CN105629364B - Wavelength selective super-surface device - Google Patents

Abstract

The invention discloses a wavelength-selective metasurface device, belonging to the technical field of metamaterials, comprising substrates arranged sequentially from bottom to top and a metasurface composed of anisotropic nano unit structure arrays. The metasurface includes a plurality of electromagnetic regions. The nanostructures in the same electromagnetic region have the same shape and size, and the nanostructures in different electromagnetic regions have different shapes or the same shape and different sizes. The nanostructure array in each electromagnetic region only generates electromagnetic waves of specific wavelengths. Preset electromagnetic response, enabling wavelength selection. The invention can make incident light of different wavelengths generate OAM (orbital angular momentum) of different topological charges, and the ultra-thin multi-wavelength optical device designed on the basis of the invention has wide application in future wireless communication systems.

Description

A Wavelength Selective Metasurface Device

technical field

The invention relates to the field of metamaterial research, in particular to a wavelength-selective metasurface device.

Background technique

With the development of communication technology, due to the limitations of conventional coding and channel technology, the capacity and spectral efficiency of traditional optical fiber systems are approaching the limit, which cannot meet the needs of transmitting large amounts of information. Not only that, but the security of the transmitted data is also facing challenges Serious challenges. In order to solve this problem, to further improve system capacity and spectrum efficiency, and to meet the increasing demand for data transmission in future mobile data services, it is necessary to explore revolutionary and innovative technologies. In recent years, the research on Orbital Angular Momentum (OAM) technology has attracted much attention. Due to its good orthogonality and the security of carrying information, it can transmit multiple electromagnetic vortex waves on the same carrier frequency. By encoding information and multiplexing Use technology to improve the capacity and security of transmitted information, for example, OAM can be used for data transmission in terabit free space, and can perform terabit-scale multiplexing in optical fibers and information transmission in free space. Therefore, the application of OAM in wireless communication has set off a worldwide research boom.

In order to make OAM play a greater role in communication systems, devices that quickly switch OAM modes have emerged. Typical devices for switching and regulating OAM beams include helical light modulation, Q-plates, computer holograms and ring gratings, but the above devices It is inconvenient to quickly adjust the OAM mode due to its large size. Therefore, it is necessary to develop miniaturized optical devices for generating and converting OAM beams in future optical communications. Recently, as a new planar optical device, the two-dimensional material metasurface has been proved to be able to adjust the phase distribution by changing the shape and azimuth angle of its structural units. Various metasurfaces formed by arrays of unit structures The surface can generate OAM beams under the incidence of linearly polarized and circularly polarized light, but cannot be converted under the irradiation of incident electromagnetic waves of different wavelengths. Therefore, how to use an optical device to generate different OAM beams and how to effectively separate and detect a large number of OAM beams is a huge challenge for today's technology.

Contents of the invention

The technical problem to be solved by the present invention is to provide a wavelength-selective metasurface device for the deficiencies in the prior art, the metasurface includes a plurality of electromagnetic regions, and each electromagnetic region only generates a predictive effect on the electromagnetic waves incident on the region. The electromagnetic response of the design, thus realizing the selectivity to the wavelength.

The technical solution adopted by the present invention to solve the technical problem is: a wavelength-selective metasurface device, which includes substrates arranged in sequence from bottom to top and a metasurface composed of an anisotropic nano-unit structure array, and the metasurface includes For multiple electromagnetic regions, the nanostructures in the same electromagnetic region have the same shape and size, and the nanostructures in different electromagnetic regions have different shapes or the same shape and different sizes, that is, the nanohole structure array in each electromagnetic region only produces predictions for the electromagnetic waves incident on the region. The electromagnetic response of the design, the anisotropic nanostructure is etched on the ultra-thin metal or dielectric, and can also be directly fabricated on the substrate, its characteristic size is smaller than the wavelength, and the arrangement spacing is smaller than half the wavelength; the ultra-thin The value range of the thickness Tg of thin metal is: δ<Tg<λ/15 (λ is the wavelength of incident light, δ is the skin depth of the metal, μ ₀ =4π×10 ^-7 H/m, ω is the circular frequency, and σ ₀ is the electrical conductivity of the metal); the thickness of the ultra-thin medium is smaller than the wavelength of the incident light.

Wherein, the hypersurface is a plane or a curved surface.

Wherein, the anisotropic nanostructures include: holes or their complementary structures.

Wherein, the anisotropic nanostructure pattern includes: rectangle, ellipse, cross, I-shape or polygon.

Wherein, the metal includes: gold, silver, copper, gold alloy, silver alloy or copper alloy.

Wherein, the medium includes: silicon, silicon dioxide and other semiconductors, and fluoride and other transparent materials in the working band.

Wherein, the base material is a semiconductor such as silicon and silicon dioxide, and a material that is transparent in a working wavelength band such as fluoride.

Wherein, if the nanopore unit structure is fabricated on a medium, the material of the medium and the material of the base can be the same or different.

Wherein, the substrate thickness 0<Ts<λ, λ is the wavelength of incident light.

Wherein, the base surface is a plane or a curved surface.

Wherein, the thickness T of the wavelength-selective metasurface device may be smaller than the wavelength.

Wherein, the wavelength-selective metasurface device is applicable to visible light and near-infrared regions.

Compared with prior art, the beneficial effect of the present invention is:

The invention can selectively transmit light of different wavelengths to generate and focus different OAM light beams through ingenious design, and the invention is novel in design, small in size and light in weight, and has enlightening significance and wide application prospects in the field of wireless communication technology .

Description of drawings

Fig. 1 is a structural representation of the present invention;

Fig. 2 is the relationship figure of wavelength and transmission coefficient and nanopore structural unit size;

Fig. 3 is a design drawing of the present invention;

Fig. 4 is the electromagnetic distribution simulation result of the converted and focused OAM beam under different wavelengths;

Fig. 5 is the interference pattern of RCP light and the focused OAM beam under different wavelengths;

Fig. 6 is the scanning electron micrograph of sample of the present invention;

Fig. 7 is a sample testing device diagram of the present invention;

Fig. 8 is a graph showing test results of samples of the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the following examples, but should include all content in the claims. Moreover, those skilled in the art can realize all the content in the claims from the following embodiment.

Embodiment 1 of the present invention takes a preferred rectangular nanopore unit structure as an example. As shown in FIG. 1 , the wavelength-selective metasurface includes a substrate 1 and a metasurface 2 arranged in sequence from bottom to top. The metasurface is composed of two kinds of rectangular nanoholes 3 and 4 arranged in an array in a certain way on the gold film. The thickness of the substrate is Ts; the thickness of the gold film is Tg; the width of the rectangular nanohole 3 along the x-axis is w1, the length along the y-axis is L1, and the period is p1; the width of the rectangular nanohole 4 along the x-axis is w2, along the The length of the y-axis is L2 and the period is p2.

The specific method of making the wavelength-selective metasurface device and parameter optimization of the present invention is as follows:

(1) Determine and optimize the size parameters of the unit structure. Firstly, the resonance property of a single nanopore is discussed. When the left-handed circularly polarized light (LCP) is incident into the nanopore, it can be converted into right-handed circularly polarized light (RCP). As shown in Figure 2, the maximum transmission coefficient and resonance wavelength of the converted light increase with the increase of the length L of the rectangular nanohole, and the range of change is relatively large. But changing the width w, the transmission coefficient of the converted light does not change much and the resonance wavelength is blue-shifted. It can be seen that the different sizes of the unit structure have different resonant frequencies, and then the corresponding resonant wavelengths are different, as shown in FIG. 3 . Considering the change of the unit structure transmission in the wavelength range, it is convenient to design two kinds of nanopores with different sizes, and the optimized parameters are set as: incident LCPλ=930nm, w1=40nm, L1=200nm; incident LCPλ=766nm, w2= 80nm, L2=140nm.

(2) Design metasurface. In order to make the LCP light of different wavelengths incident to the metasurface device of the present invention to generate OAM beams and focused OAM beams, the phase distribution function is predefined on the metasurface (wherein, k is a wave vector, r is a radius in polar coordinates, f is a focal length, l is a topological charge value, and θ is a direction angle), the phase distribution function is generated by the helical phase Φ ₁ =lθ and Phase distribution of a focused OAM beam composition. The two nanopore structural units are arranged according to a predefined phase distribution, as shown in Fig. 1 .

(3) Use simulation software to simulate the metasurface. Setting Z=30 μm, the LCP lights of λ=930 nm and λ=766 nm are respectively incident on the regions of nanohole structure arrays 3 and 4 . As shown in Figure 4(a), when the LCP light of λ=930nm is incident, a focused OAM beam with a topological charge value l=1 is generated, and Figure 4(b) and 4(c) show the electric field distribution at x Axis, the component of the y-axis. As shown in Figure 4(d), when the LCP light of λ=766nm is incident on the metasurface, an OAM focused beam with a topological charge value of l=2 is generated, and Figure 4(e), 4(f) are its electric field Distributed on the x-axis, the component of the y-axis.

Further, linearly polarized (LP) light is incident on the metasurface, and the LP light is composed of LCP light that generates OAM beams and RCP light that generates interference. The transmitted RCP light interferes with the focused OAM beam, and the topological charge value of the OAM beam is determined by the number of vortex lobes in the resulting interference pattern. Please refer to Fig. 5(a) and 5(b), Fig. 5(a) is the interference pattern produced by LP light with a wavelength of 930 nm incident on the metasurface, the number of vortex lobes is one, that is, the topological charge value l of the OAM beam = 1. Fig. 5(b) is the interference pattern generated by the LP light with a wavelength of 766nm incident on the metasurface, and the number of vortex lobes is two, that is, the topological charge value l=2 of the OAM beam.

(4) Experimental verification. Prepare the metasurface sample of the present invention according to above-mentioned design principle, as shown in Figure 1, utilize the gold film of one deck thickness Tg=50nm to plate the gold film of thickness Tg=50nm on the clean and smooth quartz substrate, utilize focused ion beam lithography on gold A metasurface sample is prepared on the film, the width w1=40nm of the rectangular nanohole 1 along the x-axis, the length L1=200nm along the y-axis, and the period p1=400nm along the two axes; the width w2=80nm of the rectangular nanohole 2=80nm, and the length L2 =140nm, period p2=400nm. Figure 6 is the scanning electron microscope image of the sample. See Figure 7 for a sample test setup.

The sample test results are shown in Figures 8(a)-8(f). Figures 8(a) and 8(d) are the intensity distribution diagrams of the OAM focused beams with topological charge values l=1 and l=2 produced by the sample under the incidence of LCP light with wavelengths of 930nm and 766nm at a distance Z=32μm, respectively. . Figures 8(b) and 8(e) are the experimental results under the condition of Z=20 μm, it can be known that the present invention can be used to generate and focus OAM beams with different topological charge values. Figures 8c and 8f are the interference patterns of the focused OAM beam and the transmitted RCP light under the incident conditions of Z=23μm and two wavelengths of LP light. It can be seen that the topological charge value can be determined by the number of vortex lobes in the interference pattern.

It can be seen from this embodiment that the test results and the simulation results are very consistent, indicating that the present invention has the ability to optically switch the OAM mode under different incident light irradiations. The accuracy and reliability of the present invention designed by utilizing the above-mentioned principles are thus verified.

Through the above embodiments, the present invention can be better realized.

Claims (12)

1. a kind of super surface device of wavelength selective, it is characterised in that：Make different wave length by the structure of the super surface device Incident light generate and focus different topology lotus OAM (orbital angular momentum), structure includes the base successively arranged from bottom to top Bottom and the super surface being made of anisotropy nanocell structures array, the super surface include multiple electromagnetic spectrums, same electricity The nanostructure shape of magnetic area is identical with size, and the nanostructure shape difference or the identical size of shape of different electromagnetic spectrums are not Together, i.e., the nano-structure array of each electromagnetic spectrum only generates preset electromagnetic response to the electromagnetic wave for being incident to the region, In, the anisotropy nanostructure is etched on super thin metal or medium, can also be directly produced in substrate, special It levies size and is less than wavelength, arrangement spacing is less than half-wavelength；Wherein the value range of its thickness of super thin metal Tg is：δ<Tg <λ/15, λ are lambda1-wavelength, and δ is the skin depth of metal,μ₀=4 π × 10^-7H/m, ω are circular frequency, σ₀ For the conductivity of metal；The ultra-thin medium thickness is less than lambda1-wavelength；

The super surface is arranged in array according to certain way by two kinds of rectangle nano-pores in gold thin film and forms, wherein substrate With a thickness of Ts；Gold thin film with a thickness of Tg；First rectangle nano-pore (3) is w1 along the width of x-axis, and along a length of L1 of y-axis, the period is p1；Second rectangle nano-pore (4) is w2 along the width of x-axis, along a length of L2 of y-axis, period p2；

The specific method is as follows for the production of the super surface device of wavelength selective and parameter optimization：

(1) cellular construction dimensional parameters are determined and optimized, the resonant properties of single nano-pore are inquired into first, when left-handed circle Polarised light, that is, LCP is incident in nano-pore, can be exchanged into right-circularly polarized light (RCP), designs two kinds of various sizes of nano-pores, Optimal Parameters are set as：Incident LCP λ=930nm, w1=40nm, L1=200nm；Incident LCP λ=766nm, w2=80nm, L2 =140nm；

(2) super surface is designed, in order to make the LCP light of different wave length be incident on the OAM that super surface device generates OAM light beam and focusing Light beam, the predefined phase distribution function on super surfaceWherein, k is wave vector, and r is in polar coordinates Radius, f are focal length, and l is topological charge values, and θ is deflection, which is the helical phase Φ by generating OAM light beam₁ =l θ and the phase distribution for generating focusing OAM light beamComposition, by two kinds of nano-pore structure units according to predefined Phase distribution mode arranged；

(3) using simulation software to super surface carry out emulation testing, set Z=30 μm of sample distance, by λ=930nm and λ= The LCP light of 766nm is incident on respectively in nano-pore structure array region, when the LCP light incidence of λ=930nm, produces topology The OAM light beam of the focusing of charge values l=1；When the LCP light of λ=766nm is incident on super surface, producing topological charge values is l=2 OAM focus on light beam.

2. the super surface device of a kind of wavelength selective according to claim 1, which is characterized in that the super surface is flat Face or curved surface.

3. the super surface device of a kind of wavelength selective according to claim 1, which is characterized in that the anisotropy is received Rice structure include：Hole or its complementary structure.

4. the super surface device of a kind of wavelength selective according to claim 1, which is characterized in that the anisotropy is received Rice construction geometry pattern include：Ellipse, cross, I-shaped or polygon.

5. the super surface device of a kind of wavelength selective according to claim 1, which is characterized in that the metal includes： Gold, silver, copper, billon, silver alloy or copper alloy.

6. the super surface device of a kind of wavelength selective according to claim 1, which is characterized in that the medium includes：Silicon, Silica semiconductor and fluoride.

7. the super surface device of a kind of wavelength selective according to claim 1, which is characterized in that the base material is Silicon, silica semiconductor and fluoride.

8. the super surface device of a kind of wavelength selective according to claim 1, which is characterized in that if the nano unit knot Structure is produced on medium, and dielectric material may be the same or different with base material.

9. the super surface device of a kind of wavelength selective according to claim 1, which is characterized in that the substrate thickness 0< Ts<λ, λ are lambda1-wavelength.

10. the super surface device of a kind of wavelength selective according to claim 1, which is characterized in that the substrate surface is Plane or curved surface.

11. the super surface device of a kind of wavelength selective according to claim 1, which is characterized in that the wavelength selection The thickness T of the super surface device of type is less than wavelength.

12. the super surface device of a kind of wavelength selective according to claim 1, which is characterized in that the wavelength selection The super surface device of type is suitable for visible light and near infrared region.