Double-layer metasurface structure filter for multicolor visible light communication

Abstract

The invention discloses a double-layer metasurface structure filter for multicolor visible light communication, the filter is vertically integrated from bottom to top, and upper and lower layer electric field modes of the filter are subjected to coherent superposition and coupling under a phase matching condition to form a new LSPR-GMR mixed mode; the upper-layer metasurface structure is a sub-wavelength scale metal pattern, and the lower-layer metasurface structure is a sub-wavelength periodic unit based on a polycrystalline silicon material; an intermediate dielectric layer is arranged between the upper-layer metasurface and the lower-layer metasurface, physical isolation of the upper-layer metasurface and the lower-layer metasurface is achieved, and the intermediate dielectric layer serves as an energy transfer channel and a mode matcher to achieve efficient coupling between the upper-layer metasurface and the lower-layer metasurface; a substrate is arranged below the lower-layer metasurface, and a silicon wafer is selected as the substrate of the double-layer metasurface filter, provides physical support for the double-layer metasurface structure filter and serves as an active area of a Si-based photoelectric device. According to the invention, efficient and accurate selection of red light, green light and blue light is realized, and technical support is provided for high-performance optoelectronic devices and multi-color visible light communication.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of filters, in particular to a double-layer metasurface structure filter for multi-color visible light communication, and more particularly to a double-layer metasurface structure in which the upper metasurface and the lower metasurface are coupled to each other, and which is particularly suitable for efficient and accurate color separation in multi-color visible light (400-700 nm) communication. BACKGROUND

[0002] As a beneficial supplement to the sixth generation of wireless communication technology, visible light communication (VLC) has the core advantages of being able to reuse existing lighting systems, not needing to build additional base stations, being safe, and having a wide frequency band resource (400-800 THz) without authorization, and thus has great application potential in high-speed wireless communication and indoor positioning and other application scenarios. Among them, red, green and blue (RGB) three-color light-emitting diodes (LEDs) have three independent wavelength channels of red, green and blue, and can carry different data streams at the same time, so they have become the core devices supporting high-speed multi-color visible light communication (MC-VLC) systems. However, compared with laser diodes (LDs), the emission spectrum of RGB-LEDs is relatively wide, usually with a full width at half maximum of more than 50 nm, so there is mutual overlap between multi-color spectra, causing inter-color interference (ICI), which in turn reduces the signal-to-noise ratio (SNR) and severely restricts the transmission rate and reliability of multi-color visible light communication. Therefore, the multi-color visible light communication (MC-VLC) receiver must achieve efficient and accurate color separation to fundamentally solve the problem of inter-color interference.

[0003] In the color separation technology of MC-VLC systems, traditional schemes mainly use optical filters such as bandpass filters or organic dye filters to complete wavelength screening, but such schemes have the disadvantages of limited filtering accuracy, high loss, large size, poor compatibility with CMOS technology, and poor high-temperature resistance and long-term stability, and thus cannot meet the development needs of high-speed and high-density integrated MC-VLC systems.

[0004] As an artificial two-dimensional material composed of subwavelength units, a metasurface can flexibly control the phase, amplitude and polarization of light waves, accurately manipulate the wavefront of a light field, and complete directional screening of optical signals without complex optical systems, thus becoming a new path to break through the bottleneck of traditional filtering and build lightweight / integrated channel separation devices. For example, patent (CN117518316 A) 2024.02.06 [1] A single-layer silicon metasurface is used to realize the radiation control of multi-channel guided modes, although this scheme has improved the integration level, but the screening accuracy of the red, green and blue three-wavelength channels in the visible light band is limited, and it cannot effectively solve the problem of crosstalk, and the average transmittance is low. Li Guanhai et al. [2]A polychromatic full-polarization control super surface structure is proposed, which can realize the separation of multi-wavelength channels by combining super surface units, but is only applicable to the mid-infrared waveband of 2-10 μm, and cannot match the target waveband of RGB-LED. In addition, Yang Jun et al. [3] Optical absorption enhancement is achieved using a super surface, but the super surface structure designed does not have the wavelength selection function of RGB three primary colors.

[0005] In summary, for the color separation problem of multi-color visible light communication (MC-VLC), the existing optical filters compatible with standard CMOS technology have the problems of poor filtering precision, low transmittance, and poor color crosstalk suppression effect, and therefore it is urgent to develop optical filters based on new structures or new mechanisms to improve the overall performance of multi-color visible light communication.

[0006] REFERENCES [1] Li Zhongyang, Li Zhe. On-chip integrated super surface and design method, application [P]. China: CN117518316 A) 2024-02-06 [2] Li G H, Chen X S, Lu W, et al. Polychromatic full-polarization control in mid-infrared light [J]. Light: Science&Applications, 2023, 12 (1):215. [3] Yang Jun, Yang Chunli. A double-layer super surface structure absorber and its preparation method [P]. China: CN202311101079.2, 2023-12-08 SUMMARY

[0007] The present application provides a double-layer super surface structure filter for multi-color visible light communication. The present application realizes efficient and accurate selection of red, green and blue light by designing a double-layer super surface filter with upper and lower super surfaces cooperating with each other, providing technical support for high-performance optoelectronic devices and multi-color visible light communication. Details are described below: A double-layer super surface structure filter for multi-color visible light communication is vertically integrated from bottom to top. The upper and lower layers of the filter are coherent superimposed and coupled to form a new LSPR-GMR hybrid mode under phase matching conditions. The upper layer super surface structure is a metal pattern of sub-wavelength scale, and the lower layer super surface structure is a sub-wavelength periodic unit based on polycrystalline silicon material. An intermediate medium layer is arranged between the upper super surface and the lower super surface, so as to realize physical isolation of the upper super surface and the lower super surface, and simultaneously serve as an energy transmission channel and a mode matcher, so as to realize efficient coupling between the upper super surface and the lower super surface. Below the lower super surface is a substrate, and a silicon wafer is selected as the substrate of the double-layer super surface filter, so as to provide physical support for the double-layer super surface structure filter, and simultaneously serve as an active region of a Si-based optoelectronic device.

[0008] The size, shape and duty cycle of the upper super surface structure are designed according to different target wave bands of red, green and blue three primary colors.

[0009] The duty cycle of the lower super surface structure is optimized according to target wavelengths of red, green and blue three colors.

[0010] Further, when the white light mixed by the red, green and blue three primary colors irradiates the upper super surface structure, the super surface pattern excites the LSPR effect, so that the light energy of the target wave band is highly localized at the metal-insulator interface, and a strong field is formed in the pattern edge area.

[0011] The lower super surface structure excites the guided mode resonance effect and serves as a high-selectivity wavelength selector.

[0012] The transmittance of the filter is T = T top × T bot × k , T top and T bot are the transmittances of the upper super surface structure and the lower super surface structure respectively, k is a coupling coefficient of the upper super surface and the lower super surface.

[0013] The thickness of the intermediate medium layer is adjusted, so that the localized surface plasmon (LSPR) mode generated by the upper super surface structure is evanescently coupled to the lower super surface structure, and realizes phase matching with the guided mode resonance mode (GMR) generated by the lower super surface structure. When the two excitation modes satisfy the inter-mode phase matching, a coupling resonance window is formed between the upper super surface and the lower super surface, and a LSPR-GMR hybrid resonance mode is generated.

[0014] The intermediate medium layer is silicon dioxide.

[0015] The technical scheme provided by the application has the following beneficial effects: 1. Enhanced transmission efficiency of incident light field: by regulating the mode phase between the upper layer super surface excited mode and the lower layer super surface excited mode, the target wavelength can achieve efficient resonance energy transfer between the upper and lower layer super surface, and the average transmittance can reach more than 90%, far exceeding the transmittance of traditional optical filter; 2. Narrowband filtering and reducing inter-color crosstalk: by using the "peak misalignment resonance" between the upper layer localized surface plasmon resonance (LSPR) and the lower layer guided mode resonance (GMR) mode, the transmission window of the double layer super surface structure filter can be reduced, and the full width at half maximum of the wavelength response of the filter can be controlled within 80nm; the high selectivity of narrowband filtering can effectively suppress the stray light outside the target wavelength range, and significantly improve the color purity and signal recognition ability of the optical filter; 3. Compact structure, easy to integrate: the super surface structure filter can be prepared by using traditional microelectronic process, which has good compatibility with standard CMOS process, so that the monolithic integration of super surface filter and optoelectronic device can be realized, and the device volume can be significantly reduced; 4. The geometric structure parameters of the super surface pattern can be flexibly adjusted to adapt to different optical frequency bands, which greatly improves the practicability and flexibility of the super surface optical filter. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a schematic diagram of a single layer super surface structure filter; Figure 2 is a schematic diagram of the transmission curve of a single layer super surface structure filter for red, green and blue light; Figure 3 is a schematic diagram of a double layer super surface structure filter; Figure 4 is a schematic diagram of the transmission curve of the upper and lower layer super surface designed for red light, and the transmission curve of the whole double layer super surface structure filter; Figure 5 is a schematic diagram of the transmission curve of the upper and lower layer super surface designed for green light, and the transmission curve of the whole double layer super surface structure filter; Figure 6 is a schematic diagram of the transmission curve of the upper and lower layer super surface designed for blue light, and the transmission curve of the whole double layer super surface structure filter. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical scheme and advantages of the present application more clear, the embodiments of the present application are further described in detail below.

[0018] The embodiment of the present application constructs a double layer super surface high efficiency filtering structure based on near field coupling by setting a layer of intermediate medium layer with appropriate thickness between the upper layer super surface and the lower layer super surface.

[0019] Specifically, the upper layer Ag nanostructure excites local surface plasmon resonance (LSPR) at the target wavelength, generating high-field evanescent waves. The evanescent waves extend in the intermediate medium layer and produce mode coupling with the guided mode resonance (GMR) of the lower layer metasurface structure. The embodiment of the application creatively adopts the "peak-mismatching design" idea, that is, the upper and lower layer electric field modes are coherently coupled under the phase matching condition to form a new LSPR-GMR (local surface plasmon-guided mode resonance) hybrid mode. This hybrid mode uses the resonance energy transfer mechanism to efficiently transmit the light energy captured by the upper layer metasurface to the lower layer metasurface, and then to the photoelectric device below through the lower layer metasurface, thereby breaking through the efficiency bottleneck of the traditional stacked structure and realizing high transmission and narrow band filtering.

[0020] The structure of the embodiment of the application is vertically integrated from bottom to top, and can realize efficient selection of red, green and blue three primary color target wavebands. The core design and role of each layer are described as follows: 1. The upper layer metasurface structure is a metal pattern of subwavelength scale, and the geometric parameters such as size, shape and duty cycle can be optimized and designed according to the different target wavebands of red, green and blue three primary colors. When white light mixed with red, green and blue three primary colors is incident on the upper layer metasurface structure, the metasurface pattern can excite LSPR effect, so that the light energy of the target waveband is highly localized at the metal-insulator interface, especially forming a strong field in the hot spot area such as the pattern edge.

[0021] Among them, the upper layer metasurface structure is optimized and designed, which not only can realize the standing wave resonance enhancement of the target wavelength, but also can filter out the required waveband from the incident white light, thereby effectively suppressing the interference of background stray light.

[0022] 2. The lower layer metasurface structure is a subwavelength periodic unit based on polycrystalline silicon material, and the structure design is also optimized according to the duty cycle of the target wavelength of red, green and blue three primary colors. The core function of the metasurface structure is to excite guided mode resonance (GMR) effect, and it can further suppress the interference of stray light outside the target waveband as a high selectivity wavelength filter.

[0023] 3. A layer of intermediate medium layer with reasonable thickness is arranged between the upper layer metasurface and the lower layer metasurface. The intermediate medium layer not only can realize the physical isolation of the upper and lower layer metasurfaces, but also can realize the efficient coupling between the upper and lower layer metasurfaces as an energy transfer channel and a mode matcher. Therefore, the transmittance of the double-layer metasurface structure filter is T = T top × T bot × k . Among them, T top and T bot are the transmittances of the upper and lower layer metasurface structures, respectively,k is the coupling coefficient between the upper and lower metasurfaces.

[0024] By adjusting the thickness of the intermediate medium layer, the LSPR mode generated by the upper metasurface structure can be evanescently coupled to the lower metasurface structure, and the phase matching with the guided mode resonance (GMR) mode generated by the lower metasurface structure can be achieved. When the two excitation modes satisfy the phase matching between modes, the best coupling resonance window will be formed between the upper metasurface and the lower metasurface, and the LSPR-GMR hybrid resonance mode will be generated. The hybrid resonance mode can significantly enhance the optical field response of the target waveband and improve the overall wavelength selectivity of the filter.

[0025] 4. The substrate is selected as a silicon wafer as the substrate of the double-layer metasurface filter. The main functions include: 1. providing physical support for the double-layer metasurface structure filter above, avoiding deformation, falling off or damage of the upper filter during preparation, transportation and use; 2. serving as an active region of a Si-based optoelectronic device to realize monolithic integration of the filter and the optoelectronic device.

[0026] The embodiment of the present application utilizes silicon dioxide as the intermediate medium layer to establish an efficient near-field coupling energy channel between the upper and lower metasurfaces. When white light mixed with red, green and blue three primary colors irradiates the double-layer metasurface structure filter of the embodiment of the present application, the Ag nano-pattern of the upper metasurface can excite LSPR effect, and the strong local evanescent light field generated thereby can overlap in space with the GMR mode generated by the lower metasurface through the silicon dioxide medium layer.

[0027] The embodiment of the present application discards the traditional same-frequency superposition idea, and instead adopts a staggered peak design strategy to suppress the destructive interference between modes by using moderate frequency detuning. At the optimal coupling thickness, the excitation modes of the upper and lower metasurfaces occur coherent superposition and coupling to form an LSPR-GMR hybrid mode. The hybrid mode dominates the efficient transfer of photon energy, greatly enhances the optical field response of the target waveband, significantly improves the transmission efficiency, and effectively compresses the frequency band of the transmission spectrum.

[0028] The present application will be further explained and described in conjunction with the accompanying drawings and examples: Figure 1The single-layer metasurface filter is prepared by using a four-cornered prism nano pillar array of monocrystalline silicon vertically grown on the surface of a quartz glass substrate. The single-layer metasurface filter takes the silicon nano pillar array as a core functional unit, and uses the strong Mie resonance effect of the high refractive index silicon material in the visible light band to realize wavelength selection of RGB three-color light. For example, if the height of the nano pillar is uniform at 150 nm and the array arrangement period P is 300 nm, the wavelength selection of RGB three-color light can be realized by adjusting the cross-sectional side length of the nano pillar, wherein the corresponding side length of the red light selection is 200 nm, the corresponding side length of the green light selection is 165 nm, and the corresponding side length of the blue light selection is 130 nm.

[0029] Figure 2 The transmission efficiency curve of the single-layer metasurface filter for RGB three-color light is shown. As can be seen, the peak transmittances of the red, green and blue wavelength channels are 75%, 85% and 74% respectively. Since the all-dielectric structure has no ohmic loss, the light field is captured and re-emitted at a specific wavelength by resonance coupling of electric and magnetic dipoles in the nano pillar, thereby forming a high-transmission window. However, the single-layer metasurface filter has certain deficiencies, for example, the silicon material has slight absorption in the blue light band, which makes the transmission efficiency of the blue light channel slightly lower than that of the red and green channels. In addition, Figure 2 The results also show that the full width at half maximum of the resonance peak in the single-layer metasurface filter is wide, and thus the color purity of the transmission spectrum is not high.

[0030] Embodiment 1 To overcome the deficiencies of the single-layer metasurface filter, the embodiment of the present application proposes a double-layer metasurface filter, a three-dimensional view of which is shown in Figure 3 The double-layer metasurface filter is described in detail as follows: The embodiment of the present application is designed for 650 nm red light selection. For 650 nm wavelength selection, the transmission peaks of the upper and lower layer metasurface structures are staggered by 40 nm in design, the peak wavelength of the upper layer metasurface structure is designed as 630 nm, and the peak wavelength of the lower layer metasurface structure corresponds to 670 nm. Wavelength selection is realized by relying on the overlapping part of the light response of the two, and thus a narrower bandwidth can be obtained. In addition, the coupling efficiency between the two is adjusted by optimizing the thickness of the intermediate dielectric layer, and thus the overall transmittance of the filter is improved. The filter structure is vertically integrated from bottom to top, and the core parameters and functions of each layer are as follows: 1. The upper metasurface structure (001): The material of the upper metasurface structure is silver (Ag), and the periodic micro-nano structure of the design pattern is "square ring + cross". The optimal design parameters of the upper micro-nano structure pattern for the wavelength selection of 630 nm are as follows: the thickness of the silver layer is 20 nm, the line width of the square ring is 12.5 nm, the inner and outer side lengths are 560 nm and 585 nm respectively, the arrangement period of the square ring is 675 nm, the cross is located at the center of the square ring, each arm is 250 nm long, and the arm width is 25 nm.

[0031] When the white light mixed by RGB three primary colors irradiates the metasurface structure, the 650 nm red light excites the localized surface plasmon resonance (LSPR) effect at the upper metasurface structure, and enhances the local light field at the interface between the metal and the medium. Due to the excellent plasmonic properties of silver and the optimized design of the upper metasurface micro-nano structure, the field intensity of the 650 nm red light can be significantly enhanced in the edge area of the pattern, thereby effectively selecting the red light band and suppressing the interference light of other bands. Figure 4 The transmission spectrum curve of the upper metasurface structure acting alone is given. Figure 4 It can be seen that the transmission peak of the metasurface structure can reach 93%, and the full width at half maximum is 100 nm. It can be seen that it is impossible to achieve narrow bandwidth only by relying on a single layer of metasurface.

[0032] 2. The lower metasurface structure (003): In order to improve the compatibility of the metasurface filter of the embodiment of the present application with the standard CMOS process, the lower metasurface structure is made of heavily doped P-type polysilicon with a thickness of 110 nm, and its main function is to select the target wavelength. For the wavelength selection of 670 nm, a "I-shaped" periodically arranged sub-wavelength square structure is adopted, in which the side length of the "I-shaped" square structure is 190 nm, and the arrangement period is 350 nm. The lower metasurface GMR mode and the upper metasurface LSPR mode are coupled with each other to realize the wavelength selection of the 650 nm band and improve the spectral purity of the filtered signal. Figure 4 The transmission spectrum curve of the lower metasurface structure acting independently under the above design parameters is given. Figure 4 It can be seen that the transmission efficiency at 670 nm can reach 93.7% at most. Compared with the single-layer metasurface filter shown in Figure 2 , the transmission efficiency is obviously improved. However, the full width at half maximum of the lower metasurface structure is greater than 100 nm, and other stray light other than the red light wavelength is not completely filtered out.

[0033] 3, Intermediate dielectric layer (002): The intermediate dielectric layer is located between the upper metasurface and the lower metasurface, and mainly provides phase control and structural support. The dielectric layer used is selected from a silicon dioxide material with low refractive index and small absorption coefficient in the visible light waveband. By precisely controlling the thickness of the intermediate dielectric layer, the phase matching of the upper LSPR mode and the lower GMR mode can be achieved, and efficient near-field coupling can be realized. Figure 4 The total filtering effect of the double-layer metasurface structure filter is shown when the thickness of the silicon dioxide intermediate dielectric layer is 120 nm. At this thickness, the coupling efficiency of the upper and lower metasurfaces is best. Compared with the separate action of the upper and lower metasurfaces, the full width at half maximum of the transmission window is reduced to 75 nm, and the transmission efficiency at 650 nm wavelength reaches 91.4%.

[0034] 4, Base layer (004): The base layer is selected from a silicon wafer as the base of the double-layer metasurface filter. Its main functions include: 1) providing physical support for the double-layer metasurface structure filter above, avoiding deformation, falling off or damage of the upper filter during preparation, transportation and use; 2) serving as an active region of a Si-based optoelectronic device, realizing monolithic integration of the filter and the optoelectronic device.

[0035] Example 2 The embodiment of the present application is designed for 550 nm green light selection. For 550 nm wavelength selection, when designing the upper and lower metasurface structures, the transmission peaks of the two are staggered by 40 nm, the peak wavelength of the upper metasurface structure is designed to be 530 nm, and the peak wavelength of the lower metasurface structure corresponds to 570 nm. Wavelength selection is achieved by relying on the overlapping part of the light response of the two, so that a narrower bandwidth can be obtained. In addition, by optimizing the thickness of the intermediate dielectric layer to control the coupling efficiency between the two, the overall transmittance of the filter is improved. The filter structure is vertically integrated from bottom to top, and the core parameters and functions of each layer are as follows: 1, Upper metasurface structure (001): The upper metasurface structure is selected from a metal silver (Ag) material, and the periodic micro-nano structure of "square ring + cross" is designed. For 530 nm wavelength selection, the optimal design parameters of the upper micro-nano structure pattern are as follows: the silver layer thickness is 20 nm, the square ring line width is 12.5 nm, the inner and outer side lengths are 480 nm and 505 nm respectively, the square ring arrangement period is 575 nm, the cross is located at the center of the square ring, each arm is 210 nm long, and the arm width is 20 nm.

[0036] When the white light mixed by RGB three primary colors irradiates the super surface structure, the green light of 550 nm at the upper layer super surface structure excites the local surface plasmon resonance (LSPR) effect, and enhances the local light field at the metal and medium interface. Due to the excellent plasmonic characteristics of the metal silver and the optimized design of the upper layer super surface micro-nano structure, the field intensity of the green light of 550 nm can be significantly enhanced at the edge area of the pattern, so as to effectively select the green light band and suppress the interference light of other bands. Figure 4 The transmission spectrum curve of the upper layer super surface structure alone is given. Figure 4 It can be seen that the transmission peak of the super surface structure can reach 92.3%, and the full width at half maximum is 80 nm. Figure 2 Compared with the single layer super surface structure filter shown in the above, although the transmission efficiency is improved, the filtering bandwidth is not significantly reduced.

[0037] 2, the lower layer super surface structure (003): in order to improve the compatibility of the super surface filter of the embodiment of the application with the standard CMOS process, the lower layer super surface structure is selected to be heavily doped P type polysilicon with a thickness of 110 nm, and its main function is to select the target wavelength. For the wavelength selection of 570 nm, the sub-wavelength square structure arranged in "I type" period is adopted, wherein the side length of the "I type" square structure is 130 nm, and the arrangement period is 300 nm. The lower layer super surface GMR mode and the upper layer super surface LSPR mode are coupled with each other to realize the wavelength selection of the wave band near 650 nm and improve the spectral purity of the filtering signal. Figure 4 The transmission spectrum curve of the lower layer super surface structure alone under the above design parameters is given. Figure 4 It can be seen that the transmission efficiency at 570 nm can reach 93.7% at most. Compared with the single layer super surface structure filter shown in the above, Figure 2 Compared with the single layer super surface structure filter shown in the above, the transmission efficiency is obviously improved. However, the full width at half maximum of the lower layer super surface structure is about 90 nm, and other stray light other than the green wavelength is not completely filtered out.

[0038] 3, the intermediate medium layer (002): the intermediate medium layer is located between the upper layer super surface and the lower layer super surface, and mainly provides the phase control and structure support functions. The medium layer is selected to be the silicon dioxide material with low refractive index and small absorption coefficient in the visible light wave band. By accurately controlling the thickness control of the intermediate medium layer, the phase matching of the upper layer LSPR mode and the lower layer GMR mode can be realized, and the efficient near field coupling can be realized. Figure 4 The total filtering effect of the double layer super surface structure filter when the thickness of the silicon dioxide intermediate medium layer is 180 nm is shown. Under this thickness, the coupling efficiency of the upper and lower layer super surfaces is best. Compared with the single action of the upper and lower layer super surfaces, the full width at half maximum of the transmission window is reduced to 70 nm, and the transmission efficiency at the wavelength of 550 nm reaches 94.7%.

[0039] 4. Substrate layer (004): The substrate layer is selected to be a silicon wafer as the substrate of the double-layer metasurface filter. Its main functions include: 1. providing physical support for the double-layer metasurface structure filter above, avoiding deformation, falling off or damage of the upper filter during preparation, transportation and use; 2. serving as an active region of a Si-based optoelectronic device, realizing monolithic integration of the filter and the optoelectronic device.

[0040] Example 3 The embodiment of the present application is designed for 450 nm blue light selection. For 450 nm wavelength selection, when designing the lower and upper metasurface structures, the transmission peaks of the two are staggered by 40 nm. The peak wavelength of the upper metasurface structure is designed to be 430 nm, and the peak wavelength of the lower metasurface structure corresponds to 470 nm. Wavelength selection is achieved by relying on the overlapping part of the light response of the two, so that a narrower bandwidth can be obtained. In addition, the coupling efficiency between the two is adjusted by optimizing the thickness of the intermediate medium layer, thereby improving the overall transmittance of the filter. The filter structure is vertically integrated from bottom to top, and the core parameters and functions of each layer are as follows: 1. Upper metasurface structure (001): The upper metasurface structure is selected to be a periodic micro-nano structure of "square ring + cross" with silver (Ag) as the material. For 430 nm wavelength selection, the optimal design parameters of the upper micro-nano structure pattern are as follows: the silver layer thickness is 20 nm, the square ring line width is 20 nm, the inner and outer side lengths are 430 nm and 41 nm respectively, the square ring arrangement period is 475 nm, the cross is located at the center of the square ring, and each arm is 175 nm long and 20 nm wide.

[0041] When white light mixed by RGB three primary colors irradiates the metasurface structure, the 450 nm blue light excites a local surface plasmon resonance (LSPR) effect at the upper metasurface structure, enhancing the local light field at the metal and dielectric interface. Due to the excellent plasmonic properties of silver and the optimized design of the upper metasurface micro-nano structure, the 450 nm blue light field can be significantly enhanced in the edge region of the pattern, thereby effectively selecting the blue light band and suppressing other band interference light. Figure 4 The transmission spectrum curve of the upper metasurface structure alone is given. As shown in Figure 4 It can be seen that the transmission peak of the metasurface structure can reach 89%, and the full width at half maximum is 80 nm. Compared with Figure 2 Although the transmission efficiency is improved, the filtering bandwidth is not significantly reduced compared with the single-layer metasurface filter shown in

[0042] 2、Lower metasurface structure (003): In order to improve the compatibility of the super surface filter of the embodiment of the present application with the standard CMOS process, the lower metasurface structure is selected to be heavily doped P-type polysilicon with a thickness of 110 nm, which mainly functions to select the target wavelength. For the wavelength selection of 470 nm, a sub-wavelength square structure arranged in a "one-word type (I type)" period is adopted, wherein the side length of the "one-word type" square structure is 110 nm and the arrangement period is 290 nm. The lower metasurface GMR mode and the upper metasurface LSPR mode are coupled with each other to realize the wavelength selection in the waveband near 450 nm and improve the spectral purity of the filtered signal. Figure 4 The transmission spectrum curve of the lower metasurface structure when it independently functions under the above design parameters is given, and Figure 4 It can be seen that the transmission efficiency thereof at 470 nm can reach 92% at the highest. Compared with the single-layer metasurface structure filter shown in Figure 2 , the transmission efficiency thereof is obviously improved. However, the full width at half maximum of the lower metasurface structure is about 90 nm, and other stray light other than the blue wavelength is not completely filtered out.

[0043] 3、Intermediate dielectric layer (002): The intermediate dielectric layer is located between the upper metasurface and the lower metasurface, and mainly provides the phase control and structural support functions. The dielectric layer is selected to be silicon dioxide material with low refractive index and small absorption coefficient in the visible light waveband. By accurately controlling the thickness of the intermediate dielectric layer, the phase matching of the upper LSPR mode and the lower GMR mode can be realized, and the efficient near-field coupling can be realized. Figure 4 The total filtering effect of the double-layer metasurface structure filter when the thickness of the silicon dioxide intermediate dielectric layer is 150 nm is shown. Under this thickness, the coupling efficiency of the upper and lower metasurfaces is best. Compared with the independent functions of the upper and lower metasurfaces, the full width at half maximum of the transmission window is reduced to 70 nm, and the transmission efficiency at 450 nm wavelength reaches 90.6%.

[0044] 4、Substrate layer (004): The substrate layer is selected to be a silicon wafer as the substrate of the double-layer metasurface filter. Its main functions include: 1. providing physical support for the double-layer metasurface structure filter above, avoiding deformation, falling off or damage of the upper filter during preparation, transportation and use; and 2. serving as an active region of a Si-based optoelectronic device to realize the monolithic integration of the filter and the optoelectronic device.

[0045] The embodiment of the present application utilizes the cooperative design idea of the upper super surface and the lower super surface, realizes efficient capture and preliminary screening of target wavelength energy through the LSPR effect of the upper structure super surface, combines the secondary filtering of the GMR mode of the lower polysilicon super surface, and the mutual coupling effect between the upper and lower super surfaces, and significantly improves the filtering selection ratio of the target waveband. Simulation results show that the transmission efficiency of red, green and blue light reaches 91.4%, 94.7% and 90.6% respectively, and stray light interference outside the target waveband can be precisely suppressed. The filter structure of the embodiment of the present application can be prepared by using the CMOS post-process, realizes monolithic integration with other optical devices, and is expected to reduce the size of the device and improve the integration degree of the optoelectronic integrated circuit.

[0046] The model of each device in the embodiments of the present application is not limited unless otherwise specified, and any device that can complete the above functions can be used.

[0047] Those skilled in the art can understand that the drawings are only schematic diagrams of a preferred embodiment, and the above-mentioned serial numbers of the embodiments of the present application only describe the embodiments, and do not represent the advantages or disadvantages of the embodiments.

[0048] The above is only a preferred embodiment of the present application, and does not limit the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A dual-layer metasurface structure filter for multicolor visible light communication, characterized in that, The filter is vertically integrated from bottom to top, and the upper and lower layer electric field modes of the filter are coherently superimposed and coupled under the phase matching condition to form a new LSPR-GMR hybrid mode. The upper super surface structure is a metal pattern of subwavelength scale, and the lower super surface structure is a subwavelength period unit based on polycrystalline silicon material. An intermediate dielectric layer is arranged between the upper super surface and the lower super surface to realize physical isolation of the upper and lower super surfaces, and simultaneously serve as an energy transmission channel and a mode matcher to realize efficient coupling between the upper and lower super surfaces. A substrate is arranged below the lower super surface, and a silicon wafer is selected as the substrate of the double-layer super surface filter to provide physical support for the double-layer super surface filter, and simultaneously serve as an active region of a Si-based optoelectronic device.

2. The dual-layer metasurface structure filter for multicolor visible light communication according to claim 1, wherein, The size, shape and duty cycle of the upper super surface structure are optimized according to different target wave bands of red, green and blue three primary colors.

3. The dual-layer metasurface structure filter for multicolor visible light communication according to claim 1, wherein, The duty cycle of the lower super surface structure is optimized according to target wavelengths of red, green and blue three colors.

4. The dual-layer metasurface structure filter for multicolor visible light communication of claim 2, wherein, When white light mixed with red, green and blue three primary colors irradiates the upper super surface structure, the super surface pattern excites LSPR effect, and the light energy of the target wave band is highly localized at the metal-insulator interface to form a strong field in the pattern edge region.

5. The dual-layer metasurface structure filter for multicolor visible light communication of claim 2, wherein, The lower super surface structure excites guided mode resonance effect and serves as a high-selectivity wavelength selector.

6. The dual-layer metasurface structure filter for multicolor visible light communication of claim 2, wherein, The transmittance of the filter is T = T top × T bot × k , T top and T bot are the transmittances of the upper and lower metasurface structures, respectively, k is the coupling coefficient of the upper and lower metasurfaces.

7. The dual-layer metasurface structure filter for multicolor visible light communication of claim 1, wherein, The thickness of the intermediate dielectric layer is adjusted to make the LSPR mode generated by the upper super surface structure evanescently coupled to the lower super surface structure, and realize phase matching with the guided mode resonance mode generated by the lower super surface structure. When the two excitation modes satisfy the inter-mode phase matching, a coupling resonance window is formed between the upper super surface and the lower super surface, and a LSPR-GMR hybrid resonance mode is generated.

8. The dual-layer metasurface structure filter for multicolor visible light communication of claim 1, wherein, The intermediate dielectric layer is silicon dioxide.

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