CN111399086A - Fork-shaped grating multiplexing method based on super-surface material - Google Patents
Fork-shaped grating multiplexing method based on super-surface material Download PDFInfo
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Abstract
The invention discloses a fork grating multiplexing method based on a metamaterial, which enables a nano brick to act as a micro-nano half-wave plate by optimally designing the structural parameters of a nano brick unit, and realizes information storage of two fork gratings and reconstruction of two different vortex optical rotations. The super surface can be constructed by dielectric or metal, a specific light path based on a polarizer, the super surface and an analyzer can be constructed by utilizing the characteristics of a micro-nano half-wave plate, the design of dual-channel amplitude modulation is carried out on the super surface, the information of two binary fork gratings is encoded and converted into the rotation direction angle distribution of a nano brick array, the nano brick array is decoded by the specific light path, and two holographic images with different vortex light information are respectively generated.
Description
Technical Field
The invention belongs to the field of micro-nano optics, and particularly relates to a design method for realizing fork grating multiplexing of a metamaterial with a micro-nano half-wave plate function.
Background
The vortex light beam is a special vector light beam, the light intensity distribution of the vortex light beam is cylindrical, the phase position of the central position of the light beam has uncertainty, and the central position of the light beam carries orbital angular momentum. The advantages enable the vortex light beam to have high application value in the fields of optical control, optical communication, biomedicine, micromechanics and the like. The super surface is used as a novel optical material with sub-wavelength magnitude, and can perform precise amplitude, phase, polarization and wavelength regulation on optical waves. Because of its advantages of small size, light weight, and easy integration, a great number of novel optical elements based on super-surface have been continuously researched.
At present, many students use a super-surface to design various different vector beam generators, but most super-surfaces have single functions (only one vector beam can be generated by one super-surface structure) and complex structures, so that the practical application is greatly challenged. Therefore, a new super-surface design method is needed to increase the complexity of the super-surface optical modulation function to meet the deep application requirements.
Disclosure of Invention
In order to solve the technical problem, the invention provides a fork-shaped grating multiplexing method based on a super-surface material. The method can respectively realize two different fork grating patterns by using one super-surface sample wafer, and realizes two beams of vortex optical rotation with different topological numbers in a far field through Fraunhofer diffraction.
One of the purposes of the invention is to provide a fork-shaped grating multiplexing method based on a super surface material, which comprises the following steps:
a fork-shaped grating multiplexing method based on a super surface material comprises the following steps:
(1) preparing a super-surface material, wherein the super-surface is formed by arraying a plurality of unit structures on a plane, each unit structure is of a two-layer structure or a three-layer structure, the unit structure comprises a substrate and nano bricks arranged on the substrate, and the unit structure is formed by stacking the substrate, a dielectric layer and the nano bricks from bottom to top;
(2) setting a working wavelength by adopting an electromagnetic simulation tool, and optimizing parameters of a unit structure of the super surface so that each unit structure works as a micro-nano half-wave plate, wherein the working mode of a two-layer unit structure is a reflective type or a transmission type, and the working mode of a three-layer unit structure is a reflective type;
(3) designing a fork-shaped grating pattern, binarizing light intensity information of the fork-shaped grating pattern to obtain a binary fork-shaped grating distribution diagram, and reconstructing and assigning;
(4) multiplexing binary gray values in two different binary grating distribution diagrams to be converted into rotation angles of the nano bricks, wherein each pixel corresponds to one rotation angle and gray value information of the two binary gratings, and a unit structure array is constructed to form a super surface; the super-surface can realize independent dual-channel amplitude modulation based on two working states of the unit structure;
(5) the polarizer and the analyzer are arranged in parallel in front of and behind the super-surface, a beam of light is vertically incident and sequentially passes through the polarizer, the super-surface and the analyzer, two different working channels are established under respective working environments of two channels, and two diffraction patterns with vortex light spot patterns are obtained, so that information recording and transmission are realized.
Furthermore, in the two-layer unit structure, the nano brick is a cuboid and is made of Si and TiO2(ii) a The substrate is a cuboid, the cross section of the substrate is a square, and the substrate comprises MgF2And SiO2。
Go toIn the three-layer unit structure, the nano brick is a cuboid and is made of Si and TiO2Ag, Au, Cu and Al; the dielectric layer and the substrate are cuboids, the cross sections of the dielectric layer and the substrate are square and have the same size; the dielectric layer material comprises MgF2And SiO2(ii) a The base layer material comprises Si, Ag, Au, Cu and Al.
Further, when the unit structure is a two-layer structure, the optimization parameters comprise the length, the width and the height of the nano brick and the side length of the top surface of the substrate; when the unit structure is a three-layer structure, the optimization parameters comprise the length, the width and the height of the nano brick, the side length of the top surface of the substrate and the thickness of the dielectric layer; the above parameters are all of sub-wavelength order.
Further, the optimization goal in the step (2) is as follows: when the circular polarization light vertically enters the unit structure, the reverse polarization circular polarization light efficiency in the emergent light is highest, and the same-direction polarization circular polarization light efficiency is suppressed to be lowest.
Further, in the present invention,
the design method of the cross-shaped grating in the step (3) is as follows: intensity information in interference fringes of a normally incident plane wave and an obliquely incident vortex light on a plane z which is 0m is used for constructing a fork grating pattern; two beams of eddy optical rotation with different topological values can construct two fork grating patterns; binarizing the gray values of the two fork-shaped grating patterns, simultaneously recording the gray values on the same super surface, and designing and processing a binary fork-shaped grating;
the method for reconstructing and assigning the cross-shaped grating in the step (3) is as follows: a plane wave is normally incident to the binary fork grating pattern, and the designed vortex light is reconstructed to +/-1 order through diffraction.
Further, in the step (4), a xoy rectangular coordinate system is established with the right-angle sides of the top surface of the dielectric layer as the x-axis and the y-axis and the vertex as the origin, and the included angle between the long axis of the nano brick and the x-axis is 0-180 degrees which is the turning angle α.
Further, the method for converting the multiplexing of the two different binary grating distribution diagrams into the rotation direction angle of the nano brick in the step (4) is as follows: the polarizer and the analyzer are arranged in parallel in front of and behind the super surface, and when a beam of light passes through the polarizer, the super surface and the analyzer in sequenceThe polarization state and amplitude of the emergent light are modulated for three times, and the amplitude of the emergent light is controlled by the rotation angle α of the nano brick and the included angle theta between the transmission axes of the polarizer and the analyzer and the x axis1、θ2Determining; by optimizing theta1、θ2Determining the values of the two, establishing the corresponding relation between the amplitude of the emergent light and α, and determining the amplitude of the emergent light in two specific groups of theta1、θ2In the state, four values of α are flexibly selected, two working channels are established, independent regulation and control of binary amplitude '0' and '1' are realized, four amplitude values of the nano-brick under the two channels are distributed to be in four binary coding states of '11', '01', '00' and '10', a rotation direction angle α is in one-to-one correspondence with each pixel of a binary fork-shaped grating pattern, the unit structure is respectively and independently assigned under the two working states to realize an independent two-channel binary amplitude modulation function, and preferably, theta is selected1、θ2In the range of 0-360.
The second object of the present invention is to provide a super surface prepared by the above method.
The invention also aims to provide application of the super surface in quantum communication.
The working principle is as follows:
1. unit structure
The super surface comprises a two-layer or three-layer structure which is sequentially provided with a substrate and a nano brick (or the substrate, a dielectric layer and a top layer) from bottom to top;
wherein the content of the first and second substances,
the substrate is a square with a square top surface;
the dielectric layer is a square with a square top surface;
the nano brick is in a cuboid structure;
the side lengths of the top surfaces of the substrate and the dielectric layer are the same;
establishing a xoy rectangular coordinate system by taking the right-angle sides of the top surface of the dielectric layer or the substrate as an x axis and a y axis and the vertex as an origin, wherein the included angle between the long axis of the nano brick and the x axis is a turning angle α;
the period CS of the unit structure is the side length of the top surface of the substrate;
the super surface can be regarded as a micro-nano half-wave plate array under the design wavelength: all the nano bricks have the same geometric dimension and different rotation angles, and each nano brick unit structure can be used as a micro-nano half-wave plate.
And setting a working wavelength by adopting an electromagnetic simulation tool, and optimizing parameters of the unit structure of the super surface so that each unit structure works as a micro-nano half-wave plate. The optimization aims at: when the circular polarization light vertically enters the unit structure, the reverse polarization circular polarization light efficiency in the emergent light is highest, and the same-direction polarization circular polarization light efficiency is suppressed to be lowest. The working mode of the two-layer unit structure is a reflection type or a transmission type, and the working mode of the three-layer unit structure is a reflection type.
For the substrate-nano brick structure, the structural parameters comprise the length L, the width W, the height H and the period CS of the nano brick, and the working mode is a reflective type or a transmissive type, for the substrate-dielectric layer-nano brick structure, the structural parameters comprise the length L, the width W, the height H, the period CS and the dielectric layer thickness d of the nano brick, and the working mode is a reflective type.
If the nano brick unit structure works in a reflection (transmission) mode, the reflectivities (transmittances) of the s wave and the p wave are approximately same when the s wave and the p wave are vertically incident under the working wavelength, and the phase difference between the reflectivities is pi, the reflectivity (transmittance) of the same-direction polarization circular polarization light is suppressed to be close to 0 when L CP (RCP) light is vertically incident under the working wavelength, and the reflectivity (transmittance) of the reverse-direction polarization circular polarization light is highest.
The materials of the nano-brick can be divided into two types: dielectric nano-bricks and metal nano-bricks.
The dielectric nanobelt may be used to design a three-layer nanobelt structure (substrate, dielectric layer, nanobelt): MgF using an opaque Si substrate or metals Ag, Au, Cu, Al as a base2、SiO2Dielectric layer of equal low refractive index and transparent, dielectric Si, TiO2And constructing a top layer nano brick structure. The working principle of the nano brick structure is as follows: when s wave and p wave are incident under working wavelength, the p wave is directly reflected by Mie resonance, and the s wave passes through the nano brick and then generates multi-beam interference in the dielectric layerThen the reflected light is emitted out through the nano brick, the amplitudes of the s-wave reflected light and the p-wave reflected light are the same, and the phase difference is pi, so that the nano brick can work as a half-wave plate.
Dielectric nanobelts can also be used to design a two-layer nanobelt structure (substrate, nanobelt): using MgF2、SiO2Isolow refractive index and transparent dielectric as substrate, Si, TiO2The nano brick structure is constructed by the material with higher isorefractive index (the material with too large dispersion loss can not be selected). The working principle of the nano brick structure is as follows: when a transmission type nano brick structure is constructed, the length and the width of the nano brick are controlled, so that the equivalent refractive indexes of the nano brick in two directions are different, and s waves and p waves are directly transmitted after being vertically incident and generate a phase difference of pi; when a reflection-type nano brick structure is constructed, the Mie resonance effect in two directions of the nano brick is controlled by controlling the length and the width of the nano brick, so that an electromagnetic field is enhanced to different degrees, s waves and p waves are reflected due to the Mie resonance after being vertically incident, the reflectivity of the s waves and the reflectivity of the p waves are the same, and the phase difference is pi.
The nano-brick comprises a nano-brick incidence surface, an s-wave incident surface, a p-wave incident surface, an L CP (RCP) light, a reverse polarization circular polarization light and a reverse polarization circular polarization light, wherein the nano-brick incidence surface is a plane with a long axis direction vector of the nano-brick and a coplanar incidence direction vector, the s-wave incident light is a linearly polarized wave with a polarized state of an electric field decomposed by incident light vertical to the nano-brick incidence surface, the p-wave incident light is a linearly polarized wave with a polarized state of an electric field decomposed by incident light horizontal to the nano-brick incidence surface, the L CP (RCP) light is a left-handed (right-handed) circular polarization.
The metal nano brick can be used for designing a three-layer nano brick structure (a substrate, a dielectric layer and a nano brick): MgF using opaque silicon substrate or metal Ag, Au, Cu, Al as base2、SiO2And the dielectric medium with low refractive index and transparency is used for constructing a dielectric layer, and the materials such as Ag, Au, Cu, Al and the like are used for constructing a top layer nano brick structure. The working principle of the nano brick structure is as follows: when s wave and p wave are incident under working wavelength, the p wave is reflected directly by plasma resonance, the s wave passes through the nano brick, then the s wave is emitted through the nano brick after multi-beam interference in the dielectric layer, the amplitudes of the s wave and the p wave reflected light are the same and the phase difference is between the s wave and the p wave reflected lightIs pi and thus works as a half-wave plate.
2. Fork grating multiplexing
(1) When a beam of light passes through the polarizer, the nano-brick unit structure and the analyzer in sequence, the polarization state and the amplitude of emergent light are modulated for three times, and the amplitude of the emergent light can be expressed as
Aout＝Ain·cos(2α-θ1-θ2), (1)
Wherein A isinAnd AoutThe amplitudes of the light incident to the nano brick units and the emergent light are respectively; theta1And theta2α is the included angle between the long axis and the x axis when the nano brick rotates, the x axis is along the long direction of one side of the nano brick, when the long axis of the nano brick is coincident with the x axis, α is 0;
based on equation (1), θ can be optimized1、θ2The amplitude of emergent light is flexibly designed by value combination of the two-channel amplitude modulation method, and a two-channel binary amplitude modulation function (corresponding to four states of '00', '01', '10' and '11') is realized;
when the super-surface works as a half-wave plate at the same time, the working wavelength is set to be lambda, the range of α is 0-180 degrees, and theta1、θ2In the range of 0-360.
(2) Binaryzation is carried out on the forked grating patterns (corresponding to '0' state and '1' state), the two binary forked grating patterns can be stored in the distribution of the turning angles of the nano bricks through a dual-channel amplitude modulation formula (1) (one turning angle of the nano brick corresponds to two amplitude modulation values of the two channels), one-to-one correspondence of each binary value and the turning angle is established, then a nano brick array is established, and a corresponding super-surface sample wafer is designed;
(3) a beam of laser is vertically incident and sequentially passes through the polarizer, the super-surface sample wafer and the analyzer, so that diffraction patterns with vortex light spot patterns (different vortex light spots realized by each channel) can be observed at +/-1-level positions 0.5m away from the super-surface sample wafer in the working environment of the two channels. Multiplexing and quantum communication of the fork grating pattern are realized.
The invention has the beneficial effects that:
(1) the invention can realize the dual-channel amplitude modulation function only by combining the geometric phase regulation of the metamaterial with the Malus law;
(2) the nano brick structure can use various dielectric medium and metal structures, and has flexible design and simple structure;
(3) the dual-channel fork-shaped grating multiplexing provided by the invention is based on two choices of the rotation direction angle of the nano brick, so that the dual-channel fork-shaped grating multiplexing can be independently designed according to nearly any two different fork-shaped grating patterns, and the two working modes cannot influence each other;
(4) the nano brick provided by the invention has a sub-wavelength scale, has an ultramicro structure, can be widely applied to the field of photonic integration, and is suitable for the development trend of miniaturization and micromation in the future.
Drawings
FIG. 1 is a schematic three-dimensional structure of a nano-brick unit in an embodiment;
FIG. 2 is the polarization conversion efficiency distribution of the nano-brick unit structure in the embodiment when the incident light is circularly polarized;
FIG. 3 is a simplified optical diagram for the two-channel amplitude modulation principle in an embodiment;
FIG. 4 is a fork raster pattern recorded under channel 1 of the super surface in an embodiment;
FIG. 5 is a fork grating pattern recorded under channel 2 of the super surface in an embodiment;
in the figure, 1-silicon dioxide substrate, 2-silicon nano brick, L is the long axis dimension of the nano brick, W is the short axis dimension of the nano brick, H is the height of the nano brick, CS is the cycle dimension of the nano brick, and α is the rotation angle of the nano brick.
Detailed Description
In order to more clearly illustrate the embodiments of the present invention and/or the technical solutions in the prior art, the following description will explain specific embodiments of the present invention with reference to the accompanying drawings. It is obvious that the drawings described below are only examples of the invention, and that for a person skilled in the art, other drawings and embodiments can be obtained from them without inventive effort. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Examples
In this embodiment, a silicon nano brick with a double-layer structure is taken as an example, and the operating mode is a transmissive mode. See the silicon nano brick unit structure shown in fig. 1, and a silicon dioxide substrate 1 and a nano brick 2 constructed by dielectric silicon are sequentially arranged from bottom to top. The nano brick array is formed by periodically arranging nano brick unit structures, each nano brick has the same geometric structure size and different rotation angles, each nano brick is cuboid, and the length, the width and the height of each nano brick are sub-wavelength sizes.
The silicon nano-brick array structure-based super-surface sample wafer can be manufactured by adopting a photoetching process which is conventional in the field, and a specific preparation process is provided as follows, and comprises the following steps:
(1) coating a silicon film and photoresist on a substrate in sequence;
(2) exposing the photoresist by adopting an electron beam direct writing or a photoetching machine;
(3) and developing and etching are sequentially carried out, so that the silicon nano brick array is obtained on the silicon dioxide substrate (1).
For ease of understanding, the working principle of the nanoblock structure as a half-wave plate and the implementation of fork grating multiplexing will be explained below.
When the dielectric silicon is used for constructing the nano-brick, the unit periodic structure of the nano-brick is only half wavelength, and the long and short axis sizes of the nano-brick have difference, so the silicon nano-brick can be regarded as a micro-nano antenna with strong anisotropy. Through the optimal design, the transmission rates of the long axis and the short axis of the silicon nano brick are equal, and the phase difference of pi is formed between the transmission coefficients, so that the silicon nano brick can work as a micro-nano half-wave plate and has high polarization conversion efficiency (reverse circular polarization transmission rate).
When the fork-shaped grating multiplexing function is realized, a polarizer and an analyzer are required to be added to control the polarization direction and amplitude of light incident to the super surface and emergent light. Wherein, when the included angles between the transmission axes of the polarizer and the analyzer and the x-axis direction are 0 degree and 0 degree respectively, as shown in fig. 3, after a beam of incident light passes through the polarizer, the nano-brick unit structure and one analyzer in sequence, according to the formula (1), the amplitude of the transmission light can be expressed as
Aout＝Ain·cos(2α), (2)
When the included angles between the transmission axes of the polarizer and the analyzer and the x-axis direction are 0 degree and 90 degrees respectively, the amplitude of the transmission light can be expressed as
Aout＝Ain·sin(2α)。 (3)
The simultaneous equations (2) and (3) show that when the rotation angles of the nano-bricks are 22.5 °, 67.5 °, 112.5 ° and 157.5 °, the transmitted light in the operating states of the two polarizers and analyzers is 0.707A in this orderin、-0.707Ain、-0.707AinAnd 0.707Ain(θ1＝0°，θ2＝0°)；0.707Ain、0.707Ain、-0.707Ainand-0.707Ain(θ1＝0°，θ290 °). If it is-0.707AinMarked as state '0', 0.707AinMarked as the state '1', the binary states of '1001' and '1100' are realized in the two operating modes, respectively. If the rotation angle of the nano brick is fixed, four encoding states of '11', '01', '00' and '10' can be stored in two corresponding operating modes.
The transmission type half-wave plate based on the silicon-based super surface and the specific implementation process thereof for fork grating multiplexing are provided below.
In this embodiment, a nano brick is constructed by using a crystalline silicon material, silica is used as a substrate, a working wavelength is set to 632.8nm, and a nano brick unit structure model is shown in fig. 1.
In the first step, an existing COMSO L electromagnetic simulation tool is adopted, and geometric parameters of a nano brick unit structure are optimized for 632.8nm, levorotatory circular polarized light is set as incident light, and the optimized nano brick unit structure is optimally designed by taking the highest efficiency of the transmitted dextrorotatory circular polarized light as an optimization target.
And secondly, simulating the circular polarization conversion rate of the determined nano brick unit structure in the range of 500-700 nm by using a COMSO L electromagnetic simulation tool, wherein the same-direction polarized light and the opposite-direction polarized light respectively represent circular polarization components with the same chirality as incident light and the opposite chirality, as shown in figure 2, when the wavelength is 632.8nm, the circular polarization conversion efficiency reaches 85%, the transmission rate of the same-direction polarized light is only about 5%, and the polarization efficiency is high, so that the designed nano brick is considered to have the function of a half-wave plate, and when the optical path diagram shown in figure 3 is used for working, the super surface formed by the nano brick can be used for the polarization state and amplitude modulation of linear polarization.
And thirdly, designing a fork grating pattern. Intensity information of interference fringes of a normal incidence plane wave and an oblique incidence vortex light on a plane with the z being 0m can be used for constructing the fork-shaped grating, and binary fork-shaped grating distribution can be obtained by binarizing the intensity information. For two beams of eddy rotation with topology values l 2 and l 4, two different binary fork grating patterns can be designed, as shown in fig. 4, 5. When a plane wave is normally incident on the binary fork grating with the intensity distribution as shown in fig. 4 or fig. 5, the vortex light with l 2 or 4 can be reconstructed to ± 1 order through diffraction.
And fourthly, recording two different fork grating patterns on the super surface to realize the multiplexing of the fork gratings. Based on the multiplexing principle of the half-wave plate, two states of '0' and '1' in the corresponding two binary fork grating patterns can be converted into the rotation direction angle of the nano-brick. Let channel 1 (theta)1＝0°，θ2Recording a binary fork grating corresponding to an eddy rotation of l 2 (fig. 3) at 0 deg., channel 2(θ)1＝0°，θ290 deg. a binary fork grating corresponding to a vortex rotation of l 4 is recorded (fig. 4). Each nanoblock of the super-surface is designed one by one, and one nanoblock corresponds to one pixel of the cross-shaped grating in fig. 3 and 4, and if the corresponding intensity value in fig. 3 is '1' and the intensity value in fig. 4 is '1', the information recorded by the nanoblock is called as a '11' combination, and corresponds to a 22.5 ° rotation direction angle. Similarly, if the combination status is '01', '00' or '10' respectively,the rotation angles of the nano bricks correspond to 67.5 degrees, 112.5 degrees or 157.5 degrees respectively. According to the corresponding principle, the information of the two binary fork-shaped gratings can be completely converted into the rotation direction angle distribution of the nano-brick array, and theta is set through the light path shown in figure 31、θ2Respectively realizes the reconstruction of two beams of eddy optical rotation. The information recording of the two channels is not affected, so that two beams of completely different vortex rotation can be independently generated, the multiplexing method improves the information capacity of the super surface, and can be applied to the fields of quantum communication and the like.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any modification, equivalent replacement, and improvement made by those skilled in the art within the technical scope of the present invention should be included in the scope of the present invention.
Claims (10)
1. A fork-shaped grating multiplexing method based on a super surface material is characterized by comprising the following steps:
(1) preparing a super-surface material, wherein the super-surface is formed by arraying a plurality of unit structures on a plane, each unit structure is of a two-layer structure or a three-layer structure, the unit structure comprises a substrate and nano bricks arranged on the substrate, and the unit structure is formed by stacking the substrate, a dielectric layer and the nano bricks from bottom to top;
(2) setting a working wavelength by adopting an electromagnetic simulation tool, and optimizing parameters of a unit structure of the super surface so that each unit structure works as a micro-nano half-wave plate, wherein the working mode of a two-layer unit structure is a reflective type or a transmission type, and the working mode of a three-layer unit structure is a reflective type;
(3) designing a fork-shaped grating pattern, binarizing light intensity information of the fork-shaped grating pattern to obtain a binary fork-shaped grating distribution diagram, and reconstructing and assigning;
(4) multiplexing binary gray values in two different binary grating distribution diagrams to be converted into rotation angles of the nano bricks, wherein each pixel corresponds to one rotation angle and gray value information of the two binary gratings, and a unit structure array is constructed to form a super surface; the super-surface can realize independent dual-channel amplitude modulation based on two working states of the unit structure;
(5) the polarizer and the analyzer are arranged in parallel in front of and behind the super-surface, a beam of light is vertically incident and sequentially passes through the polarizer, the super-surface and the analyzer to establish two different working channels, and under respective working environments of the two channels, two diffraction patterns with vortex light spot patterns are obtained to realize information recording and transmission.
2. The fork-shaped grating multiplexing method based on the metamaterial according to claim 1, wherein: in the two-layer unit structure, the nano brick is a cuboid and is made of Si and TiO2(ii) a The substrate is a cuboid, the cross section of the substrate is a square, and the substrate comprises MgF2And SiO2。
3. The fork-shaped grating multiplexing method based on the metamaterial according to claim 1, wherein: in the three-layer unit structure, the nano brick is a cuboid and is made of Si and TiO2Ag, Au, Cu and Al; the dielectric layer and the substrate are cuboids, the cross sections of the dielectric layer and the substrate are square and have the same size; the dielectric layer material comprises MgF2And SiO2(ii) a The base layer material comprises Si, Ag, Au, Cu and Al.
4. The fork-shaped grating multiplexing method based on the metamaterial according to claim 1, wherein: when the unit structure is a two-layer structure, the optimization parameters comprise the length, the width and the height of the nano brick and the side length of the top surface of the substrate; when the unit structure is a three-layer structure, the optimization parameters comprise the length, the width and the height of the nano brick, the side length of the top surface of the substrate and the thickness of the dielectric layer; the above parameters are all of sub-wavelength order.
5. The fork-shaped grating multiplexing method based on the metamaterial according to claim 4, wherein the optimization goal in the step (2) is to: when the circular polarization light vertically enters the unit structure, the reverse polarization circular polarization light efficiency in the emergent light is highest, and the same-direction polarization circular polarization light efficiency is suppressed to be lowest.
6. The fork-shaped grating multiplexing method based on the metamaterial according to claim 1, wherein the design method of the fork-shaped grating in the step (3) is as follows: intensity information in interference fringes of a normally incident plane wave and an obliquely incident vortex light on a plane z which is 0m is used for constructing a fork grating pattern; two beams of eddy optical rotation with different topological values can construct two fork grating patterns; binarizing the gray values of the two fork-shaped grating patterns, simultaneously recording the gray values on the same super surface, and designing and processing a binary fork-shaped grating;
the fork grating reconstruction and assignment method comprises the following steps: a beam of plane wave is normally incident on the binary fork-shaped grating, and the designed vortex light is reconstructed to +/-1 order through diffraction.
7. The multiplexing method of the fork-shaped grating based on the metamaterial according to claim 1, wherein in the step (4), a xoy rectangular coordinate system is established by taking the right-angle sides of the top surface of the dielectric layer as an x-axis and a y-axis and the vertex as an origin, and the included angle between the long axis of the nano-brick and the x-axis is in the range of 0-180 degrees of a rotation angle α.
8. The method for multiplexing the fork-shaped grating based on the metamaterial according to claim 7, wherein the method for converting the multiplexing of the two different binary grating distribution patterns into the rotation angle of the nano-brick in the step (4) is characterized in that a polarizer and an analyzer are arranged in parallel in front of and behind the super-surface, when a beam of light passes through the polarizer, the super-surface and the analyzer in sequence, the polarization state and the amplitude of the emergent light are modulated three times, the amplitude of the emergent light is adjusted by the rotation angle α of the nano-brick, and the included angle theta between the transmission axes of the polarizer and the analyzer and the x axis1、θ2Determining; by optimizing theta1、θ2Determining the values of the two, establishing the corresponding relation between the amplitude of the emergent light and α, and determining the amplitude of the emergent light in two specific groups of theta1、θ2Under the state, four values of α are flexibly selected, two working channels are established, the independent regulation and control of binary amplitude '0' and '1' are realized, and a bi-pass is givenThe four amplitude values of the sub-track nano-bricks are distributed in four binary coding states of '11', '01', '00' and '10', the rotation direction angle α is in one-to-one correspondence with each pixel of the binary fork grating pattern, and the unit structure is independently assigned to realize an independent two-channel binary amplitude modulation function in two working states.
9. A super-surface prepared by the fork grating multiplexing method of any one of claims 1 to 8.
10. Use of a super-surface prepared by a fork grating multiplexing method according to claim 9 in quantum communication.
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