Polarization multiplexing all-dielectric metasurface structure color device based on gallium phosphide

Abstract

The invention discloses a polarization multiplexing all-dielectric metasurface structure color device based on gallium phosphide. The device is composed of periodically arranged metasurface units, and each unit sequentially comprises a transparent quartz substrate 1, a TiO2 reflecting layer 2 and an all-dielectric nano resonator located on the TiO2 reflecting layer 2 from bottom to top. The nano resonator is composed of a GaP nano column 3 and a SiO2 impedance matching layer 4 covering the top of the GaP nano column 3. The material cost is low, the manufacturing process is mature, and the designed device shows obvious optical response difference under irradiation of different polarized lights. By utilizing the characteristics of high refractive index and low loss of a gallium phosphide material in a medium-long wave region of visible light, a single reflection peak of which the reflection efficiency is up to 99% and the bandwidth is less than 16nm is realized under X polarization of a visible light wave band; and a stable multi-peak spectrum is formed under Y polarization to serve as a spectrum fingerprint, so that high-quality display and polarization multiplexing functions are realized in the same device. The device is suitable for the fields of high-color-gamut display, optical anti-counterfeiting and the like.

Description

Technical Field

[0001] This invention relates to the fields of nanophotonics and metasurface technology, and more specifically, to a structural color device based on all-dielectric materials, particularly a polarization-multiplexed high-saturation structural color device. Background Technology

[0002] Structural colors are produced by scattering, diffraction, or interference of light waves through nanostructures. Compared to traditional colors that rely on chemical dyes, they offer advantages such as high resolution, high stability, and resistance to fading. Although metallic nanostructures have been extensively studied in early structural color devices, their unavoidable ohmic losses in the visible light band significantly limit reflection efficiency and color saturation, making it difficult to meet the demands of high-quality displays and refined optical markings. All-dielectric material systems, represented by titanium dioxide and gallium phosphide, effectively improve the reflection efficiency and color stability of structural color devices by exciting low-loss Mie resonances in subwavelength scale structures, becoming an important research direction. Among them, gallium phosphide, as a semiconductor material with a band gap located at the short-wavelength end of the visible light spectrum, has a high refractive index and low absorption loss in the long-wavelength region of the visible light spectrum, and is widely considered an excellent material for achieving high-quality structural colors.

[0003] However, existing all-dielectric structural color designs still face two major challenges: limited saturation and color gamut, and a lack of design dimensionality. While all-dielectric materials have low loss, the presence of higher-order resonance modes or background scattering in the nanostructure still introduces stray light beyond the main reflection peak, leading to reduced color saturation. Most metasurfaces are static, and each pixel can only display one color. Polarization multiplexing technology has been proposed to address this issue. It utilizes the difference in response of anisotropic nanostructures to different polarized light to encode two independent information channels in the same physical space, which holds great potential in optical anti-counterfeiting. Currently, there is an urgent need for a novel device structure that can simultaneously achieve ultra-high saturation and dual-channel polarization multiplexing functionality. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing devices in terms of color saturation, spectral purity, and information carrying capacity, and to provide a polarization-multiplexed all-dielectric metasurface high-saturation structural color device that enables independent spectral control of incident light with orthogonal polarization states, thereby achieving both high-quality structural color display and polarization multiplexing information encoding functions in the same physical structure.

[0005] The objective of this invention is achieved as follows:

[0006] A polarization-multiplexed all-dielectric metasurface structured color device comprises periodically arranged unit structures, including, from bottom to top: a transparent SiO2 substrate 1, a TiO2 reflective layer 2, GaP nanopillars 3, and a SiO2 impedance matching layer 4, with thicknesses h1, h2, h3, and h4, respectively. The GaP nanopillars 3 and the SiO2 impedance matching layer 4 are both elliptical projections in the XY plane, with different lengths along their first and second axes to achieve a polarization-sensitive anisotropic response.

[0007] Preferably, the transparent SiO2 substrate has a thickness of h1, a length of Px=360nm, and a width of Py=180nm.

[0008] Preferably, the transparent TiO2 substrate has a thickness of h2, a length of Px=360nm, and a width of Py=180nm.

[0009] As a preferred option, the nanoresonator uses GaP and SiO2, where the GaP thickness is h3 and the SiO2 thickness is h4, the major axis is Dx=180nm and the minor axis is Dy=100nm.

[0010] Because this invention employs the aforementioned technical solution, compared to existing structural color devices, the device structure is relatively simple, consisting entirely of dielectric materials, resulting in low loss. The selected GaP, TiO2, and SiO2 materials all exhibit low optical loss and good optical stability in the visible light band, which is beneficial for obtaining structural color output with high reflection efficiency and high color purity. Simultaneously, through a rational structural design, this invention achieves polarization multiplexing spectral modulation functionality within a single metasurface, significantly enhancing the device's information carrying capacity and design freedom while ensuring high-saturation display performance. Furthermore, the device structure does not rely on complex multi-material, multi-layer nanopatterns, exhibiting good compatibility with existing micro / nano fabrication processes. It offers advantages such as controllable manufacturing costs, good repeatability, and ease of large-scale fabrication, thus possessing significant practical value in display, information multiplexing, and related optical applications. Attached Figure Description

[0011] Figure 1 This is a three-dimensional structural diagram of a polarization-multiplexed metasurface structured color device.

[0012] Figure 2 This is the reflection spectrum curve of this structure under X-polarized and Y-polarized light incident.

[0013] Figure 3 These are the chromaticity coordinates of x-polarized light in the CIE 1931 chromaticity space.

[0014] Figure 4 It is a diagram showing the electric and magnetic field distributions at the resonant wavelength.

[0015] Figure 5 This is a conceptual diagram illustrating the application of polarization multiplexing in optical encryption. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0017] like Figure 1 As shown, this invention proposes a polarization-multiplexed all-dielectric metasurface high-saturation structural color device. The device consists of a four-layer structure, primarily comprising a transparent SiO2 substrate 1, a TiO2 reflective layer 2, GaP nanopillars 3, and SiO2 nanopillars 4.

[0018] As an example, a TiO2 layer is deposited on a SiO2 substrate, with GaP and SiO2 nanopillars on the TiO2. From bottom to top, the thicknesses are h1, h2, h3, and h4, respectively. The transparent SiO2 substrate has a thickness of h1, a length of Px = 360 nm, and a width of Py = 180 nm. The TiO2 reflective layer has a thickness of h2, a length of Px = 360 nm, and a width of Py = 180 nm. The nanoresonator uses GaP and SiO2, where the GaP thickness is h3 and the SiO2 thickness is h4, with a major axis of Dx = 180 nm and a minor axis of Dy = 100 nm.

[0019] The trichromatic stimulus values ​​of the reflected color of the nanostructure unit, calculated based on the reflectance spectrum, are expressed as follows:

[0020] The chromaticity coordinates obtained based on the three color stimulus values ​​of the object are:

[0021] The simulation results of the polarization multiplexing structured color device implemented in this embodiment, obtained using the three-dimensional finite-difference time-domain (FDTD) method, are as follows: Figure 2 As shown in the figure, calculations reveal a reflection peak at 535.3 nm in the x-polarized light reflection spectrum, reaching a high level of 99%. Meanwhile, multiple resonance peaks appear in the y-polarized light.

[0022] Figure 3 These are the chromaticity coordinates of x-polarized light in the CIE1931 color space, demonstrating the distribution characteristics of the structural color in the visible light chromaticity space.

[0023] Figure 4 It is a diagram showing the electric and magnetic field distributions at the resonant wavelength.

[0024] Figure 5This is a schematic diagram illustrating the display effect of a polarization-multiplexed structured color device under different polarization conditions. The same metasurface area produces a clear and saturated structured color under X-polarized incident light, while exhibiting different colors or indistinguishable patterns under Y-polarized incident light.

[0025] It should be noted that although the embodiments described above are illustrative, they are not intended to limit the invention. Therefore, the invention is not limited to the specific embodiments described above. Any other embodiments obtained by those skilled in the art under the guidance of this invention without departing from its principles are considered to be within the protection scope of this invention.

Claims

1. A gallium phosphide-based polarization-multiplexed all-dielectric metasurface structured color device. Within one cycle, from bottom to top, it includes: A transparent SiO2 substrate (1), a TiO2 reflective layer (2), and a nano-resonator. The nano-resonator is a multilayer stacked structure, including a GaP nanopillar (3) and a SiO2 impedance matching layer (4), with thicknesses of h1, h2, h3, and h4 from bottom to top, respectively.

2. The polarization-multiplexed all-dielectric metasurface structured color device according to claim 1, characterized in that: The projections of the GaP nanopillars (3) and the SiO2 impedance matching layer (4) in the device plane are both non-circular symmetrical shapes, with a first axis and a second axis that are perpendicular to each other and of different sizes, so as to generate an in-plane anisotropic polarization-selective response.

3. The polarization-multiplexed all-dielectric metasurface structured color device according to claim 1 or 2, characterized in that: The transparent substrate (1) is a quartz substrate with a thickness of h1, a length of Px=360nm, and a width of Py=180nm.

4. The polarization-multiplexed all-dielectric metasurface structured color device according to claim 1, characterized in that: The reflective layer (2) is composed of TiO2, with a thickness of h2, a length of Px=360nm, and a width of Py=180nm.

5. The polarization-multiplexed all-dielectric metasurface structured color device according to claim 1, characterized in that: The GaP nanopillars (3) have a thickness of h3, a major axis of Dx=180nm, and a minor axis of Dy=100nm.

6. The polarization-multiplexed all-dielectric metasurface structured color device according to claim 1, characterized in that: The SiO2 impedance matching layer (4) has a thickness of h4, a major axis of Dx=180nm, and a minor axis of Dy=100nm.

7. The polarization-multiplexed all-dielectric metasurface structured color device according to claim 1, characterized in that: Under a selected polarization state, the full width at half maximum (FWHM) of the structural color reflection peak of the device in the visible light band is less than 30 nm, and the peak reflection efficiency is not less than 90%.

8. The polarization-multiplexed all-dielectric metasurface structured color device according to claim 2, characterized in that: By adjusting the geometric dimensions of the first axis and the second axis respectively, the wavelength of the reflection peak under the corresponding orthogonal polarization state can be independently controlled without changing the physical position of the device, so as to realize the structured color display of multi-channel polarization multiplexing, which can be used for optical anti-counterfeiting identification or information hiding applications.

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