THz full-band spatial imaging system based on spatial resolution layer and superconducting microwave dynamic inductance detector array imaging chip

Abstract

The invention discloses a THz full-band space imaging system based on a space resolution layer and a superconducting microwave dynamic inductance detector array imaging chip, and belongs to the field of signal detection. The system comprises an MKID detector array module, a spatial resolution layer module, a microwave signal coupling and amplification module, a signal mixing and acquisition module, an image reconstruction and processing module, a THz wave source and calibration module, a low-temperature superconducting module and a microwave signal source and excitation module. Through the design of the MKID detector array, full-band detection of terahertz waves can be realized, and the sensitivity and accuracy of the detection system are greatly improved. By introducing the spatial resolution layer, spatial information is converted into a time domain signal, so that spatial imaging of terahertz waves is realized, and the spatial resolution of the system is improved. And by adopting a digital acquisition system and a rapid signal processing algorithm, real-time acquisition and analysis of signals can be realized, and the real-time performance of the system is further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of signal detection, and more specifically, particularly relates to a THz full-band spatial imaging system based on a spatial resolution layer and a superconducting microwave dynamic inductance detector array imaging chip. Background Art

[0002] Security inspection (security check) is an important part of preventing extreme terrorist activities and passengers from carrying prohibited dangerous goods. It shoulders the mission of maintaining social order and the safety of people's lives and property. Therefore, it is extremely necessary to deploy security inspection equipment in public gathering places such as airports, stations, and subways for targeted human and object security inspections. The currently commonly used solution is a metal detection door combined with a manual body search. Although this method is simple and direct, it has many limitations, such as: slow inspection speed, only metals can be detected for prohibited items (that is, non-metallic items carried may be missed, such as ceramic knives), it is impossible to conduct a comprehensive inspection of the human body, and contact-based manual body searches have the problem of infringing privacy. Human security inspection technology urgently needs to be updated.

[0003] For long-distance passive THz real-time imaging, the radiation power of the object to be measured at room temperature is very weak, so the detector is required to have low noise and high sensitivity, and the noise equivalent power (NEP) needs to be below the order of 10-14 W / Hz1 / 2. Currently, the only detector that meets this indicator is the superconducting detector working at low temperature. This is a weak light detection technology developed in the past two decades. The energy gap of superconducting materials is relatively small (= meV, 2~3 orders of magnitude lower than the semiconductor band gap). A photon with energy exceeding the energy gap can break up several Cooper pairs. Therefore, superconducting devices have a very wide response spectrum and are very sensitive to photons from visible light to infrared to THz bands. In addition, superconducting detectors have extremely low dark count rates, high detection efficiency and detection speed.

[0004] There are three main types of superconducting detectors that are widely studied: superconducting nanowire single photon detector (SNSPD), thermosensitive superconducting edge sensor (TES) and microwave dynamic inductance detector (MKID). Among them, SNSPD uses the loss of superconductivity in the hot spot area formed after photons are incident on the nanowire to realize photon detection. It has an extremely fast response speed and is therefore mainly used in the fields of quantum communication and optical quantum communication; TES uses superconducting thin films with extremely large slopes of superconducting transition curves to realize photon detection. At present, it has achieved applications in high-efficiency photon counting and photon energy resolution, and has also preliminarily demonstrated its application in passive imaging; MKID uses the dynamic inductance of superconducting materials to respond sensitively to radiation energy to realize photon detection. MKID is usually made into a superconducting resonator structure. When photons are absorbed, the resonant frequency and quality factor of the resonator will decrease. Compared with TES, the advantages of MKID are that it is relatively easy to prepare and does not require precise temperature control, and it is easier to expand to large-scale arrays and read. TES involves the SQUID process on the chip, which is sensitive to temperature fluctuations. If you want to expand it to a large array detector, the complexity of the readout circuit will be greatly increased: MKID usually only involves micro-machining of a single layer of metal film, which is less affected by temperature fluctuations. Its frequency domain multiplexing feature makes MKID very easy to expand (for example, it can be integrated in a 1GHz bandwidth). 103 resonators), and all resonators can be read through the same feed line and a cryogenic amplifier. This advantage makes MKID currently mainly used in millimeter / submillimeter waveband astronomical imaging, such as the Antarctic Submillimeter Aperture Telescope (BLAST.TNG), the Multi-Band Submillimeter Wave Imaging System (MUSIC), and the European Millimeter Wave Astronomical Telescope Project (NIKA).

[0005] It can be seen that superconducting microwave dynamic inductance detectors are one of the important ways to realize high-sensitivity large array TH2 detectors due to their low noise and easy scalability, and have broad application prospects. Therefore, our goal is to develop high-performance terahertz (600 GHz, 500 um) superconducting MKID array imaging chips and systems for human security inspection and explore related device physics. The reason for choosing 600 GHZ is that this band has good clothing penetration, small air propagation attenuation rate and high signal frequency. In fact, researchers at Cardiff University first demonstrated the application of MKID in passive TH imaging in 2016. This work prepared a superconducting Al MKID array detector chip with 152 pixels, and achieved a noise equivalent temperature difference (NETD) of ~0.1 K / Hz1 / 2 at the detection frequency band of 350 GHz, and the resolution of the target object 3~5 m away was about 1.3 cm.

[0006] In the prior art, invention patent CN109000792A discloses a superconducting microwave dynamic inductance detector with distinguishable photon number and energy, including the following technical features: Technical feature 1: A superconducting microwave dynamic inductance detector with distinguishable photon number and energy, characterized in that: it includes a superconducting resonator with a lumped structure; the resonator includes an interdigital capacitor for suppressing second-level impurity noise in the substrate and an inductor strip as a light absorption area; the inductor strip is embedded in the interdigital capacitor and connected in parallel with the interdigital capacitor, the inductor strip includes at least one layer of TiN film, the superconducting transition temperature of the TiN film is 0.9K, the thickness is 20nm, and the area is 10mX10m; the material of the interdigital capacitor is A film, the superconducting transition temperature of which is 1.2K, the thickness is 200nm, the line width is 5Hm, and the area is 0.6mmX0.6m; the Si substrate located below the inductor strip is in a suspended state, and the thickness of the Si substrate is 10; A layer of anti-reflection film is uniformly arranged on the upper surface of the film, and a layer of anti-reflection film is uniformly arranged below it. Technical feature 2: The superconducting microwave dynamic inductance detector with distinguishable photon number and energy is characterized in that the material of the inductance strip is TiN or TiN / Ti / TiN film, the area is 10mX0 and the thickness is 20nm, the superconducting transition temperature is 0.9K, the area of ​​the cross-finger capacitor is 0.6mmX0.6mm, the line width is 5, its material is Al or N, the superconducting transition temperature is greater than 1K, the material of the anti-reflection film is a-Si, SiNx or Si2; the material of the anti-reflection film is Ag, Au or Al.

[0007] Invention patent CN112611719A discloses a terahertz photoacoustic single-pixel imaging device and imaging method, including the following technical features: Technical feature one: A terahertz photoacoustic single-pixel imaging device, characterized in that it includes a light source module, a spatial light modulation module, a terahertz light modulation module, a terahertz photoacoustic detection module and a processing module; the light source module is used to output a pump laser beam and a terahertz light beam; the equal-interval light modulation module is used to receive the pump laser beam, and modulate the pump laser beam according to a preset single-pixel imaging modulation pattern and transmit it to the terahertz light modulation module: the terahertz light modulation module is adjacent to the object to be imaged, and is used to receive the terahertz light beam, and modulate the terahertz light beam according to the single-pixel imaging pattern and transmit it to the object to be imaged. Technical feature 2: The terahertz photoacoustic detection module is arranged at the output end of the terahertz light modulation module, and the terahertz photoacoustic detection module includes a terahertz photoacoustic material and an ultrasonic detector, the terahertz photoacoustic material is used to generate a photoacoustic signal under the excitation of the terahertz light passing through the object to be imaged, the ultrasonic detector is used to convert the photoacoustic signal into an electrical signal, and the processing module is connected to the ultrasonic detector, and is used to realize single-pixel imaging of the object to be imaged according to the electrical signal. Technical feature 3: The light source module includes a pulse laser, a beam splitter, a first reflector group, a second reflector group, a grating, a half-wave plate, a first lens, and a nonlinear crystal; the beam splitter is used to divide the pulse laser output by the pulse laser into a first light beam and a second light beam, the first light beam sequentially passes through the first reflector group, the grating, the half-wave plate, and the first lens, and then focuses on the nonlinear crystal to excite the terahertz light beam, and the second light beam is used as the pump laser beam, and after passing through the second reflector group, it is incident on the spatial light modulation module.

[0008] Existing technical solutions can detect THz light, but there are still obstacles in spatial imaging, and THz light in different spatial positions cannot be distinguished well; there are also solutions that use optical spectrometry for spatial resolution, but they have the disadvantages of being slow and unable to form images in one go. Summary of the invention

[0009] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0010] In view of the above or existing problems of THz full-band spatial imaging systems based on a spatial resolution layer and a superconducting microwave dynamic inductance detector array imaging chip, the present invention is proposed.

[0011] In order to solve the above technical problems, the present invention provides the following technical solutions: The embodiment of the present invention provides a THz full-band spatial imaging system based on a spatial resolution layer and a superconducting microwave dynamic inductance detector array imaging chip, comprising: an MKID detector array module, which is used to realize full-band detection of terahertz waves through a plurality of superconducting microwave resonator pixels, and realizes spatial imaging based on time resolution by combining with the spatial resolution layer; The spatial resolution layer module is used to control the terahertz signals at different spatial positions to pass through the liquid crystal points at different times and be transmitted to the MKID detector array through the double-layer structure of the liquid crystal panel and the waveguide plate, thereby achieving spatial resolution; The microwave signal coupling and amplification module is used to transmit the detected microwave signal to the low-temperature superconducting amplifier through the feeder, and then after further processing by the room-temperature amplifier, it is sent to the mixer for I / Q signal demodulation, and finally the digital acquisition system is used for time domain analysis; The signal mixing and acquisition module is used to mix the signal with the reference signal in the mixer to obtain I and Q voltage outputs as the amplitude and phase information of the signal. The mixed signal is processed by low-pass filtering and digitally acquired through the A / D card; The image reconstruction and processing module is used to reconstruct the information at different times into a terahertz spatial imaging image through a time domain signal processing algorithm. A THz wave source and calibration module, which is used to generate THz waves through a temperature-adjustable blackbody source and transmit the signals to the MKID detector array in the sample box through a THz low-pass filter and a horn antenna; Low-temperature superconducting module, used for MKID detector array to absorb terahertz photons transmitted from THz wave source under low-temperature conditions. The current change caused by the photon energy triggers the phase and amplitude change of microwave signal. The microwave signal source and excitation module are used to generate microwave signals and transmit them to the MKID detector array through the feeder. The excitation signal is used to match the resonant frequency of the detector and trigger the microwave signal change when the detector receives terahertz photons.

[0012] As a preferred solution of the THz full-band spatial imaging system based on the spatial resolution layer and the superconducting microwave dynamic inductance detector array imaging chip of the present invention, wherein: the full-band detection of terahertz waves is realized by multiple superconducting microwave resonator pixels, and spatial imaging based on time resolution is realized by combining with the spatial resolution layer, including: The liquid crystal panel controls the light transmission state of each liquid crystal point according to preset rules through horizontal and vertical control lines. Each liquid crystal point turns to the light transmission state in sequence, allowing the terahertz waves at different spatial positions to pass through the corresponding liquid crystal point. When terahertz waves are emitted from an external source and pass through the spatial resolution layer, each liquid crystal dot gradually transmits signals from different spatial locations.

[0013] As a preferred solution of the THz full-band spatial imaging system based on the spatial resolution layer and the superconducting microwave dynamic inductance detector array imaging chip of the present invention, wherein: the double-layer structure of the liquid crystal panel and the waveguide plate controls the terahertz signals at different spatial positions to pass through the liquid crystal points at different times and transmit to the MKID detector array to achieve spatial resolution, including: If the liquid crystal panel contains m×n liquid crystal pixels, the light transmittance state of each pixel is changed by controlling the voltage, the refresh period of the liquid crystal panel is δt, and the light transmittance state control formula is:

[0014] Wherein, P(t) represents the light transmittance state of the liquid crystal pixel, and t represents time; When a certain pixel of the liquid crystal panel is turned on, the terahertz signal will pass through the liquid crystal point and be transmitted to the MKID detector array by the waveguide plate. Assume that the transmission efficiency of the waveguide plate is η wg , which represents the efficiency of the waveguide plate in transmitting the terahertz signal transmitted through the liquid crystal panel to the MKID array. The signal transmission formula is:

[0015] Among them, S out (t) is the terahertz signal transmitted to the MKID detector array, S in (t) is the incident signal transmitted from the liquid crystal panel, η wg is the transmission efficiency of the waveguide plate, P(t) is the light transmittance state of the liquid crystal panel; When a liquid crystal pixel is turned on, the terahertz wave signal from that spatial position will be transmitted to the corresponding pixel in the MKID detector array. The refresh time of each liquid crystal point is δt. If the liquid crystal panel has m×n pixels, the refresh time of each pixel is δt, and the refresh cycle of the entire panel is:

[0016] The time required to scan a complete image is the refresh time of m×n pixels.

[0017] As a preferred solution of the THz full-band spatial imaging system based on the spatial resolution layer and the superconducting microwave dynamic inductance detector array imaging chip of the present invention, wherein: the I / Q signal is sent to the mixer for demodulation, and finally the time domain analysis is performed through the digital acquisition system, including: The I and Q signals are digitized through an analog-to-digital converter. The ADC converts the analog signal into a digital signal so that the signal can be processed and analyzed in subsequent digital signal processing. The digitized I / Q signal enters the digital signal processing system, and Fourier transform analysis is performed on the I / Q signal to obtain spectrum information.

[0018] As a preferred solution of the THz full-band spatial imaging system based on the spatial resolution layer and the superconducting microwave dynamic inductance detector array imaging chip of the present invention, wherein: the digitized I / Q signal enters the digital signal processing system, and the I / Q signal is subjected to Fourier transform analysis to obtain spectrum information, including: Perform fast Fourier transform on the digitized I / Q signal to convert the time domain signal to the frequency domain and obtain its spectrum information, which is defined as:

[0019] Where N is the number of FFT points, k is the frequency index, and X[k] is the frequency domain signal. Through FFT, the amplitude and phase information of the signal at each frequency component are obtained; By analyzing the amplitude of the FFT result, the power spectrum density of the signal is obtained, which reflects the power distribution of the signal at each frequency. The calculation formula of PSD is:

[0020] Among them, |X[k]| represents the amplitude of X[k]. By analyzing the PSD, the main frequency components, bandwidth and power distribution characteristics of the signal can be identified.

[0021] As a preferred solution of the THz full-band spatial imaging system based on the spatial resolution layer and the superconducting microwave dynamic inductance detector array imaging chip of the present invention, wherein: the signal is mixed with the reference signal in the mixer to obtain I and Q voltage outputs as the amplitude and phase information of the signal, including: In the mixer, the input signal S(t) and the reference signal LO(t) are multiplied to obtain the mixed output:

[0022] Substituting into the signal expression:

[0023] Expand the above equation using trigonometric identities:

[0024] Difference frequency component (f IF =|f S -f LO ∣ is the required intermediate frequency signal, which contains the amplitude and phase information of the signal; the sum frequency component (fsum =f S +f LO ) are filtered out.

[0025] As a preferred solution of the THz full-band spatial imaging system based on the spatial resolution layer and the superconducting microwave dynamic inductance detector array imaging chip of the present invention, wherein: the collected time-domain microwave signal is reconstructed into a terahertz spatial imaging image by a time-domain signal processing algorithm, including: If the received time domain signal is S(t), where t is the time variable, S(t) is the received signal whose amplitude and phase vary with time. For each pixel i, the received signal is reflected by the target object:

[0026] Where S(t) is the received time domain signal, R is the receiving area, F(r) is the scattering coefficient of the target object, r0 is the position of the detector, |r-r0| is the path length of the signal propagation, δ(t-|r-r0| / c) is the delay function, and c is the speed of light; The signals at different time points are projected into space, and the spatial image of the target is gradually reconstructed. For each time point t, the distance from the point to the detector is calculated, and the information is projected back in space. Finally, all the projection results are accumulated to obtain the spatial image. The mathematical formula is as follows:

[0027] Where I(x,y) is the image intensity at the spatial position (x,y), S(t) is the signal collected at time t, p(t,x,y) is the weight function projected to the spatial position (x,y) at time t, describing the contribution of the time domain signal to the spatial pixel.

[0028] As a preferred solution of the THz full-band spatial imaging system based on the spatial resolution layer and the superconducting microwave dynamic inductance detector array imaging chip of the present invention, wherein: the terahertz wave is generated by the black body source with adjustable temperature, and the signal is transmitted to the MKID detector array in the sample box through the THz low-pass filter and the horn antenna, including: The generated terahertz radiation passes through a terahertz low-pass filter to filter out high-frequency components to ensure signal purity. The filtered terahertz signal is converted into a spatial mode and radiated directionally through a horn antenna to achieve efficient signal transmission.

[0029] As a preferred solution of the THz full-band spatial imaging system based on the spatial resolution layer and the superconducting microwave dynamic inductance detector array imaging chip of the present invention, wherein: under the low temperature condition, the MKID detector array absorbs the terahertz photons transmitted from the THz wave source, and the current change caused by the photon energy triggers the phase and amplitude change of the microwave signal, including: When the energy of the terahertz photon is absorbed and causes the current to change, the resonator of the MKID detector shifts in frequency. The inductance and interdigital capacitance of the MKID detector form a resonator, and its resonant frequency is given by the following formula:

[0030] Where f0 is the resonant frequency, L is the inductance, and C is the capacitance; After absorbing photons, the change in current causes the inductive reactance of the superconducting inductor to change, resulting in a shift in the resonant frequency. The relationship between the shift Δf and the current change ΔI is expressed by the following formula:

[0031] The change in frequency affects the phase and amplitude of the microwave signal passing through the MKID detector. Specifically, the phase and amplitude changes of the microwave signal are expressed by complex numbers:

[0032] Where V(t) is the voltage response of the microwave signal, A(t) is the signal amplitude, f is the signal frequency, and ϕ(t) is the signal phase; When the number of absorbed photons increases, the current change will cause the signal amplitude A(t) to change, and the current change will cause the resonant frequency to change, which in turn causes the signal phase φ(t) to change. As a preferred solution of the THz full-band spatial imaging system based on the spatial resolution layer and the superconducting microwave dynamic inductance detector array imaging chip of the present invention, the excitation signal is used to match the resonance frequency of the detector to induce the microwave signal change when the detector receives the terahertz photon, including: When terahertz photons are absorbed by the detector, they cause the excitation of carriers in the superconducting material, resulting in a change in its inductance; Since the frequency of the excitation signal matches the resonant frequency of the detector, the phase and amplitude of the microwave signal change accordingly. By monitoring the changes in the microwave signal, data about the terahertz photon information is obtained. Specifically, the impedance change of the detector is expressed by the following formula:

[0033] Where R is the resistance, ω is the angular frequency of the excitation signal, and L is the inductance; When a terahertz photon is absorbed, L changes, resulting in a change in Z, which in turn causes a change in the phase and amplitude of the microwave signal. The terahertz photon is detected through microwave measurement equipment for detection and analysis.

[0034] The beneficial effects of the present invention are as follows: the present invention can realize full-band detection of terahertz waves through the design of MKID detector array, greatly improving the sensitivity and accuracy of the detection system. By introducing a spatial resolution layer, spatial information is converted into a time domain signal, thereby realizing spatial imaging of terahertz waves and improving the spatial resolution of the system. By adopting a digital acquisition system and a fast signal processing algorithm, real-time acquisition and analysis of signals can be realized, further improving the real-time performance of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0036] Figure 1 A schematic structural diagram of a THz full-band spatial imaging system based on a spatial resolution layer and a superconducting microwave dynamic inductance detector array imaging chip provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0037] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0038] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0039] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0040] Example 1 Reference below Figure 1 , which is an embodiment of the present invention.

[0041] S1: MKID detector array module, used to achieve full-band detection of terahertz waves through multiple superconducting microwave resonator pixels, and to achieve spatial imaging based on time resolution by combining with the spatial resolution layer.

[0042] Preferably, the liquid crystal panel controls the light transmission state of each liquid crystal dot according to a preset rule through horizontal and vertical control lines, and each liquid crystal dot turns into a light transmission state in sequence, allowing the terahertz waves at different spatial positions to pass through the corresponding liquid crystal dot; When terahertz waves are emitted from an external source and pass through the spatial resolution layer, each liquid crystal dot gradually transmits signals from different spatial locations.

[0043] Furthermore, in the terahertz spatial imaging detector of the present invention, the spatial resolution layer is composed of a liquid crystal panel and a waveguide plate, which is responsible for converting spatial information into a time series signal, thereby achieving spatial resolution.

[0044] The liquid crystal panel is composed of horizontal and vertical control lines, forming an m×n matrix, with each intersection corresponding to a liquid crystal pixel. By controlling the light transmittance state of each liquid crystal pixel, the terahertz wave at a specific position can be selectively allowed to pass. The waveguide plate is located behind the liquid crystal panel and is used to guide the terahertz wave passing through the liquid crystal pixel to the MKID detector array. During operation, the liquid crystal panel controls the light transmittance state of each liquid crystal pixel in turn according to preset rules. When a liquid crystal pixel is set to the light transmittance state, the terahertz wave at the corresponding spatial position passes through the pixel and is transmitted by the waveguide plate to the MKID detector array for detection.

[0045] In this way, terahertz signals at different spatial locations are received by the detector at different time points, achieving time encoding of spatial information.

[0046] S2: Spatial resolution layer module, which is used to control the terahertz signals at different spatial positions to pass through the liquid crystal points at different times and be transmitted to the MKID detector array through the double-layer structure of the liquid crystal panel and the waveguide plate, thereby achieving spatial resolution.

[0047] Preferably, if the liquid crystal panel includes m×n liquid crystal pixels, the light transmittance state of each pixel is changed by controlling the voltage, the refresh period of the liquid crystal panel is δt, and the light transmittance state control formula is:

[0048] Wherein, P(t) represents the light transmittance state of the liquid crystal pixel, and t represents time; When a certain pixel of the liquid crystal panel is turned on, the terahertz signal will pass through the liquid crystal point and be transmitted to the MKID detector array by the waveguide plate. Assume that the transmission efficiency of the waveguide plate is η wg, which represents the efficiency of the waveguide plate in transmitting the terahertz signal transmitted through the liquid crystal panel to the MKID array. The signal transmission formula is:

[0049] Among them, S out (t) is the terahertz signal transmitted to the MKID detector array, S in (t) is the incident signal transmitted from the liquid crystal panel, η wg is the transmission efficiency of the waveguide plate, P(t) is the light transmittance state of the liquid crystal panel; When a liquid crystal pixel is turned on, the terahertz wave signal from that spatial position will be transmitted to the corresponding pixel in the MKID detector array. The refresh time of each liquid crystal point is δt. If the liquid crystal panel has m×n pixels, the refresh time of each pixel is δt, and the refresh cycle of the entire panel is:

[0050] The time required to scan a complete image is the refresh time of m×n pixels.

[0051] Further, the voltage signal source of the liquid crystal panel is configured, the refresh period δt of each liquid crystal pixel is set according to the required spatial resolution, and the transmission efficiency η of the waveguide plate is set wg , ensuring that it can effectively transmit the terahertz signal through the liquid crystal panel, the liquid crystal panel starts the refresh cycle, and each liquid crystal pixel switches its light transmittance state P(t) in turn according to the voltage signal. Each turned-on liquid crystal pixel allows the terahertz wave from that spatial position to pass through and is transmitted to the MKID array through the waveguide plate; after the terahertz signal passes through the liquid crystal panel, it is transmitted by the waveguide plate to the corresponding pixel in the MKID detector array. The amplitude and phase changes of the microwave signal in the MKID array detection signal reflect the terahertz signal at the corresponding spatial position of each liquid crystal pixel.

[0052] S3: Microwave signal coupling and amplification module, which is used to transmit the detected microwave signal to the low-temperature superconducting amplifier through the feeder, and then after further processing by the room-temperature amplifier, it is sent to the mixer for I / Q signal demodulation, and finally time domain analysis is performed through the digital acquisition system.

[0053] Preferably, the I and Q signals are digitized through an analog-to-digital converter, and the ADC converts the analog signal into a digital signal so that the signal is processed and analyzed in subsequent digital signal processing. The digitized I / Q signal enters the digital signal processing system, and the I / Q signal is subjected to Fourier transform analysis to obtain spectrum information.

[0054] Furthermore, the digitized I / Q signal is subjected to a fast Fourier transform to convert the time domain signal into the frequency domain to obtain its spectrum information, which is defined as:

[0055] Where N is the number of FFT points, k is the frequency index, and X[k] is the frequency domain signal. Through FFT, the amplitude and phase information of the signal at each frequency component are obtained; By analyzing the amplitude of the FFT result, the power spectrum density of the signal is obtained, which reflects the power distribution of the signal at each frequency. The calculation formula of PSD is:

[0056] Among them, |X[k]| represents the amplitude of X[k]. By analyzing the PSD, the main frequency components, bandwidth and power distribution characteristics of the signal can be identified.

[0057] Furthermore, the digitized I / Q signal is subjected to Fourier transform to obtain the spectrum information of the signal. The basic formula of Fourier transform is as follows:

[0058] Among them, x(t) is the time domain signal, X(f) is the frequency domain signal, f is the frequency, and t is the time; For discrete digital I / Q signals, discrete Fourier transform (DFT) is used, and its formula is:

[0059] Where N is the number of sampling points of the signal, k is the frequency index, and x[n] is the nth sample of the signal in the time domain; After Fourier transform, the obtained spectrum data represents the distribution of the signal in the frequency domain. Through visualization tools, the spectrum graph can be plotted to view the frequency characteristics of the signal.

[0060] Through spectrum analysis, we can extract the main frequency components, bandwidth, center frequency, frequency offset and other information of the signal. We can detect the peak value of the spectrum graph, find the specific frequency points of the signal, and further analyze the nature of the signal. We can extract the center frequency of the signal from the spectrum and identify whether the signal has frequency offset.

[0061] S4: Signal mixing and acquisition module, used to mix the signal with the reference signal in the mixer to obtain I and Q voltage outputs as the amplitude and phase information of the signal. The mixed signal is processed by low-pass filtering and digitally acquired through the A / D card.

[0062] Preferably, in the mixer, the input signal S(t) and the reference signal LO(t) are multiplied to obtain a mixing output:

[0063] Substituting into the signal expression:

[0064] Expand the above equation using trigonometric identities:

[0065] Difference frequency component (f IF =|f S -f LO ∣ is the required intermediate frequency signal, which contains the amplitude and phase information of the signal; the sum frequency component (f sum =f S +f LO ) are filtered out.

[0066] S5: Image reconstruction and processing module, used to reconstruct the information at different times into terahertz spatial imaging images through the time domain signal processing algorithm.

[0067] Preferably, if the received time domain signal is S(t), where t is a time variable, S(t) is a received signal whose amplitude and phase vary with time, for each pixel i, the received signal is reflected by the target object:

[0068] Where S(t) is the received time domain signal, R is the receiving area, F(r) is the scattering coefficient of the target object, r0 is the position of the detector, |r-r0| is the path length of the signal propagation, δ(t-|r-r0| / c) is the delay function, and c is the speed of light; The signals at different time points are projected into space, and the spatial image of the target is gradually reconstructed. For each time point t, the distance from the point to the detector is calculated, and the information is projected back in space. Finally, all the projection results are accumulated to obtain the spatial image. The mathematical formula is as follows:

[0069] Where I(x,y) is the image intensity at the spatial position (x,y), S(t) is the signal collected at time t, p(t,x,y) is the weight function projected to the spatial position (x,y) at time t, describing the contribution of the time domain signal to the spatial pixel.

[0070] Furthermore, assuming that the target object is a planar reflective surface, its scattering coefficient F(r) is uniform in space. In this case, the received signal depends only on the distance r between the target object and the detector, and the change in signal strength at different positions is only related to the propagation path length and delay time.

[0071] The signal S(t) represents the signal reflected from the target object. The propagation path length |r-r0| affects the propagation time delay of the signal. The weight function p(t,x,y) describes the relationship between the time delay and the spatial coordinates (x,y). Through the above steps, combined with the signals at each time point, the spatial position and reflection intensity of the target object can be reconstructed.

[0072] S6: THz wave source and calibration module, used to generate THz waves through a temperature-adjustable blackbody source, and transmit the signal to the MKID detector array in the sample box through a THz low-pass filter and a horn antenna.

[0073] Preferably, the generated terahertz radiation passes through a terahertz low-pass filter to filter out high-frequency components to ensure signal purity, and the filtered terahertz signal is converted into a spatial mode and radiated directionally through a horn antenna to achieve efficient signal transmission.

[0074] Furthermore, a temperature-adjustable blackbody source is used as a terahertz radiation generating device. By adjusting the temperature of the blackbody source, terahertz radiation of the required frequency band is generated. The generated terahertz radiation is introduced into a terahertz low-pass filter. The filter is used to filter out high-frequency components to ensure the purity of the signal. A filter with a suitable cutoff frequency is selected to meet specific application requirements. The filtered terahertz signal is converted into a spatial mode and radiated in a direction through a horn antenna. The horn antenna can focus and transmit the terahertz signal in a direction, thereby improving the efficiency and quality of signal transmission. The terahertz signal passing through the horn antenna is transmitted to the MKID (microwave energy detector) detector array in the sample box. The MKID detector array works under low temperature conditions and can detect the terahertz signal transmitted thereto with high sensitivity. The detector array converts the received terahertz signal into an electrical signal and digitizes it through an analog-to-digital converter (ADC). The digitized signal is reconstructed into a terahertz spatial imaging image by a time domain signal processing algorithm to convert information at different times.

[0075] S7: Low-temperature superconducting module, used under low-temperature conditions, the MKID detector array absorbs terahertz photons transmitted from the THz wave source, and the current changes caused by the photon energy trigger phase and amplitude changes of the microwave signal.

[0076] Preferably, when the energy of the terahertz photon is absorbed and causes a current change, the resonator of the MKID detector shifts in frequency, and the inductance and interdigital capacitance of the MKID detector form a resonator, whose resonant frequency is given by the following formula:

[0077] Where f0 is the resonant frequency, L is the inductance, and C is the capacitance; After absorbing photons, the change in current causes the inductive reactance of the superconducting inductor to change, resulting in a shift in the resonant frequency. The relationship between the shift Δf and the current change ΔI is expressed by the following formula:

[0078] The change in frequency affects the phase and amplitude of the microwave signal passing through the MKID detector. Specifically, the phase and amplitude changes of the microwave signal are expressed by complex numbers:

[0079] Where V(t) is the voltage response of the microwave signal, A(t) is the signal amplitude, f is the signal frequency, and ϕ(t) is the signal phase; When the number of absorbed photons increases, the current change will cause the signal amplitude A(t) to change, and the current change will cause the resonant frequency to change, which in turn causes the signal phase φ(t) to change. Furthermore, when the MKID detector array receives photons from a terahertz source, each detector pixel absorbs terahertz photons of a certain energy. Photon absorption causes the current in the superconducting inductor to change, and the change in current produces a corresponding change in inductive reactance through the detector inductor. The change in current causes the frequency f0 of the resonator to shift, and the frequency change is Δf, which is proportional to the current change ΔI. Due to the change in resonant frequency, the amplitude and phase of the microwave signal change over time. The amplitude and phase changes of the signal can be calculated by the above formula. The collected signal is digitized by an analog-to-digital converter (ADC), and the changes in the signal amplitude and phase are analyzed by a time domain signal processing algorithm to obtain detailed information of the signal.

[0080] S8: Microwave signal source and excitation module, used to generate microwave signals and transmit them to the MKID detector array through feeders. The excitation signal is used to match the resonant frequency of the detector and trigger microwave signal changes when the detector receives terahertz photons.

[0081] Preferably, when terahertz photons are absorbed by the detector, they cause excitation of carriers in the superconducting material, causing its inductance to change; Since the frequency of the excitation signal matches the resonant frequency of the detector, the phase and amplitude of the microwave signal change accordingly. By monitoring the changes in the microwave signal, data about the terahertz photon information is obtained. Specifically, the impedance change of the detector is expressed by the following formula:

[0082] Where R is the resistance, ω is the angular frequency of the excitation signal, and L is the inductance; When terahertz photons are absorbed, L changes, resulting in a change in Z, which in turn causes changes in the phase and amplitude of the microwave signal. The terahertz photons are detected and analyzed through microwave measurement equipment to achieve detection.

[0083] Furthermore, the terahertz radiation emitted by a temperature-adjustable blackbody source or other terahertz photon source enters the experimental area. The terahertz wave is filtered out by a low-pass filter to remove high-frequency components to ensure the purity of the signal.

[0084] The filtered terahertz signal undergoes spatial mode conversion through a horn antenna and is radiated toward the object to be measured.

[0085] The terahertz photons reflected by the object to be measured are transmitted through space to the detector array. The inductance of each detector changes due to photon absorption, resulting in a change in impedance. The signal is mixed with the reference signal through a mixer to generate an I / Q signal; the signal is converted into a digital signal through an ADC and transmitted to the digital signal processing unit for Fourier transform analysis. The spatial image of the target object is reconstructed through time domain signal processing and spatial projection, and the terahertz reflection characteristics of the target are finally presented through a display device.

[0086] In the description of the present invention, it should be noted that the terms “first”, “second” and “third” are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0087] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0088] In the several embodiments provided by the present invention, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. The device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some communication interfaces, and the indirect coupling or communication connection of devices or units can be electrical, mechanical or other forms.

[0089] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0090] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

[0091] Finally, it should be noted that the above-described embodiments are only specific implementations of the present invention, which are used to illustrate the technical solutions of the present invention, rather than to limit them. The protection scope of the present invention is not limited thereto. Although the present invention is described in detail with reference to the above-described embodiments, ordinary technicians in the field should understand that any technician familiar with the technical field can still modify the technical solutions recorded in the above-described embodiments within the technical scope disclosed by the present invention, or can easily think of changes, or make equivalent replacements for some of the technical features therein; and these modifications, changes or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

[0092] In addition, although the operations of the method of the present invention are described in a specific order in the drawings, this does not require or imply that the operations must be performed in this specific order, or that all the operations shown must be performed to achieve the desired results. Additionally or alternatively, some steps may be omitted, multiple steps may be combined into one step, and / or one step may be decomposed into multiple steps.

Claims

1. A THz full-band spatial imaging system based on a spatial resolution layer and a superconducting microwave dynamic inductance detector array imaging chip, characterized in that: include: MKID detector array module, which is used to realize full-band detection of terahertz waves through multiple superconducting microwave resonator pixels, and realize spatial imaging based on time resolution by combining with the spatial resolution layer; The spatial resolution layer module is used to control the terahertz signals at different spatial positions to pass through the liquid crystal points at different times and be transmitted to the MKID detector array through the double-layer structure of the liquid crystal panel and the waveguide plate, thereby achieving spatial resolution; The microwave signal coupling and amplification module is used to transmit the detected microwave signal to the low-temperature superconducting amplifier through the feeder, and then after further processing by the room-temperature amplifier, it is sent to the mixer for I / Q signal demodulation, and finally the digital acquisition system is used for time domain analysis; The signal mixing and acquisition module is used to mix the signal with the reference signal in the mixer to obtain I and Q voltage outputs as the amplitude and phase information of the signal. The mixed signal is processed by low-pass filtering and digitally acquired through the A / D card; The image reconstruction and processing module is used to reconstruct the information at different times into a terahertz spatial imaging image through a time domain signal processing algorithm. A THz wave source and calibration module, which is used to generate THz waves through a temperature-adjustable blackbody source and transmit the signals to the MKID detector array in the sample box through a THz low-pass filter and a horn antenna; Low-temperature superconducting module, used for MKID detector array to absorb terahertz photons transmitted from THz wave source under low-temperature conditions. The current change caused by the photon energy triggers the phase and amplitude change of microwave signal. The microwave signal source and excitation module are used to generate microwave signals and transmit them to the MKID detector array through the feeder. The excitation signal is used to match the resonant frequency of the detector and trigger the microwave signal change when the detector receives terahertz photons.

2. The THz full-band spatial imaging system based on the spatial resolution layer and the superconducting microwave dynamic inductance detector array imaging chip according to claim 1, characterized in that: The method realizes full-band detection of terahertz waves by using multiple superconducting microwave resonator pixels, and realizes spatial imaging based on time resolution by combining with the spatial resolution layer, including: The liquid crystal panel controls the light transmission state of each liquid crystal point according to preset rules through horizontal and vertical control lines. Each liquid crystal point turns to the light transmission state in sequence, allowing the terahertz waves at different spatial positions to pass through the corresponding liquid crystal point. When terahertz waves are emitted from an external source and pass through the spatial resolution layer, each liquid crystal dot gradually transmits signals from different spatial locations.

3. The THz full-band spatial imaging system based on the spatial resolution layer and the superconducting microwave dynamic inductance detector array imaging chip according to claim 1, characterized in that: The double-layer structure of the liquid crystal panel and the waveguide plate is used to control the terahertz signals at different spatial positions to pass through the liquid crystal points at different times and be transmitted to the MKID detector array to achieve spatial resolution, including: If the liquid crystal panel contains m×n liquid crystal pixels, the light transmittance state of each pixel is changed by controlling the voltage, the refresh period of the liquid crystal panel is δt, and the light transmittance state control formula is: Wherein, P(t) represents the light transmittance state of the liquid crystal pixel, and t represents time; When a certain pixel of the liquid crystal panel is turned on, the terahertz signal will pass through the liquid crystal point and be transmitted to the MKID detector array by the waveguide plate. Assume that the transmission efficiency of the waveguide plate is η wg , which represents the efficiency of the waveguide plate in transmitting the terahertz signal transmitted through the liquid crystal panel to the MKID array. The signal transmission formula is: Among them, S out (t) is the terahertz signal transmitted to the MKID detector array, S in (t) is the incident signal transmitted through the liquid crystal panel, η wg is the transmission efficiency of the waveguide plate, P(t) is the light transmittance state of the liquid crystal panel; When a liquid crystal pixel is turned on, the terahertz wave signal from that spatial position will be transmitted to the corresponding pixel in the MKID detector array. The refresh time of each liquid crystal point is δt. If the liquid crystal panel has m×n pixels, the refresh time of each pixel is δt, and the refresh cycle of the entire panel is: The time required to scan a complete image is the refresh time of m×n pixels.

4. The THz full-band spatial imaging system based on the spatial resolution layer and the superconducting microwave dynamic inductance detector array imaging chip according to claim 1, characterized in that: The signal is sent to the mixer for I / Q signal demodulation and finally analyzed in the time domain by the digital acquisition system, including: The I and Q signals are digitized through an analog-to-digital converter. The ADC converts the analog signal into a digital signal so that the signal can be processed and analyzed in subsequent digital signal processing. The digitized I / Q signal enters the digital signal processing system, and Fourier transform analysis is performed on the I / Q signal to obtain spectrum information.

5. The THz full-band spatial imaging system based on the spatial resolution layer and the superconducting microwave dynamic inductance detector array imaging chip according to claim 4, characterized in that: The digitized I / Q signal enters the digital signal processing system, and Fourier transform analysis is performed on the I / Q signal to obtain spectrum information, including: Perform fast Fourier transform on the digitized I / Q signal to convert the time domain signal to the frequency domain and obtain its spectrum information, which is defined as: Where N is the number of FFT points, k is the frequency index, and X[k] is the frequency domain signal. Through FFT, the amplitude and phase information of the signal at each frequency component are obtained; By analyzing the amplitude of the FFT result, the power spectrum density of the signal is obtained, which reflects the power distribution of the signal at each frequency. The calculation formula of PSD is: Among them, |X[k]| represents the amplitude of X[k]. By analyzing the PSD, the main frequency components, bandwidth and power distribution characteristics of the signal can be identified.

6. The THz full-band spatial imaging system based on the spatial resolution layer and the superconducting microwave dynamic inductance detector array imaging chip according to claim 1, characterized in that: The signal is mixed with a reference signal in a mixer to obtain I and Q voltage outputs as amplitude and phase information of the signal, including: In the mixer, the input signal S(t) and the reference signal LO(t) are multiplied to obtain the mixed output: Substituting into the signal expression: Expand the above equation using trigonometric identities: Difference frequency component (f IF =|f S -f LO ∣ is the required intermediate frequency signal, which contains the amplitude and phase information of the signal; the sum frequency component (f sum =f S +f LO ) are filtered out.

7. The THz full-band spatial imaging system based on the spatial resolution layer and the superconducting microwave dynamic inductance detector array imaging chip according to claim 1, characterized in that: The collected time-domain microwave signals are processed by a time-domain signal processing algorithm to reconstruct information at different times into a terahertz spatial imaging image, including: If the received time domain signal is S(t), where t is the time variable, S(t) is the received signal whose amplitude and phase vary with time. For each pixel i, the received signal is reflected by the target object: Where S(t) is the received time domain signal, R is the receiving area, F(r) is the scattering coefficient of the target object, r0 is the position of the detector, |r-r0| is the path length of the signal propagation, δ(t-|r-r0| / c) is the delay function, and c is the speed of light; The signals at different time points are projected into space, and the spatial image of the target is gradually reconstructed. For each time point t, the distance from the point to the detector is calculated, and the information is projected back in space. Finally, all the projection results are accumulated to obtain the spatial image. The mathematical formula is as follows: Where I(x,y) is the image intensity at the spatial position (x,y), S(t) is the signal collected at time t, p(t,x,y) is the weight function projected to the spatial position (x,y) at time t, describing the contribution of the time domain signal to the spatial pixel.

8. The THz full-band spatial imaging system based on the spatial resolution layer and the superconducting microwave dynamic inductance detector array imaging chip according to claim 1, characterized in that: The method generates terahertz waves through a temperature-adjustable blackbody source, and transmits the signals to a MKID detector array in a sample box through a THz low-pass filter and a horn antenna, including: The generated terahertz radiation passes through a terahertz low-pass filter to filter out high-frequency components to ensure signal purity. The filtered terahertz signal is converted into a spatial mode and radiated directionally through a horn antenna to achieve efficient signal transmission.

9. The THz full-band spatial imaging system based on the spatial resolution layer and the superconducting microwave dynamic inductance detector array imaging chip according to claim 1, characterized in that: Under low temperature conditions, the MKID detector array absorbs terahertz photons transmitted from the THz wave source, and the current change caused by the photon energy triggers the phase and amplitude changes of the microwave signal, including: When the energy of the terahertz photon is absorbed and causes the current to change, the resonator of the MKID detector shifts in frequency. The inductance and interdigital capacitance of the MKID detector form a resonator, and its resonant frequency is given by the following formula: Where f0 is the resonant frequency, L is the inductance, and C is the capacitance; After absorbing photons, the change in current causes the inductive reactance of the superconducting inductor to change, resulting in a shift in the resonant frequency. The relationship between the shift Δf and the current change ΔI is expressed by the following formula: The change in frequency affects the phase and amplitude of the microwave signal passing through the MKID detector. Specifically, the phase and amplitude changes of the microwave signal are expressed by complex numbers: Where V(t) is the voltage response of the microwave signal, A(t) is the signal amplitude, f is the signal frequency, and ϕ(t) is the signal phase; When the number of absorbed photons increases, the current change will cause the signal amplitude A(t) to change, and the current change will cause the resonant frequency to change, which in turn causes the signal phase φ(t) to change.

10. The THz full-band spatial imaging system based on the spatial resolution layer and the superconducting microwave dynamic inductance detector array imaging chip according to claim 1, characterized in that: The excitation signal is used to match the resonance frequency of the detector, causing the detector to change the microwave signal when receiving the terahertz photon, including: When terahertz photons are absorbed by the detector, they cause the excitation of carriers in the superconducting material, resulting in a change in its inductance; Since the frequency of the excitation signal matches the resonant frequency of the detector, the phase and amplitude of the microwave signal change accordingly. By monitoring the changes in the microwave signal, data about the terahertz photon information is obtained. Specifically, the impedance change of the detector is expressed by the following formula: Where R is the resistance, ω is the angular frequency of the excitation signal, and L is the inductance; When a terahertz photon is absorbed, L changes, resulting in a change in Z, which in turn causes a change in the phase and amplitude of the microwave signal. The terahertz photon is detected through microwave measurement equipment for detection and analysis.

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