Full Stokes polarimeter and preparation method thereof

Abstract

The invention belongs to the technical field of light polarization measurement, and discloses a full stokes polarimeter and a preparation method thereof. The full stokes polarimeter comprises a substrate, a metal electrode, an anisotropic crystal material film and an insulating packaging material film, a plurality of pairs of metal electrodes are positioned on the substrate; the two pairs of metal electrodes and the anisotropic crystal material film form a detection unit; in each detection unit, the anisotropic crystal material film covers the metal electrode; comprising at least two detection units, and the detection units are distributed on a substrate in a central symmetry mode and located on the same plane. A set torsion angle is formed between the crystal orientations of the anisotropic crystal material films of the detection units; the insulating packaging material film covers the anisotropic crystal material film. The full-polarization Stokes parameter sensor can identify full-polarization Stokes parameters, has the characteristics of miniaturization, integration, high sensitivity and quick response, and has wide application prospects in the fields of optical fiber communication, sensing and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of light polarization measurement, and in particular relates to a full-Stokes polarimeter and a preparation method thereof. Background Art

[0002] Polarization, as one of the basic properties of light, plays a key role in many fields including astronomical observation, remote sensing technology, military reconnaissance, medical diagnosis, and optical fiber communication. In optical networks, real-time and online analysis of the polarization state of light is particularly important.

[0003] Currently, limited by the numerous bulky optoelectronic mechanical components in complex systems, traditional polarimeter needs to use a series of optoelectronic components with numerous splitting routes (including lenses, prisms, polarizers, wave plates, filters, photodetectors and mechanical rotating parts) arranged in series on the optical path, which makes it difficult to achieve equipment miniaturization, system integration and fast device response.

[0004] Stokes parameters (S0, S1, S2, and S3) can be used to fully describe the polarization state of light. The acquisition of Stokes parameters is one of the key technologies for optical polarization detection. Stokes parameter S1 represents the intensity of the linear horizontal or vertical polarization component (its polarization angle is defined as 0 degrees or 90 degrees), parameter S2 represents the intensity of linear ±45 degree polarized light, parameter S3 characterizes the intensity of the left-handed or right-handed circular polarization component, and parameter S0 defines the total intensity of the incident light. Since four independent Stokes parameters need to be retrieved, namely light intensity, two linear polarization components, and one circular polarization component, the detection of the polarization state usually requires four measurements or four specific polarization-resolving detectors to obtain the four Stokes parameters.

[0005] Linear dichroism is a property of the electromagnetic spectrum that detects and distinguishes between polarized light absorbed parallel to and perpendicular to the orientation axis. This property is closely related to the morphology and orientation of the material or device structure, whether in anisotropic crystal structures or in anisotropic device modes. Unlike the hexagonal lattices of two-dimensional materials such as graphene and molybdenum disulfide, which are insensitive to polarized light, layered black phosphorus crystals, as an anisotropic crystalline material, exhibit significant anisotropy due to their rectangular lattices. In black phosphorus, phosphorus atoms are arranged in two alternating rows, forming upward and downward folds, showing an "armchair" shape only in the x-axis direction and a "zigzag" shape in the y-axis, which makes the electrons and photons in black phosphorus show obvious anisotropy within the layer. For polarization sensing, when the initial polarization state (0°) of the incident light is along the "armchair" direction of black phosphorus, it corresponds to the maximum polarization response. However, a single black phosphorus unit cannot accurately identify the linear polarization state because the light responses of different polarization angles (θ) overlap twice in the range of 0 to 180 degrees, making it impossible to distinguish between θ and (180 degrees - θ). Summary of the invention

[0006] The purpose of the present invention is to provide a full-Stokes polarimeter and a preparation method thereof, which can identify full-Stokes polarization and has the characteristics of miniaturization, integration, high sensitivity and fast response, by integrating anisotropic crystal materials and electrode structures on the end face of an optical fiber in view of the shortcomings of existing polarimeter that it is difficult to achieve equipment miniaturization, system integration and rapid response of devices.

[0007] Specifically, the present invention is implemented by adopting the following technical solutions.

[0008] In one aspect, the present invention provides a full-Stokes polarimeter for obtaining Stokes parameters, comprising a substrate, a plurality of pairs of metal electrodes, an anisotropic crystal material film, and an insulating packaging material film; The plurality of pairs of metal electrodes are located on the substrate; Two pairs of the metal electrodes and a piece of the anisotropic crystal material film constitute a detection unit; in each detection unit, the anisotropic crystal material film covers the metal electrode; the full-Stokes polarimeter comprises at least two detection units, each detection unit is centrally symmetrically distributed on the substrate and is located on the same plane; the crystal directions of the anisotropic crystal material film of each detection unit form a set torsion angle; The insulating packaging material film covers the anisotropic crystal material film.

[0009] Furthermore, the substrate is an optical fiber end face, and the detection units are symmetrically distributed on the optical fiber end face relative to the axis of the optical fiber.

[0010] Furthermore, the substrate includes but is not limited to silicon, glass, polymer, and ceramic; and the insulating packaging material film is made of transparent material.

[0011] Furthermore, the two pairs of metal electrodes are composed of three metal electrodes, one metal electrode is grounded, and the other two are respectively used as output electrodes.

[0012] Furthermore, the torsion angle is 10-80 degrees.

[0013] Furthermore, the anisotropic crystalline material film is black phosphorus or black phosphorus arsenic.

[0014] Furthermore, there are two detection units, the electrode lines of the metal electrodes in each detection unit are in the same direction, the crystal boundary direction of one piece of anisotropic crystal material film is in the same direction as the electrode line direction of the electrode it covers, and the cutting edge direction of another piece of anisotropic crystal material film is in the same direction as the electrode line direction of the electrode it covers; or There are three or more detection units, the electrode line directions of the metal electrodes in each detection unit are centrally symmetrically distributed, and the crystal boundary directions of the anisotropic crystal material films in each detection unit are respectively consistent with the electrode line directions of their corresponding metal electrodes.

[0015] Furthermore, the material of the metal electrode is gold.

[0016] Furthermore, the thickness of the metal electrode is 40-100 nm, the line width of the metal electrode is 0.5-1 μm, and the spacing between adjacent metal electrodes in the detection unit is 0.5-1 μm; the thickness of the anisotropic crystal material is 20-60 nm; and the thickness of the insulating packaging material film is 5-20 nm.

[0017] On the other hand, the present invention also provides a method for preparing a full-Stokes polarimeter, which is used to prepare the above-mentioned full-Stokes polarimeter, comprising: (1) Spin-coating a resist layer on the plane of the substrate, exposing and developing the resist layer to obtain an electrode pattern; and physically vapor depositing metal and removing excess resist to obtain the metal electrode; (2) obtaining a mechanically exfoliated anisotropic crystalline material film on a substrate, and then cutting the anisotropic crystalline material film in a direction that is twisted relative to a crystal boundary direction; (3) The cut anisotropic crystal material films are transferred to the substrates respectively, and covered on several pairs of the metal electrodes to form detection units respectively.

[0018] The beneficial effects of the full Stokes polarimeter and the preparation method thereof of the present invention are as follows: The full-Stokes polarimeter of the present invention can identify full-Stokes polarization and has the characteristics of miniaturization, integration, high sensitivity and rapid response.

[0019] Traditional polarimeter requires a series of photoelectric components with numerous splitting paths to be arranged in series on the optical path, which is complex, time-consuming, energy-consuming and costly. The full-Stokes polarimeter of the present invention integrates photoelectric materials into the end face of the optical fiber, and uses a single compact device for real-time, in-situ detection and identification, thus realizing an ultra-compact polarimeter integrated with the end face of the optical fiber.

[0020] The full-Stokes polarimeter of the present invention arranges several pairs of optical fiber end-face metal electrodes in parallel on the same plane, thereby realizing parallel integration of multiple detection units on the same plane.

[0021] The full-Stokes polarimeter of the present invention utilizes a calibration-free black phosphorus twisting method to achieve precise control of the black phosphorus twist angle by arbitrarily selecting black phosphorus nanosheets and cutting them along a certain angle direction within 10-80 degrees relative to the crystal boundary, thereby accurately realizing a multi-unit twist structure in an extremely small optical fiber core area (effective area radius is 5 μm).

[0022] The photosensitive element of the full Stokes polarimeter of the present invention is not limited to black phosphorus, and any semiconductor material with anisotropy can be used as a photosensitive material. The polarimeter based on the crystal twist structure prepared by the present invention can identify the Stokes parameters of full polarization, and has the characteristics of miniaturization, integration, high sensitivity and rapid response, and has broad application prospects in the fields of optical fiber communication, sensing, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the structure of embodiment 1 of the present invention.

[0024] Figure 2 It is a structural diagram of embodiment 2 of the present invention.

[0025] Figure 3 It is a structural diagram of embodiment 3 of the present invention.

[0026] Figure 4 2 is a diagram of polarization resolution performance of an embodiment of the present invention, wherein (a), (b), (c), and (d) are schematic diagrams of photovoltage changes with QWP angle when the initial linear polarization angle is 30 degrees, 40 degrees, 50 degrees, and 60 degrees, respectively.

[0027] Figure 5 It is a schematic diagram of the decoupling process of the neural network parsing full Stokes parameters according to an embodiment of the present invention.

[0028] Figure 6 4 is a full Stokes prediction recognition result diagram of an embodiment of the present invention.

[0029] Markings in the figure: 1-substrate, 2-metal electrode, 3-anisotropic crystal material film, 4-insulating packaging material film. DETAILED DESCRIPTION

[0030] The present invention is further described in detail below in conjunction with embodiments and with reference to the accompanying drawings.

[0031] One embodiment of the present invention introduces a full-Stokes polarimeter, comprising a substrate 1, a plurality of pairs of metal electrodes 2, an anisotropic crystal material film 3, and an insulating packaging material film 4. The plurality of pairs of metal electrodes 2 are located on the substrate 1.

[0032] Among them, two pairs of metal electrodes 2 and a piece of anisotropic crystal material film 3 constitute a detection unit. In each detection unit, the anisotropic crystal material film 3 covers the metal electrode 2. The full Stokes polarimeter includes at least two detection units, each of which is centrally symmetrically distributed on the substrate 1 and is on the same plane.

[0033] Preferably, in another embodiment, the two pairs of metal electrodes 2 are composed of three metal electrodes 2, one metal electrode is grounded, and the other two are respectively used as output electrodes.

[0034] Preferably, in another embodiment, the material of the metal electrode 2 is gold, and the thickness is 40 nm.

[0035] The anisotropic crystal material film 3 of this embodiment may be black phosphorus, black phosphorus arsenic, etc. Preferably, the anisotropic crystal material film 3 is black phosphorus, and the thickness is 25 nm.

[0036] Preferably, in another embodiment, the line width of the metal electrode 2 at the end face of the optical fiber is 750 nm, and the spacing between adjacent metal electrodes 2 in each detection unit is 1 μm.

[0037] The crystal directions (armchair directions) of the anisotropic crystal material films 3 of different detection units form a certain torsion angle, preferably, the torsion angle ranges from 10 to 80 degrees. The torsion angle is controlled by cutting the anisotropic crystal material film. Figure 1 In the full-Stokes polarimeter shown, there are two detection units, the electrode line directions of the metal electrodes in each of the detection units are consistent, the crystal boundary direction of a piece of black phosphorus film is consistent with the electrode line direction (X1 direction) of the metal electrode; the cutting edge direction of another piece of black phosphorus is consistent with the electrode line direction (X1 direction), and there is a torsion angle (for example, 60 degrees) between its crystal boundary direction (X2 direction) and the X1 direction.

[0038] Preferably, in another embodiment, the number of detection units of the full-Stokes polarimeter is three or more, the electrode line directions of the metal electrodes in each detection unit are centrally symmetrically distributed, and the crystal boundary directions of the anisotropic crystal material films in each detection unit are respectively consistent with the electrode line directions of their corresponding metal electrodes.

[0039] like Figure 2 As shown, the full-Stokes polarimeter includes three detection units, and the crystal boundary direction of the black phosphorus film in each detection unit is consistent with the electrode line direction (X1, X2, X3) of its corresponding metal electrode; there is a torsion angle between the crystal boundary directions (X1, X2, X3) of the black phosphorus film in each detection unit.

[0040] like Figure 3As shown, the full-Stokes polarimeter includes four detection units, and the crystal boundary direction of the black phosphorus film in each detection unit is consistent with the electrode line direction (X1, X2, X3, X4) of its corresponding metal electrode; there is a torsion angle between the crystal boundary directions (X1, X2, X3, X4) of the black phosphorus film in each detection unit.

[0041] The insulating packaging material film 4 covers the anisotropic crystal material film 3 .

[0042] Preferably, in another embodiment, the substrate 1 is an optical fiber end face, and each detection unit is symmetrically distributed on the optical fiber end face relative to the axis of the optical fiber. The substrate of the Stokes polarimeter of the present invention is not limited to the optical fiber end face, and has good compatibility with various planar systems. In another embodiment, the substrate includes but is not limited to silicon-based, glass, polymer, ceramic, etc. When a substrate material such as ceramic is used, the insulating packaging material film 4 is made of a transparent material, and light passes through the insulating packaging material film 4 from outside the insulating packaging material film 4 to the anisotropic crystal material film 3.

[0043] Preferably, the insulating packaging material is hexagonal boron nitride with a thickness of 10 nm.

[0044] The working principle of the present invention is as follows: The twisted structure of anisotropic crystalline materials is an effective approach for polarized light sensing. By using several black phosphorus units with different twist angles, a phase shift is introduced in the polarization response curve, enabling unambiguous detection of polarization.

[0045] Under the combined effects of photovoltaic and photothermoelectric mechanisms, the photovoltage and intensity relationship of anisotropic crystalline materials (such as black phosphorus) is nonlinear, resulting in a significant change in the photovoltage generated in the electrode pair with changes in the incident light intensity. The intensity distribution of the fundamental mode light field in the core of a single-mode optical fiber decreases radially from the center to the outside. The arrangement of the electrodes is designed according to the light field distribution characteristics, and the two pairs of electrodes in each detection unit have different detection ranges to help accurately identify the light intensity. For polarization sensing, a single black phosphorus unit cannot accurately identify the linear polarization state because the light response of different polarization angles (θ) overlaps twice in the range of 0 to 180 degrees, resulting in the inability to distinguish between θ and (180 degrees-θ). By utilizing the twist angle between each detection unit integrated by black phosphorus film and electrode, a phase shift is introduced in the polarization response curve, so that linear polarization can be clearly detected. At the same time, the wire grating electrode structure also enhances polarization sensitivity. In addition, the anisotropic electric field originating from the Schottky barrier near the black phosphorus-metal contact reduces the symmetry of black phosphorus and leads to the generation of a net circularly polarized photocurrent. The structure-induced symmetry breaking and nonlinear photocarrier generation in the twisted black phosphorus unit cell, together with the light field modulation by the antenna-like electrodes, enable the device to sense linearly, circularly, and elliptically polarized light, as well as light intensity.

[0046] Those skilled in the art can understand that, based on the above working principle, the photosensitive element of the full-Stokes polarimeter of the present invention is not limited to black phosphorus, and any semiconductor material with anisotropy can be used as a photosensitive material.

[0047] The photovoltage signal output by the full Stokes polarimeter of the present invention is trained by using a neural network (such as a back propagation neural network BPNN) and utilizing the light response under different polarization states to achieve regression prediction of the Stokes parameters. Those skilled in the art will appreciate that the neural network is only one solution, and there are other solutions, such as solving analytical formulas, to achieve regression prediction of the Stokes parameters.

[0048] The method for preparing the full-Stokes polarimeter of the present invention comprises the following steps: (1) Spin-coating a resist layer on the plane of the substrate, and performing exposure, development and other processes to obtain a resist layer with an electrode pattern; and physically depositing metal and removing excess resist to obtain the metal electrode; (2) obtaining a mechanically exfoliated anisotropic crystalline material film on a substrate, and then cutting the anisotropic crystalline material film in a direction that is twisted relative to a crystal boundary direction; (3) The cut anisotropic crystal material films are transferred to the substrates respectively, and covered on the pairs of metal electrodes to form detection units respectively. The several anisotropic material nanosheets can be obtained by cutting the same material multiple times, or by cutting multiple materials.

[0049] In order to verify the performance of the full-Stokes polarimeter of the present invention, the following test system is used for testing, including a light source, a single-mode optical fiber, a coupler, a collimator, a polarizer, a half-wave plate (Half-Wave Plate, HWP), a quarter-wave plate (Quarter-Wave Plate, QWP), a variable optical attenuator, a power meter, a digital source meter, an acquisition card and the full-Stokes polarimeter of the present invention.

[0050] During the test, the light output by the light source is connected to the coupler through a single-mode optical fiber, and the optical fiber connected to the coupler is connected to the collimator. The polarization angle of the incident light output by the collimator is fixed by the polarizer and can be changed by rotating the HWP. The helicity of the light can be modulated by the QWP placed after the polarizer and the HWP. The variable optical attenuator placed after the QWP is used to modulate the intensity of the light and is connected to a 95:5 optical fiber coupler with a power meter to monitor the light intensity. The output port of another single-mode optical fiber connected to the coupler is connected to the full-Stokes polarimeter of the present invention, and the electrode leads of the polarimeter are fixed on the customized acquisition chip by flying wire assembly, and the acquisition chip is connected to the acquisition card. The electrical signal of the sample can be acquired through a digital source meter connected to the acquisition card.

[0051] The circularly polarized photovoltage and the linearly polarized photovoltage with different initial linear polarizations are used as a function of the QWP angle. The helicity of the light is continuously modulated by the QWP placed after the polarizer and the HWP, and the measured photoresponse is the result of the rotation angle φ relative to the QWP at different initial linear polarization states. Figure 5 As shown, the chiral photovoltage induced by left-circularly polarized light and right-circularly polarized light remains constant despite the change in the initial linear polarization state. Figure 5 The photovoltage generated can be quantitatively expressed as: V = V C sin (2φ) + V L cos (4φ + φ0) + V0, Where φ is the angle of QWP; V C is the amplitude of the helicity-dependent circularly polarized photocurrent effect (CPGE) voltage; V L is the amplitude of the linear polarization-sensitive linear photogalvanic effect (LPGE) voltage with a phase shift φ0, and V0 is the polarization-independent background voltage; φ0 is related to the angle between the initial linearly polarized light and the black phosphorus crystal orientation.

[0052] Due to the different linear polarization light responses of black phosphorus, the change of the initial linear polarization state will cause V L , φ0 and V0, resulting in different shapes and amplitudes of the photovoltage curves. CThe value of changes little with the initial linear polarization state. During a full 180° QWP modulation cycle, the light transitions through a series of polarization states: linear (0°), elliptical (0°-45°), left circular (45°), elliptical (45°-90°), linear (90°), elliptical (90°-135°), right circular (135°), elliptical (135°-180°), and back to linear (180°). Under different HWP configurations, the linear and elliptical polarization states change, further expanding the range of polarization states that the device can detect.

[0053] As mentioned above, the photoresponse of each detection unit combines the helicity-dependent CPGE voltage and the linear polarization-sensitive LPGE voltage. The LPGE voltage of each detection unit exhibits a phase shift due to the different φ0 values ​​caused by the different crystal orientations of the twisted black phosphorus units. This phase shift enables the twisted black phosphorus units to produce different photoresponses to polarized light with different helicities, thereby facilitating the full-range recognition of different polarization states.

[0054] The decoupling process of using neural network to analyze the full Stokes parameters is as follows Figure 6 As shown. For the photovoltage signal output of the coupled polarization-intensity information on the four pairs of electrodes, full Stokes polarization detection can be achieved by using the machine learning method - BPNN. For the acquisition of Stokes parameters, power regression and polarization prediction are achieved one by one by cascading two layers of prediction factors.

[0055] like Figure 6 As shown, at different working wavelengths, the polarization state of the random input ( Figure 6 The hollow circle shows the polarization state of the device in this embodiment ( Figure 6 We quantify the error in the Stokes parameter prediction as the average solid angle deviation σ = arccos((S1S1' + S2S2' + S3S3') / S0S0'), where S i and S i ' (i = 1,2,3) are the input and predicted Stokes parameters, respectively. The average solid angle deviation of the measured results for S0, S1, S2, and S3 is within 6°.

[0056] The full-Stokes polarimeter of the present invention can identify full-Stokes polarization and has the characteristics of miniaturization, integration, high sensitivity and rapid response.

[0057] Traditional polarimeter requires a series of photoelectric components with numerous splitting paths to be arranged in series on the optical path, which is complex, time-consuming, energy-consuming and costly. The full-Stokes polarimeter of the present invention integrates photoelectric materials into the end face of the optical fiber, and uses a single compact device for real-time, in-situ detection and identification, thus realizing an ultra-compact polarimeter integrated with the end face of the optical fiber.

[0058] The full-Stokes polarimeter of the present invention arranges several pairs of optical fiber end-face metal electrodes in parallel on the same plane, thereby realizing parallel integration of multiple detection units on the same plane.

[0059] The full-Stokes polarimeter of the present invention utilizes a calibration-free black phosphorus twisting method to achieve precise control of the black phosphorus twist angle by arbitrarily selecting black phosphorus nanosheets and cutting them along a certain angle direction within 10-80 degrees relative to the crystal boundary, thereby accurately realizing a multi-unit twist structure in an extremely small optical fiber core area (effective area radius is 5 μm).

[0060] The photosensitive element of the full Stokes polarimeter of the present invention is not limited to black phosphorus, and any semiconductor material with anisotropy can be used as a photosensitive material. The polarimeter based on the crystal twist structure prepared by the present invention can identify the Stokes parameters of full polarization, and has the characteristics of miniaturization, integration, high sensitivity and rapid response, and has broad application prospects in the fields of optical fiber communication, sensing, etc.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent replacement and improvement made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A full Stokes polarimeter for obtaining Stokes parameters, characterized in that It includes a substrate, several pairs of metal electrodes, an anisotropic crystal material film, and an insulating packaging material film; The plurality of pairs of metal electrodes are located on the substrate; Two pairs of the metal electrodes and a piece of the anisotropic crystal material film constitute a detection unit; in each detection unit, the anisotropic crystal material film covers the metal electrode; the full-Stokes polarimeter comprises at least two detection units, each detection unit is centrally symmetrically distributed on the substrate and is located on the same plane; the crystal directions of the anisotropic crystal material film of each detection unit form a set torsion angle; The insulating packaging material film covers the anisotropic crystal material film.

2. The full Stokes polarimeter according to claim 1, characterized in that The substrate is an optical fiber end face, and each detection unit is symmetrically distributed on the optical fiber end face relative to the axis of the optical fiber.

3. The full Stokes polarimeter according to claim 1, characterized in that The substrate includes but is not limited to silicon, glass, polymer, and ceramic; the insulating packaging material film is made of transparent material.

4. The full-Stokes polarimeter according to claim 1, characterized in that The two pairs of metal electrodes are composed of three metal electrodes, one metal electrode is grounded, and the other two are used as output electrodes.

5. The full Stokes polarimeter according to claim 1, characterized in that The torsion angle is 10-80 degrees.

6. The full-Stokes polarimeter according to claim 1, characterized in that The anisotropic crystal material film is black phosphorus or black phosphorus arsenic.

7. The full-Stokes polarimeter according to claim 1, characterized in that There are two detection units, the electrode lines of the metal electrodes in each detection unit are in the same direction, the crystal boundary direction of one anisotropic crystal material film is in the same direction as the electrode lines of the electrode it covers, and the cutting edge direction of another anisotropic crystal material film is in the same direction as the electrode lines of the electrode it covers; or There are three or more detection units, the electrode line directions of the metal electrodes in each detection unit are centrally symmetrically distributed, and the crystal boundary directions of the anisotropic crystal material films in each detection unit are respectively consistent with the electrode line directions of their corresponding metal electrodes.

8. The full-Stokes polarimeter according to claim 1, characterized in that The material of the metal electrode is gold.

9. The full-Stokes polarimeter according to claim 2, characterized in that: The thickness of the metal electrode is 40-100 nm, the line width of the metal electrode is 0.5-1 μm, and the spacing between adjacent metal electrodes in the detection unit is 0.5-1 μm; the thickness of the anisotropic crystal material is 20-60 nm; and the thickness of the insulating packaging material film is 5-20 nm.

10. A method for preparing a full-Stokes polarimeter, for preparing a full-Stokes polarimeter according to any one of claims 1 to 9, characterized in that: include: (1) spin coating a resist layer on the plane of the substrate, exposing and developing the resist layer to obtain a resist layer with an electrode pattern; The metal electrode is obtained by physical vapor deposition of metal and removal of excess resist; (2) obtaining a mechanically exfoliated anisotropic crystalline material film on a substrate, and then cutting the anisotropic crystalline material film in a direction that is twisted relative to a crystal boundary direction; (3) The cut anisotropic crystal material films are transferred to the substrates respectively, and covered on several pairs of the metal electrodes to form detection units respectively.

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