阅读说明：本技术 一种基于全介质超表面的偏振无关的红外消色差偏折器 (Polarization-independent infrared achromatic polarization deflector based on all-dielectric super-surface ) 是由 徐挺 于 2020-12-15 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偏振无关的红外消色差偏折器,其特征在于：所述红外消色差偏折器采用n个结构单元排列得到,n＞1；所述结构单元包括基底以及设置在基底上的微纳结构。本发现公布的偏振无关的红外消色差偏折器厚度薄(波长量级),易于集成,有望用在红外隐身等领域。(The invention discloses an infrared achromatic deflector based on polarization independence of an all-dielectric super surface, which is characterized in that: the infrared achromatic deflection device is obtained by arranging n structural units, wherein n is more than 1; the structure unit comprises a substrate and a micro-nano structure arranged on the substrate. The polarization-independent infrared achromatic polarization deflector disclosed by the discovery is thin in thickness (wavelength magnitude), easy to integrate and expected to be used in the fields of infrared stealth and the like.)

1. The utility model provides an infrared achromatism polarization beam splitter that polarization is irrelevant based on all-dielectric metasurface which characterized in that: the infrared achromatic deflection device is obtained by arranging n structural units, wherein n is more than 1; the structure unit comprises a substrate and a micro-nano structure arranged on the substrate.

2. The all-dielectric-metasurface-based polarization-independent infrared achromatic deflector of claim 1, wherein: the infrared achromatic deflection device is of a one-dimensional structure or a two-dimensional structure.

3. The all-dielectric-metasurface-based polarization-independent infrared achromatic deflector of claim 1, wherein: the arrangement of the structural units is according to a specific reference phase and the partial derivative of the phase to the frequency, and the arrangement of the structural units simultaneously meets the following requirements:

(1) the reference phase on the super-surface should satisfy the distribution of formula 1:

wherein, alpha is an incident angle, and theta is an emergent wave deflection angle; lambda [ alpha ]₀Is a reference wavelength;

(2) phase positionThe partial derivative for the frequency ω should satisfy the relationship of equation 2:

wherein c, α, θ and x are the light speed, the incident angle, the emergent wave deflection angle and the one-dimensional spatial position coordinate, respectively.

4. The all-dielectric-metasurface-based polarization-independent infrared achromatic deflector of claim 1, wherein: the cross section of the micro-nano structure is a centrosymmetric or anisotropic graph.

5. The all-dielectric-metasurface-based polarization-independent infrared achromatic deflector of claim 1, wherein: the number of the micro-nano structures is 1 to 3.

6. The all-dielectric-metasurface-based polarization-independent infrared achromatic deflector of claim 1, wherein: the substrate and the micro-nano structure are made of dielectric materials with low loss and high transmittance on infrared bands, the dielectric materials are barium fluoride, calcium fluoride, silicon, germanium or infrared chalcogenide glass, and the substrate and the micro-nano structure can be made of the same or different dielectric materials.

7. The all-dielectric-metasurface-based polarization-independent infrared achromatic deflector of claim 1, wherein: the structural unit substrate is periodic, and the period p of the substrate is less than or equal to the wavelength of infrared light.

8. The all-dielectric-metasurface-based polarization-independent infrared achromatic deflector of claim 1, wherein: the ratio of the height to the length (or width) of the micro-nano structure is less than 7: 1.

Technical Field

The invention belongs to the field of nanophotonics, and particularly relates to an all-dielectric super-surface based polarization-independent infrared achromatic polarizer.

Background

Optical elements have important applications in various aspects of daily life, for example, lenses with focusing power can be used for imaging and the like; polarizers having the ability to generate and inspect polarized light can be used in photography and the like. However, the large volume and thick thickness of conventional optical elements limits their integration into compact miniaturized optical devices.

In recent years, the advent of super-surfaces has provided a range of planar, ultra-thin and lightweight alternative optical elements. The super surface is a two-dimensional plane structure constructed by arranging a plurality of sub-wavelength artificial atoms according to specific functional requirements, and the wave is regulated and controlled by utilizing phase change on an interface. Since it can effectively control phase, polarization, amplitude, etc., the super-surface has been widely applied to optical elements such as lenses, wave plates, polarizers, etc.

Among the various optical elements, the beam deflector is one of the most basic optical elements. The optical fiber can control the propagation direction of light beams and has important application in the fields of sensing, optical communication and the like. In recent years, super-surface deflectors based on super-surfaces have been widely studied, for example, in 2015, Xiaoqiang Su et al realized super-surface deflectors of electrically-tuned terahertz frequency band; in 2016, Ai-Qun Liu et al realized achromatic deflection at three frequencies of 10.5GHZ, 12GHZ and 14GHZ by an air pressure control system; in 2017, by using a silicon dioxide substrate and a titanium dioxide microcolumn, Ting Xu et al realize a super-surface deflector in visible light wave bands (450nm, 532nm and 633 nm); in 2018, Xudong Cui et al also realized a 532nm super-surface deflector; in 2019, Xiangang Luo et al utilize phase change materials, based on MIM structure, to realize that the dispersion angle of 10.6um incident waves is continuously adjustable within +/-60 degrees; in the same year, Sangg-Eun Mun et al realized a wavelength selective polarizer using Fano resonant hypersurface; yuan Hsing Fu et al realized a 940nm large area pixellated super surface deflector.

In summary, while there is currently a great deal of research on ultra-surface polarizers, polarization independent achromatic ultra-surface polarizers are lacking in the infrared band.

The invention content is as follows:

the invention aims to overcome the defects of the prior art and provide an all-dielectric-super-surface-based polarization-independent infrared achromatic polarizer.

In order to achieve the purpose, the invention adopts the following technical scheme: the utility model provides an infrared achromatism polarization beam splitter that polarization is irrelevant based on all-dielectric metasurface which characterized in that: the infrared achromatic deflection device is obtained by arranging n structural units, wherein n is more than 1; the structure unit comprises a substrate and a micro-nano structure arranged on the substrate.

Furthermore, the infrared achromatic deflection device is of a one-dimensional structure or a two-dimensional structure.

Furthermore, the arrangement of the structural units is according to a specific reference phase and the partial derivative of the phase to the frequency, and the arrangement of the structural units simultaneously needs to satisfy the following requirements:

(1) the reference phase on the super-surface should satisfy the distribution of formula 1:

wherein, alpha is an incident angle, and theta is an emergent wave deflection angle; lambda [ alpha ]₀Is a reference wavelength;

(2) phase positionThe partial derivative for the frequency ω should satisfy the relationship of equation 2:

wherein c, α, θ and x are the light speed, the incident angle, the emergent wave deflection angle and the one-dimensional spatial position coordinate, respectively.

Furthermore, the cross section of the micro-nano structure is a centrosymmetric or anisotropic graph.

Furthermore, the number of the micro-nano structures is 1 to 3.

Further, the substrate and the micro-nano structure are made of dielectric materials with low loss and high transmittance on infrared bands, the dielectric materials are barium fluoride, calcium fluoride, silicon, germanium or infrared chalcogenide glass, and the same or different dielectric materials can be adopted for the substrate and the micro-nano structure.

Further, the structural unit substrate is periodic, and the period p of the substrate is less than or equal to the wavelength of infrared light.

Further, the ratio of the height to the length (or width) of the micro-nano structure is less than 7: 1.

first, a one-dimensional super-surface deflector was studied. In the one-dimensional super-surface structure, when the working wave band (lambda)_min～λ_max) When the incident angle of (a) is α, if the emergent light is to realize θ angle deflection, the reference phase and the phase-to-frequency polarization thereof respectively need to satisfy the following relations:

wherein λ is₀X and c respectively represent a reference wavelength, a one-dimensional space coordinate and a light speed; in equations (1) and (2), the signs in front of the first equation on the right of the equal sign correspond to outgoing waves in the cases of 4 and 3 in fig. 1, respectively, and the signs in front of the second equation correspond to incoming waves in the cases of 2 and 1, respectively.

According to the working wave band, the substrate and the micro-nano structure on the substrate adopt dielectric materials with low loss and high transmittance, such as barium fluoride, calcium fluoride, germanium, infrared chalcogenide glass and the like.

To realize the polarization-independent characteristic of the super-surface to the incident wave, the section of the micro-nano structure parallel to the substrate is usually a centrosymmetric figure, such as: round, square, etc.; further, the shape may be rectangular or the like.

And determining the period P of the structural unit and the height H of the micro-nano structure. If the subsequent processing is convenient, the micro-nano structure preferably adopts a low depth-to-width ratio, for example, less than or equal to 7: 1.

A series of structural units meeting specific reference phase and phase-to-frequency deviation are obtained through simulation by simulation software (such as FDTD), and then the structural units are arranged to form the one-dimensional super-surface deflector. And repeatedly arranging the one-dimensional super-surface structures in the vertical direction to form the two-dimensional super-surface deflector.

The invention has the following beneficial effects:

(1) the invention provides an ultra-thin (wavelength magnitude) achromatic deflection device, which is beneficial to being combined with an integrated optical system compared with the traditional deflector.

(2) The super-surface deflectors disclosed by the invention can be periodically and repeatedly arranged in space, and the size limitation of an achromatic device based on a super surface is broken through.

(3) The super-surface deflector can be applied to the infrared stealth aspect, particularly in the atmospheric window wave band, and the achromatic deflector which is irrelevant to the wave band polarization can enable electromagnetic waves radiated by a human body or an object to be emitted in the same direction at the same time, so that the detected probability is reduced, and the infrared stealth purpose is achieved.

Drawings

FIG. 1 shows two different incident conditions and two different emergent conditions at the same incident angle for the super-surface deflector of the present invention.

FIG. 2 is a schematic diagram of an exemplary super-surface achromatic deflector, normal incidence, with waves of different wavelengths (λ)_min～λ_max) And exit along the same angle.

Fig. 3 is a perspective view of three different types of structural units in example 1, where P is 8 μm and H is 10 μm, and the substrate and pillar materials are both silicon.

FIG. 4 is a perspective view of three different types of structural units of example 1.

FIG. 5 is a perspective view of an achromatic super-surface deflector of example 1, one-dimensional polarization independent.

Fig. 6 is a phase distribution of an outgoing wave obtained by simulating an achromatic super surface polarizer having no relation to one-dimensional polarization when the incident wave is a left-hand circularly polarized wave in example 1.

Fig. 7 is a phase distribution of an outgoing wave obtained by simulating an achromatic super-surface polarizer having no relation to one-dimensional polarization when an incident wave is a right-handed circularly polarized wave in example 1.

FIG. 8 is a top view of an achromatic super surface deflector, two-dimensional polarization independent, according to example 2.

FIG. 9 is an oblique view of the two-dimensional polarization-independent achromatic super-surface polarizer of example 2.

The specific implementation mode is as follows:

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.

An infrared achromatic deflection device based on polarization independence of an all-dielectric super surface is obtained by arranging n structural units, wherein n is larger than 1. The structure unit comprises a substrate and a micro-nano structure arranged on the substrate.

Selecting a reference wavelength λ, a band of operation that is required to achieve polarization independent achromatic polarization deflection (as shown in FIG. 2)₀Angle of incidence α, and angle of deflection θ, in this embodiment. They are respectively: 9.5-11 μm, 0 DEG and 10 deg.

Example 1

In the one-dimensional super-surface structure, if the above-mentioned deflection effect is to be achieved, the reference phase and the phase deviation with respect to the frequency need to satisfy the following relationship:

where x and c represent the coordinate and the speed of light, respectively, and θ is 10 °, λ₀＝11um。

Selecting materials and micro-nano structure shapes. In this embodiment, the substrate and the micro-nano structure are made of silicon materials. If polarization-independent characteristics are to be realized, the section of the micro-nano structure parallel to the substrate is generally a centrosymmetric figure such as a circle, a square and the like. In this embodiment, we use a microcolumn with a rectangular cross section to achieve polarization independent properties for the incident wave. Fig. 3 and 4 are perspective and top views of three different types of structural units used in the present embodiment.

And (5) simulating the structural unit. The depth-to-width ratio of the micro-nano structure is smaller than 7:1, which is beneficial to subsequent processing and preparation. In addition, the structural unit period P and the height H of the micro-nano structure are fixed to 8 μm and 10 μm, respectively. And simulating structural units with different micro-nano structure sizes by using FDTD, wherein boundary conditions in the x direction, the y direction and the z direction of the structural units are respectively set as period, period and PML, and a series of structural units which accord with specific reference phase and phase pair frequency partial derivatives given by theoretical calculation are obtained. It is noted that the super-surface based optical components are very fault tolerant, allowing for a slight deviation of the reference phase and phase-to-frequency deviation of the structural elements obtained by simulation.

And (5) simulating the one-dimensional super-surface deflector. Arranging the obtained micro-nano structures meeting the requirements into a one-dimensional super-surface deflector, and simulating the deflection effect by using FDTD, wherein the boundary conditions in the x, y and z directions are respectively set as PML, Periodic and PML. Fig. 5 is an oblique view of the one-dimensional super-surface deflector in the present embodiment, and fig. 6 and 7 are phase distributions of outgoing waves when a left-handed circularly polarized wave and a right-handed circularly polarized wave are incident, respectively. The one-dimensional super-surface polarizer in this embodiment is suitable for any polarization state (e.g., linear polarization) because any polarization state can be formed by superimposing two crossed polarization states (e.g., left-handed circular polarization and right-handed circular polarization).

Example 2

And designing a two-dimensional super-surface deflector. The one-dimensional super-surface deflectors are repeatedly arranged along the vertical direction (i.e., the y direction) to form a two-dimensional super-surface deflector, as shown in fig. 8 and 9. In addition, large size polarization independent achromatic super surface polarizers can also be obtained by periodic alignment along the x-direction.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.