency fm2 corresponds to the length (second optical path length) of the second optical path L2 of the second terahertz wave W2. In this terahertz system, it is possible to easily detect the state or characteristics of the detection object 81 based on the difference in optical path length (optical path difference) between the first terahertz wave W1 and the second terahertz wave W2 that are irradiated onto the detection object 81.

[0110] 17 shows the configuration of a modified terahertz system 305. This terahertz system 305 includes a first transmitter 11, a second transmitter 12, a third transmitter 13, a fourth transmitter 14, a fifth transmitter 15, and a receiver 41. The third to fifth transmitters 13 to 15 include third to fifth application circuits configured similarly to the first transmitter 11 and the second transmitter 12.

[0111] The first transmitting device 11 includes a first oscillation element 21. The first transmitting device 11 is configured to apply a first drive signal, on which a first modulation signal of a first modulation frequency fm1 is superimposed, to the first oscillation element 21. The first oscillation element 21 oscillates in response to the applied first drive signal, and emits a first terahertz wave W1.

[0112] The second transmitting device 12 includes a second oscillation element 22. The second transmitting device 12 is configured to apply a second drive signal, on which a second modulation signal of a second modulation frequency fm2 is superimposed, to the second oscillation element 22. The second oscillation element 22 oscillates in response to the applied second drive signal and emits a second terahertz wave W2.

[0113] The third transmission device 13 includes a third oscillation element 23. The third transmission device 13 is configured to apply a third drive signal onto which a third modulation signal of a third modulation frequency fm3 is superimposed, to the third oscillation element 23. The third oscillation element 23 oscillates in response to the applied third drive signal, and emits a third terahertz wave W3.

[0114] The fourth transmitting device 14 includes a fourth oscillation element 24. The fourth transmitting device 14 is configured to apply a fourth drive signal onto which a fourth modulation signal of a fourth modulation frequency fm4 is superimposed, to the fourth oscillation element 24. The fourth oscillation element 24 oscillates in response to the applied fourth drive signal, and emits a fourth terahertz wave W4.

[0115] The fifth transmission device 15 includes a fifth oscillation element 25. The fifth transmission device 15 is configured to apply a fifth drive signal, on which a fifth modulation signal of a fifth modulation frequency fm5 is superimposed, to the fifth oscillation element 25. The fifth oscillation element 25 oscillates in response to the applied fifth drive signal, and emits a fifth terahertz wave W5.

[0116] The detecting element 51 of the receiving device 41 is disposed at a position where it detects the first to fifth terahertz waves W1 to W5. In one example, the detecting element 51 is disposed on the opposite side of the detection object 81 from the first to fifth oscillation elements 21 to 25. The detecting element 51 detects the first to fifth terahertz waves W1 to W5 that have passed through the detection object 81.

[0117] The receiving device 41 outputs a received signal S23 corresponding to the detection result of the detecting element 51. Figures 18 and 19 show examples of signal strength at frequencies obtained by demodulating electromagnetic waves in the terahertz band detected by the detecting element 51. In Figures 18 and 19, the horizontal axis represents frequency and the vertical axis represents signal strength.

[0118] The control device 70 acquires frequency data by performing a fast Fourier transform on the time-series data of the received signal S23. The control device 70 detects the envelope WE1 of the frequency data to obtain the characteristics of the detection object 81. In one example, the control device 70 obtains the transmission characteristics of the detection object 81 as the characteristics of the detection object 81. These transmission characteristics are obtained by detecting the envelope WE1 of the signal intensity at each of the first to fifth modulation frequencies fm1 to fm5. In other words, it is possible to obtain spectral information of the discrete first to fifth modulation frequencies fm1 to fm5.

[0119] Fig. 18 shows the detection results of the first to fifth terahertz waves W1 to W5 when they are not transmitted through the detection object 81. Fig. 19 shows the detection results of the first to fifth terahertz waves W1 to W5 when they are transmitted through the detection object 81. In one example, as shown in Figs. 18 and 19, at the third modulation frequency fm3, a difference occurs in the signal intensity depending on whether the detection object 81 is present or not. In this way, spectral information on the detection object 81 can be easily obtained.

[0120] The detection element 51 may be disposed at a position where it detects the reflected waves of the first to fifth terahertz waves W1 to W5 reflected by the detection object 81. In this case, it is possible to easily obtain the characteristics related to the reflection of the detection object 81.

[0121] 20 shows the configuration of a modified terahertz system 306. This terahertz system 306 includes a first transmitting device 11, a second transmitting device 12, a third transmitting device 13, a first receiving device 41, a second receiving device 42, and a third receiving device 43. The third receiving device 43 includes a receiving circuit configured similarly to the receiving circuit 60 of the first receiving device 41.

[0122] The first transmitting device 11 includes a first oscillation element 21. The first transmitting device 11 is configured to apply a first drive signal, on which a first modulation signal of a first modulation frequency fm1 is superimposed, to the first oscillation element 21. The first oscillation element 21 oscillates in response to the applied first drive signal, and emits a first terahertz wave W1.

[0123] The second transmitting device 12 includes a second oscillation element 22. The second transmitting device 12 is configured to apply a second drive signal, on which a second modulation signal of a second modulation frequency fm2 is superimposed, to the second oscillation element 22. The second oscillation element 22 oscillates in response to the applied second drive signal and emits a second terahertz wave W2.

[0124] The third transmission device 13 includes a third oscillation element 23. The third transmission device 13 is configured to apply a third drive signal onto which a third modulation signal of a third modulation frequency fm3 is superimposed, to the third oscillation element 23. The third oscillation element 23 oscillates in response to the applied third drive signal, and emits a third terahertz wave W3.

[0125] The first to third receiving devices 41 to 43 each include a first to third detecting element 51 to 53. At least one of the first to third detecting elements 51 to 53 is disposed at a position where it detects at least two of the first to third terahertz waves W1 to W3.

[0126] The first to third detection elements 51 to 53 may be disposed at positions to detect reflected waves reflected by the detection object 81. The first detection element 51 may be disposed at a position to detect reflected waves of the first to third terahertz waves W1 to W3 reflected by the detection object 81, and the second detection element 52 and the third detection element 53 may be disposed at positions to detect the first to third terahertz waves W1 to W3 that have passed through the detection object 81. Furthermore, the first detection element 51 and the second detection element 52 may be disposed at a position to detect reflected waves of the first to third terahertz waves W1 to W3 that have passed through the detection object 81, and the third detection element 53 may be disposed at a position to detect the first to third terahertz waves W1 to W3 that have passed through the detection object 81.

[0127] Although not shown, two detection elements may be arranged at positions to detect the reflected waves of the first to third terahertz waves W1 to W3 reflected by the detection object 81, and two detection elements may be arranged at positions to detect the first to third terahertz waves W1 to W3 that have passed through the detection object 81. In other words, the number of detection elements may be greater than the number of oscillation elements.

[0128] [Notes] The technical ideas that can be understood from the present disclosure are described below. Note that, for the purpose of aiding understanding and not intending to be limiting, the components described in the notes are given the reference symbols of the corresponding components in the embodiments. The reference symbols are shown as examples to aid understanding, and the components described in each note should not be limited to the components indicated by the reference symbols.

[0129] [Supplementary Note 1] A terahertz system including: a first oscillation element (21) capable of oscillating a first terahertz wave (W1); a first application circuit (30A) that applies to the first oscillation element (21) a first drive signal (Sd1) having a first modulation signal (Sm1) of a first modulation frequency (fm1) superimposed thereon; a second oscillation element (22) capable of oscillating a second terahertz wave (W2); a second application circuit (30B) that applies to the second oscillation element (22) a second drive signal (Sd2) having a second modulation signal (Sm2) superimposed thereon, the second modulation frequency (fm2) being different from the first modulation frequency (fm1); and a first detection element (51) that is arranged at a position to detect the first terahertz wave (W1) and the second terahertz wave (W2).

[0130] [Supplementary Note 2] The terahertz system according to Supplementary Note 1, wherein the first terahertz wave (W1) is a terahertz wave having a first oscillation frequency, and the second terahertz wave (W2) is a terahertz wave having a second oscillation frequency different from the first oscillation frequency.

[0131] [Supplementary Note 3] The terahertz system according to Supplementary Note 1 or Supplementary Note 2, further comprising a derivation unit (70) that derives signal intensities at the first modulation frequency (fm1) and the second modulation frequency (fm2) based on a detection result of the first detection element (51).

[0132] [Supplementary Note 4] The terahertz system according to any one of Supplementary Note 1 to Supplementary Note 3, further comprising an estimation unit (70) that estimates reception intensities of the first terahertz wave (W1) and the second terahertz wave (W2) based on signal intensities at the first modulation frequency (fm1) and the second modulation frequency (fm2).

[0133] [Supplementary Note 5] The terahertz system according to any one of Supplementary Note 1 to Supplementary Note 4, wherein the first oscillation element (21) and the second oscillation element (22) are arranged side by side in a first direction (Ys), and the first detection element (51) is arranged at a position spaced apart from the first oscillation element (21) and the second oscillation element (22) in a second direction (Xs) perpendicular to the first direction.

[0134] [Supplementary Note 6] The terahertz system according to Supplementary Note 5, wherein the first detection element (51) is disposed between the first oscillation element (21) and the second oscillation element (22) in the first direction (Ys).

[0135] [Supplementary Note 7] The terahertz system according to any one of Supplementary Note 1 to Supplementary Note 6, wherein the first detection element (51) is arranged at a position where it detects reflected waves (W1r, W2r) of the first terahertz wave (W1) and the second terahertz wave (W2) reflected by a detection object (81).

[0136] [Supplementary Note 8] The terahertz system according to any one of Supplementary Note 1 to Supplementary Note 6, wherein the first oscillation element (21) is arranged so that the first detection element (51) detects the first terahertz wave (W1) reflected by a detection object (81) or a reflecting member, and the second oscillation element (22) is arranged so that the first detection element (51) detects the second terahertz wave (W2) transmitted through the detection object (81).

[0137] [Supplementary Note 9] The terahertz system according to any one of Supplementary Note 1 to Supplementary Note 8, wherein a first distance of a first optical path (L1) through which the first terahertz wave (W1) propagates and a second distance of a second optical path (L2) through which the second terahertz wave (W2) propagates are different from each other.

[0138] [Supplementary Note 10] The terahertz system according to Supplementary Note 9, further comprising an estimation unit (70) that estimates the presence or absence of a detection target (81) on at least one of the first optical light path (L1) and the second optical light path (L2) based on signal intensities at the first modulation frequency (fm1) and the second modulation frequency (fm2).

[0139] [Supplementary Note 11] The terahertz system according to Supplementary Note 9, further comprising an estimation unit (70) that estimates a state of the detection target (81) with respect to at least one of the first optical light path (L1) and the second optical light path (L2) based on signal intensities at the first modulation frequency (fm1) and the second modulation frequency (fm2).

[0140] [Supplementary Note 12] The terahertz system according to Supplementary Note 11, wherein the estimation unit (70) estimates a transmittance of the detection object (81) in the terahertz band.

[0141] [Supplementary Note 13] The terahertz system according to Supplementary Note 11, wherein the estimation unit (70) estimates a reflectance of the detection object (81) in the terahertz band.

[0142] [Supplementary Note 14] The terahertz system according to Supplementary Note 11, wherein the estimation unit (70) estimates a polarization state of the detection object (81) in the terahertz band.

[0143] [Supplementary Note 15] The terahertz system according to any one of Supplementary Note 1 to Supplementary Note 14, wherein the first oscillation element (21) and the second oscillation element (22) include any one of a resonant tunneling diode, a Tannett diode, an IMPATT diode, a GaAs-based field effect transistor, a GaN-based FET, a high electron mobility transistor, a heterojunction bipolar transistor, a CMOSFET, and an SBD.

[0144] [Supplementary Note 16] The terahertz system according to any one of Supplementary Note 1 to Supplementary Note 15, wherein the first detection element (51) detects a signal intensity of an electromagnetic wave in the terahertz band.

[0145] [Supplementary Note 17] The terahertz system according to any one of Supplementary Note 1 to Supplementary Note 16, wherein the first detection element (51) includes any one of a resonant tunneling diode, a Tannett diode, an IMPATT diode, a GaAs-based field effect transistor, a GaN-based FET, a high electron mobility transistor, a heterojunction bipolar transistor, a CMOSFET, an SBD, a calorimeter, and a microbolometer.

[0146] [Supplementary Note 18] The terahertz system according to any one of Supplementary Note 1 to Supplementary Note 17, wherein the first application circuit (30A) includes: a first bias circuit (32A) that generates a DC first bias voltage (VB11); a first signal generation circuit (31A) that generates the first modulation signal (Sm1); and a first superimposition circuit (33A) that generates the first drive signal (Sd1) by superimposing the first modulation signal (Sm1) on the first bias voltage (VB11), and the second application circuit (30B) includes: a second bias circuit (32B) that generates a DC second bias voltage (VB12); a second signal generation circuit (31B) that generates the second modulation signal (Sm2); and a second superimposition circuit (33B) that superimposes the second modulation signal (Sm2) on the second bias voltage (VB12).

[0147] [Supplementary Note 19] The terahertz system according to any one of Supplementary Note 1 to Supplementary Note 18, comprising a plurality of oscillation elements including the first oscillation element (21) and the second oscillation element (22), and the first detection element (51) is arranged at a position to detect a plurality of terahertz waves including at least the first terahertz wave (W1) of the first oscillation element (21) and the second terahertz wave (W2) of the second oscillation element (22) among the plurality of oscillation elements.

[0148] [Supplementary Note 20] The terahertz system according to Supplementary Note 19, further comprising a plurality of detection elements including the first detection element (51), wherein the plurality of detection elements are arranged to detect terahertz waves from at least two oscillation elements among the plurality of oscillation elements.

[0149] [Supplementary Note 21] The terahertz system according to Supplementary Note 3, wherein the derivation unit (70) frequency-converts time-series data obtained from the output signal of the first detection element (51) to obtain signal intensities at the first modulation frequency (fm1) and the second modulation frequency (fm2).

[0150] [Supplementary Note 22] The terahertz system according to Supplementary Note 21, wherein the derivation unit (70) detects an envelope of the output signal of the first detection element (51).

[0151] [Supplementary Note 23] A terahertz system comprising: a first oscillation element (21) capable of oscillating terahertz waves of a first oscillation frequency; a first application circuit (30A) that applies to the first oscillation element (21) a first drive signal (Sd1) on which a modulation signal of a first modulation frequency (fm1) lower than the first oscillation frequency is superimposed; a second oscillation element (22) capable of oscillating terahertz waves of a second oscillation frequency different from the first oscillation frequency; a second application circuit (30B) that applies to the second oscillation element (22) a second drive signal (Sd2) on which a modulation signal of a second modulation frequency (fm2) different from the first modulation frequency (fm1) is superimposed; and a first detection element (51) that detects the terahertz waves of the first oscillation frequency and the terahertz waves of the second oscillation frequency.

[0152] The above description is merely illustrative. Those skilled in the art will recognize that many more possible combinations and permutations are possible other than the components and methods (manufacturing processes) listed for the purpose of illustrating the technology of the present disclosure. The present disclosure is intended to embrace all alternatives, modifications, and variations that fall within the scope of the present disclosure, including the claims.

[0153] REFERENCE SIGNS LIST 10... terahertz system, 11-15... first to fifth transmitters, 21-25... first to fifth oscillators, 30A... first application circuit, 30B... second application circuit, 31A, 31B... signal generation circuit, 32A, 32B... bias circuit, 33A, 33B... superimposition circuit, 41-43... first to third receivers, 51-53... first to third detectors, 60... receiver circuit, 61... bias circuit, 62... extraction circuit, 63... signal processing circuit, 70... control device, 81... object to be detected, 82... reflecting member, 100... terahertz element, 110... substrate, 120... insulating layer, 130... active element, 140... Antenna, 141...first antenna member, 142...second antenna member, 301 to 306...terahertz system, fm1 to fm5...first to fifth modulation frequencies, L1...first optical path, L2...second optical path, S21...detection signal, S23...received signal, Sd1...first drive signal, Sd2...second drive signal, Sm1...first modulation signal, Sm2...second modulation signal, VB11...first bias voltage, VB12...second bias voltage, VB21...bias voltage, W1 to W5...first to fifth terahertz waves, W1r, W2r...reflected waves, WE1...envelope, WF1...first waveform, WF2...second waveform

Claims

1. A terahertz system comprising: a first oscillation element capable of oscillating a first terahertz wave; a first application circuit that applies to the first oscillation element a first drive signal having a first modulation frequency superimposed thereon; a second oscillation element capable of oscillating a second terahertz wave; a second application circuit that applies to the second oscillation element a second drive signal having a second modulation frequency superimposed thereon, the second modulation frequency being different from the first modulation frequency; and a first detection element positioned to detect the first terahertz wave and the second terahertz wave.

2. The terahertz system according to claim 1, wherein the first terahertz wave is a terahertz wave of a first oscillation frequency, and the second terahertz wave is a terahertz wave of a second oscillation frequency different from the first oscillation frequency.

3. A terahertz system according to claim 1 or 2, further comprising a derivation unit that derives signal intensities at the first modulation frequency and the second modulation frequency based on the detection result of the first detection element.

4. A terahertz system according to any one of claims 1 to 3, comprising an estimation unit that estimates the reception intensities of the first terahertz wave and the second terahertz wave based on the signal intensities at the first modulation frequency and the second modulation frequency.

5. A terahertz system according to any one of claims 1 to 4, wherein the first oscillation element and the second oscillation element are arranged side by side in a first direction, and the first detection element is arranged at a position spaced apart from the first oscillation element and the second oscillation element in a second direction perpendicular to the first direction.

6. The terahertz system according to claim 5, wherein the first detection element is disposed between the first oscillation element and the second oscillation element in the first direction.

7. A terahertz system according to any one of claims 1 to 6, wherein the first detection element is arranged at a position where it detects the first terahertz wave and the second terahertz wave reflected by an object to be detected.

8. A terahertz system according to any one of claims 1 to 6, wherein the first oscillation element is arranged so that the first detection element detects the first terahertz wave reflected by the object to be detected or a reflecting member, and the second oscillation element is arranged so that the first detection element detects the second terahertz wave that has passed through the object to be detected.

9. A terahertz system according to any one of claims 1 to 8, wherein a first distance of a first optical path along which the first terahertz wave propagates and a second distance of a second optical path along which the second terahertz wave propagates are different from each other.

10. The terahertz system according to claim 9, further comprising an estimation unit that estimates the presence or absence of a detection target in at least one of the first optical light path and the second optical light path based on the signal strength at the first modulation frequency and the second modulation frequency.

11. The terahertz system according to claim 9, further comprising an estimation unit that estimates the state of the object to be detected with respect to at least one of the first optical light path and the second optical light path based on the signal strength at the first modulation frequency and the second modulation frequency.

12. The terahertz system according to claim 11, wherein the estimation unit estimates the transmittance of the object to be detected in the terahertz band.

13. The terahertz system according to claim 11, wherein the estimation unit estimates the reflectance of the object to be detected in the terahertz band.

14. The terahertz system according to claim 11, wherein the estimation unit estimates the polarization state of the object to be detected in the terahertz band.

15. The terahertz system according to any one of claims 1 to 14, wherein the first oscillation element and the second oscillation element include any of a resonant tunneling diode, a Tannett diode, an IMPATT diode, a GaAs-based field effect transistor, a GaN-based FET, a high electron mobility transistor, a heterojunction bipolar transistor, a CMOSFET, or an SBD.

16. A terahertz system according to any one of claims 1 to 15, wherein the first detection element detects the signal intensity of electromagnetic waves in the terahertz band.

17. The terahertz system according to any one of claims 1 to 16, wherein the first detection element includes any one of a resonant tunneling diode, a Tannett diode, an IMPATT diode, a GaAs-based field effect transistor, a GaN-based FET, a high electron mobility transistor, a heterojunction bipolar transistor, a CMOSFET, an SBD, a calorimeter, and a microbolometer.

18. A terahertz system according to any one of claims 1 to 17, wherein the first application circuit includes: a first bias circuit that generates a first DC bias voltage; a first signal generation circuit that generates the first modulation signal; and a first superimposition circuit that generates the first drive signal by superimposing the first modulation signal on the first bias voltage; and the second application circuit includes: a second bias circuit that generates a second DC bias voltage; a second signal generation circuit that generates the second modulation signal; and a second superimposition circuit that superimposes the second modulation signal on the second bias voltage.

19. A terahertz system according to any one of claims 1 to 18, comprising a plurality of oscillation elements including the first oscillation element and the second oscillation element, and the first detection element is arranged at a position to detect a plurality of terahertz waves including at least the first terahertz wave of the first oscillation element and the second terahertz wave of the second oscillation element among the plurality of oscillation elements.

20. The terahertz system according to claim 19, comprising a plurality of detection elements including the first detection element, the plurality of detection elements being arranged to detect terahertz waves from at least two oscillation elements among the plurality of oscillation elements.

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