CN-119575534-B - Broadband wave plate and polarization grating based on sub-wavelength structure

CN119575534BCN 119575534 BCN119575534 BCN 119575534BCN-119575534-B

Abstract

The application provides a broadband wave plate and a polarization grating based on a sub-wavelength structure, and relates to the technical field of optical elements. The broadband wave plate comprises a substrate, an anti-reflection layer positioned on one side of the substrate, and a periodically arranged columnar sub-wavelength structure positioned on the other side of the substrate, wherein the columnar sub-wavelength structure comprises a plurality of dielectric sub-wavelength structure layers with different refractive indexes. Based on the broadband wave plate and the polarization grating provided by the application, as the columnar sub-wavelength structure comprises a plurality of medium sub-wavelength structure layers with different refractive indexes, the refractive index of the columnar sub-wavelength structure can be matched with the refractive index of air, so that the reflection of light is effectively reduced, and the transmittance and the polarization conversion efficiency are improved.

Inventors

LUO XIANGANG
ZHANG FEI
PU MINGBO
HE XINYE
LIAO MINGHAO
JIN JINJIN

Assignees

中国科学院光电技术研究所

Dates

Publication Date: 20260512
Application Date: 20241231

Claims (7)

1. A broadband wave plate, the broadband wave plate comprising: A substrate; an anti-reflection layer positioned at one side of the substrate; A periodically arranged columnar sub-wavelength structure positioned on the other side of the substrate; The columnar sub-wavelength structure comprises a plurality of medium sub-wavelength structure layers with different refractive indexes; The columnar sub-wavelength structure comprises a first medium sub-wavelength structure layer made of a manufacturing material comprising a silicon material and a second medium sub-wavelength structure layer made of a manufacturing material comprising a zinc sulfide material; The columnar sub-wavelength structures are arranged along a second direction, each columnar sub-wavelength structure extends along a first direction, and gaps are reserved between adjacent columnar sub-wavelength structures; Wherein the first direction and the second direction are perpendicular to each other; wherein the period of the broadband wave plate comprises 1-3 microns; The width of the columnar sub-wavelength structure in the second direction in the direction parallel to the substrate comprises 0.5-2.5 microns, and the width of the columnar sub-wavelength structure in the second direction is smaller than the period of the broadband wave plate; the height of the first dielectric sub-wavelength structure layer comprises 2-5 microns in a direction perpendicular to the substrate, and the height of the second dielectric sub-wavelength structure layer comprises 0.5-2 microns.
2. The broadband wave plate of claim 1, wherein the refractive index of the dielectric sub-wavelength structure layer is greater nearer the substrate.
3. The broadband wave plate of claim 1, wherein the anti-reflection layer comprises a first sub-layer and a second sub-layer; the first sub-layer is positioned on one side, far away from the substrate, of the second sub-layer, the refractive index of the first sub-layer is smaller than that of the second sub-layer, and the refractive index of the second sub-layer is smaller than that of the substrate.
4. The broadband wave plate of claim 1, wherein the period of the broadband wave plate comprises 1 micron to 3 microns; The width of the columnar sub-wavelength structure in the second direction in the direction parallel to the substrate comprises 0.5-2.5 microns, and the width of the columnar sub-wavelength structure in the second direction is smaller than the period of the broadband wave plate; The height of the first dielectric sub-wavelength structure layer comprises 4-7 microns in a direction perpendicular to the substrate, and the height of the second dielectric sub-wavelength structure layer comprises 0.5-2 microns.
5. A polarization grating comprising a plurality of broadband waveplates as set forth in any one of claims 1-4.
6. The polarization grating of claim 5, wherein the plurality of columnar sub-wavelength structures in each of the broadband wave plates are aligned in a uniform direction, and the columnar sub-wavelength structures in adjacent two of the broadband wave plates are aligned in different directions.
7. The polarization grating of claim 6, wherein the angular spacing between the columnar sub-wavelength structures in any two adjacent broadband waveplates is uniform.

Description

Broadband wave plate and polarization grating based on sub-wavelength structure Technical Field The application relates to the technical field of optical elements, in particular to a broadband wave plate and a polarization grating based on a sub-wavelength structure. Background A broadband wave plate is an optical element for adjusting the phase of light, which can maintain the stability of phase retardation over a wide wavelength range, and thus plays an important role in an optical system. By controlling the phase delays of different wavelengths of light, the broadband wave plate can achieve effective adjustment and control of light. The broadband wave plate can effectively reduce the dependence of phase delay on wavelength, so that the broadband wave plate has important application value in various fields such as spectral shaping, polarization imaging, broadband laser source research and the like. However, the existing broadband wave plate is mainly concentrated in the visible and near infrared bands. In the long-wave infrared band (8-14 microns), dielectric silicon materials are widely used to design sub-wavelength structures due to their compatibility with semiconductor processing techniques. However, the reflection loss of the existing sub-wavelength structure of the silicon material is strong, and the absolute polarization conversion efficiency of the wave plate of the sub-wavelength structure can be affected. Disclosure of Invention In order to at least overcome the defects in the prior art, the application aims to provide a broadband wave plate and a polarization grating based on a sub-wavelength structure, which are used for solving the technical problem that the reflection loss of the sub-wavelength structure (especially in a long-wave infrared band) of the existing silicon material is strong, so that the polarization conversion efficiency of the corresponding broadband wave plate is low. In a first aspect, an embodiment of the present application provides a broadband wave plate based on a sub-wavelength structure, where the broadband wave plate includes: A substrate; an anti-reflection layer positioned at one side of the substrate; A periodically arranged columnar sub-wavelength structure positioned on the other side of the substrate; the columnar sub-wavelength structure comprises a plurality of dielectric sub-wavelength structure layers with different refractive indexes. In the implementation manner, since the columnar sub-wavelength structure comprises a plurality of medium sub-wavelength structure layers with different refractive indexes, the refractive index of the columnar sub-wavelength structure can be adjusted and impedance matching is achieved with air, so that light reflection is effectively reduced, and the transmittance and polarization conversion efficiency are improved. The technical problem that the polarization conversion efficiency of a corresponding broadband wave plate is low due to strong reflection loss of a medium sub-wavelength structure (particularly in a long-wave infrared band) of the existing silicon material is solved. In one possible implementation, the refractive index of the dielectric sub-wavelength structure layer is greater nearer the substrate. In the implementation manner, the refractive index of the medium sub-wavelength structure layer which is closer to the substrate is larger, so that the columnar sub-wavelength structure and air can be subjected to impedance matching, the reflection of light is effectively reduced, and the transmittance and the polarization conversion efficiency are improved. In one possible implementation, the columnar sub-wavelength structure includes a first dielectric sub-wavelength structure layer of a fabrication material including a silicon material, and a second dielectric sub-wavelength structure layer of a fabrication material including a zinc sulfide material. In the implementation mode, the zinc sulfide material has a lower refractive index in a long-wave infrared band and is between silicon and air, and the silicon, the zinc sulfide and the air can form impedance matching, so that interface reflection of a sub-wavelength structure is effectively reduced, and absolute polarization conversion efficiency of the broadband wave plate and the polarization grating is improved. In one possible implementation, the anti-reflection layer comprises a first sub-layer and a second sub-layer, wherein the first sub-layer is positioned on one side of the second sub-layer away from the substrate, the refractive index of the first sub-layer is smaller than that of the second sub-layer, and the refractive index of the second sub-layer is smaller than that of the substrate. In the above implementation manner, the transmittance of the substrate side can be further improved by providing a plurality of antireflection layers. In one possible implementation manner, a plurality of the columnar sub-wavelength structures are arranged along a second dire