阅读说明：本技术 基于全介质超表面结构的全斯托克斯偏振检测器 (Full stokes polarization detector based on full-medium super-surface structure ) 是由 徐挺 郭仕豪 任永泽 霍鹏程 于 2021-10-27 设计创作，主要内容包括：本发明公开了一种基于全介质超表面的全斯托克斯偏振检测器,包括：基底以及基底上全介质超表面纳米结构单元形成的纳米单元阵列；所述基底采用介质材料,所述全介质超表面纳米结构单元为各向异性结构,当光波入射到超表面上时,经过纳米单元阵列的偏振-相位调制,透射光波分别聚焦到三组正交偏振基矢上,即0°/90°线偏振、45°/135°线偏振、左旋/右旋圆偏振,通过测量六个偏振态的聚焦强度,可以获得入射光的偏振态分布。本发明设计的全斯托克斯偏振检测器具有超薄的厚度(纳米量级),有利于器件与纳米光子学系统相结合,可以实现小体积、对入射角度不敏感的入射光全斯托克斯偏振检测。(The invention discloses a full Stokes polarization detector based on a full-medium super surface, which comprises: the nano-cell array is formed by a substrate and all-dielectric super-surface nano-structure units on the substrate; the substrate is made of a dielectric material, the all-dielectric super-surface nano structure unit is of an anisotropic structure, when light waves are incident on the super surface, through polarization-phase modulation of the nano unit array, transmitted light waves are respectively focused on three groups of orthogonal polarization basis vectors, namely 0-degree/90-degree linear polarization, 45-degree/135-degree linear polarization and left-hand/right-hand circular polarization, and the polarization state distribution of the incident light can be obtained by measuring the focusing intensity of six polarization states. The full Stokes polarization detector designed by the invention has ultrathin thickness (nanometer magnitude), is beneficial to the combination of a device and a nanometer photonic system, and can realize the incident light full Stokes polarization detection with small volume and insensitivity to the incident angle.)

1. An all-stokes polarization detector based on an all-dielectric super-surface structure, which is characterized by comprising: the nano-cell array is formed by a substrate and all-dielectric super-surface nano-structure units on the substrate; the substrate is made of a dielectric material, the all-dielectric super-surface nano structure unit is of an anisotropic structure, when light waves are incident on the super surface, through polarization-phase modulation of the nano unit array, transmitted light waves are respectively focused on three groups of orthogonal polarization basis vectors, namely 0-degree/90-degree linear polarization, 45-degree/135-degree linear polarization and left-hand/right-hand circular polarization, and the polarization state distribution of the incident light can be obtained by measuring the focusing intensity of six polarization states.

2. The all-dielectric-metasurface-structure-based all-stokes polarization detector of claim 1, wherein: the phase distribution (x, y) of the nano-cell array conforms to formula 1:

wherein: subscripts n ═ 1,2, …,6 respectively represent linearly polarized light of 0 °, 45 °, 90 °, 135 °, and left-hand and right-hand circular polarizations, f represents the focal length of the super-surface, and the position coordinate of the focal point is (x)_n,y_n)。

3. The all-dielectric-metasurface-structure-based all-stokes polarization detector of claim 1, wherein: the dielectric constant ratio of the substrate to the all-dielectric super-surface nano-structure unit is 1: 1-1: 5.

4. The all-dielectric-metasurface-structure-based all-stokes polarization detector of claim 1, wherein: the substrate is made of low-dielectric constant and low-loss materials, and the materials are transparent glass, calcium fluoride, barium fluoride, infrared chalcogenide glass or silicon.

5. The all-dielectric-metasurface-structure-based all-stokes polarization detector of claim 1, wherein: the all-dielectric super-surface nano-structure unit is made of a low-loss dielectric material or a semiconductor material with a high dielectric constant, wherein the material is gallium nitride, hafnium oxide, titanium dioxide, silicon nitride or germanium.

6. The all-dielectric-metasurface-structure-based all-stokes polarization detector of claim 1, wherein: the all-dielectric super-surface nano structure units are arranged on the substrate in a quasi-periodic or periodic manner, the side length of the substrate of each periodic unit is P, P is 0.5 lambda-lambda, and lambda is the wavelength of incident light waves.

7. The all-dielectric-metasurface-structure-based all-stokes polarization detector of claim 1, wherein: the height of the all-dielectric super-surface nano-structure unit is H, the shape and the size of the cross section of the all-dielectric super-surface nano-structure unit are characteristic sizes, H is 0.4 lambda-1.2 lambda, the characteristic size is 0.2P-0.8P, P is 0.5 lambda-lambda, and lambda is the wavelength of incident light waves.

8. The all-dielectric-metasurface-structure-based all-stokes polarization detector of claim 1, wherein: the cross section of the all-dielectric super-surface nano-structure unit is in a centrosymmetric geometric figure and is rectangular or elliptical.

9. The all-dielectric-metasurface-structure-based all-stokes polarization detector of claim 1, wherein: the arrangement of the nanometer unit array is hexagonal close packing distribution, positive direction array distribution or circular array distribution.

10. The all-dielectric-metasurface-structure-based all-stokes polarization detector of claim 1, wherein: the wavelength of the incident light wave is 250 nm-20 mu m.

Technical Field

The invention belongs to the field of nanophotonics, and particularly relates to an optical full-stokes polarization detector based on a full-medium super-surface structure.

Background

Polarization is one of inherent properties of light, and the information of a light source, the shape information of the surface of an object, such as stress change and the like, can be obtained by measuring the polarization state of the light, so that the polarization information detection of the light can be used for satellite remote sensing, biomedical imaging and the like. The measurement of polarization information for optical fields has been one of the research hotspots in the field of nanophotonics. For conventional polarization measurement methods, there can be roughly three categories: (1) the time-sharing measurement method comprises the steps that different polarization component results are obtained in a time resolution sacrifice mode by rotating a camera rotating wheel; (2) the amplitude-splitting imaging method is used for separating different polarized light components in a prism light splitting mode so as to obtain different polarized components; (3) the sub-focal plane method arranges different polarization detection arrays at different positions of an imaging focal plane, thereby obtaining different polarization components. Optical polarization detectors have been proposed since the 21 st century and are known as one of the hot spots of research.

At present, the polarization measurement method involves different optical paths or optical elements, is large in size and complex in structure, or can only measure partial Stokes information, and obviously, the requirements on the existing integrated miniaturized optical system are contradictory.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides an all-Stokes polarization detector based on an all-dielectric super-surface structure.

In order to achieve the purpose, the invention adopts the following technical scheme: an all-dielectric-super-surface-structure-based all-stokes polarization detector, comprising: the nano-cell array is formed by a substrate and all-dielectric super-surface nano-structure units on the substrate; the substrate is made of a dielectric material, the all-dielectric super-surface nano structure unit is of an anisotropic structure, when light waves are incident on the super surface, through polarization-phase modulation of the nano unit array, transmitted light waves are respectively focused on three groups of orthogonal polarization basis vectors, namely 0-degree/90-degree linear polarization, 45-degree/135-degree linear polarization and left-hand/right-hand circular polarization, and the polarization state distribution of the incident light can be obtained by measuring the focusing intensity of six polarization states.

Further, the phase distribution (x, y) of the nano-unit array conforms to formula 1:

wherein: the subscripts n ═ 1,2, …, and 6 respectively represent linearly polarized light of 0 °, 45 °, 90 °, and 135 °, andand left-hand circular polarization and right-hand circular polarization, f represents the focal length of the super surface, and the position coordinate of the focal point is (x)_n,y_n)。

Furthermore, the dielectric constant ratio of the substrate to the all-dielectric super-surface nano-structure unit is 1: 1-1: 5.

Furthermore, the substrate is made of low-dielectric constant and low-loss materials, and the materials are transparent glass, calcium fluoride, barium fluoride, infrared chalcogenide glass or silicon.

Furthermore, the all-dielectric super-surface nano-structure unit is made of a low-loss dielectric material or a semiconductor material with a high dielectric constant, wherein the material is gallium nitride, hafnium oxide, titanium dioxide, silicon nitride or germanium.

Furthermore, the all-dielectric super-surface nano-structure units are arranged on the substrate in a quasi-periodic or periodic manner, the side length of the substrate of each periodic unit is P, P is 0.5 lambda-lambda, and lambda is the wavelength of incident light waves.

Furthermore, the height of the all-dielectric super-surface nano-structure unit is H, the shape and the size of the cross section of the all-dielectric super-surface nano-structure unit are characteristic sizes, H is 0.4 lambda-1.2 lambda, the characteristic size is 0.2P-0.8P, P is 0.5 lambda-lambda, and lambda is the wavelength of incident light waves.

Furthermore, the cross section of the all-dielectric super-surface nano-structure unit is in a centrosymmetric geometric figure and is rectangular or elliptical.

Furthermore, the arrangement of the nanometer unit array is hexagonal close packing distribution, positive direction array distribution or circular array distribution.

Furthermore, the wavelength of the incident light wave is 250 nm-20 μm.

According to the super-surface full-Stokes polarization detection, the high-refractive-index low-loss material is selected as the nano-structure unit, and the high polarization conversion efficiency can be realized by adjusting the size and the rotation angle of the nano-structure unit; the whole super-surface array is formed by selecting the nano unit structure with specific parameters, and the full Stokes polarization detection of the wide waveband can be realized. The cross section of the nano-structure unit is elliptical or rectangular, and the unit structures of the same super-surface array are the same in shape.

Therefore, compared with the prior art, the invention has the following beneficial effects:

1. the optical full-stokes polarization detection designed by the invention has ultrathin thickness (sub-wavelength nanometer magnitude), and is beneficial to the combination of a device and a nanometer photonic system.

2. The substrate is made of a low-loss material with a low dielectric constant, and the material of the super-surface structure is a low-loss dielectric material or a semiconductor material with a high dielectric constant, so that the super-surface full-stokes polarization detection technology designed by the invention has excellent polarization detection and polarization imaging effects.

3. The polarization detection and the polarization imaging based on the super-surface structure can realize full Stokes parameter measurement, small volume, insensitivity to incident angle, broadband full Stokes polarization detection and the like, and the characteristics are difficult to realize in the traditional polarization detection. The invention has important application in the polarization detection of micron-scale vector beams with spatial distribution.

Drawings

Fig. 1 is a schematic diagram of a nano-unit structure according to an embodiment of the present invention, wherein 1-titania, 2-silica glass, H-600nm, P-450 nm, and θ is a corner of the structure. Dx and Dy are the major axis and the minor axis of the elliptical structure, respectively, and the specific parameters are shown in Table 1.

Fig. 2 is a graph of phase and transmission coefficient of a nano-cell structure under linearly polarized light incidence according to an embodiment of the present invention.

FIG. 3 is a graph of polarization conversion ratio and phase retardation of the nano-cell structure under linearly polarized light incidence according to the embodiment of the invention.

FIG. 4 is a schematic diagram of a super-surface structure designed in an embodiment of the present invention.

Fig. 5 is a graph showing the distribution of the intensity of transmitted light and stokes parameters obtained from the multiplication of the intensity distribution of transmitted light when a single wavelength (530nm) of incident light (roman numerals i-vi represent 0 °, 90 °, 45 °, 135 ° of linearly polarized and right-circularly polarized light, and left-circularly polarized light, respectively) with different polarization states is irradiated on a super-surface, as simulated in the embodiment of the present invention.

Fig. 6 is a result of stokes parameters on a poincare sphere obtained from light intensity distribution in an embodiment of the present invention.

FIG. 7 is a graph showing the results of light intensity distributions obtained under different polarization states and different wavelengths in the embodiment of the present invention.

FIG. 8 is a schematic diagram of a super-surface array designed according to an embodiment of the present invention, with a partial enlarged view in the circle.

Detailed Description

In order to make the technical solutions better understood by those skilled in the art, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only partial embodiments of the present application, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

It should be noted that the terms "comprises" and "comprising," and any variations thereof, in the description and claims of this application and the above-described drawings, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

Examples

Quartz glass is used as a substrate, and titanium dioxide is used as a nano-structure unit material.

An all-dielectric super-surface nano-structure unit with different structure sizes and rotation angles is designed based on optical all-dielectric super-surface structure full-Stokes polarization detection and polarization imaging, and the cross section of the nano-structure unit can be any geometric figure, such as a rectangle or an ellipse. The substrate is a low-dielectric constant low-loss material, such as transparent glass, calcium fluoride, barium fluoride, infrared chalcogenide glass, and the like. The material of the all-dielectric super-surface nano-structure unit is a low-loss dielectric material or a semiconductor material with a higher dielectric constant, such as gallium nitride, hafnium oxide, titanium dioxide, silicon nitride, germanium and the like. In this embodiment, a titanium dioxide column with an elliptical cross section is taken as an example, all-dielectric super-surface nano-structure units for optical all-stokes polarization detection and polarization imaging are arranged on a substrate in a quasi-periodic or periodic manner, each periodic unit is a micro-structure super-surface unit, as shown in fig. 1, the micro-structure super-surface unit includes two parts, 1 is the titanium dioxide dielectric column, 2 is a quartz glass substrate, the period P is 450nm, P is the side length of each periodic unit substrate, the height of the all-dielectric super-surface nano-structure unit is H600 nm, and the characteristic dimensions are Dx and Dy.

TABLE 1

When 0-degree linear polarization incident light irradiates on the super-surface nanometer unit structure, a phase distribution and transmission coefficient graph of the structure can be obtained according to a finite element algorithm, and 8 × 8 unit structures (structural parameters Dx and Dy are detailed in table 1) can be found by dispersing 2 pi phases into eight-order phases and simultaneously ensuring higher transmission coefficients of the unit structures, as shown in fig. 2. Meanwhile, through simulation calculation, the polarization conversion rate and the phase change diagram of the obtained nanostructure element are shown in fig. 3, wherein #1 to #8 respectively represent the structural schematic diagrams of 8 half-wave plates selected when designing the super surface.

Assuming that the focal length of the super-surface is f, the position coordinate of the focal point is (x)_n,y_n) Then, the phase distribution of the designed super-surface at any position (x, y) is:

where the subscript n ═ 1,2, …,6 denotes 0 °, 45 °, 90 °, 135 °, left-hand circular polarization and right-hand circular polarization, respectively.

Wherein, for the incidence of the orthogonal polarized light of 45 degrees and 135 degrees, the generated super-surface structure is equivalent to that the super-surface generated by the incident light of 0 degrees and 90 degrees is rotated by 45 degrees relative to the x-axis as a whole.

For incidence of left-handed and right-handed circularly polarized light, the phase distribution of the generated super-surface structure at the space (x, y) is as follows:

where θ (x, y) is the corner of the resulting structure at (x, y).

According to the design, the distribution of the designed super-surface unit structure is shown in FIG. 4. The method comprises 3 parts of super-surface spatial multiplexing, wherein 1-aiming at 0-degree and 90-degree polarized light, 2-aiming at 45-degree and 135-degree polarized light, and 3-aiming at left-handed and right-handed circularly polarized light.

For any polarized light incident on the super surface, the transmitted light can always be focused on the focal points of the 6 polarization states, and by obtaining the light intensity distribution of each focal point, by using the following formula,

S₀＝I；S₁＝l₀-I₉₀；S₂＝I₄₅-I₁₃₅；S₃＝I_RCP-I_LCP

wherein I represents the total intensity of incident light, I₀、I₄₅、I₉₀、I₁₃₅、I_RCP、I_LCPRespectively represent the light intensity of linearly polarized light of 0 degrees, 45 degrees, 90 degrees and 135 degrees, and the light intensity of right-handed (RCP) and left-handed (LCP) circularly polarized light.

The stokes parameter S ═ S of the emergent light can be obtained₀,S₁,S₂,S₃]And further polarization information of the emergent light can be obtained. For example by separately enteringThe emitted light intensity distributions of the I-vi polarized light rays (respectively representing 0 °, 90 °, 45 °, 135 °, RCP, and LCP) are respectively shown in the first row of fig. 5, and the S parameter obtained from the light intensity distributions of the 6 focal points is shown in the second row of fig. 5.

The obtained S-parameters can be plotted on a poincare sphere, the results of which are shown in fig. 6. The simulation result is very close to the theoretical calculation result, and the super surface is proved to have a good polarization detection effect.

Secondly, the above results can be generalized to other wavelengths in the visible band: 480nm, 580nm, 630nm, simulated using FDTD, as shown in FIG. 7.

The invention has broadband response aiming at the full Stokes polarization detection of incident light, has the same deflection focusing effect at other wavelengths of a visible light waveband, and can detect the full Stokes information of a plurality of wavelengths of the visible light waveband by utilizing a single super surface.

The array structure which is arranged in a regular hexagonal close-packed mode is expanded from a single super-surface structure, as shown in fig. 8, compared with the traditional round and square arrangement, the structure has higher functional unit density and higher spatial resolution, and the optical field detection and the optical field imaging with spatial distribution can be realized by utilizing an algorithm.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.