CN106990547A - The super surface of dolphin shape cellular circular array - Google Patents

Abstract

A novel dolphin-shaped cell circular array metasurface for generating local composite polarized light fields. The metasurface is a circular array-shaped micro-nano metal structure, which is composed of N (N≥3 and N is a positive integer) dolphin-shaped metal cell structures arranged in equiangular rotation to form a circular array. The dolphin-shaped metal cell binds the incident light energy to the surface of the structure, and finally generates a local focused strong field at the tip of each dolphin-shaped cell. Changing the structure factor m (m>1) can adjust the enhancement factor of the focus field; due to the dolphin At the same time, the incident linearly polarized light can be converted into a helical phase beam; the intensity of the z-direction component E _z of the transmitted light field accounts for the ratio of the total light field E intensity with the It decreases with the increase of propagation distance, but the effect of E _z phase spiral becomes better with the increase of propagation distance. The invention can be used as an optical tweezers and an optical angular momentum controller, and has important application value in the fields of broadband optical communication, optical imaging, nanometer manipulation and the like.

Description

Dolphin-shaped cell circle array metasurface

technical field

The invention belongs to the field of optics and optoelectronics technology, and relates to light field polarization modulation, nanometer manipulation, and surface plasmon excitation, in particular to a novel dolphin-shaped cellular circular array metasurface for generating local compound polarized light fields.

Background technique

When light passes through a structured material with subwavelength features, its propagation constant can depend on its polarization state, even if all its components are optically isotropic. At present, many kinds of subwavelength optical devices have been designed, which can control the polarization state of the light field, that is, the spin angular momentum. At the same time, the orbital angular momentum related to the space degree of freedom of the light field can also be adjusted. Orbital angular momentum has been identified as a useful degree of freedom to enhance the information-carrying capacity of photons due to its infinite size, and due to singularities of phase and intensity, optical manipulation and metrology have found wide-ranging applications.

In recent years, the use of metasurfaces to control orbital angular momentum has become one of the research hotspots in the field of vortex beams. Metasurfaces are artificial plasmonic arrays with one-dimensional or two-dimensional subwavelength periods, and have received increasing attention in recent years. Since the thickness of the metasurface is extremely small compared with the operating wavelength, the metasurface can be regarded as a discontinuous interface that changes the amplitude and phase of the incident light suddenly, so the metasurface is usually used for light field modulation, such as intensity modulation, phase regulation, polarization regulation, etc. The most widely used method today is to use nanoscale rectangular parallelepiped metal nanorods to form metasurfaces by arranging them in different arrays. Based on the Pancharatnam-Berry phase change principle, the incident left-handed/right-handed circularly polarized light is adjusted to a transmitted vector vortex beam. , the proposed single plasmon metasurface, silicon nanorod metasurface, etc. are all based on the above principles to control circularly polarized light into vortex beams, and the physical model of such control has also been established. However, in the existing research results, there is still insufficient research on how to control linearly polarized light into a vortex beam.

To sum up, the present invention innovatively starts from the design of the cell structure and array form, and proposes a novel dolphin-shaped cell circular array metasurface that generates a local compound polarized light field. The metasurface is a circular array-shaped micro-nano metal structure, and a circular array is formed by a plurality of dolphin-shaped metal cell structures arranged in equiangular rotation. The number of dolphin-shaped cells arranged on the circular array is N, and the connection line between the geometric center of the dolphin-shaped cell and the geometric center of the circular array divides the circle into N equal parts, and the central axis of the dolphin-shaped cellular structure always points to the center of the circular array. The dolphin-shaped metal cell binds the incident light energy to the surface of the structure, and finally generates a local strong field at the tip of each dolphin-shaped cell. A structure factor m (m>1) is proposed. By changing the value of the structure factor m, the Realize the function of regulating the enhancement factor of the focus field. On the basis of this innovation, due to the structure of the dolphin-shaped metal cells themselves and the circular array structure arranged at equal angles, the invention innovatively converts the incident linearly polarized light into a helical phase beam. The ratio of the intensity of the z-direction component E _z of the transmitted light field to the total light field E intensity decreases with the increase of the propagation distance, but the better the phase spiral effect of E _z is with the increase of the propagation distance.

Contents of the invention

The invention provides a novel dolphin-shaped cell circle array metasurface for generating a local compound polarized light field. The metasurface is a circular array-shaped micro-nano metal structure, and a circular array is formed by a plurality of dolphin-shaped metal cell structures arranged in equiangular rotation. The central axis of the dolphin-shaped cell structure always points to the center of the circle array. The geometric structure of the dolphin-shaped metal cell is composed of two semi-crescent structures connected by cross-sections with opposite tips, and the semi-crescent structure is obtained by intercepting two semi-cylindrical bodies. The number of dolphin-shaped cells arranged on the circular array is N (N ≥ 3 and N is a positive integer), the line connecting the geometric center of the dolphin-shaped cell and the geometric center of the circular array divides the circle into N equal parts, and the structure of the dolphin-shaped cell The central axis always points to the center of the circle array, the radius of the circle array (i.e. the distance from the center of the circle array to the geometric center of the dolphin-shaped structure) is R, and the included angle α=360°/N between the geometric centers of two adjacent dolphin-shaped cell structures, Wherein the radii of half cylinder 1 and half cylinder 2 intercepting the dolphin-shaped cellular structure are respectively R ₁ and R ₂ and satisfy the relational formula R ₂ =mR ₁ (wherein m>1), m is defined as the structure factor, two cylinders The body cross-section circle is inscribed, the distance between the center of the cross-section d=(m-1)R ₁ , and the distance between the two tips of the dolphin-shaped cell structure d'=2(R ₁ +R ₂ ).

In the dolphin-shaped cell circular array metasurface, the dolphin-shaped metal cells bind the incident light energy to the surface of the structure, and finally generate a local strong field at the tip of each dolphin-shaped cell, changing the structure factor m can adjust the focusing field enhancement factor; due to the structure of the dolphin-shaped metal cells and the circular array structure arranged at an equal angle, the incident linearly polarized light can be converted into a helical phase beam, and the intensity of the z-direction component E _z of the transmitted light field accounts for the total light The ratio of field E intensity decreases with the increase of propagation distance, but the effect of E _z phase spiral becomes better with the increase of propagation distance.

Advantage and positive effect of the present invention:

In the dolphin-shaped cell circle array metasurface, the dolphin-shaped metal cell binds the incident light energy to the surface of the structure, and finally generates a local strong field at the tip of each dolphin-shaped cell, changing the structure factor m (m>1 ) can adjust the enhancement factor of the focusing field; due to the structure of the dolphin-shaped metal cells and the circular array structure arranged at an equal angle, the incident linearly polarized light can be converted into a helical phase beam, and the z-direction component of the transmitted light field E _z The ratio of the intensity of to the total light field E intensity decreases with the increase of propagation distance, but the effect of E _z phase spiral becomes better with the increase of propagation distance. At the same time, the superstructured surface has the advantages of simple fabrication and convenient integration of lumped components on the structured surface. The invention can be used as an optical tweezers and an optical angular momentum controller, and has important application value in the fields of broadband optical communication, optical imaging, nanometer manipulation and the like.

Description of drawings

Figure 1 is a dolphin-shaped cell circular array metasurface composed of dolphin-shaped metal cell structures that can generate local strong fields at the tip of each dolphin-shaped cell and can produce polarization changes in the transmitted light field. Among them: (a) is a schematic diagram of the cross-sectional geometry of the dolphin-shaped metal cellular structure; (b) is a geometric diagram of the cross-sectional geometry of the metasurface structure of the dolphin-shaped circular array of cells (taking N=8 as an example).

Fig. 2 shows the focus produced by the tip of the dolphin-shaped metal cell structure when linearly polarized light propagating along the z direction and polarized in the x direction is incident on a dolphin-shaped metal cell structure with a fixed large cylinder radius R ₂ =300nm and different structure factors m Schematic diagram of the intensity distribution of the light field. Among them: (a) is a schematic diagram of the intensity distribution of the focused light field when light is incident on a dolphin-shaped metal cell structure with a structure factor of m=1.5 (where the legend on the right is the logarithmic value obtained by the natural base of the enhancement factor); (b) is Schematic diagram of the intensity distribution of the focused light field when light is incident on a dolphin-shaped metal cell structure with a structure factor m=2 (where the legend on the right is the logarithmic value of the enhancement factor obtained from the natural base); (c) is the light incident on the structure factor m Schematic diagram of the intensity distribution of the focused light field when the dolphin-shaped metal cell structure is =3 (wherein the legend on the right is the logarithmic value obtained from the natural base of the enhancement factor).

Figure 3 is a schematic diagram of the intensity and phase distribution of the transmitted field at different distances behind the metasurface when linearly polarized light propagating along the z direction and polarized in the x direction is incident on the dolphin-shaped cellular circular array metasurface (taking N=8 as an example ). Where: (a) is a schematic diagram of the intensity distribution of the transmitted field at D=1000nm behind the dolphin-shaped circular cell array metasurface; (b) is the Ez of the transmitted field at D=1000nm behind the dolphin-shaped circular cell array _metasurface Schematic diagram of component phase distribution; (c) is a schematic diagram of the intensity distribution of the transmitted field at D=2000nm behind the dolphin-shaped cellular array metasurface; (d) is the transmitted field at D=2000nm behind the dolphin-shaped cellular array metasurface The schematic diagram of the phase distribution of the E _z component; (e) is a schematic diagram of the intensity distribution of the transmitted field at D=3000nm behind the dolphin-shaped circular cell array metasurface; (f) is the D=3000nm place behind the dolphin-shaped circular cellular array metasurface Schematic diagram of the phase distribution of the _Ez component of the transmitted field.

Fig. ⁴ _{shows the light field intensity |E z |} The ratio of the total light field intensity |E| ² and the phase distribution of the E _z component of the transmitted field (take N=8 as an example). Among them: (a) is the ratio of the optical field intensity |E _z | ² of the transmitted field z component E _z at D = 400nm behind the dolphin-shaped cellular circular array metasurface to the total optical field intensity |E| ² ; (b) It is a schematic diagram of the E _z component phase distribution of the transmission field at D=400nm behind the dolphin-shaped cell circle metasurface; (c) is the transmission field z component E _z at D=800nm behind the dolphin-shaped cell circle metasurface The ratio of the light field intensity |E _z | ² to the total light field intensity |E| ² ; (d) is a schematic diagram of the phase distribution of the E _z component of the transmitted field at D=800nm behind the dolphin-shaped cell circular array metasurface; (e ) is the ratio of the optical field intensity |E _z | ² of the transmitted field z component E _z at D = 2000nm behind the metasurface of the dolphin-shaped cell circle array to the total optical field intensity |E| ² ; (f) is the dolphin-shaped cell Schematic diagram of the phase distribution of the E _z component of the transmitted field at D=2000nm behind the metasurface of the cell circle array.

detailed description

Example 1

As shown in Figure 1, the dolphin-shaped cellular circular array metasurface provided by the present invention is a circular array-shaped micro-nano metal structure, and a circular array is formed by a plurality of dolphin-shaped metal cellular structures equiangularly rotated. The central axis of the metal cell structure always points to the center of the circle array. The geometric structure of the dolphin-shaped metal cell is composed of two semi-crescent structures connected in cross-sections with opposite tips, and the semi-crescent structure is composed of two semi-cylinders intercepted. The number of dolphin-shaped cells arranged on the circular array is N (N ≥ 3 and N is a positive integer), the line connecting the geometric center of the dolphin-shaped cell and the geometric center of the circular array divides the circle into N equal parts, and the structure of the dolphin-shaped cell The central axis always points to the center of the circle array, the radius of the circle array (i.e. the distance from the center of the circle array to the geometric center of the dolphin-shaped structure) is R, and the included angle α=360°/N between the geometric centers of two adjacent dolphin-shaped cell structures, Wherein the radii of half cylinder 1 and half cylinder 2 intercepting the dolphin-shaped cellular structure are respectively R ₁ and R ₂ and satisfy the relational formula R ₂ =mR ₁ (wherein m>1), m is defined as the structure factor, two cylinders The body cross-section circle is inscribed, the distance between the center of the cross-section d=(m-1)R ₁ , and the distance between the two tips of the dolphin-shaped cell structure d'=2(R ₁ +R ₂ ).

The fabrication of the metasurface of the dolphin-shaped circular array of cells in the present invention can be realized by direct-current magnetron sputtering against the target and focused ion beam etching techniques. The specific steps are as follows:

(1) Sputtering gold, silver, aluminum, copper and other nanometal films on glass substrates such as quartz or semiconductor substrates such as silicon by using the direct current magnetron sputtering method of the opposite target;

(2) Using focused ion beam etching technology or electron beam direct writing technology to etch the metal dolphin-shaped circular array structure on the nanometal film.

Specific application example 1

The specific parameters of the dolphin-shaped cell circle array metasurface are as follows:

The material of the dolphin-shaped metal cell is silver, and the incident wavelength λ=660nm. At this time, the refractive index of the silver material is n _Ag =0.049889+4.4869i. The metasurface is a circular array micro-nano metal structure, which is composed of multiple dolphin-shaped metal cell structures rotated at an equal angle. The geometric structure of the dolphin-shaped metal cell is connected by two semi-crescent-shaped structures with opposite tips. Composition, in which the half-crescent structure is intercepted by two half-cylinders. The number of dolphin-shaped cells arranged on the circular array is N=8, the line connecting the geometric center of the dolphin-shaped cell and the geometric center of the circular array divides the circle into N=8 equal parts, and the central axis of the dolphin-shaped cell structure always points to the circular array The center of the circle, the radius of the circle array (i.e. the distance from the center of the circle array to the geometric center of the dolphin-shaped structure) is R=1 μm, and the included angle α=360°/N=45° between the geometric centers of two adjacent dolphin-shaped cellular structures, intercept The radius R ₂ of the half cylinder 2 of the dolphin-shaped cellular structure is 300nm, and the structure factor m=2, so the radius R ₁ of the half cylinder 1 is 150nm. The cross-sectional circles of the two cylinders are inscribed. According to the above parameters, the distance between the centers of the cross-sections is d=150nm, and the distance between the two tips of the dolphin-shaped cellular structure is d′=900nm.

Fig. 2 shows the focus produced by the tip of the dolphin-shaped metal cell structure when linearly polarized light propagating along the z direction and polarized in the x direction is incident on a dolphin-shaped metal cell structure with a fixed large cylinder radius R ₂ =300nm and different structure factors m Schematic diagram of the intensity distribution of the light field. Among them: (a) is a schematic diagram of the intensity distribution of the focused light field when light is incident on a dolphin-shaped metal cell structure with a structure factor of m=1.5 (where the legend on the right is the logarithmic value obtained by the natural base of the enhancement factor); (b) is Schematic diagram of the intensity distribution of the focused light field when light is incident on a dolphin-shaped metal cell structure with a structure factor m=2 (where the legend on the right is the logarithmic value of the enhancement factor obtained from the natural base); (c) is the light incident on the structure factor m Schematic diagram of the intensity distribution of the focused light field when the dolphin-shaped metal cell structure is =3 (wherein the legend on the right is the logarithmic value obtained from the natural base of the enhancement factor). It can be seen from the results that when the structure factor m=1.5, the enhancement factor is about e ⁷ ≈1.0966×10 ³ ; when the structure factor m=2, the enhancement factor is about e ⁶ ≈4.0343×10 ² ; when the structure factor When m=3, the enhancement factor is about e ⁴ ≈5.4598×10 ¹ . From this analysis, when the structure factor m is changed, the curvature of the dolphin-shaped cell structure curve will increase due to the decrease of m, thus forming a more ideal structural tip, and the enhancement factor will increase with the decrease of m. Therefore, changing the structure factor m (m>1) can adjust the enhancement factor of the focusing field.

Figure 3 is a schematic diagram of the intensity and phase distribution of the transmitted field at different distances behind the metasurface when linearly polarized light propagating along the z direction and polarized in the x direction is incident on the dolphin-shaped cellular circular array metasurface (taking N=8 as an example ). Where: (a) is a schematic diagram of the intensity distribution of the transmitted field at D=1000nm behind the dolphin-shaped circular cell array metasurface; (b) is the Ez of the transmitted field at D=1000nm behind the dolphin-shaped circular cell array _metasurface Schematic diagram of component phase distribution; (c) is a schematic diagram of the intensity distribution of the transmitted field at D=2000nm behind the dolphin-shaped cellular array metasurface; (d) is the transmitted field at D=2000nm behind the dolphin-shaped cellular array metasurface The schematic diagram of the phase distribution of the E _z component; (e) is a schematic diagram of the intensity distribution of the transmitted field at D=3000nm behind the dolphin-shaped circular cell array metasurface; (f) is the D=3000nm place behind the dolphin-shaped circular cellular array metasurface Schematic diagram of the phase distribution of the _Ez component of the transmitted field. It is not difficult to see from the calculation results that when the incident light hits the metasurface of the dolphin-shaped cellular circular array, the focusing field of the inner ring makes a spiral phase light field at the center of the circular array. With the increase of the propagation distance, the spiral phase light field Gradually diverge, the phase vortex at the center becomes more and more obvious, as the distance continues to increase, the vortex characteristics are not very obvious, that is, when the linearly polarized light is incident on the metasurface of the dolphin-shaped cell circle array, a local area can be generated behind the metasurface Spiral phase light field.

Fig. ⁴ _{shows the light field intensity |E z |} The ratio of the total light field intensity |E| ² and the phase distribution of the E _z component of the transmitted field (take N=8 as an example). Among them: (a) is the ratio of the optical field intensity |E _z | ² of the transmitted field z component E _z at D = 400nm behind the dolphin-shaped cellular circular array metasurface to the total optical field intensity |E| ² ; (b) It is a schematic diagram of the E _z component phase distribution of the transmission field at D=400nm behind the dolphin-shaped cell circle metasurface; (c) is the transmission field z component E _z at D=800nm behind the dolphin-shaped cell circle metasurface The ratio of optical field intensity |E _z | ² to the total optical field intensity |E| ² ; (d) is a schematic diagram of the phase distribution of the E _z component of the transmitted field at D=800nm behind the dolphin-shaped cell circular array metasurface; (e ) is the ratio of the optical field intensity |E _z | ² of the transmitted field z component E _z at D = 2000nm behind the metasurface of the dolphin-shaped cell circle array to the total optical field intensity |E| ² ; (f) is the dolphin-shaped cell Schematic diagram of the phase distribution of the E _z component of the transmitted field at D=2000nm behind the metasurface of the cell circle array. It can be seen from the results that when D ₌ 400nm, the optical field intensity |Ez| ^{2 of the Ez component accounts for the highest proportion of 80% of the total optical field intensity |E|2 ;} when D ₌ 800nm, _Ez The light field intensity | _Ez | ² of the component |E|2 has dropped to 45% of the total light field intensity |E| ² ; when D=2000nm, the light field intensity | _Ez | ² of the _Ez component accounts for the total light field The proportion of intensity |E| ² is only up to 20%. But as the distance D increases, the phase spiral effect at the center of the _z component of the transmitted field E increases significantly. In summary, the ratio of the intensity of the z-direction component E _z of the transmitted light field to the total light field E intensity decreases with the increase of the propagation distance, but the better the phase spiral effect of E _z is with the increase of the propagation distance.

Claims (5)

1. a kind of new super surface of dolphin shape cellular circular array for producing local composite polarizing light field.The super surface is circular array The micro-nano metal structure of shape, is angularly rotated by multiple dolphin shape metal structure cells and is arranged to make up circular array.Dolphin shape member The circular array center of circle is pointed to forever in the axis of born of the same parents' structure.Dolphin shape metal cellular geometry is by two and half crescent structures with point The opposite state section in end connects composition, wherein half crescent structure is intercepted by two semicylinders and obtained.

2. the super surface of dolphin shape cellular circular array according to claim 1, it is characterised in that the dolphin arranged on circular array Shape cellular quantity is N (N >=3 and N is positive integer), and the line of dolphin shape cellular geometric center and circular array geometric center divides circle Into N equal portions, the circular array center of circle is pointed in the axis of dolphin shape structure cell forever, circular array radius (i.e. circular array center to sea The distance at globefish shape construction geometry center) be R, angle α=360 °/N of the geometric center of two neighboring dolphin shape structure cell, its The radius of the middle semicylinder 1 for intercepting dolphin shape structure cell and semicylinder 2 is respectively R₁And R₂And meet relational expression R₂= mR₁(wherein m ＞ 1), m is defined as structure factor, and two cylinder sections circle is inscribe relation, section distance of center circle d=(m-1) R₁, sea The spacing d '=2 (R at the tip of globefish shape structure cell two₁+R₂)。

3. the super surface of dolphin shape cellular circular array according to claim 1 or 2, it is characterised in that dolphin shape metal cellular will Incident light energy is bound to body structure surface, and final in each dolphin shape cellular tip generation local high field, changes structure factor m The enhancer of regulatable focusing.

4. the super surface of dolphin shape cellular circular array according to claim 1 or 2 or 3, it is characterised in that due to dolphin shape gold Belong to cellular self structure and equiangularly arranged circular array structure, while incident linearly polarized light can be converted into spiral shell Revolve phase light beam.

5. the super surface of dolphin shape cellular circular array according to claim 1 or 2 or 3 or 4, it is characterised in that Transmission field z Durection component E_zIntensity account for the ratio of total light field E intensity and increase with propagation distance and reduce, but increase E with propagation distance_zPhase Spiral effect is better.