Method for improving polarization extinction ratio in meta-structure surface polarization imaging

Abstract

The invention discloses a method for improving the polarization extinction ratio in polarization imaging of a super-structure surface, and relates to the technical field of polarization imaging. Specific linear polarizers are added in front of different quadrants on the pixel surface of the detector according to the sizes of the polarization metasurface and the pixel surface of the detector and different focused polarization states, the linear polarizers can be in any form, and when a focused light beam passes through the specific linear polarizers, the polarization extinction ratio is further improved. The method is easy to integrate with a detector pixel, does not need to sacrifice other imaging characteristics of the super-structure surface, improves the polarization extinction ratio of the super-structure surface during polarization imaging while not reducing the imaging quality of the original super-structure surface, and improves the imaging quality of the super-structure surface. And the system accords with the trend of function integration and miniaturization of an optical system, and has positive significance.

Description

Technical Field

[0001] The present invention belongs to the technical field of polarization imaging, and more specifically, relates to a method for improving the polarization extinction ratio in metasurface polarization imaging. Background Art

[0002] With the continuous development and maturity of autonomous driving technology, drone reconnaissance technology, and remote sensing fields, new requirements have been put forward for information detection. Traditional imaging technology usually relies on the intensity of light, known as intensity imaging, which can only obtain the intensity information of an object and cannot further obtain higher-dimensional information. Polarization imaging is a technology that uses the polarization state of light to obtain images. After light waves interact with the object surface, they can exhibit different polarization states during propagation, such as linear polarization, circular polarization, and elliptical polarization. Therefore, polarization imaging can extract more information by analyzing the polarization characteristics of light to meet the imaging requirements of complex scenarios. And these polarization information can be used to analyze the shape of the target, surface roughness, texture orientation, and physical and chemical properties of materials, etc. Based on its characteristics, polarization information detection has been widely used in medical imaging, materials science, and security monitoring, etc.

[0003] However, traditional polarization information detection devices usually contain a variety of optical elements, such as various polarizers and prisms, with complex structures and large volumes, and cannot well meet the trend of miniaturization and easy integration of optical elements. The metasurface that emerged in recent years is a type of artificial material based on subwavelength structures, which naturally has the characteristics of small size, light weight, and easy integration, and is considered a new generation of optical materials. Research has proven its ability to control the amplitude, phase, polarization, and other characteristics of electromagnetic waves, with many potential applications. These characteristics can perfectly adapt to the trends of miniaturization and integration of optical systems, which provides a new solution idea for polarization imaging. Metasurface polarization imaging can achieve single-chip real-time imaging, but it is often limited by factors such as micro-nano structure databases, design methods, and processing errors, and there is a certain gap between its effect and traditional polarization imaging. Among them, the polarization extinction ratio is an important evaluation criterion for polarization imaging. A high polarization extinction ratio is beneficial to enhancing image contrast, improving the signal-to-noise ratio, enhancing target detection ability, and improving image quality. However, it is difficult to achieve a relatively high polarization extinction ratio only through a single metasurface, and it will sacrifice other imaging characteristics. Therefore, a method is needed to improve the polarization extinction ratio in metasurface polarization imaging. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for improving the polarization extinction ratio in metasurface polarization imaging. By adding different linear polarizers in front of the detector pixels, the unwanted polarized light is filtered out without sacrificing other imaging characteristics of the metasurface. While not reducing the original imaging quality of the metasurface, the polarization extinction ratio in metasurface polarization imaging is improved, the target detection ability is enhanced, and it is also convenient for design and processing.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is: it can be designed for metasurface polarization imaging in different bands. Metasurface polarization imaging generally refers to focusing specific polarizations in incident polychromatic light sources or other polarized light sources to different focal positions. Metasurface polarization imaging has 4 focal points, that is, polarizations of 4 different polarization states are focused to 4 different focal points, which are focused into four quadrants. The specific positions of the focal points are determined according to the size of the detector pixel plane. Here, in order to maximize the utilization efficiency of the pixel plane, the positions of the focal points are the central positions of the four quadrants of the detector pixel plane respectively. Assuming the number of pixels of the detector is M×N, where M represents the number of horizontal pixels and N represents the number of vertical pixels, and the size of a single pixel is P×P, then the size of the detector pixel plane is MP×NP. The four focal point positions are located at the centers of the four quadrants, which are (MP / 4,NP / 4), (-MP / 4,NP / 4), (-MP / 4,-NP / 4), (MP / 4,-NP / 4). When light of different polarization states is focused separately, due to factors such as the metasurface design method and the metasurface processing accuracy, the polarization states at each focused focal point are not completely ideal, that is, there are also beams of other polarization states focused here, which will reduce the polarization extinction ratio of the metasurface polarization imaging and is not conducive to subsequent target detection, polarization recovery, etc. Of course, the polarization extinction ratio can be improved by improving the design of the metasurface, but it will often reduce the imaging quality of the metasurface, including the focusing efficiency.

[0006] By adding a linear polarizer in front of the detector pixel, which can be in any form, the polarization extinction ratio is further improved. Specifically, it is embodied as adding a linear polarizer in front of each of the four quadrants of the detector pixel plane. For example, adding a corresponding linear polarizer in front of the first quadrant, only allowing specific polarization to pass through, improving the polarization extinction ratio. This is also the reason for setting the different focal point positions at the centers of the four quadrants. By adding linear polarizers with different angles in front of the four quadrants, the unwanted polarized light is filtered out, further improving the polarization extinction ratio of the metasurface polarization imaging. This will improve the polarization extinction ratio in metasurface polarization imaging without reducing the original imaging quality of the metasurface, enhance the target detection ability, and at the same time, the production process of the polarizer is mature, and the addition of large-area polarizers also reduces the process difficulty in aspects such as integration and alignment, and reduces the corresponding costs.

[0007] The beneficial effects produced by adopting the above technical solutions are as follows:

[0008] 1. The method for improving the polarization extinction ratio in metasurface polarization imaging proposed by the present invention adds a linear polarizer in front of the detector pixel, which can effectively reduce the influence of the reduction of the polarization extinction ratio caused by processing accuracy, design conditions, etc. during the imaging process of metasurface polarization imaging, and can effectively improve the polarization extinction ratio during metasurface imaging, which is beneficial to subsequent target detection, recognition, and polarization detection. Compared with the traditional method of processing a small-area polarization wire grid on the detector pixel surface of the sub-focal plane, the manufacturing process of the polarizer is mature, and the addition of a large-area polarizer also reduces the process difficulty in terms of integration, alignment, etc., and does not require precise alignment;

[0009] 2. Compared with the previous methods that focused on improving the polarization extinction ratio of metasurface polarization imaging in design, this method does not need to sacrifice other imaging characteristics of the metasurface, does not require additional design and sacrifice of a certain focusing efficiency, and reduces the design pressure while not reducing the original imaging quality of the metasurface. For example, when simultaneously considering achromatism and polarization extinction ratio, this method can allocate more design inputs to the achromatism part to improve the imaging quality;

[0010] 3. The method for improving the polarization extinction ratio of metasurface polarization imaging proposed by the present invention can be applied to polarization imaging in any band, such as visible light, infrared band, etc., to improve its polarization extinction ratio, and is easy to integrate with the detector pixel itself, conforming to the trend of functional integration and miniaturization of optical systems, which has positive significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a three-dimensional schematic diagram of the method for improving the polarization extinction ratio in metasurface polarization imaging of the present invention;

[0012] Figure 2 is a schematic diagram of metasurface polarization imaging in the method for improving the polarization extinction ratio in metasurface polarization imaging of the present invention;

[0013] Figure 3 is a schematic diagram of integrating a linear polarizer on the detector pixel surface in the method for improving the polarization extinction ratio in metasurface polarization imaging of the present invention;

[0014] In the figure: 1. polychromatic light source, 2. polarization metasurface, 3. linear polarizer, 4. polarization focusing focus, 5. detector pixel surface. DETAILED DESCRIPTION OF THE INVENTION

[0015] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without making creative efforts shall fall within the protection scope of the present application.

[0016] A method for improving the polarization extinction ratio in metasurface polarization imaging can be designed for metasurface polarization imaging in different bands. As Figure 1 shown, when a polychromatic light source 1 is incident on a polarization metasurface 2, the polarization metasurface 2 will focus the polarized light of different polarization states on the detector pixel plane 5 respectively after passing through a linear polarizer 3, forming a polarization focusing focus 4. This polarization focusing focus 4 has a higher polarization extinction ratio. Next, it will be introduced in two parts.

[0017] As Figure 2As shown, metasurface polarization imaging generally refers to focusing specific polarizations in an incident polychromatic light source or other polarized light sources to different focal points at different positions. Generally, metasurface polarization imaging has 4 focal points, that is, polarizing light with 4 different polarization states is focused to 4 different focal points, which are focused into four quadrants. Here, 4 different linear polarization states of 0°, 45°, 90°, and 135° are selected for focusing. Of course, other polarization states can also be selected. The specific positions of the focal points are determined according to the size of the detector pixel plane 5. Here, in order to maximize the utilization efficiency of the pixel plane, the positions of the focal points are the respective central positions of the four quadrants of the detector pixel plane 5. Assume that the number of pixels of the detector is M×N, where M represents the number of horizontal pixels and N represents the number of vertical pixels, and the size of a single pixel is P×P. Then the size of the detector pixel plane 5 is MP×NP. The four focal point positions are located at the centers of the four quadrants, which are (MP / 4, NP / 4), (-MP / 4, NP / 4), (-MP / 4, -NP / 4), and (MP / 4, -NP / 4) respectively. Taking a common long-wave infrared detector as an example, the number of pixels of the detector is 1280×1024, that is, there are 1280 pixels horizontally and 1024 pixels vertically, and the size of a single pixel is 12×12 μm. Therefore, the size of the detector pixel plane 5 is 15360×12288 μm, and the four focal point positions are located at the centers of the four quadrants, which are (3840, 3072), (-3840, 3072), (-3840, -3072), and (3840, -3072) respectively, with the unit of μm. The detector converts the obtained optical signal into an electrical signal through subsequent processing and then outputs it as an image, which is metasurface polarization imaging. However, when light with different polarization states is focused separately, due to factors such as the metasurface design method and metasurface processing accuracy, the polarization states at each focused focal point are not completely ideal, that is, there are also other polarized light beams focused here, which will reduce the polarization extinction ratio of metasurface polarization imaging and is not conducive to subsequent target detection, polarization recovery, etc. Of course, the polarization extinction ratio can be improved by improving the design of the metasurface, but it will often reduce the imaging quality of the metasurface, including the focusing efficiency.

[0018] By adding a linear polarizer 3 in front of the detector pixel 5, which can be in any form, the polarization extinction ratio can be further improved, specifically by adding a linear polarizer 3 in front of each of the four quadrants of the detector pixel plane 5. As Figure 3As shown. Combining the detector pixel plane 5 with the corresponding linear polarizer 3 and integrating them into one body to improve the polarization extinction ratio of the metasurface. This is because the linear polarizer only allows the polarization component with the same direction as the linear polarizer to pass through. The metasurface itself already has a high polarization extinction ratio when performing polarization imaging and focusing. The addition of the linear polarizer further improves the polarization extinction ratio. Taking the above-mentioned metasurface polarization imaging as an example, it is reflected in adding a 45° linear polarizer to the first quadrant of the detector pixel plane 5, allowing only 45° linearly polarized light to pass through. Adding a 0° linear polarizer to the second quadrant of the detector pixel plane 5, allowing only 0° linearly polarized light to pass through. Adding a 135° linear polarizer to the third quadrant of the detector pixel plane 5, allowing only 135° linearly polarized light to pass through. Adding a 90° linear polarizer to the fourth quadrant of the detector pixel plane 5, allowing only 90° linearly polarized light to pass through. This is also the reason for setting different focal positions at the centers of the four quadrants. By adding four different linear polarizers 3 in front of the four quadrants of the detector pixel plane 5 to filter out the unwanted polarized light, the polarization extinction ratio of the metasurface polarization imaging is further improved. This will improve the polarization extinction ratio during metasurface polarization imaging without reducing the original imaging quality of the metasurface, enhance the target detection ability. At the same time, the manufacturing process of the polarizer is mature, and the addition of a large-area polarizer also reduces the process difficulty in aspects such as integration and alignment, and reduces the corresponding costs.

[0019] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes, should be covered within the protection scope of the present invention.

Claims

1. A method for improving the polarization extinction ratio in metasurface polarization imaging, characterized in that Design for metasurface polarization imaging in different bands. When a polychromatic light source (1) is incident on the polarization metasurface (2), the polarization metasurface (2) will focus polarized light with different polarization states on the detector pixel plane (5) respectively after passing through the linear polarizer (3), forming polarization focused foci (4), and the polarization focused foci (4) have a high polarization extinction ratio.

2. A method for improving the polarization extinction ratio in metasurface polarization imaging according to claim 1, characterized in that The polarization metasurface (2) focuses polarized light with different polarization states to the center positions of the respective four quadrants of the detector pixel plane (5). Then the positions of the four polarization focused foci (4) are (MP / 4, NP / 4), (-MP / 4, NP / 4), (-MP / 4, -NP / 4), (MP / 4, -NP / 4) respectively, where M represents the number of horizontal pixels of the detector pixel, N represents the number of vertical pixels of the detector pixel, and P represents the size of the detector pixel.

3. A method for improving the polarization extinction ratio in metasurface polarization imaging according to claim 2, characterized in that, According to the size of the polarization metasurface (2) and the detector pixel plane (5), and according to the different polarization states of focusing, different linear polarizers (3) are added in front of different quadrants of the detector pixel plane (5), and the linear polarizer (3) should cover the entire quadrant.

4. A method for improving the polarization extinction ratio in metasurface polarization imaging according to claim 3, characterized in that, The added linear polarizer (3) is in any form, and other linear polarizers (3) can be customized according to requirements. The linear polarizer (3) is combined with different types of wave plates to perform polarization filtering on elliptically polarized light and improve the polarization extinction ratio.

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