A continuous domain bound state metasurface device and a spectral modulation method thereof

Abstract

This invention discloses a continuous-domain bound-state metasurface device and its spectral modulation method, relating to the field of metasurface technology. The metasurface device includes a transparent dielectric substrate, an electro-optic material thin film, and an electro-optic material grating. The electro-optic material thin film covers the transparent dielectric substrate, and the electro-optic material grating is disposed on the electro-optic material thin film. The electro-optic material grating includes multiple periodic units arranged side by side, and each periodic unit includes two electro-optic material ridges. This invention continuously modulates the refractive index of the electro-optic material ridges by applying different voltages, thereby achieving spectral modulation of the continuous-domain bound-state metasurface device. No fabrication of the continuous-domain bound-state metasurface device is required, eliminating fabrication errors and ensuring high-precision spectral modulation. Simultaneously, by applying voltage, structural geometric asymmetry can be compensated, eliminating the need to manufacture multiple sets of devices, improving efficiency and reducing costs.

Description

Technical Field

[0001] This invention relates to the field of metasurface technology, and in particular to a continuous-domain bound-state metasurface device and its spectral modulation method. Background Technology

[0002] Bound states in the continuous (BIC) are special eigenstates in open systems whose energy lies within the radiation continuous spectrum yet remains localized. Their physical essence stems from wave interference cancellation or symmetry protection mechanisms, allowing the mode to coexist with extended states without radiating energy into free space. Quasi-continuous bound states (quasi-BIC, q-BIC) are excitable high-quality factor resonance states that evolve from continuous bound states through perturbations or symmetry breaking. In metasurface systems, by breaking the symmetry of the continuous bound state unit structure, continuous bound states can be transformed into quasi-continuous bound states, enabling them to be excited by incident light of specific polarization or angle. By altering the degree of asymmetry in the unit structure, the optical behavior of continuous bound states can be tuned, demonstrating unique application potential in optical sensing, narrowband filtering, and spectral selective enhancement.

[0003] However, most of the continuous-domain bound-state metasurface devices that have attracted much attention in recent years rely solely on micro- and nano-fabrication techniques to achieve geometric asymmetries in the metasurface structure and excite quasi-continuous-domain bound-state modes. However, due to the limitations of fabrication precision, the nanostructure dimensions inevitably contain fabrication errors, leading to resonant frequency shifts and affecting spectral modulation accuracy. Once the device is fabricated, properties such as structural asymmetry remain fixed. Achieving different asymmetries typically requires fabricating multiple sets of devices, resulting in low fabrication efficiency, high costs, and difficulty in achieving fine and dynamic spectral modulation. These limitations restrict the application performance and scope of metasurface devices. Summary of the Invention

[0004] Based on the shortcomings of the existing technology, the present invention provides a continuous domain bound state metasurface device and its spectral modulation method, which solves the problems of device processing errors affecting spectral modulation accuracy and the inability to achieve different asymmetries after device processing.

[0005] The present invention adopts the following technical solution: In a first aspect, the present invention provides a continuous domain bound state metasurface device, comprising a transparent dielectric substrate, an electro-optic material thin film, and an electro-optic material grating; the electro-optic material thin film covers the transparent dielectric substrate, the electro-optic material grating is disposed on the electro-optic material thin film, the electro-optic material grating comprises a plurality of periodic units arranged in a continuous parallel arrangement, each periodic unit comprising two electro-optic material ridge strips with identical structures; wherein, the refractive index of the sidewall of the electro-optic material ridge strip on the left side of each periodic unit is modulated by applying a voltage along the width direction.

[0006] Preferably, the transparent dielectric substrate is silicon dioxide.

[0007] Preferably, the electro-optic material in the electro-optic material thin film and the electro-optic material grating is an electro-optic crystal material.

[0008] Preferably, the thickness of the electro-optic material film is 200nm-500nm.

[0009] Preferably, the periodicity constant of the periodic unit is 0.5μm-1.5μm, the height is 200nm-500nm, and the center-to-center distance between the two electro-optic material ridge strips in each periodic unit is 250nm-750nm.

[0010] Secondly, the present invention provides a method for spectral modulation of a continuous-domain bound metasurface device, comprising the following steps: Incident light is incident perpendicularly onto an electro-optic material grating, wherein the wavelength of the incident light is 1.61 μm–1.63 μm; A voltage along its width direction is applied to the electro-optic material ridge strip on the left side of each periodic unit. The refractive index of the electro-optic material ridge strip is continuously modulated by the electro-optic effect, thereby realizing the control of the spectrum of the continuous domain bound state metasurface device.

[0011] Compared with the prior art, the above-mentioned at least one technical solution adopted by the present invention can achieve the following beneficial effects: This invention proposes a continuous-domain bound-state metasurface device, comprising a transparent dielectric substrate, an electro-optic material thin film, and an electro-optic material grating. The electro-optic material thin film covers the transparent dielectric substrate, and the electro-optic material grating is disposed on the electro-optic material thin film. The electro-optic material grating includes multiple periodic units arranged along the z-axis, and each periodic unit includes two electro-optic material ridges arranged along the z-axis. When no voltage is applied, the geometric parameters and refractive index of the entire metasurface device are identical, and the metasurface supports continuous-domain bound-state modes. When different voltages are applied, the refractive index of the electro-optic material ridges is continuously modulated using the electro-optic effect, thereby achieving spectral control of the continuous-domain bound-state metasurface device. No fabrication of the continuous-domain bound-state metasurface device is required, eliminating fabrication errors and ensuring high-precision spectral modulation. Simultaneously, by applying voltage, structural geometric asymmetry can be compensated, eliminating the need to manufacture multiple sets of devices, improving efficiency and reducing costs. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a structural diagram of a continuous-domain bound metasurface device according to the present invention; Figure 2 This is a cross-sectional schematic diagram of a periodic unit in a continuous domain bound metasurface device according to the present invention; Figure 3 The transmission spectra of a continuous-domain bound metasurface device of the present invention under different applied voltages are shown below. Figure 4 This is a cross-sectional schematic diagram of a periodic unit in a quasi-continuous domain bound metasurface device according to the present invention; Figure 5 The transmission spectra of a quasi-continuous domain bound state metasurface device of the present invention under different applied voltages are shown.

[0014] In the figure: 1-transparent dielectric substrate, 2-electro-optic material thin film, 3-electro-optic material grating. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] To address the above problems, this invention provides a continuous-domain bound-state metasurface device, such as... Figure 1 As shown, it specifically includes a transparent dielectric substrate 1, an electro-optic material thin film 2, and an electro-optic material grating 3. The transparent dielectric substrate 1 is silicon dioxide. Silicon dioxide is transparent and readily available, and is a widely used optical substrate material. Its thickness has no special requirements, as long as it is greater than the optical thickness.

[0017] An electro-optic material thin film 2 is coated on a transparent dielectric substrate 1, and an electro-optic material grating 3 is disposed on the electro-optic material thin film 2. The electro-optic material in the electro-optic material thin film 2 and the electro-optic material grating 3 is an electro-optic crystal material. The thickness of the electro-optic material thin film is 200 nm-500 nm.

[0018] The electro-optic grating 3 comprises multiple periodic units arranged along the z-axis, each periodic unit including two electro-optic material ridges arranged along the z-axis. The period constant of each periodic unit is 0.5μm-1.5μm, the height is 200nm-500nm, and the center-to-center distance between the two electro-optic material ridges within each periodic unit is 250nm-750nm.

[0019] Based on the same concept, this invention also provides a method for spectral modulation of continuous-domain bound metasurface devices, comprising the following steps: S1: Place the continuous domain bound metasurface device in the working environment.

[0020] S2: Incident light is incident perpendicularly along the negative y-axis onto the electro-optic material grating 3, with a wavelength of 1.61 μm–1.63 μm. Different z-axis voltages are applied to the electro-optic material ridge strips on the left side of each periodic unit through electrodes. The refractive index of the electro-optic material ridge strips is continuously modulated using the electro-optic effect, thereby changing the refractive index symmetry of the two electro-optic ridge strips in the grating. This allows for precise, dynamic, continuous, and on-demand control of the continuous domain bound-state resonant frequency and linewidth.

[0021] Example 1: Reference Figure 1 and Figure 2 The continuous-domain bound-state metasurface device in this embodiment consists of a transparent dielectric substrate 1, an electro-optic material thin film 2, and an electro-optic material grating 3 composed of the same electro-optic material. The transparent dielectric substrate 1 is made of silicon dioxide, with a thickness of... h1. No special requirements (as long as it is greater than the optical thickness). 2. Electro-optic material thin film 2 is selected from x-cut lithium niobate, its thickness... h 2 is 300nm. The change in refractive index relies on the electro-optic effect of the electro-optic crystal material. Lithium niobate is one of the most widely used electro-optic crystal materials, with a large electro-optic coefficient and a significant electro-optic effect. The electro-optic grating 3 is composed of the same x-cut lithium niobate, periodically arranged along the z-direction, with a period constant of... P =1μm, including the center-to-center spacing of two lines arranged along the z-direction. D =500nm x-cut lithium niobate ridge strip, ridge strip width d Both are 300nm, high h All three are 300nm, forming a geometrically symmetrical structure.

[0022] The periodic unit cell of the metasurface was numerically simulated using the finite-difference time-domain (FDTD) method. Linearly polarized parallel light with a wavelength range of 1.61 μm to 1.63 μm was used as excitation during the simulation. The z-direction was set as a periodic boundary condition, and the y-direction was set as a perfect matched layer (PML).

[0023] When no voltage is applied, the geometric parameters and refractive index of the two x-cut lithium niobate ridge strips within each periodic cell are exactly the same (e.g., Figure 2 As shown). At this point, the metasurface supports continuous-domain bound state modes, and the transmission spectrum exhibits high transmission properties across the entire wavelength range (e.g., Figure 3 (The voltage shown is 0). To achieve dynamic control from continuous-domain bound state to quasi-continuous-domain bound state, a voltage is applied to the left-hand x-cut lithium niobate ridge sidewall within each periodic unit. The higher the voltage, the greater the spectral control range (resonance frequency and linewidth variation). This embodiment uses a voltage range of 0V-30V as an example.

[0024] The refractive index variation of x-cut lithium niobate material conforms to the following: ; in, This is the unusual refractive index of lithium niobate, taken as 2.14 without applied voltage. It is the change in the unusual refractive index of lithium niobate. This is an electro-optic coefficient of lithium niobate, which is taken as 30.8 pm / V in this embodiment. U It is the voltage applied across the lithium niobate strip. It is the width of the lithium niobate strip.

[0025] The relationship between the spectral properties of the metasurface and the applied voltage was verified using the finite-difference time-domain numerical simulation method. Figure 3 The graph shows the changes in the transmission spectrum of the metasurface under different applied voltages. When no voltage is applied (applied voltage is 0), the geometry and refractive index properties of the metasurface grating structure exhibit perfect symmetry, supporting continuous-domain bound-state modes, and the transmission spectrum displays high transmission across the entire wavelength range. After applying a voltage, the symmetry of the refractive index is disrupted, and a sudden drop in transmittance occurs near 1.618 μm. The continuous-domain bound-state mode transforms into a quasi-continuous-domain bound-state mode. The greater the applied voltage, the greater the refractive index asymmetry, the more significant the decrease in light transmittance, and the greater the changes in wavelength and linewidth of the quasi-continuous-domain bound-state mode.

[0026] In summary, by applying voltage, dynamic, continuous, precise, and on-demand modulation of the transformation from a continuous domain bound state to a quasi-continuous domain bound state is achieved.

[0027] Example 2: like Figure 4 As shown, this embodiment also provides a quasi-continuous domain bound-state metasurface device, which is composed of a transparent dielectric substrate, an electro-optic material thin film, and an electro-optic material grating composed of the same electro-optic material. The transparent dielectric substrate is silicon dioxide, with a thickness of... h 4. No special requirements (as long as it is greater than the optical thickness). The electro-optic material thin film should be X-cut lithium niobate or other commonly used electro-optic crystal materials, with a thickness of... h 5 represents 300 nm. The electro-optic grating consists of x-cut lithium niobate or other commonly used electro-optic crystal materials arranged in ridges, periodically along the z-axis, with a period constant of . P 1 = 1 μm, including the center-to-center spacing of two lines arranged along the z-axis. D 1=500nm lithium niobate or other commonly used electro-optic materials ridge strips, electro-optic material ridge strip height h All 6 are 300nm, and the width of the ridge strip of the electro-optic material on the left is... d 1 represents 300 nm, and the width of the ridge strip of the electro-optic material on the right is... d The wavelength is 298 nm, resulting in a geometrically asymmetric structure. This type of geometrically asymmetric structure is commonly seen in processing errors caused by optical micro-nano fabrication.

[0028] The metasurface periodic structure was numerically simulated using the finite-difference time-domain numerical simulation method, with the simulation settings being the same as those in Example 1.

[0029] When no voltage is applied, the two electro-optic material ridges within each periodic unit have the same refractive index, exhibiting refractive index symmetry. However, the geometric parameters of the two ridges differ, thus breaking the geometric symmetry. In this case, the metasurface supports a quasi-continuous bound state mode, and the transmission spectrum exhibits high transmission properties over a wide wavelength range and low transmission properties in a narrow wavelength range (around 1.617 μm). Figure 5(The voltage shown is 0). To achieve dynamic control from quasi-continuous bound state to continuous bound state, a z-axis voltage is applied to the sidewall of the left electro-optic material ridge strip within each periodic unit. The higher the voltage, the greater the spectral control range (resonance frequency and linewidth variation). This embodiment uses a voltage range of 0V-30V as an example.

[0030] The change in refractive index of lithium niobate material under applied voltage is the same as in Example 1.

[0031] The relationship between the spectral properties of the metasurface and the applied voltage was verified using the finite-difference time-domain numerical simulation method. Figure 5 The diagram shows the changes in the transmission spectrum of the metasurface under different applied voltages. Without applied voltage (0 μV), the refractive index of the metasurface grating structure is symmetrical, but its geometric parameters are asymmetrical, supporting a quasi-continuous bound state mode. The transmission spectrum exhibits high transmission over a wide wavelength range and low transmission in a narrow wavelength range (around 1.617 μm). Applying a voltage disrupts the refractive index symmetry of the metasurface grating structure. As the voltage increases, the geometric and refractive index asymmetries of the metasurface grating structure compensate for each other. At approximately 22 V, the refractive index asymmetry completely compensates for the geometric asymmetry, achieving a continuous bound state mode where refractive index and geometric asymmetries coexist. This means that the refractive index asymmetry caused by the electro-optic effect compensates for the geometric asymmetry caused by processing errors. Further increasing the voltage further increases the degree of refractive index asymmetry in the metasurface grating structure, and the optical mode of the metasurface changes from a continuous bound state to a quasi-continuous bound state mode dominated by refractive index asymmetry.

[0032] In summary, by applying voltage, mutual compensation between structural geometric asymmetry and refractive index asymmetry is achieved, thereby enabling dynamic, continuous, precise, and on-demand modulation from quasi-continuous domain bound states to continuous domain bound states and then back to quasi-continuous domain bound states.

[0033] This invention combines the geometric asymmetry and refractive index asymmetry of a device, supports mutual compensation between geometric and refractive index asymmetry, realizes the correction of metasurface processing errors, and has the ability to dynamically, precisely, and on demand switch between quasi-continuous domain bound state and continuous domain bound state modes.

[0034] This invention can be applied to high-sensitivity spectral detection, tunable narrowband filtering and precision spectral modulation, and has advantages such as high sensitivity and high accuracy.

[0035] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0036] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for spectral modulation of a continuous-domain bound-state metasurface device, characterized in that, The continuous domain bound state metasurface device includes a transparent dielectric substrate (1), an electro-optic material thin film (2), and an electro-optic material grating (3); the electro-optic material thin film (2) covers the transparent dielectric substrate (1), and the electro-optic material grating (3) is disposed on the electro-optic material thin film (2). The electro-optic material grating (3) includes a plurality of periodic units arranged in a continuous parallel arrangement, and each periodic unit includes two electro-optic material ridge strips of the same height; wherein, the refractive index of the sidewall of the electro-optic material ridge strip on the left side of each periodic unit is modulated by applying a voltage along the width direction. The spectral modulation method includes the following steps: The incident light is incident perpendicularly onto the electro-optic material grating (3), and the wavelength of the incident light is 1.61 μm–1.63 μm; A voltage along its width direction is applied to the electro-optic material ridge strip on the left side of each periodic unit. The refractive index of the electro-optic material ridge strip is continuously modulated by the electro-optic effect, thereby realizing the control of the spectrum of the continuous domain bound state metasurface device. The periodic unit has a period constant of 0.5μm-1.5μm and a height of 200nm-500nm. The center-to-center distance between the two electro-optic material ridges in each periodic unit is 250nm-750nm. The electro-optic material ridges on the left and right sides have the same height but different widths, forming a geometrically asymmetrical structure. A voltage of 0V-30V is applied to the geometrically asymmetrical structure, and the asymmetry of the refractive index and the geometric asymmetry compensate for each other.

2. The spectral modulation method for a continuous-domain bound-state metasurface device as described in claim 1, characterized in that, The transparent dielectric substrate (1) is silicon dioxide.

3. The spectral modulation method for a continuous-domain bound-state metasurface device as described in claim 1, characterized in that, The electro-optic material in the electro-optic material thin film (2) and the electro-optic material grating (3) is an electro-optic crystal material.

4. The spectral modulation method for a continuous-domain bound-state metasurface device as described in claim 1, characterized in that, The thickness of the electro-optic material film is 200nm-500nm.

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