Pluggable polarization imaging system based on metasurface and traditional optics and construction method

Abstract

The invention discloses a pluggable polarization imaging system based on a metasurface and traditional optics and a construction method, and relates to the technical field of polarization imaging. When the metasurface is not inserted or pulled out, the polarization imaging system has a light intensity imaging function; when the super-structure surface is inserted into the imaging system, the polarization imaging system has a polarization imaging function; after the polychromatic light source is incident to the refraction lens of the imaging system, the polychromatic light source is focused and irradiated to the surface of the metasurface, different polarization components in the polychromatic light source are split and deflected to corresponding positions by the surface of the metasurface, and different polarization imaging focuses are formed on the pixel surface of the detector, so that polarization imaging is realized. The imaging system constructed by the invention not only solves the problems of huge volume and difficulty in integration of a traditional polarization imaging mode, but also solves the problems of large aperture and dispersion of a super-structure surface imaging mode, and the whole optical system can adopt different imaging modes for different scenes due to the pluggable characteristic.

Description

Technical Field

[0001] The present invention belongs to the field of polarization imaging technology, and more specifically, relates to a pluggable polarization imaging system based on metasurfaces and traditional optics and a construction method. Background Art

[0002] In recent years, the continuous development and maturity of fields such as autonomous driving, drone reconnaissance, and remote sensing have put forward new requirements for information detection. Traditional cameras primarily acquire information by recording the intensity, wavelength, and spatial distribution of light. However, imaging based solely on light intensity cannot meet the needs of imaging complex scenes, and higher-dimensional imaging is becoming increasingly important. As an electromagnetic wave, light has inherent properties such as amplitude and frequency, as well as polarization. When light interacts with matter, its polarization state changes with changes in the object's surface morphology, internal structure, or chemical composition. This polarization information can be used to analyze properties such as the target's shape, surface roughness, texture orientation, and three-dimensional topography. Due to its unique characteristics, polarization information detection has been widely used in fields such as biomedicine, remote sensing, and astronomy. However, previous polarization imaging systems typically include multiple optical components, such as Wollaston prisms, polarizers, and wave plates. These complex and bulky structures do not well meet the trend towards miniaturization and easy integration of optical components.

[0003] Metasurfaces are novel electromagnetic wave manipulation components composed of subwavelength structures on a two-dimensional plane. They have been shown to arbitrarily manipulate the wavelength, amplitude, polarization, and other components of electromagnetic waves. Due to their high integration, multifunctionality, and lightweight design, optical components based on metasurfaces offer advantages over traditional devices in wavefront manipulation, polarization control, frequency selection, and detection imaging. While extensive research has been conducted on polarization imaging using metasurfaces, limitations in their processing and design methods have hindered their ability to simultaneously address functional requirements such as aperture, dispersion, and polarization. For example, achieving polarization imaging while simultaneously achieving large-aperture achromatic aberration is difficult. These limitations hinder the practical application of metasurfaces. For these reasons, we propose a pluggable polarization imaging design method based on metasurfaces and traditional optics. This method addresses the issues of aperture and dispersion in polarization imaging, providing support for the practical application of metasurfaces. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a pluggable polarization imaging system and construction method based on metasurface and traditional optics. When the metasurface is not inserted, the polarization imaging system can realize conventional intensity imaging. After the metasurface is inserted, the polarization imaging system can realize polarization imaging, thereby improving the ability of the entire imaging system to obtain higher-dimensional information.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a pluggable polarization imaging system based on metasurface and traditional optics. When the metasurface is not inserted or pulled out, the polarization imaging system functions as light intensity imaging; after the polychromatic light source is incident on the refractive lens of the imaging system, it is focused on the detector pixel surface to form an imaging focus, thereby realizing light intensity imaging; when the metasurface is inserted, the polarization imaging system functions as polarization imaging; after the polychromatic light source is incident on the refractive lens of the imaging system, it is focused and irradiated onto the metasurface, and different polarization components in the polychromatic light source are split and deflected by the metasurface to corresponding positions, and different polarization imaging focuses are formed on the detector pixel surface, thereby realizing polarization imaging; the metasurface is composed of a metasurface substrate and a metasurface structure; in the imaging system without the metasurface and the imaging system with the metasurface, the refractive lens of the imaging system and the detector pixel surface remain unchanged.

[0006] The pluggable polarization imaging system construction method can be designed for any wavelength band and aperture. By inserting a metasurface into the design of a traditional intensity imaging system, polarization information can be acquired, improving the ability to obtain higher-dimensional information. First, the optical system parameters, such as the operating wavelength, entrance pupil diameter, f-number, and back working distance, must be determined. Then, a design is performed for the traditional intensity imaging system. This can be accomplished using optical design software such as Zemax OpticStudio and Code V, ensuring that the designed traditional intensity imaging system meets the required optical system specifications. This article uses Zemax OpticStudio as an example for design demonstration. After the traditional intensity imaging system design is completed, Binary Surface 1 is inserted between the last surface of the designed optical system and the pixel surface as a metasurface. This is because the metasurface is essentially a diffraction element and can be implemented using Binary Surface 1. The working distance between Binary Surface 1 and the pixel surface is determined based on actual requirements, and the thickness of Binary Surface 1 should be subtracted from the thickness of the last surface. Based on the definition of Binary Surface 1, its polynomial parameters are set as variables. Using the Add Optimization Wizard, operators are added to optimize Binary Surface 1. Binary surface 1 acts as a deflection light, so a corresponding offset is required. The offset should match the size of the detector target surface. Here, it is assumed that the size of the detector target surface is M×N, and the focus offset is It is ensured that the offset can be achieved by setting the operand at the center of each quadrant. During the optimization process, the traditional light intensity imaging system designed previously should remain unchanged. After the optimization is completed, the polynomial parameters of the binary surface 1 will be obtained, and the phase value of the entire binary surface 1 can be obtained by calculation, that is, the phase value of the metasurface, which can be regarded as the ideal phase of the metasurface. Since the previous optical system has been fully designed and bears most of the optical focal length, the binary surface 1 plays the role of beam deflection in the entire optical system, and its phase value distribution is generally a linear distribution, which provides a solution for the design and implementation of large-area metasurfaces.

[0007] After obtaining the optimized binary surface 1 phase value, it can be used to match the metasurface structure. As mentioned above, the metasurface phase is nearly linear, so only the phase value within a 2π period can be matched, and then it can be arrayed along the linear direction to achieve the desired function. The matching formula is as follows

[0008]

[0009] Here, the micro-nanostructure that minimizes δ is selected as the micro-nanostructure at this position, where δ represents the difference between the transmittance and phase response of the selected micro-nanostructure in the complex domain and the theoretical phase, t x represents the transmittance of the micro-nanostructure, represents the phase of the micro-nanostructure in the complex domain, represents the theoretical complex domain phase value at that position. The phase plane only needs to be optimized once. The phase planes required for different polarizations can be obtained by symmetric and flipping the optimized phase plane, and then matching them accordingly. Once all is completed, the structures required for each polarization are randomly arranged to form the final layout.

[0010] The beneficial effects of adopting the above technical solution are:

[0011] 1. The present invention proposes a pluggable polarization imaging system based on a metasurface and traditional optics. Compared to traditional polarization imaging systems, it has the advantages of larger aperture, greater compactness, and greater integration. Furthermore, its pluggable nature allows the entire optical system to adopt different imaging modes for different scenarios. For example, in reconnaissance operations, a suspicious target can be searched without inserting a metasurface, and then the polarization imaging function can be used to identify and track the target by inserting a metasurface.

[0012] 2. Compared with traditional polarization imaging and metasurface polarization imaging methods, the pluggable polarization imaging construction method of the present invention is easy to understand and implement. It not only solves the problems of large size and difficulty in integration of traditional polarization imaging methods, but also solves the problems of large aperture and dispersion faced by metasurface imaging. By combining the advantages of both, it realizes large-aperture, achromatic, and polarization imaging functions.

[0013] 3. The pluggable polarization imaging construction method based on metasurfaces and traditional optics proposed in the present invention is simple and easy to understand. The linear metasurface phase value only needs to match a phase segment, and the array obtains the overall phase surface. It is easy to program and implement, and can be implemented at any wavelength, such as visible light, mid-infrared, and far-infrared. This has positive significance for the functional integration and miniaturization of optical systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a stereoscopic schematic diagram of the pluggable polarization imaging based on metasurface and traditional optics of the present invention.

[0015] Figure 2 Schematic diagram of a specific implementation case of pluggable polarization imaging based on metasurface and traditional optics of the present invention.

[0016] Figure 3 Phase distribution map and contour map of the metasurface in the pluggable polarization imaging based on the metasurface and traditional optics of the present invention.

[0017] Figure 4 This is a linear fitting diagram of the metasurface phase in the pluggable polarization imaging based on the metasurface and traditional optics of the present invention, as well as a diagram of the results using grid phase inversion.

[0018] Figure 5 This is a diagram showing the metasurface structure matching results for one segment of the linear fitting in the pluggable polarization imaging based on the metasurface and traditional optics of the present invention.

[0019] Figure 6 This is a flow chart of the pluggable polarization imaging design method based on metasurfaces and traditional optics of the present invention.

[0020] In the figure: 1. Polychromatic light source, 2. Refractive lens of the imaging system, 3. Detector pixel surface, 4. Imaging focus, 5. Metasurface substrate, 6. Metasurface structure, 7. Imaging focus with different polarizations. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0022] like Figure 1 The figure shows a stereoscopic diagram of the pluggable polarization imaging based on metasurface and traditional optics of the present invention. Figure 1(a) Schematic diagram of the optical system when the metasurface is not inserted (pulled out). In this case, the optical system functions as light intensity imaging. Figure 1 (b) Schematic diagram of the optical system when the metasurface is inserted, where the optical system functions as polarization imaging. The optical system when the metasurface is not inserted consists of a polychromatic light source 1, an imaging system refractive lens 2, a detector pixel plane 3, and an imaging focus 4. After the polychromatic light source 1 is incident on the imaging system refractive lens 2, it is focused on the detector pixel plane 3 to form the imaging focus 4, achieving light intensity imaging. The optical system when the metasurface is inserted consists of a polychromatic light source 1, an imaging system refractive lens 2, a metasurface, a detector pixel plane 3, and different polarization imaging focuses 7. The metasurface consists of a metasurface substrate 5 and a metasurface structure 6. After the polychromatic light source 1 is incident on the imaging system refractive lens 2, it is focused and irradiated onto the metasurface, where different polarization components are split and deflected by the metasurface to corresponding positions, forming different polarization imaging focuses 7 on the detector pixel plane 3. It should be emphasized that the refractive lens parameters and detector pixel surface of the optical system with and without the metasurface are the same and will not change with the insertion and removal; different polarization imaging focuses are used as examples here and can be designed according to different application scenarios. The construction process of the metasurface can be divided into four parts, such as Figure 6 As shown, it includes designing a traditional light intensity imaging system according to the optical system parameter requirements so that it can bear most of the optical focal length, inserting a binary plane 1 in front of the image plane, setting corresponding polynomial variables, and optimizing with corresponding operands, deriving the obtained ideal binary plane 1 phase value, and performing linear fitting on it in rows and columns, and matching and arraying the phase value completed by the linear fitting with the next 2π period of the maximum wavelength, and finally realizing the design.

[0023] Before designing the entire optical system, the parameter requirements of the optical system should be clarified. Here, we take the mid-wave infrared band as an example: working band 4~4.8μm, entrance pupil diameter 75mm, F=2, and back working distance>50mm. First, design a traditional optical imaging system according to the system requirements. Using Zemax OpticStudio software as an example, after setting and optimizing the relevant parameters, we can obtain an optical system that meets our parameter requirements. Figure 2 As shown in (a), it consists of two lenses made of silicon and germanium. Figure 2(b)(c) show the point diagram and MTF curve of the optical system in the corresponding band. It can be seen that the RMS is within the Airy disk and the MTF curve is close to the diffraction limit, which shows the feasibility of the optical system. Further, a binary surface 1 is inserted between the last surface of the designed optical system and the pixel surface as a metasurface. The working distance between the binary surface 1 and the pixel surface is determined according to the actual indicators. Then, according to the polynomial phase definition of the binary surface 1, its polynomial phase parameters are set as variables, and the operands CENX and CENY are used to determine the focus offset. Here, in order to facilitate the subsequent metasurface design, we will deflect the offset to the X direction. The detector target surface size used is 640×512@15μm, and the calculated offset is 3.07mm. When performing the next optimization, the original optical system parameters should be kept unchanged. At the same time, the thickness of the metasurface and the thickness of the last piece of the optical system should be the same as the distance from the last piece of the original optical system to the phase surface. The optimized binary surface 1 is shown in the figure below. Figure 2 As shown in (d), it can be seen that the light is deflected after passing through the binary surface 1. Figure 2 (e) (f) The point diagrams and MTF curves also show that the quality of the imaging effect remains consistent with the original one, demonstrating the feasibility of the optical system after inserting the metasurface.

[0024] The optimized binary face 1 phase is as follows Figure 3 As shown, its phase contour diagram is as follows Figure 3 As shown, it can be seen that the phase value of binary plane 1 is approximately linear, which means that the phase matching of the entire amplitude can be achieved through the phase array, which will greatly reduce the amount of calculation. Figure 3 Taking the wavelength of 4.4μm as an example, each wavelength has a different phase plane during optimization, and all of them should be considered during matching. The ideal phase value of the binary surface 1 obtained by optimization is used as the ideal phase value of the metasurface, and a linear fit is performed on it, such as Figure 4 As shown, the fitted linear phase is reversed back to the original model using the grid phase function of Zemax OpticStudio software. The three-dimensional schematic diagram after reverse substitution is shown in Figure 4 As shown in Figure 2, the reverse substitution results confirm the feasibility of linear fitting. The ideal phase value after linear fitting is matched with the metasurface structure, and the matching formula is as follows:

[0025]

[0026] Here, the micro-nanostructure that minimizes δ is selected as the micro-nanostructure at this position, where δ represents the difference between the transmittance and phase response of the selected micro-nanostructure in the complex domain and the theoretical phase, t x represents the transmittance of the micro-nanostructure, represents the phase of the micro-nanostructure in the complex domain, Indicates the theoretical complex domain phase value of the position. The matching result is as follows Figure 5 As shown, the broken line represents the ideal phase of the metasurface, and the circles represent the phase values ​​that the metasurface structure can provide. This indicates that there is a certain error except for certain wavelengths. The average wavefront error between the ideal and actual phases is calculated to be less than 0.07, which is acceptable and confirms the feasibility of this solution. Phase plane matching only needs to be optimized once, because the phase planes required for different polarizations can be obtained by symmetric flipping of the ideal phase plane, resulting in consistent matching results. Once all matching is complete, the structures required for each polarization are randomly arranged to form the final layout.

[0027] The above are only preferred specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with this technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solutions and inventive concepts of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A pluggable polarization imaging system based on metasurfaces and traditional optics, characterized in that: When the metasurface is not inserted or removed, the polarization imaging system functions as light intensity imaging; after the polychromatic light source (1) is incident on the refractive lens (2) of the imaging system, it is focused on the detector pixel surface (3) to form an imaging focus (4), thereby realizing light intensity imaging; When inserted into the metasurface, the polarization imaging system functions as polarization imaging; after the polychromatic light source (1) is incident on the refractive lens (2) of the imaging system, it is focused and irradiated onto the metasurface, and different polarization components in the polychromatic light source (1) are split and deflected to corresponding positions by the metasurface, and different polarization imaging focuses (7) are formed on the detector pixel surface (3), thereby realizing polarization imaging; The metasurface is composed of a metasurface substrate (5) and a metasurface structure (6); in an imaging system without the metasurface and an imaging system with the metasurface, the imaging system refractive lens (2) and the detector pixel surface (3) remain unchanged.

2. A method for constructing a pluggable polarization imaging system based on a metasurface and traditional optics as claimed in claim 1, characterized in that: The build steps are: Step 1: First, use Zemax OpticStudio optical software to design the light intensity imaging system according to the imaging system parameter requirements, so that the light intensity imaging system takes on most of the optical power; Step 2: insert the binary surface 1 before the detector pixel surface (3), set the corresponding polynomial variables, and optimize with the corresponding operands to obtain the phase value of the ideal binary surface 1, and derive the obtained phase value; Step 3: Perform linear fitting on the derived phase values ​​in rows and columns to obtain fitted phase values; Step 4: Match the fitted phase value within a 2π period at the maximum wavelength with the micro-nanostructure in the database to obtain a micro-nanostructure within a 2π period; Step 5: Array the obtained micro-nanostructures to obtain a metasurface, and finally complete the entire polarization imaging system.

3. The method for constructing a pluggable polarization imaging system based on metasurface and traditional optics according to claim 1, characterized in that: The metasurface deflects light as it passes through it, with different polarization states having different offsets. The offsets are determined according to the settings. Once the different polarizations are matched, the overall layout design can be achieved by simply merging their respective layouts into one.

4. The method for constructing a pluggable polarization imaging system based on metasurface and traditional optics according to claim 2, characterized in that: In step 3, linear fitting can be performed on the central part, and different rows or columns can be linearly fitted separately according to the phase surface of the metasurface.

5. The method for constructing a pluggable polarization imaging system based on metasurface and traditional optics according to claim 2, characterized in that: In step 4, the matching formula is as follows: Here, the micro-nanostructure that minimizes δ is selected as the micro-nanostructure at this position, where δ represents the difference between the transmittance and phase response of the selected micro-nanostructure in the complex domain and the theoretical phase, t x represents the transmittance of the micro-nanostructure, represents the phase of the micro-nanostructure in the complex domain, It represents the theoretical complex domain phase value of the position; at the same time, the phase plane only needs to be optimized once, and the phase planes required for different polarizations can be obtained by symmetry and flipping the optimized phase plane, and the corresponding matching can be completed; after all is completed, the structures required for each polarization are randomly arranged to form the final layout.

Images