Design method of on-chip integrated metasurface related to angle multiplexing and application of on-chip integrated metasurface

Abstract

The invention discloses a design method and application of an on-chip integrated metasurface with respect to angle multiplexing, which breaks through the traditional multiplexing in the orthogonal x and y directions by exploring and utilizing the direction dependence of circuitous phase manipulation driven by guided waves; by optimizing and introducing roundabout phase responses of other angles, for all pre-designed beam incident angles, different images can be independently coded on different z planes by combining the characteristics of a Fresnel region multilayer z plane, and on-chip total space 3D holography is demonstrated by using a conjugate relationship of optical responses driven by opposite on-chip illumination. A plurality of holographic images can be observed in the whole space. According to the method, a plurality of angles are introduced through calculation optimization, the optical information storage density is greatly improved, the holographic quality represented by the angle multiplexing holography has low background noise and crosstalk, and it is indicated that the method has wide application prospects in the fields of data storage, 3D display and the like.

Description

Technical Field

[0001] The present invention relates to the fields of micro-nano optics, integrated photonics technology, and optical display, and particularly to a design method and application of an on-chip integrated metasurface for angular multiplexing. Background Art

[0002] As a two-dimensional artificial material, metasurface exhibits great potential due to its excellent ability to manipulate the amplitude, phase, and polarization of light waves in the field of nano-photonics. This ability to manipulate the light field at the sub-wavelength scale has promoted the development of various practical functions, including beam steering and spectral engineering. A typical metasurface interacts with spatially illuminated light waves from free space to provide optical functions. To further manipulate in-plane waves and improve the compactness of optical systems, optical metasurfaces have recently been combined with waveguide-based integrated photonics. Photonic integrated circuits modulate guided light waves by integrating optical devices onto waveguide-based optical chips, which provides a promising approach to meet the needs of next-generation high-speed information processing and communication. Multifunctional metasurfaces integrated on compact photonic integrated circuits show the ability to control off-chip radiation and promote various on-chip functions.

[0003] However, due to the limited waveguide driving method, most holographic multiplexing methods for free-space metasurfaces cannot be directly applied to on-chip integrated metasurfaces. Although several on-chip metasurfaces for multiplexing holography have recently been demonstrated by using the hybridization or superposition of phased arrays, their design strategies limit the construction of high information capacity. Moreover, with the increasing demand for high information capacity, improving the angular multiplexing ability of emerging on-chip holographic applications remains a challenge. Summary of the Invention

[0004] To overcome the deficiencies of the above-mentioned prior art, the present invention provides a design method and application of an on-chip integrated metasurface for angular multiplexing, which is used to improve the multiplexing ability and optical information storage capacity of the on-chip integrated metasurface.

[0005] According to one aspect of the specification of the present invention, a design method of an on-chip integrated metasurface for angular multiplexing is provided, including: Constructing a unit structure for forming an on-chip integrated metasurface, the unit structure including a planar substrate, a waveguide layer located above the planar substrate, and nanostructures disposed on the working surface of the waveguide layer, and the sizes of all the nanostructures included in the on-chip integrated metasurface are the same; Taking the positions of the nanostructures in their respective unit structures as phase influencing factors, introducing multiple incident angles, and iteratively optimizing the positions of the nanostructures at the corresponding incident angles to obtain a designed on-chip integrated metasurface for angular multiplexing.

[0006] As a further technical solution, the nanostructure is a square columnar structure; taking two sides parallel to the working surface of the waveguide layer as the x-axis and y-axis respectively to establish an xoy coordinate system, the periods of the nanostructure in the x-axis direction and y-axis direction are both P. When the waveguide transmission direction is along a specifically designed incident angle, its detour phase modulation is expressed as: φ d +βn; where φ d represents the detour phase within the period, β is the propagation constant related to the wavelength, and βn represents the transmission phase accumulated by the guided wave propagation.

[0007] As a further technical solution, the detour phase is expressed as: φ d = 2πΔd / P d ; where Δd represents the coordinate position of the nanostructure in its respective unit structure along the waveguide transmission direction, and P d is the period of the nanostructure in its respective unit structure along the waveguide transmission direction, and the phase optimization weights corresponding to each transmission direction are the same.

[0008] As a further technical solution, using the simulated annealing or gradient descent algorithm of inverse design, combined with the optical diffraction angular spectrum transmission method, the position of the nanostructure in the metasurface is optimized to obtain the overall phase distribution of the on-chip integrated metasurface.

[0009] As a further technical solution, according to the obtained phase distribution of the on-chip integrated metasurface, combined with the principle of detour phase modulation, the coordinate position of the nanostructure in its respective period along the guided wave transmission direction is obtained.

[0010] As a further technical solution, taking the position of the nanobrick in the unit structure as a phase influencing factor, multiple incident angles are uniformly selected at intervals from 0° to 360°, and after selecting multiple working distances, the position of each nanobrick in the period is optimized.

[0011] As a further technical solution, the calculation and optimization for multiple incident angles and working distances are both the optimization of the position Δx and Δy of the nanobrick in the period.

[0012] As a further technical solution, the material of the planar substrate is silicon dioxide, the material of the waveguide layer is silicon nitride, and the material of the nanostructure is silicon.

[0013] According to one aspect of the specification of the present invention, an on-chip integrated metasurface is provided, which is designed by using the design method of the on-chip integrated metasurface for angle multiplexing described above.

[0014] According to one aspect of the present invention, there is provided an application of an on-chip integrated metasurface for angle multiplexing, wherein a laser of a selected working wavelength is coupled along a plurality of pre-designed waveguide transmission directions to be incident on a waveguide layer in the on-chip integrated metasurface for transmission, and a microscope is used to observe above the on-chip integrated metasurface. In each waveguide transmission direction, a plurality of target holographic images meeting the designed number can be observed in sequence by adjusting the working distance of the objective lens of the microscope.

[0015] Compared with the prior art, the present invention has the following beneficial effects: Compared with the traditional metasurface with circuitous phase encoding that is completely decoupled from the x and y directions, the present invention introduces multiple angles through computational optimization, which greatly improves the optical information storage density. In addition, the holographic quality exhibited by this directional multiplexing holography has low background noise and crosstalk, which indicates that the present invention has broad application prospects in the fields of data storage and 3D display. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, a brief introduction is given below to the drawings used in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 It is a schematic diagram of the arrangement of local nanostructures and their positions in the angle-multiplexed on-chip integrated metasurface provided in an embodiment of the present invention.

[0018] Figure 2 It is a diagram of the simulation results of the three-dimensional holographic projection of the angle-multiplexed on-chip integrated metasurface in an embodiment of the present invention.

[0019] Figure 3 It is a schematic diagram of observing the angle multiplexing measurement of the angle multiplexing on-chip integrated metasurface in an embodiment of the present invention.

[0020] Figure 4 It is a diagram of the experimental results of three-dimensional holographic projection of the angle-multiplexed on-chip integrated metasurface in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] It should be noted that: As the demand for high information capacity increases, improving the angular multiplexing capability of emerging on-chip holographic applications remains a challenge. Therefore, using simple designs and structures to realize on-chip integrated metasurfaces based on angular multiplexing to expand the optical information storage capacity has significant research significance and practical value.

[0022] In order to implement an on-chip integrated metasurface based on angular multiplexing to expand the optical information storage capacity, the present invention designs an on-chip integrated metasurface for angular multiplexing to improve the multiplexing ability of the on-chip integrated metasurface and the optical information storage capacity.

[0023] The length and width of the silicon meta-atoms of the metasurface are both sub-wavelength sizes. The present invention mainly includes the following contents: 1. Construct a unit structure of the on-chip integrated metasurface. The unit structure includes a planar substrate, a waveguide layer above the planar substrate, and nanostructures disposed on the working surface of the waveguide layer. The sizes of all the nanostructures included in the on-chip integrated metasurface are the same; taking the positions of the nanostructures in their respective unit structures as phase influencing factors, by introducing multiple incident angles, optimizing the positions of the nanostructures under the corresponding incident angles, and after iterative optimization, the designed on-chip integrated metasurface for angular multiplexing can be obtained.

[0024] 2. The nanostructure is a square columnar structure; taking two sides parallel to the working surface of the waveguide layer as the x-axis and the y-axis respectively to establish an xoy coordinate system. The periods of the nanostructure along the x-axis direction and the y-axis direction are both P. When the waveguide transmission direction is along a specifically designed incident angle, its phase modulation of detour can be expressed as: φ d + βn; where φ d represents the detour phase within a period, β is the propagation constant related to the wavelength, and βn represents the transmission phase accumulated by the guided wave propagation.

[0025] 3. The detour phase is expressed as: φ d =2πΔd / P d ; where Δd represents the coordinate position of the nanostructure along the waveguide transmission direction in its respective unit structure, and P d is the period of the nanostructure along the waveguide transmission direction in its respective unit structure. The phase optimization weights corresponding to each transmission direction are the same.

[0026] 4. Using the reverse design simulated annealing or gradient descent algorithm, combined with the optical diffraction angular spectrum transmission method, optimize the positions of the nanostructures in the metasurface, and finally the overall phase distribution of the on-chip metasurface can be obtained.

[0027] 5. The material of the planar substrate is silicon dioxide, the material of the waveguide layer is silicon nitride, and the material of the nanostructure is silicon.

[0028] 6. Laser with a selected working wavelength is coupled and incident along multiple pre-designed waveguide transmission directions into the waveguide layer in the on-chip integrated metasurface for transmission. Observation is carried out above the on-chip integrated metasurface using a microscope. Under each waveguide transmission direction, by adjusting the working distance of the objective lens of the microscope, multiple target holographic images meeting the designed quantity can be observed in sequence. Generally speaking, the angle multiplexing on-chip integrated metasurface we proposed can improve the multiplexing ability of the on-chip integrated metasurface, enhance the optical information storage capacity, and has great potential in 3D display.

[0029] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some but not all of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. In addition, the technical features in each embodiment or a single embodiment provided by the present invention can be combined with each other arbitrarily to form a new technical solution. This combination is not restricted by the order of steps and / or the structural composition mode, but must be based on what can be realized by those of ordinary skill in the art. When the combination of technical solutions results in contradictions or cannot be realized, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope required by the present invention.

[0030] The embodiments of the present invention provide a specific implementation process for realizing an angle multiplexing design method based on an on-chip integrated metasurface.

[0031] As an embodiment, the on-chip integrated metasurface is formed by optimizing the positions of the nanobricks. Figure 1 It is a partial schematic diagram of the on-chip integrated metasurface designed in the embodiment. The nanobrick array is arranged on the silicon nitride waveguide layer on the silica transparent substrate. The nanobrick structure is a rectangular columnar structure, and its dimensional parameters include a length L = 90 nm, a width W = 90 nm, and a height H = 380 nm. Taking the directions of two sides parallel to the working surface of the waveguide layer as the x-axis and y-axis respectively to establish an xoy coordinate system, the major axis and minor axis of the nanobrick are both parallel to the working surface of the waveguide layer, and the periods of the unit structure along the x-axis and y-axis are both P = 500 nm.

[0032] Taking the positions of the nanobricks in the unit structure as the phase optimization factors, for multiple incident angles selected at uniform intervals from 0° to 360°, and after selecting multiple working distances, the positions of each nanobrick within the period are optimized. Specifically, the calculation and optimization for multiple incident angles and working distances are both optimizations of the positions Δx and Δy of the nanobricks within the period. When the waveguide transmission direction is along a specific designed incident angle, its folded phase modulation can be expressed as: φ d +βn; where φ d represents the folded phase within the period, β is the propagation constant related to the wavelength, and βn represents the transmission phase accumulated by the guided wave propagation; the folded phase is expressed as: φ d = 2πΔd / P d ; where, Δd represents the coordinate position of the nanostructure along the waveguide transmission direction in its respective unit structure, which can be calculated from the incident angle in combination with Δx and Δy, and P d is the period of the nanostructure along the waveguide transmission direction in its respective unit structure. The phase optimization weights corresponding to each transmission direction are the same.

[0033] The optimization calculation can be divided into two stages. In the first stage, using reverse optimization algorithms (such as simulated annealing algorithm, gradient descent algorithm, etc.) and optical diffraction calculation methods (such as angular spectrum transmission method, etc.), by optimizing multiple incident angles, the folded phase distribution of the on-chip integrated metasurface is calculated. At the same time, using the characteristics of Fresnel diffraction, the design of multiple different holographic images can be realized. Therefore, in the first stage, the phase distribution of the on-chip integrated metasurface can be determined according to the target image. In the second stage, according to the obtained phase distribution of the on-chip integrated metasurface, combined with the principle of folded phase modulation, the coordinate positions of the nanostructures along the guided wave transmission direction within their respective periods are obtained (for example, when the guided wave propagates along the x direction, the coordinate position of the nanostructure in the x direction is adjusted), and finally the complete design of the three-dimensional holographic angle multiplexing on-chip integrated metasurface is realized.

[0034] As Figure 2 shown by the optimized holographic calculation results, eight incident angles and three working distances in the z direction are selected for the optimization of the holographic image. By optimizing the positions of the nanobricks, the distances along the incident angle of the waveguide can be calculated respectively in combination with different incident angles to modulate the folded phase. For this kind of angle multiplexing design method, the storage capacity of optical information can be greatly expanded.

[0035] Figure 3It is a diagram of the device for experimental measurement of holographic image observation. The laser is incident along a pre-designed direction and coupled into the waveguide. By adjusting the objective lens at the designed working distance, the holographic image can be observed. By changing the working distance of the objective lens in the z direction, multiple designed holographic images can be observed, forming a three-dimensional holographic image. And by changing the incident angle, the switching of the target holographic image can be achieved. At each incident angle, there are multiple working distances in the z direction, and the measurement results are as Figure 4 shown.

[0036] In summary, through exploring and utilizing the direction dependence of the waveguide-driven detour phase manipulation, the present invention breaks through the traditional multiplexing in the orthogonal x and y directions. By optimizing, the detour phase responses at other angles are introduced. For all pre-designed beam incident angles, combined with the characteristics of the Fresnel zone multi-layer z plane, different images can be independently encoded in different z planes. Moreover, by utilizing the conjugate relationship of the optical responses driven by the opposite on-chip illuminations to demonstrate on-chip full-space 3D holography, it enables the observation of multiple holographic images in the full space. Compared with the traditional metasurface that uses the detour phase encoding with complete decoupling in the x and y directions, by computationally optimizing and introducing multiple angles, the optical information storage density is greatly improved. And this angle multiplexing holography exhibits holographic quality with low background noise and crosstalk, indicating that the present invention has broad application prospects in the fields of data storage and 3D display, etc.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features. And these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A design method for an on-chip integrated metasurface with angular multiplexing, characterized in that Including: Constructing a unit structure for an on-chip integrated metasurface, the unit structure including a planar substrate, a waveguide layer located above the planar substrate, and nanostructures disposed on a working surface of the waveguide layer, and all the nanostructures included in the on-chip integrated metasurface having the same size; Taking the positions of the nanostructures in their respective unit structures as phase influencing factors, introducing multiple incident angles, and iteratively optimizing the positions of the nanostructures at the corresponding incident angles to obtain a designed on-chip integrated metasurface with angle multiplexing.

2. The design method of the on-chip integrated metasurface for angular multiplexing according to claim 1, wherein The nanostructure is a square columnar structure; taking two sides parallel to the working surface of the waveguide layer as the x-axis and the y-axis respectively to establish an xoy coordinate system, the periods of the nanostructure in the x-axis direction and the y-axis direction are both P. When the waveguide transmission direction is along a specifically designed incident angle, its detour phase modulation is expressed as: φ d +βn; where φ d represents the detour phase within the period, β is the propagation constant related to the wavelength, and βn represents the transmission phase accumulated by the guided wave propagation.

3. The design method of the on-chip integrated metasurface for angular multiplexing according to claim 2, wherein The detour phase is expressed as: φ d = 2πΔd / P d ; where Δd represents the coordinate position of the nanostructure along the waveguide transmission direction in its respective unit structure, and P d is the period of the nanostructure along the waveguide transmission direction in its respective unit structure, and the phase optimization weights corresponding to each transmission direction are the same.

4. The design method of the on-chip integrated metasurface for angular multiplexing according to claim 1, wherein Using an inverse design simulated annealing or gradient descent algorithm, and combining with an optical diffraction angular spectrum transmission method to optimize the positions of the nanostructures in the metasurface to obtain the overall phase distribution of the on-chip integrated metasurface.

5. The design method of the on-chip integrated metasurface for angular multiplexing according to claim 4, wherein According to the obtained phase distribution of the on-chip integrated metasurface, and combining with the principle of detour phase modulation, obtaining the coordinate positions of the nanostructures along the waveguide transmission direction in their respective periods.

6. The design method of the on-chip integrated metasurface for angular multiplexing according to claim 1, characterized in that Taking the positions of the nanobricks in the unit structure as phase influencing factors, selecting multiple incident angles at uniform intervals from 0° to 360°, and optimizing the positions of each nanobrick in the period after selecting multiple working distances.

7. The design method of the on-chip integrated metasurface for angular multiplexing according to claim 6, wherein The calculation and optimization for multiple incident angles and working distances are both the optimization of the positions Δx and Δy of the nanobricks in the period.

8. The design method of the on-chip integrated metasurface for angular multiplexing according to claim 1, characterized in that The material of the planar substrate is silicon dioxide, the material of the waveguide layer is silicon nitride, and the material of the nanostructures is silicon.

9. An on-chip integrated metasurface, characterized in that, Designed by using the design method described in any one of claims 1-8.

10. An application of an on-chip integrated metasurface for angular multiplexing, wherein the on-chip integrated metasurface is designed by using the design method described in any one of claims 1-8, characterized in that, Using a laser with a selected working wavelength to be coupled and incident along a plurality of pre-designed waveguide transmission directions into the waveguide layer in the on-chip integrated metasurface for transmission, and observing above the on-chip integrated metasurface by using a microscope. Under each waveguide transmission direction, by adjusting the working distance of the objective lens of the microscope, a plurality of target holographic images satisfying the designed quantity can be sequentially observed.

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