Superstructure surface capable of realizing multi-dimensional optical parametric multiplexing and various image processing functions and design method thereof

Abstract

The application discloses a superstructure capable of realizing multi-dimensional optical parametric multiplexing and multiple image processing functions and a design method thereof. The superstructure is jointly constituted by a fused quartz substrate and a silicon nano-brick structure. Through the joint regulation and control mechanism of geometric phase and transmission phase, four image processing functions of two-dimensional edge detection, horizontal edge detection, vertical edge detection and 45-degree edge detection of image information on the same device are realized by constructing a complex amplitude regulation structure supporting multiple wavelengths and multiple polarization state responses. The design is based on Fourier space filtering theory, a complex amplitude structure with a specific frequency domain transfer function is constructed, and the image processing performance is verified by 4F optical system calculation simulation. The application significantly improves the functional integration of the superstructure image processing system, and has good expansibility and compatibility.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of micro-nano optics, and more particularly relates to a super-structured surface capable of realizing multi-dimensional optical parameter multiplexing and multiple image processing functions and a design method thereof. BACKGROUND

[0002] In the information age with growing image data, optical image processing has attracted the attention of a large number of researchers due to its advantages of high efficiency, high throughput and low power consumption. At present, the research on optical image processing devices is mainly based on two methods: one is Fourier space filtering method, and the other is Green function method. Among them, the Fourier method has become the mainstream direction of research due to its wide application and mature theoretical system. The Fourier method uses a pair of lenses to realize the spatial frequency transformation of the original data, performs spatial spectrum filtering through a traditional pure phase or pure amplitude modulation mask, and reconstructs the processed data through inverse transformation. However, most traditional optical elements cannot realize the modulation of complex filter with amplitude and phase modulation at the same time, and the function is single. The development of super-structured surface (Metasurface) provides more possibilities for all-optical image processing. As a kind of planar artificial super material, super-structured surface has the characteristics of compact structure, easy integration and flexible control. Through the interaction between light and artificial microstructure, super-structured surface can flexibly control the frequency, amplitude, phase, polarization and other parameters of light at subwavelength scale, so as to realize various novel functions. Although super-structured surface for image processing has been widely studied, its multi-dimensional optical parameter multiplexing capability and function integration capability still need to be further explored. SUMMARY

[0003] In order to overcome the shortcomings of the prior art, the present application provides a super-structured surface capable of realizing multi-dimensional optical parameter multiplexing and multiple image processing functions and a design method thereof, so as to solve the problem of lack of multiple multiplexing functions in the prior art.

[0004] According to one aspect of the present application, a super-structured surface capable of realizing multi-dimensional optical parameter multiplexing and multiple image processing functions is provided, which is suitable for being integrated in the frequency spectrum plane of a 4F system and used for realizing multiple image processing functions under different incident light parameter states. The super-structured surface comprises a substrate layer and a micro-nano structure layer located above the substrate layer. The substrate layer is divided into a plurality of periodic unit structures with consistent size. The micro-nano structure layer comprises a plurality of nano pillars. Each unit structure and a nano pillar located on the working surface thereof constitute a nano pillar structure unit.

[0005] As a further technical solution, the length, width and period parameters of the nano pillars and the unit structures are designed so that the corresponding complex amplitude modulation effect is generated under the incidence of light with different wavelengths and different polarization states.

[0006] As a further technical solution, the super-structured surface is placed on the Fourier plane of the 4F system, and is used as a frequency domain filter to realize multiple processing functions of the input image.

[0007] As a further technical solution, the optical image to be processed is incident in a transmission manner, and by setting different incident wavelengths and polarization states, four image processing functions of two-dimensional edge detection, horizontal edge detection, vertical edge detection and 45-degree direction edge detection of the image are realized in the 4F system.

[0008] As a further technical solution, the super-structured surface adopts a joint coding strategy of geometric phase and transmission phase to realize multiplexing control in the wavelength and polarization two optical parameter dimensions.

[0009] As a further technical solution, the super-structured surface selects two groups of nanostructures with high polarization conversion efficiency at target wavelengths and low conversion efficiency at non-target wavelengths, and sets eight-level phase control to realize independent control of four complex amplitude distributions at two target wavelengths and two polarization states.

[0010] As a further technical solution, the material of the substrate layer is fused quartz, and the material of the micro-nano structure layer is silicon.

[0011] According to one aspect of the present application, a design method of a super-structured surface capable of realizing multi-dimensional optical parameter multiplexing and multiple image processing functions is provided, comprising:

[0012] Based on a computing software platform, the frequency domain filtering process in the 4F optical system is simulated by using fast Fourier transform and fast inverse Fourier transform, the frequency domain transfer function is extracted by associating the spatial convolution operator corresponding to the three image processing functions and the spiral filter, and then the processing effect of the four designed frequency domain filters on the image in the 4F system is calculated and verified.

[0013] According to the transmission phase control principle, a nanostructure unit model is constructed in an electromagnetic simulation software to realize the design target of high polarization conversion efficiency at target wavelengths and low polarization conversion efficiency at non-target wavelengths and phase response covering 0-2π, two groups of nano-pillar structures are selected by structure parameter scanning to regulate two target wavelengths, and a structure library with eight-level phase steps is formed for subsequent complex amplitude configuration.

[0014] According to the joint control principle of geometric phase and transmission phase, a complex amplitude distribution structure is designed to support multi-optical parameter multiplexing, the corresponding complex amplitude distribution is calculated for four incident conditions of left circularly polarized light and right circularly polarized light at different wavelengths, and the required structure parameters and nanostructure rotation angles of each pixel are obtained by inversion to complete the global arrangement design of the super-structured surface structure array.

[0015] As a further technical solution, the method further comprises:

[0016] The designed super-structured surface structure is simulated by an electromagnetic simulation software, and complex amplitude responses thereof under four kinds of incident light states are obtained, the obtained complex amplitude responses are further imported into a calculation software, and operation effects of the complex amplitude responses as spectral plane frequency domain filters in a 4F system are simulated through fast Fourier transform and fast inverse Fourier transform, and effectiveness and applicability of the complex amplitude responses in multiple image processing tasks are verified.

[0017] As a further technical solution, the designed frequency domain transfer functions realize four functions of two-dimensional edge detection, horizontal edge detection, vertical edge detection and 45-degree direction edge detection respectively.

[0018] Compared with the prior art, the present application has the beneficial effects that:

[0019] (1) The integration of multiple image processing functions on a single device platform is realized, and the functional density and scalability of the super-structured surface optical image processing are significantly improved;

[0020] (2) Based on the combined design framework of geometric phase and transmission phase joint control, the complex amplitude control ability of the super-structured surface under the input condition of multiple-dimensional light parameters is enhanced;

[0021] (3) The super-structured surface has good compatibility and integrability, is suitable for image processing core devices in future all-optical computing systems, and has broad application prospects in the fields of high-resolution imaging, medical image analysis and optical computing. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0023] Figure 1 is a schematic diagram of the phase distribution of the frequency domain filter for realizing four image processing functions designed in the embodiment of the present application;

[0024] Figure 2 is a schematic diagram of the nano-pillar unit structure in the embodiment of the present application;

[0025] Figure 3 is a polarization conversion efficiency and phase response performance parameter diagram of two groups of micro-nano structures selected in the embodiment of the present application;

[0026] Figure 4is the target phase distribution map set in the embodiment of the application based on four incident light conditions (different wavelengths and polarization states);

[0027] Figure 5 is the overall arrangement schematic diagram of the super-structured surface nano structure array in the embodiment of the application;

[0028] Figure 6 is the complex amplitude distribution map of the super-structured surface in the embodiment of the application under four incident light states, obtained by electromagnetic simulation;

[0029] Figure 7 is the 4F optical system structure schematic diagram based on the calculation software built in the embodiment of the application, used for verifying the image processing function of the frequency domain filter;

[0030] Figure 8 is the four image processing function schematic diagram of the super-structured surface as the spectral plane filter in the 4F system under different optical parameter conditions, including two-dimensional edge detection, horizontal edge detection, vertical edge detection and 45-degree direction edge detection effect.

[0031] Figure 9 is the overall function schematic diagram of the super-structured surface provided in the embodiment of the application. DETAILED DESCRIPTION

[0032] In order to solve the problem of lacking multiple multiplexing functions in the prior art, the application provides a super-structured surface capable of realizing multi-dimensional optical parameter multiplexing and multiple image processing functions and a design method thereof. The super-structured surface is jointly constituted by a fused quartz substrate and a silicon nano brick structure; by combining the joint regulation and control mechanism of geometric phase and transmission phase, the four image processing functions of two-dimensional edge detection, horizontal edge detection, vertical edge detection and 45-degree edge detection of image information on the same device are realized by constructing a complex amplitude regulation and control structure supporting multiple wavelength and multiple polarization state responses. The design is based on Fourier space filtering theory, a complex amplitude structure with a specific frequency domain transfer function is constructed, and the image processing performance is verified by 4F optical system calculation simulation. Compared with the traditional electronic calculation method and single-function optical element, the method significantly improves the functional integration of the super-structured surface image processing system, and has good expansibility and compatibility. It can be imagined that the super-structured surface with multiple image processing functions and multi-dimensional optical parameter multiplexing has a broad application prospect in high-resolution imaging, all-optical computing, medical image processing and the next generation of intelligent optical systems.

[0033] The super-structured surface provided by the application is suitable for being integrated in the 4F system spectral plane, and is used for realizing multiple image processing functions under different incident optical parameter states.

[0034] The super-structured surface is sequentially composed of a micro-nano structure layer and a substrate layer from top to bottom; the substrate layer is divided into a plurality of periodic unit structures with consistent sizes, and the micro-nano structure layer includes a plurality of nano pillars, each unit structure and a nano pillar located on a working surface thereof form a nano pillar structure unit. By selecting two groups of nano structures with high polarization conversion efficiency at target wavelengths and low conversion efficiency at non-target wavelengths, and setting eight-level phase control, independent control of four kinds of complex amplitude distributions at two target wavelengths and two polarization states is realized.

[0035] The micro-nano structure layer is a nano pillar of silicon with a thickness of 500 nanometers.

[0036] The super-structured surface is designed by the length, width and period parameters of the nano pillar and the unit structure, so that corresponding complex amplitude control effects are generated under the incidence of light with different wavelengths and different polarization states. When the super-structured surface is placed on the Fourier plane of a 4F system, it can be used as a frequency domain filter to realize multiple processing functions of the input image. The super-structured surface adopts a joint coding strategy of geometric phase and transmission phase to realize multiplexing control in the wavelength and polarization two optical parameter dimensions. The optical image to be processed is incident in a transmission manner, and by setting different incident wavelengths and polarization states, four image processing functions of two-dimensional edge detection, horizontal edge detection, vertical edge detection and 45-degree direction edge detection can be realized in the 4F system.

[0037] The design method of the on-chip super-structured surface includes the following steps:

[0038] Step 1, based on a calculation software platform, the frequency domain filtering process in a 4F optical system is simulated by using fast Fourier transform (FFT) and fast inverse Fourier transform (IFFT). By associating the spatial convolution operator corresponding to the three image processing functions with the spiral filter, the frequency domain transfer function is extracted, and then the processing effect of the designed four frequency domain filters on the image in the 4F system is calculated and verified. The designed frequency domain transfer function realizes four functions of two-dimensional edge detection, horizontal edge detection, vertical edge detection and 45-degree direction edge detection.

[0039] Step 2, according to the transmission phase control principle, a nano structure unit model is constructed in an electromagnetic simulation software to realize high polarization conversion efficiency at target wavelengths and low polarization conversion efficiency at non-target wavelengths and phase response covering The design target, by scanning a large number of structure parameters, two groups of nano pillar structures that can control two target wavelengths are selected to form a structure library with eight-level phase steps for subsequent complex amplitude configuration.

[0040] Step 3, according to the joint regulation principle of geometric phase and transmission phase, a complex amplitude distribution structure for supporting multi-optical parametric multiplexing is designed. For the four kinds of incident conditions of left circularly polarized light (LCP) and right circularly polarized light (RCP) at different wavelengths, the corresponding complex amplitude distribution is calculated, and the structure parameters and nanometer structure rotation angle required by each pixel are obtained by inversion, and the global arrangement design of the super surface structure array is completed.

[0041] Step 4, the designed super surface structure is simulated by electromagnetic simulation software, and the complex amplitude response under four kinds of incident light states is obtained. The obtained complex amplitude distribution is further imported into the calculation software, and the operation effect of the frequency domain filter in the 4F system is simulated by fast Fourier transform and inverse fast Fourier transform, and the effectiveness and applicability in multiple image processing tasks are verified.

[0042] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application. In addition, the technical features in each embodiment or single embodiment provided by the present application can be combined with each other to form new technical solutions. This combination is not restricted by the order of steps and / or structure composition mode, but must be based on the realization of ordinary skilled in the art. When the combination of technical solutions contradicts each other or cannot be realized, it should be considered that the combination of technical solutions does not exist and is not within the scope of protection required by the present application.

[0043] The present embodiment is a kind of super surface design method that can realize multi-dimensional optical parametric multiplexing and multiple image processing functions, specifically related to frequency domain filter construction based on complex amplitude regulation, nanostructure design and image processing function verification, its overall function is as shown in Figure 9 .

[0044] In the present embodiment, first, a simulation model of 4F Fourier optical system is constructed by using calculation software, and the spatial frequency domain filtering process in the optical system is simulated by fast Fourier transform (FFT) and inverse fast Fourier transform (IFFT). For image processing, a spiral phase filter with typical feature extraction function and three convolution operators are preselected, corresponding to two-dimensional edge detection, horizontal edge detection, vertical edge detection and 45 degree direction edge detection function, respectively, to obtain the frequency domain transfer function corresponding to each function as the basis for subsequent super surface complex amplitude design. Figure 1 The phase of the frequency domain transfer function required for the four image processing functions is shown.

[0045] Subsequently, based on the principle of transmission phase, a nanostructure unit model was established in electromagnetic simulation software. Figure 2 The unit cell structure of this metasurface is shown, which is a fused silica substrate-silicon nanopillar structure. The dimensional parameters of the micro / nanostructure include the period P of the working surface of the unit cell, the length L, width W, and height H of the cuboid nanopillars, and the substrate thickness S. The x-axis and y-axis are defined along two sides parallel to the working surface, thus establishing a right-handed coordinate system xyz. The design goal of the unit cell micro / nanostructure is to achieve operating wavelengths of (…). and Under these conditions, a high polarization conversion efficiency (RCP→LCP or LCP→RCP) phase response is achieved, while interference is suppressed at non-target wavelengths. Through extensive structural parameter scanning, two sets of corresponding... and The transmission phase unit is designed as an eight-level discrete phase, covering 0-2π, to ensure the accuracy of phase control. Figure 3 The two selected pairs of corresponding pairs are shown. and The performance parameters of the micro / nano structures.

[0046] To achieve complex amplitude modulation, a combined modulation mechanism of geometric phase and transmission phase is incorporated into the structural design. This is applied to four different incident conditions ( The complex amplitude value of each spatial pixel is calculated using the constructed complex amplitude frequency domain transfer function. Figure 4 The phase design targets under four incident conditions are shown. The nanostructure parameters and rotation angles corresponding to each pixel can be deduced from the complex amplitude value required for each pixel, and finally the spatial arrangement of the nanostructures of the entire metasurface is obtained. Figure 5 A schematic diagram of the overall arrangement of the metasurface is shown. Due to limitations in computational resources and simulation time, a complex amplitude of 100*100 pixels was designed for testing in this example.

[0047] Based on electromagnetic simulation software, the designed metasurface structures were simulated in various ways. and The ability to modulate the complex amplitude of LCP and RCP incident light at different wavelengths was demonstrated, resulting in four independent complex amplitude distribution maps. Figure 6 The complex amplitudes obtained under incident light of different wavelengths and polarization states are shown. Simulation results demonstrate that this metasurface can achieve a preset frequency domain filter function under different wavelengths and polarization conditions.

[0048] Finally, the obtained complex amplitude data was imported into the calculation software, and the FFT and IFFT methods were called in the 4F system model to verify its image processing performance. Figure 7 A 4F system image processing model based on computing software was demonstrated. Figure 8The four image processing effects provided by the designed super-structure surface are demonstrated. The image processing results show:

[0049] (1) Under the condition of light incidence, the super-structure surface can realize two-dimensional edge detection of the image;

[0050] (2) Under the condition of light incidence, the super-structure surface can realize horizontal edge detection of the image;

[0051] (3) Under the condition of light incidence, the super-structure surface can realize vertical edge detection of the image;

[0052] (4) Under the condition of light incidence, the super-structure surface can realize 45-degree edge detection of the image;

[0053] (5) Under the condition of multiple light parameters composite input, the fusion reconstruction of multiple image processing functions is realized, and the multi-dimensional light parameter multiplexing capability of the designed super-structure is verified.

[0054] Through the complete process from extraction, structure design to image processing effect verification in the frequency domain transfer function, a super-structure surface with multi-dimensional light parameter multiplexing capability and multiple image processing functions is constructed. The design not only realizes the multiplexed image processing function under different wavelengths and polarization states, but also improves the integration and functional density of the super-structure surface in the optical computing system, providing a new technical path for efficient and low-power all-optical image processing. Overall, the super-structure surface device that can realize multi-dimensional light parameter multiplexing and image processing function expansion has the potential to be used as the core image processing device in future all-optical computing systems, especially in high-resolution imaging, medical image analysis, and integrated optical computing applications, showing broad application prospects.

[0055] In summary of the above embodiments, the super-structure surface described in the application is designed based on the Fourier space filtering theory, and the complex amplitude is accurately controlled in the frequency domain of the light field, thereby realizing the spatial multiplexing and composite execution of four image processing functions of two-dimensional edge detection, horizontal edge detection, vertical edge detection, and 45-degree edge detection. The super-structure surface adopts a super-structure unit array structure, and combines the cooperative control mechanism of geometric phase and transmission phase to realize multiplexed response to polarization state and wavelength two light parameters at the structure level. By constructing a nano-brick structure with discrete phase steps, the differentiated response and function switching of multiple input light parameters are realized under the condition of meeting the required complex amplitude for different image processing functions.

[0056] ​​​​Further, the present application proposes a systematic design process of the metasurface: firstly, a frequency domain filter model is constructed according to a target image processing task, and a required complex amplitude regulation characteristic is deduced reversely; then, parameter scanning and optimization are performed on the structural unit based on an electromagnetic simulation software, so as to realize high-precision phase control and polarization selectivity; finally, the effectiveness and stability of the metasurface in an actual imaging task are evaluated through image processing verification in a light field simulation and calculation environment.

[0057] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the present application.

Claims

1. A metasurface capable of multidimensional optical parameter multiplexing and various image processing functions, characterized in that, The metasurface is suitable for integration into the spectral plane of a 4F system to achieve various image processing functions under different incident light parameters. The metasurface includes a substrate layer and a micro / nano structure layer above the substrate layer. The substrate layer is divided into multiple periodic unit structures of the same size. The micro / nano structure layer includes several nanopillars. Each unit structure and a nanopillar on its working surface constitute a nanopillar structure unit. The metasurface, by designing the length and width of the nanopillars and the periodic parameters of the unit structure, can generate corresponding complex amplitude modulation effects under the incident light of different wavelengths and polarization states. The metasurface employs a joint encoding strategy of geometric phase and transmission phase to achieve multiplexing and control of two optical parameters: wavelength and polarization. The metasurface achieves independent control of four complex amplitude distributions under two target wavelengths and two polarization states by selecting two sets of nanostructures with high polarization conversion efficiency for the target wavelength and low polarization conversion efficiency for the non-target wavelength, and setting eight-level phase modulation.

2. The metasurface capable of multidimensional optical parameter multiplexing and various image processing functions according to claim 1, characterized in that, When the metasurface is placed on the Fourier surface of the 4F system, it is used as a frequency domain filter to realize various processing functions for the input image.

3. The metasurface capable of multidimensional optical parameter multiplexing and various image processing functions according to claim 1, characterized in that, The optical image to be processed is incident in a transmission manner. By setting different incident wavelengths and polarization states, four image processing functions are realized in the 4F system: two-dimensional edge detection, horizontal edge detection, vertical edge detection, and 45-degree edge detection.

4. The metasurface capable of multidimensional optical parameter multiplexing and various image processing functions according to claim 1, characterized in that, The substrate layer is made of fused silica, and the micro / nano structure layer is made of silicon.

5. A design method for a metasurface capable of multidimensional optical parameter multiplexing and various image processing functions, characterized in that, include: Based on a computing software platform, the frequency domain filtering process in a 4F optical system is simulated using Fast Fourier Transform and Fast Inverse Fourier Transform. By associating the spiral filter with the spatial convolution operators corresponding to the three image processing functions, the frequency domain transfer function is extracted. Then, the image processing effects of the four designed frequency domain filters in the 4F system are calculated and verified. Based on the principle of transmission phase modulation, a nanostructure unit model is constructed in electromagnetic simulation software. The design goal is to achieve high polarization conversion efficiency at the target wavelength, low polarization conversion efficiency at the non-target wavelength, and a phase response covering 0-2π. Through structural parameter scanning, two sets of nanopillar structures that modulate the two target wavelengths are selected to form a structure library with eight phase steps for subsequent complex amplitude configuration. Based on the principle of joint control of geometric phase and transmission phase, a complex amplitude distribution structure is designed to support multi-optical parametric multiplexing. For four incident conditions of left-handed and right-handed circularly polarized light at different wavelengths, the corresponding complex amplitude distribution is calculated, and the structural parameters and nanostructure rotation angle required for each pixel are obtained by inversion, thus completing the global arrangement design of the metasurface structure array.

6. The design method for a metasurface capable of multidimensional optical parameter multiplexing and multiple image processing functions according to claim 5, characterized in that, The method further includes: The designed metasurface structure was simulated using electromagnetic simulation software to obtain its complex amplitude response under four incident light conditions. The obtained complex amplitude response was further imported into calculation software, and its operation as a spectral surface frequency domain filter in a 4F system was simulated using fast Fourier transform and fast inverse Fourier transform to verify its effectiveness and applicability in various image processing tasks.

7. The design method for a metasurface capable of multidimensional optical parameter multiplexing and multiple image processing functions according to claim 5, characterized in that, The designed frequency domain transfer function realizes four functions: two-dimensional edge detection, horizontal edge detection, vertical edge detection, and 45-degree edge detection.

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