A wavelength-dependent dual-function all-dielectric metasurface structure

Abstract

The present invention discloses a wavelength-dependent dual-function all-medium metasurface structure, comprising a substrate layer, an upper nanostructure and a lower nanostructure; the upper nanostructure and the lower nanostructure are respectively arranged on the upper end face and the lower end face of the substrate layer, the upper nanostructure is composed of an arrangement of elliptical or rectangular nanocolumns of the same specification but different placement angles, and the lower nanostructure is composed of an arrangement of elliptical or rectangular nanocolumns of another specification but different placement angles; the placement angles of the elliptical or rectangular nanocolumns in the upper nanostructure and the lower nanostructure are determined according to the desired phase distribution. The present invention can switch between two specific functions according to different incident wavelengths, and can improve the integration of the optical system.

Description

Technical Field

[0001] The present invention relates to the field of nano-optical technology, and in particular to a wavelength-dependent dual-function all-medium metasurface structure. Background Art

[0002] Metasurface structures are a type of beam control device developed in recent years. Specifically, by designing a specific sub-wavelength structure, the amplitude, phase or polarization state of the beam can be changed. Currently, metasurface structures have been successfully applied to realize beam splitters, beam generators, planar (achromatic) lenses, super-resolution imaging, etc. With the development of optical technology, the requirements for the integration and functional reusability of optical devices are becoming higher and higher. For metasurface structures, if the same structure can realize multiple functions, it will be beneficial to improve the integration of optical devices. Summary of the invention

[0003] In view of the deficiencies in the prior art, the present invention aims to provide a wavelength-dependent dual-function all-dielectric metasurface structure that can realize different functions at two different wavelengths.

[0004] In order to achieve the above object, the present invention adopts the following technical solution:

[0005] A wavelength-dependent dual-function all-dielectric metasurface structure comprises a substrate layer, an upper nanostructure and a lower nanostructure; the upper nanostructure and the lower nanostructure are respectively arranged on the upper end face and the lower end face of the substrate layer, the upper nanostructure is composed of a plurality of elliptical or rectangular nanocolumns of the same specification but with different arrangement angles, and the lower nanostructure is composed of a plurality of elliptical or rectangular nanocolumns of another specification and with different arrangement angles; the arrangement angle of each elliptical or rectangular nanocolumn in the upper nanostructure and the lower nanostructure is determined according to a desired phase distribution.

[0006] Furthermore, the upper nanostructure and the lower nanostructure are both made of materials with high refractive index and low loss.

[0007] Furthermore, for circularly polarized light with a set incident wavelength of λ1, the upper nanocolumn structure is an equivalent half-wave plate, and the lower nanocolumn structure is an equivalent full-wave plate; and for circularly polarized light with a set incident wavelength of λ2, the lower nanocolumn structure is an equivalent half-wave plate, and the upper nanocolumn structure is an equivalent full-wave plate.

[0008] The beneficial effects of the present invention are:

[0009] The provided wavelength-dependent dual-function all-dielectric metasurface structure can switch between two specific functions according to the incident wavelength, thereby improving the integration of the optical system. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is an overall schematic diagram of a supersurface structure in an embodiment of the present invention;

[0011] Figure 2 for Figure 1 Schematic diagram of the cross-section of the upper nanopillar of the mesostructure;

[0012] Figure 3 for Figure 1 Schematic diagram of the cross-section of the lower nanopillar of the mesostructure;

[0013] Figure 4 Schematic diagram of the connection between the upper nanocolumns, the substrate layer and the lower nanocolumns in an embodiment of the present invention;

[0014] Figure 5 It is a schematic diagram of the principle of the metasurface structure realizing the dual functions of a plane axicon mirror and a plane lens in an embodiment of the present invention;

[0015] Figure 6 A light field evolution diagram of a zero-order Bessel beam generated when the metasurface structure in an embodiment of the present invention realizes the function of a plane axicon when the incident wavelength is λ1;

[0016] Figure 7 This is a light field evolution diagram of the metasurface structure in an embodiment of the present invention, which realizes the function of a plane lens when the incident wavelength is λ2, thereby achieving light beam focusing. DETAILED DESCRIPTION

[0017] The present invention will be further described below in conjunction with the accompanying drawings. It should be noted that this embodiment is based on the technical solution and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to this embodiment.

[0018] This embodiment provides a wavelength-dependent dual-function all-dielectric metasurface structure, such as Figure 1-4 As shown, it includes a substrate layer 1, an upper nanostructure 2 and a lower nanostructure 3. An upper nanostructure 2 and a lower nanocolumn structure layer 3 are respectively provided on the upper end surface and the lower end surface of the substrate layer 1, the upper nanostructure 2 is composed of a plurality of elliptical nanocolumns 21 of the same specification but with different placement angles, and the lower nanostructure 3 is composed of a plurality of elliptical nanocolumns 31 of another specification but with different placement angles. In this embodiment, for a set incident wavelength λ1=780nm, the upper elliptical nanocolumns are equivalent to half-wave plates, and the lower elliptical nanocolumns are equivalent to full-wave plates; for a set incident wavelength λ2=660nm, the lower elliptical nanocolumns are equivalent to half-wave plates, and the upper elliptical nanocolumns are equivalent to full-wave plates.

[0019] The specifications of the upper and lower elliptical nanocolumns that meet the above requirements are: the long axis a1 of the upper elliptical nanocolumn is 238 nm, the short axis b1 is 70 nm, the height h1 is 600 nm, and the unit cell size is S x =S y =300nm; the long axis a2 of the lower elliptical nanocolumn is 248nm, the short axis b2 is 94nm, the height h2 is 800nm, and the unit cell size is S x =S y =300nm. Under a certain wavelength of incidence, the full-wave plate has little effect on the phase distribution of the light field; for the half-wave plate, the desired phase distribution can be obtained by controlling the placement angle θ1 or θ2 of the upper or lower elliptical nanocolumns, thereby realizing the function of incident at a specific wavelength.

[0020] Furthermore, the substrate layer 1 is made of silicon dioxide, and the upper elliptical nanocolumns 21 and the lower elliptical nanocolumns 31 are both made of silicon material.

[0021] Figure 5 It shows the principle diagram of the metasurface structure in this embodiment that can realize a dual-function device of a plane axicon mirror and a plane lens at different wavelengths. Figure 5 (a) is a schematic diagram showing the principle of generating a zero-order Bessel beam with an incident wavelength of λ1=780nm through a metasurface structure; Figure 5 (b) shows the expected phase distribution of the designed planar axicon, while Figure 5 (c) is the corresponding layout diagram of the upper elliptical nanostructure. Figure 5 (d) is a schematic diagram showing the principle of focusing a light beam with an incident wavelength of λ2=660nm through a metasurface structure onto a point on the axis; Figure 5 (e) shows the expected phase distribution of the designed flat lens, while Figure 5 (e) is the corresponding arrangement diagram of the lower elliptical nanostructure.

[0022] For a zero-order Bessel beam generated with an incident wavelength of λ1 = 780 nm, the phase distribution must satisfy the following formula:

[0023]

[0024] For the incident focused beam of λ2=660nm, the phase distribution must satisfy the following formula:

[0025]

[0026] Where NA is the numerical aperture and f is the preset focal length. Phase distribution According to the formula and The angles θ1 and θ2 of the elliptical nanocolumns at corresponding positions on the upper nanostructure 2 and the lower nanostructure 3 are determined.

[0027] Figure 6 The evolution process of the metasurface structure in this embodiment as a plane axicon mirror with NA=0.7 to generate a zero-order Bessel beam is described. Figure 6 (a) shows the normalized light field distribution on the xz plane after the light beam passes through the metasurface structure; Figure 6 (b) shows the normalized light field distribution on the xy plane at different transmission distances; Figure 6 (c) is the corresponding transverse normalized intensity distribution. Figure 6 From the simulation results of (a)-(c), it can be seen that the light intensity at the center of the beam is extremely strong while the side lobes of the beam are very weak, and the light intensity is max =15.3μm, the main lobe width is basically unchanged, which meets the basic transmission characteristics of Bessel beams. Its half-maximum full width FWHM is about 440nm, which is very close to the theoretical limit of 400nm, indicating that the designed structure can well realize the function of the axicon to generate Bessel beams.

[0028] Figure 7 The evolution of the metasurface structure in this implementation case as a plane lens with f=15 μm for beam focusing is described. Figure 7 (a) shows the normalized light field distribution on the xz plane after the light beam passes through the metasurface structure; Figure 7 (b) represents the normalized light field distribution on the xy plane near the focus position; Figure 7 (c) The corresponding transverse normalized intensity distribution. Figure 7 (a)-(c) show that the plane lens provides strong focusing ability near the designed focusing position f = 15.4μm, and obtains a highly symmetrical focal spot. The full width at half maximum (FWHM) of the focal spot is 480nm, close to the diffraction limit value (0.5λ / NA = 467nm), indicating that the designed structure achieves good focusing performance of the plane lens.

[0029] For those skilled in the art, various corresponding changes and modifications can be made according to the above technical solutions and concepts, and all of these changes and modifications should be included in the protection scope of the claims of the present invention.

Claims

1. A wavelength-dependent dual-function all-dielectric metasurface structure, characterized in that: It comprises a substrate layer, an upper nanostructure and a lower nanostructure; the upper nanostructure and the lower nanostructure are respectively arranged on the upper end surface and the lower end surface of the substrate layer, the upper nanostructure is mainly composed of a plurality of elliptical nanocolumns of the same specification but with different arrangement angles, and the lower nanostructure is mainly composed of a plurality of elliptical nanocolumns of another specification and with different arrangement angles; the arrangement angle of each elliptical nanocolumn in the upper nanostructure and the lower nanostructure is determined according to the desired phase distribution; wherein, for circularly polarized light with a set incident wavelength of λ1, the upper nanostructure is an equivalent half-wave plate, and the lower nanostructure is an equivalent full-wave plate; and for circularly polarized light with a set incident wavelength of λ2, the lower nanostructure is an equivalent half-wave plate, and the upper nanostructure is an equivalent full-wave plate; When the incident wavelength λ1 is set to 780nm, the upper nanostructure is an equivalent half-wave plate, and the lower nanostructure is an equivalent full-wave plate; when the incident wavelength λ2 is set to 660nm, the lower nanostructure is an equivalent half-wave plate, and the upper nanostructure is an equivalent full-wave plate; Among them, the specifications of the upper elliptical nanocolumns and the lower elliptical nanocolumns are: the long axis a1 of the upper elliptical nanocolumns is 238nm, the short axis b1 is 70nm, the height h1 is 600nm, and the unit cell size is Sx=Sy=300nm; the long axis a2 of the lower elliptical nanocolumns is 248nm, the short axis b2 is 94nm, the height h2 is 800nm, and the unit cell size is Sx=Sy=300nm.

2. The wavelength-dependent dual-function all-dielectric metasurface structure according to claim 1, characterized in that: The upper nanostructure and the lower nanostructure are both made of materials with high refractive index and low loss.

Images