Medium-wave infrared metasurface cross-polarization regulation and control device and method and application

Abstract

The invention belongs to the technical field of optical devices, and particularly relates to a medium-wave infrared metasurface cross-polarization regulation and control device and method and application. The medium-wave infrared metasurface cross-polarization regulation and control device is formed by periodically arranging metal microstructure layers on the upper layer of a dielectric layer and attaching a metal film layer to the lower layer of the dielectric layer. The thickness of the three-layer structure of the device is far smaller than the working wavelength. In a medium-wave infrared band of 3-4.2 microns, for normal incident linearly polarized light with an incident angle of 0 degree, the polarization direction of reflected light is orthogonal to incident light, the polarization conversion efficiency of the device is greater than 99%, and efficient conversion from the linearly polarized light to the orthogonal polarization direction can be realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical devices, in particular to a middle-wave infrared super surface orthogonal polarization control device, method and application. BACKGROUND

[0002] The description of the background of the present application belongs to the related art related to the present application, and is only used to illustrate and facilitate the understanding of the content of the present application, and should not be understood as the applicant's explicit recognition or presumption that the present application is the prior art on the date of the first filing of the application.

[0003] Polarization is one of the basic properties of light, and the trajectory described by the direction and amplitude of the electric field vector of light at any point in space over time during light propagation. The polarization phenomenon of light has a wide range of applications in imaging, optical communication, positioning and navigation, and molecular detection. In the application of these fields, polarization devices are always used to detect and control the polarization state of light to obtain the required polarized light. With the increasing demand for polarization imaging and optical communication applications, the performance requirements for polarization devices that can detect and control the polarization state of light are also increasing. Not only high-performance polarization devices are needed, but also polarization devices need to be miniaturized and micro-sized for integration into other optical devices and systems.

[0004] Traditional polarization devices include birefringent crystal wave plates and polarization gratings. Taking a birefringent crystal as an example for analysis, a beam of light is incident into the birefringent crystal, and the refraction through the medium becomes two beams of light. One beam follows the refraction law and is called ordinary light (o light), and the other beam does not follow the refraction law and is called extraordinary light (e light). Due to the different propagation speeds, the phase of o light lags behind or leads ahead of the phase of e light, and the phase difference between the two beams of light is nkd, where n is the refractive index, k is the wave vector, and d is the thickness of the medium. For different application scenarios, the phase difference is adjusted by adjusting the values of n and d, and when nkd is equal to mπ, m is an integer, linearly polarized light is converted to its orthogonal polarization direction. The manufacturing of birefringent crystal wave plates mainly includes material selection, cutting, polishing, and film coating processes.

[0005] The birefringent crystal polarizing device is made of natural materials, and the interaction between the molecules, atoms of the natural materials and the electromagnetic wave magnetic field is weak, so that the permeability of the natural materials is very close to 1 at high frequencies (such as the infrared range). Therefore, the conventional electromagnetic device constructed by using the natural materials usually needs to be thick enough and present a certain curved shape to ensure the accumulation of a proper propagation phase to realize the required wave manipulation function. In terms of the working waveband, the change of the wavelength leads to the change of the wave vector, and the value of the propagation phase also changes, so that the conversion from linear polarization to circular polarization cannot be realized, and therefore the working waveband of the birefringent crystal material is narrow. In addition, the impedance mismatch between the air and the natural materials which usually do not show a magnetic response also reduces the efficiency of the conventional device. For the polarization grating, a sufficient thickness is also required to accumulate the propagation phase to realize the regulation of the polarization. These problems make the conventional polarization regulation device have a small working bandwidth and a large volume, which is difficult to meet the miniaturization and microfabrication requirements. SUMMARY

[0006] The purpose of the embodiments of the present application is to provide a middle wave infrared metasurface orthogonal polarization regulation device and method and application. The device of the present application has a small thickness, a wide working waveband and high polarization regulation efficiency.

[0007] The purpose of the embodiments of the present application is achieved by the following technical solutions:

[0008] In a first aspect, the embodiments of the present application provide a middle wave infrared metasurface orthogonal polarization regulation device, which is composed of a metal microstructure layer periodically arranged on an upper layer of a dielectric layer and a metal thin film layer attached to a lower layer of the dielectric layer.

[0009] Further, the thickness of the metal microstructure layer is 50 nm; the thickness of the dielectric layer is 0.36 μm; and the thickness of the metal thin film layer is 50 nm.

[0010] Further, the material of the metal microstructure layer is gold; the material of the dielectric layer is silicon dioxide; and the material of the metal thin film layer 3 is gold.

[0011] Further, the length and width of the metal microstructure layer 1 are 0.36 μm and 0.12 μm, respectively.

[0012] Further, the period of each metasurface structure unit composed of the metal microstructure, the dielectric and the metal thin film is 1.2 μm.

[0013] In a second aspect, the embodiments of the present application provide a use method of a middle wave infrared metasurface orthogonal polarization regulation device, and the middle wave infrared metasurface orthogonal polarization regulation device is the above-mentioned middle wave infrared metasurface orthogonal polarization regulation device. The finite element simulation is used to simulate the linearly polarized light with the polarization direction of the x direction incident on the metasurface polarization regulation device.

[0014] In a third aspect, the embodiments of the present application provide an application of the middle wave infrared metasurface orthogonal polarization modulation device, characterized in that the middle wave infrared metasurface orthogonal polarization modulation device is applied to polarization modulation in a middle wave infrared waveband of 3-4.2 μm.

[0015] The embodiments of the present application have the following beneficial effects:

[0016] In the middle wave infrared waveband of 3-4.2 μm, for linearly polarized light of normal incidence with an incident angle of 0°, the polarization direction of reflected light is orthogonal to that of incident light, and the polarization conversion efficiency of the device is greater than 99%, which can realize efficient conversion of linearly polarized light to its orthogonal polarization direction. The device has a wide application prospect in the field of middle wave infrared polarization modulation. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 FIG. 1 is a structural schematic diagram of a middle wave infrared metasurface orthogonal polarization modulation device according to an embodiment of the present application;

[0018] Figure 2 FIG. 2 shows the reflectivity of the same direction polarization component Rxx and the orthogonal polarization component Ryx of reflected light when the incident light changes in the middle wave infrared metasurface orthogonal polarization modulation device according to an embodiment of the present application;

[0019] Figure 3 FIG. 3 shows the polarization conversion rate of the middle wave infrared metasurface orthogonal polarization modulation device according to an embodiment of the present application. DETAILED DESCRIPTION

[0020] The present application will be further described with reference to the embodiments.

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, in the following description, different "an embodiment" or "embodiments" do not necessarily refer to the same embodiment. Different embodiments can be replaced or combined, and other embodiments can be obtained by those skilled in the art without creative labor.

[0022] The metasurface solves the problems faced by traditional polarization modulation devices. The metasurface is a two-dimensional, ultra-thin metamaterial composed of a periodic or non-periodic array of artificially designed structural units. By designing different structural units, the required electromagnetic response characteristics are achieved. The structural units that make up the metasurface usually include a multilayer structure composed of metal and dielectric or an all-dielectric structure, and the geometric parameters of these structures are smaller than the working wavelength of the device, in the subwavelength range. Unlike traditional polarization modulation devices, the metasurface no longer requires sufficient thickness and curved shape as well as fixed wavelength to accumulate the propagation phase. The metasurface interacts with the subwavelength structural units of the incident light, and obtains reflected light or transmitted light with different amplitudes and phases from the incident light, thereby achieving the modulation of the polarization. Therefore, the metasurface polarization modulation device is small in size, wide in working wavelength range, and easy to integrate into other optical devices.

[0023] For the existing birefringent crystal polarization modulation devices with a working wavelength in the mid-infrared, there are problems such as high device thickness, small working wavelength range, and inability to cover the entire mid-infrared. The inventors propose the following related solutions:

[0024] As shown in Figure 1 , a mid-infrared metasurface orthogonal polarization modulation device is composed of a periodic arrangement of a metal microstructure layer 1 on the upper layer of a dielectric layer 2, and a metal thin film layer 3 attached to the lower layer of the dielectric layer.

[0025] In some embodiments of the present application, the thickness of the metal microstructure layer 1 is 50 nm; the thickness of the dielectric layer 2 is 0.36 μm; and the thickness of the metal thin film layer is 50 nm.

[0026] By adjusting the geometric size of the microstructure layer 1 and the thickness of the dielectric layer 2, the proportion of the co-polarization component and the orthogonal polarization component in the reflected electromagnetic wave and the phase difference between the two can be controlled. Using the above parameters, the metasurface polarization modulation device required by the present application can be obtained, which works in the mid-infrared waveband and converts the polarization direction of linearly polarized light to the orthogonal direction of the incident light.

[0027] In some embodiments of the present application, the material of the metal microstructure layer is gold; the material of the dielectric layer is silicon dioxide; and the material of the metal thin film layer 3 is gold.

[0028] In some embodiments of the present application, the length and width of the metal microstructure layer 1 are 0.36 μm and 0.12 μm, respectively.

[0029] In some embodiments of the present application, the period of each metasurface structural unit composed of a metal microstructure, a dielectric, and a metal thin film is 1.2 μm. As shown in Figure 1 , a 3x3 metasurface array is formed according to the above contents.

[0030] The application embodiment provides a use method of a middle wave infrared super surface orthogonal polarization modulation device.

[0031] The application embodiment provides application of the middle wave infrared super surface orthogonal polarization modulation device.

[0032] When a linearly polarized light with a specified direction is incident on the super surface device, the incident light interacts with the three-layer structure of the super surface, a part of the light is directly reflected by the metal microstructure of the top layer of the super surface, and the remaining light enters the super surface structure, the light is reflected between the structure units of the metal microstructure layer 1 of the top layer of the super surface and the metal thin film layer 3 of the bottom layer, wherein the same direction polarization component is eliminated by interference, and the orthogonal polarization component is superimposed by interference, thereby realizing orthogonal polarization conversion.

[0033] In order to describe the performance of the super surface polarization modulation device, the polarization conversion efficiency PCR (polarization conversion ratio) is used to represent the performance of the device, and specifically for the linearly polarized incident light with the polarization direction along the x-axis direction, wherein represents the intensity of the reflection light component with the polarization direction along the x-axis in the reflection light, and represents the intensity of the reflection light component with the polarization direction along the y-axis in the reflection light. The closer the value of PCR is to 1, the more obvious the polarization conversion effect is.

[0034] The finite element simulation is used to simulate the linearly polarized light with the polarization direction along the x-axis direction incident on the super surface polarization modulation device, and the result is shown in Figures 2-3 . Figure 2 The reflectivity of the same direction polarization component Rxx and the orthogonal polarization component Ryx of the reflection light when the incident light changes in the range of 3-4.2 is given, and it can be seen from the figure that the orthogonal polarization component is about equal to 1, which is the polarized light with the polarization direction orthogonal to the polarization direction of the incident light. Figure 3 The polarization conversion rate of the super surface polarization modulation device is given, and it can be seen that in the wave band of 3-4.2 μm, the polarization conversion efficiency of the device is greater than 99%.

[0035] The thickness of the three-layer structure of the device is much smaller than the working wavelength. In the middle wave infrared wave band of 3-4.2 μm, for the linearly polarized light with the normal incidence angle of 0°, the polarization direction of the reflection light is orthogonal to the incident light, the polarization conversion efficiency of the device is greater than 99%, and the conversion from the linearly polarized light to the orthogonal polarization direction can be realized. The device has a wide application prospect in the field of middle wave infrared polarization modulation.

[0036] It should be noted that the above embodiments can be freely combined as needed. The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A mid-wave infrared metasurface orthogonal polarization modulation device, characterized in that, It consists of a metal microstructure layer arranged periodically on top of a dielectric layer, and a metal thin film layer attached to the bottom of the dielectric layer.

2. The mid-wave infrared metasurface orthogonal polarization modulation device according to claim 1, characterized in that, The thickness of the metal microstructure layer is 50 nm; the thickness of the dielectric layer is 0.36 μm; and the thickness of the metal thin film layer is 50 nm.

3. The mid-wave infrared metasurface orthogonal polarization modulation device according to claim 1, characterized in that, The metal microstructure layer is made of gold; the dielectric layer is made of silicon dioxide; and the metal thin film layer 3 is made of gold.

4. The mid-wave infrared metasurface orthogonal polarization modulation device according to claim 1, characterized in that, The length and width of the metal microstructure layer 1 are 0.36 μm and 0.12 μm, respectively.

5. The mid-wave infrared metasurface orthogonal polarization modulation device according to claim 1, characterized in that, Each metasurface structural unit, composed of a metal microstructure, a dielectric, and a metal thin film, has a period of 1.2 μm.

6. A method for using a mid-wave infrared metasurface orthogonal polarization modulation device, characterized in that, The mid-wave infrared metasurface orthogonal polarization control device is the mid-wave infrared metasurface orthogonal polarization control device according to any one of claims 1-5; finite element simulation is used to simulate linearly polarized light with polarization direction x incident on the metasurface polarization control device.

7. An application of a mid-wave infrared metasurface orthogonal polarization modulation device, characterized in that, The mid-wave infrared metasurface orthogonal polarization control device according to any one of claims 1-5 is applied to polarization control in the mid-wave infrared band of 3-4.2μm.

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