On-chip metasurface and design method thereof, and method for realizing color routing based on on-chip metasurface

Abstract

The invention belongs to the technical field of micro-nano optics, and discloses an on-chip metasurface and a design method thereof, and a method for realizing color routing based on the on-chip metasurface. A unit structure of the on-chip metasurface comprises a nano structure layer, an optical waveguide layer and a dielectric substrate layer, wherein the nano structure layer is composed of diatomic nano bricks and has geometric asymmetry; a plurality of diatomic nano bricks contained in the on-chip metasurface form one or more groups of nano brick arrays; the geometric sizes of all diatomic nano bricks contained in each group of nano brick arrays are the same, and the geometric sizes of the diatomic nano bricks contained in different groups of nano brick arrays are different; each group of nano brick arrays is used for selectively extracting a certain narrow-band spectrum, and the nano brick arrays of different groups are used for selectively extracting different spectrum ranges; and coding the color information of the image into the on-chip metasurface by taking the geometric dimension of the diatomic nano brick as an adjusting parameter. According to the invention, wavelength selective extraction and multicolor routing image display are realized based on the on-chip metasurface.

Description

Technical Field

[0001] The present invention belongs to the field of micro-nano optical technology, and more specifically, relates to an on-chip metasurface and a design method thereof, and a method for realizing color routing based on the on-chip metasurface. Background Art

[0002] In the development of chip-integrated and miniaturized nanophotonic devices, the integration of metasurfaces into optical waveguides as a compact platform for manipulating and guiding planar light waves has attracted widespread attention from researchers. Recently, by carefully designing subwavelength nanostructures on waveguides, on-chip integrated metasurfaces can precisely control the amplitude, phase, and polarization of extracted light and realize a variety of functions, including directional beam steering, on-chip superlenses, vortex beam generators, metasurface holography, and screen displays. Due to the on-chip propagation scheme, this technology has the unique advantages of no zero-order background interference, multi-level cascading capabilities, and compatibility with other micro-on-chip devices, which can promote the creation of advanced chip-integrated metasurface optical devices.

[0003] On-chip metasurfaces have achieved considerable success in phase modulation, using mechanisms such as resonant phase or detour phase for phase manipulation; amplitude modulation is achieved through nanostructure size or dual metaatom interference; polarization control utilizes geometric phase and other phase co-modulation mechanisms. Despite the above progress, these methods have limited control over the spectral properties of the outcoupled light and cannot achieve wavelength-selective light extraction. Typically, when the waveguide is perturbed by on-chip metaatoms, the extracted light waves exhibit broadband response and do not have wavelength-selective properties. To date, there is still no feasible strategy for on-chip integrated metasurfaces to achieve wavelength-selective extraction.

[0004] Wavelength modulation and selective extraction control on waveguide-integrated metasurface platforms are crucial for advancing integrated photonic applications such as wavelength division multiplexing and color routing. Therefore, unlocking the freedom of on-chip wavelength selective extraction is a key challenge in this field.

[0005] In addition, it is worth mentioning that although traditional free-space metasurfaces or multilayer films can realize color filters and routing functions, these approaches are based on spatial multiplexing and suffer from severe energy utilization efficiency (EUE) loss because a considerable portion of the incident light outside the wavelength filter passband is wasted. Summary of the invention

[0006] The present invention solves the problem in the prior art that wavelength selective extraction cannot be achieved based on the on-chip metasurface by providing an on-chip metasurface and a design method thereof, and a method for achieving color routing based on the on-chip metasurface.

[0007] In a first aspect, the present invention provides a method for designing an on-chip metasurface, comprising the following steps:

[0008] Constructing a unit structure of an on-chip metasurface, the unit structure includes a nanostructure layer, an optical waveguide layer, and a dielectric substrate layer arranged in sequence from top to bottom, the nanostructure layer is composed of diatomic nanobricks, and the diatomic nanobricks have geometric asymmetry; a plurality of diatomic nanobricks contained in the on-chip metasurface constitute one or more groups of nanobrick arrays; all diatomic nanobricks contained in each group of nanobrick arrays have the same geometric size, and diatomic nanobricks contained in nanobrick arrays of different groups have different geometric sizes; each group of nanobrick arrays is used for selective extraction of a narrowband spectrum, and nanobrick arrays of different groups are used for selective extraction of different spectral ranges;

[0009] The geometric size of the diatomic nanobricks in each group of nanobrick arrays is used as an adjustment parameter to encode the color information of the image into the on-chip metasurface.

[0010] Preferably, an xoy coordinate system is established in the direction parallel to the two sides of the working surface of the optical waveguide layer, and the rotation angles of two nanobricks in the diatomic nanobricks in the i-th group of nanobrick array about the y-axis are θ i , 180°-θ i , and 0°<θ i <90°; the rotation angles of all diatomic nanobricks contained in each group of nanobrick arrays are designed the same.

[0011] Preferably, when the several diatomic nanobricks contained in the on-chip metasurface constitute multiple groups of nanobrick arrays, multiple nanobrick arrays of different types are horizontally cascaded, and the on-chip metasurface selectively extracts waveguides of different wavelengths from different spatial positions to free space for color routing.

[0012] Preferably, the diatomic nanobrick is composed of two rectangular nanobricks with the same geometric size; the geometric size of the diatomic nanobrick in the i-th group of nanobrick array is set to: L i =L 0 ×S i , W i =W 0 ×S i , P i =P x =P y =P 0 ×S i Among them, L i is the length of the diatomic nanobrick in the i-th nanobrick array, W i is the width of the diatomic nanobrick in the i-th group of nanobrick array, P i is the period of the diatomic nanobricks in the i-th group of nanobrick arrays, Px and P y are the periods of the diatomic nanobricks along the x-axis and y-axis, L 0 is the reference length, W 0 is the reference width, P 0 is the base period, S i is the scaling factor of the ith nanobrick array, S i >0; different groups of nanobrick arrays have different scaling factors; the wavelength corresponding to the spectral peak extracted by the nanobrick array increases with the increase of the scaling factor; the geometric size of the diatomic nanobricks in each group of nanobrick arrays is determined according to the color information of the image.

[0013] Preferably, the reference length and the reference width are both sub-wavelength sizes; the waveguide propagates along the x-axis, and the local displacement between the diatomic nanobricks along the x-axis is P x / 2.

[0014] Preferably, the on-chip metasurface design method further comprises: using the rotation angle of the diatomic nanobricks in each group of nanobrick arrays as an adjustment parameter, and encoding the intensity information of the image into the on-chip metasurface.

[0015] Preferably, the asymmetry factor α of the i-th group of nanobrick arrays is i Defined as α i = sinθ i ; The spectral intensity extracted from the nanobrick array increases with the increase of the asymmetry factor; The rotation angle design of the diatomic nanobricks in each group of nanobrick arrays is determined based on the intensity information of the image.

[0016] In a second aspect, the present invention provides an on-chip metasurface obtained by using the above-mentioned on-chip metasurface design method.

[0017] In the third aspect, the present invention provides a method for realizing color routing based on an on-chip metasurface, which encodes the color information of an image into the on-chip metasurface in a spatial mapping manner, wherein a plurality of diatomic nanobricks contained in the on-chip metasurface constitute multiple groups of nanobrick arrays, and multiple nanobrick arrays of different types are horizontally cascaded; the on-chip metasurface is used to selectively extract waveguides of different wavelengths from different spatial positions to free space for color routing, thereby realizing image display of multi-color routing.

[0018] Preferably, the color information and intensity information of the image are encoded into the on-chip metasurface to achieve image display with multi-color routing and controllable spectral intensity.

[0019] One or more technical solutions provided in the present invention have at least the following technical effects or advantages:

[0020] (1) The unit structure of the on-chip metasurface in the present invention includes a nanostructure layer, an optical waveguide layer and a dielectric substrate layer arranged in sequence from top to bottom, the nanostructure layer is composed of diatomic nanobricks, and the diatomic nanobricks have geometric asymmetry; the diatomic nanobricks contained in the on-chip metasurface constitute one or more groups of nanobrick arrays; the geometric dimensions of all diatomic nanobricks contained in each group of nanobrick arrays are the same, and the geometric dimensions of diatomic nanobricks contained in nanobrick arrays of different groups are different; each group of nanobrick arrays is used for selective extraction of a certain narrowband spectrum, and nanobrick arrays of different groups are used for selective extraction of different spectral ranges; the present invention uses the geometric dimensions of diatomic nanobricks in each group of nanobrick arrays as adjustment parameters to encode the color information of the image into the on-chip metasurface. The diatomic nanobricks in the present invention have geometric asymmetry, which can cause the guided mode to leak into the free space. By adjusting the geometric dimensions of the diatomic nanobricks, the selective extraction of the guided wave into the free space can be achieved, and the selective extraction of a certain wavelength range or multiple groups of wavelength ranges can be achieved. That is, the present invention realizes wavelength selective extraction based on the on-chip metasurface.

[0021] (2) Based on the above scheme, the rotation angle of the diatomic nanobrick is adjusted to achieve intensity-adjustable wavelength-selective extraction.

[0022] (3) When the on-chip metasurface provided by the present invention comprises a plurality of diatomic nanobricks forming a plurality of nanobrick arrays, an on-chip color router using a cascade multiplexing strategy is obtained, which can be applied to image display. All the extracted energy is fully utilized to construct the corresponding wavelength channels. The design of the present invention overcomes the limitation of spatial multiplexing utilization efficiency. When the propagation loss is negligible, there will be no loss of energy utilization efficiency. In addition, due to the on-chip propagation mechanism, the generated image display can effectively suppress zero-order background light interference. The on-chip metasurface proposed by the present invention has the advantages of miniaturization and integration, and has great potential in the application of information routing in the next generation of wearable display devices, wavelength division multiplexing and integrated photonic systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the unit structure of the on-chip metasurface constructed by the present invention.

[0024] Figure 2 Schematic diagram of a diatomic nanobrick composed of two parallel and two inclined nanobricks, respectively, corresponding to the transition from the BIC mode to the quasi-BIC mode.

[0025] Figure 3 is a schematic diagram of the nanobrick array.

[0026] Figure 4 is a schematic diagram of a diatomic nanobrick. Figure 4 (a) and Figure 4 (b) is when TE 0 When the mode is incident from the x direction, the electric field intensity distribution in the xy plane is simulated under the two conditions of rotation angle θ = 0° and θ = 20°; Figure 4 (c) shows the electric field intensity distribution in the yz plane when the rotation angle θ=0°, θ=20° and θ=40°.

[0027] Figure 5 is the extracted spectrum obtained by simulation. Among them, Figure 5 (a) shows the simulated extracted spectral profile of the nanobrick array when the rotation angle changes from 0° to 20°; Figure 5 (b) is the simulated extracted spectrum of the nanobrick array when the length L changes from 120nm to 180nm; Figure 5 (c) is the extracted spectrum line graph of the nanobrick array when the rotation angle θ = 0°, θ = 10° and θ = 20°; Figure 5 (d) in the figure is the extracted spectral line graph of the nanobrick array when the scaling factor S changes from 0.85 to 1.

[0028] Figure 6 is the simulated electric field intensity distribution of different wavelengths extracted from the waveguide. Figure 6 (a) is the simulated electric field intensity distribution with a wavelength of 572 nm extracted from the waveguide; Figure 6 (b) is the simulated electric field intensity distribution with a wavelength of 608 nm extracted from the waveguide; Figure 6 (c) in the figure is the simulated electric field intensity distribution with a wavelength of 652 nm extracted from the waveguide.

[0029] Figure 7 A conceptual illustration of an on-chip metasurface capable of color routing.

[0030] Figure 8 is the extracted spectrum of arrays of different sizes obtained by simulation. Among them, Figure 8 (a) in the figure is the extracted spectra of simulated arrays of different sizes, where the number N along the propagation direction (x-axis) varies from 1 to 50; Figure 8 (b) is from Figure 8 A line graph of the maximum extraction efficiency is plotted in the spectrum in (a).

[0031] Fig. 9 is the extracted spectrum of different array samples measured experimentally. Among them, Fig. 9 (a) shows the experimental extracted spectra of different arrays when the rotation angle θ changes from 0° to 30°; Fig. 9 (b) shows the experimental extracted spectra of different arrays when the scaling factor S varies from 0.88 to 1.

[0032] Fig.10This is a conceptual diagram corresponding to a method for realizing color routing based on an on-chip metasurface provided by the present invention.

[0033] Fig.11 It is a measurement device and corresponding spectrum based on on-chip metasurface to realize color routing. Fig.11 (a) shows the experimental measurement setup used to characterize on-chip near-field micro-imaging display. Fig.11 (b) is a comparison of the extracted spectral profiles obtained by measuring the traditional grating coupler and the solution of the present invention.

[0034] Fig.12 This is a functional demonstration of the on-chip metasurface provided by the present invention in terms of color routing. Fig.12 (a) to (c) show the functional schematic diagrams of the conventional grating coupler and the solution of the present invention when the guided waves with wavelengths of 640 nm and 530 nm propagate simultaneously from the x-direction, as well as the optical microscope images of the corresponding designed "R" and "G" letters; Fig.12 (d) to (f) show the functional schematic diagrams of the conventional grating coupler and the solution of the present invention when the guided wave with a wavelength of 640 nm propagates from the x direction, as well as the optical microscope images of the corresponding designed "R" and "G" letters; Fig.12 (g) to (i) show the functional schematics of the conventional grating coupler and the solution of the present invention when a guided wave with a wavelength of 530 nm propagates from the x-direction, as well as optical microscope images of the corresponding designed "R" and "G" letters.

[0035] Fig.13 This is an experimental demonstration of multi-color image display based on color pixels of on-chip metasurface. Fig.13 (a) shows a schematic diagram of designing a three-dimensional multi-color nanoprinted on-chip metasurface pattern to achieve simultaneous adjustment of color and brightness; Fig.13 (b) shows the captured stereoscopic “3D” optical image (Demonstration 1).

[0036] Fig.14 This is an experimental demonstration of a two-color grayscale image of “red flowers and green leaves” based on an on-chip metasurface (Demonstration 2).

[0037] Among them, 1-nanobrick, 2-optical waveguide layer, 3-dielectric substrate layer. DETAILED DESCRIPTION

[0038] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0039] Embodiment 1:

[0040] Embodiment 1 provides a method for designing an on-chip metasurface, comprising the following steps:

[0041] Step 1: Construct the unit structure of the on-chip metasurface.

[0042] The unit structure comprises a nanostructure layer, an optical waveguide layer and a dielectric substrate layer arranged in sequence from top to bottom, the nanostructure layer is composed of diatomic nanobricks, and the diatomic nanobricks have geometric asymmetry.

[0043] The plurality of diatomic nanobricks contained in the on-chip metasurface form a group of nanobrick arrays. All diatomic nanobricks contained in the group of nanobrick arrays have the same geometric dimensions. The group of nanobrick arrays is used for selective extraction of a narrow-band spectrum.

[0044] Step 2: Using the geometric dimensions of the diatomic nanobricks in the group of nanobrick arrays as adjustment parameters, the color information of the image is encoded into the on-chip metasurface.

[0045] The diatomic nanobrick is composed of two rectangular nanobricks with the same geometric size. An xoy coordinate system is established in the direction parallel to the two sides of the working surface of the optical waveguide layer. The rotation angles of the two nanobricks in the diatomic nanobricks in the nanobrick array about the y-axis are θ and 180°-θ respectively, and 0°<θ<90°; the rotation angles of all diatomic nanobricks contained in the nanobrick array are designed to be the same.

[0046] In a preferred solution, it may also include: using the rotation angle of the diatomic nanobricks in the group of nanobrick arrays as an adjustment parameter to encode the intensity information of the image into the on-chip metasurface.

[0047] Specifically, while keeping the geometric dimensions of the structure unchanged, the intensity of the extracted spectrum can be adjusted by changing the geometric asymmetry of the diatomic nanobrick, that is, changing the rotation angle θ. For example, as the rotation angle θ increases from 0° to 20°, the extracted intensity increases accordingly.

[0048] The on-chip metasurface in Example 1 is an on-chip non-local metasurface that supports symmetry-protected bound states (BICs) in a continuum. When the rotation angle θ of the diatomic nanobrick is 0°, it is in an undisturbed symmetry-protected BIC mode and has a larger wave vector, which limits the guided wave to propagate within the waveguide instead of being extracted into the free space. As asymmetry gradually arises (θ>0°), disturbances are applied to the di-meta-atomic pairs, and the effective lattice period doubles, causing the guided mode to leak into the free space. The diatomic nanobricks (i.e., di-meta-atomic pairs) in Example 1 have geometric asymmetry, 0°<θ<90°, so the guided mode can leak into the free space. By adjusting the geometric dimensions of the diatomic nanobricks, selective extraction of the guided wave into the free space can be achieved, that is, wavelength-selective light extraction can be achieved. In the preferred embodiment in which the rotation angle of the diatomic nanobricks is adjusted, narrow-band spectral extraction with adjustable intensity can be achieved.

[0049] Embodiment 2:

[0050] Embodiment 2 provides a method for designing an on-chip metasurface, comprising the following steps:

[0051] Step 1: Construct the unit structure of the on-chip metasurface.

[0052] The unit structure comprises a nanostructure layer, an optical waveguide layer and a dielectric substrate layer arranged in sequence from top to bottom, the nanostructure layer is composed of diatomic nanobricks, and the diatomic nanobricks have geometric asymmetry.

[0053] The several diatomic nanobricks contained in the on-chip metasurface constitute multiple groups of nanobrick arrays; all the diatomic nanobricks contained in each group of nanobrick arrays have the same geometric dimensions, and the diatomic nanobricks contained in different groups of nanobrick arrays have different geometric dimensions; each group of nanobrick arrays is used to selectively extract a narrow-band spectrum, and different groups of nanobrick arrays are used to selectively extract different spectral ranges.

[0054] Step 2: Using the geometric dimensions of the diatomic nanobricks in each group of nanobrick arrays as adjustment parameters, the color information of the image is encoded into the on-chip metasurface.

[0055] Among them, multiple nanobrick arrays of different groups are horizontally cascaded, and the on-chip metasurface selectively extracts guided waves of different wavelengths from different spatial locations into free space for color routing.

[0056] The diatomic nanobrick is composed of two rectangular nanobricks with the same geometric size; the geometric size of the diatomic nanobrick in the i-th group of nanobrick array is set to: L i =L 0 ×S i , W i =W0 ×S i , P i =P x =P y =P 0 ×S i Among them, L i is the length of the diatomic nanobrick in the i-th nanobrick array, W i is the width of the diatomic nanobrick in the i-th group of nanobrick array, P i is the period of the diatomic nanobricks in the i-th group of nanobrick arrays, P x and P y are the periods of the diatomic nanobricks along the x-axis and y-axis, L 0 is the reference length, W 0 is the reference width, P 0 is the reference period, S i is the scaling factor of the ith nanobrick array, S i >0; different groups of nanobrick arrays have different scaling factors; the wavelength corresponding to the spectral peak extracted by the nanobrick array increases with the increase of the scaling factor; the geometric size of the diatomic nanobricks in each group of nanobrick arrays is determined according to the color information of the image.

[0057] By precisely adjusting the scaling factor of the nanobrick array, that is, overall increasing or decreasing the period and size of the unit structure, wavelength-selective extraction and routing of the outcoupled light can be achieved, resulting in narrowband spectral extraction.

[0058] The reference length and the reference width are both sub-wavelength sizes; the waveguide propagates along the x-axis, and the local displacement between the diatomic nanobricks along the x-axis is P x / 2.

[0059] In a preferred solution, it may also include: using the rotation angle of the diatomic nanobricks in each group of nanobrick arrays as an adjustment parameter, and encoding the intensity information of the image into the on-chip metasurface.

[0060] The asymmetry factor α of the i-th group of nanobrick arrays i Defined as α i = sinθ i ; The spectral intensity extracted from the nanobrick array increases with the increase of the asymmetry factor; The rotation angle design of the diatomic nanobricks in each group of nanobrick arrays is determined based on the intensity information of the image.

[0061] The difference between Example 2 and Example 1 is that the on-chip metasurface of Example 2 comprises several diatomic nanobricks forming multiple groups of nanobrick arrays, that is, Example 2 adopts cascade multiplexing to achieve wavelength selective light extraction, and the on-chip metasurface can also achieve multi-color routing.

[0062] Embodiment 2 can achieve selective extraction and routing of guided waves into free space by precisely adjusting the geometric asymmetry and scaling factor of the diatomic nanobricks in multiple groups of nanobrick arrays, while generating intensity-adjustable narrowband spectral extraction.

[0063] Embodiment 3:

[0064] Embodiment 3 provides an on-chip metasurface, which is obtained by using the design method of the on-chip metasurface described in Embodiment 1 or Embodiment 2.

[0065] Embodiment 4:

[0066] Embodiment 4 provides a method for realizing color routing based on an on-chip metasurface, which encodes the color information of an image into the on-chip metasurface as described in Embodiment 2 by means of spatial mapping, wherein a plurality of diatomic nanobricks contained in the on-chip metasurface constitute multiple groups of nanobrick arrays, and multiple nanobrick arrays of different types are horizontally cascaded; the on-chip metasurface is used to selectively extract waveguides of different wavelengths from different spatial positions to free space for color routing, thereby realizing multi-color routing image display.

[0067] On the basis of the above scheme, the intensity information of the image can also be encoded into the on-chip metasurface, that is, the preferred scheme encodes the color information and intensity information of the image into the on-chip metasurface to realize the image display of multi-color routing with controllable spectral intensity.

[0068] The preferred scheme encodes the color and intensity information of the image into dual-metastructure atom pairs with different geometric sizes and rotation angles, and demonstrates the realization of multi-color routing image display by horizontally cascading different BIC-assisted pixels.

[0069] The present invention is further described below in conjunction with parameters.

[0070] See also Figure 1 The unit structure of the on-chip metasurface (i.e., the on-chip non-localized metasurface) includes a nanostructure layer, an optical waveguide layer 2, and a dielectric substrate layer 3 arranged in sequence from top to bottom. The nanostructure layer is composed of diatomic nanobricks, for example, a pair of tilted amorphous silicon (α-Si) nanobricks 1, and the long axis size (i.e., length) of the nanobrick 1 is L, the short axis size (i.e., width) is W, and the height is H, which can be 380nm. θ is the tilt angle (i.e., rotation angle) of the long axis of a nanobrick in the diatomic nanobrick relative to the y axis. The periods along the x and y directions are respectively represented by P x and P y The optical waveguide layer 2 may be made of Si 3 N 4The planar waveguide has a thickness of 220 nm and a relatively high effective refractive index (n is about 2.05). The dielectric substrate layer 3 can be made of SiO with a thickness of 500 μm. 2 Substrate.

[0071] The key working principle of the on-chip color routing metasurface (i.e., BIC-assisted router) provided by the present invention is based on the concept of quasi-bound states in a continuous medium (q-BIC). The inversion symmetry of the dimetatom pairs in the plane is broken by applying a spatially varying perturbation (see Figure 2 ), which can convert the guided wave mode (bound wave) into a free-space light field mode (quasi-bound wave). Figure 2 where θ is the tilt angle of the BIC-assisted diatomic nanobricks, and the local displacement between diatomic nanobricks along the x direction is designed to be P x / 2. Specifically, the symmetry-protected BIC structure (θ=0°) is in an undisturbed state with a large wave vector, which restricts the guided wave to propagate within the waveguide instead of being extracted into free space. As asymmetry gradually arises (θ>0°), perturbations are applied to the dual-metasilicon atom pairs, doubling the effective lattice period, causing the guided mode to leak into free space due to the perturbation of the doubling period.

[0072] Figure 3 The q-BIC nanostructure array designed by the present invention is demonstrated in TE 0 3D schematic diagram under mode incidence conditions. Then we calculated the in-plane electric field strength |E| of the double super-atomic pair. 2 The distribution is simulated to show the patterns of BIC and q-BIC being excited on the periodic array. Specifically, Figure 4 (a) and Figure 4 (b) is when TE 0 When the mode is incident from the x direction, the simulated electric field intensity (|E|) in the xy plane at the rotation angle θ = 0° and θ = 20° 2 ) distribution. The corresponding parameters are L = 130nm, W = 65nm, P x =P y =400nm and H=380nm. Figure 4 (c) shows the electric field intensity distribution (|E|) in the yz plane when the rotation angle θ = 0°, θ = 20°, and θ = 40°. 2 ).

[0073] The photon leakage behavior of the symmetry-protected metasurface is fundamentally determined by the asymmetry factor α, which is defined as the sine of the rotation angle θ, i.e., α = sinθ. The asymmetry factor α controls the extracted light intensity, allowing the intensity of the spectrum to be tuned by changing the rotation angle θ. The simulated electric field intensity (|E|) on the yz cross section at θ = 0°, 20°, and 40°2 ) distribution, corresponding to Figure 4 (c) in the figure shows a clear intensity variation, indicating that the greater the asymmetry, the stronger the off-chip extraction intensity.

[0074] Figure 5 (a) is the extracted spectral profile of the simulated on-chip BIC dual-metastructure atomic array when the rotation angle changes from 0° to 20°, that is, Figure 5 The simulated 2D extracted spectrum shown in (a) as a function of θ shows sharp peaks against a low spectral background in the broadband visible range.

[0075] Figure 5 (c) in the figure is a detailed extracted spectrum display, specifically the extracted spectrum line diagram of the BIC dual-meta-atomic array when the rotation angle θ = 0°, θ = 10° and θ = 20°. It can be seen that as the rotation angle θ increases from 0° to 20°, the extracted intensity increases accordingly, confirming that the extracted spectrum intensity can be adjusted by adjusting the asymmetry parameter.

[0076] In addition to intensity control, wavelength-selective extraction of the outcoupled light can also be achieved by tuning the size of the dual metaatom pair. Figure 5 (b) is the simulated extracted spectrum of the BIC dual superstructure atomic array when the length L changes from 120nm to 180nm. The corresponding parameters are W = 60nm, P x =P y =400nm and H = 380nm. It can be seen that as the length L increases from 120nm to 180nm (the width is fixed at 60nm), the peak position of the simulated extracted spectrum red-shifts from 602nm to 680nm.

[0077] We further numerically investigate the dependence of the extracted spectra on the unit cell size multiplied by the scaling factor S (given by L = L 0 ×S,W=W 0 ×S、P=P 0 ×S given), Figure 5 (d) shows the extracted spectrum line diagram of the BIC dual superstructure atomic array when the scaling factor S changes from 0.85 to 1, while keeping θ fixed at 20°. When S = 1, the corresponding parameter is L 0 =160nm, W 0 =60nm and P 0 =400nm. The results show that when θ = 20°, adjusting S from 0.85 to 1 will shift the spectral peak from 580nm to 660nm.

[0078] To illustrate the unique color routing function more intuitively, we predefine an array of dimetatom pairs with a continuously gradient length L varying from 95 nm to 170 nm (keeping W fixed at 60 nm), and arrange the BIC-assisted dimetatom pairs along the propagation direction (x-axis). Figure 6 is the simulated electric field intensity (|E|) at wavelengths of 572 nm, 608 nm, and 652 nm extracted from the waveguide in the embodiment of the present invention. 2 ) distribution, where Figure 6 (a) is the simulated electric field intensity distribution with a wavelength of 572 nm extracted from the waveguide; Figure 6 (b) is the simulated electric field intensity distribution with a wavelength of 608 nm extracted from the waveguide; Figure 6 (c) is the simulated electric field intensity distribution with a wavelength of 652nm extracted from the waveguide, and the black arrow indicates the propagation direction of the guided wave. The simulated electric field intensity |E| of the array on the xz cross section 2 The distribution shows that guided waves with different wavelengths will be strongly extracted into free space from their respective different locations. Therefore, this on-chip cascade can selectively extract guided waves with different wavelengths from different spatial locations into free space for color routing.

[0079] Compared to free-space metasurfaces, the on-chip metasurfaces provided by the present invention have a distinct advantage in horizontally cascading multiple structures. This allows the integration of periodic BIC-assisted arrays to selectively extract and route guided waves, such as Figure 7 When the broadband light guide encounters the red extraction array, light waves of other colors (such as yellow and green) continue to propagate without energy efficiency loss. It is worth noting that the on-chip extraction efficiency itself is relatively low (less than about 7%); however, the emphasis here on no energy efficiency loss means that due to the on-chip cascading strategy, all the extracted energy is fully utilized to construct the corresponding wavelength channels without energy blocking or waste caused by traditional spatial multiplexing schemes.

[0080] In addition, we further numerically study the BIC-assisted extracted spectra of M × N unit cell periodic arrays, where N varies from 1 to 50. Here, M and N are the row number (y direction) and column number (x direction) of the array, respectively, where M approaches infinity due to the periodic boundary conditions in the y direction. Specifically, Figure 8 (a) in the figure is the extracted spectra of simulated arrays of different sizes, where the number N along the propagation direction (x-axis) varies from 1 to 50; Figure 8 (b) is from Figure 8The maximum extraction efficiency is plotted against the spectrum in (a). The spectra and maximum extraction efficiency of these arrays show that the peak extraction increases as the array size N along the x-direction increases. Note that after N>20, the extraction efficiency peak reaches saturation (about 0.5) and does not increase significantly even with increasing array size.

[0081] To experimentally demonstrate narrowband wavelength selective extraction and intensity modulation in an on-chip nonlocal metasurface, we fabricated the designed samples using plasma enhanced chemical vapor deposition (PECVD) and conventional electron beam lithography (EBL). A broadband polarized laser (500nm to 800nm) was end-faceted coupled into the waveguide using a fiber collimator. For a fixed scaling factor (S=1), as the asymmetry parameter increases, Fig. 9 (a) shows the experimental extraction spectra of different arrays when the rotation angle θ changes from 0° to 30°, showing that the extracted intensity increases simultaneously, thus experimentally verifying the continuous intensity adjustment by introducing an asymmetric parameter. We further prepared another set of on-chip samples with the scaling factor S varying from 0.88 to 1 (keeping the rotation angle θ fixed at 25°). Fig. 9 (b) shows the experimental extracted spectra of different arrays when the scaling factor S changes from 0.88 to 1. It can be seen that as the scaling factor increases, the measured extraction peak position red-shifts from 570nm to 630nm, which is consistent with the theoretical change trend.

[0082] To further explore the selective extraction and routing capabilities, we demonstrated its potential application in micro-image display. Fig.10 A conventional on-chip grating outcoupler (GO) is schematically compared with the proposed BIC-assisted router (BIC-RO), highlighting the transition from broadband outcoupling to narrowband wavelength selective extraction. Using our designed on-chip BIC-assisted dual meta-atom array, we fabricated solid color fonts of the letters “R” and “G”, as well as the traditional GO-formed “R” and “G” letters for comparison. To evaluate the on-chip color routing display performance, we used an optical microscope with a 50x objective and a CCD camera to focus near the sample surface and capture the light intensity distribution extracted from the on-chip pattern. Fig.11 (a) shows the experimental measurement setup used to characterize on-chip near-field micro-image display, which mainly includes laser, polarizer, lens, objective lens and CCD. Fig.11(b) shows the experimental extraction spectra of green and red RO by conventional GO and the BIC-assisted router proposed in the present invention, confirming that BIC-RO achieves narrowband (about 20nm) wavelength selective extraction, while conventional GO is broadband (about 60nm) outcoupling. GO composed of a single meta-atomic pixel is deliberately used as a comparison because its extraction intensity at red and green wavelengths lacks contrast.

[0083] To further illustrate the practical selective extraction and routing capabilities of the on-chip BIC-assisted metasurface, Fig.12 The figure schematically shows the extraction performance of the conventional GO and the BIC-RO proposed in the present invention under different wavelength combinations of guided wave incidence. When the red (640nm) and green (530nm) guided waves are incident, the corresponding Fig.12 In (a), conventional broadband GO extracts two wavelengths simultaneously without obvious contrast, causing the letters "R" and "G" to appear yellow due to the mixture of red and green, corresponding to Fig.12 In contrast, the BIC-RO proposed in the present invention only extracts the red and green wavelengths, respectively, showing different red and green colors, corresponding to Fig.12 Similarly, when only red (640nm) (see Fig.12 (d)) or green (530nm) (see Fig.12 When the guided wave is incident, the traditional GO will extract the corresponding color non-selectively (see Fig.12 (e) and Fig.12 ), while BIC-RO can selectively extract red (see Fig.12 (f)) and green (see Fig.12 ), thus successfully demonstrating color routing in micro-image display.

[0084] Next, by encoding color information and brightness information (i.e., intensity information) into different dual meta-atomic pairs with different geometric sizes and tilt angles (i.e., rotation angles), we can create on-chip three-dimensional and multi-color nanoprinted images. First, we choose a three-dimensional "3D" pattern as the target image, see Fig.13 (a) in the figure. Using the parameter matching method, the image is pixelated and then segmented into different color and intensity channels, and each pixel is matched to the closest color and intensity of the BIC-assisted dual meta-atomic array. In Demo 1, two different patterns were made, and the red and green stereoscopic "3D" images were experimentally obtained, such as Fig.13This highlights the difference in extracted color and intensity between the BIC-assisted dual-meta-atoms at different tilt angles and zoom factors. Second, we show the display of the two-color (650nm and 560nm) grayscale image “Red Flower and Green Leaves” (i.e., Demonstration 2) (see Fig.14 ). The images all show vivid colors and smooth brightness transitions. It is worth noting that, thanks to the on-chip propagation scheme, the captured images are not disturbed by the zero-order background and do not require additional optical elements such as polarization analyzers.

[0085] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for designing an on-chip metasurface, characterized in that: The following steps are involved: Constructing a unit structure of an on-chip metasurface, the unit structure comprising a nanostructure layer, an optical waveguide layer and a dielectric substrate layer arranged in sequence from top to bottom, the nanostructure layer being composed of diatomic nanobricks, and the diatomic nanobricks having geometric asymmetry; The plurality of diatomic nanobricks included in the on-chip metasurface form one or more groups of nanobrick arrays; All diatomic nanobricks contained in each group of nanobrick arrays have the same geometrical size, while diatomic nanobricks contained in nanobrick arrays of different groups have different geometrical sizes; Each group of nanobrick arrays is used to selectively extract a certain narrow-band spectrum, and different groups of nanobrick arrays are used to selectively extract different spectral ranges; The geometric size of the diatomic nanobricks in each group of nanobrick arrays is used as an adjustment parameter to encode the color information of the image into the on-chip metasurface.

2. The method for designing an on-chip metasurface according to claim 1, characterized in that: The xoy coordinate system is established in the direction parallel to the two sides of the working surface of the optical waveguide layer. The rotation angles of the two nanobricks in the diatomic nanobricks in the i-th group of nanobrick array about the y-axis are θ i , 180°-θ i , and 0°<θ i <90°; all diatomic nanobricks contained in each group of nanobrick arrays have the same rotation angle design.

3. The method for designing an on-chip metasurface according to claim 1, characterized in that: When the several diatomic nanobricks included in the on-chip metasurface form multiple groups of nanobrick arrays, multiple nanobrick arrays of different types are horizontally cascaded, and the on-chip metasurface selectively extracts waveguides of different wavelengths from different spatial positions to free space for color routing.

4. The method for designing an on-chip metasurface according to claim 2, characterized in that: The diatomic nanobrick is composed of two rectangular nanobricks with the same geometric size; the geometric size of the diatomic nanobrick in the i-th group of nanobrick array is set to: L i =L0×S i , W i =W0×S i , P i =P x =P y =P0×S i Among them, L i is the length of the diatomic nanobrick in the i-th nanobrick array, W i is the width of the diatomic nanobrick in the i-th group of nanobrick array, P i is the period of the diatomic nanobricks in the i-th group of nanobrick arrays, P x and P y are the periods of the diatomic nanobricks along the x-axis and y-axis respectively, L0 is the reference length, W0 is the reference width, P0 is the reference period, S i is the scaling factor of the ith nanobrick array, S i >0; different groups of nanobrick arrays have different scaling factors; the wavelength corresponding to the spectral peak extracted by the nanobrick array increases with the increase of the scaling factor; the geometric size of the diatomic nanobricks in each group of nanobrick arrays is determined according to the color information of the image.

5. The method for designing an on-chip metasurface according to claim 4, characterized in that: The reference length and the reference width are both sub-wavelength sizes; The guided wave propagates along the x-axis, and the local displacement between the diatomic nanobricks along the x-axis is P x / 2.

6. The method for designing an on-chip metasurface according to claim 2, characterized in that: Also includes: The rotation angle of the diatomic nanobricks in each group of nanobrick arrays is used as an adjustment parameter to encode the intensity information of the image into the on-chip metasurface.

7. The method for designing an on-chip metasurface according to claim 6, characterized in that: The asymmetry factor α of the i-th group of nanobrick arrays i Defined as α i = sinθ i ; The spectral intensity extracted from the nanobrick array increases with the increase of the asymmetry factor; The rotation angle design of the diatomic nanobricks in each group of nanobrick arrays is determined based on the intensity information of the image.

8. An on-chip metasurface, characterized in that: It is obtained by adopting the design method of the on-chip metasurface as described in any one of claims 1-7.

9. A method for implementing color routing based on an on-chip metasurface, characterized in that: The color information of the image is encoded into the on-chip metasurface as claimed in claim 8 by adopting a spatial mapping method, wherein the on-chip metasurface comprises a plurality of diatomic nanobricks forming a plurality of nanobrick arrays, and a plurality of nanobrick arrays of different types are horizontally cascaded; the on-chip metasurface is utilized to selectively extract waveguides of different wavelengths from different spatial positions to free space for color routing, thereby realizing multi-color routing image display.

10. The method for implementing color routing based on an on-chip metasurface according to claim 9, characterized in that: The color information and intensity information of the image are encoded into the on-chip metasurface to realize image display of multi-color routing with controllable spectral intensity.

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