An incident angle-insensitive polarization encoding structural color device based on gallium nitride composite dielectric metasurface

Abstract

The application discloses an incident angle-insensitive polarization encoding structural color device based on a gallium nitride composite medium metasurface. The device is composed of periodically arranged metasurface structure units, each of which comprises, from bottom to top, a transparent quartz substrate 3, a GaN elliptical cylinder layer 2 and a SiO2 elliptical cylinder layer 1 covering the top of the GaN elliptical cylinder layer 2. The GaN elliptical cylinder and the SiO2 elliptical cylinder form a composite medium resonance structure, and the polarization selective narrowband reflection in the visible light band is realized by adjusting the geometric parameters. The device designed by the application produces a high-performance structural color with a reflection efficiency of up to 99.9% and a bandwidth of less than 13 nm under X-polarized light incidence in the visible light band; the reflectivity is close to zero under Y-polarized incidence, and the polarization encoding function is realized. Meanwhile, the reflection peak position and the structural color response remain stable within the range of 0-60° incident angles. The device has high polarization selectivity and wide-angle stability, and can be applied to the fields of new display, information encryption and optical anti-counterfeiting.

Description

Technical Field

[0001] This invention relates to the fields of nanophotonics, optical metasurfaces and structural color display technology, and particularly to an incident angle-insensitive polarization-coded structural color device based on a gallium nitride composite dielectric metasurface, specifically belonging to all-dielectric structural color devices and polarization-selective optical coding devices in the visible light band. Background Technology

[0002] Structural colors are colors generated by the interaction between micro / nano structures and light. They do not rely on traditional pigment absorption mechanisms and offer advantages such as high resolution, durability, and integrability. Existing research shows that structural colors can be achieved through various methods, including multilayer thin films, photonic crystals, and metasurfaces. Among these, metasurface structural colors have attracted attention due to their small unit size, high design freedom, and ease of achieving narrowband resonance. Related reviews indicate that metasurface-based structural colors typically achieve narrower spectral linewidths, higher efficiency, and higher display resolution.

[0003] However, traditional structural color devices generally suffer from angle-sensitivity, meaning that as the incident angle changes, the reflection or transmission resonant peaks shift, causing the displayed color to change with the viewing angle, making it difficult to meet the requirements of stable display and anti-counterfeiting coding. Existing research has focused on improving angle-insensitive structural colors, such as using high-refractive-index particles, matching layers, or specific resonant structures to reduce angle dependence. However, their implementation often relies on complex structures or a limited angle range, still making it difficult to simultaneously achieve high saturation, high efficiency, and wide-angle stability.

[0004] In terms of materials, while metallic plasmon structures can produce distinct structural colors, they typically suffer from drawbacks such as high ohmic losses and limited efficiency. Therefore, increasing research is shifting towards all-dielectric metasurfaces. Gallium nitride (GaN), as a dielectric material with high refractive index and low absorption loss, has been used in visible-light metasurface devices. Introducing silicon dioxide as an impedance matching layer can effectively improve the brightness and purity of the structural color. Therefore, there is an urgent need for a GaN-based composite dielectric metasurface structural color device to simultaneously achieve narrow-band structural color, high polarization selectivity, and color stability over a wide incident angle range in the visible light band, thereby meeting the application requirements of high color gamut displays, polarization encoding, and optical anti-counterfeiting. Summary of the Invention

[0005] The purpose of this invention is to provide an incident angle-insensitive polarization-coded structured color device based on a gallium nitride composite dielectric metasurface, so as to solve the problems of incident angle sensitivity, insufficient polarization selectivity and limited efficiency in the visible light region of existing structured color devices.

[0006] The objective of this invention is achieved as follows:

[0007] An incident angle-insensitive polarization-encoded structured color device based on a gallium nitride composite dielectric metasurface is disclosed. The device comprises periodically arranged metasurface units, each of which, from bottom to top, includes a GaN elliptical cylinder 2 on a quartz substrate 3 and a SiO2 elliptical cylinder 1 at the top of the GaN elliptical cylinder, with thicknesses h3, h2, and h1, respectively. The GaN and SiO2 elliptical cylinders together constitute a composite dielectric resonant unit, where the SiO2 elliptical cylinder is used to adjust the impedance difference between the incident light and the high-refractive-index GaN structure, thereby improving the resonant coupling conditions and suppressing spectral drift caused by angle changes. When x-polarized light is incident, the device forms a narrow-band high-reflectance spectrum in the visible light band and exhibits a structured color. When y-polarized light, orthogonal to the x-polarized light, is incident, the reflection response is significantly reduced, thus achieving polarization encoding. Furthermore, within the incident angle range of 0° to 60°, the main reflection peak of the structured color remains relatively stable, satisfying the design goal of angle insensitivity.

[0008] As a preferred option, the transparent SiO2 substrate (3) has a thickness of h3, a length of Px=280nm, and a width of Py=280nm.

[0009] Preferably, the GaN elliptical cylindrical layer (2) has a thickness of h2, a major axis of a = 200 nm, and a minor axis of b = 80 nm.

[0010] As a preferred embodiment, the SiO2 elliptical cylindrical layer (1) has a thickness of h1, a major axis of a=200nm, and a minor axis of b=80nm.

[0011] Because this invention employs the above-described technical solution, compared to existing structural color devices, the device structure is relatively simple, consisting entirely of dielectric materials with low loss. A composite dielectric metasurface unit is constructed using GaN and SiO2, utilizing high-refractive-index, low-loss materials to achieve a narrow-band resonant response in the visible light region. Impedance matching and resonant modulation are achieved through a top SiO2 elliptical cylinder, reducing interface reflection and improving angular stability. This device exhibits significantly different optical responses under x-polarization and y-polarization, while maintaining structural color stability over a wide incident angle range, making it suitable for applications such as high color gamut displays, optical anti-counterfeiting, and polarization multiplexing imaging. Furthermore, the device structure does not rely on complex multi-material, multi-layer nanopatterns, exhibiting good adaptability to existing micro-nano fabrication processes. It offers advantages such as controllable manufacturing costs and good repeatability, thus possessing significant practical value in optical anti-counterfeiting, polarization multiplexing imaging, and related optical applications. Attached Figure Description

[0012] Figure 1 This is a three-dimensional structural schematic diagram of the metasurface unit of the present invention.

[0013] Figure 2 This is a schematic diagram of the reflection spectrum of the present invention under X-polarized and Y-polarized light incident conditions.

[0014] Figure 3 This is a diagram showing the electric and magnetic field distributions at the resonant wavelength of the device of this invention.

[0015] Figure 4 This is a schematic diagram illustrating the stability of the reflection spectrum of the present invention under different incident angles. 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 an incident angle-insensitive polarization-encoded structural color device based on a gallium nitride composite dielectric metasurface. The device consists of a three-layer structure, including a GaN elliptical cylinder (2) on a quartz substrate (3) and a SiO2 elliptical cylinder (1) located on top of the GaN elliptical cylinder.

[0018] As an example, a GaN elliptical cylinder layer is deposited on a transparent quartz substrate (3), and a SiO2 elliptical cylinder (1) is placed on top of the GaN elliptical cylinder (2). From bottom to top, the thicknesses are h3, h2, and h1, respectively. The transparent SiO2 substrate has a thickness of h3, a length of Px = 280 nm, and a width of Py = 280 nm. The GaN elliptical cylinder layer has a thickness of h2, a major axis of a = 200 nm, and a minor axis of b = 80 nm. The top SiO2 elliptical cylinder layer has a thickness of h1, a major axis of a = 200 nm, and a minor axis of b = 80 nm.

[0019] 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 426 nm in the reflection spectrum under x-polarized light, reaching a high level of 99%. In contrast, the reflection spectrum under y-polarized light approaches zero.

[0020] Figure 3 It is a diagram showing the electric and magnetic field distributions at the resonant wavelength.

[0021] Figure 4 This is a schematic diagram showing the stability of the reflection spectrum as the incident angle changes from 0 to 60 degrees.

[0022] 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. An incident angle-insensitive polarization-coded structured color device based on a gallium nitride composite dielectric metasurface. Its characteristics are: The system includes a quartz substrate and a periodic metasurface array disposed on the quartz substrate. The periodic metasurface array is composed of multiple metasurface units. Each metasurface unit includes, from bottom to top, a transparent SiO2 substrate (3), a GaN reflective layer (2), and a SiO2 impedance matching layer (1), with thicknesses of h3, h2, and h1 from bottom to top, respectively. The GaN elliptical cylinder and the SiO2 elliptical cylinder are coaxially arranged, and their major axes are aligned.

2. The device according to claim 1, characterized in that: Both the GaN elliptical cylinder and the SiO2 elliptical cylinder have elliptical cross-sections, and the major axis of the GaN elliptical cylinder is greater than its minor axis.

3. The device according to claim 1 or 2, characterized in that, The GaN elliptical cylinder (2) and the SiO2 elliptical cylinder (1) are arranged periodically along the array direction, and the center distance between adjacent metasurface units is equal.

4. The device according to any one of claims 1 to 3, characterized in that, The electric field direction of the x-polarized light is parallel to the major axis of the GaN elliptical cylinder (2), and the electric field direction of the y-polarized light is perpendicular to the major axis of the GaN elliptical cylinder (2).

5. The device according to claims 1 to 4, characterized in that: The transparent quartz substrate (3) has a thickness of h3 and a period of Px=Py=280nm.

6. The device according to claims 1 to 5, characterized in that... The gallium nitride elliptical cylindrical layer (2) has a thickness of h2, a major axis of a=200nm, and a minor axis of b=80nm.

7. The device according to claims 1 to 6, characterized in that: The SiO2 elliptical cylindrical layer (1) has a thickness of h1, a major axis of a=200nm, and a minor axis of b=80nm.

8. The device according to claims 1 to 7, characterized in that: The device has a full width at half maximum (FWHM) of less than 13 nm under x-polarized light incident in the visible light band, and its peak reflectivity can reach 99%.

9. The device according to any one of claims 1 to 8, characterized in that, The device displays the structural color corresponding to the reflection peak under x-polarized light incidence and hides polarization-encoded information under y-polarized light incidence.

10. The device according to any one of claims 1 to 9, characterized in that, The device is used for structural color display, information encryption, or optical anti-counterfeiting.

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