A metasurface device design method for image enhancement and an imaging system thereof

Abstract

The application discloses a kind of super surface device design method for image enhancement and its imaging system, the method comprises: numerical simulation calculation is carried out based on initial complex amplitude distribution function, the complex amplitude distribution function indicating the optical response of super surface device at different positions is obtained;Super surface device includes a plurality of target nano units embedded in different positions of preset substrate;Initial complex amplitude distribution function is obtained based on inverse fourier transform result of Laplacian operator and Gaussian operator;According to preset database and complex amplitude distribution function, the structure parameters of the plurality of target nano units of super surface device at different positions of preset substrate are determined;According to the structure parameters of the plurality of target nano units of super surface device at different positions of preset substrate, the structure of super surface device is determined.The embodiment of the application can improve the imaging contrast and definition of imaging system under strong scattering environment conditions, and can be widely applied in nanostructure application field.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of nanostructure applications, and particularly to a metasurface device design method for image enhancement and an imaging system thereof. BACKGROUND

[0002] Optical imaging technology relies on the characteristics of light and photons to obtain accurate information of a target object. In a traditional incoherent imaging system, imaging is regarded as a linear process, in which the system utilizes ballistic photons to create a direct image of the target. These photons follow a straight path and do not experience deflection when passing through a medium, thereby ensuring clear imaging of the target object. However, in biological tissues, fog, haze, and turbid water, photons can experience multiple scattering due to collisions with particles or absorption by the medium during propagation. These multiple-scattered photons are referred to as scattered photons, which are generally regarded as interference factors in the imaging process, masking the information carried by the ballistic photons, resulting in a decrease in image contrast. Therefore, image enhancement for the scattering imaging process is very important.

[0003] In the prior art, image enhancement for the scattering imaging process is mainly achieved through post-processing algorithms, such as digital image post-processing algorithms, image enhancement methods based on physical models or neural networks, etc. However, in the face of a strong scattering environment, ballistic photons are overwhelmed by the background generated by scattered photons, so that any post-processing technology cannot recover useful information, resulting in a significant decrease in imaging contrast and clarity of the imaging system. SUMMARY

[0004] Therefore, to solve one of the above problems, the purpose of an embodiment of the present application is to provide a metasurface device design method for image enhancement and an imaging system thereof, which can improve the imaging contrast and clarity of the imaging system under strong scattering environmental conditions.

[0005] In one aspect, an embodiment of the present application provides a metasurface device design method for image enhancement, comprising:

[0006] performing numerical simulation calculation based on an initial complex amplitude distribution function to obtain a complex amplitude distribution function; the complex amplitude distribution function indicates optical responses of a metasurface device at different positions; the metasurface device comprises a preset substrate and a plurality of target nano units embedded at different positions of the preset substrate; the initial complex amplitude distribution function is obtained based on inverse Fourier transform results of a Laplace operator and a Gaussian operator;

[0007] performing matching according to a preset database and the complex amplitude distribution function to determine structure parameters of the plurality of target nano units of the metasurface device at different positions of the preset substrate; the preset database comprises structure parameters of each nano unit in a preset nano unit set and optical responses of the nano unit under incidence of a preset wavelength light source.

[0008] According to the structure parameters of the target nano units at different positions of the preset substrate, the structure of the metasurface device is determined.

[0009] Specifically, the numerical simulation calculation based on the initial complex amplitude distribution function to obtain the complex amplitude distribution function comprises:

[0010] Obtain a point spread function of an imaging system in the presence of a scattering medium;

[0011] According to a numerical calculation method, the initial complex amplitude distribution function is used to modulate the point spread function to obtain a modulated point spread function;

[0012] Determine the relationship between the contrast of the modulated point spread function and a preset threshold, and adjust the parameters of the initial complex amplitude distribution function according to the result until the contrast of the modulated point spread function meets the requirements, and determine the complex amplitude distribution function according to the adjusted initial complex amplitude distribution function.

[0013] Specifically, the optical response includes phase response and amplitude response; the preset database is constructed by the following method:

[0014] Obtain a preset set of nano units and determine the structure parameters of each nano unit in the preset set of nano units;

[0015] Calculate the phase response and amplitude response of each nano unit in the preset set of nano units under the incidence of a preset wavelength light source, and form a preset database according to the calculation results.

[0016] Specifically, the calculation of the phase response and amplitude response of the nano units in the preset set of nano units under the incidence of a preset wavelength light source comprises:

[0017] Determine the total degrees of freedom of each nano unit in the preset set of nano units and a preset light wavelength;

[0018] According to the total degrees of freedom of each nano unit, determine the range of the degrees of freedom parameters, and discretize the range of the degrees of freedom parameters according to a preset interval;

[0019] According to the discretized range of the degrees of freedom parameters, the numerical simulation method is used to simulate scanning of each degree of freedom parameter of each nano unit to determine the phase response and amplitude response of the nano unit to the preset light wavelength.

[0020] Specifically, the structure parameters include geometric dimensions; the structure parameters of the target nano units of the metasurface device at each position of the preset substrate are determined by the following method:

[0021] determine the target amplitude response and the target phase response of the metasurface device at the corresponding position on the preset substrate according to the complex amplitude distribution function;

[0022] the amplitude response of each nanocell in the preset nanocell set under the preset wavelength light source is matched with the target amplitude response of the metasurface device at the corresponding position on the preset substrate, to obtain a plurality of nanocells satisfying the first matching requirement;

[0023] the phase response of the plurality of nanocells satisfying the first matching requirement under the preset wavelength light source is matched with the target phase response of the metasurface device at the corresponding position on the preset substrate, to determine nanocells satisfying the second matching requirement;

[0024] the geometric size of the nanocell satisfying the second matching requirement is determined, and the geometric size of the target nanocell of the metasurface device at the corresponding position on the preset substrate is determined according to the geometric size of the nanocell satisfying the second matching requirement.

[0025] Specifically, the structure parameters further include an in-plane rotation angle; if there is no nanocell satisfying the second matching requirement, the structure parameters of the metasurface device at the corresponding position on the preset substrate are determined by the following method:

[0026] the in-plane rotation angle of the nanocell satisfying the first matching requirement is adjusted until the adjusted nanocell satisfies the second matching requirement, and the in-plane rotation angle of the adjusted nanocell is determined;

[0027] the geometric size of the nanocell satisfying the second matching requirement is determined, and the geometric size of the target nanocell of the metasurface device at the corresponding position on the preset substrate is determined according to the geometric size of the nanocell satisfying the second matching requirement.

[0028] the in-plane rotation angle of the nanocell satisfying the second matching requirement is determined, and the in-plane rotation angle of the target nanocell of the metasurface device at the corresponding position on the preset substrate is determined according to the in-plane rotation angle of the nanocell satisfying the second matching requirement.

[0029] On the other hand, the embodiment of the present application also provides an imaging system for image enhancement, comprising:

[0030] an imaging device;

[0031] a metasurface device obtained according to the method described above; the metasurface device is arranged on the Fourier plane of the imaging device.

[0032] Optionally, a plurality of target nanocells in the metasurface device are elliptical cylinders with the same short axis length and different long axis lengths.

[0033] Optionally, the target nanocell in the metasurface device includes a target nanocell embedded in the cured electron beam photoresist.

[0034] Optionally, the material of the target nano-unit is optical glass or optical film.

[0035] Implementing the embodiments of the present application includes the following beneficial effects:

[0036] The embodiment provides a metasurface device design method for image enhancement and an imaging system thereof; the method of the present application obtains a complex amplitude distribution function indicating the optical response of a metasurface at different positions through numerical simulation calculation based on an initial complex amplitude distribution function; then, the complex amplitude distribution function is matched with a preset database to determine the nano-unit structure parameters of the target nano-unit of the corresponding metasurface device at different positions, so as to determine the structure of the metasurface device; wherein the initial complex amplitude distribution function is determined according to the inverse Fourier transform results of the Laplace operator and the Gaussian operator; the metasurface corresponding to the metasurface complex amplitude distribution function obtained based on the initial complex amplitude distribution function can reduce the background light and high-frequency noise of the point spread function output by the imaging system through the full-optical convolution operation of the Laplace operator and the Gaussian operator under strong scattering environment conditions, thereby improving the imaging contrast and clarity of the imaging system under strong scattering environment conditions. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is a step flowchart of a metasurface device design method for image enhancement provided by the embodiment of the present application;

[0038] Figure 2 is a schematic diagram of a complex amplitude distribution function provided by the embodiment of the present application;

[0039] Figure 3 is a schematic diagram of the total degrees of freedom of a nano-unit provided by the embodiment;

[0040] Figure 4 is a structural block diagram of an imaging system provided by the embodiment of the present application;

[0041] Figure 5 is a schematic diagram of the imaging effect of the metasurface device applied by the embodiment of the present application under a scattering environment. DETAILED DESCRIPTION

[0042] The present application will be further described in detail below in combination with the drawings and specific embodiments. For the step numbers in the following embodiments, only the setting is for the convenience of description, and the order between the steps is not limited in any way, and the execution order of each step in the embodiment can be adaptively adjusted according to the understanding of those skilled in the art.

[0043] The following explains several terms involved in the present application:

[0044] Metasurface: As a two-dimensional array of subwavelength nanostructures, metasurfaces have shown great potential in light field manipulation due to their high precision and multi-dimensional control. In the field of information technology, the modulation of light waves by metasurfaces can achieve information processing, optical computing, and image processing, which are traditionally dependent on computer and other electronic devices. Compared to electrical signal processing, photonic processing has the advantages of light speed and parallel processing, making it one of the most promising research directions for solving the problem of computing power in the rapid development of artificial intelligence.

[0045] Point spread function: For a given object point, ballistic photons form an ideal impulse response on the imaging plane.

[0046] Fourier transform: A mathematical tool that converts signals or functions from the time domain (or spatial domain) to the frequency domain, revealing that any periodic or non-periodic signal can be decomposed into a superposition of sinusoidal waves (or complex exponential functions) of different frequencies. Through Fourier transform, we can analyze the frequency components, amplitudes, and phase information of signals, widely used in signal processing, image analysis, physics, engineering, and other fields, and is an indispensable analysis method in modern science and technology.

[0047] As shown in Figure 1 The present application provides a metasurface device design method for image enhancement, which includes the following steps.

[0048] S100: Numerical simulation calculation based on initial complex amplitude distribution function to obtain complex amplitude distribution function; the complex amplitude distribution function indicates the optical response of the metasurface device at different positions; the metasurface device includes a preset substrate and a plurality of target nanometer units embedded in different positions of the preset substrate; the initial complex amplitude distribution function is obtained based on the inverse Fourier transform result of the Laplace operator and the Gaussian operator.

[0049] The complex amplitude distribution function obtained by numerical simulation calculation based on the initial complex amplitude distribution function composed of the Laplace operator and the Gaussian operator is used to design the metasurface device, which can effectively shape the point spread function when the scattering medium exists in the system.

[0050] S200: Matching according to the preset database and the complex amplitude distribution function to determine the structure parameters of the plurality of target nanometer units of the metasurface device at different positions of the preset substrate; the preset database includes the structure parameters of each nanometer unit in the preset nanometer unit set and its optical response under the incidence of the preset wavelength light source.

[0051] According to the matching of the nano-unit structure and its structure parameters in the preset database and the complex amplitude distribution function, the nano-unit capable of meeting the complex amplitude distribution function is determined, and finally the structure parameters of the target nano-unit at different positions of the super surface device on the preset substrate are determined according to the structure parameters of the nano-unit meeting the requirements.

[0052] S300: Determine the structure of the super surface device according to the structure parameters of the target nano-unit at different positions of the super surface device on the preset substrate.

[0053] According to the structure parameters of the target nano-unit at different positions of the super surface device on the preset substrate, the structure of the target nano-unit of the super surface device is confirmed one by one to determine the structure of the entire super surface device.

[0054] The method also includes a preparation method of a super surface device for image enhancement, comprising:

[0055] S400: Prepare a plurality of target nano-units on the preset substrate by a patterning arrangement method to complete the preparation of the super surface device for image enhancement.

[0056] On the preset substrate at different positions, a film layer with the thickness of the target nano-unit is prepared by etching, deposition and other methods.

[0057] Among them, the material of the target nano-unit can be selected according to the wavelength range of the incident light, including but not limited to silicon and titanium dioxide; the patterning preparation method of the nano-unit is one or more of electron beam direct writing, ultraviolet lithography and laser direct writing.

[0058] Specifically, in step S100, the process of obtaining the complex amplitude distribution function based on the initial complex amplitude distribution function includes:

[0059] S110: Obtain the point spread function of the imaging system in the presence of scattering medium.

[0060] The point spread function output by the imaging system when imaging in a strong scattering environment is obtained as the basis for subsequent numerical simulation calculation.

[0061] Among them, the imaging system provided in this embodiment is a single-lens imaging system with fixed focal length and 1 times magnification, and the point spread function of the single-lens imaging system in the presence of scattering medium is obtained as the data basis according to experimental measurement.

[0062] Further, when the object point is located at twice the focal length of the lens, if there is no scattering medium in the imaging link, the light emitted by the object point passes through the single-lens system without a metasurface, and an ideal impulse response is formed at the imaging plane, i.e., twice the focal length behind the lens. If there is a scattering medium in the link, the scattered light after scattering with the scattering particles will become the background light of the imaging plane, thereby affecting the imaging quality.

[0063] S120: According to the numerical calculation method, the point spread function is modulated by using the initial complex amplitude distribution function to obtain the modulated point spread function.

[0064] According to the numerical calculation method, the point spread function of the imaging system and the initial complex amplitude distribution function are convolved with the Laplace operator and the Gaussian operator to obtain the modulated point spread function. If there is no metasurface device on the Fourier plane of the lens, the imaging point spread function is only the Fourier transform of the system pupil function. If a functional device is added to the Fourier plane of the imaging system, the original imaging system point spread function in the frequency domain can be regulated and controlled.

[0065] In principle, the point spread function of the imaging system can be described by derivation, as shown in formula (1). Figure 4 If a point light source located on the object plane is considered, as shown in formula (2), the field distribution on the image plane can be represented as formula (3). l 1= 2f x o ,y o After the plane wave emitted by the point light source passes through the lens and the metasurface device on the back focal plane of the lens, it reaches the image plane with an image distance of 2. Under the paraxial approximation, according to the Fresnel diffraction principle, the field distribution on the image plane can be represented as formula (1). l = 2f

[0066] (1)

[0067] (2)

[0068] (3)

[0069] In the above formulas, Lambda is the working wavelength, represents the wave number, , , is the coordinate of the rectangular coordinate system on the lens plane, is the coordinate of the rectangular coordinate system on the plane where the metasurface device is located, f is the focal length, represents convolution operation, ​​​​Pupil function of the imaging system, is the initial complex amplitude distribution function.

[0070] If the Fourier plane of the lens has no super surface device, the imaging point spread function of the lens is only the Fourier transform of the pupil function of the system, so formula (1) shows that the super surface device can realize the convolution operation of the origin point spread function of the imaging system and the initial complex amplitude distribution function; formula (2) is the Fourier transform of the pupil function of the imaging system; formula (3) is the Fourier transform of the initial complex amplitude distribution function. The convolution kernel of the convolution operation is the initial complex amplitude distribution function plus the previous phase coefficient, and usually only the light intensity information is considered when considering the result of the imaging plane, so the phase coefficient can be ignored, so the modulated point function of the system can be expressed as the convolution operation result of the point spread function of the imaging system and the initial complex amplitude distribution function.

[0071] Because the main effect of scattering on imaging is to reduce the contrast of the image, the Laplace operator can highlight the high-frequency detail information of the image, so as to improve the imaging contrast, at the same time, the Gaussian operator can effectively suppress the noise brought by scattering, and the initial complex amplitude distribution function, is obtained according to the inverse Fourier transform of the Laplace operator and the Gaussian operator, and the specific derivation is as follows:

[0072] (4)

[0073] Formula (4) shows that the initial complex amplitude distribution function is obtained according to the inverse Fourier transform result of the Laplace operator and the Gaussian operator.

[0074] (5)

[0075] Formula (5) is the calculation process of the inverse Fourier transform of the Laplace operator.

[0076] (6)

[0077] Formula (6) is the calculation process of the inverse Fourier transform of the Gaussian operator.

[0078] Substitute the variable x = x F R, y = y F / R , and the initial complex amplitude distribution function is obtained:

[0079] (7)

[0080] Formula (7) is the derivation result of the initial complex amplitude distribution function, wherein SigmaDifferent values are taken, R is the radius of the super surface image processing device, and the embodiment of the application is set to 0.5 millimeters.

[0081] S130: judging the contrast of the modulated point spread function and the preset threshold, adjusting the parameters of the initial complex amplitude distribution function according to the result of the judgment, until the contrast of the modulated point spread function meets the requirements, and determining the complex amplitude distribution function according to the adjusted initial complex amplitude distribution function.

[0082] The contrast of the point spread function is defined as an index for judging whether the system can image with high quality, and the parameters of the initial complex amplitude distribution function are adjusted to make the contrast of the modulated point spread function meet the index requirements, so as to determine the parameter values of the initial complex amplitude distribution function. Finally, the adjusted initial complex amplitude distribution function is the super surface complex amplitude distribution function.

[0083] Optionally, the contrast of the point spread function and the transmittance of the super surface device designed according to the initial complex amplitude distribution function can also be comprehensively evaluated as a comprehensive evaluation index to determine the parameter values of the initial complex amplitude distribution function.

[0084] Specifically, as shown in Figure 2 FIG. 1 is a schematic diagram of a complex amplitude distribution function constructed by an embodiment of the method, wherein the left vertical axis indicates the normalized amplitude distribution (target amplitude) of the super surface device corresponding to the complex amplitude distribution function at different plane positions, the right vertical axis indicates the phase response (target phase) of the super surface device corresponding to the complex amplitude distribution function at different plane positions, and the horizontal axis indicates the plane position of the super surface device corresponding to the complex amplitude distribution function.

[0085] Specifically, the optical response includes the phase response and the amplitude response; the preset database in step S200 is constructed by the following method:

[0086] S210: obtaining a preset set of nano units and determining the structure parameters of each nano unit in the preset set of nano units.

[0087] The structure parameters of each nano unit in the preset set of nano units are determined as the data basis for subsequent database construction.

[0088] S220: calculating the phase response and the amplitude response of each nano unit in the preset set of nano units under the incidence of a preset wavelength light source, and forming a preset database according to the calculation results.

[0089] The phase response and the amplitude response of each nano unit in the preset set of nano units under the incidence of a preset wavelength light source are calculated, and the purpose is to match the target phase and the target amplitude of the super surface period indicated by the complex amplitude distribution function; the preset database is constructed according to the calculation results.

[0090] Specifically, in step S220, the process of calculating the phase response and amplitude response of the nanocell in the preset nanocell set under the incidence of the preset wavelength light source includes:

[0091] S221: determining the total degrees of freedom of each nanocell in the preset nanocell set and the preset light wavelength.

[0092] The total degrees of freedom of each nanocell structure and the preset light wavelength are determined as a data basis.

[0093] As shown in the total degrees of freedom of the nanocell provided by the embodiment. Figure 3 As shown in the total degrees of freedom of the nanocell provided by the embodiment. The nanocell includes a base and a structure embedded in the HSQ, and each degree of freedom includes the period U of the unit, the height H of the structure, the long axis length L x and the in-plane rotation angle Theta , and the short axis length of the ellipse is L y , which is fixed at 80 nanometers in the embodiment of the application.

[0094] Optionally, the material of the nanocell structure can be c-Si, and the material of the base can be SiO2.

[0095] Optionally, the preset light wavelength in the embodiment of the application is 633 nanometers. If a different design wavelength is selected, the design process remains unchanged, and the same idea can be used to redesign.

[0096] S222: determining the degree of freedom parameter range according to the total degrees of freedom of each nanocell, and discretizing the degree of freedom parameter range according to a preset interval.

[0097] Specifically, for the degrees of freedom such as the period, height, and geometric parameters of the structure of the nanocell, a reasonable parameter range can be determined according to actual needs, and the parameter range is discretized according to a certain interval, which is used for scanning the structural optical response of each parameter.

[0098] S223: according to the discretized degree of freedom parameter range, the numerical simulation method is used to simulate and scan each degree of freedom parameter of each nanocell, to determine the phase response and amplitude response of each degree of freedom parameter of the nanocell to the preset light wavelength.

[0099] According to the numerical simulation method, the degrees of freedom parameters of each nanocell are simulated and calculated to determine the phase response and amplitude response of each nanocell structure to the preset light wavelength.

[0100] The numerical simulation includes but is not limited to the finite difference time domain method, the finite element difference method, the coupled wave analysis method, etc.

[0101] Specifically, the structural parameters include geometric dimensions; the structural parameters of the target nano unit of the metasurface device at each position on the preset substrate in step S200 are determined by the following method:

[0102] S231: According to the complex amplitude distribution function, the target amplitude response and the target phase response of the metasurface device at the corresponding position on the preset substrate are determined.

[0103] The complex amplitude distribution function indicates the optical response of the designed metasurface device at different positions on the preset substrate, wherein the optical response includes the target amplitude phase and the target phase amplitude.

[0104] S232: The amplitude response of each nano unit in the preset nano unit set under the incidence of the preset wavelength light source is matched with the target amplitude response of the metasurface device at the corresponding position on the preset substrate to obtain a plurality of nano units satisfying the first matching requirement.

[0105] According to the matching of the amplitude response of each nano unit in the preset nano unit set under the incidence of the preset wavelength light source and the target amplitude response of the metasurface device at the corresponding position on the preset substrate, the nano unit satisfying the target amplitude response is first determined.

[0106] Specifically, the target amplitude is determined according to the size of the metasurface image processing device and the target unit position, and is calculated by formula (7), wherein the device radius R is selected as 0.5 mm, the unit period U is selected as 260 nm, the target nano unit height H is selected as 400 nm, and the elliptical short axis length is fixed as 80 nm. Therefore, in the embodiment of the present application, the mapping relationship between the target nano unit elliptical long axis length and the amplitude is constructed, and specifically when the long axis length changes from 90 nm to 190 nm, the conversion efficiency will change from close to 0 to close to 100%. After normalizing the calculated amplitude distribution, the geometric dimensions of the target nano unit at each position can be mapped one by one according to the required amplitude value, i.e. the circularly polarized light conversion efficiency.

[0107] S233: The phase response of the plurality of nano units satisfying the first matching requirement under the incidence of the preset wavelength light source is matched with the target phase response of the metasurface device at the corresponding position on the preset substrate to determine the nano unit satisfying the second matching requirement.

[0108] The nano unit satisfying the target phase response is selected from the nano structural unit satisfying the target amplitude response, and is used as the finally determined target nano unit.

[0109] Specifically, according to the requirement of formula (7), the phase distribution is a constant, the nano unit matching the target phase response is selected as the final target nano unit structure.

[0110] S234: determining the geometric size of the target nano-unit at the corresponding position of the metasurface device on the preset substrate according to the geometric size of the nano-unit satisfying the second matching requirement.

[0111] According to the geometric size in the structure parameter of the nanostructure satisfying the complex amplitude distribution function, the structure parameter of the target nano-unit at different positions of the metasurface device designed according to the complex amplitude distribution function on the preset substrate is determined.

[0112] Specifically, the structure parameter further includes an in-plane rotation angle; in step S200, if there is no nano-unit satisfying the second matching requirement, the structure parameter of the metasurface device at the corresponding position on the preset substrate is determined by the following method:

[0113] S241: adjusting the in-plane rotation angle of the nano-unit satisfying the first matching requirement until the adjusted nano-unit satisfies the second matching requirement, and determining the in-plane rotation angle of the adjusted nano-unit.

[0114] On the basis of the nano-unit structure, rotating a specific angle can adjust the phase of the nano-unit structure, so that the phase response of the adjusted nano-unit structure is the same as the target phase response.

[0115] Among them, the requirement of formula (7) is that the phase distribution is a constant, and a specific angle can be rotated on the basis of each target nano-unit to keep the phase constant.

[0116] S242: determining the geometric size of the target nano-unit at the corresponding position of the metasurface device on the preset substrate according to the geometric size of the adjusted nano-unit; and determining the in-plane rotation angle of the target nano-unit at the corresponding position of the metasurface device on the preset substrate according to the in-plane rotation angle of the adjusted nano-unit.

[0117] According to the determined geometric size and in-plane rotation angle of the target nano-unit, the geometric size and in-plane rotation angle of the target nano-unit at the corresponding position of the metasurface device on the preset substrate are determined, and the structure parameter confirmation of the target nano-unit at different positions of the metasurface on the preset substrate is completed.

[0118] Wherein, the incident light beam used in the embodiment of the application is right circularly polarized light, and by using the geometric phase characteristics of the target nano-unit, the conversion efficiency of the outgoing left circularly polarized light can be controlled by adjusting the geometric size, so as to realize the change of the conversion efficiency from 0 to 100%. In addition, by adjusting the in-plane rotation angle of the target nano-unit alone, the phase response of the outgoing left circularly polarized light component can be controlled. It should be noted that the incident light can also be right circularly polarized light, and the corresponding outgoing light component is left circularly polarized light.

[0119] The implementation of the embodiment of the application includes the following beneficial effects:

[0120] In this embodiment, we design a metasurface image processing device to realize the all-optical operation of Laplacian operator and Gaussian operator to achieve the general influence of scattering medium on point spread function. Due to the suppression of background light by Laplacian operator and the processing of noise by Gaussian operator, the background light and high-frequency noise of point spread function are reduced, thereby improving the imaging contrast and clarity of the imaging system.

[0121] On the other hand, the embodiment of the present application also provides an imaging system for image enhancement, comprising:

[0122] An imaging device;

[0123] The metasurface device obtained by the above method embodiment; the metasurface device is arranged on the Fourier plane of the imaging device.

[0124] Specifically, as shown in the figure, Figure 4 The embodiment provides a metasurface imaging system for improving the imaging depth in a strong scattering environment, which comprises an imaging lens 1-1 and a metasurface device arranged on the back focal length f (i.e. Fourier plane) of the lens in sequence along the light propagation direction.

[0125] Optionally, the target nanometer units in the metasurface device are elliptical cylinders with the same short axis length and different long axis lengths.

[0126] The nanometer units in the system embodiment are elliptical cylinders with the same short axis length and different long axis lengths, which aims to construct the mapping relationship between the long axis length of the target nanometer unit and the amplitude, and keep the short axis length and other structural parameters of the target nanometer unit unchanged, i.e. the long axis length of the nanometer unit and the amplitude response of the nanometer unit after receiving the preset wavelength light source can be one-to-one corresponding, which is convenient for matching with the nanometer units in the preset nanometer unit library to determine the structural parameters of the target nanometer unit.

[0127] Optionally, the target nanometer units in the metasurface device include target nanometer units embedded in the cured electron beam photoresist.

[0128] As shown in the figure, Figure 4 The metasurface device comprises a two-dimensional structure array composed of a substrate and target nanometer units, wherein the two-dimensional structure array is composed of a glass substrate 1-2 and target nanometer units 1-4 embedded in an HSQ protective layer 1-3. Embedding the target nanometer units into the cured HSQ photoresist can better fix and protect the target nanometer units. In addition, the material of the substrate selected by the embodiment of the present application is glass material, which aims to carry the prepared target nanometer units, and can be replaced by any medium meeting the performance requirements.

[0129] Optionally, the material of the target nanometer unit is optical glass or optical film.

[0130] Specifically, the material of the nano unit includes an optical medium material, and considering the transmittance of the incident light of the final structure, therefore, a full medium structure can be adopted. The material of the target nano unit includes, but is not limited to, optical glass or optical film, the optical film includes, but is not limited to, titanium dioxide and the like, and the optical glass includes, but is not limited to, a semiconductor such as silicon.

[0131] For the embodiment of the system, the general influence of the scattering medium on the point spread function is considered, the super surface image processing device is added to the Fourier plane of the single lens imaging system, the Laplace operator and the Gaussian operator are implemented by full optical operation, due to the suppression of the background light by the Laplace operator and the processing of the noise by the Gaussian operator, the background light and the high frequency noise of the point spread function are reduced, and the imaging contrast and the definition of the imaging system are improved, the super surface device can be used for object imaging in a scattering environment, biological tissue imaging and other related application scenarios which need to improve the imaging quality. For example, Figure 5 As shown in the figure, Figure 5 The imaging effect of the super surface device in a scattering environment is shown, including the imaging results before and after using the super surface device and the results of image post-processing enhancement, wherein, Figure 5 Fig. (1) in the figure is the imaging result before using the super surface device, Figure 5 Fig. (2) in the figure is the imaging result after using the super surface device; Figure 5 Fig. (3) in the figure is the result of post-processing enhancement of the imaging result before using the super surface device, Figure 5 Fig. (4) in the figure is the result of post-processing enhancement of the imaging result after using the super surface device. When the imaging system images the microstructure of the fundus, the imaging effect is blurred due to tissue lesions and other conditions, in this case, the super surface device is added to the fundus imaging system, which can improve the imaging contrast and restore the image details.

[0132] Further, the core of the imaging system in the embodiment of the system to realize image enhancement is to combine the frequency domain filtering capability of the lens Fourier plane, to realize the image enhancement function by designing a control function (i.e. the complex amplitude distribution function in this paper) which can be applied in a strong scattering environment, and the super surface (nano unit) is one of the complex amplitude control methods selected in this embodiment, which can not be limited to selecting other devices such as spatial light modulator which can also control the complex amplitude of light to realize this function.

[0133] It can be seen that the contents in the method embodiment are applicable to the system embodiment, the system embodiment specifically realizes the same functions as the method embodiment, and achieves the same beneficial effects as the method embodiment.

[0134] In addition, the embodiment of the present application further discloses a computer program product or a computer program, which is stored in a computer readable storage medium. The processor of the computer device can read the computer program from the computer readable storage medium, and the processor executes the computer program, so that the computer device executes the method described above.

[0135] The embodiment of the present application further provides a computer readable storage medium, which stores a processor executable program. The processor executable program is used for implementing the method described above when being executed by a processor. Similarly, the contents in the method embodiment described above are applicable to the storage medium embodiment. The storage medium embodiment specifically implements the functions same as the method embodiment, and achieves the beneficial effects same as the method embodiment.

[0136] It can be understood that all or some steps in the method disclosed above, the system can be implemented as software, firmware, hardware and appropriate combination thereof. Some or all physical components can be implemented as software executed by a processor, such as a central processing unit, a digital signal processor or a microprocessor, or as hardware, or as an integrated circuit, such as an application specific integrated circuit. Such software can be distributed on a computer readable medium, which can include computer storage media (or non-transitory media) and communication media (or transitory media). As known by those skilled in the art, the term computer storage media includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tapes, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired information and can be accessed by a computer. In addition, as known by those skilled in the art, communication media generally includes computer readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism, and can include any information delivery medium.

[0137] The above is a specific description of the preferred embodiments of the present application, but the present application is not limited to the described embodiments. Those skilled in the art can make various equivalent modifications or replacements without departing from the spirit of the present application, and these equivalent modifications or replacements are all included in the scope defined by the claims of the present application.

Claims

1. A metasurface device design method for image enhancement, characterized in that, include: Numerical simulation calculations are performed based on the initial complex amplitude distribution function to obtain the complex amplitude distribution function; The complex amplitude distribution function indicates the optical response of the metasurface device at different locations; the metasurface device includes a preset substrate and several target nanounits embedded at different locations on the preset substrate; the initial complex amplitude distribution function is obtained based on the inverse Fourier transform results of the Laplace operator and the Gaussian operator; The structural parameters of several target nanounits at different locations on a preset substrate are determined by matching the preset database and the complex amplitude distribution function; the preset database includes the structural parameters of each nanounit in the preset nanounit set and their optical response under the incident light source of a preset wavelength. The structure of the metasurface device is determined based on the structural parameters of several target nanounits at different positions on a preset substrate. The numerical simulation calculation based on the initial complex amplitude distribution function yields the complex amplitude distribution function, including: Obtain the point spread function of the imaging system in the presence of a scattering medium; According to the numerical calculation method, the point spread function is modulated using the initial complex amplitude distribution function to obtain the modulated point spread function; Determine the relationship between the contrast of the modulated point spread function and a preset threshold. Adjust the parameters of the initial complex amplitude distribution function according to the determination result until the contrast of the modulated point spread function meets the requirements. Determine the complex amplitude distribution function based on the adjusted initial complex amplitude distribution function.

2. The method of claim 1, wherein, The optical response includes phase response and amplitude response; the preset database is constructed in the following manner: Obtain a preset set of nanounits and determine the structural parameters of each nanounit in the preset set of nanounits; The phase response and amplitude response of each nanounit in the preset nanounit set are calculated under the incident light source of a preset wavelength, and a preset database is formed based on the calculation results.

3. The method of claim 2, wherein, The calculation of the phase response and amplitude response of the nanounits in the preset nanounit set under the incident light source of a preset wavelength includes: Determine the total degrees of freedom of each nanounit in the preset nanounit set and the preset light wavelength; The range of degree-of-freedom parameters is determined based on the total degree of freedom of each nanounit, and the range of degree-of-freedom parameters is discretized at preset intervals; Based on the discretized range of degree-of-freedom parameters, numerical simulation is used to simulate and scan the degree-of-freedom parameters of each nanounit, and to determine the phase response and amplitude response of each nanounit to a preset wavelength of light.

4. The method of claim 2, wherein, The structural parameters include geometric dimensions; the structural parameters of the target nanounits at each location on the preset substrate for the metasurface device are determined in the following manner: Based on the complex amplitude distribution function, determine the target amplitude response and target phase response of the metasurface device at the corresponding position on the preset substrate; The amplitude response of each nanounit in the preset nanounit set under the incident light source of the preset wavelength is first matched with the target amplitude response of the metasurface device at the corresponding position of the preset substrate to obtain a number of nanounits that meet the first matching requirements. According to phase responses of a plurality of nano units satisfying the first matching requirement under incidence of a preset wavelength light source and target phase responses of the metasurface device at corresponding positions on a preset substrate, a nano unit satisfying a second matching requirement is determined; According to a geometric size of the nano unit satisfying the second matching requirement, a geometric size of a target nano unit at the corresponding position on the preset substrate of the metasurface device is determined.

5. The method of claim 4, wherein, The structural parameters further include an in-plane rotation angle; if there is no nano unit satisfying the second matching requirement, the structural parameters of the metasurface device at the corresponding position on the preset substrate are determined by the following method: Adjusting the in-plane rotation angle of the nano unit satisfying the first matching requirement until the adjusted nano unit satisfies the second matching requirement, and determining the in-plane rotation angle of the adjusted nano unit; According to the geometric size of the adjusted nano unit, the geometric size of the target nano unit at the corresponding position on the preset substrate of the metasurface device is determined; According to the in-plane rotation angle of the adjusted nano unit, the in-plane rotation angle of the target nano unit at the corresponding position on the preset substrate of the metasurface device is determined.

6. An imaging system for image enhancement, characterized by Comprise: An imaging device; The metasurface device obtained by the method according to any one of claims 1-5; the metasurface device is arranged on a Fourier plane of the imaging device.

7. The system of claim 6, wherein, A plurality of target nano units in the metasurface device are elliptic cylinders with the same minor axis length and different major axis lengths.

8. The system of claim 6, wherein, The target nano units in the metasurface device include target nano units embedded in cured electron beam photoresist.

9. The system of claim 6, wherein, The material of the target nano units includes optical glass or optical film. The material of the target nano units includes optical glass or optical film.

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