Polarization optical device

Abstract

The invention relates to a polarization optical device which comprises a substrate, silicon columns with different sizes are periodically arranged on the substrate, and each silicon column applies different phase shifts to incident light components with different wavelengths and different polarization state angles in incident light according to the size of the silicon column. Therefore, the incident light components with different wavelengths and different polarization state angles are converged at different focuses. According to the invention, the independent phase regulation and control and achromatic principle are utilized, the function of the broadband polarizing lens is realized, and the miniaturization of a polarization optical device is facilitated.

Description

Technical Field

[0001] The invention relates to the technical field of broadband polarization optics, and in particular to a polarization optical device. Background Art

[0002] Metasurfaces are two-dimensional structures composed of metaatoms with special electromagnetic properties arranged in a certain way. They can flexibly control the amplitude, phase, polarization, etc. of incident light and have powerful light field manipulation capabilities. In recent years, polarization-related research has attracted widespread attention at home and abroad, among which how to obtain polarization information of broadband light is the core issue in this field.

[0003] Traditional detection technology requires the combination of multiple complex optical devices such as polarizers, wave plates, lenses, etc. to modulate the polarization and wavefront of light, making the entire system complex and bulky and unable to meet the needs of miniaturized integration. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a polarization optical device, which can realize the miniaturization of a broadband polarization lens.

[0005] The technical solution adopted by the present invention to solve its technical problem is: to provide a polarization optical device, including a substrate, on which silicon pillars of different sizes are periodically arranged to form a silicon pillar array, each silicon pillar applies different phase shifts to incident light components of different wavelengths and different polarization angles in the incident light according to its size, so that the incident light components of different wavelengths and different polarization angles converge at different focal points.

[0006] Furthermore, the different focal points are located on the same focusing plane, and the focusing plane is perpendicular to the silicon pillar array.

[0007] Furthermore, the silicon pillar array satisfies the set phase distribution:

[0008]

[0009] in, is the phase shift applied by the current silicon column to the incident light component with wavelength λ and polarization state angle n, f is the distance from the optical center of the optical device to the focal plane, and r is the distance from the center position of the current silicon column to the focal point F λ,n The radial distance of the focal point F λ,n is the preset focus of the incident light component with wavelength λ and polarization state angle n, r λ,n The focus F λ,n The distance to the center of the focal plane, C λ,n is a constant.

[0010] Furthermore, the constant C λ,nis the constant C that is solved by the optimization algorithm to minimize the deviation between the phase distribution function and the known optimal phase distribution. λ,n is obtained by taking the optimal estimate of .

[0011] Furthermore, the silicon pillar array is divided into a first region, a second region, a third region and a fourth region in a clockwise direction; the silicon pillars in the first region and the third region apply different phase shifts to a first incident light component and a second incident light component at two different polarization angles in a first band, so that the first incident light component converges at a first focus, and the second incident light component converges at a second focus; the silicon pillars in the second region and the fourth region apply different phase shifts to a third incident light component and a fourth incident light component at two different polarization angles in the second band, so that the third incident light component converges at a third focus, and the fourth incident light component converges at a fourth focus.

[0012] Furthermore, the different focal points are located on the same focusing plane, the focusing plane is perpendicular to the silicon pillar array, the first focus, the second focus, the third focus, and the fourth focus are respectively located at the center of the second quadrant, the fourth quadrant, the first quadrant, and the third quadrant of the focusing plane, and the first quadrant, the second quadrant, the third quadrant, and the fourth quadrant of the focusing plane correspond to the projections of the first area, the second area, the third area, and the fourth area on the focusing plane, respectively.

[0013] Furthermore, the polarization state angles of the first incident light component, the third incident light component, the second incident light component and the fourth incident light component increase by 45° respectively.

[0014] Furthermore, the polarization state angle of the first incident light component is an integer multiple of 45°.

[0015] Furthermore, the arrangement period of the silicon pillar array is smaller than the operating wavelength.

[0016] Furthermore, the height of the silicon pillar is set so that its phase shift adjustment range covers a multiple of 2π.

[0017] Furthermore, the cross section of the silicon column is rectangular or elliptical.

[0018] Beneficial Effects

[0019] Due to the adoption of the above technical solution, the present invention has the following advantages and positive effects compared with the prior art: the present invention utilizes the polarization-related independent phase control and achromatic principle, selects silicon pillars with different side lengths and arranges them periodically based on the set phase distribution, and introduces a constant term C related to wavelength and polarization state into the phase distribution function. λ,n To eliminate chromatic aberration, incident waves of different wavelengths and polarization states converge at different focal points, thereby realizing the miniaturization of broadband polarization lenses. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic structural diagram of a super surface unit according to an embodiment of the present invention;

[0021] Figure 2 Schematic diagram of the metalens principle of an embodiment of the present invention;

[0022] Figure 3 Schematic diagram of the silicon pillar arrangement according to an embodiment of the present invention. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0024] An embodiment of the present invention relates to a broadband polarization optical device, comprising: a silicon substrate, silicon pillars of different sizes are periodically arranged on the upper part of the substrate, and the silicon pillars are located at the center of a metasurface unit.

[0025] like Figure 1 In the metasurface unit shown, the cross section of the silicon pillar is an anisotropic cross-sectional shape, preferably a rectangular or elliptical shape, so that the waveguide modes polarized along the x-axis and y-axis have different equivalent refractive indices. Each silicon pillar imposes a polarization-dependent phase delay on the transmitted wave, and this anisotropy for orthogonal polarization states is the key to achieving independent regulation.

[0026] According to the transmission phase control principle, the phase shift φ imposed by the metasurface unit on the x and y polarization wave components in the incident light x and φ y The lengths of the silicon pillars along the x and y directions are l x and l y The metasurface can be regarded as a birefringent device with its main axis along the x and y directions. The required transmission phase φ is selected by selecting the two geometric parameters of the silicon column side length. x and φ y By setting the column height h, the phase control range of the unit structure covers multiple 2π phases, and the period p is set smaller than the working wavelength to avoid the generation of high-order diffraction and reduce energy loss.

[0027] The functional expression of the phase distribution of the entire meta-lens is as follows:

[0028]

[0029] in, is the phase shift applied by the current silicon column to the incident light component with wavelength λ and polarization angle n, f is the distance from the optical center of the optical device to the focal plane, and r is the distance from the center position of the current silicon column to the focal point F λ,n The radial distance of the focal point F λ,n is the preset focus of the incident light component with wavelength λ and polarization state angle n, r λ,n Focus F λ,n Distance to the center of the focal plane, C λ,n It is a constant related to wavelength and polarization state, which enables the metalens to achieve achromatic focusing within a certain broadband.

[0030] In order to find a suitable constant C λ,n , the error function of formula (2) is used to evaluate the theoretical phase distribution function φ of each incident light component λ,n (r) The phase distribution obtained by using the closest metasurface unit arrangement in the metasurface unit library compared to the known best phase distribution The deviation E on the entire meta-lens plane is solved by feedback iteration using the particle swarm algorithm to find the optimal constant C that minimizes the deviation E. λ,n , minimizing the inaccuracies in the phase control required to focus the light at individual focal points.

[0031]

[0032] Each silicon pillar can independently control the incident orthogonal polarized light, so it is necessary to realize the multi-dimensional phase distribution design of multiple wavelengths and polarization states. Under a certain phase distribution, the most suitable silicon pillar at each position is selected in the metasurface unit library to form the broadband polarization metalens of this embodiment.

[0033] like Figure 2 As shown in the figure, after the phase distribution of the metalens is determined, light is incident from the bottom, and the light of different wavelengths and polarization states is focused at different focal points through the designed device. The entire metalens is divided into four functional areas: for the two bands of blue light and green light, the X-polarized light and Y-polarized light (corresponding to 0° and 90°) of green light are focused at the center of the second quadrant and the fourth quadrant on the focusing plane respectively; the 45° polarized light and 135° polarized light of blue light are focused at the center of the first quadrant and the third quadrant on the focusing plane respectively. Figure 3The arrangement of silicon pillars at the center of the metalens is shown. The four quadrants have different functions. The first quadrant focuses X-polarized green light on the center point of the second quadrant on the focal plane, while the second, third, and fourth quadrants converge 45° polarized blue light, Y-polarized green light, and 135° polarized blue light to the center points of the third, fourth, and first quadrants on the focal plane. When the metasurface unit library cannot cover the required polarization state angle, the required phase shift can be achieved by rotating the silicon pillars. For example, in order to control the polarization state of 45° to 135°, the silicon pillars in the second and fourth quadrants can be rotated 45°, while the silicon pillars in the first and third quadrants keep the rotation angle at 0°.

Claims

1. A polarization optical device, characterized in that: The invention comprises a substrate on which silicon pillars of different sizes are periodically arranged to form a silicon pillar array. Each silicon pillar applies different phase shifts to incident light components of different wavelengths and different polarization angles in the incident light according to its size, so that the incident light components of different wavelengths and different polarization angles converge at different focal points.

2. The optical device according to claim 1, characterized in that The different focal points are located on the same focusing plane, and the focusing plane is perpendicular to the silicon pillar array.

3. The optical device according to claim 2, characterized in that: The silicon pillar array satisfies the set phase distribution: in, is the phase shift applied by the current silicon column to the incident light component with wavelength λ and polarization state angle n, f is the distance from the optical center of the optical device to the focal plane, and r is the distance from the center position of the current silicon column to the focal point F λ,n The radial distance of the focal point F λ,n is the preset focus of the incident light component with wavelength λ and polarization state angle n, r λ,n The focus F λ,n The distance to the center of the focal plane, C λ,n is a constant.

4. The optical device according to claim 3, characterized in that: The constant G λ,n The constant G that minimizes the deviation between the phase distribution function and the known optimal phase distribution is solved by an optimization algorithm. λ,n is obtained by taking the optimal estimate of .

5. The optical device according to claim 1, characterized in that: The silicon pillar array is divided into a first area, a second area, a third area and a fourth area in a clockwise direction; the silicon pillars in the first area and the third area apply different phase shifts to the first incident light component and the second incident light component of two different polarization angles in the first band, so that the first incident light component converges at a first focus, and the second incident light component converges at a second focus; the silicon pillars in the second area and the fourth area apply different phase shifts to the third incident light component and the fourth incident light component of two different polarization angles in the second band, so that the third incident light component converges at a third focus, and the fourth incident light component converges at a fourth focus.

6. The optical device according to claim 5, characterized in that: The different focal points are located on the same focusing plane, the focusing plane is perpendicular to the silicon pillar array, the first focus, the second focus, the third focus, and the fourth focus are respectively located at the center of the second quadrant, the fourth quadrant, the first quadrant, and the third quadrant of the focusing plane, and the first quadrant, the second quadrant, the third quadrant, and the fourth quadrant of the focusing plane correspond to the projections of the first area, the second area, the third area, and the fourth area on the focusing plane, respectively.

7. The optical device according to claim 6, characterized in that: The polarization state angles of the first incident light component, the third incident light component, the second incident light component and the fourth incident light component increase by 45° in sequence.

8. The optical device according to claim 6, characterized in that: The polarization state angle of the first incident light component is an integer multiple of 45°.

9. The optical device according to claim 1, characterized in that: The arrangement period of the silicon pillar array is smaller than the working wavelength.

10. The optical device according to claim 1, characterized in that: The cross section of the silicon column is rectangular or elliptical.

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