Terahertz polarization multiplexing metasurface calculus filter and image processing method and device

Abstract

The invention discloses a terahertz polarization multiplexing metasurface calculus filtering device and an image processing method and device, and relates to the technical field of calculus image processing. The calculus filter, namely the polarization multiplexing metasurface, is a structural unit array formed by micron-sized structural units through two-dimensional periodic continuation, each structural unit is composed of a metal film and a rectangular hole formed in the center of the metal film, and the two rectangular holes are the same in size and different in rotation angle. Furthermore, an image processing method and device based on the terahertz polarization multiplexing metasurface are designed, the polarization multiplexing metasurface is placed on a common focal plane of a 4f optical system, and a polarization-dependent coherent transfer function is applied to a spatial spectrum of an input image; therefore, differential and integral processing functions of the image are realized on the two cross-polarization channels at the same time. Experiments verify that a terahertz time-domain spectroscopy system is used, and prove that differential and integral characteristics of an input image can be kept at the same time, and differential and integral operations of the image are realized. Under the condition that a coherent light source is not needed, differential and integral processing of the image can be achieved in the terahertz frequency band, the performance is high, the structure is simple, and wide application prospects are achieved in the fields of terahertz image processing, optical simulation calculation and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of calculus image processing, and particularly relates to a terahertz polarization multiplexing metasurface calculus filter, an image processing method and device. BACKGROUND

[0002] Image processing plays a key role in diversified applications such as machine learning, autonomous driving, machine vision and microscopic imaging. The advent of the big data era has brought great challenges to high-speed and efficient image processing, and the current field still mainly relies on electronic computing. Although digital image processing has high flexibility, it is limited by the necessary analog-to-digital converter, and has limitations in speed, power consumption and complexity. These defects are particularly prominent when studying non-repetitive and rare phenomena such as nonlinear dynamics. The use of optical analog image processing technology can break through the above limitations, as its inherent parallelism can achieve high-speed operation and low power consumption. Optical analog image processing based on Fourier optics principles has made significant progress. However, traditional optical devices have defects such as difficulty in integration, large size and limited functionality.

[0003] A metasurface is a kind of artificial subwavelength material with advantages such as small size, easy integration and diverse functions, providing a new platform for optical analog image processing. So far, optical analog image processing has mainly developed two strategies. One of the typical methods is to design a time and space modulation metasurface based on the Green function, which can directly achieve the required spatial differentiation. Although this kind of processor has the advantage of compactness, it is severely dependent on specific resonance conditions, requiring specific incident angles and working wavelengths, resulting in narrow working bandwidth and poor versatility. The other strategy is to replace the bulky filter elements in the 4f system with metasurfaces, and to achieve the required transfer function by controlling the complex amplitude transmittance thereof. Although lacking compactness, this architecture provides higher flexibility for diversified operations.

[0004] Although significant progress has been made in the emerging paradigm of optical analog processors in recent years, most optical analog image processors still have two obvious limitations: their working range is mainly limited to the visible light band and its extended band, and they can usually only perform a single image processing task. Terahertz waves occupy the frequency band between infrared and microwaves, and have great potential in the fields of biosensing, nondestructive testing and imaging. Parallel multi-task processing is crucial for accelerating the computing process and improving energy efficiency, and its performance far exceeds that of electronic devices. However, this feature has not been fully developed in optical analog processors. Although parallel time-domain differentiation of multiple signals has been achieved at different carrier frequencies, there are still few examples of simultaneous processing of different operations for image processing. SUMMARY

[0005] In view of the above problems, the present application provides a terahertz polarization multiplexing metasurface calculus filter, an image processing method and device.

[0006] The application provides a terahertz polarization multiplexing super surface micro integral filter, which is composed of a structure unit array formed by two-dimensional period extension of a micron-level structure unit; the structure unit array is referred to as a terahertz polarization multiplexing super surface; wherein the structure unit is a single-layer metal material structure; a through rectangular hole is designed at a central part of the single-layer metal material structure; the length and width of the structure unit are denoted as T x , T y , T y =T x , also referred to as a period; the thickness of the single-layer metal material structure is denoted as H; the length and width of the rectangular hole at the central part are denoted as L x , L y ; the height of the rectangular hole is denoted as L z , L z =H; the rotation angle of the rectangular hole is denoted as θ; the rotation angle is defined as the angle of rotation between the length direction of the rectangular hole structure and the x direction in a counterclockwise direction; these parameters are all parameters that are optimized according to needs.

[0007] In the application, the structure unit is optimized according to the following method: an electromagnetic simulation method is used to make linearly polarized light sources normally incident on the structure unit of the terahertz polarization multiplexing super surface at a fixed working frequency; through structure parameter scanning, the same polarization transmission coefficient of the linearly polarized light source is maximized and the cross-polarization transmission coefficient is close to 0, and at the same time, the same polarization and cross-polarization transmission coefficients of another polarization are both close to 0, which is considered to be the optimal structure.

[0008] Preferably, in the structure unit, the thickness of the single-layer metal material structure is 100 μm, and the working frequency point is selected as 0.7 THz; the metal material is selected as molybdenum.

[0009] Preferably, in the rectangular hole structure, the length L x is 215 μm, the width L y is 50 μm, the period T y =T x of the structure unit is 250 μm, and the rotation angle θ is 0 or π / 2.

[0010] The polarization multiplexing in the terahertz polarization multiplexing super surface micro integral filter refers to that the structure unit with two different rotation angles θ is contained in the super surface array, and the units are arranged so that the super surface exhibits different coherent transfer functions for two orthogonal linearly polarized lights, thereby respectively realizing the differential and integral processing functions of images. When the incident light is a first linearly polarized light, the whole super surface realizes high-pass filtering and differential operation; when the incident light is a second linearly polarized light orthogonal to the first linearly polarized light, the whole super surface realizes low-pass filtering and integral operation; the incident light is x or y polarized light.

[0011] In the present application, the arrangement of the structural units with two different rotation angles θ is as follows: taking the center of the metasurface as the center, it is divided into a circular region and an annular region surrounding the circular region; the rotation angle θ of all structural units in the circular region is set to 0 or π / 2, and the rotation angle θ of all structural units in the annular region is set to π / 2 or 0, that is, the rotation angle of the rectangular hole in the two regions always differs by π / 2.

[0012] The radius of the circular region is denoted as R1, and the outer diameter of the annular region is denoted as R2; the radius of the circular region and the outer diameter of the annular region are determined according to the aperture of the 4f optical system and the required image spatial frequency spectrum range.

[0013] According to another aspect of the present application, an image processing method based on a terahertz polarization multiplexing metasurface micro-integration filter is provided, which comprises placing a polarization multiplexing metasurface on a common focal plane of a 4f optical system, and applying a polarization-dependent coherent transfer function to the spatial spectrum of an input two-dimensional image; after passing through the second lens of the 4f system, performing Fourier transform on the modulated optical signal to finally obtain the differential and integral processing results of the input image.

[0014] According to another aspect of the present application, an image processing device based on a terahertz polarization multiplexing metasurface micro-integration filter is provided, which comprises a terahertz antenna 1, a mirror 2, a mask 3, a first lens 4, a terahertz polarization multiplexing metasurface micro-integration filter 5, a second lens 6, and a terahertz receiver 7.

[0015] Among them, the terahertz polarization multiplexing metasurface is placed on the spectral plane of the 4f system; the terahertz antenna 1 emits a terahertz spherical wave, which is converted into a terahertz plane wave after passing through the mirror 2, and then passes through the mask 3 to obtain a specific two-dimensional image on the object plane of the 4f optical system; the first lens 4 performs Fourier transform on the terahertz beam carrying two-dimensional image information; the terahertz polarization multiplexing metasurface micro-integration filter 5 is used to apply a polarization-dependent coherent transfer function to the spatial spectrum of the input two-dimensional image; the second lens 6 is used to perform Fourier transform on the modulated spectrum of the two-dimensional image, thereby obtaining the differential or integral processing results of the initial two-dimensional image on the image plane of the 4f system; the terahertz receiver 7 is used to obtain the processed image results;

[0016] The terahertz polarization multiplexing metasurface micro-integration filter applies a polarization-dependent coherent transfer function to the spatial spectrum of the input two-dimensional image, wherein the two coherent transfer functions are related to the complex amplitude pass rate of the polarization multiplexing metasurface, which is expressed by the formula:

[0017] The circular region function is defined as:

[0018]

[0019] Where (f x ,f y () represents the frequency domain coordinates, f c The cutoff frequency is determined by the radius R1 of the circular portion in the metasurface arrangement. The value f = 10cm is the focal length of the first and second lenses, and λ is the wavelength of the incident wave.

[0020] When the first linearly polarized light is incident, the correlation transfer function exerted by the metasurface on the input image spectrum is expressed as:

[0021] H1(f x ,f y )=1-cir(f x ,f y ,f c )

[0022] When the second linearly polarized light is incident, the correlation transfer function exerted by the metasurface on the input image spectrum is expressed as:

[0023] H2(f x ,f y ) = cir(f x ,f y ,f c )

[0024] Specifically, for a metasurface array arranged in the same configuration, when the first linearly polarized light is incident, its complex amplitude transmittance function in the frequency domain is as follows: With zero frequency as the center and radius f... c Within the circular region, there is a low transmittance close to 0. Outside the circular region, in the annular region, there is high and uniform transmittance. When the second linearly polarized light is incident, its complex amplitude transmittance function behaves in the opposite frequency domain to that of the first polarized light: within a radius of f centered at zero frequency... c Within the circular region, there is a uniformly high transmittance. However, within the annular region outside the circular region, there is a transmittance close to zero.

[0025] The beneficial technical effects of this invention are:

[0026] This invention proposes a terahertz polarization-multiplexed metasurface calculus and integrator filter, along with an image processing method and apparatus. For the first time, it achieves parallel processing of image differentiation and integration in the terahertz frequency band. By placing the terahertz polarization-multiplexed metasurface on the common focal plane of a 4f system and applying a polarization-dependent coherent transfer function to modulate the spatial spectrum of the input image, it can simultaneously output differentiation and integration results, significantly improving the parallel processing capability and computational efficiency of optical simulation calculations. The designed metasurface can stably perform image differentiation and integration processing in the terahertz frequency band, achieving efficient computation without relying on a coherent light source. The system exhibits strong robustness and a wider range of applications. Compared to traditional optical differentiation systems, this invention utilizes a metasurface to achieve functional integration and system simplification, reducing system complexity and providing greater flexibility for diverse operations. This scheme provides an innovative optical simulation computing platform for terahertz image processing, such as non-destructive testing, and has significant application value and broad development prospects in fields such as biomedical imaging, industrial inspection, and computer vision. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structural unit of the terahertz polarization multiplexing metasurface calculus filter provided by the present invention.

[0028] Figure 2 This is a schematic diagram of the array arrangement of the terahertz polarization multiplexing metasurface calculus filter according to an embodiment of the present invention.

[0029] Figure 3 These are physical images of three different sizes of metasurfaces manufactured using laser cutting technology in embodiments of the present invention.

[0030] Figure 4 This is a flowchart of an image processing method based on a terahertz polarization multiplexing metasurface integral calculus filter, as described in an embodiment of the present invention.

[0031] Figure 5 This is a schematic diagram of the structure of an image processing device based on a terahertz polarization multiplexing metasurface integral calculus filter, as described in an embodiment of the present invention.

[0032] Figure 6 The diagram shows the differential and integral simulation results when the original input light field carries a quadrilateral shape and x and y linearly polarized light is incident on three polarization multiplexing metasurfaces with different size configurations, namely R1 of 2.5 mm, 5 mm and 7.5 mm.

[0033] Figure 7 The diagram shows the differential and integral simulation results when the original input light field carries the information of a hexagonal star and x and y linearly polarized light is incident on three polarization multiplexing metasurfaces with different sizes, namely R1 of 2.5 mm, 5 mm and 7.5 mm.

[0034] Figure 8 The diagram shows the differential and integral experimental results of the terahertz receiver when the original input light field carries information that is quadrilateral and three different sizes of polarization multiplexing metasurfaces with R1 of 2.5 mm, 5 mm and 7.5 mm are placed on the common focal plane of the 4f system.

[0035] Figure 9 The diagram shows the differential and integral experimental results of the terahertz receiver when the original input light field carries a hexagonal star and three different polarization multiplexing metasurfaces with R1 of 2.5 mm, 5 mm and 7.5 mm are placed on the common focal plane of the 4f system. Detailed Implementation

[0036] The present invention will be described in detail below with reference to the embodiments and accompanying drawings. It should be understood that the following embodiments are merely to enable those skilled in the art to better understand and implement the present invention, and are not intended to limit the scope of the present invention in any way.

[0037] The first embodiment of the present invention proposes a terahertz polarization multiplexing metasurface integral-time filter, which is a structural unit array composed of micron-level structural units extended in two-dimensional periodicity.

[0038] Specifically, Figure 1 A schematic diagram of a single structural unit is given, wherein the period of the structural unit is equal in the x and y directions, i.e., T. x =T y =250μm. A through rectangular hole is provided at the center of the metal structure. The length L of this rectangular hole is... x It is 215μm in diameter and has a width of L. y It is 50μm in diameter and has a height of L. z The thickness H of the metal layer is equal to 100 μm. The rotation angle of the rectangular hole is defined as the angle of counterclockwise rotation between the length direction and the x-direction of the rectangular hole structure, which is taken as 0 or π / 2 here; the operating frequency is 0.7 THz; and molybdenum is selected as the metal material.

[0039] The structural unit parameter optimization method described herein is explained in detail here.

[0040] We selected the operating frequency band as 0.7 THz. In the electromagnetic simulation software, we established a system as follows: Figure 1 The structural unit model is shown. Unit cell boundary conditions are set in the x and y directions, and open (add space) boundary conditions are set in the z direction. Linearly polarized light is used as a terahertz source and is incident perpendicularly on the structural unit.

[0041] The length L of the rectangular aperture is scanned within its suitable subwavelength range. x and width L y When the incident light polarization direction is orthogonal to the length direction of the rectangular aperture, the same-polarization transmission coefficient in that polarization direction is maximized. Simultaneously, the transmission coefficients of other polarization components are ensured to be close to zero. Based on this objective, the optimal solution is determined: through scanning, a set of optimal parameters was found: L x =215μm, L y =50μm. Under these parameters, for structural units with θ=0, when y-polarized light is incident, the same-polarization transmission coefficient reaches its peak at 0.7THz, exceeding 0.9, while the cross-polarization transmission coefficient is close to 0. For structural units with θ=π / 2, when y-polarized light is incident, both the same-polarization and cross-polarization coefficients are close to 0 at this frequency, which satisfies the polarization multiplexing function requirements.

[0042] Specifically, the polarization multiplexing described in this invention is achieved by arranging structural units with two different rotation angles θ on a metasurface in a specific manner. For example... Figure 2 As shown, a circular region and an annular region surrounding the center of the metasurface are defined. In this embodiment, the rotation angle θ of all structural units within the circular region is set to 0, while the rotation angle θ of all structural units within the annular region is set to π / 2. It is understood that these angle settings can be interchanged; that is, π / 2 for the circular region and 0 for the annular region, as long as the orientation of the rectangular holes in the two regions always differs by π / 2.

[0043] The radius R1 of the circular region and the outer diameter R2 of the annular region need to be specifically determined based on the numerical aperture of the 4f optical system used and the spatial spectral range of the image to be processed, in order to ensure effective coverage of the required spectral components.

[0044] Figure 3 These are images of three different metasurfaces with varying sizes, made from laser-cut molybdenum sheets. The outer diameter R2 of the annular region on all three metasurfaces is 25 mm, while the radii R1 of the circular regions are different, at 2.5 mm, 5 mm, and 7.5 mm respectively.

[0045] The working principle of this differential-integral filter is as follows: when placed on the spectral plane of a 4f system, it exhibits different coherent transfer functions under two orthogonal linear polarization incident conditions. Specifically, for a metasurface with a central circular structural unit rotation angle of 0° and an annular structural unit rotation angle of π / 2°, when the incident light is x-polarized, the metasurface acts as a high-pass filter, performing differentiation on the spatial spectrum of the input image; when the incident light is y-polarized, the metasurface acts as a low-pass filter, performing integration on the spatial spectrum of the input image. Therefore, by simply changing the polarization state of the input light or rotating the metasurface by 90 degrees, polarization multiplexing on a single metasurface can simultaneously achieve differentiation and integration of the input image.

[0046] The second embodiment of this invention proposes an image processing method based on a terahertz polarization multiplexing metasurface calculus-integral filter, such as... Figure 4 As shown. The method includes placing a polarization multiplexing metasurface on the common focal plane of a 4f optical system, applying a polarization-dependent coherent transfer function to the spatial spectrum of the input two-dimensional image to modulate the spectrum of the two-dimensional image; after passing through the second lens of the 4f system, performing a Fourier transform on the modulated optical signal to obtain the differential and integral processing results of the input image.

[0047] In a third embodiment of the present invention, an image processing device based on a terahertz polarization multiplexing metasurface calculus-integral filter is proposed, such as... Figure 5 The system includes a terahertz antenna 1, a parabolic mirror 2, a mask 3, a first lens 4, a terahertz polarization multiplexing metasurface calculus filter 5, a second lens 6, and a terahertz receiver 7. The terahertz polarization multiplexing metasurface 5 is placed on the spectral plane of the 4f system. The terahertz antenna 1 emits a terahertz spherical wave, which is converted into a terahertz plane wave after passing through the parabolic mirror 2, and then passes through the mask 3 to obtain a specific two-dimensional image on the object plane of the 4f optical system. The first lens 4 performs a Fourier transform on the terahertz beam carrying the two-dimensional image information. The terahertz polarization multiplexing metasurface 5 is used to apply a polarization-dependent coherent transfer function to the spatial spectrum of the input two-dimensional image. The second lens 6 is used to perform a Fourier transform on the modulated spectrum of the two-dimensional image to obtain the differential or integral processing result of the initial two-dimensional image on the image plane of the 4f system. The terahertz receiver 7 is used to acquire the processed image result.

[0048] The terahertz polarization-multiplexed metasurface calculus filter described in the second and third embodiments of the present invention applies a polarization-dependent coherent transfer function to the spatial spectrum of the input two-dimensional image. The two coherent transfer functions are related to the complex amplitude transmittance of the polarization-multiplexed metasurface. For a metasurface with a central circular structural unit rotation angle of 0 and an annular structural unit rotation angle of π / 2, the polarization-dependent transfer function is expressed by the following formula:

[0049] The circular region function is defined as follows:

[0050]

[0051] Where (f x ,f y () represents the frequency domain coordinates, f c The cutoff frequency is determined by the radius R1 of the circular portion in the metasurface arrangement. The value f = 10cm is the focal length of the first and second lenses, and λ is the wavelength of the incident wave.

[0052] When x-polarized light is incident, the correlation transfer function exerted by the metasurface on the input image spectrum is expressed as:

[0053] H1(f x ,f y )=1-cir(f x ,f y ,f c )

[0054] When y-polarized light is incident, the correlation transfer function exerted by the metasurface on the input image spectrum is expressed as:

[0055] H2(f x ,f y ) = cir(f x ,f y ,f c )

[0056] Specifically, for a metasurface array arranged in the same configuration, when x-polarized light is incident, its complex amplitude transmittance function in the frequency domain is as follows: With zero frequency as the center and radius f... c Within the circular region, there is a low transmittance close to 0. Outside the circular region, in the annular region, there is high and uniform transmittance. When y-polarized light is incident, its complex amplitude transmittance function behaves in the opposite frequency domain to that of the first polarized light: within a radius of f centered at zero frequency... c Within the circular region, it exhibits uniformly high transmittance. However, within the annular region outside the circular region, it has transmittance close to zero. Based on this, the metasurface can simultaneously perform differentiation and integration processing on the input image under different polarized light incidence conditions.

[0057] The technical effects of the present invention were further verified through simulation.

[0058] Figure 6 , 7Using a metasurface with a central circular structural unit rotation angle of 0 and a ring-shaped structural unit rotation angle of π / 2, and taking the original input light field carrying information in the form of a quadrilateral and a hexagon as examples, simulations were performed at 0.7 THz on three different polarization-multiplexed metasurfaces with R1 configurations of 2.5 mm, 5 mm, and 7.5 mm. Figure 6 , 7 (a) represents the original input optical field of the terahertz polarization multiplexing metasurface. For example... Figure 6 , 7 As shown in (b), (d), and (f), when x-polarized light is incident, the original input image undergoes differential processing. In this case, the terahertz polarization multiplexing metasurface acts as a high-pass filter. As R1 increases, the cutoff frequency in the frequency domain also increases, meaning only higher-frequency, sharper edge information can pass through. Therefore, as R1 increases, the differentiated edges gradually become thinner and sharper. When y-polarized light is incident, the original input image undergoes integral processing. In this case, the metasurface acts as a low-pass filter. The previously blocked area for x-polarization becomes a light-passing area. Therefore, as R1 increases, the cutoff frequency in the frequency domain also increases. The highest frequency allowed by the low-pass filter becomes higher, and more high-frequency details are preserved. Figure 6 , 7 As can be seen from (c), (e), and (g), the image result after integral processing also changes from blurry to relatively clear.

[0059] The technical effects of the present invention were further verified through experiments.

[0060] Figure 8 , 9 Based on the device proposed in this invention, the information carried by the original input light field is a quadrilateral or hexagonal star, and the rotation angle of the central circular structural unit of the metasurface is 0, while the rotation angle of the annular structural unit is π / 2. Then, when three polarization multiplexing metasurfaces with different sizes (R1 of 2.5 mm, 5 mm, and 7.5 mm) are placed on the common focal plane of the 4f system, the differential and integral experimental results detected by the terahertz receiver are shown in the figure. Figure 8 , 9 (a) represents the original input optical field of the terahertz polarization multiplexing metasurface. Figure 8 , 9 (b), (d), and (f) are the differential results of the input image under different sized metasurface configurations. Figure 8 , 9 (c), (e), and (g) represent the integral results of the input image obtained under different metasurface configurations of varying sizes. It can be seen that the device based on a terahertz polarization-multiplexed metasurface differential-integral filter can simultaneously perform differentiation and integration processing on the original input image under different linear polarizations, and the experimental results are consistent with…Figure 6 , 7 The simulation results are basically consistent.

Claims

1. A terahertz polarization multiplexed metasurface calculus filter, characterized in that, The structure unit array is composed of microstructure units through two-dimensional periodic extension; the structure unit array is called a terahertz polarization multiplexing super surface; wherein the structure unit is a single-layer metal material structure; the center part of the metal material single-layer structure is designed with a through rectangular hole; the length and width of the structure unit are denoted as T x , T y , T y =T x , also called period; the thickness of the single-layer metal material structure is denoted as H, the length and width of the rectangular hole in the middle part are denoted as L x , L y , the height of the rectangular hole is denoted as L z =H, and the rotation angle of the rectangular hole is denoted as θ, wherein the rotation angle is defined as the angle of the length direction of the rectangular hole structure and the x direction in counterclockwise rotation; these parameters are all parameters that need to be optimized; Here, the polarization multiplexing refers to that the array contains structural units with two different rotation angles θ, and the units are arranged so that the metasurface exhibits different coherent transfer functions for two orthogonal linearly polarized lights, thereby respectively realizing differential and integral processing of images.

2. The terahertz polarization multiplexed metasurface calculus filter of claim 1, wherein, The structural units are optimized in parameters by the following method: using electromagnetic simulation method, a linearly polarized light source is normally incident on the structural units of the polarization multiplexing metasurface at a fixed operating frequency, and by scanning the structural parameters, the co-polarized transmission coefficient of the linearly polarized light is maximized and the cross-polarized transmission coefficient is close to 0, while the co-polarized and cross-polarized transmission coefficients of the other polarization are both close to 0, which is considered as the optimal structure.

3. The terahertz polarization multiplexed metasurface calculus filter of claim 1, wherein, In the structural units, the thickness of the single-layer metal material structure is H=100μm, and the operating frequency point is selected as 0.7THz; the metal material is selected as molybdenum.

4. The terahertz polarization multiplexed metasurface calculus filter of claim 1, wherein, The rectangular hole structure, length L x is 215 μm, width L y is 50 μm, the period T y of the structure unit x is 250 μm, and the rotation angle θ is 0, π / 2.

5. The terahertz polarization multiplexed metasurface calculus filter of claim 1, wherein, Specifically, when the incident wave is a first linearly polarized light, the metasurface as a whole realizes high-pass filtering and differential operation; when the incident light is a second linearly polarized light orthogonal to the first linearly polarized light, the metasurface as a whole realizes low-pass filtering and integral operation.

6. The terahertz polarization multiplexed metasurface calculus filter of claim 1 and 5, wherein, The incident linearly polarized light is x or y polarized light.

7. The terahertz polarization multiplexed metasurface calculus filter of claim 1 and 5, wherein, The arrangement of the structural units with two different rotation angles θ is that the center of the metasurface is taken as the center of a circle, and is divided into a circular region and an annular region surrounding the circular region; the rotation angle θ of all structural units in the circular region is set to 0 or π / 2, and the rotation angle θ of all structural units in the annular region is set to π / 2 or 0, that is, the rotation angles of the rectangular holes in the two regions always differ by π / 2.

8. The terahertz polarization multiplexed metasurface calculus filter device of claim 7, wherein, The radius of the circular region is denoted as R1, and the outer diameter of the annular region is denoted as R2; the radius of the circular region and the outer diameter of the annular region are determined according to the aperture of the 4f optical system and the required image spatial frequency spectrum range.

9. An image processing method based on terahertz polarization multiplexing metasurface calculus filter, characterized in that: The method comprises placing a terahertz polarization multiplexing metasurface on the common focal plane of a 4f optical system to impose a polarization-dependent coherent transfer function on the spatial spectrum of an input two-dimensional image; after the second lens of the 4f system, the modulated optical signal is subjected to Fourier transform, and finally the differential and integral processing results of the input image are obtained.

10. An image processing device based on terahertz polarization multiplexed metasurface calculus filter, characterized in that: The application relates to a 4f system for terahertz image processing, which comprises a terahertz antenna (1), a mirror (2), a mask (3), a first lens (4), a terahertz polarization multiplexing super surface micro integration filter (5), a second lens (6) and a terahertz receiver (7); wherein the polarization multiplexing super surface is arranged on the frequency spectrum plane of the 4f system; the terahertz antenna (1) emits a terahertz beam, the terahertz spherical wave is converted into a terahertz plane wave after passing through the mirror (2), and then the terahertz plane wave passes through the mask (3) to obtain a specific two-dimensional image related to the mask (3) on the object plane of the 4f optical system; the first lens (4) performs Fourier transform on the terahertz beam carrying the two-dimensional image information; the terahertz polarization multiplexing super surface micro integration filter (5) is used for applying a polarization-dependent coherent transfer function to the spatial spectrum of the input two-dimensional image; the second lens (6) is used for performing Fourier transform on the frequency spectrum of the two-dimensional image after modulation, so that the differential or integral processing result of the initial two-dimensional image is obtained on the image plane of the 4f system; and the terahertz receiver (7) is used for obtaining the processed image result.

11. The image processing method and apparatus based on terahertz polarization multiplexing metasurface filter according to claims 9 and 10, characterized in that, The terahertz polarization multiplexing super surface applies a polarization-dependent coherent transfer function to the spatial spectrum of the input two-dimensional image, and the two kinds of coherent transfer functions are related to the complex amplitude pass rate of the polarization multiplexing super surface, which is expressed by a formula as follows: The circular area function is defined as: where (f x ,f y ) is the frequency domain coordinate, f c is the cutoff frequency, which is determined by the radius R1 of the circular part in the super surface arrangement, The f = 10 cm is the focal length of the first and second lenses, and the λ is the wavelength of the incident wave. When the first linearly polarized light is incident, the related transfer function applied by the super surface to the input image spectrum is expressed as: H1(f x ,f y ) = 1 - cir(f x ,f y ,f c ) When the second linearly polarized light is incident, the related transfer function applied by the super surface to the input image spectrum is expressed as: H2(f x ,f y ) = cir(f x ,f y ,f c ) Specifically, for the same arrangement of the metasurface array, when the first linearly polarized light is incident, the complex amplitude transmission function of the metasurface array in the frequency domain is as follows: in the circular region with a radius of f c centered at zero frequency, it has a low transmission close to 0. In the annular region outside the circular region, it has a high and uniform transmission; and when the second linearly polarized light is incident, the complex amplitude transmission function of the metasurface array in the frequency domain is opposite to that of the first polarized light: in the circular region with a radius of f c centered at zero frequency, it has a uniform high transmission. In the annular region outside the circular region, it has a transmission close to 0.

Images