A full stokes polarimeter and method of making the same

Abstract

The application belongs to the technical field of optical polarization measurement, and discloses a full-Stokes polarimeter and a preparation method thereof. The full-Stokes polarimeter comprises a substrate, metal electrodes, an anisotropic crystal material film and an insulating packaging material film. A plurality of pairs of metal electrodes are arranged on the substrate. Two pairs of metal electrodes and a piece of anisotropic crystal material film constitute a detection unit. In each detection unit, the anisotropic crystal material film covers the metal electrodes. The full-Stokes polarimeter comprises at least two detection units, and the detection units are symmetrically distributed at the center of the substrate and are located on the same plane. The crystal directions of the anisotropic crystal material films of the detection units form a set of twist angles. The insulating packaging material film covers the anisotropic crystal material film. The full-Stokes polarimeter can identify the Stokes parameters of full polarization, and has the characteristics of miniaturization, integration, high sensitivity and fast response, and has wide application prospects in the fields of optical fiber communication and sensing.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical polarization measurement, and particularly relates to a full-Stokes polarimeter and a preparation method thereof. BACKGROUND

[0002] Polarization, as one of the basic characteristics 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, due to the limitations of numerous heavy optoelectromechanical components in complex systems, traditional polarimeters require a series of optoelectronic components (including lenses, prisms, polarizers, wave plates, optical filters, photodetectors, and mechanical rotating parts) with numerous optical splitting routes to be arranged in series in the optical path, making it difficult to achieve device miniaturization, system integration, and rapid response of devices.

[0004] Stokes parameters (S0, S1, S2, and S3) can be used to completely describe the polarization state of light, and the acquisition of Stokes parameters is one of the key technologies of optical polarization detection. Stokes parameter S1 represents the intensity of linear horizontal or vertical polarization (with its polarization angle defined as 0 degrees or 90 degrees), parameter S2 represents the intensity of linear ±45-degree polarized light, parameter S3 represents the intensity of left-handed or right-handed circularly polarized components, and parameter S0 defines the total intensity of the incident light. Since four independent Stokes parameters need to be retrieved, i.e., 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 allows detection and discrimination by comparing the absorption of light polarized parallel and perpendicular to the orientation direction axis. This property is closely related to the morphology and direction of the material or device structure, whether in a crystal structure with anisotropy or in an anisotropic device mode. Unlike the hexagonal lattice of two-dimensional materials such as graphene and molybdenum disulfide, which are insensitive to polarized light, layered black phosphorus crystals, as a kind of anisotropic crystal material, exhibit significant anisotropy due to their rectangular lattice. In black phosphorus, phosphorus atoms are arranged in two rows in an alternating manner, forming upward and downward folds, only showing a "handrail chair" shape in the x-axis direction and a "zigzag" shape in the y-axis direction, which makes the electrons and photons in black phosphorus exhibit obvious anisotropy within the layer. For polarization sensing, when the initial polarization state (0°) of the incident light is along the "handrail chair" 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 response at different polarization angles (θ) overlaps twice in the range of 0 degrees to 180 degrees, resulting in the inability to distinguish between θ and (180 degrees-θ). SUMMARY

[0006] The present application aims at: in view of the fact that the existing polarimeter is difficult to realize device miniaturization, system integration and device fast response, integrating the crystal material with anisotropy and the electrode structure on the end face of an optical fiber, providing 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.

[0007] Specifically, the present application is implemented by adopting the following technical scheme.

[0008] In one aspect, the present application 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.

[0009] The plurality of pairs of metal electrodes are located on the substrate.

[0010] Two pairs of the metal electrodes and one piece of the anisotropic crystal material film constitute a detection unit; in each detection unit, the anisotropic crystal material film covers the metal electrodes; the full Stokes polarimeter comprises at least two detection units, each detection unit is symmetrically distributed at the center of the substrate and is located on the same plane; the crystal directions of the anisotropic crystal material films of each detection unit form a set twist angle.

[0011] The insulating packaging material film covers the anisotropic crystal material film.

[0012] Further, the substrate is the end face of an optical fiber, and each detection unit is symmetrically distributed on the end face of the optical fiber relative to the axis of the optical fiber.

[0013] Further, the substrate includes but is not limited to silicon-based, glass, polymer, and ceramic; and the insulating packaging material film is made of transparent material.

[0014] Further, the two pairs of metal electrodes are composed of three metal electrodes, one of which is grounded, and the other two are used as output electrodes.

[0015] Further, the twist angle is 10-80 degrees.

[0016] Further, the anisotropic crystal material film is black phosphorus or black phosphorus arsenic.

[0017] Further, the detection unit is two, the electrode line directions of the metal electrodes in each detection unit are consistent, the crystal boundary direction of one piece of the anisotropic crystal material film is consistent with the electrode line direction of the electrode covered thereby, and the cutting edge direction of the other piece of the anisotropic crystal material film is consistent with the electrode line direction of the electrode covered thereby; or

[0018] The number of the detection units is three or more, and the electrode line direction of the metal electrode in each detection unit is symmetrically distributed in the center, and the crystal boundary direction of the anisotropic crystal material film in each detection unit is consistent with the electrode line direction of the corresponding metal electrode.

[0019] Further, the material of the metal electrode is gold.

[0020] Further, 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.

[0021] On the other hand, the application also provides a preparation method of a full Stokes polarimeter, which is used to prepare the full Stokes polarimeter described above, comprising:

[0022] (1) spin-coating a resist layer on the plane of the substrate, and after exposure and development, obtaining a resist layer with an electrode pattern; through physical vapor deposition of metal and removal of excess resist, obtaining the metal electrode;

[0023] (2) obtaining a mechanically exfoliated anisotropic crystal material film on the substrate, and then cutting the anisotropic crystal material film at a torsion angle with respect to the crystal boundary direction;

[0024] (3) transferring the cut anisotropic crystal material film to the substrate respectively to cover a plurality of metal electrodes to form each detection unit.

[0025] The full Stokes polarimeter and the preparation method thereof have the following advantages:

[0026] The full Stokes polarimeter can identify full Stokes polarization, and has the characteristics of miniaturization, integration, high sensitivity and fast response.

[0027] The traditional polarimeter needs to use a series of photoelectric elements with a large number of light splitting routes arranged in series in the optical path, which is complex, time-consuming, energy-consuming and high-cost. The full Stokes polarimeter of the application integrates photoelectric materials into the end face of the optical fiber, uses a single compact device for real-time and in-situ detection and identification, and realizes an ultra-compact fiber end face integrated polarimeter.

[0028] The full Stokes polarimeter of the application arranges a plurality of pairs of metal electrodes on the same plane in parallel, realizes parallel integration of a plurality of detection units on the same plane.

[0029] The full-Stokes polarimeter of the application realizes accurate control of the black phosphorus twist angle by arbitrarily selecting a black phosphorus nanosheet and cutting along a certain angle direction within 10-80 degrees relative to the crystal boundary by using a black phosphorus twist method without calibration, and accurately realizes a multi-unit twist structure in a very small fiber core area (effective area radius of 5 μm).

[0030] The photosensitive element of the full-Stokes polarimeter of the application is not limited to black phosphorus, and anisotropic semiconductor materials can be used as photosensitive materials. The polarimeter based on the crystal twist structure prepared by the application can identify full-polarization Stokes parameters, and has the characteristics of miniaturization, integration, high sensitivity and fast response, and has wide application prospects in the fields of optical fiber communication, sensing and the like. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a structural schematic diagram of embodiment 1 of the application.

[0032] Figure 2 is a structural schematic diagram of embodiment 2 of the application.

[0033] Figure 3 is a structural schematic diagram of embodiment 3 of the application.

[0034] Figure 4 is a polarization resolution performance diagram of the embodiment of the application, wherein (a), (b), (c), and (d) are schematic diagrams of the change of the photovoltage with the QWP angle under the initial linear polarization angles of 30 degrees, 40 degrees, 50 degrees, and 60 degrees, respectively.

[0035] Figure 5 is a decoupling process schematic diagram of the neural network for analyzing full-Stokes parameters of the embodiment of the application.

[0036] Figure 6 is a full-Stokes prediction recognition result diagram of the embodiment of the application.

[0037] In the figure, 1 is a substrate, 2 is a metal electrode, 3 is an anisotropic crystal material film, and 4 is an insulating packaging material film. DETAILED DESCRIPTION

[0038] The application will be further described in detail below in combination with embodiments and with reference to the accompanying drawings.

[0039] One embodiment of the application introduces a full-Stokes polarimeter, which comprises 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.

[0040] Two pairs of metal electrodes 2 and an anisotropic crystalline material thin film 3 constitute a detection unit. In each detection unit, the anisotropic crystalline material thin film 3 covers the metal electrodes 2. The all-Stokes polarimeter includes at least two detection units, each of which is centrally symmetrically distributed on the substrate 1 and is located on the same plane.

[0041] Preferably, in another embodiment, the two pairs of metal electrodes 2 consist of three metal electrodes 2, one of which is grounded and the other two are used as output electrodes.

[0042] Preferably, in another embodiment, the metal electrode 2 is made of gold and has a thickness of 40 nm.

[0043] In this embodiment, the anisotropic crystalline material film 3 can be black phosphorus, black phosphorus arsenic, etc. Preferably, the anisotropic crystalline material film 3 is black phosphorus with a thickness of 25 nm.

[0044] Preferably, in another embodiment, the linewidth of the optical fiber end face metal electrode 2 is 750 nm, and the spacing between adjacent metal electrodes 2 in each detection unit is 1 μm.

[0045] The anisotropic crystalline material thin films 3 of different detection units form a certain torsion angle with each other. Preferably, the torsion angle ranges from 10 to 80 degrees. The torsion angle is controlled by cutting the anisotropic crystalline material thin film. Figure 1 In the full Stokes polarimeter shown, there are two detection units. The electrode lines of the metal electrodes in each detection unit are aligned. The crystal boundary direction of one black phosphorus film is aligned with the electrode line direction (X1 direction) of the metal electrode. The cutting edge direction of the other black phosphorus film is aligned with the electrode line direction (X1 direction). Therefore, there is a torsion angle (e.g., 60 degrees) between its crystal boundary direction (X2 direction) and the X1 direction.

[0046] Preferably, in another embodiment, the total Stokes polarimeter has three or more detection units, and the electrode lines of the metal electrodes in each detection unit are centrally symmetrically distributed. The crystal boundary direction of the anisotropic crystalline material thin film in each detection unit is consistent with the electrode line direction of its corresponding metal electrode.

[0047] like Figure 2 As shown, the all-Stokes polarimeter includes three detection units. 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.

[0048] like Figure 3As shown, the full-Stokes polarimeter includes four detection units, the crystal boundary direction of the black phosphorus thin film in each detection unit is consistent with the electrode line direction (X1, X2, X3, X4) of the corresponding metal electrode; there is a twist angle between the crystal boundary directions (X1, X2, X3, X4) of the black phosphorus thin film in each detection unit.

[0049] The anisotropic crystal material thin film 3 is covered by the insulating encapsulation material thin film 4.

[0050] Preferably, in another embodiment, the substrate 1 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. The substrate of the Stokes polarimeter of the present application 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 the substrate material is ceramic, the insulating encapsulation material thin film 4 is made of transparent material, and the light from the outside of the insulating encapsulation material thin film 4 penetrates through the insulating encapsulation material thin film 4 to the anisotropic crystal material thin film 3.

[0051] Preferably, the insulating encapsulation material is hexagonal boron nitride, and the thickness is 10 nm.

[0052] The working principle of the present application is as follows:

[0053] The twisted structure of the anisotropic crystal material is an effective way for polarized light sensing. By using several black phosphorus units with different twist angles, phase shifts are introduced in the polarization response curve, so that the polarization can be clearly detected.

[0054] Under the combined action of photovoltaic and photothermal mechanisms, the intensity dependence of the photovoltage of the anisotropic crystal material (such as black phosphorus) is nonlinear, resulting in a significant change in the photovoltage generated in the electrode pair with the change in the intensity of the incident light. The intensity distribution of the fundamental mode light field of the single-mode fiber core decreases radially from the center. According to the light field distribution characteristics, the arrangement of the electrodes is designed, and the two pairs of electrodes in each detection unit have different detection ranges, which help to 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 degrees to 180 degrees, resulting in the inability to distinguish between θ and (180 degrees-θ). By using the twist angle between the detection units each integrated by a black phosphorus thin film and an electrode, a phase shift is introduced in the polarization response curve, so that the linear polarization can be clearly detected. At the same time, the linear grating-shaped electrode structure also enhances the polarization sensitivity. In addition, the anisotropic electric field originating from the Schottky barrier near the black phosphorus-metal contact reduces the symmetry of the black phosphorus and leads to the generation of net circularly polarized photocurrent. The structure-induced symmetry breaking and the generation of nonlinear photo-carriers in the twisted black phosphorus unit, as well as the light field modulation of the antenna-shaped electrode, enable the device to sense linear, circular and elliptical polarized light, as well as light intensity.

[0055] Those skilled in the art can understand that, based on the above working principle, the element for photosensitive of the full-Stokes polarimeter of the present application is not limited to black phosphorus, and any semiconductor material with anisotropy can be used as photosensitive material.

[0056] The photovoltage signal output by the full-Stokes polarimeter of the present application is trained by using a neural network (such as a back propagation neural network BPNN) to realize the regression prediction of the Stokes parameters by using the light response under different polarization states. Those skilled in the art can understand that the neural network is only one solution, and there are other solutions, such as analytical formula solution, to realize the regression prediction of the Stokes parameters.

[0057] The preparation method of the full-Stokes polarimeter described above comprises the following steps:

[0058] (1) spin-coating a resist layer on the plane of the substrate, and after exposure, development and other processes, an electrode patterned resist layer is obtained; by physical vapor deposition of metal and removing the excess resist, the metal electrode is obtained;

[0059] (2) obtaining a mechanically exfoliated anisotropic crystal material film on the substrate, and then cutting the anisotropic crystal material film at a torsion angle relative to the crystal boundary direction;

[0060] (3) transferring the cut anisotropic crystal material film to the substrate respectively to cover a plurality of metal electrodes to form a plurality of detection units. The plurality of anisotropic material nanosheets can be obtained by cutting the same sheet of material multiple times, or by cutting multiple sheets of material.

[0061] In order to verify the performance of the full-Stokes polarimeter of the present application, 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 (HWP), a 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 application.

[0062] At the time of testing, the light output by the light source is coupled into a single-mode fiber access coupler, and the fiber output of the coupler accesses a collimator. The polarization angle of the incident light output by the collimator is fixed by a polarizer, and can be changed by rotating the HWP. The helicity of the light can be modulated by a QWP placed after the polarizer and the HWP. A variable optical attenuator placed after the QWP is used to modulate the intensity of the light, and is connected to a 95:5 fiber coupler with a power meter to monitor the light intensity. The output port of the other single-mode fiber accessed by the coupler is connected to the full-Stokes polarimeter of the present application, and the electrode leads of the polarimeter are fixed by a set of flying wires assembled on a custom-made acquisition chip, which is connected to an acquisition card. The electrical signal of the sample can be acquired by a digital source meter connected to the acquisition card.

[0063] Circularly polarized light and linearly polarized light voltages with different initial linear polarizations are adopted as a function of the QWP angle. The helicity of the light is continuously modulated by a QWP placed after the polarizer and the HWP, and the measured optical response is the result in different initial linear polarization states with respect to the QWP rotation angle φ. As shown in FIG. 3, although the initial linear polarization state changes, the chiral optical voltage induced by left and right circularly polarized light remains constant. Figure 5 Figure 5 The optical voltage generated in the present application can be quantitatively expressed as:

[0064] V = V C sin (2φ) + V L cos (4φ + φ0) + V0,

[0065] where φ is the angle of the QWP; V C is the amplitude of the helicity-dependent circular photogalvanic effects (CPGE) voltage; V L is the amplitude of the linearly polarized sensitive linear photogalvanic effects (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 direction.

[0066] Due to the different linearly polarized light responses of black phosphorus, the change in the initial linear polarization state will cause changes in V L , φ0 and V0, resulting in different shapes and amplitudes of the optical voltage curve. In contrast, V C ​The value of hardly changes with the initial linear polarization state. During a complete 180° QWP modulation cycle, light undergoes a series of polarization state transitions: 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.

[0067] As previously mentioned, the photoresponse of each detector unit combines a CPGE voltage related to helicity and a linearly polarization-sensitive LPGE voltage. Due to the different φ0 values ​​caused by the different crystal orientations of the twisted black phosphorus units, the LPGE voltage of each detector unit exhibits a phase shift. This phase shift enables the twisted black phosphorus units to produce different photoresponses to polarized light with different helicities, thereby facilitating the full-range identification of different polarization states.

[0068] The decoupling process of using neural networks to analyze the full Stokes parameters is as follows: Figure 6 As shown, for the photovoltage signal output coupled with polarization-intensity information on four pairs of electrodes, full Stokes polarization detection can be achieved using a machine learning method—BPNN. For obtaining the Stokes parameters, power regression and polarization prediction are achieved sequentially by cascading two layers of predictive factors.

[0069] like Figure 6 As shown, the polarization state of a random input at different operating wavelengths ( Figure 6 (shown by the hollow circle) and the polarization state predicted by the device in this embodiment ( Figure 6 Comparing the results with those of a solid sphere (as shown), good consistency is observed. 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 measurement results of S0, S1, S2 and S3 is within 6°.

[0070] The all-Stokes polarimeter of the present invention can identify all-Stokes polarization and features miniaturization, integration, high sensitivity and fast response.

[0071] Traditional polarimeters need to use a series of photoelectric elements with a large number of light splitting routes arranged in series in the light path, and the system is complex, time-consuming, energy-consuming and high-cost. The full Stokes polarimeter of the application realizes real-time, in-situ detection and identification by integrating photoelectric materials into the end face of an optical fiber using a single compact device, and realizes an ultra-compact fiber end face integrated polarimeter.

[0072] The full Stokes polarimeter of the application arranges a plurality of pairs of fiber end face metal electrodes in parallel on the same plane, realizes parallel integration of a plurality of detection units on the same plane.

[0073] The full Stokes polarimeter of the application realizes accurate control of the black phosphorus twist angle by arbitrarily selecting black phosphorus nanosheets and cutting along a certain angle direction within 10-80 degrees relative to the crystal boundary, and accurately realizes a multi-unit twist structure in a very small fiber core area (effective area radius of 5 mu m).

[0074] The photosensitive element of the full Stokes polarimeter of the application is not limited to black phosphorus, and anisotropic semiconductor materials can also be used as photosensitive materials. The polarimeter based on the crystal twist structure prepared by the application can identify full polarization Stokes parameters, and has the characteristics of miniaturization, integration, high sensitivity and fast response, and has wide application prospects in the fields of optical fiber communication, sensing and the like.

[0075] The above only describes the preferred embodiments of the application and is not intended to limit the application. Any modification, equivalent replacement and improvement made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A full Stokes polarimeter for obtaining Stokes parameters, characterized in that, It includes a substrate, several pairs of metal electrodes, an anisotropic crystalline material thin film, and an insulating encapsulation material thin film; The plurality of pairs of metal electrodes are located on the substrate; Two pairs of metal electrodes and one anisotropic crystalline material thin film constitute a detection unit; in each detection unit, the anisotropic crystalline material thin film covers the metal electrodes; the all-Stokes polarimeter includes at least two detection units, each detection unit is centrally symmetrically distributed on the substrate and is all on the same plane; the crystal orientations of the anisotropic crystalline material thin films of each detection unit form a predetermined torsion angle; there are two detection units, the electrode lines of the metal electrodes in each detection unit are aligned, the crystal boundary direction of one anisotropic crystalline material thin film is aligned with the electrode line direction of the electrode it covers, and the cutting edge direction of another anisotropic crystalline material thin film is aligned with the electrode line direction of the electrode it covers; or there are three or more detection units, the electrode lines of the metal electrodes in each detection unit are centrally symmetrically distributed, and the crystal boundary direction of the anisotropic crystalline material thin film in each detection unit is aligned with the electrode line direction of its corresponding metal electrode. The insulating encapsulation material film covers the anisotropic crystal material film.

2. The all-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 all-Stokes polarimeter according to claim 1, characterized in that, The insulating encapsulation material film is made of a transparent material.

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

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

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

7. The all-Stokes polarimeter according to claim 1, characterized in that, The metal electrode is made of gold.

8. The all-Stokes polarimeter according to claim 2, characterized in that, The metal electrode has a thickness of 40-100 nm and a linewidth of 0.5-1 μm. The spacing between adjacent metal electrodes within the detection unit is 0.5-1 μm. The anisotropic crystal material has a thickness of 20-60 nm. The insulating encapsulation material film has a thickness of 5-20 nm.

9. A method for preparing a full Stokes polarimeter, used to prepare a full Stokes polarimeter according to any one of claims 1-8, characterized in that, include: (1) A resist layer is spin-coated on the plane of the substrate, and after exposure and development, a resist layer with an electrode pattern is obtained; The metal electrode is obtained by physical vapor deposition of metal and removal of excess resist. (2) Obtain an anisotropic crystalline material film that has been mechanically peeled off on a substrate, and then cut the anisotropic crystalline material film in a direction that is at a twist angle relative to the direction of the crystal boundary. (3) The cut anisotropic crystal material films are transferred to the substrate and covered on several pairs of metal electrodes to form each detection unit.

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