Spinning selection adjustable ultra-narrow band filter and spinning selection adjusting method thereof

Abstract

The invention discloses a spin selection adjustable ultra-narrow band filter and a spin selection adjusting method thereof, and belongs to the field of optical filters and chiral optics. The filter is of a metasurface structure with a torsional scatterer, and the metasurface structure comprises a substrate, torsional scatterer units arranged on the substrate in a periodic array mode, and a methyl methacrylate layer covering the surfaces of the substrate and the torsional scatterer units. The torsion type scatterer unit is a non-closed annular body, staggered notches are formed in the circumferential face of the non-closed annular body in the vertical direction, the included angle between the staggered notches is adjustable, and the spinning selection characteristic is adjusted and controlled by adjusting the included angle between the staggered notches. The spin selection characteristic is regulated and controlled by changing the torsion angle of the upper-layer silicon structure relative to the lower-layer silicon structure.

Description

Technical Field

[0001] The invention belongs to the field of optical filter devices and chiral optics, and in particular relates to a spin-selective adjustable ultra-narrowband filter and a spin-selective adjustment method thereof. Background Art

[0002] Optical filters usually refer to devices that can control the transmission of light of a specific frequency or wavelength. There are many types of optical filters. According to the structure, they include diffraction grating filters, stimulated Brillouin scattering filters, resonant ring filters, etc. According to the function, they include bandpass filters, edge filters, multi-channel filters, etc. According to the working band, they include ultraviolet filters, visible light filters, infrared filters, etc. The rich structure, function, and working band of optical filters also make them widely used in many fields such as communication, sensing, Raman spectroscopy, and fluorescence imaging. As an important component for light wave transmission control, the development of optical filters has been relatively mature so far. A number of industries have been formed at home and abroad that can mass produce traditional optical filter components. Common companies include Semrock, Andover, Asahi, Alluxa, Delta, etc. In recent years, with the vigorous development of biology, physics, chemistry and other fields at the nano level, higher requirements have been put forward for the resolution, versatility, and ease of integration of optical technology and optical devices. As one of the most important optical transmission control components, the development of new functions, improvement of resolution, and improvement of ease of integration of optical filters are particularly important.

[0003] Optical metasurfaces are expected to provide an effective way to develop new high-resolution and easy-to-integrate optical filters. Optical metasurfaces, which are two-dimensional arrangements of rationally designed subwavelength scatterers, introduce mutations in optical properties through the interaction of light waves with the unit structures and functional arrangements of these scatterers, achieve the regulation and manipulation of phase, polarization and amplitude, and reduce dependence on propagation effects. Filter devices based on metasurfaces include the powerful light field control capabilities of metasurfaces, as well as the advantages of small size, light weight and easy integration, providing a new paradigm for optical and even electromagnetic wave filtering devices. At present, filter devices based on metasurfaces mainly include color filtering, polarization filtering, chirality filtering, etc. Chirality filtering, also known as spin-selective filtering, is the selective filtering of two beams of light with opposite chirality. It usually refers to the transmission and reflection characteristics of incident left-handed circularly polarized light and right-handed circularly polarized light with significant differences. Chirality refers to the property of lacking mirror reflection symmetry in geometry. In recent years, it has become a frontier hotspot in world scientific research. Left-handed circularly polarized light and right-handed circularly polarized light are typical pairs of light fields with opposite chirality. Spin-selective narrowband filters can provide new chiral degrees of freedom for optical systems by regulating the transmission of left-handed circularly polarized light and right-handed circularly polarized light, and provide strong technical support for chiral molecule identification, basic research on optical topology, and new light field regulation and application. At present, commercial narrowband optical filters usually do not include spin-selective filtering functions, and have low resolution in the wavelength domain. The bandwidth of a typical narrowband filter is about 30nm, and the bandwidth of Alluxa's infrared band ultra-narrowband filter is 0.15nm. Therefore, it is necessary to study optical filters that have both spin-selective functions, high spectral resolution, and good integration, and to develop narrowband optical filters based on metasurfaces to provide new optical components for the development and prosperity of nanoscience.

[0004] In view of this, in order to achieve high resolution of the filter in the spectral domain and maximize the chirality, the present invention introduces bound states in the continuous domain (BICs) mode into the metasurface. Summary of the invention

[0005] Technical issues to be solved:

[0006] In order to avoid the shortcomings of the prior art, the present invention provides a spin-selective adjustable ultra-narrowband filter device based on a high-Q metasurface and a spin-selective adjustment method thereof, which utilizes a twisted silicon double-layer metasurface structure to excite the BICs mode, and realizes the regulation of the spin-selective characteristics by changing the twist angle of the upper silicon structure relative to the lower silicon structure. In other words, when the twist angle of the upper silicon structure relative to the lower silicon structure is φ, the transmittance of the metasurface to vertically incident left-handed circularly polarized light is close to 1, and the transmittance to vertically incident right-handed circularly polarized light is close to 0; and when the twist angle of the upper silicon structure relative to the lower silicon structure is -φ, the transmittance of the metasurface to vertically incident left-handed circularly polarized light is close to 0, and the transmittance to vertically incident right-handed circularly polarized light is close to 1. The present invention solves the problem that the existing narrowband optical filters usually do not include spin-selective filtering functions, have low resolution in the wavelength domain, and are not easy to integrate.

[0007] The technical solution of the present invention is: a spin-selective adjustable ultra-narrowband filter, the filter is a super-surface structure with a twisted scatterer, the super-surface structure includes a substrate, twisted scatterer units arranged on the substrate in a periodic array form, and a methyl methacrylate layer covering the substrate and the twisted scatterer unit surface;

[0008] The torsional scatterer unit is a non-closed annular body, and staggered notches are arranged on the circumference of the non-closed annular body in the vertical direction, and the angle between the staggered notches is adjustable. The spin selection characteristics are regulated by adjusting the angle between the staggered notches.

[0009] A further technical solution of the present invention is: the material of the substrate is a silicon dioxide substrate, and the material of the twisted scatterer unit is silicon.

[0010] A further technical solution of the present invention is that the twisted scatterer unit is composed of two layers of annular broken silicon with the same size coaxially stacked along the normal direction of the silicon dioxide substrate, and the breaks of the two layers of annular broken silicon are staggered to form a twisted double-layer structure.

[0011] A further technical solution of the present invention is: the period of the annular broken silicon is 3000±300nm; its outer ring surface radius is 1000±100nm, the inner ring surface radius is 600±60nm, the axial height is 600±60nm, and the breaking width is 10nm to 20nm.

[0012] A further technical solution of the present invention is: the annular broken silicon placed on the surface of the silicon dioxide substrate in the torsional scatterer unit is the first layer of annular broken silicon, the broken axial symmetry plane of the first layer of annular broken silicon is the 0 position, and the torsion angle of the broken axial symmetry plane of the second layer of annular broken silicon relative to the 0 position is +20° to +30° or -20° to -30°.

[0013] A further technical solution of the present invention is: the operating wavelength range of the filter is 4549nm to 5560nm, and the corresponding transmission spectrum half-width is 0.0075nm to 0.0095nm.

[0014] A further technical solution of the present invention is that the methyl methacrylate layer completely wraps the inner and outer annular surfaces and the top surface of each twisted scatterer unit, and the distance between the bottom surface of the twisted scatterer unit and the top outer surface of the methyl methacrylate layer is greater than 10 μm.

[0015] A method for adjusting the spin selectivity of a spin-selective adjustable ultra-narrowband filter, the specific steps are as follows:

[0016] Arranging a plurality of twisted scatterer units in a periodic array on a silicon dioxide substrate and covering them with a polymethyl methacrylate layer to form a metasurface structure with twisted scatterers;

[0017] When the broken angle between the second layer of annular broken silicon and the first layer of annular broken silicon in the twisted scatterer unit is adjusted to +20° to +30°, the transmittance of the metasurface structure to vertically incident left-handed circularly polarized light is greater than 0.95, and the transmittance to vertically incident right-handed circularly polarized light is less than 0.034;

[0018] When the breaking angle between the second layer of annular broken silicon and the first layer of annular broken silicon in the twisted scatterer unit is adjusted to -20° to -30°, the transmittance of the metasurface structure to vertically incident left-handed circularly polarized light is less than 0.034, and the transmittance to vertically incident right-handed circularly polarized light is greater than 0.95.

[0019] A further technical solution of the present invention is that when the breaking angle between the second layer of annular broken silicon and the first layer of annular broken silicon is adjusted to +20° to +30°, the Q value is maintained at 6×10 5 , the circular dichroism CD value is 0.91 to 0.97.

[0020] A further technical solution of the present invention is that when the breaking angle between the second layer of annular broken silicon and the first layer of annular broken silicon is adjusted to -20° to -30°, the Q value is maintained at 6×10 5 , the circular dichroism CD value is -0.97 to -0.91.

[0021] Beneficial Effects

[0022] The beneficial effect of the present invention is that the metasurface structure of the present invention can realize the regulation of spin selection characteristics by adjusting the twisting direction of the scatterer unit, that is, when the broken twist angle of the double-layer twisted annular broken silicon is set, different optical responses are generated to vertically incident left-handed circularly polarized light and right-handed circularly polarized light, so as to realize ultra-narrow-band spin-selective filtering.

[0023] The specific advantages are as follows:

[0024] 1. The present invention utilizes a double-layer structure of annular broken silicon to excite the BICs mode, which can achieve selective transmission of vertically incident left-handed circularly polarized light and right-handed circularly polarized light, with a Q value of up to 6×10 5 The CD value can reach up to 0.97, achieving high Q value chiral filtering.

[0025] 2. The torsional scatterer structure adopted in the present invention is immune to torsional perturbations, that is, when the torsional angle changes within a reasonable range, the chiral filter device can still maintain a relatively large Q value and CD value.

[0026] 3. The structural solution adopted in the present invention can make the spin selection property completely opposite by changing the twisting direction, thereby realizing the adjustable spin selection. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic structural diagram of a twisted annular broken silicon metasurface chiral filter device provided by the present invention;

[0028] Figure 2 The transmission spectrum of the twisted annular broken silicon metasurface chiral filter device provided by the present invention when the twist angle is 20 degrees under the irradiation of vertically incident left-handed circularly polarized light and right-handed circularly polarized light;

[0029] Figure 3 The transmission spectrum of the twisted annular broken silicon metasurface chiral filter device provided by the present invention when the twist angle is -20 degrees under the irradiation of vertically incident left-handed circularly polarized light and right-handed circularly polarized light.

[0030] Explanation of the reference numerals: 1. twisted scatterer unit, 11. second layer of annular broken silicon, 12. first layer of annular broken silicon; 2. methyl acrylate layer; 3. silicon dioxide substrate. DETAILED DESCRIPTION

[0031] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0032] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0033] In recent years, with the vigorous development of biology, physics, chemistry and other fields at the nano level, higher requirements have been put forward for the resolution, versatility and easy integration of optical technology and optical devices. As one of the most important optical transmission control components, the development of new functions, the improvement of resolution and the improvement of easy integration of optical filters are particularly important. Spin-selective narrowband filters can provide new chiral degrees of freedom for optical systems through the transmission control of left-handed circularly polarized light and right-handed circularly polarized light, and provide strong technical support for the identification of chiral molecules, basic research on optical topology, new light field control and application. At present, commercial narrowband optical filters usually do not include spin-selective filtering functions, and have low resolution in the wavelength domain. The bandwidth of typical narrowband filters is about 30nm, and the bandwidth of Alluxa's infrared band ultra-narrowband filter is 0.15nm. The filter device based on metasurface encompasses the powerful light field control ability of metasurface, as well as the advantages of small size, light weight and easy integration. Therefore, it is necessary to study optical filters with spin-selective functions, high spectral resolution and good integration, and develop narrowband optical filters based on metasurfaces to provide new optical filtering components for the development and prosperity of nanoscience.

[0034] Based on the above problems, the present invention introduces bound states in continuous domain (BICs) mode into the metasurface, and provides a spin-selective adjustable ultra-narrowband filter device based on high-Q metasurface and a spin-selective adjustment method thereof.

[0035] Among them, BICs refers to an electromagnetic mode that is located in the continuous spectrum of the radiation mode but is completely decoupled from the radiation. It has no leakage and an infinite quality factor, which can significantly improve the resolution in the wavelength domain. Because geometric perturbations can cause the BIC mode to collapse, the ideal BIC mode cannot be obtained experimentally, and what is usually obtained is a quasi-BICs mode. Due to the high Q value of the quasi-BICs mode, it is widely used in electromagnetics, acoustics, thermal, fluid and other fields. BIC has an integer topological charge, which is broken by the C of BIC. 2Symmetry can generate circularly polarized points (C points) with half-integer topological charge. In this process, the topological charge is conserved, so the generation of such C points is topologically protected, which is its non-negligible advantage. The experimental performance of C points is the selectivity of the transmission / reflection spectrum for left-handed circularly polarized light and right-handed circularly polarized light, corresponding to high Q value, ultra-narrow band, and chirality-maximized filter devices.

[0036] The present invention discloses a spin-selection adjustable ultra-narrowband filter, wherein the filter is a super-surface structure with a twisted scatterer, wherein the super-surface structure includes a substrate, twisted scatterer units arranged on the substrate in a periodic array, and a methyl methacrylate layer covering the substrate and the twisted scatterer unit surface; the twisted scatterer unit is a non-closed annular body, and the circumference of the non-closed annular body is provided with dislocation notches in the vertical direction, and the angle between the dislocation notches is adjustable, and the spin selection characteristic is regulated by adjusting the angle between the dislocation notches. The structural scheme adopted by the present invention can make the spin selection property completely opposite by changing the direction of torsion, realize the adjustable spin selection, and be immune to torsion perturbation, that is, when the torsion angle changes within a reasonable range, the chiral filter device can still maintain a large Q value and CD value.

[0037] Specifically, the material of the substrate is a silicon dioxide substrate, and the material of the twisted scatterer unit is silicon.

[0038] Specifically, the twisted scatterer unit is formed by coaxially stacking two layers of annular broken silicon with the same structure and size along the normal direction of the silicon dioxide substrate, and the breaks of the two layers of annular broken silicon are staggered, forming a twisted double-layer structure.

[0039] Specifically, the period of the annular broken silicon is 3000±300nm; the radius of its outer ring surface is 1000±100nm, the radius of its inner ring surface is 600±60nm, the axial height is 600±60nm, and the breaking width is 10nm to 20nm.

[0040] Specifically, the annular broken silicon placed on the surface of the silicon dioxide substrate in the torsional scatterer unit is the first layer of annular broken silicon, with the broken axial symmetry plane of the first layer of annular broken silicon as position 0, and the torsion angle of the broken axial symmetry plane of the second layer of annular broken silicon relative to position 0 is +20° to +30° or -20° to -30°.

[0041] Specifically, the methyl methacrylate layer completely wraps the inner and outer annular surfaces and the top surface of each twisted scatterer unit, and the distance between the bottom surface of the twisted scatterer unit and the top outer surface of the methyl methacrylate layer is greater than 10 μm.

[0042] The present invention provides a method for adjusting the spin selectivity of a spin-selective adjustable ultra-narrowband filter, and the specific steps are as follows:

[0043] Step 1: Arrange a number of twisted scatterer units in a periodic array on a silicon dioxide substrate and cover them with a polymethyl methacrylate layer to form a metasurface structure with twisted scatterers;

[0044] Step 2: When the broken angle between the second layer of annular broken silicon and the first layer of annular broken silicon in the twisted scatterer unit is adjusted to +20° to +30°, the transmittance of the metasurface structure to vertically incident left-handed circularly polarized light is greater than 0.95, and the transmittance to vertically incident right-handed circularly polarized light is less than 0.034;

[0045] Step 3: When the breaking angle between the second layer of annular broken silicon and the first layer of annular broken silicon in the twisted scatterer unit is adjusted to -20° to -30°, the transmittance of the metasurface structure to vertically incident left-handed circularly polarized light is less than 0.034, and the transmittance to vertically incident right-handed circularly polarized light is greater than 0.95.

[0046] Specifically, when the breaking angle between the second layer of annular broken silicon and the first layer of annular broken silicon is adjusted to +20° to +30°, the Q value is maintained at 6×10 5 , the circular dichroism CD value is 0.91 to 0.97.

[0047] Specifically, when the breaking angle between the second layer of annular broken silicon and the first layer of annular broken silicon is adjusted to -20° to -30°, the Q value is maintained at 6×10 5 , the circular dichroism CD value is -0.97 to -0.91.

[0048] The above technical solution is further described below in conjunction with the accompanying drawings:

[0049] This embodiment is a spin-selective tunable ultra-narrowband filter device based on a high-Q metasurface, which achieves high Q value and high chiral contrast by exciting a chiral BICs mode.

[0050] Reference Figure 1 As shown, the spin-selective adjustable ultra-narrowband filter device includes a silicon dioxide substrate 3 , a first layer of annular broken silicon 12 , a second layer of annular broken silicon 11 , and a polymethyl methacrylate (PMMA) layer 2 .

[0051] The first layer of annular broken silicon and the second layer of annular broken silicon are abutted and coaxially arranged, and the second layer of annular broken silicon is twisted at a certain angle φ relative to the first layer of annular broken silicon, thereby forming a twisted double-layer structure.

[0052] The geometric dimensions of the first layer of annular broken silicon are set to: a period of 3000nm, an outer ring radius of 1000nm, an inner ring radius of 600nm, an axial height of 600nm, a broken width of 12nm, and the material is silicon.

[0053] The geometric dimensions of the second layer of annular broken silicon are set to: a period of 3000nm, an outer ring radius of 1000nm, an inner ring radius of 600nm, an axial height of 600nm, a broken width of 12nm, and the material is silicon.

[0054] In this embodiment, the second layer of annular broken silicon is twisted relative to the first layer of annular broken silicon around a vertical axis passing through the center of the cross section of the annular column at an angle θ=20 degrees or -20 degrees.

[0055] The spin-selective adjustable ultra-narrowband filter device realizes adjustable spin selection by changing the twisting angle of the second layer of annular broken silicon relative to the first layer of annular broken silicon, that is, when the twisting angle of the second layer of annular broken silicon relative to the first layer of annular broken silicon is 20 degrees, vertically incident left-handed circularly polarized light is almost completely transmitted, while vertically incident right-handed circularly polarized light is almost completely blocked; and when the twisting angle of the second layer of annular broken silicon relative to the first layer of annular broken silicon is -20 degrees, vertically incident right-handed circularly polarized light is almost completely transmitted, while vertically incident left-handed circularly polarized light is almost completely blocked.

[0056] In the filter device, when the twist angle of the second layer of annular broken silicon relative to the first layer of annular broken silicon is 20 degrees, Figure 2 As shown, the central wavelength of the transmission wave is 5054.29nm, the full width at half maximum of the transmission spectrum is 0.008nm, and the Q value is as high as 6×10 5 , CD value is as high as 0.91.

[0057] In the filter device, when the twist angle of the second layer of annular broken silicon relative to the first layer of annular broken silicon is -20 degrees, Figure 3 As shown, the central wavelength of the transmission wave is 5054.29nm, the full width at half maximum of the transmission spectrum is 0.008nm, and the Q value is as high as 6×10 5 , the CD value is as high as -0.92.

[0058] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A spin-selective adjustable ultra-narrowband filter, characterized in that: The filter is a super surface structure with a twisted scatterer, and the super surface structure includes a substrate, twisted scatterer units arranged on the substrate in a periodic array form, and a methyl methacrylate layer covering the substrate and the twisted scatterer unit surface; The torsional scatterer unit is a non-closed annular body, and staggered notches are arranged on the circumference of the non-closed annular body in the vertical direction, and the angle between the staggered notches is adjustable. The spin selection characteristics are regulated by adjusting the angle between the staggered notches.

2. The spin-selective adjustable ultra-narrowband filter according to claim 1, characterized in that: The material of the substrate is a silicon dioxide substrate, and the material of the twisted scatterer unit is silicon.

3. The spin-selective adjustable ultra-narrowband filter according to claim 2, characterized in that: The twisted scatterer unit is formed by coaxially stacking two layers of annular broken silicon with the same structure and size along the normal direction of the silicon dioxide substrate, and the breaks of the two layers of annular broken silicon are staggered, forming a twisted double-layer structure.

4. The spin-selective adjustable ultra-narrowband filter according to claim 3, characterized in that: The period of the annular broken silicon is 3000±300nm; the radius of its outer ring surface is 1000±100nm, the radius of its inner ring surface is 600±60nm, the axial height is 600±60nm, and the breaking width is 10nm to 20nm.

5. The spin-selective adjustable ultra-narrowband filter according to claim 4, characterized in that: The annular broken silicon placed on the surface of the silicon dioxide substrate in the twisted scatterer unit is the first layer of annular broken silicon. The broken axial symmetry plane of the first layer of annular broken silicon is the 0 position, and the twist angle of the broken axial symmetry plane of the second layer of annular broken silicon relative to the 0 position is +20° to +30° or -20° to -30°.

6. The spin-selective adjustable ultra-narrowband filter according to claim 5, characterized in that: The operating wavelength range of the filter is 4549nm-5560nm, and the corresponding transmission spectrum half-width is 0.0075nm-0.0095nm.

7. The spin-selective adjustable ultra-narrowband filter according to claim 1, characterized in that: The methyl methacrylate layer completely wraps the inner and outer annular surfaces and the top surface of each twisted scatterer unit, and the distance between the bottom surface of the twisted scatterer unit and the top outer surface of the methyl methacrylate layer is greater than 10 μm.

8. A method for adjusting the spin selectivity of the spin-selective adjustable ultra-narrowband filter according to any one of claims 1 to 7, characterized in that The specific steps are as follows: Arranging a plurality of twisted scatterer units in a periodic array on a silicon dioxide substrate and covering them with a polymethyl methacrylate layer to form a metasurface structure with twisted scatterers; When the broken angle between the second layer of annular broken silicon and the first layer of annular broken silicon in the twisted scatterer unit is adjusted to +20° to +30°, the transmittance of the metasurface structure to vertically incident left-handed circularly polarized light is greater than 0.95, and the transmittance to vertically incident right-handed circularly polarized light is less than 0.034; When the breaking angle between the second layer of annular broken silicon and the first layer of annular broken silicon in the twisted scatterer unit is adjusted to -20° to -30°, the transmittance of the metasurface structure to vertically incident left-handed circularly polarized light is less than 0.034, and the transmittance to vertically incident right-handed circularly polarized light is greater than 0.

95.

9. The spin selective regulation method according to claim 8, characterized in that: When the breaking angle between the second layer of annular broken silicon and the first layer of annular broken silicon is adjusted to +20° to +30°, the Q value is maintained at 6×10 5 , the circular dichroism CD value is 0.91 to 0.

97.

10. The spin selective regulation method according to claim 8, characterized in that: When the breaking angle between the second layer of annular broken silicon and the first layer of annular broken silicon is adjusted to -20° to -30°, the Q value is maintained at 6×10 5 , the circular dichroism CD value is -0.97 to -0.91.

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