A high-order poincare sphere beam polarization measurement method based on a super-structured surface
Patent Information
- Application Number
- CN202311722456.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-12-14
- Publication Date
- 2026-10-23
- Estimated Expiration
- 2043-12-14
AI Technical Summary
同时，这些偏振解析器件由多种特定结构(每种结构对特定偏振态响应)分区或者交错排布而成，该策略会极大地降低器件的空间分辨率
[0020]1、本发明采用基于非交错排列的超构表面结构设计的高阶庞加莱球光束偏振测定方法，将入射的高阶庞加莱球光束转化为横截面上特定的光场分布图案，通过分析特定图案的形状、位置特性，解析入射高阶庞加莱球光束的光学奇点(m和n)、偏振方位角(ψ)和椭偏度角(χ)，从而得到超构表面偏振测定仪器。与传统的偏振解析器件相比，一方面可以克服现有器件空间分辨率低的缺陷。另一方面，通过单次测量就可以实现高阶庞加莱球光束偏振态的测定，且具有小型化的尺寸、高测量精度和直接读数的优势，具有广阔的应用前景，在集成化的偏振成像、遥感、通讯等领域具有特别深远的意义。
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Figure CN117760561B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the fields of micro-nano optics and metrology, and more specifically, relates to a method for measuring the polarization of a high-order Poincaré sphere beam based on a metasurface. Background Technology
[0002] As one of the fundamental properties of electromagnetic waves, polarization describes the vector nature of the electric field oscillation of electromagnetic waves and determines the interaction between electromagnetic waves and matter. It has important applications in many fields such as communication, sensing, imaging, and microscopy. Traditional polarization measurement methods typically utilize a combination of optical elements (such as polarizers, beam splitters, q-plates, and forked gratings) to measure the energy intensity under different orthogonal polarization states, and then use inversion calculations to accurately determine optical singularities and Stokes parameters. However, traditional polarization state measurement methods introduce a series of optical elements, leading to a large testing system and complex measurement process, which is inconsistent with the trend of miniaturization and integration of photonic devices. Metasurfaces can achieve efficient control of all degrees of freedom (amplitude, phase, polarization, etc.) of incident light within the subwavelength dimension, providing a significant opportunity for the miniaturization and integration of photonic devices. Compared with traditional polarization measurement methods, metasurface polarization measurement technology is planar, easy to integrate, and simple to measure, and has become one of the important means of modern polarization measurement.
[0003] Most existing metasurface polarization techniques focus on resolving the polarization state of scalar beams on Poincaré spheres and the optical singularity of beams on higher-order Poincaré spheres. However, these polarization-resolving devices are composed of partitioned or staggered arrangements of various specific structures (each responding to a specific polarization state), a strategy that significantly reduces the spatial resolution of the devices. Summary of the Invention
[0004] The technical problem to be solved by the present invention is to provide a method for measuring the polarization of a high-order Poincaré sphere beam based on a metasurface. The resulting metasurface polarization measuring instrument has high spatial resolution and ultra-thin thickness. A single measurement can completely resolve the polarization state of the incident light. It is simple and meets the requirements of photonic device integration.
[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:
[0006] A method for determining the polarization of a high-order Poincaré sphere beam based on a metasurface includes the following steps:
[0007] Step 1: A metasurface structure is constructed using an array of elliptical cylindrical dielectrics with different geometric dimensions and elliptical cross-sections. The phase distribution of the metasurface structure is analytically obtained based on its modulation effect on the incident high-order Poincaré sphere beam. The phase of the metasurface structure is composed of a combination of left- and right-handed rotating multiplexed angular lenses and vortex focusing lenses. The final phase distribution of the metasurface structure is shown in the following equation:
[0008]
[0009]
[0010] and represents the phase distribution of the right-handed and left-handed components, respectively; l0 represents the second-order phase coefficient; a represents the azimuth angle of the metasurface structure plane; e represents the exponent with base e; and i represents the complex unit. λ represents the lens phase; λ represents the working wavelength; f represents the focal length of the superlens; l represents the topological charge of the vortex field; x and y represent the coordinate values of the lens plane, respectively.
[0011] The transmission characteristics of each of the aforementioned medium elliptical cylinders can be represented by a Jones matrix, which characterizes the mapping relationship between the incident and emitted light fields, as shown in the following equation:
[0012]
[0013] and Represent the propagation phase along the major and minor axes of the dielectric elliptical cylinder, respectively; R represents the rotation matrix with orientation θ; the metasurface structure with independent phase modulation under circular polarization simultaneously satisfies the formula
[0014] The independent phase modulation under the circular polarization basis is obtained; the phase of the metasurface structure is decomposed into phase modulation under the circular polarization basis;
[0015] Step 2: Using the finite-difference time-domain numerical calculation method combined with periodic boundary conditions, scan the transmission characteristics of dielectric elliptical cylinders with different geometric dimensions to obtain the transmittance map, transmission phase map, and polarization conversion rate map of the dielectric elliptical cylinders with varying dimensions.
[0016] Step 3: Arrange each dielectric elliptical cylinder according to the phase distribution of the metasurface structure to form the metasurface structure; generate a fabrication layout file and use micro-nano fabrication techniques to fabricate the device to obtain the physical metasurface structure.
[0017] Step 4: Place the actual metasurface structure in the constructed test optical path. By controlling the angle between the linear polarizer, quarter-wave plate, and vortex wave plate, obtain an arbitrary polarized beam on the higher-order Poincaré sphere. By aligning the optical axis of the generated higher-order Poincaré sphere beam with the center of the metasurface structure, a specific light field distribution pattern can be obtained on the imaging surface at a specific position away from the actual metasurface structure. By analyzing the generated light field distribution pattern, obtain the optical singularity (m and n), polarization degree angle (χ), and polarization azimuth angle (ψ) of the incident beam. The final measured polarization state is expressed as |m,n,ψ,χ>.
[0018] Preferably, the obtained polarization state can be characterized in the form of a clock, with four pointers representing the four parameters m, n, ψ, and χ of the polarization state, respectively, to obtain a readable metasurface polarization measuring instrument.
[0019] The beneficial effects of adopting the above technical solution are as follows:
[0020] 1. This invention employs a method for measuring the polarization of a high-order Poincaré sphere beam based on a non-interlaced metasurface structure. The incident high-order Poincaré sphere beam is transformed into a specific optical field distribution pattern on its cross-section. By analyzing the shape and positional characteristics of this specific pattern, the optical singularities (m and n), polarization azimuth angle (ψ), and ellipticity angle (χ) of the incident high-order Poincaré sphere beam are determined, thus yielding a metasurface polarization measuring instrument. Compared to traditional polarization resolving devices, this method overcomes the low spatial resolution of existing devices. Furthermore, it allows for the determination of the polarization state of a high-order Poincaré sphere beam in a single measurement, and offers advantages such as miniaturization, high measurement accuracy, and direct reading. It has broad application prospects and profound significance in integrated polarization imaging, remote sensing, and communication fields.
[0021] 2. This invention utilizes the light field modulation characteristics of metasurfaces to achieve accurate determination of the polarization state of incident high-order Poincaré sphere beams in a single measurement based on a subwavelength structure with unit structure size smaller than the working wavelength; replacing the traditional polarization measurement device (multiple optical elements cascaded) and complex measurement process (multiple measurements with rotating polarizers). Attached Figure Description
[0022] Figure 1 This is a schematic diagram of the polarization measurement process involved in the high-order Poincaré sphere beam polarization measurement based on metasurfaces in this invention.
[0023] Figure 2 The diagram shows the metasurface unit structure and transmission characteristics of the present invention; a is a side view and a top view of the unit structure; b is a graph showing the polarization conversion rate as a function of the long and short axes of the structure; c is a graph showing the phase of the incident light under x-polarized light as a function of the long and short axes of the structure.
[0024] Figure 3 Images showing the process of measuring the polarization of a high-order Poincaré sphere beam (0th order) using the metasurface of this invention; a is the light field pattern generated by the metasurface under different polarization states; b is the corresponding energy map along the outer ring of the pattern; c is the corresponding energy map along the central ring of the pattern; d is an image showing the incident polarization state as readable by four pointers.
[0025] Figure 4 Images show the process of measuring the polarization of high-order Poincaré sphere beams (1st and 2nd order) using the metasurface of this invention; a) is the light field pattern generated by the metasurface under different polarization states; b) is a diagram showing the incident polarization state in a four-pointer readable format; c) is a diagram showing the recovery of the 1st-order Poincaré sphere beam; d) is the light field pattern generated by the metasurface under different polarization states; e) is a diagram showing the incident polarization state in a four-pointer readable format; f) is a diagram showing the recovery of the 2nd-order Poincaré sphere beam. Detailed Implementation
[0026] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.
[0027] The specific process of polarization measurement is as follows: a non-interlaced metasurface can transform an incident high-order Poincaré sphere beam into a specific optical field distribution pattern on its cross-section. These patterns are two elliptical Gaussian spots on the outer ring and a petal-shaped optical field pattern in the central region. Based on the position and energy intensity of the two elliptical Gaussian spots on the outer ring, the optical singularity (m and n represent the topological charge of right-handed and left-handed vortex circularly polarized light, respectively) and ellipticity angle (χ) of the incident high-order Poincaré sphere beam can be resolved. Analyzing the petal-shaped optical field pattern in the central region yields the polarization azimuth angle (ψ) of the incident high-order Poincaré sphere beam. Therefore, based on the metasurface, the polarization state |m,n,ψ,χ> of the incident high-order Poincaré sphere beam can be obtained through a single measurement.
[0028] This invention enables high-order Poincaré sphere beam polarization measurement based on non-interlaced metasurfaces. The metasurface structure in this method consists of an array of dielectric pillars with different geometric dimensions and elliptical cross-sections. By combining the transmission phase and geometric phase of the dielectric elliptical pillars with the phase distribution of the metasurface device, a specific dielectric elliptical pillar structure is selected to achieve the arrangement of the metasurface. Based on the geometric dimensions and in-plane rotation angle of the dielectric elliptical pillars, an array arrangement structure is formed; and the device is fabricated using micro-nano fabrication techniques to obtain a physical prototype of the metasurface structure.
[0029] The method for measuring the polarization of a higher-order Poincaré sphere beam on a metasurface disclosed in the embodiments is as follows: Figure 1 As shown, the polarization of incident light is measured under laser irradiation at a wavelength of 633 nm. The specific implementation method is as follows:
[0030] Step 1: The metasurface used for measuring the polarization of the high-order Poincaré sphere beam is composed of an array of titanium dioxide elliptical cylinders with different elliptical cross-sections. The phase distribution of the metasurface structure is analytically obtained based on the modulation effect on the incident high-order Poincaré sphere beam. The phase of the metasurface structure is formed by a combination of left- and right-handed rotating angular lenses and vortex focusing lenses, and its final phase can be decomposed into a superposition of orthogonal circular polarization bases (left-handed and right-handed circular polarization). The arrangement of the metasurface is achieved by combining the transmission phase and geometric phase of the titanium dioxide elliptical cylinders with the calculated phase of the metasurface structure. The geometric dimensions of the titanium dioxide elliptical cylinders include height h, major axis Lx, minor axis Ly, in-plane rotation angle θ, and the period Λ of the metasurface structural unit.
[0031] The height H of the titanium dioxide elliptical cylinder and the period Λ of the metasurface unit were determined using the finite-difference time-domain method. The transmission characteristics of the unit structure were calculated as a function of the major axis Lx and minor axis Ly of the titanium dioxide elliptical cylinder. For an incident wavelength of 633 nm, the refractive index of the titanium dioxide elliptical cylinder used in the example was n = 2.28. The phase and polarization conversion rate of titanium dioxide elliptical cylinders of different sizes along the x-axis were obtained through parameter scanning. From the obtained electric field results, the phase after passing through titanium dioxide elliptical cylinders of different sizes was determined to be φx, ensuring that the phase covers the range of 0 to 2π, while guaranteeing a sufficiently large polarization conversion rate. Based on the obtained phase distribution of the metasurface structure, metasurface units that meet the conditions were searched pixel by pixel. Thus, the arrangement and size of the metasurface structure were determined.
[0032] Step Two: Generate processing files based on the metasurface structure determined in Step One. Determine the range of variation for the major and minor axes of the titanium dioxide elliptical cylinder to be 100nm-350nm, as shown in the attached document. Figure 2 As shown.
[0033] Step 3: Using the processing files of the metasurface obtained in Step 2, prepare the required transmissive metasurface structure using micro-nano processing methods such as titanium dioxide coating, electron beam exposure, and subsequent etching.
[0034] Step 4: Place the fabricated metasurface structure in the experimental optical path. By controlling the angles between the linear polarizer, quarter-wave plate, and vortex waveplate, obtain an arbitrary polarized beam on a higher-order Poincaré sphere. By aligning the optical axis of the generated higher-order Poincaré sphere beam with the center of the metasurface structure, a specific light field distribution pattern can be obtained on the imaging plane at a specific position relative to the metasurface structure. By analyzing the generated light field distribution pattern, obtain the optical singularity, polarization degree angle, and polarization azimuth angle of the incident beam. The obtained polarization state is represented as |m,n,ψ,χ>. Characterize the obtained polarization state in a clock-like manner (three pointers represent hours, minutes, and seconds), with four pointers representing the four parameters m,n,ψ,χ of the polarization state, ultimately obtaining a readable metasurface polarization measuring instrument. (See attached image) Figure 3 As shown in the diagram, the determination of polarization states on a 0th-order Poincaré sphere is illustrated here. When the incident light has six specific polarization states, different light field patterns appear on the imaging plane. By analyzing the light field patterns, the optical singularity, degree of polarization angle, and polarization azimuth angle of the incident beam are obtained. The polarization states are represented by four pointers |m,n,ψ,χ>. Based on the same principle, Figure 4 The figure illustrates the determination of polarization states on first-order and second-order Poincaré spheres. Different light field patterns appear on the imaging plane when the incident light has six specific polarization states. By analyzing the light field patterns, the optical singularity, degree of polarization angle, and polarization azimuth angle of the incident beam are obtained. The polarization states are represented by four pointers: |m,n,ψ,χ>. The figure also shows the reconstruction results of the beam polarization states on the first-order and second-order Poincaré spheres.
[0035] This invention presents a high-order Poincaré sphere beam polarization determination technique that utilizes a non-interlaced metasurface structure to accurately determine the polarization state |m,n,ψ,χ> of an incident high-order Poincaré sphere beam in a single measurement. It features an ultra-thin thickness (nanometer-scale), meeting the integration requirements of photonic devices. Compared to traditional polarization determination devices, this technique employs a non-interlaced metasurface to reduce the spatial resolution of the device, enabling the determination of the polarization state of a high-order Poincaré sphere beam in a single measurement. Furthermore, it offers advantages such as miniaturization, high measurement accuracy, and direct reading, demonstrating broad application prospects.
[0036] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A method for determining the polarization of a high-order Poincaré sphere beam based on a metasurface, characterized in that, Includes the following steps: Step 1: A metasurface structure is constructed using an array of elliptical cylindrical dielectrics with different geometric dimensions and elliptical cross-sections. The phase distribution of the metasurface structure is analytically obtained based on its modulation effect on the incident high-order Poincaré sphere beam. The phase of the metasurface structure is formed by a combination of left- and right-handed rotating angular lenses and vortex focusing lenses. The final phase distribution of the metasurface structure is shown in the following equation: and represents the phase distribution of the right-handed and left-handed components, respectively; l0 represents the second-order phase coefficient; a represents the azimuth angle of the metasurface structure plane; e represents the exponent with base e; and i represents the complex unit. λ represents the lens phase; f represents the working wavelength; l represents the focal length of the superlens; x and y represent the topological charge of the vortex field; and x and y represent the coordinate values of the lens plane, respectively. The transmission characteristics of each of the aforementioned medium elliptical cylinders are represented by a Jones matrix J, which characterizes the mapping relationship between the incident and emitted light fields, as shown in the following equation: and Let R(θ) represent the propagation phase along the major and minor axes of the dielectric elliptical cylinder, respectively; R(θ) represents the rotation matrix with orientation θ; the metasurface structure with independent phase modulation under circular polarization simultaneously satisfies the formula... |R> and |L> are the Dirac notation for right-handed and left-handed circular polarization bases, respectively; independent phase modulation is obtained under the circular polarization base; the phase of the metasurface structure is decomposed into phase modulation under the circular polarization base; Step 2: Using the finite-difference time-domain numerical calculation method combined with periodic boundary conditions, scan the transmission characteristics of dielectric elliptical cylinders with different geometric dimensions to obtain the transmittance map, transmission phase map, and polarization conversion rate map of the dielectric elliptical cylinders with varying dimensions. Step 3: Arrange each dielectric elliptical cylinder according to the phase distribution of the metasurface structure to form the metasurface structure; generate a fabrication layout file and use micro-nano fabrication techniques to fabricate the device to obtain the physical metasurface structure. Step 4: Place the physical metasurface structure in the constructed test optical path. By controlling the angles between the linear polarizer, quarter-wave plate, and vortex waveplate, obtain an arbitrary polarized beam on a higher-order Poincaré sphere. By aligning the optical axis of the generated higher-order Poincaré sphere beam with the center of the metasurface structure, obtain a specific light field distribution pattern on the imaging surface at a specific position away from the physical metasurface structure. By analyzing the generated light field distribution pattern, obtain the optical singularities m and n, polarization degree angle χ, and polarization azimuth angle ψ of the incident beam. The final measured polarization state is expressed as |m,n,ψ,χ>.
2. The method for measuring the polarization of a high-order Poincaré sphere beam based on a metasurface according to claim 1, characterized in that, The obtained polarization state is characterized in the form of a clock, and four pointers are used to represent the four parameters of the polarization state, m, n, ψ, and χ, respectively, to obtain a readable metasurface polarization measuring instrument.