A spin-decoupled full-angle directional deflection metasurface device

Abstract

The present invention discloses a spin-decoupled all-angle directional deflection metasurface device, which includes a substrate and a supercell formed by arranging a plurality of metal sub-unit structures in a two-dimensional manner and arranged periodically in the xy plane; the supercell is composed of 16 sub-units arranged in an N×M square layout, and the single metasurface adopts a V-shaped and rectangular metal micro-nano structure to realize independent control of the phase of cross-polarization of light in different circular polarization states along any plane. This dual-functional metasurface not only improves the integration of the metasurface, but also provides a solution for realizing spin-decoupled all-angle directionality. The proposed spin-decoupled all-angle directional deflection metadevice has good application prospects and can be used for polarization beam splitting, steering, and polarization measurement in spin-based nanophotonic systems, etc.

Description

Technical Field

[0001] The present invention belongs to the technical field of micro-nano optics, and particularly relates to a spin-decoupled all-angle directional deflection metasurface device. Background Art

[0002] A metasurface is a two-dimensional planar form of periodic or random nanostructures, which provides unprecedented capabilities for manipulating light fields at the sub-wavelength scale and has become an important branch in the field of nano-optics. The ability of metasurfaces to arbitrarily manipulate the amplitude, phase, and polarization of light has opened the door to various applications, such as anomalous refraction, metasurface lenses, directional surface plasmon polariton excitation, vortex beam generation, and holography. This technology is striving to overcome the deficiencies of traditional optical elements. In the past, single-functional metasurfaces have been proven to have various application potentials, and the current development trend in nanophotonics is to integrate multiple functions into the same device, which has promoted the emergence of multi-functional metasurfaces.

[0003] In recent years, spin-dependent metasurfaces with broadband responses designed using the Pancharatnam-Berry (PB) phase have attracted extensive attention. The PB phase is only related to the directions of the same meta-atoms and can achieve the separation of cross-polarization of circularly polarized light. At the same time, there are also single structures used to achieve radiation control of left and right circularly polarized light, but the left and right circularly polarized light emitted by these metasurfaces is symmetric in the same plane. To achieve asymmetric beam deflection in the same plane, a method combining dynamic phase and geometric phase has been proposed to achieve spin decoupling. And achieving spin-decoupled beam deflection at all angles has become an urgent problem to be solved. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide a spin-decoupled all-angle directional deflection metasurface device, which realizes that the deflection directions of the emitted left and right circularly polarized lights are not coplanar.

[0005] Technical Solution: The spin-decoupled all-angle directional deflection metasurface device of the present invention includes a substrate and a supercell formed by arranging a plurality of metal sub-unit structures in a two-dimensional manner and arranged periodically in the xy plane; the supercell is composed of 16 sub-units arranged in an N×M square layout, where N = M = 4; the 16 sub-units are composed of two basic structures, namely, v-shaped or rectangular structures formed according to different rotation angles.

[0006] Further, the material of the substrate is silicon dioxide.

[0007] Further, the material of the metal sub-unit is silver.

[0008] Furthermore, the supercell composed of 16 sub-units has a phase gradient along the x-direction for the cross-polarized beam of left-circularly polarized light incident normally, and a phase gradient along the y-direction for the cross-polarized beam of right-circularly polarized light incident normally.

[0009] Furthermore, the 16 sub-units have 4 basic unit structures, namely two rectangular unit structures A and B, and two V-shaped unit structures C and D.

[0010] Furthermore, the size of the unit structure A is that the width W is 130 - 170 nm and the length L is 430 - 470 nm; the size of the unit structure B is that the width W is 110 - 130 nm and the length L is 290 - 310 nm.

[0011] Furthermore, the size of the unit structure C is that β = 60°, the arm length a is 350 - 370 nm, and the arm width b is 90 - 110 nm; the size of the unit structure D is that the opening angle β = 60°, the arm length a is 290 - 310 nm, and the arm width b is 90 - 110 nm.

[0012] Furthermore, the period and thickness of each sub-unit forming the supercell are equal, that is, P = 500 nm and t = 40 nm.

[0013] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: By adopting the method of combining dynamic phase and geometric phase, the present invention ingeniously designs a two-dimensional gradient phase distribution, so that the left-circularly polarized light only has a phase gradient along the x-direction and no phase gradient in the remaining directions, while for the right-circularly polarized light, it only shows a phase gradient change along the y-direction and no phase gradient in the remaining directions. Thus, not only the non-coplanar separation of left and right circularly polarized lights is realized, but also refraction within the full angle can be achieved by changing the displacement of the unit structure. The present invention realizes the independent control of the phase of cross-polarization of lights with different circular polarization states along any plane. This dual-functional metasurface not only improves the integration degree of the metasurface, but also provides a solution for realizing spin decoupling and full-angle orientation. The proposed spin decoupling and full-angle orientation deflecting metadevice has good application prospects and can be used for polarization beam splitting, steering, and polarization measurement in spin-based nanophotonic systems, etc. Description of the Drawings

[0014] Figure 1 is the three-dimensional schematic diagram of the spin decoupling and full-angle orientation deflecting metasurface device in Embodiment 1;

[0015] Figure 2 is the three-dimensional schematic diagram of two basic structures in Embodiment 1;

[0016] Figure 3 is the top view of two basic structures in Embodiment 1;

[0017] Figure 4 It is a schematic structural diagram of a single metasurface pixel unit in Embodiment 1. Among them, 4(a) is the sorting of sub-units that make up the supercell, and 4(b) is the top view of the supercell;

[0018] Figure 5 It is the dynamic phase and rotation angle diagram of 16 sub-units in Embodiment 1;

[0019] Figure 6 It is the electric field distribution diagram of the cross-polarization of circularly polarized incident light in Embodiment 1; among them, 6(a) is the electric field distribution diagram of the cross-polarization of left circularly polarized incident light in the x-z plane, and 6(b) is the electric field distribution diagram of the cross-polarization of right circularly polarized incident light in the y-z plane;

[0020] Figure 7 It is the energy distribution diagram of circularly polarized incident light in Embodiment 1; among them, 7(a) is the energy distribution diagram of left circularly polarized incident light, and 7(b) is the energy distribution diagram of right circularly polarized incident light. Detailed implementation manners

[0021] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0022] Embodiment

[0023] This embodiment provides a spin-decoupled all-angle directional deflection metasurface device, as Figure 1 shown, including a substrate 1 and a supercell 2 formed by arranging a plurality of metal sub-unit structures in a two-dimensional manner in a periodic arrangement in the xy plane. The supercell 2 is composed of 16 sub-units arranged in an N×M square arrangement, where N = M = 4. The 16 sub-units are composed of two basic structures, a V-shaped or rectangular structure formed according to different rotation angles, as Figure 2 、 Figure 3 shown

[0024] The cross-polarized light beam of the left circularly polarized light incident perpendicularly is refracted along the x direction by the supercell 2 composed of 16 sub-units, and the cross-polarized light beam of the right circularly polarized light incident perpendicularly is refracted along the y direction. In this embodiment, the 16 sub-units are arranged in a 4×4 square arrangement, that is, it is required to achieve a 90° phase increment along the x direction for the cross-polarized light beam of the incident left circularly polarized light, and there is no gradient change for the right circularly polarized light in this direction; while along the y direction, the right circularly polarized light has a 90° phase increment, but the left circularly polarized light has no phase increment in this direction, so that the phases of the two polarized lights can be independently controlled to make the light beam refract along different planes.

[0025] In this embodiment, a method combining dynamic phase and geometric phase is introduced according to the required metasurface phase requirements to design the phase carried by the cross-polarization of circularly polarized light. By using the method of combining dynamic phase and geometric phase, when the incident light is left- and right-circularly polarized light, the required phases of the outgoing cross-polarized beams are φ ± ("+" and "-" represent left-circularly polarized light and right-circularly polarized light respectively), which can be obtained by adding the dynamic phase and the geometric phase, and the rotation angle of the structure has a geometric phase for the cross-polarized light of where α represents the rotation angle of the unit structure. Therefore, we can obtain the following formula

[0026]

[0027] So the dynamic phase and the corresponding rotation angle are

[0028]

[0029] The combined regulation of dynamic phase and geometric phase is beneficial to realizing spin-decoupled full-angle directional deflection. In this embodiment, φ + The phase increments along x and φ - along y are set to -120°, -30°, 60° and 150° in sequence.

[0030] In this embodiment, the substrate material is silicon dioxide, and the metal sub-unit structure material is silver. The opening angle of the V-shaped is β, the arm length is a, and the arm width is b; the width of the rectangle is W and the length is L. The period and thickness are p = 500 nm and t = 40 nm respectively. The V-shaped arm width b = 100 nm, and the arm length a is varied between 270 - 440 nm. The rectangle width W is varied in the range of 100 nm - 180 nm, and the length L is varied in the range of 300 nm - 450 nm. The structure parameters are optimized by the electromagnetic simulation software CST, and the covered dynamic phase is the entire 360°.

[0031] According to the phase increments of φ + along x and φ - along y, which are set to -120°, -30°, 60° and 150° in sequence, and formulas (4) and (5), the required 4 unit structures are determined. Two of them are rectangular structures. The size of unit structure A is width W = 150 nm and length L = 450 nm; the size of unit structure B is width W = 120 nm and length L = 300 nm; the other two are V-shaped structures. The size of unit structure C is arm length a = 360 nm and arm width b = 100 nm; the size of unit structure D is arm length a = 300 nm and arm width b = 100 nm. The dynamic phases of unit structures A - D for the incident circular polarization of λ = 1064 nm are 66°, 105°, -30° and 19° respectively. Figure 4(a) The 16 sub-units that make up the supercell (2), #1, #8, #11, #14 are selected to have a rectangular structure with a width W = 150 nm and a length L = 450 nm; #2, #5, #12, #15 are selected to have a rectangular structure with a width W = 120 nm and a length L = 300 nm; #3, #6, #9, #16 are selected to have a V-shaped structure with an arm length a = 360 nm and an arm width b = 100 nm; #4, #7, #10, #13 are selected to have a V-shaped structure with an arm length a = 300 nm and an arm width b = 100 nm. The rotation angles of the 16 sub-units are as Figure 5 shown, and the rotation angles of each other are different, thus forming a supercell as shown in Figure 4 (b).

[0032] According to the generalized Snell's law, in uniform air, light is incident perpendicularly along the z-axis. If the metasurface has a phase gradient in the x-direction, the refraction angle is If the metasurface has a phase gradient in the y-direction, the refraction angle is By controlling the x and y directions to achieve the total period of the entire 360° phase gradient, the refraction angle of the outgoing light is controlled. As shown in Figure 6 the electric field distribution diagram of the cross-polarization of circularly polarized incident light, Figure 6 (a) The left circularly polarized light is incident perpendicularly on the metasurface, and the outgoing right circularly polarized light is refracted at an angle of θ tx = 32.15° with the positive z-axis direction in the x-Z plane and refracted in the negative x-axis direction, Figure 6 (b) The right circularly polarized light is incident perpendicularly on the metasurface, and the outgoing right circularly polarized light is refracted at an angle of θ ty = 32.15° with the positive z-axis direction in the y-z plane and refracted in the negative y-axis direction. As shown in Figure 7 the energy distribution diagram of circularly polarized incident light, which can also confirm that when left and right circularly polarized lights are incident on the metasurface, the cross-polarized beams are refracted and distributed along the x-direction and y-direction respectively.

[0033] The above results verify the spin-decoupled all-angle directional deflection metasurface device. As long as any selection of two-dimensional arrangements N and M and the overall translation of the sub-unit structure are made, arbitrary control of the cross-polarization refraction azimuth angles of left and right circularly polarized lights can be achieved.

Claims

1. A spin-decoupled full-angle directional deflection metasurface device, characterized in that, it includes a substrate (1) and a supercell (2) formed by arranging multiple metal sub-unit structures in a two-dimensional manner and arranged periodically in the xy plane; the supercell (2) is composed of 16 sub-units arranged in an N×M square layout, where N = M = 4; each row and each column of the 16 sub-units include two rectangular unit structures A, B and two V-shaped unit structures C, D, and the V-shaped or rectangular structures are formed according to different rotation angles; the supercell (2) composed of 16 sub-units has a phase gradient along the x direction for the cross-polarized light beam of the right-handed circularly polarized light incident perpendicularly, and has a phase gradient along the y direction for the cross-polarized light beam of the left-handed circularly polarized light incident perpendicularly.

2. The spin-decoupled full-angle directional deflection metasurface device according to claim 1, characterized in that, the material of the substrate (1) is silicon dioxide.

3. The spin-decoupled full-angle directional deflection metasurface device according to claim 1, characterized in that, the material of the metal sub-unit is silver.

4. The spin-decoupled full-angle directional deflection metasurface device according to claim 1, characterized in that, the size of the unit structure A is that the width W is 130 - 170 nm and the length L is 430 - 470 nm; the size of the unit structure B is that the width W is 110 - 130 nm and the length L is 290 - 310 nm.

5. The spin-decoupled full-angle directional deflection metasurface device according to claim 1, characterized in that, the size of the unit structure C is that the opening angle β = 60°, the arm length a is 350 - 370 nm, and the arm width b is 90 - 110 nm; the size of the unit structure D is that the opening angle β = 60°, the arm length a is 290 - 310 nm, and the arm width b is 90 - 110 nm.

6. The spin-decoupled full-angle directional deflection metasurface device according to claim 1, characterized in that, the period and thickness of each sub-unit constituting the supercell (2) are equal, that is, P = 500 m, t = 40 nm.

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