Continuous domain bound state metasurface device and spectrum regulation and control method thereof

Abstract

The invention discloses a continuous domain bound state metasurface device and a spectrum regulation and control method thereof, and relates to the technical field of metasurface, the metasurface device comprises a transparent medium substrate, an electro-optical material film and an electro-optical material grating; the electro-optical material film covers the transparent medium substrate, the electro-optical material grating is arranged on the electro-optical material film, the electro-optical material grating comprises a plurality of periodic units which are arranged side by side, and each periodic unit comprises two electro-optical material ridge-shaped strips. When different voltages are applied, the refractive index of the ridge-shaped strip of the electro-optical material is continuously modulated by using the electro-optical effect, so that the spectrum of the continuous domain bound state metasurface device is regulated and controlled. The continuous domain bound state metasurface device does not need to be machined, machining errors do not exist, and high-precision spectrum modulation is guaranteed. Meanwhile, by applying the voltage, the geometric asymmetry of the structure can be compensated, multiple groups of devices do not need to be manufactured, the efficiency is improved, and the cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of metasurfaces, and particularly to a bound state in the continuum metasurface device and its spectral regulation method. Background Art

[0002] A bound state in the continuum (BIC) is a special eigenstate in an open system where the energy lies within the radiative continuum spectrum but can remain localized. Its physical essence stems from the mechanism of destructive wave interference or symmetry protection, enabling this mode to coexist with extended states without radiating energy into free space. A quasi-bound state in the continuum (quasi-BIC, q-BIC) is an excitable high-quality factor resonance state evolved from the bound state in the continuum through perturbation or symmetry breaking. In the metasurface system, by breaking the symmetry of the bound state in the continuum unit structure, the bound state in the continuum can be transformed into a quasi-bound state in the continuum, enabling it to be excited by incident light with a specific polarization or angle. By changing the degree of asymmetry of the unit structure, the optical behavior of the bound state in the continuum can be regulated, showing unique application potential in the fields of optical sensing, narrowband filtering, and spectral selectivity enhancement.

[0003] However, most of the bound state in the continuum metasurface devices that have received wide attention in recent years solely achieve the geometric asymmetry of the metasurface structure based on micro-nano processing technology to excite the quasi-bound state in the continuum mode. However, affected by the processing accuracy, there will inevitably be processing errors in the size of the nanostructure, which will in turn lead to the shift of the resonance frequency and affect the spectral modulation accuracy. Once the device is processed, various properties such as the degree of structural asymmetry are fixed. To achieve different degrees of asymmetry, usually multiple sets of devices need to be manufactured, with low processing efficiency and high cost, and it is difficult to achieve fine and dynamic spectral modulation. This limits the application performance and fields of the metasurface device. Summary of the Invention

[0004] Based on the defects existing in the above-mentioned prior art, the present invention provides a bound state in the continuum metasurface device and its spectral regulation method, which solves the problems that the device is affected by processing errors, affecting the spectral modulation accuracy, and the device cannot achieve different degrees of asymmetry after being processed.

[0005] The present invention adopts the following technical solutions: 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, and the electro-optic material grating is disposed on the electro-optic material thin film. The electro-optic material grating includes a plurality of periodically arranged units arranged side by side continuously, and each periodic unit includes two electro-optic material ridge-shaped strips with the same structure; wherein, the side wall of the electro-optic material ridge-shaped strip on the left side of each periodic unit modulates its refractive index by applying a voltage along the width direction.

[0006] Preferably, the transparent dielectric substrate is silica.

[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 thin film is 200 nm - 500 nm.

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

[0010] In a second aspect, the present invention provides a spectral modulation method for a continuous domain bound state metasurface device, comprising the following steps: Vertically incident an incident light on the electro-optic material grating, and the wavelength of the incident light is 1.61 μm - 1.63 μm; Apply a voltage along the width direction to the electro-optic material ridge-shaped strip on the left side of each periodic unit, and continuously modulate the refractive index of the electro-optic material ridge-shaped strip by using the electro-optic effect to achieve the spectral modulation of the continuous domain bound state metasurface device.

[0011] Compared with the prior art, the above at least one technical solution adopted by the present invention can achieve the following beneficial effects: The present invention proposes a continuous-domain bound state metasurface device, which 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, the electro-optic material grating is arranged on the electro-optic material thin film, and the electro-optic material grating includes a plurality of periodic units arranged along the z direction, and each periodic unit includes two electro-optic material ridge-shaped strips arranged along the z direction. When no voltage is applied, the geometric parameters and refractive indices of the entire metasurface device are exactly the same, and the metasurface supports the continuous-domain bound state mode. When different magnitudes of voltage are applied, the refractive index of the electro-optic material ridge-shaped strip is continuously modulated by using the electro-optic effect, so as to realize the regulation of the spectrum of the continuous-domain bound state metasurface device. There is no need to process the continuous-domain bound state metasurface device, and there is no processing error, which ensures high-precision spectrum modulation. At the same time, by applying voltage, the geometric asymmetry of the structure can be compensated, and there is no need to manufacture multiple groups of devices, which improves the efficiency and reduces the cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0013] Figure 1 It is a structural diagram of a continuous-domain bound state metasurface device of the present invention; Figure 2 It is a cross-sectional schematic diagram of a periodic unit in a continuous-domain bound state metasurface device of the present invention; Figure 3 It is a transmission spectrum diagram of a continuous-domain bound state metasurface device of the present invention under different applied voltages; Figure 4 It is a cross-sectional schematic diagram of a periodic unit in a quasi-continuous-domain bound state metasurface device of the present invention; Figure 5 It is a transmission spectrum diagram of a quasi-continuous-domain bound state metasurface device of the present invention under different applied voltages.

[0014] In the figure: 1 - transparent dielectric substrate, 2 - electro-optic material thin film, 3 - electro-optic material grating. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0015] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0016] Based on the above problems, the present invention provides a continuous domain bound state metasurface device, as Figure 1 shown, which 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 made of silica. Silica is transparent and easily available, and is a widely used optical substrate material. There is no special requirement for its thickness, and it only needs to be greater than the optical thickness.

[0017] 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 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 material grating 3 includes a plurality of periodic units arranged along the z direction. Each periodic unit includes two electro-optic material ridge-shaped strips arranged along the z direction. The period constant of each periodic unit is 0.5 μm - 1.5 μm, the height is 200 nm - 500 nm, and the center distance between the two electro-optic material ridge-shaped strips in each periodic unit is 250 nm - 750 nm.

[0019] Based on the same concept, the present invention also provides a spectral regulation method for a continuous domain bound state metasurface device, including the following steps: S1: Place the continuous domain bound state metasurface device in the working environment.

[0020] S2: Vertically incident the incident light along the negative y-axis direction onto the electro-optic material grating 3. The wavelength of the incident light is 1.61 μm - 1.63 μm. Apply different magnitudes of z-direction voltages to the electro-optic material ridge-shaped strip on the left side of each periodic unit through an electrode, and continuously modulate the refractive index of the electro-optic material ridge-shaped strip by using the electro-optic effect, so as to change the refractive index symmetry of the two electro-optic ridge-shaped strips in the grating, and realize the fine, dynamic, continuous, and on-demand regulation of the resonance frequency and linewidth of the continuous domain bound state.

[0021] Embodiment 1: Refer to Figure 1 and Figure 2 , the continuous domain bound state metasurface device of this embodiment is composed 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 selected as silica, and the thickness h1. There are no special requirements (as long as it is greater than the optical thickness). The electro-optic material thin film 2 is made of x-cut lithium niobate, and its thickness h 2 is 300 nm. Among them, the change in refractive index depends on the electro-optic effect of the electro-optic crystal material. Lithium niobate is one of the most widely used electro-optic crystal materials at present, with a relatively large electro-optic coefficient and obvious electro-optic effect. The electro-optic material grating 3 is composed of the same x-cut lithium niobate, arranged periodically along the z direction, and the period constant is P = 1 μm, including two x-cut lithium niobate ridge-shaped strips arranged along the z direction with a center spacing D = 500 nm, and the width of the ridge-shaped strip d is 300 nm for both, and the height h 3 is 300 nm for both, forming a geometrically symmetric structure.

[0022] The finite-difference time-domain (FDTD) numerical simulation method is used to numerically simulate the periodic unit of the metasurface. When simulating, linearly polarized parallel light with a wavelength range of 1.61 μm - 1.63 μm is used as the excitation, the z direction is set as the periodic boundary condition (Periodic), and the y direction is set as the perfect matched layer (PML).

[0023] When no voltage is applied, the geometric parameters and refractive indices of the two x-cut lithium niobate ridge-shaped strips in each periodic unit are exactly the same (as Figure 2 shown). At this time, the metasurface supports the bound state in the continuum mode, and the transmission spectrum shows high transmission properties in the entire band (as Figure 3 shown when the voltage is 0). To achieve the dynamic regulation from the bound state in the continuum to the quasi-bound state in the continuum, a voltage is applied to the side wall of the left x-cut lithium niobate ridge-shaped strip in each periodic unit. The greater the voltage, the greater the spectral regulation range (the change in resonance frequency and linewidth). In this embodiment, the voltage range of 0 V - 30 V is taken as an example.

[0024] The change in the refractive index of the x-cut lithium niobate material conforms to the following: ; Among them, is the extraordinary refractive index of lithium niobate, which is taken as 2.14 when no voltage is applied, is the change in the extraordinary refractive index of lithium niobate, is an electro-optic coefficient of lithium niobate, which is taken as 30.8 pm / V in this embodiment, U is the voltage applied across the lithium niobate strip, is the width of the lithium niobate strip.

[0025] The relationship between the spectral characteristics of the metasurface and the applied voltage is verified by the finite-difference time-domain numerical simulation method.Figure 3 The variation of the transmission spectrum of the metasurface under different applied voltages is shown. When no voltage is applied (the applied voltage is 0), both the geometric and refractive index properties of the metasurface grating structure have perfect symmetry, supporting the bound state in the continuum mode, and the transmission spectrum shows high transmission properties across the entire band. After applying the voltage, the symmetry of the refractive index of the structure is broken, and there is a sudden drop in the transmittance of the spectrum near 1.618 μm. The bound state in the continuum mode transforms into a quasi-bound state in the continuum mode. The greater the applied voltage, the greater the refractive index asymmetry, the more significant the reduction in light transmittance, and the greater the changes in the wavelength and linewidth of the quasi-bound state in the continuum mode.

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

[0027] Example 2: As Figure 4 shown, this example also provides a quasi-bound state in the continuum metasurface device, which consists 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 selected as silica, and the thickness h 4 has no special requirements (as long as it is greater than the optical thickness). The electro-optic material thin film is selected as x-cut lithium niobate or other common electro-optic crystal materials, and the thickness h 5 is 300 nm. The electro-optic material grating is composed of x-cut lithium niobate or other common electro-optic crystal material ridge strips, which are periodically arranged along the z-direction, and the period constant is P 1 = 1 μm, including two lithium niobate or other common electro-optic material ridge strips arranged along the z-direction with a center spacing D 1 = 500 nm. The height h 6 of the electro-optic material ridge strips is 300 nm. The width d 1 of the left electro-optic material ridge strip is 300 nm, and the width d 2 of the right electro-optic material ridge strip is 298 nm, forming a geometrically asymmetric structure. This geometrically asymmetric structure is commonly found in processing errors caused by optical micro-nano processing.

[0028] The finite-difference time-domain numerical simulation method is used to numerically simulate the periodic structure of the metasurface, and the simulation settings are the same as those in Example 1.

[0029] When no voltage is applied, the refractive indices of the two electro-optic material ridge strips in each period unit are the same, having refractive index symmetry, but the geometric parameters of the two ridge strips are different, and the geometric symmetry is broken. At this time, the metasurface supports the quasi-bound state in the continuum mode, and the transmission spectrum shows high transmission properties in a wide band and low transmission properties at a narrow band (near the wavelength of 1.617 μm) (as Figure 5When the voltage shown is 0). To achieve the dynamic regulation of the bound state in the quasi-continuous domain to the bound state in the continuous domain, a z-direction voltage is applied to the side wall of the ridge-shaped strip of the electro-optic material on the left side within each periodic unit. The greater the voltage, the greater the spectral regulation range (the change in resonance frequency and linewidth). In this embodiment, the voltage range of 0V - 30V is taken as an example.

[0030] When applying the voltage, the variation law of the refractive index of the lithium niobate material is the same as that in Embodiment 1.

[0031] The relationship between the spectral characteristics of the metasurface and the applied voltage is verified by the finite-difference time-domain numerical simulation method. Figure 5 Shows the change of the transmission spectrum of the metasurface for different applied voltages. When no voltage is applied (when the applied voltage is 0), the refractive index of the metasurface grating structure has symmetry, but the geometric parameters are asymmetric, supporting the bound state mode in the quasi-continuous domain, and the transmission spectrum shows high transmission properties in the wide wavelength band and low transmission properties at the narrow wavelength band (near the wavelength of 1.617 μm). After applying the voltage, the symmetry of the refractive index of the metasurface grating structure is also broken. As the voltage increases, the asymmetry between the geometry and the refractive index of the metasurface grating structure compensates for each other. Until the voltage is about 22V, the asymmetry of the refractive index of the metasurface grating structure exactly compensates for the geometric asymmetry, realizing the bound state mode in the continuous domain with coexistence of refractive index and geometric asymmetry, that is, the refractive index asymmetry caused by the electro-optic effect compensates for the geometric asymmetry caused by the processing error. Further increasing the voltage, the degree of refractive index asymmetry of the metasurface grating structure continues to increase, and the optical mode of the metasurface changes from the bound state in the continuous domain to the bound state mode in the quasi-continuous domain dominated by refractive index asymmetry.

[0032] In summary, by applying the voltage, the mutual compensation between the geometric asymmetry and the refractive index asymmetry of the structure is realized, and then the dynamic, continuous, fine and on-demand modulation from the bound state in the quasi-continuous domain to the bound state in the continuous domain and then to the bound state in the quasi-continuous domain is realized.

[0033] The present invention can combine the geometric asymmetry of the device with the refractive index asymmetry, support the mutual compensation between the geometry and the refractive index asymmetry, realize the correction of the processing error of the metasurface, and have the ability of dynamic, fine and on-demand switching between the bound state in the quasi-continuous domain and the bound state in the continuous domain.

[0034] The present invention can be applied to the fields of high-sensitivity spectral detection, tunable narrow-band filtering and precision spectral modulation, and has advantages such as high sensitivity and high precision.

[0035] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

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

Claims

1. A continuous domain bound state metasurface device, characterized in that It 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 continuously arranged and side-by-side periodic units, and each periodic unit includes two electro-optic material ridge-shaped strips with the same structure; wherein, the side wall of the electro-optic material ridge-shaped strip on the left side of each periodic unit modulates its refractive index by applying a voltage in the width direction.

2. The continuous domain bound state metasurface device according to claim 1, wherein The transparent dielectric substrate (1) is silicon dioxide.

3. The continuous domain bound state metasurface device according to 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. A continuous domain bound state metasurface device according to claim 1, characterized in that The thickness of the electro-optic material thin film is 200 nm - 500 nm.

5. A continuous domain bound state metasurface device according to claim 1, characterized in that The period constant of the periodic unit is 0.5 μm - 1.5 μm, the height is 200 nm - 500 nm, and the center distance between the two electro-optic material ridge-shaped strips in each periodic unit is 250 nm - 750 nm.

6. A spectral regulation method for a continuous-domain bound state metasurface device according to any one of claims 1-5, characterized in that, It includes the following steps: Vertically incident the incident light on the electro-optic material grating (3), and the wavelength of the incident light is 1.61 μm - 1.63 μm; Apply a voltage in the width direction to the electro-optic material ridge-shaped strip on the left side of each periodic unit, and continuously modulate the refractive index of the electro-optic material ridge-shaped strip by using the electro-optic effect to realize the regulation of the spectrum of the continuous domain bound state metasurface device.

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