Polarization detection system based on semiconductor plasmon millimeter wave detector and application

Abstract

The invention belongs to the technical field of photoelectric detection, and particularly relates to a polarization detection system based on a semiconductor plasmon millimeter wave detector and application. A semiconductor plasmon millimeter wave detector is used in a free space polarization detection system to replace a traditional Horn antenna, the bottleneck problems of blind response, low sensitivity and difficulty in integration of a traditional millimeter wave polarization detection technology are solved, the angular differential resolution of a weak signal area can be improved by 60 times, and the resolution ratio of the antenna is improved by 60 times. And the requirements of industrial scenes on in-situ lossless high-precision characterization of anisotropic materials are met. The system is mainly applied to industrial scenes such as electronic packaging performance evaluation, advanced manufacturing quality control, aerospace structure material detection and the like, provides a high-precision and miniaturization solution for polarization characteristic detection of millimeter wave frequency band materials, is adaptive to a production line online detection module, and has industrial mass production potential and important industrial application value.

Description

Technical Field

[0001] This invention belongs to the field of photoelectric detection technology, specifically, it relates to a polarization detection system and its application based on a semiconductor plasmon millimeter-wave detector. Background Technology

[0002] Millimeter-wave polarization detection is a core technology for industrial information sensing systems, such as dielectric parameter characterization and anisotropic material diagnosis. Its core requirement is to simultaneously achieve "wide frequency coverage, full-angle resolution, and high sensitivity" and "miniaturized integration" in free-space scenarios. However, existing technological approaches have significant bottlenecks. First, traditional millimeter-wave receiving technologies, such as waveguides, parallel-plate capacitors, and resonant cavities, rely on confined spaces or planar sample shapes, and are only suitable for low-frequency bands (<20GHz) and miniaturized, regular samples. They cannot meet the detection needs of large-scale, irregular industrial components (such as aero-engine blades and large electronic packaging substrates). Secondly, although the free-space detection method based on traditional Horn antennas has broken through the limitations of space and sample shape and can cover a wide frequency range (30-110GHz), it has key performance defects: in the weak signal range, due to insufficient electromagnetic coupling efficiency, a "blind response platform" with no signal change will appear, making it impossible to achieve continuous detection at all angles; at the 95° characteristic angle, the angle differential sensitivity (d / dθ) is extremely low, making it difficult to distinguish the subtle orientation differences of anisotropic materials; and the macroscopic antenna structure is bulky and cannot be adapted to miniaturized, integrated industrial systems (such as online detection modules for production lines).

[0003] In summary, planar semiconductor sensors (such as semiconductor plasmon detectors) have become a key direction for overcoming bottlenecks due to their compact size and potential for large-scale monolithic integration. However, existing technologies only focus on optimizing the performance of individual detector units (such as metasurface-enhanced plasmon field strength), and have not formed a system-level integrated solution for "polarization detection." Furthermore, they lack quantitative comparative verification with traditional horn antennas, failing to meet the dual requirements of "high precision + integration" in industrial scenarios. Therefore, it is urgent to construct a polarization detection system based on semiconductor plasmon millimeter-wave detectors to solve the problems of "blind response and difficulty in integration" in traditional technologies, and to achieve in-situ, non-destructive, high-precision characterization of anisotropic materials. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a polarization detection system and its application based on a semiconductor plasmon millimeter-wave detector. This invention constructs a free-space polarization detection system by integrating a millimeter-wave transmitter, a receiving unit, and a signal processing unit. In this system, a semiconductor plasmon millimeter-wave detector replaces the traditional Horn antenna as the receiving unit. The detector's antenna structure and metasurface micro / nano structures enhance the electromagnetic coupling efficiency and polarization dependence of the semiconductor surface plasmons, overcoming the blind response and sensitivity bottlenecks of traditional Horn antennas. Simultaneously, it maintains the integrated advantages of a planar structure, ensuring that the system meets high-precision detection requirements while being adaptable to miniaturized industrial applications. The system of this invention can be applied to in-situ non-destructive characterization of anisotropic materials.

[0005] The objective of this invention can be achieved through the following technical solutions.

[0006] A polarization detection system based on a semiconductor plasmonic millimeter-wave detector includes a millimeter-wave transmitter, a receiving unit, and a signal processing unit; wherein,

[0007] Millimeter-wave transmitters used to provide stable millimeter waves with transverse magnetic polarization;

[0008] The receiving unit, which is a semiconductor plasmonic millimeter-wave detector, is used to enhance the electromagnetic coupling efficiency of semiconductor surface plasmon polaritons (SPPs) by utilizing metasurface micro / nano structures and ohmic contact metal-semiconductor-metal structures (OMSMs).

[0009] The signal processing unit includes an amplifier circuit and a data acquisition module, which is used to amplify the photocurrent signal and quantize its sensitivity.

[0010] During operation, the anisotropic material is placed between the millimeter-wave transmitter and the receiver unit to detect the polarization characteristics of the material in the millimeter-wave band, thereby achieving in-situ non-destructive characterization of the anisotropic material.

[0011] In this invention, the millimeter-wave transmitter is a solid-state source with an output power of 10-20 dBm, and its operating frequency band covers the Ka and W bands. The polarization mode of the transmitted millimeter waves is set to transverse magnetic TM polarization to match the antenna gain and metasurface field strength enhancement design of the receiving unit.

[0012] In this invention, the receiving unit comprises, from bottom to top, a substrate layer, a semiconductor plasmon layer, a metasurface layer, and an ohmic contact metal-semiconductor-metal OMSM structure; wherein, the substrate layer is made of GaAs material; the semiconductor plasmon layer is an indium antimonide (InSb) thin film with a negative real part of its dielectric constant in the detection band and a room temperature electron mobility ≥2.97 × 10⁻⁶. 4 cm 2 ・V -1 ・s-1 The metasurface layer is located on the surface of the plasmonic layer on the semiconductor surface and has a vertical slot array structure. Its slots are orthogonal to the transverse magnetic TM polarization. The ohmic contact metal-semiconductor-metal OMSM structure includes Ti electrodes and Au electrodes. The semiconductor plasmonic layer is exposed between the electrodes, and an antenna layer is provided on the electrodes.

[0013] In this invention, the substrate layer thickness is 0.5-1.5 mm, the semiconductor plasmon layer thickness is 0.5-10 μm, the vertical slot period is 500 nm-2 μm, the slot width is 1 / 3-1 / 2 of the vertical slot period, and the depth is 200 nm-1 μm; the length of the exposed semiconductor plasmon layer between the electrodes is 20-150 μm, satisfying the subwavelength constraint; the antenna layer length is 1.36-2 mm or 3.75-5.66 mm, matching the half wavelength of Ka-band millimeter waves.

[0014] In this invention, the receiving unit is prepared by the following method:

[0015] (i) Preparation of the substrate layer: GaAs material is selected;

[0016] (ii) Growth of semiconductor plasmonic layer: InSb thin film is epitaxially grown on GaAs substrate using metal-organic chemical vapor deposition (MOCVD) process;

[0017] (iii) Fabrication of metasurface layer: A vertical trench array is formed on the surface of InSb thin film by ultraviolet lithography and etching process, while ensuring that the trench channels are orthogonal to the TM polarization;

[0018] (iv) Fabrication of OMSM structure and antenna: Ti electrodes and Au gold electrodes are deposited at both ends of the InSb thin film using electron beam evaporation or vacuum thermal evaporation to form ohmic contact electrodes, exposing the InSb layer between the electrodes; at the same time, an antenna layer matching half wavelength of the millimeter wave band is fabricated and integrated with the electrodes to complete the fabrication of semiconductor plasmon millimeter wave detector.

[0019] In this invention, the signal processing unit uses a low-noise preamplifier and a lock-in amplifier to amplify the photocurrent signal and suppress dark current noise. The data acquisition module acquires the lock-in amplifier voltage signal to the computer via a GPIB card, generates a polarization response curve through data normalization processing by the data software, and obtains the angular differential sensitivity d / dθ by differentiating the curve, thus quantifying the polarization detection accuracy.

[0020] The present invention also provides an application of the above-mentioned polarization detection system based on a semiconductor plasmonic millimeter-wave detector in polarization detection, the application method of which is as follows:

[0021] (a) A millimeter-wave transmitter outputs a target frequency band millimeter wave with TM polarization, which is incident on the anisotropic material to be tested;

[0022] (b) Modulated millimeter waves are incident on the receiving unit, and non-equilibrium electrons are induced after the plasmons SPP relax;

[0023] (c) The signal processing unit applies a bias current to drive the non-equilibrium electrons to flow in a directional manner to generate photocurrent. The amplified signal is recorded by the data acquisition module to generate a normalized polarization response curve and calculate the angle differential sensitivity d / dθ to complete polarization detection.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] This invention achieves a performance breakthrough through the structural design of the receiving unit: it employs a metasurface vertical slot array and TM polarization orthogonally enhances the SPP excitation intensity, improving the non-equilibrium electron generation efficiency. This system outperforms traditional Horn antennas in terms of full-angle resolution, angular differential sensitivity, integration, and detection method. Specifically, in terms of full-angle resolution, this system exhibits no blind response and continuous response in weak signal regions (such as the metal mesh orientation in this embodiment, i.e., the angle between the millimeter-wave polarization angle modulated by anisotropic materials and the ideal detection angle of the detector is 75-105°), avoiding missed detections and adapting to full-angle material characterization. In contrast, traditional Horn antennas... A blind response plateau appears in the weak signal region; in terms of angular differential sensitivity, the d / dθ of this system is 0.00485 at 95°, which is 60 times higher than the sensitivity of the traditional Horn antenna, and can accurately distinguish subtle orientation differences; in terms of integration, this system adopts a planar structure with a size ≤10mm×10mm, which facilitates the on-chip integration of the signal receiving unit and the processing unit, while the traditional Horn antenna has a macroscopic volume (≥50mm×50mm) and is difficult to integrate; in terms of detection method, both are free space non-contact, but this system can achieve in-situ non-destructive testing without disassembling the sample, making it more suitable for online testing on the production line.

[0026] The system of this invention adopts a free-space non-contact detection method, which can realize in-situ non-destructive characterization of anisotropic materials. Specific application scenarios include electronic packaging performance evaluation (such as large electronic packaging substrate inspection), advanced manufacturing quality control, aerospace structural material inspection (such as aero-engine blade inspection), and it is compatible with online inspection modules for production lines, providing technical support for diversified industrial information sensing systems. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of a polarization detection system (the receiving unit is a semiconductor surface plasmon millimeter-wave detector).

[0028] Figure 2 This is a schematic diagram of a semiconductor surface plasmon millimeter-wave detector.

[0029] Figure 3This is a schematic diagram of a polarization detection system (the receiving unit is a Horn antenna).

[0030] Figure 4 The diagram illustrates the normalized polarization response of a system based on a Horn antenna and a semiconductor surface plasmon millimeter-wave detector.

[0031] Figure 5 The angle differential sensitivity d / dθ is given near 95° in the weak signal region.

[0032] In the diagram, the numbers represent: 1 for the substrate layer, 2 for the semiconductor plasmon layer and metasurface layer, 3 for the left metal electrode and antenna layer, and 4 for the right metal electrode and antenna layer. Detailed Implementation

[0033] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0034] like Figure 1 As shown, the millimeter-wave polarization detection system in this invention adopts a modular architecture of "transmitter-polarization modulation-receiver-signal processing". The millimeter-wave transmitter uses a commercially available solid-state source, operating in the 26.5-40 GHz (Ka band) and 75-110 GHz (W band) frequency bands, with an output power of 10-20 dBm, providing stable millimeter waves in the target frequency band. The transmitted millimeter-wave polarization mode is set to transverse magnetic (TM) polarization to match the detector antenna gain and metasurface field enhancement design. The polarization modulation unit uses a wire mesh to simulate anisotropic materials, with a linewidth of 2.5 mm, an air gap of 1 mm, and an effective diameter of 15 cm. It can rotate 360° (in 5° increments), changing the millimeter-wave polarization state by rotation to simulate the orientation changes of anisotropic materials in industrial scenarios. The receiving unit is a semiconductor plasmon millimeter-wave detector.

[0035] like Figure 2 As shown, the semiconductor plasmon millimeter-wave detector structure, from top to bottom, consists of a substrate layer 1, a semiconductor plasmon layer and a metasurface layer 2, and an ohmic contact metal-semiconductor-metal structure (OMSM). The substrate layer is made of GaAs material with high insulation and low dielectric loss, with a thickness of 0.5-1.5 mm. The semiconductor plasmon layer 2 is a 0.5-10 μm indium antimonide (InSb) thin film epitaxially grown on the substrate layer using metal-organic chemical vapor deposition (MOCVD) technology, meeting the requirements of high room temperature electron mobility (≥2.97 × 10⁻⁶). 4 cm 2 ・V -1 ・s -1 And the effective mass of small electrons. Its dielectric response conforms to the Drude model. , The relative permittivity at infinite frequency, The vacuum permittivity, Where γ is the plasma frequency of the material, and γ is the damping coefficient. ,in For the effective mass of electrons, To ensure electron mobility, the real part of the dielectric constant is negative within the target frequency band to excite surface plasmons (SPPs) on the semiconductor. The metasurface layer is a vertical trench array. In a specific embodiment, the period is 500 nm, the trench width is 170 nm, and the depth is 400 nm. The trench channels are orthogonal to the transverse magnetic TM polarization, which can enhance the SPP excitation intensity and promote the generation of non-equilibrium electrons induced by SPP. The OMSM structure refers to the metal electrodes and antennas integrated at both ends of the semiconductor plasmon layer. The two sides of the OMSM include a left metal electrode and antenna layer 3 and a right metal electrode and antenna layer 4, respectively. In a specific embodiment, it consists of a 20 nm thick Ti electrode and a 300 nm thick Au electrode. The length of the semiconductor plasmon layer exposed between the electrodes is 30 μm. The antenna length matches half the wavelength of the Ka band (4.7 mm), which can enhance the polarization-modulated millimeter-wave coupling effect. The signal processing unit includes an SR570 low-noise preamplifier circuit (bias current 0.1-15mA) and a data acquisition module (sampling rate 1kHz), which can amplify the photocurrent signal, normalize it to obtain the polarization response curve, and calculate the angle differential sensitivity d / dθ.

[0036] The aforementioned millimeter-wave polarization detection system achieves high-precision detection through a process of "polarization modulation-enhanced reception-signal analysis". First, the millimeter-wave transmitter outputs TM-polarized millimeter waves (e.g., 31.2 GHz), which penetrate the metal wire mesh of the polarization modulation unit. By rotating the mesh (0°-360°), the polarization state of the millimeter wave is changed, simulating the modulation characteristics of anisotropic materials on polarization. Then, the modulated millimeter wave is incident on the receiving unit (semiconductor surface plasmon polariton millimeter-wave detector). The vertical slot array of the OMSM structure and metasurface layer focuses the millimeter-wave energy onto the surface of the InSb layer. The enhanced local electric field excites surface plasmons (SPPs) in the InSb layer. After relaxation, the SPPs induce non-equilibrium electrons. Finally, the signal processing unit applies a bias current to drive the directional flow of non-equilibrium electrons to generate photocurrent and suppress dark current noise. The amplified signal is recorded by the data acquisition module to generate a normalized polarization response curve. The derivative of the curve is obtained by taking the angle differential d / dθ, which quantifies the polarization detection sensitivity.

[0037] The following are specific examples.

[0038] Example 1

[0039] This embodiment conducts a comparative experiment on polarization detection between a semiconductor plasmonic detector and a traditional Horn antenna: the transmitter uses a commercially available solid-state source with a fixed output of 31.2 GHz millimeter wave (Ka band), TM polarization, and a power of 15 dBm; the polarization modulation unit is a metal wire mesh (2.5 mm linewidth, 1 mm air gap, 15 cm diameter), which can rotate 360° (in increments of 5°); Figure 1 As shown, the receiving unit is a semiconductor plasmonic detector (GaAs substrate 1.0mm, InSb layer 730μm, metasurface vertical trench array period 500nm, OMSM electrode spacing 30μm, connected to SR570 preamplifier, bias current 5mA). Figure 3 As shown, the reference receiving unit is a commercial Horn antenna (operating frequency band 30-40GHz, output connected to the same model SR570 preamplifier); the signal processing stage records the signal through a data acquisition module (NI cDAQ-9178), with a sampling rate of 1kHz, and each angle is tested 3 times and the average value is taken.

[0040] Experimental steps:

[0041] First, system calibration was performed. The wire mesh was fixed at θ0=0°, and the reference signal was recorded using two receiving units when there was no mesh, ensuring that the transmitter power was stable (fluctuation ≤0.1dBm). Next, a full-angle polarization response test was conducted. Keeping the transmitter power constant, the wire mesh was rotated from 0° to 360°, and the signal was recorded every 5°, obtaining two sets of normalized polarization response curves. The results are as follows: Figure 4 As shown; then, signal data in the weak signal range around 95° is extracted, and the response continuity of the two is compared; finally, the first derivative of the polarization response curve is calculated to obtain the angular differential d / dθ, and the sensitivity values ​​of characteristic angles such as 95° are compared, as shown. Figure 5 As shown.

[0042] Experimental results and analysis show that within the full angular range (0°-360°), both exhibit a basically consistent polarization response trend, verifying the system stability. However, in the weak signal region, the traditional Horn antenna shows a significant blind response plateau (signal amplitude fluctuation <0.01), while the semiconductor surface plasmon millimeter-wave detector has a continuous response (fluctuation <0.05) without a plateau. At the 95° characteristic angle, the traditional Horn antenna has d / dθ = 0.00008, while the semiconductor surface plasmon millimeter-wave detector has d / dθ = 0.00485, and the ideal sin... 2 The θ derivative (reference) is -0.00868, indicating that the polarization detection sensitivity of the semiconductor surface plasmon millimeter-wave detector can reach 60 times that of the traditional Horn antenna (0.00485 / 0.00008≈60.6). It can still accurately distinguish the subtle orientation differences of anisotropic materials in the weak signal region near 90°.

[0043] In summary, the optimized system of this invention exhibits no blind response and continuous response (signal amplitude fluctuation <0.05) in weak signal regions (such as the metal mesh orientation in the embodiment, i.e., the angle between the millimeter-wave polarization angle modulated by anisotropic materials and the ideal detection angle of the detector is 75-105°). At the 95° characteristic angle, the angle differential sensitivity d / dθ is 0.00485, which is 60 times higher than the sensitivity of the traditional Horn antenna, and can accurately distinguish the subtle orientation differences of anisotropic materials. At the same time, the system adopts a planar structure with a size ≤10mm×10mm, which can be monolithically integrated and adapted to miniaturized industrial application scenarios. This invention represents a significant performance breakthrough and has substantial industrial value. Firstly, it addresses the core issues of traditional Horn antennas—blind response and low sensitivity—achieving continuous detection across all angles with a 60-fold increase in sensitivity, meeting the requirements for high-precision anisotropic characterization. Secondly, in terms of integration, the planar detector structure can be monolithically integrated on a large scale, reducing its size to 1 / 25th that of a traditional Horn antenna, making it suitable for miniaturized industrial systems. Regarding industrial adaptability, it employs free-space non-contact detection, enabling in-situ non-destructive testing without damaging samples, allowing direct application in online inspection scenarios on production lines such as electronic packaging and aerospace. Furthermore, the detector is fabricated using conventional micro-nano processes such as MOCVD and ultraviolet lithography, resulting in a lower system cost than quantum well detectors, making it suitable for industrial mass production and providing a reliable solution for the industrial application of millimeter-wave polarization detection technology.

[0044] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A polarization detection system based on a semiconductor plasmonic millimeter-wave detector, characterized in that, It includes a millimeter-wave transmitter, a receiving unit, and a signal processing unit; among which, Millimeter-wave transmitter for providing stable millimeter waves with transverse magnetic™ polarization; The receiving unit is a semiconductor plasmonic millimeter-wave detector used to convert incident millimeter-wave signals into photocurrent signals. It utilizes metasurface micro-nano structures and metal antennas to enhance electromagnetic coupling efficiency. It excites surface plasmons (SPPs) at the ohmic contact metal-semiconductor-metal OMSM structure and relaxes them to generate non-equilibrium electrons. After applying an external bias voltage, the non-equilibrium electrons flow in a directional manner to form a photocurrent signal. The signal processing unit includes an amplifier circuit and a data acquisition module, which is used to amplify the photocurrent signal and quantize its sensitivity. During operation, the anisotropic material is placed between the millimeter-wave transmitter and the receiver unit to detect the polarization characteristics of the material in the millimeter-wave band, thereby achieving in-situ non-destructive characterization of the anisotropic material.

2. The polarization detection system based on a semiconductor plasmonic millimeter-wave detector according to claim 1, characterized in that, The millimeter-wave transmitter is a solid-state source with an output power of 10-20dBm. It operates in the Ka and W bands and its transmitted millimeter-wave polarization mode is set to transverse magnetic TM polarization to match the antenna gain and metasurface field strength enhancement design of the receiving unit.

3. The polarization detection system based on a semiconductor plasmonic millimeter-wave detector according to claim 1, characterized in that, The receiving unit, from bottom to top, consists of a substrate layer, a semiconductor plasmon layer and a metasurface layer, and an ohmic contact metal-semiconductor-metal OMSM structure; wherein, the substrate layer is made of GaAs material; the semiconductor plasmon layer is an indium antimonide (InSb) thin film with a negative real part of dielectric constant in the detection band and an electron mobility ≥2.97×10⁻⁶ at room temperature. 4 cm 2 ・V -1 ・s -1 The metasurface layer is located on the surface of the plasmonic layer on the semiconductor surface and has a vertical slot array structure. Its slots are orthogonal to the transverse magnetic TM polarization. The ohmic contact metal-semiconductor-metal OMSM structure includes Ti electrodes and Au electrodes. The semiconductor plasmonic layer is exposed between the electrodes, and an antenna layer is provided on the electrodes.

4. The polarization detection system based on a semiconductor plasmonic millimeter-wave detector according to claim 3, characterized in that, The substrate layer thickness is 0.5-1.5 mm, the semiconductor plasmon layer thickness is 0.5-10 μm, the vertical slot period is 500 nm-2 μm, the slot width is 1 / 3-1 / 2 of the vertical slot period, and the depth is 200 nm-1 μm. The exposed length of the semiconductor plasmon layer between the electrodes is 20-150 μm, satisfying the subwavelength constraint. The antenna layer length is 1.36-2 mm or 3.75-5.66 mm, matching the half wavelength of Ka-band millimeter waves.

5. The polarization detection system based on a semiconductor plasmonic millimeter-wave detector according to claim 4, characterized in that, The receiving unit is prepared by the following method: (i) Preparation of the substrate layer: GaAs material is selected; (ii) Growth of semiconductor plasmonic layer: InSb thin film is epitaxially grown on GaAs substrate using metal-organic chemical vapor deposition (MOCVD) process; (iii) Fabrication of metasurface layer: A vertical trench array is formed on the surface of InSb thin film by ultraviolet lithography and etching process, while ensuring that the trench channels are orthogonal to the TM polarization; (iv) Fabrication of OMSM structure and antenna: Ti electrodes and Au gold electrodes are deposited at both ends of the InSb thin film using electron beam evaporation or vacuum thermal evaporation to form ohmic contact electrodes, exposing the InSb layer between the electrodes; at the same time, an antenna layer matching half wavelength of the millimeter wave band is fabricated and integrated with the electrodes to complete the fabrication of semiconductor plasmon millimeter wave detector.

6. The polarization detection system based on a semiconductor plasmonic millimeter-wave detector according to claim 1, characterized in that, In the signal processing unit, the amplification circuit uses a low-noise preamplifier and a lock-in amplifier to amplify the photocurrent signal and suppress dark current noise. The data acquisition module acquires the lock-in amplifier voltage signal to the computer through a GPIB card, generates a polarization response curve through data normalization processing by the data software, and obtains the angular differential sensitivity d / dθ by differentiating the curve to quantify the polarization detection accuracy.

7. The application of the polarization detection system based on a semiconductor plasmonic millimeter-wave detector as described in any one of claims 1-6 in polarization detection, characterized in that, The application method is as follows: (a) A millimeter-wave transmitter outputs a target frequency band millimeter wave with TM polarization, which is incident on the anisotropic material to be tested; (b) Modulated millimeter waves are incident on the receiving unit, and non-equilibrium electrons are induced after the plasmons SPP relax. (c) The amplification circuit applies a bias current to drive the non-equilibrium electrons to flow in a directional manner to generate photocurrent. The amplified signal is recorded by the data acquisition module to generate a normalized polarization response curve and calculate the angle differential sensitivity d / dθ to complete polarization detection and realize non-destructive characterization of anisotropic materials.

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