Edge-enhanced zoom Moire super lens based on incoherent light and design method of edge-enhanced zoom Moire super lens

Abstract

The invention discloses an incoherent light-based edge-enhanced zoom Moire superlens and a design method thereof.The Moire superlens comprises two layers of superlenses with the centers aligned, each layer of superlens is provided with a substrate and an optical metasurface arranged on the substrate, and the optical metasurface is used for regulating and controlling the amplitude, phase and polarization state of incident light; the optical metasurface is provided with a plurality of micro-nano structure units which are used for polarization multiplexing and are arranged periodically. One layer of super lens is fixed and the other layer of super lens is rotated to realize continuous zooming regulation and control; the optical metasurfaces of the two layers of superlenses modulate an x polarization component and a y polarization component in incoherent incident light to generate different optical transfer functions, digital difference is carried out on an image formed by a polarization channel, and edge enhancement imaging is achieved. According to the invention, edge enhancement imaging of continuous zooming can be realized under incoherent light illumination, and high integration level, high efficiency and multi-mode imaging capability are realized.

Description

Technical Field

[0001] This invention relates to the field of superlens design technology, specifically to an edge-enhancing zoom moiré superlens based on incoherent light and its design method. Background Technology

[0002] Superlenses are composed of subwavelength-scale micro- and nano-structure units, possessing the ability to freely control electromagnetic wave response and being compatible with micro- and nano-fabrication processes. However, most moiré superlenses are designed for the visible light band, and their application in the infrared band is rarely mentioned.

[0003] Optical edge enhancement imaging, as an efficient image preprocessing method, has important application value in fields such as machine vision, biomedical imaging, and target recognition. Traditional edge enhancement imaging systems are mostly based on 4F optical systems and spatial filters, rely on coherent laser illumination, have a large system size, and are difficult to achieve continuous zoom and dynamic adjustment. In addition, traditional methods are not good at edge detection under incoherent light (such as natural light and LED light sources), which limits their application in everyday imaging scenarios.

[0004] In recent years, metasurfaces, as two-dimensional artificial structures, have provided new pathways for the integration and functionalization of imaging systems due to their flexible control over light fields and compact structural characteristics. Existing research has proposed using metasurfaces for edge detection; for example, metasurfaces based on spiral phase plates can achieve edge enhancement imaging under coherent light, and edge detection under incoherent light can be achieved by constructing an effective optical transfer function through image difference using polarization multiplexing or wavelength multiplexing techniques. However, existing technologies still have many shortcomings: lack of continuous zoom capability, most edge-enhancing metalenses have fixed focal lengths and cannot adapt to different imaging distances and target sizes; dependence on specific illumination conditions, most systems still require lasers or narrowband filtering, making it difficult to work under broadband ambient light; limited functionality: most devices can only achieve edge enhancement or conventional imaging, making it difficult to achieve multimodal imaging within the same system; complex structure: such as relying on multilayer films, photonic crystals, etc., which are difficult to fabricate and have low integration. Therefore, there is an urgent need for a metalens system that combines zoom capability, incoherent light compatibility, multimodal imaging capabilities, and a compact structure. Summary of the Invention

[0005] To overcome the defects and shortcomings of existing technologies, this invention provides an edge-enhancing zoom moiré superlens based on incoherent light and its design method, which can achieve continuous zoom edge-enhancing imaging under incoherent light illumination and has high integration, high efficiency and multimodal imaging capabilities.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The present invention provides an edge-enhanced zoom moiré superlens based on incoherent light, comprising: two center-aligned superlenses, each superlens having a substrate and an optical metasurface disposed on the substrate, the optical metasurface being used to control the amplitude, phase and polarization state of the incident light;

[0008] The optical metasurface is provided with multiple micro / nano structure units that are polarization multiplexed and arranged periodically;

[0009] Continuous zoom control is achieved by fixing one layer of the superlens and rotating the other layer of the superlens.

[0010] The optical metasurfaces of the two superlenses modulate the x-polarization and y-polarization components in the incoherent incident light, respectively, to generate different optical transfer functions. Digital difference is then applied to the image formed by the polarization channel to achieve edge enhancement imaging.

[0011] As a preferred technical solution, the first layer of the two-layer superlens is a polarization-insensitive superlens, and the second layer is a polarization-sensitive superlens. The phase distribution of the edge-enhancing zoom moiré superlens is obtained by superimposing the polarization-insensitive superlens and the polarization-sensitive superlens.

[0012] As a preferred technical solution, the optical metasurfaces of the two superlenses are a first optical metasurface and a second optical metasurface, respectively.

[0013] The first micro / nano structural unit of the first optical metasurface adopts a circular nanopillar structure. Adjacent circular nanopillar structures are arranged in a periodic array to compensate for phase and work together with the second optical metasurface to achieve continuous adjustment of focal length.

[0014] The second micro / nano structural unit of the second optical metasurface adopts a rectangular nanopillar structure and an elliptical nanopillar structure. Both the elliptical and rectangular nanopillar structures are arranged in a periodic array to independently control x-polarized and y-polarized light.

[0015] This invention also provides a design method for an edge-enhancing zoom moiré superlens based on incoherent light, comprising the following steps:

[0016] The structural parameters of the micro / nano structure units are determined based on the target shape of the micro / nano structure units of the optical metasurface.

[0017] The target phase distribution of the micro / nano structural unit is determined based on the correspondence between the propagation phase and the structural parameters.

[0018] Based on the target phase, micro / nano structure units of corresponding size are assigned to each position of the optical metasurface of each layer of the superlens, and phase mapping and micro / nano structure unit selection are performed.

[0019] Moiré zoom relationship is established based on the optical metasurface of two layers of superlenses. Continuous zoom control is achieved by fixing one layer of superlenses and rotating the other layer.

[0020] The optical metasurfaces of the two superlenses modulate the x-polarization and y-polarization components in the incoherent incident light, respectively, to generate different optical transfer functions. Digital difference is then applied to the image formed by the polarization channel to achieve edge enhancement imaging.

[0021] As a preferred technical solution, the structural parameters of the micro / nano structural units are determined based on the target shape of the optical metasurface micro / nano structural units, specifically including:

[0022] The shape of the micro-nano structure unit of the optical metasurface is determined based on the transmittance of the micro-nano structure unit.

[0023] Based on the shape of the micro / nano structure unit of the optical metasurface, the radius of the circular nanopillar, the major and minor axes of the elliptical nanopillar, and the length and width of the rectangular nanopillar are fixed. The height and period of the micro / nano structure unit are scanned to obtain the first transmittance result of the micro / nano structure unit.

[0024] Based on the shape of the micro / nano structure unit of the optical metasurface, the height and period of the micro / nano structure unit are fixed, and the radius of the circular nanopillar, the major and minor axes of the elliptical nanopillar, and the length and width of the rectangular nanopillar are scanned to obtain the second transmittance result of the micro / nano structure unit.

[0025] Based on the first and second transmittance results, micro / nano structure units that simultaneously meet the requirements of high transmittance and target phase modulation are selected, and the optimal design range of the structural parameters of the micro / nano structure units is determined.

[0026] As a preferred technical solution, the target phase distribution of the micro / nano structural unit is determined based on the correspondence between the propagation phase and structural parameters, specifically including:

[0027] Parameter scanning and unit library construction and screening are performed based on the structural parameters of micro-nano structural units;

[0028] A propagation phase library was constructed by scanning the size of anisotropic nanopillars under x and y linear polarization, respectively.

[0029] A polarization-insensitive lens is designed for the first optical metasurface, and a polarization-sensitive lens is designed for the second optical metasurface.

[0030] The phase distribution of the edge-enhancing zoom moiré superlens is obtained by superimposing polarization-insensitive and polarization-sensitive superlenses.

[0031] As a preferred technical solution, based on the target phase, micro / nano structural units of corresponding sizes are assigned to each position on the optical metasurface of each layer of the superlens, and phase mapping and micro / nano structural unit selection are performed, specifically including:

[0032] The transmission phase distribution of the first optical metasurface under x and y polarization is calculated and expressed as:

[0033] ;

[0034] in, This represents the transmission phase distribution of the micro / nano structural units of the first optical metasurface under x and y polarization. Indicates the operating wavelength. Polar coordinates representing micro / nano structures This indicates the rotation angle of the first optical metasurface. Indicates focal length;

[0035] Discretize the continuous phase distribution to obtain the propagation phase of the first optical metasurface at each coordinate (x, y);

[0036] The transmission phase distribution of the second optical metasurface under x-polarization is calculated and expressed as:

[0037] ;

[0038] in, This represents the transmission phase distribution of the micro / nano structural units of the second optical metasurface under x-polarization. Indicates the rotation angle of the second optical metasurface;

[0039] The transmission phase distribution of the second optical metasurface under y-polarization is calculated as follows:

[0040] ;

[0041] The propagation phase of the second optical metasurface at each coordinate (x, y) is solved.

[0042] As a preferred technical solution, a moiré zoom relationship is established based on the optical metasurfaces of the two-layer superlens, specifically including:

[0043] The transmission phase distribution of the moiré superlens under x-polarization is calculated as follows:

[0044] ;

[0045] in, This represents the transmission phase distribution of the moiré superlens under x-polarization. Indicates the operating wavelength. Represents the polar coordinates of the superlens micro / nano structure unit. This represents the relative rotation angle between the first and second optical metasurfaces. Indicates focal length;

[0046] The transmission phase distribution of the moiré superlens under y-polarization is calculated as follows:

[0047] ;

[0048] in, This represents the transmission phase distribution of the moiré superlens under y-polarization. Indicates the rotation angle of the second optical metasurface;

[0049] The equivalent focal length of the entire moiré superlens The relative rotation angle Δθ between the two metasurfaces satisfies the following relationship:

[0050] ;

[0051] Continuous adjustment of the focal length is achieved by rotating the second optical metasurface.

[0052] As a preferred technical solution, the optical metasurfaces of the two-layer superlens modulate the x-polarization component and y-polarization component of the incoherent incident light, respectively. In the spatial frequency domain, the input-output relationship is expressed as:

[0053] ;

[0054] in, and These are the spectra of the input object and the output image, respectively. is the optical transfer function, and k is the spatial frequency vector.

[0055] As a preferred technical solution, different optical transfer functions are generated as follows: and ,in, It exhibits low-pass characteristics. Qualcomm characteristics;

[0056] Digital difference is performed on the image formed by the polarization channel to construct the optical transfer function. , is represented as:

[0057] ;

[0058] Among them, optical transfer function The response at the center of the spatial frequency domain is close to zero.

[0059] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0060] (1) The present invention adopts the technical solution of polarization multiplexing and double-layer moiré metasurface structure, which solves the technical problem that the traditional edge detection system relies on coherent laser light source and cannot work under broadband ambient light. It achieves the technical effect of directly realizing edge enhancement imaging under incoherent light illumination such as natural light and LED, which significantly expands its application range in daily scenarios.

[0061] (2) Based on the coordinated control of propagation phase and moiré phase, and combined with the mechanical zoom scheme of relative rotation of two-layer metasurface, this invention solves the technical problem of traditional zoom systems relying on the axial displacement of multiple lens groups and having a complex and bulky structure. It achieves the technical effect of 1-2 times continuous optical zoom by simply adjusting the relative angle of the two-layer metasurface, thus making the system compact, reliable and flexible focal length adjustment capability.

[0062] (3) The present invention uses a polarization multiplexing structure to enable the superlens to generate optical transfer functions with low-pass and high-pass characteristics for x- and y-polarized light. Combined with the digital image difference processing scheme, it solves the technical problem that existing edge enhancement devices have single functions and are difficult to realize multimodal imaging in the same system. It achieves the technical effect of realizing edge enhancement imaging and conventional bright field imaging in the same compact structure by switching polarization, thereby providing an efficient solution for real-time, multimodal optical detection. Attached Figure Description

[0063] Figure 1 (a) in the diagram is a schematic diagram of a circular nanopillar structure in the xz plane;

[0064] Figure 1 (b) is a schematic diagram of a circular nanopillar structure in the xy plane;

[0065] Figure 1 (c) in the diagram is a schematic diagram of a rectangular nanopillar structure in the xz plane;

[0066] Figure 1 (d) in the diagram is a schematic diagram of a rectangular nanopillar structure in the xy plane;

[0067] Figure 1 (e) in the diagram is a schematic diagram of an elliptical nanopillar structure in the xz plane;

[0068] Figure 1 (f) in the figure is a schematic diagram of the elliptical nanopillar structure in the xy plane;

[0069] Figure 1 (g) in the diagram is a schematic diagram of the edge-enhanced zoom moiré superlens structure in the xz plane;

[0070] Figure 1 (h) in the diagram is a schematic diagram of the edge-enhanced zoom moiré superlens structure in the xy plane;

[0071] Figure 2 (a) in the figure is a graph showing the relationship between the structural parameters and transmittance of the micro / nano structure unit of the present invention;

[0072] Figure 2 (b) in the figure is a schematic diagram showing the relationship between the structural parameters and the transmission phase of the micro / nano structure unit of the present invention;

[0073] Figure 3 This is a flowchart illustrating the edge-enhanced zoom moiré superlens design method based on incoherent light according to the present invention.

[0074] Figure 4 (a) is a schematic diagram of the electric field intensity distribution in the xz plane of the edge-enhanced zoom moiré superlens of the present invention under the x-linear polarization direction;

[0075] Figure 4 (b) is a schematic diagram of the electric field intensity distribution in the xy plane of the edge-enhanced zoom moiré superlens of the present invention under the x-linear polarization direction;

[0076] Figure 4 (c) is a schematic diagram of the electric field intensity distribution in the y direction at the focal point of the edge-enhanced zoom moiré superlens of the present invention when x=0 in the x-linear polarization direction;

[0077] Figure 5 (a) is a schematic diagram of the electric field intensity distribution in the xz plane corresponding to the y-linear polarization direction of the edge-enhanced zoom moiré superlens of the present invention;

[0078] Figure 5 (b) is a schematic diagram of the electric field intensity distribution in the xy plane of the edge-enhanced zoom moiré superlens of the present invention under the y-linear polarization direction;

[0079] Figure 5 (c) is a schematic diagram of the electric field intensity distribution in the y direction at the focal point of the edge-enhanced zoom moiré superlens of the present invention when x=0 in the y-linear polarization direction. Detailed Implementation

[0080] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0081] Example

[0082] First, it should be noted that an optical metasurface is an optical device made of subwavelength-sized, anisotropic or isotropic micro-nano structures arrayed at subwavelength intervals on a substrate. It can flexibly and effectively control the phase, amplitude, and polarization characteristics of electromagnetic waves through artificial design. A moire-metalens is a composite structure composed of two center-aligned optical metasurfaces, and its equivalent phase is extremely sensitive to the relative rotation angle between the two layers.

[0083] The core function of a superlens relies on phase modulation, including resonant phase modulation, geometric phase modulation, and propagation phase modulation. Propagation phase, also known as transmission phase, is a mechanism for phase modulation achieved through the optical path difference generated when electromagnetic waves propagate in a waveguide-like structure. Propagation phase has unique advantages over resonant and geometric phase: it combines polarization insensitivity with broadband phase modulation capabilities, while achieving low loss. Its polarization independence is due to the high symmetry of isotropic microstructures (such as cylindrical and cross-shaped antennas); its phase stability is suitable for broadband communication and imaging. Furthermore, this mechanism allows for the use of entirely dielectric materials, thus avoiding the ohmic losses of metals. Based on these advantages, this embodiment selects transmission phase as the core modulation mechanism.

[0084] Based on this, this embodiment provides an edge-enhancing zoom moiré superlens based on incoherent light. This superlens, through a polarization-multiplexed metasurface structure, enables edge-enhancing imaging directly under incoherent light illumination (such as natural light or LED light) without relying on traditional coherent laser sources and complex 4F spatial filtering systems. It determines the shape and structural parameters of the micro / nano structure units by combining the propagation phase and using the finite-difference time-domain (FDTD) method for numerical analysis and parameter optimization. Secondly, by utilizing the mapping relationship between the propagation phase and structural parameters, appropriate parameters are assigned to units at different positions on the metasurface, thereby constructing two functionally distinct metasurfaces (a first optical metasurface M1 and a second optical metasurface M2). The first optical metasurface M1 is designed to be polarization-insensitive, while the second optical metasurface M2 is designed to be polarization-sensitive. Together, they can generate two independent and differentiated wavefront modulations of the x-polarization and y-polarization components in the incoherent incident light. This differential modulation manifests as two different optical transfer functions at the system level. Ultimately, by performing digital difference on the images formed by these two polarization channels, an effective Laplacian convolution kernel (i.e., a high-pass filter) can be constructed in the algorithm to achieve background suppression and edge enhancement. The entire system has a compact structure, and the micro-nano structure units in this embodiment have simple shapes and are easy to fabricate.

[0085] like Figure 1As shown in (g)-(h) in this embodiment, the edge-enhancing zoom moiré superlens has two layers of superlenses. The two layers of superlenses are aligned at their centers to form a moiré structure. After fixing the first layer of superlenses, the second layer of superlenses is rotated to achieve zoom control. The first layer of superlenses is a polarization-insensitive superlens, and the second layer of superlenses is a polarization-sensitive superlens. The phase distribution of the edge-enhancing zoom moiré superlens is obtained by superimposing the polarization-insensitive superlens and the polarization-sensitive superlens.

[0086] The first layer of the superlens includes a first substrate and a first optical metasurface M1 disposed on the first substrate. The first substrate is used to support the first optical metasurface. Both the first substrate and the first optical metasurface are made of silicon.

[0087] The first optical metasurface is used to control the amplitude, phase, and polarization state of incident light. The first optical metasurface has multiple polarization-multiplexed and periodically arranged first micro / nano structure units, such as... Figure 1 As shown in (a)-(b), the first micro / nano structure unit adopts a circular nanopillar structure. The circular nanopillar structure is used to optimize the control function of the optical metasurface. Adjacent cylinders are arranged in a periodic array. Their phase response is independent of polarization and is used to compensate for the phase. It works together with the second optical metasurface M2 to achieve continuous adjustment of the focal length.

[0088] The second-layer superlens includes a second substrate and a second optical metasurface M2 disposed on the second substrate. The second substrate is used to support the second optical metasurface. Both the second substrate and the second optical metasurface are made of silicon.

[0089] The second optical metasurface is used to control the amplitude, phase, and polarization state of incident light. The second optical metasurface has multiple polarization-multiplexed and periodically arranged second micro / nano structure units, such as... Figure 1 As shown in (c)-(f), the second micro / nano structure unit adopts a rectangular nanopillar structure and an elliptical nanopillar structure. Both the elliptical and rectangular nanopillar structures are arranged in a periodic array, and their phase response has polarization sensitivity, which is used to independently control x-polarized light and y-polarized light.

[0090] In this embodiment, the multi-shaped cylindrical design of the first and second micro-nano structural units provides rich control methods for the metasurface, enabling it to optimize the light control capability in multiple dimensions. Among them, the circular nanopillars, rectangular nanopillars and elliptical nanopillars are arranged in a uniform array with the same height and the same arrangement period of adjacent nanopillars, but the parameters of different structures are different.

[0091] Specifically, the circular nanopillar of the first micro / nano structure unit has a period P = 2.5 μm, a height H = 1.2 μm, and its length L and width W are selected according to the desired propagation phase;

[0092] The period of the rectangular nanopillar of the second micro / nano structure unit is also P = 2.5 μm, and the height is H = 1.2 μm. Its side length is selected according to the required propagation phase.

[0093] The period of the elliptical nanopillar of the second micro / nano structure unit is also P = 2.5 μm, and the height is H = 1.2 μm. Its side length is selected according to the required propagation phase.

[0094] like Figure 2 As shown in (a)-(b), the finite-difference time-domain method (FDTD) is used to perform numerical analysis on the micro-nano structure unit, and the parameter scanning optimization design of the micro-nano structure unit is carried out to select structural parameters with 2π phase coverage and high transmittance.

[0095] In this embodiment, the edge-enhanced zoom moiré superlens modulates the optical field through a first optical metasurface M1 and a second optical metasurface M2. The first and second optical metasurfaces are aligned at their centers. The first optical metasurface M1 provides the basic phase for zoom, while the second optical metasurface M2 endows the system with polarization diversity processing capabilities. This ensures that the anisotropic units of the second optical metasurface M2 can simultaneously and independently generate the two wavefronts required for x- and y-polarized light, so that the x- and y-polarized channels respectively present conventional spherical waves and vortex waves carrying topological charges. Finally, through systematic and goal-oriented optimization design of the geometric parameters of micro- and nanostructure units such as circular nanopillars, rectangular nanopillars, and elliptical nanopillars, the entire system achieves the best balance in terms of phase accuracy, optical efficiency, functional realization, and manufacturability, thereby ultimately realizing continuously zoomable edge-enhanced imaging under incoherent light.

[0096] like Figure 3 As shown, this embodiment provides a design method for an edge-enhanced zoom moiré superlens based on incoherent light, including the following steps:

[0097] S1: Based on the target shape of the micro / nano structure unit of the optical metasurface, determine the structural parameters of the micro / nano structure unit. The structural parameters include radius, major semi-axis, minor semi-axis, length, width, height, and period, specifically including:

[0098] S11: Determine the shape of the micro / nano structure unit of the optical metasurface based on the transmittance of the micro / nano structure unit and considering manufacturing tolerances.

[0099] S12: Based on the shape of the micro / nano structure unit of the optical metasurface, the radius of the circular nanopillar, the major and minor semi-axes of the elliptical nanopillar, and the length and width of the rectangular nanopillar are fixed. The height and period of the micro / nano structure unit are scanned to obtain the first transmittance result of the micro / nano structure unit.

[0100] S13: Based on the shape of the micro / nano structure unit of the optical metasurface, the height and period of the micro / nano structure unit are fixed, and the radius of the circular nanopillar, the major and minor axes of the elliptical nanopillar, and the length and width of the rectangular nanopillar are scanned to obtain the second transmittance result of the micro / nano structure unit.

[0101] S14: Combining the first and second transmittance results, we screen out micro / nano structural units that simultaneously meet the requirements of high transmittance and target phase modulation, thereby determining the optimal design range of their structural parameters.

[0102] In this embodiment, the scanning range of the radius of the circular nanopillar is: The scanning range of the semi-major axis of the elliptical nanopillar is The scanning range of the short semi-axis of the elliptical nanopillar is The scanning range of the length of the rectangular nanopillar is The scanning range of the rectangular nanopillars is [width value missing]. ;

[0103] In this embodiment, the operating wavelength (λ=4μm), aperture (D=100 μm), and initial focal length of the superlens are determined according to the system's operating parameter requirements. and its zoom range ( =80-120μm), and it is determined that both the substrate and the optical metasurface on the substrate are made of silicon, and the first optical metasurface M1 uses a polarization-insensitive structure, while the second optical metasurface M2 uses a polarization-sensitive structure;

[0104] S2: Determine the target phase distribution of the micro / nano structural unit based on the correspondence between the propagation phase and the structural parameters;

[0105] Specifically, parameter scanning and unit library construction and screening are carried out based on the structural parameters of micro and nano structural units. A propagation phase library is constructed by scanning the size of circular nanopillars to design polarization-insensitive units for the first optical metasurface M1. A propagation phase library is constructed by scanning the size of anisotropic nanopillars under x and y linear polarization to design polarization-sensitive units for the second optical metasurface M2. After establishing the corresponding unit library, sufficient data support is provided for the subsequent phase matching of the corresponding optical metasurfaces.

[0106] In this embodiment, the finite-difference time-domain (FDTD) method is used to perform parameter scanning on the circular nanopillars of the first optical metasurface M1, scanning their radius r and height h to obtain their transmission phase and transmittance. Structural units that can cover the 0-2π phase range and have a transmittance higher than 90% are selected to construct the first optical metasurface M1. Similarly, parameter scanning is performed on the rectangular and elliptical nanopillars of the second optical metasurface M2 to select structural parameters that can cover the 0-2π phase range and have high transmittance.

[0107] S3: Assign micro / nano structure units of corresponding sizes to each position of the first optical metasurface M1 and the second optical metasurface M2 according to the target phase, and perform phase mapping and micro / nano structure unit selection;

[0108] The target phase distribution of the first optical metasurface M1 and the second optical metasurface M2 under x-polarized light and y-polarized light incident light is calculated based on the ideal phase formula.

[0109] Specifically, the target phase distribution is calculated using the following formula. Then, the continuous phase distribution is discretized to determine the propagation phase φ(x,y) that the first optical metasurface M1 needs to provide at each coordinate (x,y):

[0110] ;

[0111] in, This represents the transmission phase distribution of the first optical metasurface M1 micro / nano structure unit under x and y polarization. Indicates the operating wavelength. The polar coordinates of the superlens micro / nano structure unit are represented by r = , , This represents the coordinates of the center point of the micro / nano structure unit. This represents the rotation angle of the first optical metasurface M1. Indicates focal length;

[0112] The transmission phase distribution of the second optical metasurface M2 micro / nano structure unit under x-polarization is expressed as follows:

[0113] ;

[0114] in, This indicates the rotation angle of the second optical metasurface M2;

[0115] The transmission phase distribution of the second optical metasurface M2 micro / nano structure unit under y-polarization is expressed as follows:

[0116] ;

[0117] Solve for the propagation phase φ(x,y) that the second optical metasurface M2 needs to provide for the x-polarized light and y-polarized light at each coordinate (x,y).

[0118] Based on the target phase, micro / nano structure units of appropriate size are assigned to each position of the first optical metasurface M1 and the second optical metasurface M2. Phase mapping and micro / nano structure unit selection are performed. This process essentially discretizes the continuous mathematical phase distribution into specific physical structure parameters. Through a pre-built phase-structure correspondence database, the most suitable micro / nano structure unit is selected for each position, thereby physically and accurately realizing the target phase distribution of the first optical metasurface M1 and the second optical metasurface M2, ensuring that the entire moiré super lens system can achieve the expected zoom and edge enhancement functions.

[0119] Based on the working parameters of the optical metasurface, the structural parameters of the micro / nano structural units are adjusted so that the structural parameters satisfy the transmission phase distribution of the micro / nano structural units, and the final structural parameters of the micro / nano structural units are determined.

[0120] S4: Lay out metasurfaces, arrange the selected micro / nano structural units into a first optical metasurface M1 and a second optical metasurface M2, establish the moiré zoom relationship, and integrate the metasurface layout with the moiré zoom system.

[0121] Specifically, based on the unit library selected in step S2 and the phase calculated in step S3, the corresponding micro / nano structure units are placed at the corresponding positions of the first optical metasurface M1 and the second optical metasurface M2 to complete the construction of the metasurface. Finally, the metasurface array is arranged on the substrate to obtain the superlens.

[0122] The expression for the phase distribution of a moiré superlens and the calculation of the target focal length are shown below:

[0123] ;

[0124] In the above formula, This represents the transmission phase distribution of the moiré superlens under x-polarization. Indicates the operating wavelength. The polar coordinates of the superlens micro / nano structure unit are represented by r = , , This represents the coordinates of the center point of the micro / nano structure unit. This represents the relative rotation angle between the first optical metasurface M1 and the second optical metasurface M2. Indicates focal length.

[0125] ;

[0126] In the above formula, This represents the transmission phase distribution of the moiré superlens under y-polarization. Indicates the operating wavelength. The polar coordinates of the superlens micro / nano structure unit are represented by r = , , This represents the coordinates of the center point of the micro / nano structure unit. This represents the relative rotation angle between the first optical metasurface M1 and the second optical metasurface M2. This indicates the rotation angle of the second optical metasurface M2. Indicates the target focal length.

[0127] At this point, the equivalent focal length of the entire moiré superlens is... The relative rotation angle Δθ between the two metasurfaces satisfies the following relationship:

[0128] ;

[0129] By rotating the second optical metasurface M2 (Δθ changing from 40° to 90°), the focal length can be continuously adjusted between 80 μm and 120 μm.

[0130] S5: Perform system simulation verification to obtain the optical transfer function (OTF) under different polarized light directions, and perform image difference calculation to obtain edge-enhanced images;

[0131] In the spatial frequency domain, the relationship between the system's input and output can be expressed as:

[0132] ;

[0133] in, and These are the spectra of the input object and the output image, respectively. is the optical transfer function of the system, and k is the spatial frequency vector.

[0134] The superlens of this invention produces two different optical transfer functions (OTFs) for incident x-polarized and y-polarized light, respectively. and , It exhibits low-pass characteristics and is used to capture bright-field images that contain background information. Due to its unique phase distribution, it exhibits high-pass characteristics, exhibiting high sensitivity to image edges and high-frequency details. Through subsequent digital image processing, the images formed by the two polarization channels are differentiated, thereby constructing an effective optical transfer function at the algorithm level. , is represented as:

[0135] ;

[0136] The optical transfer function The response is close to zero at the center of the spatial frequency domain (k=0) (corresponding to the uniform background of the image), but is enhanced at high-frequency components. Functionally, it is equivalent to an isotropic high-pass filter, which ultimately achieves the purpose of background suppression and edge feature enhancement of the input image under incoherent illumination, and can effectively extract the edge information of the image.

[0137] Finally, the operating wavelength was determined using FDTD Solutions software. X-polarized and Y-polarized light incident on Figure 1 (g) Simulation of the designed superlens;

[0138] The results are as follows Figure 4 As shown in (a)-(c), x-polarized light along When light is incident on the superlens along the positive axis and interacts with the micro / nano structure, the intensity distribution of the light field in the xz plane corresponding to different relative rotation angles Δθ and the light spot on the focal plane clearly show the continuous change of the focal length. Figure 4 In the diagram, (a) represents the output electric field of the superlens. The distribution of surfaces Figure 4 In the diagram, (b) is the focal plane of the superlens. The output electric field distribution is shown in the figure. It can be seen that the focused spot energy is concentrated, and the designed superlens has good focusing characteristics.

[0139] The results are as follows Figure 5 As shown in (a)-(c), y-polarized light along When incident on the superlens in the positive direction of the axis, it can be seen from the figure that the focal plane spot is circular, which is determined by the spiral phase it carries.

[0140] This embodiment calculates the OTF and performs differential to obtain an effective OTF, which is zero at the center and enhanced at the periphery in the spatial frequency domain, possessing ideal Laplacian convolution kernel characteristics, thus explaining the principle that the system can achieve isotropic edge enhancement.

[0141] In summary, this invention, based on a superlens design utilizing polarization multiplexing and moiré zoom, achieves continuous zoom edge enhancement imaging under incoherent light through simple mechanical rotation. This system is compact and multifunctional, providing an effective technical path for developing next-generation compact and intelligent optical imaging systems. The superlens comprises a substrate and an optical metasurface disposed on the substrate. Both the substrate and the metasurface are made of silicon. The metasurface is composed of periodically arranged micro / nano structures, resulting in a simple unit structure that reduces the requirements for processing conditions. The superlens constructed in this invention aims to solve the problem of simultaneously achieving edge detection and continuous zoom under incoherent light, and the resulting bulky system structure.

[0142] This invention achieves polarization multiplexing by precisely designing and optimizing the phase of micro / nano structural units and combining propagation phase. It also achieves continuous zooming through the double-layer rotation mechanism of a moiré superlens and integrates the complex spatial filtering process into a compact planar lens by combining the polarization multiplexing of optical metasurfaces with simple digital image differential. This replaces the bulky 4F optical system required for traditional edge detection and gives the system advantages such as continuous zooming capability, high imaging resolution, and good system integration.

[0143] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An edge-enhancing zoom moiré superlens based on incoherent light, characterized in that, It includes: two center-aligned superlenses, each superlens having a substrate and an optical metasurface disposed on the substrate, the optical metasurface being used to control the amplitude, phase and polarization state of the incident light; The optical metasurface is provided with multiple micro / nano structure units that are polarization multiplexed and arranged periodically; Continuous zoom control is achieved by fixing one layer of the superlens and rotating the other layer of the superlens. The optical metasurfaces of the two superlenses modulate the x-polarization and y-polarization components in the incoherent incident light, respectively, to generate different optical transfer functions. Digital difference is then applied to the image formed by the polarization channel to achieve edge enhancement imaging.

2. The edge-enhancing zoom moiré superlens based on incoherent light according to claim 1, characterized in that, The first layer of the two-layer superlens is a polarization-insensitive superlens, and the second layer is a polarization-sensitive superlens. The phase distribution of the edge-enhancing zoom moiré superlens is obtained by superimposing the polarization-insensitive superlens and the polarization-sensitive superlens.

3. The edge-enhancing zoom moiré superlens based on incoherent light according to claim 1, characterized in that, The optical metasurfaces of the two superlenses are the first optical metasurface and the second optical metasurface, respectively; The first micro / nano structural unit of the first optical metasurface adopts a circular nanopillar structure. Adjacent circular nanopillar structures are arranged in a periodic array to compensate for phase and work together with the second optical metasurface to achieve continuous adjustment of focal length. The second micro / nano structural unit of the second optical metasurface adopts a rectangular nanopillar structure and an elliptical nanopillar structure. Both the elliptical and rectangular nanopillar structures are arranged in a periodic array to independently control x-polarized and y-polarized light.

4. The design method of the edge-enhancing zoom moiré superlens based on incoherent light according to any one of claims 1-3, characterized in that, Includes the following steps: The structural parameters of the micro / nano structure units are determined based on the target shape of the micro / nano structure units of the optical metasurface. The target phase distribution of the micro / nano structural unit is determined based on the correspondence between the propagation phase and the structural parameters. Based on the target phase, micro / nano structure units of corresponding size are assigned to each position of the optical metasurface of each layer of the superlens, and phase mapping and micro / nano structure unit selection are performed. Moiré zoom relationship is established based on the optical metasurface of two layers of superlenses. Continuous zoom control is achieved by fixing one layer of superlenses and rotating the other layer. The optical metasurfaces of the two superlenses modulate the x-polarization and y-polarization components in the incoherent incident light, respectively, to generate different optical transfer functions. Digital difference is then applied to the image formed by the polarization channel to achieve edge enhancement imaging.

5. The design method of the edge-enhancing zoom moiré superlens based on incoherent light according to claim 4, characterized in that, Based on the target shape of the micro / nano structural unit of the optical metasurface, the structural parameters of the micro / nano structural unit are determined, specifically including: The shape of the micro-nano structure unit of the optical metasurface is determined based on the transmittance of the micro-nano structure unit. Based on the shape of the micro / nano structure unit of the optical metasurface, the radius of the circular nanopillar, the major and minor axes of the elliptical nanopillar, and the length and width of the rectangular nanopillar are fixed. The height and period of the micro / nano structure unit are scanned to obtain the first transmittance result of the micro / nano structure unit. Based on the shape of the micro / nano structure unit of the optical metasurface, the height and period of the micro / nano structure unit are fixed, and the radius of the circular nanopillar, the major and minor axes of the elliptical nanopillar, and the length and width of the rectangular nanopillar are scanned to obtain the second transmittance result of the micro / nano structure unit. Based on the first and second transmittance results, micro / nano structure units that simultaneously meet the requirements of high transmittance and target phase modulation are selected, and the optimal design range of the structural parameters of the micro / nano structure units is determined.

6. The design method of the edge-enhancing zoom moiré superlens based on incoherent light according to claim 4, characterized in that, Based on the correspondence between propagation phase and structural parameters, the target phase distribution of micro / nano structural units is determined, specifically including: Parameter scanning and unit library construction and screening are performed based on the structural parameters of micro-nano structural units; A propagation phase library was constructed by scanning the size of anisotropic nanopillars under x and y linear polarization, respectively. A polarization-insensitive lens is designed for the first optical metasurface, and a polarization-sensitive lens is designed for the second optical metasurface. The phase distribution of the edge-enhancing zoom moiré superlens is obtained by superimposing polarization-insensitive and polarization-sensitive superlenses.

7. The design method of the edge-enhancing zoom moiré superlens based on incoherent light according to claim 4, characterized in that, Based on the target phase, micro / nano structural units of corresponding sizes are assigned to each position on the optical metasurface of each layer of the superlens. Phase mapping and selection of micro / nano structural units are performed, specifically including: The transmission phase distribution of the first optical metasurface under x and y polarization is calculated and expressed as: ； in, This represents the transmission phase distribution of the micro / nano structural units of the first optical metasurface under x and y polarization. Indicates the operating wavelength. Polar coordinates representing micro / nano structures This indicates the rotation angle of the first optical metasurface. Indicates focal length; Discretize the continuous phase distribution to obtain the propagation phase of the first optical metasurface at each coordinate (x, y); The transmission phase distribution of the second optical metasurface under x-polarization is calculated and expressed as: ； in, This represents the transmission phase distribution of the micro / nano structural units of the second optical metasurface under x-polarization. Indicates the rotation angle of the second optical metasurface; The transmission phase distribution of the second optical metasurface under y-polarization is calculated as follows: ； The propagation phase of the second optical metasurface at each coordinate (x, y) is solved.

8. The design method of the edge-enhancing zoom moiré superlens based on incoherent light according to claim 4, characterized in that, The moiré zoom relationship is established based on the optical metasurface of two layers of superlenses, specifically including: The transmission phase distribution of the moiré superlens under x-polarization is calculated as follows: ； in, This represents the transmission phase distribution of the moiré superlens under x-polarization. Indicates the operating wavelength. Represents the polar coordinates of the superlens micro / nano structure unit. This represents the relative rotation angle between the first and second optical metasurfaces. Indicates focal length; The transmission phase distribution of the moiré superlens under y-polarization is calculated as follows: ； in, This represents the transmission phase distribution of the moiré superlens under y-polarization. Indicates the rotation angle of the second optical metasurface; The equivalent focal length of the entire moiré superlens The relative rotation angle Δθ between the two metasurfaces satisfies the following relationship: ； Continuous adjustment of the focal length is achieved by rotating the second optical metasurface.

9. The design method of the edge-enhancing zoom moiré superlens based on incoherent light according to claim 4, characterized in that, The optical metasurfaces of the two-layer superlens modulate the x-polarization and y-polarization components of the incoherent incident light, respectively. In the spatial frequency domain, the input-output relationship is expressed as: ； in, and These are the spectra of the input object and the output image, respectively. is the optical transfer function, and k is the spatial frequency vector.

10. The design method of the edge-enhancing zoom moiré superlens based on incoherent light according to claim 9, characterized in that, Different optical transfer functions are represented as follows: and ,in, It exhibits low-pass characteristics. Qualcomm characteristics; Digital difference is performed on the image formed by the polarization channel to construct the optical transfer function. , represented as: ； Among them, optical transfer function The response at the center of the spatial frequency domain is close to zero.

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