Focal Plane Split Polarization Detector Based on the Collaborative Design of Metasurface and Pixel Mesa

Abstract

A split focal plane polarization detector based on the collaborative design of metasurface and pixel mesa, comprising: a metasurface structure, which selects a pixel-level full Stokes polarization-sensitive metasurface structure, including a plurality of metasurface structure units distributed in an array, for preliminary polarization decoupling and directional convergence; a focal plane pixel array that is pixel-level registered with the metasurface structure, including a multi-plane array composed of a plurality of pixels, and each pixel is provided with a mesa; the side length of each mesa ranges from 2 to 3 times the full width at half maximum of the spot converged by the metasurface structure unit, so as to balance the energy utilization efficiency of each pixel for the light field, suppress the optical signal crosstalk in the non-converging center region and even adjacent pixels, and further improve the polarization extinction ratio on the basis of the polarization decoupling of the metasurface structure. The present invention realizes preliminary polarization decoupling, and the collaborative design of the combined secondary pixel mesa suppresses the crosstalk between adjacent pixels, breaking through the polarization extinction performance of a single metasurface.

Description

Technical Field

[0001] The present invention belongs to the technical fields of nanophotonics and photodetectors, and particularly relates to a split focal plane polarization detector based on the synergistic effect of a metasurface and a pixel mesa. Background Art

[0002] Infrared detection refers to the technical process of converting an incident infrared radiation signal into an electrical signal output. Compared with visible light and near-infrared detection, infrared detection utilizes the self-radiation of an object and has unique advantages such as all-weather operation and strong anti-interference ability. It can detect targets in low-light or dark environments and plays an important role in military, civilian, and medical fields.

[0003] Infrared polarization detection technology is a new type of optoelectronic detection technology that obtains target information by analyzing the polarization characteristics of infrared radiation. Based on the polarization characteristics of light waves, infrared polarization detection technology can obtain the polarization characteristics of the target infrared radiation light wave on the basis of intensity detection, which can reflect its dielectric material, surface morphology, and physical and chemical properties. Traditional polarization detection technologies include time-sharing, amplitude-splitting, and aperture-splitting schemes, which have disadvantages such as large volume, complex system, and low stability.

[0004] Due to the requirements of lightweight, high integration, high stability, and real-time full polarization detection, the split focal plane (DoFP) polarization integration detection scheme based on a pixel-level polarization-sensitive structure has also become a key development direction for the new generation of infrared detection technology. The split focal plane based on a pixel-level polarization-sensitive structure is an efficient polarization imaging technology that captures the polarization characteristics of a scene by integrating a tiny polarization element array on the focal plane of a camera. It can simultaneously obtain information on multiple polarization states, thus greatly improving the imaging speed and accuracy.

[0005] However, since the wavelength of infrared light waves is in the same order of magnitude as the size of the absorption pixels, simply integrating a pixel-level polarization-sensitive micro-nano structure on a traditional pixel will cause serious interference to the orthogonal information reception between adjacent pixels due to the diffraction effect, and the dispersion effect also makes it difficult to achieve high-efficiency spectral splitting and polarization extinction over a wide spectral band. Infrared detection itself is a weak signal, and if the energy utilization rate and polarization discrimination are low due to the dispersion effect or micro-structure energy loss, it will limit its application. Benefiting from the powerful phase modulation ability of the metasurface structure, it is possible to customize the transmission and light field local channel directional convergence for the detected optical signal at the pixel level. The light field components carrying different polarization and spectral information are directionally transmitted to the corresponding pixel absorption area, and at the same time, the directional spatial compression of the light field also avoids interference to the orthogonal information between adjacent pixels.

[0006] In the sub-focal plane polarization detection scheme, especially in the infrared band, due to the pixel size being comparable to the wavelength, the signal crosstalk between adjacent pixels is relatively large and difficult to efficiently suppress. Therefore, it is difficult to improve the polarization extinction ratio. The existing polarization / spectral functional layers based on planar micro-nano structures mainly focus on the optimization of achromatism, or monochromatic full polarization, or wide-spectrum partial polarization, or shorter wavelengths or large-sized lenses. There is little co-optimization of the planar optical functional layer from the perspective of integrated devices, and it is difficult to be integrated and efficiently applied in sub-focal plane detectors with small infrared pixel sizes. For sub-focal plane detectors with small infrared pixel sizes, there are extremely strict requirements for the area, thickness, weight, and most importantly, the performance indicators of the optical functional layer. In this context, traditional optical elements optimized for large sizes or single wavelengths are difficult to directly apply to miniaturized infrared detection systems.

[0007] Therefore, how to solve the problems of signal crosstalk and difficult improvement of polarization extinction ratio in the prior art, and provide a method to improve the accuracy of polarization detection, as well as its performance and application scope, is a technical problem that needs to be urgently solved by those skilled in the art. Summary of the Invention

[0008] The object of the present invention is to propose a sub-focal plane polarization detector based on the collaborative design of a metasurface and a pixel mesa, aiming at the problems in the prior art.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] A sub-focal plane polarization detector based on the collaborative design of a metasurface and a pixel mesa, comprising:

[0011] A metasurface structure, which selects a pixel-level full Stokes polarization-sensitive metasurface structure, including a plurality of metasurface structure units distributed in an array, for preliminary polarization decoupling and directional convergence;

[0012] A focal plane pixel array pixel-level registered with the metasurface structure, including a multi-plane array composed of a plurality of pixels, and each pixel is provided with a mesa;

[0013] The side length of the mesa of the focal plane pixel array is in the range of 2-3 times the full width at half maximum of the spot converged by the metasurface structure unit, so as to balance the energy utilization efficiency of each pixel for the light field, suppress the optical signal crosstalk in the non-converging center region and even adjacent pixels, and further significantly improve the polarization extinction ratio on the basis of the polarization decoupling of the metasurface structure.

[0014] While adopting the above technical solutions, the present invention can also adopt or combine the following technical solutions:

[0015] As a preferred technical solution of the present invention: the metasurface structure includes a all-dielectric substrate and metasurface structure units on the all-dielectric substrate. The metasurface structure units are nano-column arrays formed by micro-nano processing at the micro-nano scale. Every 2 X 1 metasurface structure units form an orthogonal polarization multiplexing sub-unit to achieve polarization state regulation and spectral splitting and focusing; each focal plane pixel matches the metasurface structure directly above it to form a sub-unit, and every 2 X 3 sub-units form a super-pixel structure to achieve full Stokes regulation of 6 polarization states.

[0016] As a preferred technical solution of the present invention: each orthogonal polarization multiplexing sub-unit respectively realizes the spectral splitting and focusing effects of linearly polarized light at 0 degrees / 90 degrees, linearly polarized light at 45 degrees / 135 degrees, and left-handed / right-handed circularly polarized light. The target focal points of the focusing are respectively located at the center positions of the absorption regions of two pixels matching the 2 X 1 unit;

[0017] In each orthogonal polarization multiplexing sub-unit, the spatial distribution of the required phase is:

[0018]

[0019] where, is any spatial position in the lens plane, is the spatial position of the lens focus in the focal plane, is the working wavelength, is the target focal length.

[0020] As a preferred technical solution of the present invention: each nano-column in the nano-column array adopts an anisotropic structure to produce different phase regulation effects on different polarizations,

[0021] Perform achromatic aberration treatment on the nano-columns in the target working band,

[0022] If the target working band is λ∈{λ_min,λ_max}, the phase required for the central wavelength λ_cen is regarded as the basic phase, and the phase difference at the boundary of the target working band is regarded as the dispersion phase. Meeting both of them can ensure that the superatom meets the phases of each wavelength.

[0023] The side length of the nano-column substrate is P, which is set to be equivalent to 1 / 2 of the working wavelength, and a hexagonal or square array arrangement is selected;

[0024] The height of the nano-column is H, which is set to be equivalent to the working wavelength;

[0025] The nano-column adopts an ellipse or a rectangle, and each nano-column needs to be scanned at multiple frequencies in the target working band to extract the basic phase and the dispersion phase.

[0026] As a preferred technical solution of the present invention: an anti-reflection interface is introduced on the non-microstructure side of the metasurface structure, and the anti-reflection interface is an anti-reflection microstructure or an optical anti-reflection film, which is used to reduce the reflection loss of light energy during transmission.

[0027] As a preferred technical solution of the present invention: the mesa is a semiconductor convex structure where the pixel is located, the pixel is square, and the mesa is square.

[0028] Compared with the prior art, a split focal plane polarization detector based on the collaborative design of a metasurface and a pixel mesa of the present invention has the following beneficial effects: by using a first-level pixel-level fully Stokes polarization-sensitive metasurface structure, preliminary polarization decoupling and directional convergence are realized. The mesa size of the second-level focal plane pixel array is combined and set to be in the range of 2-3 times the full width at half maximum of the spot converged by the metasurface structure, taking into account the energy utilization efficiency of each pixel for the light field, and suppressing the optical signal crosstalk in the non-converging center region and even adjacent pixels. On the basis of the first-level polarization decoupling, the polarization extinction ratio is further significantly improved, solving the problem that it is difficult for the first-level small-size metasurface structure to reach the application level due to phase discontinuity and micro-nano processing errors, especially when the working wavelength is in the infrared band and above. A collaborative design method that can break through the performance limitations of small-size metasurfaces is provided, breaking through the polarization extinction ratio limit that a single metasurface can reach, and realizing a high polarization extinction ratio at the application level.

[0029] In the present invention, the pixel-level alignment between the metasurface structure and the focal plane pixel array ensures the on-chip integration ability of the device, which helps to improve the stability of the device detection performance; through the collaborative design of the metasurface and the pixel mesa, the "filtering" light mode of the ordinary microlens metasurface is converted into a beam splitting mode, which more effectively distributes and utilizes the energy of the incident light, reduces energy loss, and significantly improves the energy utilization efficiency; different polarization states of light are separated and converged to the central region of the corresponding pixel through the metasurface orthogonal polarization multiplexing sub-units, realizing efficient pixel-level light concentration, reducing the interference between adjacent pixels, and improving the polarization detection accuracy; based on the superpixel composed of 2 X 3 sub-units, full Stokes regulation of 6 polarization states is realized, realizing the comprehensive regulation of the polarization state of light waves, and through real-time detection by the detector, a large amount of polarization information can be captured in a short time, providing key information for subsequent optical processing, greatly improving the imaging speed and efficiency, and realizing a real-time snapshot working mode, which has broad application prospects in many fields such as photon communication, satellite remote sensing, bio-optical imaging, sensing and detection, quantum optics, integrated optical systems, and security monitoring and anti-counterfeiting. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a three-dimensional structure schematic diagram of a split focal plane polarization detector based on the collaborative design of a metasurface and a pixel mesa of the present invention;

[0031] Figure 2 It is the top view of the 2×3 tabletop plane in the present invention;

[0032] Figure 3 It is the schematic three-dimensional structure diagram of the superpixel formed by the 2×3 metasurface and the corresponding focal plane pixel array in the present invention;

[0033] Figure 4 It is the schematic longitudinal cross-sectional view of the polarization splitting of the metasurface structure for splitting 0 / 90-degree linearly polarized light;

[0034] Figure 5 It is the simulation result of the broadband full-polarization detection performance of the present invention;

[0035] Figure 6 It is the variation of the full width at half maximum of the converging light spot with the wavelength after the 0-degree linearly polarized light passes through the metasurface structure for splitting 0 / 90-degree linearly polarized light;

[0036] Figure 7 It is the energy utilization efficiency on the focal plane when the tabletop size changes after the 4-micron 0-degree linearly polarized light passes through the metasurface structure;

[0037] Figure 8 It is the variation result of the polarization extinction ratio (S parameter, which can be converted between the two) with the tabletop size under the incidence of linearly polarized light in the present invention;

[0038] Figure 9 It is the variation result of the polarization extinction ratio (S parameter, which can be converted between the two) with the tabletop size under the incidence of left-handed circularly polarized light in the present invention;

[0039] In the attached drawings, the metasurface structure 1; the tabletop 2; the focal plane pixel array 3. Detailed implementation manners

[0040] Next, the implementation method, principle design and technical effects of the present invention will be further described in detail with reference to the attached drawings and specific embodiments.

[0041] The purpose of the present invention is to propose a on-chip sub-focal plane polarization detector with the advantages of high integration, high energy utilization efficiency, high polarization extinction ratio, real-time snapshot acquisition, etc.

[0042] A sub-focal plane polarization detector based on the collaborative design of a metasurface and a pixel tabletop in the present invention mainly includes two functional structures: a metasurface structure unit sensitive to the full polarization for regulating the optical signal of the detected scene; and a focal plane pixel array 3 structure for photoelectric conversion that is pixel-level registered with the metasurface structure unit.

[0043] The metasurface structure unit includes:

[0044] A full Stokes polarization-sensitive superpixel unit structure is composed of 2×3 sub-pixels. The 2×3 superpixel structure includes three 2×1 structures, namely, a 0° / 90° linear polarization beam splitting structure, a 45° / 135° linear polarization beam splitting structure, and a left-handed / right-handed circular polarization beam splitting structure. Each 2×1 structure can achieve the separation and directional convergence of a set of orthogonal polarizations.

[0045] The design method of the metasurface structure is as follows:

[0046] In the first step, calculate the phase response distribution and transmittance distribution of the superatom unit structure under different input light sources (polarization, spectrum). Calculate the phase response (transmission phase) of superatoms with different geometric sizes to an input light source with a fixed wavelength and polarization by the finite-difference time-domain method, and change the wavelength and polarization to collect the phase responses of the superatoms to different input light sources to form a superatom library.

[0047] In the second step, determine the target light field modulation effect according to parameters such as the geometric size of the pixel, the integration distance between the metasurface and the mesa, and the pixel center distance, and calculate the required phase space distribution according to the following superlens phase formula:

[0048]

[0049] where, is any spatial position in the lens plane, is the spatial position of the lens focus in the focal plane, is the working wavelength, is the target focal length.

[0050] In the third step, through the particle swarm optimization algorithm, select superatoms matching the required target phase from the superatom database, and determine the superatom size at each spatial position to form the metasurface design.

[0051] Only the transmission phase is introduced in the 0° / 90° linear polarization beam splitting structure, that is, the aspect ratio of the elliptical cylinder is changed to match the phase required for broadband beam splitting and convergence. The 45° / 135° linear polarization beam splitting structure is obtained by rotating the 0° / 90° linear polarization beam splitting structure by 45°.

[0052] The left-handed / right-handed circular polarization beam splitting structure introduces a geometric phase on the basis of the transmission phase, that is, the aspect ratio of the elliptical cylinder and the rotation angle around the center of the ellipse are changed.

[0053] The structure of the focal plane pixel array 3 mainly includes an upper contact layer, a light absorption region, and a lower contact layer in its physical structure. The mesa structure corresponding to each pixel generally refers to the semiconductor protrusion structure where the pixel is located after removing the air groove, which is usually composed of an epitaxial layer of semiconductor material. It is the region for light absorption and photoelectric conversion of each pixel, and also plays a role in electrical isolation between adjacent pixels.

[0054] It should be noted that since the pixel size is closely related to the spatial resolution, and the size of the pixel shows a gradually decreasing trend, it is difficult to ensure ideal continuous phase modulation with a finite number of discrete phase points on a finite size, and errors are inevitable in micro-nano processing. From the perspective of design and preparation, it is currently difficult for a single metasurface structure to achieve a high polarization extinction ratio.

[0055] The collaborative design scheme proposed by the present invention can break through the design and processing limitations of a single metasurface. The key lies in the design of the size of the mesa 2 of the pixel array.

[0056] Considering that the pixel shape is square, the center-to-center distance of the pixel, that is, the side length of the square pixel, is D, and the size of the square mesa is d. In the present invention, the side length of the mesa specifically refers to the side of the pixel that receives light, which is responsible for capturing incident light and converting it into an electrical signal. Reasonably designing the size of the square mesa is beneficial to breaking through the polarization extinction ratio of a single metasurface. The specific design method for the size of the square mesa is as follows:

[0057] The metasurface has a converging effect on the light field. Generally, there are two important indicators for measuring the converging effect, namely the focusing efficiency and the full width at half maximum (FWHM) of the focused spot. These two indicators are closely related to the determination of the mesa size proposed by the present invention. The focusing efficiency is generally defined as the ratio of the light intensity of the spot within 2 - 3 times the FWHM to the total light intensity on the focal plane. Theoretically, the FWHM of the focused spot on the focal plane is DL = 0.514λ / NA, and the calculated value of the FWHM of the focused spot is generally close to the theoretical limit. Setting the mesa size within the range of 2 - 3 times the FWHM can not only ensure the focusing efficiency and energy utilization efficiency, but also suppress the influence of diffracted light caused by non-perfect focusing on the polarization extinction ratio.

[0058] The mesa 2 structure corresponding to the pixel generally refers to the semiconductor protrusion structure where the pixel is located after removing the air groove, which is usually composed of an epitaxial layer of semiconductor material. It is the region for light absorption and photoelectric conversion of each pixel, and also plays a role in electrical isolation between adjacent pixels.

[0059] Pixels in a large-area array detector are generally square or rectangular, which is convenient for arrangement and processing and can improve the filling ratio of the entire pixel area. The pixel center distance is generally selected considering factors such as spatial resolution, manufacturing process limitations, optical interference, electrical isolation, heat dissipation, etc. In this invention, a case with a pixel center distance of 30 μm is discussed. If the pixel shape or center distance size is adjusted, the tabletop size selection scheme is also applicable. Combining with the optimization of the tabletop size, the full width at half maximum (FWHM) of the focused spot on the focal plane is DL = 0.514 λ / NA, where NA is the numerical aperture. We propose that when the square tabletop size is set at 2 - 3 times the full width at half maximum, the focusing efficiency and further suppression of crosstalk between adjacent pixels can be balanced on the receiving surface, and the polarization extinction ratio can be improved.

[0060] A split focal plane polarization detector based on the collaborative design of a metasurface and tabletop size, comprising: a fully polarization-sensitive metasurface structure unit for regulating the optical signal of the detected scene; and a focal plane structure unit pixel-level registered with the metasurface.

[0061] The metasurface structure unit described above includes:

[0062] A superpixel structure that combines 2×3 sub-pixels into a full Stokes polarization splitting and converging structure. The superpixel structure includes three 2×1 splitting and converging structures, namely, a 0-degree / 90-degree linear polarization splitting structure, a 45-degree / 135-degree linear polarization splitting structure, and a left-handed / right-handed circular polarization splitting structure;

[0063] Only the transmission phase is introduced in the 0-degree / 90-degree linear polarization splitting structure, that is, the aspect ratio of the elliptical cylinder is changed to match the phase required for broadband splitting and convergence;

[0064] The 45-degree / 135-degree linear polarization splitting structure is obtained by rotating the 0-degree / 90-degree linear polarization splitting structure by 45 degrees;

[0065] Both the transmission phase and the geometric phase are introduced in the left-handed / right-handed circular polarization splitting structure, that is, the aspect ratio of the elliptical cylinder and the rotation angle around the center of the ellipse are changed.

[0066] The focal plane structure unit described above includes:

[0067] A periodic pixel array, where the semiconductor protrusion structure where the pixel is located after removing the air groove, that is, the tabletop structure, and the tabletop size is an important parameter emphasized in this patent;

[0068] Compared with the prior art, a split focal plane polarization detector based on the collaborative design of a metasurface and a pixel mesa of the present invention has the following beneficial effects: The metasurface realizes preliminary polarization decoupling and focusing performance. However, due to the phase discontinuity under small-sized pixels and the errors in micro-nano processing and three-dimensional integration, it is difficult to achieve a high polarization extinction ratio at the application level only relying on the metasurface, especially in the infrared band. The metasurface decomposes and converges the polarization in three groups of orthogonal polarization basis vectors, and the light spot converges within the pixel mesa, and the full width at half maximum of the converged light spot is about DL = 0.514 λ / NA. The present invention innovatively proposes to carry out collaborative design on the sizes of the metasurface and the pixel mesa. When the pixel mesa size is set to 2-3 times the full width at half maximum size of the metasurface-converged light spot, the energy utilization efficiency can be taken into account, the diffraction light crosstalk in the non-central region and even the adjacent pixel region can be suppressed, the polarization extinction ratio can be further significantly improved, the signal crosstalk between adjacent pixels can be reduced, and thus the detection accuracy and imaging quality can be improved.

[0069] Among them, the polarization detection method based on the split focal plane type can ensure high integration; the super pixel can detect the full Stokes polarization information at one time to ensure real-time snapshot full polarization detection; the spectroscopic working mode is used instead of the filtering mode to ensure high energy utilization efficiency; the polarization decoupling metasurface structure and the pixel mesa are collaboratively designed to break through the polarization extinction ratio limit that a single metasurface can reach and ensure a high polarization extinction ratio.

[0070] The primary metasurface proposed by the present invention realizes preliminary polarization decoupling, and the collaborative design with the secondary pixel mesa further suppresses the crosstalk between adjacent pixels and breaks through the polarization extinction performance of a single metasurface.

[0071] The method proposed by the present invention is easy to be integrated on a chip.

[0072] In the present invention, the pixel-level alignment design method ensures the integration degree, and the conversion from the "filtering" mode of the ordinary microlens to the spectroscopic mode ensures the energy utilization efficiency; the further pixel-level light condensing performance reduces the information crosstalk between adjacent pixels; the super pixel simultaneously decomposes and detects the full polarization mode to enable the real-time snapshot working mode. Embodiment 1

[0073] A split focal plane polarization detector based on the collaborative design of a metasurface and a pixel mesa of the present invention will introduce the device working principle and method from two successive parts: from the all-dielectric metasurface regulation to the split focal plane polarization detection:

[0074] As Figure 1As shown, the detected optical signal is incident on the metasurface structure 1. Here, taking the target working wavelength range of 3.5 - 4.5 μm as an example for design, this structure can perform optical field directional convergence regulation on the full Stokes polarization. Since the polarization information of the optical field can be completely decomposed on three groups of orthogonal polarization basis vectors, a superpixel is set to 2×3, as Figure 3 shown, each 2×1 orthogonal polarization multiplexing sub-unit realizes the splitting and convergence of 0 / 90-degree linearly polarized light, 45 / 135-degree linearly polarized light, and left / right circularly polarized light respectively.

[0075] As Figure 4 shown, the measured optical signal passes through the metasurface structure, and the signal is decomposed on the pair of orthogonal polarization bases of 0 / 90 degrees. The 0-degree polarized light converges to the left mesa structure, and the 90-degree polarized light converges to the right mesa structure. The mesa 2 structure includes a photosensitive layer. The three groups of orthogonal polarizations are split and converged on the 2×1 pixels respectively. Finally, the 0-degree linearly polarized light / 90-degree linearly polarized light, 45-degree linearly polarized light / 135-degree linearly polarized light, and left circularly polarized light / right circularly polarized light converge on the mesa 2 regions of 6 pixels of the 2×3 superpixel respectively.

[0076] Figure 4 shows the specific process of splitting and converging the optical field of a 2×1 pixel (corresponding to 0-degree linearly polarized light / 90-degree linearly polarized light). After the optical field carrying polarization information passes through the metasurface, the decomposition of 0-degree and 90-degree polarized light is realized and they are respectively converged to the mesa regions of two pixels. The mesa structure generally consists of an upper contact layer, a light absorption layer, a lower contact layer, etc. from top to bottom. The region pointed by the converging optical field arrow is the light absorption region in the mesa. The vertical distance between the position of the light absorption region and the position of the metasurface represents the integration distance, and the specific value is determined according to the integration method and process.

[0077] As Figure 2 is the top view of the 2×3 mesa plane of the present invention. The shape of the mesa is square, and the side length of the square is the mesa size described in the present invention; the square dotted line shows a sub-pixel region, and the side length of the pixel is equal to the center distance between adjacent pixels, that is, the pixel center distance described in the present invention; the focal plane position corresponding to the 2×3 superpixel, that is, it converges to the center region of mesa 2 of the focal plane pixel array 3.

[0078] Figure 5 demonstrates the simulation results of the broadband full-polarization detection performance of the present invention, including five working wavelengths of 3.5, 3.75, 4.0, 4.25, 4.5 μm, and the focal plane converging optical fields under six polarization states.

[0079] Due to the design errors of the pixel-level micro-lens part and the processing errors of the micro-nano structure, there is a certain gap between the convergence efficiency and achromatic aberration effect of the micro-lens and the theory. Ideally, the micro-polarizer efficiently decouples and converges each polarization signal in the absorption area of the target pixel. However, due to the imperfections in design and processing, there will actually be some diffracted light of polarization in the pixels corresponding to the entire absorption area of the micro-polarizer, that is, there is light field energy distribution throughout the focal plane except for the focused spot.

[0080] Since the focused spot on the focal plane and the pixel size are in the same order of magnitude, the size of the pixel mesa will also seriously affect the polarization extinction ratio. Appropriate groove width and passivation treatment of the sidewalls can achieve the effect of light field isolation. The present invention proposes to precisely design the size of the mesa of the detection pixel, Figure 8 which shows the change result of the polarization extinction ratio with the mesa size under the incidence of linearly polarized light in the present invention. It can be seen that with the decrease of the pixel mesa size, taking the pixel center distance D = 30 μm in the current design as an example, the polarization extinction ratio is significantly improved. When the side length of the square mesa is reduced from 30 μm to 5 μm, the polarization extinction ratio at the central wavelength increases from 19.8 to 157.5, an increase of 8 times; the minimum extinction ratio in the wide spectral range increases from 4.1 to 16.4, also an increase of 4 times. Thus, it can be seen that the closer the mesa size is to the focused spot size, the more effectively it can suppress the influence of diffracted light on the extinction ratio. The selection of the optimal mesa size takes into account both the size of the focused spot of the micro-lens and the integration error, so as to maximize the polarization detection effect. Figure 9 which shows the change of the polarization extinction ratio with the mesa size under the incidence of circularly polarized light in the present invention, presenting the same trend.

[0081] Ideally, the full width at half maximum FWHM of the focused spot on the focal plane is DL = 0.514 λ / NA, where NA is the numerical aperture. The theoretical full width at half maximum value of the focused spot of this structure is as Figure 6 shown by the dotted line. The final simulation result of the example design of this invention is as Figure 6 shown by the circular data, Figure 6 which is the change of the full width at half maximum of the converging spot with the wavelength after the 0-degree linearly polarized light passes through the metasurface structure that splits 0 / 90-degree linearly polarized light. The full width at half maximum value is extracted from the light field envelope at the midpoint of the short axis along the long axis direction of the metasurface structure that splits 0 / 90-degree linearly polarized light; the dots represent the simulation results of the 0-degree linearly polarized light (XLP), and the dashed straight line represents the theoretical calculation result. Figure 6 The full width at half maximum values of the converging spots of 0-degree linearly polarized light XLP with different wavelengths passing through the example structure are calculated, and it can be seen from the comparison that they are close to the theoretical calculation values.

[0082] Taking the wavelength of 4.0 μm as an example, the light field envelope at the midpoint of the short axis along the long axis direction of the metasurface structure that splits 0 / 90-degree linearly polarized light is taken to analyze the utilization efficiency of the light field energy. AsFigure 7 In Figure 6 , the converging light spot at 4 microns shown in 0 , if the abscissa is denoted as num, num×FWHM 0 , the ratio of the energy within the region to the total transmitted energy is defined as the energy utilization rate of the focal plane. Obviously, the larger the region for collecting energy, the larger the energy utilization rate of the focal plane and the higher the utilization efficiency of the transmitted light energy. Generally, at least 2 - 3 regions of the full width at half maximum of the focused light spot are considered, that is, the recommended tabletop size. At this time, the energy utilization efficiency and polarization extinction ratio can be better guaranteed. The specific design can balance the energy utilization efficiency and the polarization extinction ratio effect according to the actual situation to determine the final tabletop size.

[0083] The above specific implementation manners are used to explain and illustrate the present invention. They are only the preferred embodiments of the present invention and do not limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and scope of the claims of the present invention fall within the protection scope of the present invention.

Claims

1. A focal plane polarization detector based on the collaborative design of a metasurface and a pixel table, characterized by: include: The metasurface structure uses a pixel-level full-Stokes polarization-sensitive metasurface structure, including a number of metasurface structural units distributed in an array, for preliminary polarization decoupling and directional focusing; A focal plane pixel array aligned with the metasurface structure at the pixel level, comprising a multi-element plane array composed of a plurality of pixels, each pixel being provided with a table; The side length of each table is 2-3 times the half-height full width of the light spot gathered by the metasurface structure unit, so as to take into account the energy utilization efficiency of each pixel for the light field, suppress the crosstalk of the light signal gathered in the non-central area or even the adjacent pixel, and further improve the polarization extinction ratio on the basis of polarization decoupling of the metasurface structure; the metasurface structure includes a full dielectric substrate and a metasurface structure unit on the full dielectric substrate, the metasurface structure unit is a nano-column array formed by micro-nano processing at a micro-nano scale, and every 2X 1 metasurface structure unit constitutes an orthogonal polarization multiplexing sub-unit to realize polarization state regulation and splitting and convergence; each focal plane pixel matches the metasurface structure directly above it to form a sub-unit, and every 2X 3 sub-units constitute a super-pixel structure to realize full Stokes regulation and detection of 6 polarization states; Each orthogonal polarization multiplexing subunit realizes the splitting and convergence of 0 degree / 90 degree linear polarization, 45 degree / 135 degree linear polarization, left-handed / right-handed circularly polarized light, and the convergence target focus is located at the center of the absorption area of ​​the two pixels matching the 2X 1 unit.

2. The focal plane polarization detector based on the coordinated design of the metasurface and the pixel table as claimed in claim 1, characterized in that: In each orthogonal polarization multiplexing subunit, the spatial distribution of the required phase is: Where (x, y) is any spatial position in the lens plane, (x0, y0) is the spatial position of the lens focus in the focal plane, λ is the operating wavelength, and f is the target focal length.

3. The focal plane polarization detector based on the coordinated design of the metasurface and the pixel table as claimed in claim 1, characterized in that: Each nanorod in the nanorod array adopts an anisotropic structure to produce different phase control effects for different polarizations; The nanorods are achromatized in the target working band, which is λ∈{λ_min,λ_max}. The phase required by the central wavelength λ_cen is regarded as the basic phase, and the phase difference at the boundary of the target working band is regarded as the dispersion phase. If both are satisfied at the same time, it can ensure that the meta-atom satisfies the phase of each wavelength at the same time. The side length of the nanorod base is P, which is set to be equivalent to 1 / 2 of the working wavelength, and is arranged in a hexagonal or square array; The height of the nanopillar is H, which is set to be equivalent to the working wavelength; The nanocolumns are elliptical or rectangular, and multi-frequency scanning of the target working band is performed on each nanocolumn to extract the basic phase and dispersion phase.

4. The focal plane polarization detector based on the coordinated design of the metasurface and the pixel table as claimed in claim 1, characterized in that: The metasurface structure introduces an anti-reflection interface on the non-microstructure side. The anti-reflection interface is an anti-reflection microstructure or an optical anti-reflection film, which is used to reduce the reflection loss of light energy during transmission.

5. The focal plane polarization detector based on the coordinated design of the metasurface and the pixel table as claimed in claim 1, characterized in that: The mesa is a semiconductor protruding structure where the pixel is located. The pixel is square and the mesa is square.

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