JP2017161450A - Terahertz wave imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a terahertz wave imaging device that can obtain an image of a subject easily with a simple structure.SOLUTION: A signal with a terahertz band containing a plurality of frequency components with frequency intervals f1 is generated in a first com generator 11. The terahertz waves with the frequencies are guided selectively to first to n-th transmission antennas 13a to 13n. The terahertz waves with the frequencies are delivered to different portions of a subject 100. The terahertz wave is received by a reception antenna 14. A signal with a terahertz band containing a plurality of frequency components with frequency intervals f2, which is a little different from the frequency intervals f1, is generated in a second com generator 16. The signal is mixed with a reception signal with a terahertz band in mixing means 15a to be converted into a signal with a low-frequency band. Image processing means 18 having received the resulting signal generates an image of the subject 100 from the relation between sensing information corresponding to each frequency component (for example, signal intensity in which the transmission intensity is reflected) and the sensed portion of the subject 100.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a terahertz wave imaging apparatus that acquires an image of a subject using electromagnetic waves in a terahertz band.

  In recent years, a terahertz (THz) wave refers to an electromagnetic frequency band of about 0.1 to 10 THz (wavelength 3 mm to 30 μm), and this frequency band is located between radio waves and light waves. And terahertz waves can pass through various substances such as paper, plastic, vinyl, fiber, semiconductor, fat, powder, ice like radio waves, and freely surround the space with lenses and mirrors like light waves be able to. In addition, since the terahertz wave has a shorter wavelength than the radio wave band, it has a spatial resolution suitable for various imaging applications.

  There has been proposed a terahertz wave imaging apparatus that obtains an image of a subject in a non-contact / non-destructive manner by utilizing the characteristics of the terahertz wave as described above. For example, there is an imaging apparatus that can obtain a transmission image of a subject from a difference in transmittance depending on the wavelength if the subject is irradiated with two-wavelength terahertz waves and the absorption of terahertz waves is wavelength-dependent. (See Patent Document 1).

JP 2004-108905 A

  However, in the invention described in Patent Document 1, since the subject must be irradiated with terahertz waves of two wavelengths, the procedure is complicated and the time required for image acquisition becomes long. In addition, in the invention described in Patent Document 1, an optical system that splits the generated terahertz wave into measurement light for irradiating the subject and reference light for intensity reference, and simultaneously introduces the measurement light and the reference light to the intensity measuring instrument. Since it is necessary, there is a problem that the structure of the apparatus becomes complicated accordingly.

  Therefore, an object of the present invention is to provide a terahertz wave imaging apparatus that can easily acquire an image of a subject with a simple structure.

  In order to solve the above-described problem, the invention according to claim 1 is directed to a transmission unit that irradiates a subject with a transmission wave including a plurality of frequencies in the terahertz band, and a signal that the transmission wave has reached through the subject. The receiving unit that receives signals transmitted through different paths for each of the signals, and the transmission path for each frequency component received by the receiving unit correspond to the detection part of the space including the subject, and each reception information of each frequency component is detected. An image image acquisition unit that maps the pixel information of the part.

  The invention according to claim 2 is the terahertz wave imaging apparatus according to claim 1, wherein the transmission unit generates transmission-side multifrequency signal generation means for generating a terahertz band signal including a plurality of frequency components; Transmitting means configured by arranging a plurality of transmitting antennas associated with each frequency component generated by the transmitting-side multifrequency signal generating means in one or two dimensions, and generated by the transmitting-side multifrequency signal generating means A transmission wave transmission means for selectively guiding each frequency component signal to the corresponding transmission antenna, and the reception unit can receive all frequency component signals reached through the subject. Receiving means having receiving antennas arranged at various positions, and receiving wave transmission means for guiding all signals received by the receiving antennas, and obtaining the image Receiving side multi-frequency signal generating means for generating a terahertz band signal including a plurality of frequency components each having a different low frequency difference frequency from each frequency generated by the transmitting side multi-frequency signal generating means, Included in the low frequency signal obtained from the mixing means for mixing the multifrequency signal generated by the receiving side multifrequency signal generating means as a local oscillation wave with the signal of the multifrequency component received by the receiving section An image for determining the pixel information of the detection part by using each frequency component as reception information of the detection part by the corresponding transmission antenna and creating a one-dimensional or two-dimensional image image in which the plurality of transmission antennas are arranged. And a processing means.

  The invention according to claim 3 is the terahertz wave imaging apparatus according to claim 1, wherein the transmission unit generates transmission-side multifrequency signal generation means for generating a terahertz band signal including a plurality of frequency components; Transmission means having a transmission antenna for transmitting a signal including each frequency component generated by the transmission-side multifrequency signal generation means, and transmission timing of each frequency component signal generated by the transmission-side multifrequency signal generation means A plurality of receiving antennas arranged one-dimensionally or two-dimensionally to a position where signals received via the subject can be received. And only the frequency component set corresponding to each receiving antenna is selected from the signals received by each receiving antenna of the receiving means. Receiving image transmission means for guiding the image, and the image image acquisition unit includes a plurality of frequency components having different low frequencies that are different from the frequencies generated by the transmission-side multifrequency signal generation means. Receiving-side multifrequency signal generating means for generating a terahertz band signal, and mixing the multifrequency signal generated by the receiving-side multifrequency signal generating means with a signal of a multifrequency component received by the receiving section as a local oscillation wave And a plurality of reception units that determine the pixel information of the detection part by using each of the frequency components included in the low-frequency signal obtained from the mixing part as reception information of the detection part by the corresponding reception antenna. And image processing means for creating a one-dimensional or two-dimensional image image in which antennas are arranged.

  According to a fourth aspect of the present invention, in the terahertz wave imaging apparatus according to the first aspect, the transmitting unit generates a transmission-side multifrequency signal generating unit that generates a terahertz band signal including a plurality of frequency components; Transmitting means configured by arranging a plurality of transmitting antennas associated with each frequency component generated by the transmitting-side multifrequency signal generating means in one or two dimensions, and generated by the transmitting-side multifrequency signal generating means Transmission wave transmission means for selectively guiding the signal of each frequency component to the corresponding transmission antenna, and the reception unit is a plurality of antennas arranged opposite to each transmission antenna of the transmission means. Of the frequency components transmitted by the transmitting antennas facing each receiving antenna from the receiving means having the receiving antennas of Received wave transmission means for selectively guiding the image, the image image acquisition unit is a plurality of frequency components having different low frequencies different from each frequency generated by the transmission side multi-frequency signal generation means Receiving side multi-frequency signal generating means for generating a terahertz band signal including the multi-frequency signal generated by the receiving side multi-frequency signal generating means as a local oscillation wave signal of the multi-frequency component received by the receiving part Mixing means for mixing, and each frequency component included in the low frequency signal obtained from the mixing means is used as reception information of the detection part by the corresponding receiving antenna, thereby determining pixel information of the detection part, And an image processing means for creating a one-dimensional or two-dimensional image image in which the transmission antennas are arranged.

  According to a fifth aspect of the present invention, in the terahertz wave imaging apparatus according to the first aspect, the transmission unit includes a multi-frequency light generation unit that generates an optical signal including light waves of a plurality of frequencies, and pump light. By injecting seed light into the excited nonlinear optical crystal at an angle that satisfies the angle phase matching condition, idler light is generated in a direction that satisfies the non-collinear phase matching condition, and terahertz light having a frequency corresponding to each seed light is emitted. An optical parametric generator irradiated from the surface and optical signals of a plurality of frequencies generated by the multi-frequency light generating means are used as seed light, and simultaneously injected into the optical parametric generator at angles satisfying the respective angle phase matching conditions. Formed on the light exit surface of the achromatic light injection optical system and the optical parametric generator, and the terahertz light of each frequency is different. A monolithic grating coupler that emits light at a certain angle, and an imaging optical system that receives all the terahertz light emitted from the monolithic grating coupler at different angles and forms an image on the receiving part through the arrangement space of the subject. The reception unit and the image image acquisition unit receive the terahertz light from the transmission unit at the incident surface of the nonlinear optical crystal, and the terahertz light of each frequency is incident on the nonlinear optical crystal excited by the pump light. An idler light having a wavelength corresponding to the frequency of each terahertz light is disposed on the optical parametric detector that generates in the direction satisfying the angle phase matching condition, and the idler light exit surface of the optical parametric detector. Imaging means for acquiring an image having a point as pixel information.

  According to the terahertz wave imaging apparatus according to the present invention, since a plurality of frequencies in the terahertz band correspond to detection parts in a space including the subject, if the reception information of each frequency component is mapped as pixel information of each detection part, the subject Can be obtained. Accordingly, it is possible to easily obtain an image of the subject with a simple structure.

1 is a schematic configuration diagram of a first embodiment of a terahertz wave imaging apparatus according to the present invention. It is a frequency spectrum in each part of the terahertz wave imaging apparatus shown in FIG. It is a schematic block diagram of 2nd Embodiment of the terahertz wave imaging device which concerns on this invention. It is a schematic block diagram of 3rd Embodiment of the terahertz wave imaging device which concerns on this invention. It is a schematic block diagram of 4th Embodiment of the terahertz wave imaging device which concerns on this invention.

  Next, an embodiment of a terahertz wave imaging apparatus according to the present invention will be described based on the attached drawings.

  FIG. 1 shows a schematic configuration of a terahertz wave imaging apparatus 10 according to the first embodiment. 1st comb generator 11, transmission wave transmission means 12, n receiving antennas arranged in one or two dimensions (first receiving antenna 13a, second receiving antenna 13b, third receiving antenna 13c, fourth receiving antenna 13d ,..., "Transmitting unit that irradiates a subject with a transmission wave including a plurality of frequencies in the terahertz band" by the (n-2) th receiving antenna 13n-2, the (n-1) th receiving 13n-1, and the nth receiving antenna 13n) Configure.

  Further, the reception antenna 14 and the reception signal processing unit 15 constitute a “reception unit that receives a signal in which a transmission wave arrives through a subject as a signal transmitted through a different path for each frequency component”. Further, the image processing means 18 that receives the low frequency signal (detailed later) from the mixing means 15a via the mixing means 15a, the second comb generator 16 and the amplifier 17 in the received signal processing section 15 " The transmission path for each received frequency component is made to correspond to the detection part of the space including the subject, and an image image acquisition unit that maps reception information of each frequency component as pixel information of each detection part is configured.

  The first comb generator 11 is a transmission-side multi-frequency signal generating unit that generates a terahertz band signal including a plurality of frequency components, and the frequency interval of the generated frequency is constant at f1. The first comb generator 11 converts laser light of known frequency into a large number of discrete spectra, and can obtain discrete frequencies at a frequency interval f1, as shown in FIG. 2 (a). . In addition, since the output of each wavelength of the existing comb generator will attenuate | damp as it leaves | separates from a center wavelength, you may make it use the signal which made each wavelength output uniform. Further, a frequency multiplier may be used as the transmission-side multifrequency signal generating means.

  The transmission signal transmission means 12 can be selectively guided to the first to nth transmission antennas 13a to 13n by being configured with a transmission line having a filter bank structure. For example, a terahertz wave having a frequency component (f0 + f1) higher by f1 than the reference frequency f0 is sent to the first antenna 13a, a terahertz wave of f0 + 2f1 is sent to the second antenna 13b, a terahertz wave of f0 + 3f1 is sent to the third antenna 13c, and a terahertz wave of f0 + 4f1 The wave is transmitted to the fourth antenna 13d,..., The terahertz wave of f0 + (n−2) f1 is transmitted to the n−2th antenna 13n−2, and the terahertz wave of f0 + (n−1) f1 is transmitted to the n−1th antenna 13n−1. The f0 + nf1 terahertz waves are selectively guided to the nth antenna 13n.

  The first to n-th antennas 13a to 13n are highly directional antennas arranged one-dimensionally or two-dimensionally, and radiate from the first to n-th antennas 13a to 13n at least until they pass through the arrangement area of the subject 100. The terahertz wave having each frequency is prevented from interfering with a terahertz wave having an adjacent frequency. In this case, the terahertz waves of each frequency radiated from the first to n-th antennas 13a to 13n toward the subject 100 are all irradiated to different parts of the subject 100, and pass through the subject 100 to the receiving unit. The terahertz wave of each frequency that reaches the receiving antenna 14 includes information (amplitude and phase change) reflecting the absorption, reflection, and transmittance of the terahertz wave in each part of the subject 100.

  For example, when the non-transparent region 100a exists at a site where the object 100 made of a material transparent (high in transmittance) to the terahertz band electromagnetic wave is irradiated with the t0 hertz wave of f0 + (n−1) f1, f0 + ( n-1) The t1 hertz wave of f1 is reflected by the non-transmissive region 100a and cannot reach the receiving unit, or is attenuated and is in a state where an extreme decrease in intensity occurs. However, terahertz waves of other frequencies are not extremely attenuated even when transmitted through the subject 100, and can reach the receiving unit while maintaining an appropriate intensity. Therefore, it is possible to estimate from the received intensity whether each part of the subject 100 through which the terahertz wave of each frequency is transmitted is transparent or opaque. Actually, transmission attenuation occurs even in the case of the transparent subject 100, and thus it is possible to obtain the transparent subject 100 as an image image. It is assumed that a binary image that can determine the presence or absence of the opaque region 100a is obtained.

  When the first to nth antennas 13a to 13n are two-dimensionally arranged, the entire image of the subject 100 can be obtained by one-time terahertz wave irradiation, but the total number of pixels is limited to n. For this reason, sufficient resolution may not be obtained. On the other hand, when the first to n-th antennas 13a to 13n are arranged one-dimensionally, n pixels can be assigned to one row, so that the resolution of the image can be increased, but the first to n-th antennas 13a to 13n Since the irradiation sequence of terahertz waves irradiated from 13n must be moved little by little to scan the subject 100 evenly, the scanning mechanism becomes complicated and the time required for imaging also becomes longer. Therefore, whether the first to nth antennas 13a to 13n are arranged one-dimensionally or two-dimensionally may be appropriately selected according to the size and purpose of the subject. In addition, when the terahertz waves irradiated from the first to nth antennas 13a to 13n cannot be transmitted sharply through each detection unit of the subject 100, the terahertz waves of each frequency are converged using an appropriate optical system, and the subject 100 May be irradiated.

  As described above, the terahertz waves of the respective frequencies that have reached the receiving unit through the subject 100 are collectively received by the receiving antenna 14. In the reception signal processing unit 15, a reception signal including frequency components of f0 + f1, f0 + 2f1, f0 + 3f1, f0 + 4f1,..., F0 + (n−2) f1, f0 + (n−1) f1, and f0 + nf is received via the reception wave transmission unit 15b. To the mixing means 15a. A terahertz band signal including a plurality of frequency components having a frequency interval f2 is input from the second comb generator 16 to the mixing means 15a.

  The second comb generator 16 is a receiving-side multifrequency signal generating means for generating a terahertz band signal including a plurality of frequency components having a frequency interval f2 slightly different from the frequency interval f1, and the generated frequency interval is It is constant at f2. Similar to the first comb generator 11, the second comb generator 16 converts laser light having a known frequency into a large number of discrete spectra. As shown in FIG. A discrete frequency can be obtained at the interval f2. The reason why the frequency intervals f1 and f2 are slightly different is to down-convert to a low frequency corresponding to the frequency difference. Therefore, the difference frequency between f1 and f2 to the difference frequency between nf1 and nf2 is a low frequency band (a frequency band lower than the terahertz band, for example, an arbitrary frequency band such as an RF band, an IF band, an AF band). The frequency interval f2 is set in advance.

  The terahertz band reception signal and the terahertz band multi-frequency signal generated by the second comb generator 16 are input to the mixing unit 15a (see FIG. 2C), and frequency conversion by a highly sensitive superheterodyne method is performed. Thus, it is output as a signal in a low frequency band (for example, IF band) (see FIG. 2D). If | f2-f1 | = Δf, subject detection information of terahertz wave f0 + f1 is at the frequency of Δf, subject detection information of terahertz wave f0 + 2f1 is at the frequency of 2Δf, and terahertz wave f0 + 3f1 is at the frequency of 3Δf. The detection information is the terahertz wave f0 + 4f1 subject detection information at the frequency of 4Δf, and the (n−2) Δf frequency is the terahertz wave f0 + (n−2) f1 subject detection information (n−1). The frequency of Δf reflects subject detection information of terahertz wave f0 + (n−1) f1, and the frequency of nΔf reflects subject detection information of terahertz wave f0 + nf. For example, the intensity is almost zero at the frequency of (n−1) Δf corresponding to the terahertz wave f0 + (n−1) f1 in which the non-transparent region 100a is a transmission path.

  The low frequency band signal (low frequency signal) obtained by the mixing unit 15 a as described above is appropriately amplified by the amplifier 17 and supplied to the image processing unit 18. This image processing means 18 determines the pixel information of the detection part by using each frequency component included in the low frequency signal as the reception information of the detection part by the corresponding transmission antenna 13.

  For example, in FIG. 1, the leftmost detection part from the receiving antenna 14 toward the subject 100 is the first pixel, which corresponds to the subject detection information of the terahertz wave f0 + f1 of the first transmission antenna 13a, and the right detection part is The second pixel corresponds to the subject detection information of the terahertz wave f0 + 2f1 of the second transmission antenna 13b, the detection portion on the right side thereof corresponds to the subject detection information of the terahertz wave f0 + 3f1 of the third transmission antenna 13c, ..., the detection part on the right side is the (n-1) th pixel, corresponding to the subject detection information of the terahertz wave f0 + (n-1) f1 of the (n-1) th transmission antenna 13n-1, and the detection part on the right side is the nth pixel. When the pixel corresponds to the subject detection information of the terahertz wave f0 + nf1 of the nth transmitting antenna 13n, the image processing means 18 is black only in the non-transparent area in the n−1th pixel. Other pixels may create one-dimensional image image was white in all transmission regions. Of course, as described above, in consideration of transmission attenuation obtained from detection information of each frequency, a gray scale image in which white and black are expressed in a multi-level tone may be created.

  In the terahertz wave imaging apparatus 10 of the first embodiment described above, the first comb generator 11 that generates a plurality of frequencies at equal intervals in the transmission unit is used. However, the plurality of terahertz waves radiated from the transmission unit are It does not have to be generated at regular intervals, and it is only necessary that the frequency components are separated to a degree that can be separated. For example, a plurality of frequencies whose frequency intervals change with regularity may be used, or a plurality of frequencies whose frequency intervals change randomly may be used. However, since the receiving unit needs to have a function for generating a frequency that can convert each frequency of the received terahertz wave to a different low frequency, the frequency generated by the transmitting unit and the frequency generated by the receiving unit are highly accurate. It is necessary to make adjustments that correspond to the above, which is complicated. On the other hand, as in the first embodiment, the first comb generator 11 and the second comb generator 16 are used to determine the intervals between the multiple frequencies generated by the transmitter and the receiver as f1 and f2. Therefore, there is an advantage that a simple and highly accurate down-conversion can be realized.

  FIG. 3 shows a schematic configuration of the terahertz wave imaging apparatus 20 according to the second embodiment. The first comb generator 21, the transmission wave transmission means 22, and the reception antenna 23 constitute a “transmission unit that irradiates a subject with transmission waves including a plurality of frequencies in the terahertz band”.

  In addition, a plurality of receiving antennas (for example, a first receiving antenna 24a, a second receiving antenna 24b, and a third receiving antenna) arranged one-dimensionally or two-dimensionally to a position where a terahertz band signal that has reached through the subject 100 can be received. The antenna 24c,..., The (n−1) th receiving antenna 24n−1, the nth receiving antenna 24n), and the received signal processing unit 25 are configured to transmit “the signal that the transmitted wave has reached through the subject is transmitted through a different path for each frequency component A reception unit that receives the received signal as a signal. The image processing means 28 that receives the low-frequency signal from the mixing means 25a through the mixing means 25a, the second comb generator 26, and the amplifier 27 in the reception signal processing section 25, “each frequency component received by the receiving section”. Is configured to correspond to the detection part of the space including the subject, and the reception information of each frequency component is mapped as pixel information of each detection part.

  The first comb generator 21 is the same as the first comb generator 11 of the first embodiment, and is transmission-side multifrequency signal generation means for generating a terahertz band signal including a plurality of frequency components. The interval is constant at f1.

  The transmission signal transmission means 22 guides all the frequency signals (f0 + f1, f0 + 2f1, f0 + 3f1,..., F0 + (n−1) f1, f0 + nf1 terahertz waves) generated by the first comb generator 21 to the transmission antenna 23.

  On the other hand, the first to nth receiving antennas 24 a to 24 n arranged one-dimensionally or two-dimensionally at the receiving unit can receive signals that have arrived through the detection parts of the subject 100. However, these first to nth receiving antennas 24a to 24n receive signals including all frequencies radiated from the transmitting antenna 23. Therefore, the received wave transmission means 25b of the received signal processing unit 25 is provided with a filter bank corresponding to the first to nth receiving antennas 24a to 24n, and is set corresponding to the first to nth receiving antennas 24a to 24n. Only the frequency component thus obtained is selectively guided to the mixing means 25a.

  For example, only the f0 + f1 terahertz signal from the first receiving antenna 24a, only the f0 + 2f1 terahertz signal from the second receiving antenna 24b, only the f0 + 3f1 terahertz signal from the third receiving antenna 24c, ..., n-1 Only the f0 + (n−1) f1 terahertz signal is supplied from the receiving antenna 24n−1, and only the f0 + nf1 terahertz signal is supplied from the nth receiving antenna 24n to the mixing unit 25a.

  The second comb generator 26 is a receiving-side multifrequency signal generating means for generating a terahertz band signal including a plurality of frequency components having a frequency interval f2 slightly different from the frequency interval f1, and the generated frequency interval is It is constant at f2. When the multiple frequencies from the transmitter are not equally spaced, the receiving side has a function of generating a terahertz band signal including a plurality of frequency components each having a different low frequency from the transmission frequency. The frequency signal generation means may be provided.

  The terahertz band reception signal and the terahertz band multi-frequency signal generated by the second comb generator 26 are input to the mixing unit 25a, and the low frequency band (for example, IF Band) signal.

  The low frequency band signal (low frequency signal) obtained by the mixing unit 25 a as described above is appropriately amplified by the amplifier 27 and supplied to the image processing unit 28. The image processing unit 28 determines pixel information of the detection part by using each frequency component included in the low frequency signal as reception information of the detection part by the corresponding reception antenna 24.

  For example, in FIG. 3, the leftmost first detection portion where the first receiving antenna 24a faces the subject 100 is the first pixel, which corresponds to the subject detection information of the terahertz wave f0 + f1, and the second receiving antenna 24b is located on the subject 100. The second detection region facing the second pixel corresponds to the subject detection information of the terahertz wave f0 + 2f1,..., The n−1th detection region where the n−1th receiving antenna 24n−1 faces the subject 100 is the n−1th pixel. Thus, it corresponds to the subject detection information of the terahertz wave f0 + (n−1) f1, the nth detection portion where the nth reception antenna 24n faces the subject 100 is the nth pixel, and corresponds to the subject detection information of the nth reception antenna 23n. In this case, the image processing means 28 can create a one-dimensional image image in which only the (n-1) th pixel is black in the non-transparent area and all other pixels are white in the transmissive area.

  FIG. 4 shows a schematic configuration of a terahertz wave imaging apparatus 30 according to the third embodiment. First comb generator 31, transmission wave transmission means 32, n receiving antennas arranged in one or two dimensions (first receiving antenna 33a, second receiving antenna 33b, third receiving antenna 33c,..., N− 1 reception 33n-1 and nth reception antenna 33n) constitute a "transmission unit that irradiates a subject with a transmission wave including a plurality of frequencies in the terahertz band".

  Also, a plurality of receiving antennas (first receiving antenna 34a, second receiving antenna 34b, third receiving antenna 34c,..., N−1th receiving antenna) arranged to face the first to nth transmitting antennas 33a to 33n. 34n-1 and the nth receiving antenna 34n) and the reception signal processing unit 35 constitute a "reception unit that receives a signal transmitted through a subject as a signal transmitted through a different path for each frequency component". . The image processing means 38 that receives the low-frequency signal from the mixing means 35a via the mixing means 35a, the second comb generator 36, and the amplifier 37 in the reception signal processing section 35 provides "every frequency component received by the receiving section". Is configured to correspond to the detection part of the space including the subject, and the reception information of each frequency component is mapped as pixel information of each detection part.

  The first comb generator 31 is a transmission-side multifrequency signal generating means for generating a terahertz band signal including a plurality of frequency components, like the first comb generators 11 and 21 of the first and second embodiments. The generated frequency interval is constant at f1.

  The transmission signal transmission means 32 can be selectively guided to the first to n-th transmission antennas 33a to 33n by being configured with a transmission line having a filter bank structure. For example, a terahertz wave having a frequency component (f0 + f1) higher by f1 than the reference frequency f0 is sent to the first antenna 33a, a terahertz wave of f0 + 2f1 is sent to the second antenna 33b, a terahertz wave of f0 + 3f1 is sent to the third antenna 33c,. (N-1) The f1 terahertz wave is selectively guided to the (n-1) th antenna 33n-1, and the f0 + nf1 terahertz wave is selectively guided to the nth antenna 33n.

  The first to n-th antennas 33 a to 33 n are highly directional antennas arranged one-dimensionally or two-dimensionally, and radiate from the first to n-th antennas 33 a to 33 n at least until they pass through the arrangement area of the subject 100. The terahertz wave having each frequency is prevented from interfering with a terahertz wave having an adjacent frequency. In this case, the terahertz waves of each frequency radiated from the first to n-th antennas 33a to 33n toward the subject 100 are all irradiated to different parts of the subject 100, and pass through the subject 100 to the receiving unit. The terahertz waves of the respective frequencies reaching the first to nth receiving antennas 34a to 34n include information (amplitude and phase change) reflecting the absorption, reflection, and transmittance of the terahertz waves in each part of the subject 100. .

  On the other hand, in the receiving unit, the first to nth receiving antennas 34a to 34n arranged to face the first to nth transmitting antennas 33a to 33n all receive signals that have arrived through the detection parts of the subject 100. Can receive. Moreover, these first to nth receiving antennas 34a to 34n can receive only the terahertz waves having the frequencies radiated from the corresponding first to nth transmitting antennas 33a to 33n. However, after passing through the subject 100, the terahertz wave of each frequency is diffused and may be received by an antenna different from the corresponding first to nth receiving antennas 34a to 34n. Therefore, the reception wave transmission means 35b of the reception signal processing unit 35 is provided with a filter bank corresponding to the first to nth reception antennas 34a to 34n, and is set corresponding to the first to nth reception antennas 34a to 34n. Only the frequency component thus obtained is selectively guided to the mixing means 25a.

  For example, only the f0 + f1 terahertz signal from the first receiving antenna 34a, only the f0 + 2f1 terahertz signal from the second receiving antenna 34b, only the f0 + 3f1 terahertz signal from the third receiving antenna 34c, ..., n-1 Only the f0 + (n-1) f1 terahertz signal is supplied from the receiving antenna 34n-1 and only the f0 + nf1 terahertz signal is supplied from the nth receiving antenna 34n to the mixing unit 35a.

  The second comb generator 36 is a receiving-side multifrequency signal generating means for generating a terahertz band signal including a plurality of frequency components having a frequency interval f2 slightly different from the frequency interval f1, and the generated frequency interval is It is constant at f2. When the multiple frequencies from the transmitter are not equally spaced, the receiving side has a function of generating a terahertz band signal including a plurality of frequency components each having a different low frequency from the transmission frequency. The frequency signal generation means may be provided.

  The terahertz band reception signal and the terahertz band multi-frequency signal generated by the second comb generator 36 are input to the mixing unit 35a, and a low frequency band (for example, IF Band) signal.

  The low frequency band signal (low frequency signal) obtained by the mixing unit 35 a as described above is appropriately amplified by the amplifier 37 and supplied to the image processing unit 38. This image processing means 38 determines the pixel information of the detection part by using each frequency component included in the low frequency signal as reception information of the detection part by the corresponding receiving antennas 34a to 34b.

  For example, in FIG. 4, the leftmost first detection part where the first receiving antenna 34a faces the subject 100 is the first pixel, which corresponds to the subject detection information of the terahertz wave f0 + f1, and the second receiving antenna 34b is located on the subject 100. The second detection region facing the second pixel corresponds to the subject detection information of the terahertz wave f0 + 2f1,..., The n−1th detection region where the n−1th reception antenna 34n−1 faces the subject 100 is the n−1th pixel. Therefore, it corresponds to the subject detection information of the terahertz wave f0 + (n−1) f1, the nth detection portion where the nth reception antenna 34n faces the subject 100 is the nth pixel, and corresponds to the subject detection information of the nth reception antenna 34n. In this case, the image processing means 38 can create a one-dimensional image image in which only the (n-1) th pixel is black in the non-transparent area and all other pixels are white in the transmissive area.

  In the terahertz wave imaging apparatuses 10 to 30 according to the first to third embodiments described above, each of the transmission units generates a plurality of frequency terahertz waves generated by the first comb generators 11 to 31. However, the configuration of the transmission unit is not limited to these. For example, a frequency scanning antenna that can radiate a plurality of frequencies toward different angles can be used as the transmitter. The terahertz wave imaging apparatuses 10 and 30 according to the first and third embodiments obtain detection information of each part by transmitting a plurality of frequencies irradiated from the transmission unit through different parts of the subject 100. However, if terahertz waves of a plurality of frequencies are irradiated to one point of the subject 100 using an appropriate optical system, spectral information of a detection site (irradiation site) in the subject 100 can be obtained, and thus it is diverted to a spectroscopy apparatus. There is also an advantage of being able to do it.

  In addition, the terahertz wave imaging apparatuses 10 to 30 according to the first to third embodiments described above all acquire an image of a subject using the radio wave property of the terahertz wave. For example, it is also possible to acquire an image of a subject using the light wave property of a band of 1 THz or more. In the following description, for convenience, the terahertz wave may be referred to as light.

  FIG. 5 shows a schematic configuration of a terahertz wave imaging apparatus 40 according to the fourth embodiment. A light wave source (multi-frequency light generating means for generating an optical signal including light waves having a plurality of frequencies), a light injection type terahertz wave parametric generator 41, and an imaging optical system 42 are used to generate a "multi-frequency terahertz band. A “transmission unit that irradiates the subject with the included transmission waves” is configured.

  In addition, the light injection type terahertz wave parametric detector 43 arranged at a part where the irradiation light from the imaging optical system of the transmission unit reaches through the arrangement space of the subject 100 is “the signal that the transmission wave has reached through the subject”. As a signal that is received as a signal transmitted through a different path for each frequency component ", and the light injection type terahertz wave parametric detector 43 and the imaging means 44 such as a CCD camera cooperate. Thus, "the image image acquisition unit that maps the transmission path for each frequency component received by the reception unit to the detection part of the space including the subject and maps the reception information of each frequency component as pixel information of each detection part" Configure.

  The light injection type terahertz wave parametric generator 41 has an optical parametric generator using a nonlinear optical crystal (for example, lithium niobate crystal) excited by pump light, and an angle at which seed light is injected into the optical parametric generator. It comprises an achromatic light injection optical system to be adjusted and a monolithic grating coupler formed on the light exit surface of the optical parametric generator. That is, the light injection type terahertz wave parametric generator 41 can generate terahertz waves of a plurality of frequencies and radiate them at different angles for each frequency. In addition, an optical comb generator etc. can be used for the multifrequency optical signal used as the seed light which injects into the light injection type terahertz wave parametric generator 41.

  The optical parametric generator injects seed light into the nonlinear optical crystal excited with pump light at an angle that satisfies the angle phase matching condition, thereby generating idler light in a direction that satisfies the non-collinear phase matching condition. Corresponding frequency terahertz light is emitted from the exit surface. When a multi-wavelength seed beam is incident on this optical parametric generator, an achromatic light injection optical system is required in order for light of each frequency to be incident simultaneously at an angle satisfying each angle phase matching condition. . In this achromatic light injection optical system, the diffraction angle also changes when the frequency (wavelength) of the seed light changes. Therefore, the change in the diffraction angle is further adjusted by the lens system so that the required angle phase matching condition is satisfied. The optical system controls the incident angle to the nonlinear optical crystal for each frequency of the seed light.

  For example, 50 wavelengths of seed light (for example, 1068.0 nm, 1068.1 nm, 1068.2 nm,..., 1072.7 nm, 1072.8 nm, 1072.9 nm), which differ depending on the multi-frequency light generating means, are used for achromatic light injection optics. When injected into the nonlinear optical crystal simultaneously at an angle satisfying the respective angle phase matching conditions through the system, 50 different frequencies (1.056 THz, 1.082 THz, 1.109 THz,..., 2.287 THz, 2.313 THz, 2 .339 THz) are generated at the same time.

  The monolithic grating coupler is formed by carving a groove directly on the light emitting surface of the nonlinear optical crystal so that the terahertz wave of each frequency generated in the nonlinear optical crystal as described above is emitted at different angles. . By providing this monolithic grating coupler, a plurality of terahertz waves having different frequencies are radiated at different angles for each frequency.

  The terahertz waves radiated at different angles for each frequency as described above are collected by the imaging optical system 42 and imaged on the receiving unit via the arrangement space of the subject 100. In other words, the terahertz waves of different frequencies with different radiation angles reach the receiving unit through different positions of the subject 100, so the terahertz waves of the respective frequencies that reach the receiving unit through the subject 100 are Information (amplitude and phase change) reflecting the absorption, reflection, and transmittance of terahertz waves in each part is included.

  For example, in FIG. 5, the subject detection information of the terahertz wave f0 + f1 radiated at the angle θ1 is associated with the first pixel, the subject detection information of the terahertz wave f0 + 2f1 radiated at the angle θ2 is associated with the second pixel, and the angle θ3 The object detection information of the terahertz wave f0 + 3f1 radiated at 1 corresponds to the third pixel,..., The object detection information of the terahertz wave f0 + (n−1) f1 radiated at the angle θn−1 corresponds to the n−1th pixel. The object detection information of the terahertz wave f0 + nf1 emitted at the angle θn is made to correspond to the nth pixel.

  Each terahertz wave that has passed through the portion where the subject 100 is arranged as described above reaches the light injection type terahertz wave parametric detector 43 of the receiving unit. The optical injection type terahertz wave parametric detector 43 includes an optical parametric detector (including a nonlinear optical crystal) having the same configuration as the optical parametric generator of the optical injection type terahertz wave parametric generator 41 described above. The detector generates idler light from the terahertz wave of each frequency having subject detection information, and uses the idler light as pixel information of each detection part.

  That is, when terahertz waves having a plurality of frequencies are incident from the incident surface of the nonlinear optical crystal excited by pump light (any surface orthogonal to the incident surface of the pump light), each frequency corresponds to each frequency in the nonlinear optical crystal. Idler light (for example, near-infrared light) is generated in a direction that satisfies the angle phase matching condition, and idler light is emitted from a surface (idler light emission surface) opposite to the pump light incident surface. The brightness of each idler light is reflected as the transmission intensity at each detection part of the subject 100.

  Therefore, if the idler light in the infrared region emitted from the light injection type terahertz wave parametric detector 43 is taken by the imaging means 44 such as an infrared camera, an image image of the subject 100 can be obtained. If idler light in the visible light region is generated, it can be visualized by projecting the idler light emitted from the light injection type terahertz wave parametric detector 43 onto a screen or the like. Further, when the multi-frequency terahertz light emitted from the imaging optical system 42 to the subject 100 is one-dimensionally arranged, only the image image for one column is output from the light injection type terahertz wave parametric detector 43. For example, if the imaging optical system 42 sequentially scans while changing the irradiation position with respect to the subject 100, and the image images output in time series from the light injection type terahertz wave parametric detector 43 are projected onto the same plane at once. A two-dimensional image can be obtained.

  As described above, the terahertz wave imaging apparatus according to the present invention has been described based on some embodiments. However, the present invention is not limited to these embodiments, and unless the configuration described in the scope of claims is changed. All the terahertz imaging devices that can be realized in are included in the scope of rights.

10 Terahertz wave imaging apparatus (first embodiment)
DESCRIPTION OF SYMBOLS 11 1st comb generator 12 Transmission wave transmission means 13a-13n 1st-nth transmission antenna 14 Reception antenna 15 Reception signal processing part 15a Reception wave transmission means 15b Mixing means 16 2nd comb generator 18 Image processing means 100 Subject 100a Impervious area

Claims (5)

A transmitter that irradiates a subject with a transmission wave including a plurality of frequencies in the terahertz band;
A receiver that receives the signal that the transmitted wave has reached through the subject as a signal that is transmitted through a different path for each frequency component;
An image image acquisition unit that maps a transmission path for each frequency component received by the reception unit to a detection part of a space including a subject, and maps reception information of each frequency component as pixel information of each detection part;
A terahertz wave imaging apparatus. The transmitter is
Transmitting-side multifrequency signal generating means for generating a terahertz band signal including a plurality of frequency components;
A transmission unit configured by arranging a plurality of transmission antennas associated with each frequency component generated by the transmission-side multifrequency signal generation unit in one or two dimensions;
Transmission wave transmission means for selectively guiding the signal of each frequency component generated by the transmission-side multifrequency signal generation means to a corresponding transmission antenna;
Including
The receiver is
A receiving means having a receiving antenna disposed at a position capable of receiving signals of all frequency components reached through the subject;
Received wave transmission means for guiding all signals received by the receiving antenna;
Including
The image image acquisition unit
A receiving-side multifrequency signal generating means for generating a terahertz band signal including a plurality of frequency components each having a different low frequency difference from each frequency generated by the transmitting-side multifrequency signal generating means;
A mixing means for mixing the multifrequency signal generated by the receiving-side multifrequency signal generating means as a local oscillation wave with a multifrequency component signal received by the receiving section;
By using each frequency component included in the low-frequency signal obtained from the mixing means as reception information of the detection part by the corresponding transmission antenna, pixel information of the detection part is determined, and the plurality of transmission antennas are arranged Image processing means for creating a one-dimensional or two-dimensional image,
The terahertz wave imaging apparatus according to claim 1, comprising: The transmitter is
Transmitting-side multifrequency signal generating means for generating a terahertz band signal including a plurality of frequency components;
A transmission means having a transmission antenna for transmitting a signal including each frequency component generated by the transmission-side multifrequency signal generation means;
In accordance with the transmission timing of each frequency component signal generated by the transmission-side multifrequency signal generation means, transmission wave transmission means for guiding to the transmission antenna,
Including
The receiver is
A receiving means comprising a plurality of receiving antennas arranged one-dimensionally or two-dimensionally at a position where a signal that has reached through the subject can be received;
Received wave transmission means for selectively deriving only frequency components set corresponding to each reception antenna from signals received by each reception antenna of the reception means;
Including
The image image acquisition unit
A receiving-side multifrequency signal generating means for generating a terahertz band signal including a plurality of frequency components each having a different low frequency difference from each frequency generated by the transmitting-side multifrequency signal generating means;
A mixing means for mixing the multifrequency signal generated by the receiving-side multifrequency signal generating means as a local oscillation wave with a multifrequency component signal received by the receiving section;
By using each frequency component included in the low frequency signal obtained from the mixing means as reception information of the detection part by the corresponding reception antenna, pixel information of the detection part is determined, and the plurality of reception antennas are arranged Image processing means for creating a one-dimensional or two-dimensional image,
The terahertz wave imaging apparatus according to claim 1, comprising: The transmitter is
Transmitting-side multifrequency signal generating means for generating a terahertz band signal including a plurality of frequency components;
A transmission unit configured by arranging a plurality of transmission antennas associated with each frequency component generated by the transmission-side multifrequency signal generation unit in one or two dimensions;
Transmission wave transmission means for selectively guiding the signal of each frequency component generated by the transmission-side multifrequency signal generation means to a corresponding transmission antenna;
Including
The receiver is
Receiving means having a plurality of receiving antennas arranged opposite to each transmitting antenna of the transmitting means;
Received wave transmission means for selectively deriving only frequency components transmitted by transmission antennas facing each reception antenna from signals received by each reception antenna of the reception means;
Including
The image image acquisition unit
A receiving-side multifrequency signal generating means for generating a terahertz band signal including a plurality of frequency components each having a different low frequency difference from each frequency generated by the transmitting-side multifrequency signal generating means;
A mixing means for mixing the multifrequency signal generated by the receiving-side multifrequency signal generating means as a local oscillation wave with a multifrequency component signal received by the receiving section;
By using each frequency component included in the low frequency signal obtained from the mixing means as reception information of the detection part by the corresponding reception antenna, pixel information of the detection part is determined, and the plurality of transmission antennas are arranged Image processing means for creating a one-dimensional or two-dimensional image,
The terahertz wave imaging apparatus according to claim 1, comprising: The transmitter is
Multi-frequency light generating means for generating an optical signal including light waves of a plurality of frequencies;
By injecting seed light into the nonlinear optical crystal excited with pump light at an angle that satisfies the angle phase matching condition, idler light is generated in a direction that satisfies the non-collinear phase matching condition, and the terahertz frequency corresponding to each seed light is generated. An optical parametric generator in which light is emitted from the exit surface;
An achromatic light injection optical system for injecting into the optical parametric generator at the same time at an angle satisfying the respective angle phase matching conditions, using the optical signals of a plurality of frequencies generated by the multi-frequency light generation means as seed light;
A monolithic grating coupler that is formed on the light exit surface of the optical parametric generator and emits terahertz light of each frequency to different angles;
An imaging optical system that receives all the terahertz light emitted at different angles from the monolithic grating coupler and forms an image on the receiving unit through the arrangement space of the subject;
Including
The receiving unit and the image image acquiring unit are
The terahertz light from the transmitter is received by the incident surface of the nonlinear optical crystal, and the terahertz light of each frequency is incident on the nonlinear optical crystal excited by the pump light, so that the idler light having a wavelength corresponding to the frequency of each terahertz light. Optical parametric detectors respectively generated in directions that satisfy the angle phase matching condition;
An imaging unit that is disposed on an idler light exit surface of the optical parametric detector, and that obtains an image image having a bright spot of each idler light as pixel information;
The terahertz wave imaging apparatus according to claim 1, comprising:

Images