Structural color tuning device based on silicon nitride metasurface continuous domain bound state enhancement

Abstract

This invention relates to the field of optical element technology, and more particularly to a structured color modulation device based on continuous domain bound state enhancement of silicon nitride metasurfaces. The device includes a substrate and a metasurface structure disposed on the substrate, wherein the substrate is a silicon dioxide substrate, and the metasurface structure consists of multiple nanodisks arranged in a two-dimensional periodic pattern, with circular air holes formed within the nanodisks. Based on the narrow linewidth resonance characteristics of quasi-BIC, high saturation and wide color gamut structured colors are achieved. Utilizing strong polarization dependence, passive and dynamic control of color brightness can be achieved through simple polarization rotation without altering the structure itself. Silicon nitride exhibits extremely low loss in the visible light band, good compatibility with silicon dioxide substrates, and structural stability. High-contrast polarization encryption patterns are easily realized, offering broad application prospects in high-end anti-counterfeiting, information storage, and dynamic display fields. The adopted micro-nano fabrication process is standardized and mature, facilitating the actual fabrication and industrialization of the device.

Description

Technical Field

[0001] This invention relates to the field of optical element technology, and in particular to a structure color modulation device based on the continuous domain bound state enhancement of silicon nitride metasurface. Background Technology

[0002] Structural color originates from the physical interaction between micro- and nano-structures and light. With its excellent properties such as colorfastness and environmental friendliness, it has become a key technology direction in the fields of next-generation optical sensing, color printing, and information anti-counterfeiting technology.

[0003] However, traditional metallic structural colors often suffer from insufficient saturation and potential fading due to ohmic losses. While existing all-dielectric structural colors alleviate the metal loss problem, they still face material absorption or high-order Mie resonance interference in the short wavelength region, resulting in insufficient color purity and an inability to achieve high-saturation structural colors. Existing structural color schemes based on continuous-domain bound states (BICs) mostly rely on nanorod rotation to control the reflection spectral linewidth, which not only requires high fabrication precision but also has limited freedom of polarization control, making it difficult to achieve dynamic switching of color brightness and wide color gamut coverage. Therefore, there is an urgent need for a novel structural color device with low material absorption, simple structure, wide color gamut, sensitive polarization response, and easy fabrication to overcome the current technological bottlenecks. Summary of the Invention

[0004] Based on this, the purpose of this invention is to provide a structured color modulation device based on the continuous domain bound state enhancement of silicon nitride metasurface. By optimizing material selection and structural design, it can achieve the generation of structured colors with wide color gamut, high saturation, and dynamically adjustable brightness, so as to improve the problems of insufficient color saturation, weak polarization modulation capability, and large resonance interference in short wavelength region of existing structured color devices.

[0005] This invention provides the following technical solution: a structure color modulation device based on silicon nitride metasurface continuous domain bound state enhancement, comprising a silicon dioxide substrate and a metasurface structure disposed on the substrate. The metasurface structure is composed of two-dimensional periodically arranged circular nanodisks, each of which has an eccentric circular air hole. The material of the metasurface structure is silicon nitride with low visible light loss. The period P of the circular nanodisks is 290–420 nm, and the thickness H is 135 nm. By breaking the C2 rotational symmetry to excite magnetic dipole quasi-continuous domain bound states, polarization-sensitive high-saturation structure color modulation is achieved in the visible light band. By designing the offset direction of the eccentric circular air holes on the circular nanodisks in different regions of the metasurface structure, the device can present different patterns under different polarized light illumination, realizing polarization-dependent information switching for information encryption and dynamic anti-counterfeiting scenarios.

[0006] More preferably, the offset of the eccentric circular air hole is adjustable. The offset is the distance between the center of the circular nanodisk and the center of the eccentric circular air hole. By adjusting the offset, the excitation efficiency of the magnetic dipole quasi-continuous domain bound state is precisely controlled, thereby realizing the dynamic switching of the structural color brightness.

[0007] More preferably, the circular nanodisks on the metasurface structure have different structural parameters, including the radius R1 of the circular nanodisk, the radius R2 of the eccentric circular air hole, and the eccentricity L; wherein the radius R1 of the circular nanodisk is 95–165 nm, the radius R2 of the eccentric circular air hole is 40–70 nm, and the eccentricity L is 20–50 nm, and different colored pixels are generated by combining different structural parameters.

[0008] More preferably, when the polarization direction of the linearly polarized light is parallel to the offset direction of the eccentric circular air hole, a magnetic dipole quasi-continuous domain bound state is excited, generating a resonance peak with a linewidth of 1-2 nm and a reflectivity of ≥90%, exhibiting a highly saturated structural color; when the polarization direction is perpendicular to the offset direction of the eccentric circular air hole, the magnetic dipole quasi-continuous domain bound state is suppressed.

[0009] Compared with existing technologies, the beneficial effects of this invention are: 1. High-performance structural color: Based on the narrow linewidth resonance characteristics of quasi-BIC, high-saturation and wide-gamut structural colors are achieved. 2. Dynamic brightness control: Utilizing strong polarization dependence, passive and dynamic control of color brightness can be achieved through simple polarization rotation without altering the structure itself. 3. Material advantages: Silicon nitride exhibits extremely low loss in the visible light band, good compatibility with silicon dioxide substrates, and structural stability. 4. Flexible applications: It is easy to realize high-contrast polarization encryption patterns, with broad application prospects in high-end anti-counterfeiting, information storage, and dynamic display fields. 5. Feasible fabrication: The adopted micro-nano fabrication process is standardized and mature, which is conducive to the actual fabrication and industrialization of devices. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the metasurface structure of the present invention; wherein Figure 1 (a) in the figure represents the structural color generated by the metasurface through the breaking of C2 symmetry; Figure 1 (b) in the figure is a top view of a single cell of a silicon nitride metasurface and a representation of geometric parameters such as period P, nanodisk radius R1, and eccentricity L.

[0011] Figure 2 This is an intrinsic mode analysis diagram of the metasurface of the present invention; wherein Figure 2 (a) shows the band structure of a periodic metasurface without substrate or etching under TE polarization (period P = 340 nm, radius R1 = 125 nm). Figure 2In (b), the quality factor at point r in the TE mode tends to infinity. The inset shows the distribution of the magnetic field Hz in this mode, indicating that the structure supports magnetic dipole-type continuous domain bound states (BIC). Figure 2 (c) in the figure shows the reflection spectrum after introducing symmetry breaking in the plane (circular air hole radius R2=50nm, eccentricity L=30nm). A single reflection peak appears under Ey polarization, while the reflection peak is almost completely suppressed under Ex polarization, showing obvious polarization sensitivity. Figure 2 In the figure (d), the result is the multipole decomposition in the Cartesian coordinate system, in which the magnetic dipole moment contribution is dominant, which is consistent with the conclusion of the intrinsic mode analysis.

[0012] Figure 3 This is a diagram showing the influence of the nanodisk structure parameters of the present invention on the reflectance spectrum; wherein... Figure 3 (a) shows the relationship between the radius R1 of different nanodisks and the wavelength; Figure 3 (b) shows the relationship between wavelength and the position L of the circular air hole offset center at different locations.

[0013] Figure 4 The image shows the reflection spectrum and color characterization of the polarization-sensitive metasurface of this invention; wherein... Figure 4 (a) and Figure 4 (b) in the figure represents the high-saturation, wide-gamut structural color reflectance spectrum achieved by adjusting structural parameters; Figure 4 (c) in the diagram represents the distribution of reflected colors in the CIE 1931 chromaticity diagram corresponding to different structural parameters.

[0014] Figure 5 The polarization-correlated structure color map prepared for the experiment of this invention; wherein Figure 5 (a) in the diagram is a schematic diagram of the experimental optical path; Figure 5 (b) in the figure shows the relationship between the structural color brightness and the polarization angle; Figure 5 (c) in the diagram represents the structural color pattern under different polarized light illumination. Detailed Implementation

[0015] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Several embodiments of the invention are illustrated in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

[0016] It should be noted that when a component is said to be "fixed to" another component, it can be directly on the other component or there may be an intervening component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there may be an intervening component. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0018] Example 1: This example provides a structured color modulation device based on the continuum bound state enhancement of silicon nitride metasurface, such as... Figure 1 As shown, it includes a silicon dioxide substrate and a silicon nitride metasurface structure formed on the substrate. The silicon nitride metasurface structure consists of multiple nanodisks arranged in a two-dimensional periodic pattern. Each unit cell in the nanodisk is a square lattice. Each nanodisk has a circular air hole, and the center of the air hole has a set offset relative to the geometric center of the nanodisk. This structural feature breaks the original C2 rotational symmetry of the nanodisk, thereby transforming the symmetry-protected ideal continuous domain bound state (BIC) mode into a polarization-selective magnetic dipole quasi-continuous domain bound state (BIC) mode that can be excited by incident light.

[0019] In some embodiments, the nanodisc period P is 290–420 nm, such as Figure 1 As shown, the period P refers to the side length of the square unit cell (unit cell) of the nanodisk, which is also... Figure 1 The spacing between corresponding feature points (geometric centers) of adjacent nanodisks in the square array of upper nanodisks, the thickness H is 135nm, the nanodisk radius R1, the air hole radius R2 and the eccentricity L are adjustable parameters, where the eccentricity L is the distance between the center of the nanodisk and the center of the circular air hole.

[0020] Specifically, the nanodisk radius R1 is 95–165 nm, and the air hole radius R 22 The wavelength is 40–70 nm, and the eccentricity L is 20–50 nm.

[0021] Specifically, the control device in this embodiment has polarization sensitivity, exhibiting a narrow linewidth reflection peak under Ey polarized light and near-zero reflectivity under Ex polarization, thus achieving adjustable brightness structural color display.

[0022] Specifically, the core working principle of the control device in this embodiment is as follows: when the polarization direction of linearly polarized light is parallel to the offset direction of the circular air hole (defined as Ey polarization), the magnetic dipole quasi-BIC mode can be effectively excited, generating a resonance peak with narrow linewidth (about 1-2nm) and high reflectivity (>90%) at a specific wavelength, exhibiting a highly saturated structural color; when the polarization direction is perpendicular to the offset direction of the circular air hole (Ex polarization), this mode cannot be excited, the reflectivity is extremely low, and the color almost disappears. By rotating the polarization direction of the incident light, continuous and dynamic adjustment of color brightness can be achieved.

[0023] Furthermore, by spatially arranging nanodisks with different structural parameters on the metasurface structure, pixels of different colors can be generated.

[0024] Furthermore, by designing the eccentric direction of the nanodiscs in a specific pattern, it is possible to display different information (such as pattern switching) under different polarized light illumination, which greatly enhances its application potential in information encryption and dynamic anti-counterfeiting.

[0025] Example 2: Based on Example 1, the performance of the device in Example 1 is simulated using the finite-difference time-domain method and the finite element method.

[0026] Figure 2 (a) shows the band structure of the substrate-free nanodisk array metasurface structure calculated along the irreducible Brillouin zone path X´–Γ–X (where the nanodisk period P = 340 nm and the radius R1 = 125 nm). The results show that when the normalized frequency is 0.694, the eigenfrequency of the transverse electric mode at the Γ point contains only the real part and the imaginary part is zero, and the corresponding quality factor tends to infinity, which is consistent with the characteristics of an ideal BIC. Figure 2 Further analysis of the magnetic field Hz distribution at the Γ point in (b) of the model reveals that it exhibits even symmetry under z-axis rotational symmetry operation, indicating that the model is orthogonal to the incident electromagnetic field and belongs to the symmetry-protected BIC.

[0027] Furthermore, to verify the behavior of quasi-continuous bound states (quasi-BIC) in real space, this study further performed numerical simulations of the reflection spectra under two polarization states and conducted multipole decomposition analysis. For example... Figure 2 As shown in (c), under Ey polarized illumination, the structure exhibits a distinct narrow linewidth reflection peak near 502 nm, with a linewidth of only about 1 nm and a reflectivity exceeding 90%; while under Ex polarization, the reflectivity at this wavelength is close to zero, showing a strong polarization dependence. Figure 2 The multipole decomposition results in (d) show that the resonance peak mainly originates from the contribution of the magnetic dipole, which is consistent with the magnetic field distribution obtained from the intrinsic mode analysis, confirming that the mode is the magnetic dipole quasi-BIC mode.

[0028] Furthermore, to achieve structural colors with high saturation and a wide color gamut, the reflection spectrum needs to possess a single resonance peak with a narrow linewidth, and its resonance wavelength should be continuously tunable within the visible light range. Therefore, it is necessary to systematically study the influence of various geometric parameters of the metasurface structure on the reflection spectrum characteristics to guide the optimized design of the device. Under the premise of ensuring practical fabrication feasibility, this embodiment fixes the thickness of all metasurface structures (H=135nm), and systematically adjusts parameters such as the period P, nanodisk radius R1, air hole radius R2, and the offset distance L of the hole center. Among these, R2 and L, as perturbation parameters for symmetry breaking, are mainly used to control the linewidth of the resonance mode, thereby affecting color saturation. Figure 3 As shown in (a), the nanodisk radius R1 has a significant modulating effect on the reflection spectrum: when R1 is too large, the coupling between array units is enhanced, inducing a double-peak structure near 500 nm; when R1 is reduced to 125 nm, the Mie resonance enters the Rayleigh anomalous diffraction region, forming a single reflection peak covering the entire spectral range; further reducing R1 leads to a sparser array structure, significantly weakened coupling between resonators, decreased resonance intensity, and almost disappearance of resonance features in the reflection spectrum. In contrast, as... Figure 3 As shown in (b), the offset distance L of the center of the circular air hole has little effect on the resonant wavelength. This is mainly because the change of this parameter does not significantly change the overall equivalent refractive index of the structure, so the resonant wavelength remains relatively stable.

[0029] Furthermore, since metasurface structures involve numerous design parameters, this embodiment employs the finite-difference time-domain method for numerical simulation to achieve the generation of wide color gamut and high-saturation structural colors. We simulated the reflection spectrum of the visible light band (380nm to 780nm) under different polarization states, and the results are as follows: Figure 4 (a) and Figure 4 As shown in (b) of the figure, under Ey polarization, the metasurface structure exhibits a single and clear reflection peak across the entire wavelength range (represented by the colored curves in the figure), while no obvious reflection peak appears under Ex polarization (marked by the red line in the figure). Further conversion of the reflection spectrum to the CIE 1931 chromaticity diagram... Figure 4 Results (c) show that the generated structural color covers approximately 90% of the sRGB color gamut, with two color points even extending beyond the sRGB color gamut boundary. These results demonstrate that structural colors with vivid colors and wide color gamut coverage can be achieved by adjusting the parameters of the quasi-BIC (quasi-bounded continuous domain) mode.

[0030] Furthermore, polarization imaging experiments verified the performance of the structural colors generated by the magnetic dipole quasi-continuous domain bound state (MD-qBIC) resonance. The optical experimental setup is as follows: Figure 5As shown in (a): The sample was uniformly illuminated by a broadband halogen lamp, which provided a continuous spectrum covering the visible to near-infrared range. During the experiment, the Köhler illumination method was strictly used to reduce the aperture of the condenser lens to a usable state. The reflected light was collected by the same objective lens and separated from the incident light path by a beam splitter. A linear polarizer was installed in the illumination path to control the polarization state of the incident light. To analyze the polarization response, another polarizer was placed in front of the camera lens as an analyzer. A series of images were acquired by synchronously rotating the angles of the polarizer and the analyzer.

[0031] like Figure 5 As shown in (b), the colored patches fabricated based on the silicon nitride (Si3N4) metasurface structure exhibit blue, green, yellow, and orange colors, with each patch measuring 500 μm × 500 μm. Compared to the numerical simulation results, the experimental samples show a certain blue shift, mainly attributed to structural size deviations during fabrication. Nevertheless, the experimental results successfully verify that a wide color gamut of structural color coverage can be achieved by adjusting structural parameters. Due to the significant polarization-dependent optical response of this nanodisk array structure, its display brightness changes significantly with the incident polarization angle. When the polarization angle rotates from 0° (Ex polarization) to 90° (Ey polarization), the color gradually brightens from dark: under Ex polarization, the color patch is almost gray due to extremely low reflectivity; at 45° polarization, the color gradually appears; under Ey polarization, the reflectivity exceeds 90%, resulting in bright and vivid colors.

[0032] To further verify the polarization control capability, a set of coded patterns was designed by adjusting the position of the circular air holes. Specifically, the eccentricity of the nanodisk in the serpentine pattern region was set along the x-axis, and the eccentricity of the nanodisk in the "2025" number pattern region was set along the y-axis. Figure 5 As shown in (c), the serpentine pattern is excited only under Ey polarization, while the "2025" digital pattern corresponds to Ex polarization excitation, thus achieving polarization-dependent pattern switching. Specifically, under Ex polarization, the "2025" pattern appears as a bright color, while the serpentine pattern is close to gray; under Ey polarization, the brightness and darkness of the two are reversed. Under white light illumination, the patterns exhibit a different visual contrast effect compared to the single polarization condition.

[0033] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0034] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A structured color modulation device based on continuous domain bound states enhanced by silicon nitride metasurface, characterized in that, The device includes a silicon dioxide substrate and a metasurface structure disposed on the substrate. The metasurface structure consists of two-dimensionally periodically arranged circular nanodisks, each of which has an eccentric circular air hole. The metasurface structure is made of silicon nitride with low visible light loss. The period P of the circular nanodisks is 290–420 nm, and the thickness H is 135 nm. By breaking the C2 rotational symmetry to excite the quasi-continuous domain bound states of the magnetic dipole type, polarization-sensitive high-saturation structural color modulation is achieved in the visible light band. By designing the offset direction of the eccentric circular air holes on the circular nanodisks in different regions of the metasurface structure, the device can present different patterns under different polarized light illumination. The circular nanodisks on the metasurface structure have different structural parameters, including the radius R1 of the circular nanodisk, the radius R2 of the eccentric circular air hole, and the eccentricity L. Among them, the radius R1 of the circular nanodisk is 95–165 nm, the radius R2 of the eccentric circular air hole is 40–70 nm, and the eccentricity L is 20–50 nm. Different color pixels are generated by combining different structural parameters.

2. The structure color modulation device based on the continuum domain bound state enhancement of silicon nitride metasurface as described in claim 1, characterized in that, The offset of the eccentric circular air hole is adjustable. The offset is the distance between the center of the circular nanodisk and the center of the eccentric circular air hole. By adjusting the offset, the excitation efficiency of the magnetic dipole quasi-continuous domain bound state is controlled, thereby realizing the dynamic switching of the structural color brightness.

3. The structure color modulation device based on the continuum domain bound state enhancement of silicon nitride metasurface as described in claim 1, characterized in that, When the polarization direction of linearly polarized light is parallel to the offset direction of the eccentric circular air hole, a magnetic dipole quasi-continuous domain bound state is excited, generating a resonance peak with a linewidth of 1-2 nm and a reflectivity of ≥90%, exhibiting a highly saturated structural color; when the polarization direction is perpendicular to the offset direction of the eccentric circular air hole, the magnetic dipole quasi-continuous domain bound state is suppressed.

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