CN105676314A - Multi-spectral phase-type metasurface device - Google Patents

Abstract

The invention discloses a multi-spectral phase-type metasurface device and belongs to the metamaterial technical field. The multi-spectral phase-type metasurface device of the invention is composed of a nano unit structure array which is formed on ultra-thin metal or a medium through etching. According to the multi-spectral phase-type metasurface device of the invention, multi-frequency information is coded onto a metasurface; and phase regulation can be performed on electromagnetic waves of a plurality of wavelengths by using wide-band spin-orbit interaction of nanostructures on the metasurface, so that the electromagnetic waves with different wavelengths and different incident angles can be focused to a specific shape. Therefore, the multi-spectral phase-type metasurface device of the invention can be applied to the design of a multi-wavelength ultra-small optical device and an integrated optical system.

Description

A kind of super surface device of multispectral phase-type

Technical field

The present invention relates to Meta Materials technical field, particularly to a kind of super surface device of multispectral phase-type.

Background technology

In modern electromagnetism, the realization of different frequency range electromagnetic wave is independently controlling in the application such as radio communication, multispectral imaging most important. But, the existence of material dispersion limits the development of conventional art so that corresponding device and system is huge, heavy and limited performance.

As two dimension Meta Materials, super surface is proved the comprehensive regulation and control that can realize electromagnetic wave amplitude, phase place and polarization state, uses the reflection under super surface condition and the law of refraction, and wavefront can arbitrarily be modulated. Therefore many functions, are possibly realized such as Beam Control, focusing and imaging etc. Owing to super surface ratio Meta Materials is thinner, be more easy to processing, therefore think in the industry that the practical Meta Materials device of the first generation can use this technology.

Although super surface can realize many unusual functions, but present design to be also limited by a lot of shortcoming. Such as, different wave length can be carried out separate responses by phase place change by super surface, but owing to strong dispersion significantly limit super surface in broadband and multispectral application. Such as, in tradition far field imaging process, resolution limitations is in diffraction limit, it is impossible to reach the half of illumination light wavelength, and stimulated radiation loss (STED) microscopic system is one of practical method of breakthrough diffraction limit imaging. The ultimate principle of STED microscopic system is the spatial choice passivation of fluorescence molecule, and this technology to use the light beam of two kinds of wavelength, produces the hot spot of different shapes respectively. But the tradition microscopical optical system of STED fluorescent scanning is very complicated, the technology of hot spot needed for being badly in need of using an optical element to produce two kinds. But, in STED microscopic system, the focal length of traditional super surface lens is relevant with wavelength, and multispectral imaging is brought adverse effect by this.

Summary of the invention

The technical problem to be solved is in that, for the deficiencies in the prior art, it is provided that a kind of super surface device of multispectral phase-type, this device is made up of the nanohole array on super thin metal thin film. By multifrequency information is encoded on nanohole array, utilizes the spin-orbit interaction of nanometer aperture to realize frequency and select to control. Owing to spin has wide waveband characteristics, therefore the present invention can realize at different wavelengths to the optical field distribution of shaped.

This invention address that its technical problem the technical scheme is that a kind of super surface device of multispectral phase-type, including the substrate arranged successively from bottom to top and the super surface being made up of anisotropy nanocell structures array, described anisotropy nanostructured is to be etched on super thin metal or medium, also can directly be produced in substrate, its characteristic size is less than wavelength, arrangement pitches is less than half-wavelength, the thickness d span of described super thin metal is: (λ is incident electromagnetic wave wavelength to δ < d < λ/3, δ is the skin depth of metalμ₀=4 π × 10^-7H/m, ω are circular frequency, σ₀Electrical conductivity for metal);Described ultra-thin medium thickness is less than lambda1-wavelength.

Wherein, described super surface is plane or curved surface.

Wherein, described anisotropy nanostructured includes: hole or its complementary structure.

Wherein, described anisotropy nanostructured geometrical pattern includes: rectangle, ellipse, cross, I-shaped or polygon.

Wherein, described metal includes: gold, silver, copper, billon, silver alloy or copper alloy

Wherein, described medium includes: the quasiconductor such as silicon, silicon dioxide and fluoride etc. are at the transparent material of service band.

Wherein, described base material is the quasiconductor such as silicon, silicon dioxide and fluoride etc. at the transparent material of service band.

Wherein, if described nanocell structures is produced on medium, dielectric material and base material may be the same or different.

Wherein, described substrate thickness 0 < h < λ, λ is incident electromagnetic wave wavelength.

Wherein, described substrate surface is plane or curved surface.

Wherein, the thickness t of the described super surface device of multispectral phase-type is smaller than wavelength.

Wherein, the electromagnetic wave of identical incident angle, different wave length can be focused on and imaging by the described super surface device of multispectral phase-type at same position.

Wherein, the light wave of different wave length, different angles incidence can be focused on by the described super surface device of multispectral phase-type at same position.

Wherein, the described super surface device of multispectral phase-type is applicable to visible ray and near infrared region.

Compared with prior art, the beneficial effects of the present invention is: the present invention has wide waveband characteristics, controlling Different lightwave by producing the super surface of achromatism geometric phase, can make different wave length, the electromagnetic wave of different incidence angles degree realizes the focal beam spot of arbitrary shape. And present configuration is simply small and exquisite, lightweight, it is beneficial to processing.

Accompanying drawing explanation

Fig. 1 is the cellular construction schematic diagram of the present invention;

Fig. 2 be the present invention when plane wave normal incidence, super surface introduce phase place change;

Fig. 3 is when the light normal incidence of different wave length is to super surface, produces the schematic diagram focused on;

Fig. 4 is light beam (λ₂=532nm) at the distribution schematic diagram of xoz and xoy plane (z=10 μm), wherein, Fig. 4 (a) is light beam (λ₂=532nm) at the distribution schematic diagram of xoz plane, Fig. 4 (b) is light beam (λ₂=532nm) at the distribution schematic diagram of xoy plane (z=10 μm);

Fig. 5 is light beam (λ₁=405nm) at the distribution schematic diagram of xoz and xoy plane (z=10 μm), wherein, Fig. 5 (a) is light beam (λ₁=405nm) at the distribution schematic diagram of xoz plane, Fig. 5 (b) is light beam (λ₁=405nm) distribution schematic diagram of xoy plane (z=10 μm);

Fig. 6 is the strength distribution curve figure having intercepted focusing surface x direction in the embodiment of the present invention 1;

Fig. 7 is the scanning electron microscope (SEM) photograph of sample in the embodiment of the present invention 1;

Fig. 8 is sample intensity distribution of xoz plane when λ=405nm left-handed rotation incidence in the embodiment of the present invention 1;

Fig. 9 is sample xoz planar strength scattergram when λ=532nm left-handed rotation incidence in the embodiment of the present invention 1;

Figure 10 is the scanning electron microscope (SEM) photograph of sample in the embodiment of the present invention 2;

Figure 11 be in the embodiment of the present invention 2 sample in λ=532, 632.8 the numerical result of xoz planar strength and experimental result comparison diagram when with 785nm incidence, wherein, Figure 11 (a) for sample when λ=532nm incidence, numerical result (left side) and experimental result (right side) comparison diagram in xoz planar strength, Figure 11 (b) for sample when λ=632.8nm incidence, numerical result (left side) and experimental result (right side) comparison diagram in xoz planar strength, Figure 11 (c) for sample when λ=785nm incidence, numerical result (left side) and experimental result (right side) comparison diagram in xoz planar strength,

Figure 12 is that to locate wavelength at z=9 μm in the embodiment of the present invention 2 be the full width at half maximum comparison diagram that 532nm, the numerical computations of 632.8nm and 785nm and experiment measuring obtain, wherein, Figure 12 (a) for z=9 μm locate wavelength be the full width at half maximum figure that 532nm, 632.8nm and 785nm experiment measuring obtains, Figure 12 (b) be z=9 μm place wavelength be the full width at half maximum figure that 532nm, 632.8nm and 785nm numerical computations obtains;

Figure 13 is the schematic diagram focused at same position with the light wave utilizing multispectral super surface device to make different wave length, different angles incident in the embodiment of the present invention 3, wherein, Figure 13 (a) is 532nm for wavelength, angle of incidence is 0 ° of surface of intensity distribution in xoz plane, Figure 13 (b) is 632.8nm for wavelength, angle of incidence is 30 ° of surfaces of intensity distribution in xoz plane, and Figure 13 (c) is 785nm for wavelength, and angle of incidence is-30 ° of surfaces of intensity distribution in xoz plane.

Detailed description of the invention

Below in conjunction with the drawings and the specific embodiments, the present invention is described in detail, but protection scope of the present invention is not limited in example below, should include the full content in claims. And those skilled in the art can realize the full content claim from a following embodiment.

Implement process as follows:

Embodiment 1

The embodiment of the present invention 1 is for preferred oval nano-pore cellular construction, as it is shown in figure 1, this super surface device of multispectral phase-type, including the substrate 1 being arranged in order from bottom to top, super surface layer 2 and etch the nano-pore 3 in super surface layer. Wherein the thickness of substrate is h; The thickness of super surface layer is d; Material gross thickness is t; The characteristic size w (short axle) and l (major axis) of described nano-pore structure are unequal. According to this structure, set forth its design principle in detail below.

Under circularly polarized light CPL incidence, each nano-pore is equivalent to a polarizing filter, and therefore, the hole array of spatial variations can produce the polarization state of spatial variations. Due to spin of photon rail interaction, polarization state change is relevant with phase place change. Transmission light can produce the Phase delay of 2 σ α, wherein left-handed the or dextrorotation state of σ=± 1 expression circularly polarized light, and α is the deflection angle of hole main shaft. From formula it can be seen that phase place changes, it doesn't matter with lambda1-wavelength. Therefore, the present invention may be used for wideband phase modulation.

In order to realize multiline Beam Control, the present invention has used for reference the concept of holography, namely the information of all angles can be fused in a two dimensional surface, the information of each wavelength is encoded in a super surface, as shown in Figure 2, when plane wave normal incidence, the phase place change that super surface introduces can be expressed as:

$\mathrm{\&Phi;}(x,y,\mathrm{\&lambda;})=\arg \left({\mathrm{\&Sigma;}}_1^N{E}_n\right)=\arg \left({\mathrm{\&Sigma;}}_1^N{A}_n\exp \right({\mathrm{i\&Phi;}}_n\left(x,y,{\mathrm{\&lambda;}}_n\right)\left)\right),---\left(1\right)$

Wherein An and Φ n represents amplitude and the phase place of the n-th virtual light source respectively, and En is complex amplitude, and λ n represents corresponding wavelength.

For two kinds of shape hot spots of needs, a kind of is the λ 1 solid focal beam spot produced, and another kind of λ 2 is the ring-shaped light spot produced. To λ 1, incident field can be expressed as:

$E_1(x,y,{\mathrm{\&lambda;}}_1)=A_1\exp \left(i\mathrm{\&Phi;}\right(x,y,{\mathrm{\&lambda;}}_1\left)\right)=A_1\exp (-i\frac{2\mathrm{\&pi;}}{{\mathrm{\&lambda;}}_1}\sqrt{x^2+y^2+f^2})---\left(2\right)$

To λ₂, focal beam spot comprises a phase place with azimuth linear change, and mathematical form isWhereinBeing the azimuth in cylindrical coordinate, l is topological sum value. Therefore, incident field can be expressed as:

In order to simplify discussion process, it will be assumed that amplitude A₁=A₂=A, therefore the PHASE DISTRIBUTION of multi-wavelength hologram is:

Fig. 3 illustrates corresponding process, and when the light normal incidence of different wave length is to super surface, on the position of design, we can respectively obtain solid focal beam spot and hollow light spot.

Above-mentioned design principle is verified, it is achieved step is as follows:

(1) parameter is chosen as λ₁=405nm, λ₂=532nm, and l=1.Super surface lens radius is 10 μm, and solid and ring-shaped light spot sightingpiston is arranged in z=10 μm of plane, say, that focal distance f=10 μm.

(2) utilizing Vector Diffraction Theory to emulate the performance of this device, refer to Fig. 4 a, b, Fig. 4 a, b is vortex light beam (λ₂=532nm) in the distribution of xoz and xoy plane (z=10 μm), obtain a ring-shaped light spot. Fig. 5 a, b are λ₁=405nm, in the distribution of xoz and xoy plane, obtains a solid focal beam spot the position of z=10 μm. In order to compare ring-shaped light spot and solid hot spot, the present embodiment has intercepted the intensity distributions in focusing surface x direction, depicts curve (Fig. 6).

(3) sample is prepared. At SiO₂Substrate is plated 120nm gold film, uses focused ion bundle (FIB) to machined corresponding sample. Sample border circular areas diameter 10 μm. As it is shown in fig. 7, the major axis of oval nano-pore and short axle respectively 180nm and 90nm. This some holes and pitch of holes are 250nm, arrange according to hexagonal-shaped frame to increase symmetry.

(4) incident illumination is converted into circularly polarized light by linear polarizer and quarter wave plate. In a z-direction, sample is by the platform courses equipped with motor, and step-length is 0.5 μm. Along z to different xoy planes on cross polarization intensity distributions recorded by CCD. By intercepting the transversal crossing spot center position in every width figure, we can respectively obtain the intensity distributions of xoz and yz plane. The experimental result of xoz plane when Fig. 8 is λ=405nm left-handed rotation incidence, illustration therein is the result of z=10 μm of position. Similarly, lambda1-wavelength is become rear 532nm, can measure at z=10 μm of place and obtain a ring-shaped light spot. Fig. 9 illustrates the experimental result of xoz planar strength distribution, fine with what simulation result met.

Embodiment 2

The super surface device of multispectral phase-type is utilized to realize different wave length in the focusing of same position and imaging. Assume the several point sources having different wave length at same position according to above-mentioned design theory, they PHASE DISTRIBUTION on super surface can be expressed as:

$\mathrm{\&Phi;}(x,y)=\arg \left({\mathrm{\&Sigma;}}_1^N{E}_n\right)=\arg \left({\mathrm{\&Sigma;}}_1^{N}A\exp \right(i\frac{2\mathrm{\&pi;}}{{\mathrm{\&lambda;}}_n}\sqrt{x^2+y^2+f^2}\left)\right).---\left(5\right)$

For the purpose of simplicity, it is assumed that the amplitude of these light sources is equal. In the processing and design process on super surface, the present embodiment employs three different wave lengths of 532nm, 632.8nm and 785nm. Circular sample radial design is 10 μm, and focal length is f=9 μm. Figure 10 is the SEM figure of sample, and wherein nanohole array is arranged according to C6 symmetry. When three different wave length incidence, this super surface is emulated and tested. On the left of Figure 11, string is λ=532 respectively, 632.8 and the numerical result of xoz planar strength when 785nm incidence, and fine with what right side experimental result met. Wherein, Figure 11 (a) for sample when λ=532nm incidence, at numerical result (left side) and experimental result (right side) comparison diagram of xoz planar strength,

Figure 11 (b) for sample when λ=632.8nm incidence, numerical result (left side) and experimental result (right side) comparison diagram in xoz planar strength, Figure 11 (c) for sample when λ=785nm incidence, at numerical result (left side) and experimental result (right side) comparison diagram of xoz planar strength. As shown in figure 12, the present embodiment also compares the full width at half maximum that the wavelength values emulation of three, z=9 μm of place obtains with experiment measuring, present invention achieves the focusing (in other words, with diffraction limit be similar to) approximate with theoretical value as seen from the figure. Wherein, Figure 12 (a) for z=9 μm locate wavelength be the full width at half maximum figure that 532nm, 632.8nm and 785nm experiment measuring obtains, Figure 12 (b) be z=9 μm place wavelength be the full width at half maximum figure that 532nm, 632.8nm and 785nm numerical computations obtains.

Embodiment 3

Utilize the super surface device of multispectral phase-type to realize different wave length, the light wave of different angles incidence focuses at same position. Different from embodiment 2, the light wave adopting different angles incident in the present embodiment focuses at same position, and the PHASE DISTRIBUTION on corresponding super surface can be expressed as:

$\mathrm{\&Phi;}(x,y)=\arg \left({\mathrm{\&Sigma;}}_1^{N}A\exp \right(i\frac{2\mathrm{\&pi;}}{{\mathrm{\&lambda;}}_n}\sqrt{x^2+y^2+f^2}+i\left(k_{xn}x+k_{yn}y\right)\left)\right).---\left(5\right)$

Wherein kxn and kyn is the n-th oblique incidence electromagnetic wave lateral wave vector in x and y direction. Present embodiment assumes that the amplitude of these light sources is equal, and use three different wave lengths of 532nm, 632.8nm and 785nm, angle of incidence corresponding respectively is 0 °, 30 ° and-30 ° (plane of incidence is xoz plane), and focal length is 50 μm, and bore is 100 μm. Result refers to Figure 13, wherein, Figure 13 (a) is 532nm for wavelength, angle of incidence is 0 ° of surface of intensity distribution in xoz plane, Figure 13 (b) is 632.8nm for wavelength, angle of incidence is 30 ° of surfaces of intensity distribution in xoz plane, and Figure 13 (c) is 785nm for wavelength, and angle of incidence is-30 ° of surfaces of intensity distribution in xoz plane. Above-mentioned not wavelength as seen from the figure, the light wave of different incidence angles degree achieves and focuses at same position.

By above-described embodiment, the present invention can be realized preferably.

Claims (14)

1. the super surface device of multispectral phase-type, it is characterised in that: by the structure of described super surface device, multifrequency information is encoded on a super surface, makes different wave length, different angles incident electromagnetic wave be focused to given shape; Its structure includes the substrate arranged successively from bottom to top and the super surface being made up of anisotropy nanocell structures array, described anisotropy nanostructured is to be etched on super thin metal or medium, also can directly be produced in substrate, its characteristic size is less than wavelength, arrangement pitches is less than half-wavelength, and the thickness d span of described super thin metal is: δ < d < λ/3, λ are incident electromagnetic wave wavelength, δ is the skin depth of metalμ₀=4 π × 10^-7H/m, ω are circular frequency, σ₀Electrical conductivity for metal; Described ultra-thin medium thickness is less than lambda1-wavelength.

2. the super surface device of the multispectral phase-type of one according to claim 1, it is characterised in that: described super surface is plane or curved surface.

3. the super surface device of the multispectral phase-type of one according to claim 1, it is characterised in that: described anisotropy nanostructured includes: hole or its complementary structure.

4. the super surface device of the multispectral phase-type of one according to claim 1, it is characterised in that: described anisotropy nanostructured geometrical pattern includes: rectangle, ellipse, cross, I-shaped or polygon.

5. the super surface device of the multispectral phase-type of one according to claim 1, it is characterised in that: described metal includes: gold, silver, copper, billon, silver alloy or copper alloy.

6. the super surface device of the multispectral phase-type of one according to claim 1, it is characterised in that: described medium includes: the quasiconductor such as silicon, silicon dioxide and fluoride etc. are at the transparent material of service band.

7. the super surface device of the multispectral phase-type of one according to claim 1, it is characterised in that: described base material is the quasiconductor such as silicon, silicon dioxide and fluoride etc. at the transparent material of service band.

8. the super surface device of the multispectral phase-type of one according to claim 1, it is characterised in that: if described nanocell structures is produced on medium, dielectric material and base material may be the same or different.

9. the super surface device of the multispectral phase-type of one according to claim 1, it is characterised in that: described substrate thickness 0 < h < λ, λ is incident electromagnetic wave wavelength.

10. the super surface device of the multispectral phase-type of one according to claim 1, it is characterised in that: described substrate surface is plane or curved surface.

11. the super surface device of the multispectral phase-type of one according to claim 1, it is characterised in that: the thickness t of the described super surface device of multispectral phase-type is smaller than wavelength.

12. the super surface device of the multispectral phase-type of one according to claim 1, it is characterised in that: the electromagnetic wave of identical incident angle, different wave length can be focused on and imaging by the described super surface device of multispectral phase-type at same position.

13. the super surface device of the multispectral phase-type of one according to claim 1, it is characterised in that: the light wave of different wave length, different angles incidence can be focused on by the described super surface device of multispectral phase-type at same position.

14. the super surface device of the multispectral phase-type of one according to claim 1, it is characterised in that: the described super surface device of multispectral phase-type is applicable to visible ray and near infrared region.