Radial polarization splitting metasurface and its simultaneous phase shifting method

Abstract

The application provides a radial polarization splitting metasurface and a synchronous phase-shifting method thereof, and relates to the technical field of optical devices, and comprises a substrate; a surface structure arranged on the substrate, the surface structure is composed of a plurality of sub-wavelength structure units in a ring arrangement mode; wherein the sub-wavelength structure units on the same ring have the same rotation angle, and the rotation angles of the sub-wavelength structure units on different rings change with the radii of the rings, so that different phase modulations can be generated on left-handed circularly polarized light and right-handed circularly polarized light of incident linearly polarized light respectively, so that the left-handed circularly polarized light or the right-handed circularly polarized light forms a divergent light beam, and the other beam forms a convergent light beam. Through the unique ring arrangement and the sub-wavelength structure units with the rotation angle changing with the radius, different phase modulations can be respectively applied to left-handed and right-handed components of incident linearly polarized light, divergent and convergent light beams with orthogonal polarization states are efficiently generated, and a foundation is laid for dynamic measurement based on polarization phase shifting.

Description

Technical Field

[0001] This invention relates to the field of optical device technology, and specifically to a radially polarized beam-splitting metasurface and its synchronous phase-shifting method. Background Technology

[0002] Optical interferometry is one of the core techniques in modern precision measurement. Among them, co-path radial shearing interferometry is widely used in high-precision measurements such as optical component surface shape errors and laser wavefront phase due to its advantages such as compact optical path and insensitivity to environmental vibrations and airflow disturbances. The emergence of zone plate radial shearing interferometry and metasurface radial shearing interferometry has enabled on-chip integration of this technology, replacing the complex optical path of traditional radial shearing interferometry, greatly reducing system complexity and improving environmental adaptability. However, existing zone plates and metasurfaces do not support synchronous phase shifting in radial shearing interferometry, forcing their solutions to rely on algorithms such as virtual four-step phase shifting, linear carrier demodulation based on coordinate transformation, and regularized phase tracking. Compared to phase-shifting algorithms, these algorithms are slower, less accurate, and less capable of obtaining mid-to-high frequency phase difference information.

[0003] While radial shearing interferometry techniques based on mechanical phase shifting and wavelength-tuned phase shifting exist, they are all asynchronous phase shifting methods. These methods acquire multiple (usually four or more) interferograms with fixed phase differences over a time series, and then calculate the phase distribution using algorithms. This time-series phase shifting method is extremely sensitive to instantaneous disturbances such as environmental vibrations and air turbulence during the measurement process, easily introducing phase shift errors and leading to decreased phase calculation accuracy. Furthermore, it requires sequential acquisition of multiple frames, making instantaneous measurement under a single exposure impossible and hindering its application to wavefront detection in dynamic or transient processes. Although common-path design improves anti-interference capabilities to some extent, the fundamental defects caused by asynchronous measurement severely limit the application of radial shearing interferometry in high-speed, high-precision, and high-stability measurement scenarios. Therefore, there is an urgent need in this field for a novel radial shearing interferometer device capable of synchronous phase shifting to fundamentally overcome the shortcomings of existing technologies and improve overall measurement performance.

[0004] Therefore, existing technologies still need further development. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a radially polarized beam-splitting metasurface and its synchronous phase-shifting method to solve the problems existing in the prior art.

[0006] To achieve the above-mentioned technical objectives, according to a first aspect of the present invention, the present invention provides a radially polarized beam-splitting metasurface, comprising a substrate, and further comprising:

[0007] The surface structure disposed on the substrate is composed of multiple subwavelength structural units arranged in a ring.

[0008] In this system, the subwavelength structural units on the same ring have the same rotation angle, while the rotation angle of the subwavelength structural units on different rings varies with the ring radius. This allows for different phase modulations of the left-hand circularly polarized light and the right-hand circularly polarized light of the incident linearly polarized light, so that the left-hand circularly polarized light or the right-hand circularly polarized light forms a diverging beam, while the other beam forms a converging beam.

[0009] Specifically, the rotation angle of the subwavelength structural unit is calculated using the following formula:

[0010] ;

[0011] Where r represents the rotation radius of the subwavelength structural unit, i.e., the ring radius. This represents the rotation angle of the subwavelength structural unit. Indicates the wavelength of incident ray-polarized light. This indicates the focal length of the converging or diverging beam.

[0012] Specifically, the method of generating different phase modulations for the left-handed and right-handed circularly polarized incident light includes:

[0013] By rotating the subwavelength structural units on different rings by an angle in a clockwise direction At the same time, it can produce a +2θ phase modulation on left-handed circularly polarized light and a -2θ phase modulation on right-handed circularly polarized light.

[0014] Alternatively, by rotating the subwavelength structural units on different rings by an angle in a counterclockwise direction. At that time, it produces a +2θ phase modulation on right-hand circularly polarized light and a -2θ phase modulation on left-hand circularly polarized light.

[0015] Specifically, the phases of the left-handed circularly polarized light and the right-handed circularly polarized light after phase modulation are calculated using the following formula:

[0016] ;

[0017] ;

[0018] in, This indicates the phase of left-handed circularly polarized light after phase modulation. This indicates the phase of right-handed circularly polarized light after phase modulation. Indicates the wavelength of incident ray-polarized light. This indicates the focal length of the converging or diverging beam.

[0019] Specifically, the subwavelength structural unit is an anisotropic superatom that operates based on the geometric phase principle.

[0020] According to a second aspect of the present invention, a method for synchronous phase shift measurement of a radially polarized beam-splitting metasurface is provided, comprising:

[0021] S100, The beam to be tested is incident onto the radially polarized beam-splitting metasurface;

[0022] S200. The left-hand circularly polarized light and the right-hand circularly polarized light in the beam to be tested are phase-modulated by the radially polarized beam splitter surface to generate a diverging beam and a converging beam with orthogonal polarization states.

[0023] S300: The diverging beam and the converging beam interfere to form an interference image carrying the wavefront information to be measured;

[0024] S400: Acquire interference images with a fixed phase difference in different linear polarization directions;

[0025] S500. Based on the interference image, calculate the wavefront phase distribution of the beam under test;

[0026] Beneficial effects:

[0027] This invention provides a radially polarized beam splitting metasurface and its synchronous phase-shifting method. The radially polarized beam splitting metasurface provided by this invention, through its unique annular arrangement of subwavelength structural units with rotation angles varying with the radius, can apply different phase modulations to the left-hand and right-hand components of incident ray-polarized light, efficiently generating diverging and converging beams with orthogonal polarization states. This allows the metasurface to successfully introduce polarization properties into the radial shearing interferometry system, laying the physical foundation for dynamic measurement based on polarization phase shifting. This fundamentally solves the technical problems of slow measurement speed and inability to detect high-frequency phase information in traditional radial shearing interferometry, significantly improving the accuracy, efficiency, and dynamic detection capability of radial shearing interferometry. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of the radially polarized beam-splitting metasurface provided in a specific embodiment of the present invention;

[0029] Figure 2 This is a flowchart of the synchronous phase-shifting method for a radially polarized beam-splitting metasurface provided in a specific embodiment of the present invention;

[0030] The reference numerals in the above figures are as follows:

[0031] 1. Substrate; 2. Surface structure; 3. Subwavelength structural unit. Detailed Implementation

[0032] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Other similar embodiments obtained by those skilled in the art based on the embodiments in this application without creative effort should all fall within the scope of protection of this application. Furthermore, directional terms mentioned in the following embodiments, such as "up," "down," "left," and "right," are only for reference to the directions in the accompanying drawings; therefore, the directional terms used are for illustrative purposes and not for limiting the invention.

[0033] The present invention will be further described below with reference to the accompanying drawings and preferred embodiments.

[0034] Example 1

[0035] Please see Figure 1 This embodiment provides a radially polarized beam splitting metasurface, comprising a substrate 1 and a surface structure 2 disposed on the substrate 1. The surface structure 2 is composed of multiple subwavelength structural units 3 arranged in a ring. In this embodiment, the subwavelength structural units 3 on the same ring have the same rotation angle, while the rotation angles of the subwavelength structural units 3 on different rings vary with the ring radius. This special structural design enables the radially polarized beam splitting metasurface to generate different phase modulations for left-handed and right-handed circularly polarized incident light, thereby causing left-handed circularly polarized light to form a diverging beam and right-handed circularly polarized light to form a converging beam, or vice versa. This solves the technical problems of traditional time-phase shifting techniques, such as sensitivity to environmental vibrations, slow measurement speed, and inability to detect high-frequency phase information. It significantly improves the accuracy, efficiency, and dynamic detection capability of radial shear interferometry, laying a physical foundation for synchronous measurement based on polarization phase shifting.

[0036] In some specific embodiments, in the design of this radially polarized beam-splitting metasurface, the subwavelength structural unit 3 is anisotropic superatoms operating based on the geometric phase principle, such as rectangular nanopillars, rectangular holes, elliptical holes, or elliptical hole structures. This superatomic structure can effectively control the polarization state and phase of the incident beam, thereby achieving differentiated modulation of left-handed and right-handed circularly polarized light. The size of these superatoms is smaller than the operating wavelength, typically half or one-third of the wavelength. Their materials can be high-refractive-index dielectric materials such as silicon nitride, silicon dioxide, titanium dioxide, or silicon, or metal-dielectric composite structures, to achieve efficient phase modulation.

[0037] In some specific embodiments, the operating wavelength of the surface structure 2 is located in the visible light (e.g., λ=532nm) or infrared light (e.g., λ=1064nm), making it applicable to real-time monitoring of various optical systems, measurement of optical elements or beams. Furthermore, different wavelengths can be adapted by adjusting the size and period of the superatoms. In this embodiment, the substrate 1 can be silicon dioxide, and the surface structure can be silicon.

[0038] In this embodiment, all superatoms on the same ring have the same rotation angle. The rotation angle of superatoms on different rings The rotation angle of subwavelength structural unit 3 varies with the radius r. Calculated using the following formula:

[0039] ;

[0040] Where r represents the rotation radius of the superatom, i.e., the toroidal radius. This indicates the rotation angle of subwavelength structural unit 3. Indicates the wavelength of incident ray-polarized light. This indicates the focal length of the converging or diverging beam.

[0041] In this embodiment, when the subwavelength structural units 3 on different rings are rotated clockwise by an angle θ, a +2θ phase modulation is generated for left-handed circularly polarized light, and a -2θ phase modulation is generated for right-handed circularly polarized light. Alternatively, by rotating the subwavelength structural units 3 on different rings counterclockwise by an angle θ... At the same time, it generates a +2θ phase modulation on right-hand circularly polarized light and a -2θ phase modulation on left-hand circularly polarized light (the phase modulation amounts for left-hand and right-hand circularly polarized light can be interchanged). This differentiated phase modulation is the key mechanism for the radially polarized beam splitter to achieve beam separation.

[0042] Furthermore, the phases of left-handed circularly polarized light (LCP) and right-handed circularly polarized light (RCP) after phase modulation can be calculated using the following formula:

[0043] ;

[0044] ;

[0045] in, This indicates the phase of left-handed circularly polarized light after phase modulation. This indicates the phase of right-handed circularly polarized light after phase modulation. Indicates the wavelength of incident ray-polarized light. This indicates the focal length of the converging or diverging beam.

[0046] According to the above technical solution, phase modulation is performed on left-handed and right-handed circularly polarized light, which is equivalent to adding a positive lens (divergent) and a negative lens (convergent) to the LCP and RCP components respectively, so that an incident linearly polarized light beam is split into a divergent beam and a convergent beam with orthogonal polarization states.

[0047] It is understood that, through the above structural design and phase modulation mechanism, the radial polarization beam splitting metasurface in this embodiment can simultaneously achieve the separation and focusing / divergence functions of left-handed and right-handed circularly polarized light on a single optical element, greatly simplifying the complexity of the optical system and improving the system's integration and stability.

[0048] It should be noted that this embodiment provides a radially polarized beam splitting metasurface. Through its unique annular arrangement of subwavelength structural units 3 with rotation angles varying with the radius, it can apply different phase modulations to the left-hand and right-hand components of the incident ray-polarized light, efficiently generating diverging and converging beams with orthogonal polarization states. This allows the metasurface to successfully introduce polarization properties into the radial shearing interferometry system, laying the foundation for synchronous measurement based on polarization phase shifting. This fundamentally overcomes the technical problems of slow measurement speed and inability to detect high-frequency phase information in traditional time-series phase shifting technology, significantly improving the accuracy, efficiency, and dynamic detection capability of radial shearing interferometry.

[0049] Example 2

[0050] Please see Figure 2 This embodiment provides a synchronous phase-shifting measurement method for a radially polarized beam-splitting metasurface, using the radially polarized beam-splitting metasurface as described in Embodiment 1. The method includes the following steps:

[0051] S100, The beam to be tested is incident onto the radially polarized beam-splitting metasurface;

[0052] S200: The radial polarization beam splitter surface modulates the phase of the left-hand circularly polarized light and the right-hand circularly polarized light in the beam under test, respectively, to generate a diverging beam and a converging beam with orthogonal polarization states.

[0053] Specifically, in the above steps, the radially polarized beam splitter surface utilizes the phase modulation mechanism described in Example 1 to generate a +2θ phase modulation on the left-hand circularly polarized light to form a diverging beam, while simultaneously generating a -2θ phase modulation on the right-hand circularly polarized light to form a converging beam (or generating a +2θ phase modulation on the right-hand circularly polarized light to form a diverging beam, while simultaneously generating a -2θ phase modulation on the left-hand circularly polarized light to form a converging beam). These two beams have orthogonal polarization states, providing a basis for subsequent interferometric measurements.

[0054] S300: The diverging beam and the converging beam interfere to form an interference image carrying the wavefront information to be measured;

[0055] S400: Acquire interference images with a fixed phase difference in different linear polarization directions;

[0056] S500. Based on the interference image, the wavefront phase distribution of the beam under test is calculated.

[0057] Preferably, a polarization camera is used on the detection surface to acquire four interference images in the four linear polarization directions of 0°, 45°, 90°, and 135°, which are represented as follows: , , , ,in, , , and The phase differences are π / 2, π, and 3π / 2, respectively, from which the phase differences between the diverging and converging beams can be obtained. :

[0058] ;

[0059] The phase can be obtained from the phase difference using methods such as phase difference iteration based on the shear ratio or differential Zernike polynomial fitting. ;

[0060] From phase The phase difference background introduced by diverging and converging beams is subtracted. The phase information carried by the measured beam can then be obtained.

[0061] In some specific embodiments, the beam under test is linearly polarized light. Using linearly polarized light as the beam under test can fully utilize the characteristics of the radially polarized beam splitter to achieve efficient phase modulation and beam separation, thereby obtaining a clear interference image and accurate measurement results. Furthermore, the beam under test can also be unpolarized light, circularly polarized light, etc. To obtain the best results, the beam under test can first be passed through a linear polarizer to convert it into linearly polarized light before being incident perpendicularly onto the radially polarized beam splitter.

[0062] Preferably, the simultaneous acquisition of multiple interferometric images with different phase differences is completed within a single exposure time, thereby realizing dynamic measurement. This single-exposure synchronous acquisition technology can effectively avoid phase errors caused by environmental vibration or light source fluctuations during the measurement process, significantly improving measurement accuracy and stability. At the same time, single-exposure acquisition greatly shortens the measurement time, making this method applicable to real-time wavefront measurement scenarios.

[0063] It should be noted that this embodiment provides a synchronous phase-shifting method for a radially polarized beam-splitting metasurface. The radially polarized beam-splitting metasurface in this embodiment, through its unique annular arrangement of subwavelength structural units 3 with rotation angles varying with the radius, can apply different phase modulations to the left-hand and right-hand components of the incident ray-polarized light, efficiently generating divergent and converging beams with orthogonal polarization states. This allows the metasurface to successfully introduce polarization properties into the radial shearing interferometry system, laying the physical foundation for synchronous measurement based on polarization phase shifting. This fundamentally overcomes the technical problems of slow measurement speed and inability to detect high-frequency phase information in traditional time-series phase-shifting techniques, significantly improving the accuracy, efficiency, and dynamic detection capability of radial shearing interferometry.

[0064] Example 3

[0065] In a preferred embodiment, a radial shearing interferometry system is also provided, designed to achieve high-precision and high-stability synchronous phase-shifting wavefront measurement. This system includes the radial polarization beam-splitting metasurface described in Embodiment 1. This metasurface is the core of the system, capable of separating and modulating incident linearly polarized light according to its rotation direction, simultaneously generating a diverging beam and a converging beam. The radial shearing interferometry system in this embodiment also includes:

[0066] The light source module is used to provide the beam to be tested. The light source can be a laser to provide highly coherent monochromatic light, or a broadband light source with filters to reduce coherent noise. The module may also include a beam expansion and collimation system to provide parallel light incident with a suitable aperture.

[0067] The sample placement area is used to place the optical element or phase object to be tested. After the beam of light to be tested passes through or is reflected from the sample, its wavefront carries the phase information of the sample.

[0068] A polarization state preparation module is located after the light source module and before the radially polarized beam splitter. Preferably, the module includes at least one linear polarizer to convert the test beam, which may be unpolarized or circularly polarized, into linearly polarized light to meet the optimal working conditions of the radially polarized beam splitter. The module may also include a polarizer for precisely controlling the polarization state of the incident light.

[0069] The polarization phase-shifting and imaging module is crucial for achieving synchronous measurement. Its core includes a polarization-sensitive imaging device, which can be a pixel-level polarization camera (such as a polarization CMOS / CCD camera based on liquid crystal or nanowire grids). Each pixel unit integrates micro-polarizers in different directions (such as 0°, 45°, 90°, 135°), enabling the simultaneous acquisition of four interference images with different polarization directions in a single exposure. Alternatively, the module can also consist of an array of a beam splitter prism, multiple polarizers, and multiple cameras. By optically splitting the light path into multiple paths, each path is equipped with polarizers and cameras at different angles, thereby achieving synchronous multi-channel image acquisition.

[0070] The image processing and phase calculation unit is electrically connected to the polarization phase shifting and imaging module. It is usually a computer system with dedicated algorithms installed. It can receive multiple interferograms acquired synchronously and automatically and quickly calculate the phase distribution of the wavefront to be measured using phase shifting interferometry algorithms (such as the four-step phase shifting method, the least squares phase shifting algorithm, etc.). It can further analyze the results such as surface shape error and wavefront aberration.

[0071] In this embodiment, the working process of the radial shear interferometry measurement system is as follows: the light emitted from the light source is collimated and polarized, becoming linearly polarized light, which then illuminates the sample to be measured; the beam carrying sample information is incident perpendicularly on the radially polarized beam splitter; the radially polarized beam splitter modulates the LCP and RCP components in the beam into divergent and convergent light, respectively; these two orthogonally polarized beams interfere during propagation; the polarization imaging module simultaneously captures a set (e.g., four) of interferograms with a fixed phase difference within a single exposure time; the image processing and phase calculation unit processes this set of interferograms using a phase-shifting algorithm, and finally reconstructs the high-precision phase of the wavefront to be measured.

[0072] It should be noted that this embodiment provides a complete and immediately implementable measurement solution from light source to result output, rather than just an isolated device. Because the core measurement process (phase shifting) is completed within a single exposure, the system is extremely insensitive to environmental factors such as vibration, airflow disturbances, and temperature drift, enabling high-precision measurements in ordinary, non-vibration-isolated laboratory environments. The extremely short data acquisition time allows the system to measure dynamically changing wavefronts, such as monitoring the thermal deformation of optical components, changes in fluid fields, or the dynamic processes of biological samples. The entire process is automatically controlled by a computer, significantly improving measurement efficiency.

[0073] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0074] The technical features described above can be combined arbitrarily. Although not all possible combinations of these technical features are described, any combination of these technical features should be considered to be covered by this specification, provided that such combination does not contain contradictions.

[0075] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A radially polarized beam-splitting metasurface, comprising a substrate (1), characterized in that, Also includes: The surface structure (2) disposed on the substrate (1) is composed of multiple subwavelength structural units (3) arranged in a ring. Among them, the subwavelength structural units (3) on the same ring have the same rotation angle, and the rotation angle of the subwavelength structural units (3) on different rings varies with the ring radius, so that different phase modulations can be generated for the left-hand circularly polarized light and the right-hand circularly polarized light of the incident linearly polarized light, so that the left-hand circularly polarized light or the right-hand circularly polarized light forms a diverging beam, while the other beam forms a converging beam. The rotation angle of the subwavelength structural unit (3) is calculated using the following formula: ； Where r represents the rotation radius of the subwavelength structural unit (3), i.e., the ring radius. This represents the rotation angle of the subwavelength structural unit (3). Indicates the wavelength of incident ray-polarized light. This indicates the focal length of the converging or diverging beam; The method generates different phase modulations for left-handed and right-handed circularly polarized incident light, including: By rotating the subwavelength structural units (3) on different rings by an angle in the clockwise direction At the same time, it can produce a +2θ phase modulation on left-handed circularly polarized light and a -2θ phase modulation on right-handed circularly polarized light. Alternatively, by rotating the subwavelength structural units (3) on different rings by an angle in the counterclockwise direction. At that time, it produces a +2θ phase modulation on right-hand circularly polarized light and a -2θ phase modulation on left-hand circularly polarized light.

2. The radially polarized beam-splitting metasurface according to claim 1, characterized in that, The phases of the left-handed circularly polarized light and the right-handed circularly polarized light after phase modulation are calculated using the following formula: ； ； in, This indicates the phase of left-handed circularly polarized light after phase modulation. This indicates the phase of right-handed circularly polarized light after phase modulation. Indicates the wavelength of incident ray-polarized light. This indicates the focal length of the converging or diverging beam.

3. The radially polarized beam-splitting metasurface according to claim 1, characterized in that, The subwavelength structural unit (3) is an anisotropic superatom that operates based on the geometric phase principle.

4. A synchronous phase-shifting method for a radially polarized beam-splitting metasurface, characterized in that, The method, employing the radially polarized beam-splitting metasurface as described in any one of claims 1-3, comprises: S100, The beam to be tested is incident onto the radially polarized beam-splitting metasurface; S200. The left-hand circularly polarized light and the right-hand circularly polarized light in the beam to be tested are phase-modulated by the radially polarized beam splitter surface to generate a diverging beam and a converging beam with orthogonal polarization states. S300: The diverging beam and the converging beam interfere to form an interference image carrying the wavefront information to be measured; S400: Acquire interference images with a fixed phase difference in different linear polarization directions within a single exposure time; S500. Based on the interference image, the wavefront phase distribution of the beam under test is calculated.

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