Gap-type metasurfaces based on electric dipole resonance and geometric phase modulation and their fabrication methods

Abstract

This invention discloses a gap-type metasurface structure based on electric dipole resonance and geometric phase modulation. The structure consists of a bottom cuboid silver layer as a reflective layer, a middle cuboid silicon dioxide layer as a dielectric layer, and multiple sets of transmitting antennas at the top. Each set of transmitting antennas occupies a lattice and is arranged in a two-dimensional array. Within the lattice, two cuboids and a semi-cylindrical silver element are perpendicularly joined to form an "L" shape. The incident light source has a wavelength in the 2.7–4.3 μm band and is circularly polarized. The output light is chromatic aberration-free vortex light, and its polarization state is orthogonal to the circular polarization state of the incident light. The generation of vortex light requires the introduction of a helical phase distribution into the phase plane of the light. Based on the electric dipole resonance principle, the transmitting antenna, combined with the dielectric and reflective layers, can achieve a wideband, high-reflectivity half-wave conversion function for the incident light. Based on the geometric phase principle, rotating the transmitting antennas at different lattice positions by different angles can add a helical phase to the reflected light, transforming it into vortex light.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of micro-nano optics, and relates to a super-structured surface structure design, in particular to a gap-type super-structured surface based on electric dipole resonance and geometric phase modulation and a manufacturing method. BACKGROUND

[0002] Traditional optical devices (such as wave plates, optical modulators, etc.) modulate the parameters of light through the phase accumulation of light in the process of propagation (refraction, reflection) in the device. These devices have been used for a long time, but due to their volume, precision and other factors, they are not suitable for the increasingly stringent integration and miniaturization requirements of integrated optical systems. Super-structured surfaces are two-dimensional metamaterials composed of planar units with a structure size larger than an atom. They fully utilize the phase jump of super-atoms at the interface, so their thickness can be smaller than the working wavelength. At the same time, the planar structure of super-structured surfaces is easier to manufacture on a large scale. This unique property makes super-structured surfaces ideal photonic devices for planarization and miniaturization. Vortex beams have a spiral phase distribution and a ring-shaped hollow intensity distribution. Their photon carries orbital angular momentum (OAM) which can be much larger than the spin angular momentum (SAM) of the photon. Various emerging applications have appeared in the fields of optical manipulation, microscopic imaging, quantum information processing and optical communication.

[0003] At present, the use of super-structured surface in the field of integrated optics to produce vortex beams has been studied a lot, such as Wang et al. designed and manufactured a V-shaped reflective metal super-structured surface, which can produce vortex beams with topological charge of ±1 at a wavelength of 2 μm. Zhao et al. designed a wideband vortex beam emitter with a working wavelength of 1.0-2.5 μm. Huang et al. designed and manufactured a metal nanorod super-structured surface, which can produce vortex beams with topological charge of ±1 working in the visible-near infrared band of 670-1080 nm. Karimi et al. of the University of Ottawa designed an L-shaped metal super-structured surface, which can produce vortex beams with topological charge of ±2 at 780 nm. Zhao et al. designed a wideband vortex beam emitter with a working wavelength of 1.0-2.5 μm. Cao et al. designed and manufactured a T-shaped metal super-structured surface working near the C-band of 1.4-1.6 μm, which can produce vortex beams with topological charge of ±1. Many of the above studies use metal plasmonic super-structured surfaces to achieve the wideband characteristics of vortex beams, but due to ohmic loss, the beam transmittance is low, resulting in low overall system efficiency. In order to improve the efficiency of super-structured surface to produce vortex beams, many research groups at home and abroad have carried out a series of researches in the field of metal reflective super-structured surface and all-dielectric super-structured surface, and have achieved fruitful results. Yang et al. of the University of Vanderbilt designed and manufactured a reflective square brick-shaped silicon column on an ultrathin silver film, and Shalaev et al. designed a transmissive square silicon block, both of which can produce vortex beams with topological charge of ±1, and the system efficiency is greatly improved. Liu et al. of Nankai University designed a reflective super-structured surface that can produce array vortex beams. This device can not only be used as a vortex beam generator, but also as a vortex beam detector. The Luo group of the Chinese Academy of Sciences designed and manufactured an integrated super-structured surface that can simultaneously realize vortex beam generation and detection. This device can realize the dual functions of vortex beam generation and detection. Yue et al. of the University of Heriot-Watt designed a reflective metal super-structured surface that can simultaneously produce vector vortex beams and scalar vortex beams, which can produce scalar vortex beams with topological charge of ±2 and vector vortex beams with topological charge of ±1.

[0004] In order to better apply to the field of integrated optics, super-structured surface vortex beam generation develops towards wideband. The above research groups have developed super-structured surfaces that can produce vortex beams. Although some super-structured surfaces can achieve the wideband characteristics of vortex beams, there are few studies on achromatic characteristics. Although some super-structured surfaces can produce achromatic vortex beams, they use metal transmissive design, which results in low efficiency. SUMMARY

[0005] In order to increase the performance of the super-structured surface in generating broadband, achromatic vortex light, and improve the efficiency of the super-structured surface, the application provides a gap type reflective super-structured surface based on electric dipole resonance and geometric phase modulation.

[0006] The technical solution of the application is that the application provides a gap type super-structured surface based on electric dipole resonance and geometric phase modulation, which comprises a bottom reflection layer, an intermediate medium layer and a top emission layer. The bottom reflection layer is a cuboid, and silver (Ag) is used as the structural material; the intermediate medium layer is a cuboid, and silicon dioxide (SiO2) is used as the structural material; the top emission layer uses silver (Ag) as the structural material, and comprises a plurality of groups of antennas, each group of antennas is an "L" type structure, and is composed of two cuboids and two semi-cylinders, the included angle between the two cuboids is 90°, the end surface of each cuboid is completely attached to the end surface of one of the semi-cylinders, and each group of emission antennas occupies one lattice, the lattice size is sub-wavelength, and the lattices are distributed in a two-dimensional array. The upper surface of the bottom reflection layer is attached to the lower surface of the intermediate layer, and the upper surface of the intermediate medium layer is attached to the lower surface of the top emission antenna.

[0007] The lattice size occupied by the emission antenna is sub-wavelength, the lattice is a cuboid with a length of 1400nm, a width of 1400nm and a height of 120nm, and the lattices are distributed in a two-dimensional array, that is, the center distance between adjacent lattices is 1400nm.

[0008] The super-structured surface works in a 2.7-4.3μm wave band, and the working mode is reflective, and the polarization state of the incident light is circular polarization.

[0009] The height of the intermediate medium layer is 460nm, the length is 1400nm, and the width is 1400nm.

[0010] The height of the top emission antenna is 120nm, the length of the cuboid constituting the antenna is 700nm, and the width is 200nm. The radius of the semi-cylinder constituting the antenna is 100nm.

[0011] The position of the connecting point e of the two groups of cuboids is 420nm away from the bottom edge of the occupied lattice and 420nm away from the left edge of the occupied lattice.

[0012] The distance from the center of each lattice to the center of the super-structured surface is x is the horizontal coordinate value of the lattice center on the super-structured surface, y is the vertical coordinate value of the lattice center on the super-structured surface, the arctangent angle arctan(y / x) is calculated, and the arctangent angle is normalized to the range of 0-2π. Each group of emission antennas rotates around the center of the lattice it occupies by one half of the arctangent angle.

[0013] A preparation method of a gap-type super-structure surface based on electric dipole resonance and geometric phase modulation, comprising the following steps:

[0014] S1: deposit silver (Ag) on a silicon substrate by an electron gun evaporator to form a silver mirror with a thickness of 120 nm;

[0015] S2: deposit a layer of silicon dioxide on the surface of the silver mirror using plasmonic enhanced chemical vapor deposition (PECVD) as a dielectric material intermediate layer with a thickness of 460 nm;

[0016] S3: spin-coat a 100 nm thick electron beam resist (ZEP520A) on the surface of the silicon dioxide layer at a speed of 5000 rpm and bake at 180 degrees Celsius for 2 minutes, then spin-coat a highly conductive organic polymer Espacer layer on the resist layer at a speed of 1500 rpm to form a dielectric layer;

[0017] S4: expose and etch the surface of the intermediate dielectric layer in S3 by an electron beam direct writing system to form a plurality of groove structures after electron beam exposure and etching;

[0018] S5: deposit a layer of silver atoms on the groove structure of S4 by metal evaporation, with a thickness of 120 nm;

[0019] S6: peel off the excess silver, resist, and polymer light to obtain the final super-structure surface structure. Further, the acceleration voltage of the electron beam direct writing system is 100 kiloelectron volts (keV) and the current is 100 picoamperes (pA)

[0020] A use method of a gap-type super-structure surface based on electric dipole resonance and geometric phase modulation, comprising the following steps:

[0021] S1: the super-structure surface generates topological charge number ±2 vortex light. The top emitting antenna, the intermediate dielectric layer, and the bottom reflecting layer can be used as anisotropic units, and their Jones matrix is described as:

[0022] R(θ) is a rotation matrix, θ is the rotation angle of the emitting antenna, r x and r y correspond to the reflection coefficients of two orthogonal linearly polarized light when they are normally incident on the lattice, is the phase difference between them; when circularly polarized light is normally incident on the lattice, the reflected light is represented as:

[0023] wherein represents left-handed circularly polarized light, represents right-handed circularly polarized light, and ±2 is the topological charge number of the vortex light.

[0024] When r x = r y = 1, That is, the reflected light becomes vortex light with a topological charge of ±2, and the polarization state is orthogonal to that of the incident light.

[0025] S2: The incident light vertically irradiates the transmitting antenna, and the relationship between the incident electric field and the excitation electric field is derived. The metal transmitting antenna adjusts the phase of the reflected light beam by electric dipole resonance, and the induced charge does simple harmonic vibration under the excitation of external electromagnetic waves:

[0026]

[0027] where l is the arm length of the metal transmitting antenna, E ext_x and E ext_y are two components of the external excitation electric field in the x and y directions, Q x and Q y are the charge amounts of the electric dipoles formed by the antenna in the x and y directions. When the electromagnetic wave is incident on the antenna surface, reflection and refraction phenomena occur, and the incident electric field and the reflected electric field from the bottom reflection layer together act as the excitation field to excite the electric dipole oscillation of the metal antenna on the superstructure surface, generating a surface current distribution. Therefore, the incident electric field is no longer equal to the excitation electric field. The incident electric field irradiates the transmitting antenna interface from the air medium, and the reflected electric field and the transmitted electric field are distributed, where E inc+ , E ref+ , E trans+ and E ext+ represent the incident electric field, the reflected electric field, the transmitted electric field, and the excitation electric field at the antenna surface (z = 0), respectively:

[0028]

[0029] S3: After the transmitting antenna is added with a dielectric layer and a reflection layer, the relationship between the reflected electric field and the incident electric field is derived. When the incident electric field enters the SiO2 dielectric layer, it is reflected by the bottom reflection layer, and the electric field distribution is irradiated again when it irradiates the interface from the dielectric layer. Where E inc- , E ref- , E trans- and E ext- represent the incident electric field, the reflected electric field, the transmitted electric field in the SiO2 dielectric layer, and the excitation electric field at the antenna surface (z = 0), respectively. According to Maxwell's equations and the boundary conditions, the relationships between the reflected electric field, the transmitted electric field, and the excitation electric field in the dielectric layer and the incident electric field can be calculated:

[0030]

[0031] ​The interface of the super-structured surface emission layer is at z=0, and the bottom reflection layer is at z=-d. The corresponding superposition of the electric field components at the two interfaces is obtained by applying the surface boundary conditions, and the corresponding relationship between the incident electric field and the reflected electric field is obtained. Figure 4 and 5 It can be seen from the above that E inc+ represents the incident electric field, E inc- represents the electric field reflected back from the bottom reflection layer. Since the current on the antenna arm is excited by E ext+ and E ext- , the radiation electric field E rad =σ(E ext+ +E ext- ) can be obtained, and the relationship between the radiation electric field and the incident electric field can be obtained: At the interface z=0, the reflected electric field is equal to the superposition of all the electric fields located on the left side of the emission antenna excited by the incident electric field: E ref =E rad+ +E ref+ +E trans- , that is At the interface z=-d, since the incident wave band is at the interface between the near-infrared and the mid-infrared, the bottom reflection layer can be regarded as a perfect electric conductor, and the corresponding surface boundary condition is nxE=0, so the electric fields on both sides of the interface are:

[0032] E tran+ e inkd +E inc- e -inkd +E ref- e inkd +E rad e inkd =0, that is

[0033] E inc- =-2{[(n+1)e -i2nkd +n-1]I+2nσ} -1 (I+σ)E inc .

[0034] Finally, the relationship between the incident electric field and the reflected electric field is obtained: E ref =RE inc . Wherein, where the parameters σ and n are known, and only d and ω are unknown, that is, the thickness of SiO2 and the incident frequency.

[0035] S4: The super-structured surface generates wide-band and achromatic vortex light. After optimization scanning calculation, when the thickness of the intermediate medium layer SiO2 is adjusted to 460 nm, the incident wavelength is in the 2.7-4.3 μm wave band, r x =r y >0.95 and The transmitting antenna and the medium layer and the reflecting layer can realize the half-wave conversion function of wide frequency and achromatic. Meanwhile, the transmitting antenna occupies the crystal lattice which is arranged in two-dimensional array to form the superstructure surface, and each group of transmitting antenna rotates around the center of the crystal lattice by an angle which is half of the inverse tangent angle of the normalized 0~2pi of the occupied crystal lattice. The rotation angle of the transmitting antenna introduces the spiral phase to the reflected light, and the reflected light is: or 2theta is the geometric phase introduced by the change of the polarization state of the light beam, which is twice the rotation angle, and plus or minus 2 is also called the topological charge number of the vortex beam. Therefore, the designed superstructure surface can realize the function of generating the wide frequency and achromatic vortex beam with the topological charge number of plus or minus 2.

[0036] Compared with the prior art, the advantages of the present application are:

[0037] The present application provides a gap type reflective superstructure surface working in the 2.7~4.3 mu m wave band, which comprises a bottom reflecting layer with silver (Ag) as the structure material, a middle medium layer with silicon dioxide (SiO2) as the structure material and a top transmitting layer with silver (Ag) as the structure material; the bottom reflecting layer and the middle medium layer are in the shape of a cuboid, and the top transmitting layer comprises a plurality of groups of antennas, each group of antennas is in the shape of “L” and is composed of two cuboids and two semi-cylinders, the included angle between the two cuboids is 90 degrees, and the end surface of each cuboid is completely attached to the end surface of one of the semi-cylinders; the upper surface of the middle medium layer is attached to the lower surface of the top transmitting antenna, and the lower surface of the middle medium layer is attached to the upper surface of the bottom reflecting layer; the crystal lattice occupied by the transmitting antenna is sub-wavelength, and the crystal lattice is arranged in two-dimensional array distribution, and the transmitting antennas at different array positions only need to be rotated by a corresponding angle to make the reflected light introduce the spiral phase to become vortex light. The present application is used for generating the wide frequency and achromatic vortex light in the 2.7~4.3 mu m wave band, the transmitting antennas based on the geometric phase principle are high and have equal spacing, and only by changing the rotation angle of the transmitting antennas, the topological charge number of the vortex light can be controlled, the processing difficulty in the micro-nano manufacturing process is reduced, and the manufacturing cost is reduced. The “L” type antenna designed based on the electric dipole resonance principle increases the accuracy of phase control, and enhances the performance of the superstructure surface in generating the wide frequency and achromatic vortex beam. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 is the structure diagram of the reflective gap type superstructure surface provided by the present application. (According to the actual size of the 13x13 array in the figure)

[0039] Figure 2 is the top view of the superstructure surface crystal lattice structure provided by the present application.

[0040] Figure 3 is the top view of the superstructure surface crystal lattice array structure provided by the present application.

[0041] Figure 4 is a bottom reflection layer electric field distribution diagram of the super-structured surface lattice provided by the present application.

[0042] Figure 5 is a bottom reflection layer electric field distribution diagram of the super-structured surface lattice provided by the present application. DETAILED DESCRIPTION

[0043] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and do not constitute a limitation on the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0044] As shown in Figures 1-5 a gap-type super-structured surface based on electric dipole resonance and geometric phase modulation, the super-structured surface includes a bottom reflection layer, an intermediate medium layer and a top emission layer. The bottom reflection layer is a cuboid, and silver (Ag) is used as the structural material; the intermediate medium layer is a cuboid, and silicon dioxide (SiO2) is used as the structural material; the top emission layer uses silver (Ag) as the structural material, and the top emission layer includes a plurality of groups of antennas, each group of antennas is an "L" type structure, which is composed of two cuboids and two semi-cylinders, the included angle between the two cuboids is 90°, and the end face of each cuboid is completely attached to the end face of one of the semi-cylinders, and each group of emission antennas occupies a lattice, the lattice size is sub-wavelength, and the lattices are distributed in a two-dimensional array. The upper surface of the bottom reflection layer is attached to the lower surface of the intermediate layer, and the upper surface of the intermediate medium layer is attached to the lower surface of the top emission antenna.

[0045] The lattice size occupied by the emission antenna is sub-wavelength, the lattice is a cuboid with a length of 1400 nm, a width of 1400 nm and a height of 120 nm, and the lattices are distributed in a two-dimensional array, i.e. the center distance between adjacent lattices is 1400 nm.

[0046] The super-structured surface works in the 2.7-4.3 μm wave band, and the working mode is reflective, and the polarization state of the incident light is circular polarization.

[0047] The height of the intermediate medium layer is 460 nm, the length is 1400 nm, and the width is 1400 nm.

[0048] The height of the top emission antenna is 120 nm, the length of the cuboid constituting the antenna is 700 nm, and the width is 200 nm. The radius of the semi-cylinder constituting the antenna is 100 nm.

[0049] The positions of the two groups of cuboid connection points e constituting the antenna are 420 nm away from the bottom edge of the occupied lattice and 420 nm away from the left edge of the occupied lattice.

[0050] The distance from each lattice center to the center of the metasurface is x is the horizontal coordinate value of the lattice center on the metasurface, y is the vertical coordinate value of the lattice center on the metasurface, the arctangent angle arctan(y / x) is calculated, and the arctangent angle is normalized to the range of 0-2π. The rotation angle of each group of transmitting antennas around the center of the occupied lattice is half of the arctangent angle.

[0051] In the manufacture of the metasurface, first, silver (Ag) is deposited on a silicon substrate by an electron gun evaporator to form a silver mirror with a thickness of 120 nm; in the second step, a layer of silicon dioxide is deposited on the substrate using plasmonic-enhanced chemical vapor deposition (PECVD) to serve as a dielectric material spacing layer with a thickness of 460 nm; in the third step, 100 nm thick photoresist (ZEP520A) is spin-coated on the silicon dioxide layer at a speed of 5000 rpm and baked at 180 degrees Celsius for 2 minutes. Next, a layer of highly conductive organic polymer Espacer is spin-coated on the photoresist at a speed of 1500 rpm, and Espacer is a kind of organic polymer with high conductivity that can reduce positional errors caused during electron beam exposure; in the fourth step, the acceleration voltage of the electron beam direct writing system is 100 kiloelectron volts (keV) and the current is 100 picoamperes (pA). After electron beam exposure and etching, the final designed structure distribution is formed; in the fifth step, a layer of silver atoms is re-deposited by metal evaporation with a thickness of 120 nm; in the sixth step, the excess metal, photoresist, and organic polymer are peeled off, and the final required metasurface structure is obtained.

[0052] A method for using a gap-type metasurface based on electric dipole resonance and geometric phase modulation, comprising the following steps:

[0053] The transmitting antenna, the dielectric layer, and the reflective layer are taken as anisotropic units, and the Jones matrix thereof can be described as: R(θ) is a rotation matrix, θ is the rotation angle of the transmitting antenna, r x and r y respectively correspond to the reflection coefficients of two orthogonal linearly polarized lights when they are normally incident on the lattice, is the phase difference therebetween; when circularly polarized light is normally incident on the lattice, the reflected light can be represented as: wherein represents left-handed circularly polarized light, represents right-handed circularly polarized light, The transmitting antenna adjusts the phase of the reflected light beam through electric dipole resonance, and the induced charge does simple harmonic vibration under the excitation of external electromagnetic waves:

[0054]

[0055] where l is the top metal antenna arm length, E ext_x and E ext_y are the two components of the external excitation electric field in x and y directions, Q x and Q y are the charge quantities of the electric dipoles formed by the antenna in x and y directions. When the electromagnetic wave is incident on the surface of the antenna, reflection and refraction phenomena will occur. The incident electric field and the reflected electric field from the bottom reflection layer together act as the excitation field, which excites the electric dipole oscillation on the super-structured surface excitation metal antenna, and generates a surface current distribution. Therefore, the incident electric field is no longer equal to the excitation electric field. Figure 4 The figure shows the electric field distribution when the incident electric field is irradiated from the air medium to the interface of the super-structured surface unit. E inc+ , E ref+ , E trans+ and E ext+ represent the incident electric field, the reflected electric field, the transmitted electric field and the excitation electric field at the antenna surface (z = 0), respectively.

[0056]

[0057] Figure 5 The figure shows the electric field distribution when the incident electric field enters the SiO2 medium layer and is reflected by the bottom reflection layer of the super-structured unit, and then irradiates the interface again from the medium layer. E inc- , E ref- , E trans- and E ext- represent the incident electric field, the reflected electric field, the transmitted electric field and the excitation electric field at the antenna surface (z = 0) in the SiO2 medium layer, respectively. According to Maxwell's equations and the boundary conditions, the relationships between the reflected electric field, the transmitted electric field and the excitation electric field and the incident electric field in the medium layer can also be calculated:

[0058]

[0059] The super-structured surface emission layer interface is at z = 0, and the bottom reflection layer is at z = -d. The electric field components at the two interfaces can be superimposed, and the surface boundary conditions can be applied to obtain the corresponding relationship between the incident electric field and the reflected electric field. From Figure 4 and 5 , it can be seen that E inc+ represents the incident electric field, and E inc- represents the electric field reflected from the bottom reflection layer. Since the current on the antenna arm is excited by E ext+ and E ext- , the radiation electric field Erad = σ (E ext+ + E ext- ), the relationship between the radiated electric field and the incident electric field can be obtained: At the z = 0 interface, the reflected electric field is equal to the superposition of all the electric fields located on the left side of the transmitting antenna excited by the incident electric field:

[0060] E ref = E rad+ + E ref+ + E trans- , i.e. At the z = -d interface, since the incident wavelength is at the junction of the near-infrared and the mid-infrared, the bottom reflective layer can be regarded as a perfect electric conductor, and its corresponding surface boundary condition is n x E = 0, so the electric fields on both sides of the interface are: tran+ e inkd + E inc- e -inkd + E ref- e inkd + E rad e inkd = 0, i.e.

[0061] E inc- = -2{[(n + 1) e -i2nkd + n - 1] I + 2nσ} -1 (I + σ) E inc .

[0062] Finally, the relationship between the incident electric field and the reflected electric field can be obtained: E ref = RE inc . Wherein, where σ, n parameters are known, only d and ω are unknown, i.e. the thickness of SiO2 and the incident frequency. After optimization scanning calculation, when the thickness of the superstructure unit SiO2 is adjusted to 460 nm, the incident wavelength is in the wavelength band of 2.7-4.3 μm, r x = r y > 0.95 and That is, the transmitting antenna and the medium layer and the reflective layer can realize the function of wide-band, achromatic half-wave conversion. At the same time, the transmitting antenna occupies the lattice is arranged in two-dimensional array to form a superstructure surface, and each group of transmitting antenna rotates around the center of its lattice by an angle which is half of the inverse tangent angle of the normalized 0-2π of its occupied lattice. The rotation angle of the transmitting antenna introduces a spiral phase to the reflected light, and at this time the reflected light is: or 2theta is the geometric phase introduced by the change of the polarization state of the light beam, which is 2 times of the rotation angle, and ±2 is also called the topological charge number of the vortex beam. Therefore, the designed superstructure surface can realize the function of generating a wide-frequency and achromatic vortex beam with a topological charge number of ±2. On this basis, an electron beam etching method is used to prepare a high-quality superstructure surface device.

[0063] The technical indicators and basic performance parameters are as follows:

[0064] The developed superstructure surface has a length of 140 mu m, a width of 140 mu m, a height of 700 nm, a working wave band of 2.7-4.3 mu m, a circular polarization of the incident light beam, and a topological charge of the vortex beam of ±2. The reflectivity of the superstructure surface is greater than 85%, and the efficiency of generating the vortex light is higher than 78%;

[0065] The use temperature range is-30-60 DEG C.

[0066] The above only describes the preferred embodiments of the present application, and it should be noted that, for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application. The components not explicitly described in the embodiments can be realized by using the existing technology.

Claims

1. A gap-type meta-surface based on electric dipole resonance and geometric phase modulation, characterized in that, The super-structured surface comprises a bottom reflecting layer, an intermediate medium layer and a top transmitting layer; the bottom reflecting layer is a cuboid, silver is used as the structural material; the intermediate medium layer is a cuboid, silicon dioxide is used as the structural material; the top transmitting layer uses silver as the structural material, the top transmitting layer comprises a plurality of groups of antennas, each group of antennas is an "L" type structure, which is composed of two cuboids and two semi-cylinders, the included angle between the two cuboids is 90°, the end surface of each cuboid is completely attached to the end surface of one of the semi-cylinders, each group of transmitting antennas occupies a lattice, and the lattices are distributed in a two-dimensional array; the upper surface of the bottom reflecting layer is attached to the lower surface of the intermediate layer, and the upper surface of the intermediate medium layer is attached to the lower surface of the top transmitting antenna. The distance from each lattice center to the center of the metasurface is x is the horizontal coordinate value of the lattice center on the metasurface, and y is the vertical coordinate value of the lattice center on the metasurface. The arctangent angle arctan(y / x) is calculated, and the arctangent angle is normalized to the range of 0-2π; the rotation angle of each group of transmitting antennas around the lattice center occupied by the group is half of the arctangent angle.

2. The metasurface of claim 1, wherein, The lattice size occupied by the transmitting antenna is sub-wavelength, the lattice is a cuboid with a length of 1400 nm, a width of 1400 nm and a height of 120 nm, and the lattices are distributed in a two-dimensional array, that is, the center distance between adjacent lattices is 1400 nm.

3. The metasurface of claim 1, wherein, The super-structured surface works in the 2.7-4.3 μm wave band, the working mode is reflective, and the polarization state of the incident light is circular polarization.

4. The metasurface of claim 1, wherein, The height of the intermediate medium layer is 460 nm, the length is 1400 nm, and the width is 1400 nm.

5. The metasurface of claim 1, wherein, The length of the cuboid constituting the antenna is 700 nm, the width is 200 nm, and the height is 120 nm; the radius of the semi-cylinder constituting the antenna is 100 nm, and the height is 120 nm; the position of the connecting point e of the two groups of cuboids is 420 nm away from the bottom edge of the occupied lattice and 420 nm away from the left edge of the occupied lattice.

6. A method of manufacturing a superstructured surface as claimed in any one of claims 1-5, characterized in that, The method comprises the following steps: S1: a silver mirror with a thickness of 120 nm is formed on a silicon substrate by an electron gun evaporator; S2: a layer of silicon dioxide is deposited on the surface of the silver mirror by using plasmonic enhanced chemical vapor deposition, serving as a dielectric material intermediate medium layer, with a thickness of 460 nm; S3: 100 nm thick electron beam photoresist is spin-coated on the surface of the silicon dioxide layer at a speed of 5000 rpm, and baked at 180 degrees Celsius for 2 minutes, then a high-conductivity organic polymer Espacer layer is spin-coated on the photoresist layer at a speed of 1500 rpm, forming a medium layer; S4: the surface of the intermediate medium layer in S3 is exposed and etched by an electron beam direct writing system, and a plurality of groove structures are formed after electron beam exposure and etching; S5: a layer of silver atoms is deposited on the groove structure of S4 by metal evaporation, with a thickness of 120 nm; S6: the excess silver, photoresist and polymer are stripped to obtain the final super-structured surface structure.

7. The production method according to claim 6, wherein The acceleration voltage of the electron beam direct writing system is 100 kiloelectron volts and the current is 100 picoamperes.

8. A method of using the super-structured surface based on the electric dipole resonance and the geometric phase co-modulation according to any one of claims 1-5, comprising the following steps: S1: the super-structured surface generates topological charge number ±2 vortex light, the top transmitting antenna, the intermediate medium layer and the bottom reflecting layer can be used as anisotropic units, and the Jones matrix is described as: R(0) is the rotation matrix, 0 is the rotation angle of the transmitting antenna, r x and r y correspond to the reflection coefficients of the two orthogonal linearly polarized lights when they are normally incident on the lattice, respectively, is the phase difference between them; when circularly polarized light is normally incident on the lattice, the reflected light is represented as: wherein represents left-handed circularly polarized light, represents right-handed circularly polarized light, and ±2 is the topological charge number of the vortex light, when r x = r y = 1, , i.e., the reflected light becomes vortex light with a topological charge number of ±2, and the polarization state is orthogonal to that of the incident light; S2: incident light vertical irradiation launch antenna, derive incident electric field and excitation electric field relationship, metal launch antenna through electric dipole resonance mode to adjust the phase of reflected light beam, induced charge under the excitation of external electromagnetic wave does simple harmonic vibration: where l is the metal emission antenna arm length, E ext_x and E ext_y are two components of the external excitation electric field in the x and y directions, Q x and Q y are the charge quantities of the electric dipoles formed by the antenna in the x and y directions, and the electromagnetic wave is incident on the surface of the antenna, which will produce reflection and refraction phenomena. The incident electric field and the reflected electric field from the bottom reflection layer together act as the excitation field, which acts on the electric dipole oscillation of the super-structured surface excited metal antenna to produce a surface current distribution. Therefore, the incident electric field is no longer equal to the excitation electric field. The incident electric field is irradiated from the air medium to the emission antenna interface, and the reflected electric field and the transmitted electric field are distributed, where E inc+ , E ref+ , E trans+ and E ext+ represent the incident electric field, the reflected electric field, the transmitted electric field and the excitation electric field at the antenna surface (z = 0), respectively. S3: After the transmitting antenna is added with the medium layer and the reflecting layer, the relationship between the reflected electric field and the incident electric field is derived. When the incident electric field enters the SiO2 medium layer, it is reflected by the bottom reflecting layer, and the electric field distribution is irradiated to the interface again from the medium layer. Wherein E inc- , ref- , trans- , ext- E and E represent the incident electric field, the reflected electric field, the transmitted electric field in the SiO2 medium layer and the excited electric field at the antenna surface (z=0) respectively. According to Maxwell equations and boundary conditions, the relationship between the reflected electric field, the transmitted electric field and the excited electric field in the medium layer and the incident electric field can be calculated respectively. The interface of the metasurface emission layer is at z = 0, and the bottom reflection layer is at z = -d. The corresponding superposition of the electric field components at the two interfaces is obtained by applying the surface boundary conditions, and the corresponding relationship between the incident electric field and the reflected electric field is obtained, E inc+ represents the incident electric field, E inc- represents the electric field reflected back from the bottom reflection layer. Since the current on the antenna arm is excited by E ext+ and E ext- , the radiation electric field can be obtained: E rad = σ (E ext+ +E ext- ), and the relationship between the radiation electric field and the incident electric field can be obtained: At the interface z = 0, the reflected electric field is equal to the superposition of all the electric fields located on the left side of the emission antenna excited by the incident electric field: E ref = E rad+ +E ref+ +E trans- , that is At the interface z = -d, since the incident wave band is at the interface of near-infrared and mid-infrared, the bottom reflection layer can be regarded as a perfect electric conductor, and the corresponding surface boundary condition is n x E = 0. Therefore, the electric fields on both sides of the interface are: E tran+ e inkd +E inc- e -inkd +E ref- e inkd +E rad e inkd = 0, i.e. E inc- = -2{[(n + 1)e -i2nkd + 2nσ} -1 (I + σ)E inc ; The relationship between the incident electric field and the reflected electric field is finally obtained: E ref = RE inc wherein, where the parameters σ, n are known and only d and ω are unknown, i.e. the thickness of SiO2 and the incident frequency, S4: The super-structured surface generates wideband and achromatic vortex light. After optimization and scanning calculation, when the thickness of the intermediate medium layer SiO2 is 460 nm, the incident wavelength is in the 2.7-4.3 μm band, and r x = r y > 0.95 and That is, the transmitting antenna and the medium layer and the reflecting layer can realize the wideband and achromatic half-wave conversion function, and at the same time, the transmitting antenna occupies the two-dimensional array of the crystal lattice to form a super-structured surface, each group of transmitting antennas rotates around the crystal lattice center by half of the inverse tangent angle of the normalized 0-2π of the occupied crystal lattice, and the rotation angle of the transmitting antenna introduces a spiral phase to the reflected light, and at this time, the reflected light is: or 2θ is the geometric phase introduced by the change of the polarization state of the light beam, which is twice the rotation angle, and ±2 is also called the topological charge number of the vortex beam, so the designed super-structured surface can realize the function of generating a wideband and achromatic vortex beam with a topological charge number of ±2.

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