A quasi-bic chiral metasurface device based on refractive index modulation and a preparation method and application thereof

Abstract

The application relates to a quasi-BIC chiral metasurface device based on refractive index modulation and a preparation method and application thereof. The chiral metasurface device comprises a plurality of sub-wavelength structure partitions arranged sequentially along an X axis, and two adjacent sub-wavelength structure partitions are arranged in rotational symmetry relative to a Y axis. The sub-wavelength structure in the sub-wavelength structure partition comprises at least two optical medium layers arranged in a stack along a Z axis. At least one sub-wavelength structure in the sub-wavelength structure partition is arranged in an inclination relative to the Y axis, and there is a refractive index difference between the at least two optical medium layers, so that the metasurface device realizes intrinsic chirality. The metasurface device of the application realizes tunable strong intrinsic chirality at multiple wavelengths. The preparation method has the advantages of low processing difficulty, low thickness of the optical medium layer, no need for precise control of the thickness and inclination angle of the optical medium layer, compatibility with the lift-off process, and realization of high-precision large-area metasurface device preparation.

Description

Technical Field

[0001] This invention relates to the field of optical technology, and in particular to a quasi-BIC chiral metasurface device based on refractive index modulation, its fabrication method, and its application. Background Technology

[0002] Chiral metasurfaces are artificial structural materials with unique optical properties. By constructing metasurface resonant units with chiral structural characteristics, they achieve differentiated responses to left-handed polarized (LCP) and right-handed polarized (RCP) light, also known as circular dichroism (CD) response. Leveraging the sensitivity of the resonance peak position of chiral metasurface devices with high quality factors (Q values) to changes in the refractive index of the surrounding medium, specific detection of chiral molecules can be achieved. This has significant application value not only in drug screening and biomarker analysis but also in optical devices such as narrowband filters, polarization conversion, and circularly polarized lasers.

[0003] Currently, ideal chiral sensors need to simultaneously meet core requirements such as high Q-value and strong chiral response. However, conventional chiral metasurfaces often fall short of these requirements. Continuous domain bound states (BICs) are nonradiative solutions to the wave equation, theoretically possessing infinitely large Q-values. By introducing symmetry breaking and other methods, observable quasi-continuous domain bound states (quasi-BICs) with finitely large Q-values ​​can be constructed. Optical metasurfaces based on quasi-BICs have become an important strategy for achieving high Q-values ​​and high CD-value optical responses. Existing technical solutions typically break the in-plane / out-of-plane symmetry of the structure by constructing structural height differences and tilting etching, thereby achieving quasi-BIC metasurfaces with strong intrinsic chirality. However, these methods are not only difficult to fabricate and have poor repeatability, but also involve core parameters such as height differences and tilt angles that are difficult to control precisely. Furthermore, the fabrication methods are material-selective, making them difficult to extend to most other metals or dielectric materials.

[0004] Chinese patent CN118192101A discloses a circular dichroism switching device, comprising a substrate, an isolation layer, a phase change film layer, and a protective layer arranged sequentially. The isolation layer contains a plurality of silicon structural units arranged in a periodic array. Each silicon structural unit includes two silicon pillars, one end of which is connected to the upper surface of the substrate. The silicon pillars are inclined elliptical cylinders, with an angle less than 0° between them and the upper surface of the substrate. The vertical height of the silicon pillars is less than the thickness of the isolation layer. The phase change film layer is made of a chalcogenide phase change material. This circular dichroism switching device utilizes an inclined etching method to construct a chiral quasi-BIC. This method requires precise control of the tilt angle, is difficult to fabricate, and has low controllability. Furthermore, the inclined etching method is incompatible with metals and some dielectric materials, and is also difficult to use for large-area device fabrication.

[0005] Chinese Patent Publication No. CN116643416A discloses a circular dichroism enhancement device, which includes: a chiral microstructure encapsulated by a low-refractive-index material; the chiral microstructure is composed of a periodic array of symmetry-broken phase change material nanorods, each period containing: a first nanorod and a second nanorod; the length, width, and thickness of the first nanorod are l, w1, and t1, respectively, and the length, width, and thickness of the second nanorod are l, w2, and t2, respectively, where t1 = w2 and t2 = w1; the length and width form the bottom surface, the bottom surfaces of the first and second nanorods are on the same plane, and there is an angle between the length directions of the two nanorods formed by rotation about the thickness direction. The aforementioned circular dichroism enhancement device breaks the inversion symmetry by structural flipping. Not only is it difficult to accurately construct the height difference of the structure, but it also results in the phase change material germanium antimony tellurium alloy (Ge2Sb2Te5, GST) having a thickness of up to 0.51 μm under this construction strategy. The success rate of processing by etching method is low and the structural quality is poor. Furthermore, such a thick phase change material makes it difficult to uniformly and effectively switch the entire metasurface structure between crystalline and amorphous states in practical use, which can lead to device failure. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the first objective of this invention is to provide a quasi-BIC chiral metasurface device based on refractive index modulation. By maintaining the approximate symmetry of the subwavelength structure partitioning structure, the refractive index of the optical medium layer is modulated to achieve an asymmetric distribution of the refractive index in three-dimensional space. At the same time, it breaks the in-plane and out-of-plane symmetry, thereby achieving tunable strong intrinsic chirality at multiple wavelengths, with a Q value as high as 1200~1800 and a CD value as high as 0.98~0.99.

[0007] The second objective of this invention is to provide a method for fabricating quasi-BIC chiral metasurface devices based on refractive index modulation, which has the advantages of low processing difficulty, low thickness of optical medium layer, no need for precise control of the thickness and tilt angle of optical medium layer, compatibility with lift-off process, and the ability to achieve high-precision large-area metasurface device fabrication.

[0008] The third objective of this invention is to provide an application of quasi-BIC chiral metasurface devices based on refractive index modulation, which can be applied to optical devices such as narrowband filters, polarization converters, and circularly polarized lasers.

[0009] To achieve the first objective mentioned above, the present invention provides the following technical solution:

[0010] A quasi-BIC chiral metasurface device based on refractive index modulation includes multiple subwavelength structure partitions arranged sequentially along the X-axis. Adjacent subwavelength structure partitions are arranged rotationally symmetrically with respect to the Y-axis. The subwavelength structure in each subwavelength structure partition includes at least two optical dielectric layers stacked along the Z-axis. At least one subwavelength structure in each subwavelength structure partition is tilted with respect to the Y-axis, and there is a refractive index difference between at least two optical dielectric layers, so that the metasurface device achieves intrinsic chirality.

[0011] In the "subwavelength structure partitioning" of this invention, the specific meaning of "rotationally symmetric arrangement" refers to the arrangement in which a subwavelength structure coincides with another subwavelength structure after rotating around a rotation axis by a predetermined angle θ. It can also be understood as the two subwavelength structures that originally coincided in the YZ plane each rotating in opposite directions by an angle of θ / 2. For example, without limitation, it can be that two adjacent subwavelength structure partitions are arranged with double rotational symmetry (θ=180°), triple rotational symmetry (θ=120°), or quadruple rotational symmetry (θ=90°) relative to the Y-axis. Since there is a refractive index difference between at least two optical medium layers, the rotated subwavelength structure partition is structurally mirror-symmetric relative to the YZ plane, but the quadruple symmetry is broken in terms of refractive index modulation. The resulting symmetry breakage mainly destroys two symmetries: the quadruple symmetry in the XY dimension and the inversion symmetry in the Z-axis direction.

[0012] Furthermore, the subwavelength structure partition includes multiple subwavelength structure units arranged sequentially along the Y-axis, with adjacent subwavelength structures arranged in parallel, mirror-symmetric, or rotationally symmetric relative to the X-axis.

[0013] Furthermore, the subwavelength structural unit includes several subwavelength structural groups arranged in a periodic array along the XY plane, and at least one structural parameter differs between the subwavelength structures of two adjacent subwavelength structural groups.

[0014] Furthermore, the subwavelength structure group includes several subwavelength structures arranged sequentially along the X-axis, with at least one structural parameter differing between any two adjacent subwavelength structures.

[0015] Alternatively, the subwavelength structure group may include several subwavelength structures arranged sequentially along the X-axis, with different structural parameters between adjacent subwavelength structures.

[0016] Furthermore, the cross-section of the subwavelength structure is polygonal, annular, or circular, and the longitudinal section of the subwavelength structure is rectangular, trapezoidal, or parallelogram-shaped.

[0017] Furthermore, the structural parameters include the period P of the subwavelength structure, the length l of the subwavelength structure, the width w of the subwavelength structure, the angle α between the subwavelength structure and the Y-axis, the thickness t of the optical medium layer, and the material of the optical medium layer.

[0018] Preferably, the period P of the subwavelength structure is 0.25~2.50 μm;

[0019] And / or, the length of the subwavelength structure is l = 0.25~2.00 μm;

[0020] And / or, the width of the subwavelength structure is w = 0.05~1.00 μm;

[0021] And / or, the angle α between the tilted subwavelength structure and the Y-axis is 2~30°;

[0022] And / or, the thickness of the optical medium layer is t = 0.05~0.50 μm;

[0023] And / or, the optical medium layer is made of one or more of the following materials: silicon, silicon nitride, silicon dioxide, aluminum oxide, silicon carbide, titanium dioxide, gold, silver, aluminum, germanium-antimony-tellurium alloy, germanium-antimony-selenium-tellurium alloy, germanium-antimony-tellurium-sulfur alloy, vanadium oxide, antimony sulfide, and antimony selenide.

[0024] In this context, based on the array scheme of the subwavelength structures in the XY plane, the period P of the subwavelength structure refers to the center of two adjacent subwavelength structures on the X-axis (P... x ) or Y-axis (P y The distance in the direction of the X-axis; if the cross-section and longitudinal section of the subwavelength structure are both rectangular, the length l and width w of the subwavelength structure refer to the length of the long side and the short side of the projection of the subwavelength structure on the XY plane, respectively; the thickness t of the optical medium layer refers to the maximum side length of the optical medium layer in the Z-axis direction. This thickness can be gradual or constant along the X-axis or Y-axis direction. The thicknesses of two adjacent optical medium layers can be the same or different.

[0025] Furthermore, it also includes an optical substrate, wherein the subwavelength structure partition is disposed on the surface of the optical substrate.

[0026] Furthermore, the optical substrate is made of one or more of the following materials: quartz glass, calcium fluoride, silicon carbide, sapphire, and aluminum oxide.

[0027] To achieve the second objective mentioned above, the present invention provides the following technical solution:

[0028] A method for fabricating a quasi-BIC chiral metasurface device based on refractive index modulation includes the following steps:

[0029] S1. Prepare an optical substrate and divide n photolithographic regions according to the preset stacked structure of the optical medium layer of the subwavelength structure.

[0030] S2 first coats photoresist on the surface of the optical substrate, then performs electron beam exposure and development in the first photolithography area, then grows optical dielectric layers sequentially according to the preset stacked structure, and then removes the photoresist to obtain a subwavelength structure.

[0031] S3 follows S2 to sequentially fabricate subwavelength structures in the second to nth photolithographic regions to obtain metasurface devices.

[0032] Furthermore, in S2, the surface of the optical substrate is pre-cleaned using organic solvents such as deionized water, anhydrous ethanol, acetone and isopropanol, or oxygen plasma.

[0033] Further, in steps S2 and S3, a photoresist with a thickness of 200 nm to 3 μm is first spin-coated, and then baked at 100 to 180°C for 1 to 4 minutes. Subsequently, a conductive photoresist is selectively spin-coated at a speed of 1500 to 2500 rpm / min for 50 to 70 seconds, and then baked at 80 to 100°C for 3 to 5 minutes. The photoresist is not limited to, for example, PMMA, ARP 6200, ZEP, SU-8, and HSQ; the conductive photoresist is not limited to, for example, AR PC-5090, AR PC-5091, AR PC-5092, and AR PC-5094.

[0034] Furthermore, in S2 and S3, the voltage for electron beam exposure is controlled to be 8~12kV, the aperture to be 10~30μm, and the dose to be 50~300μC / cm. 2 After electron beam exposure, the conductive photoresist on the surface is washed away with ultrapure water, and the moisture is dried with nitrogen gas. Then, it is developed with a developer for 50-70 seconds and fixed with a fixer for 20-40 seconds. The developer is not limited to, for example, AR 600, AR300 and SU-8, etc., and the fixer is not limited to, for example, AR 300, IPA and deionized water, etc.

[0035] Furthermore, in S2 and S3, an optical dielectric layer is grown using one of the following deposition methods: magnetron sputtering, PECVD, electron beam evaporation, and ALD. After completion, the sample is immersed in an organic solvent to remove the photoresist and excess optical dielectric layer. The organic solvent is not limited to, for example, acetone.

[0036] To achieve the third objective mentioned above, the present invention provides the following technical solution:

[0037] Applications of a quasi-BIC chiral metasurface device based on refractive index modulation in the fabrication of narrowband filters, optical polarization converters, circularly polarized lasers, chiral molecular sensors, and chiral quantum light sources.

[0038] In summary, the beneficial technical effects of the present invention are as follows:

[0039] 1. The metasurface device of the present invention solves the core problems of traditional intrinsic chiral quasi-BIC metasurface schemes, which introduce fewer dimensions of symmetry breaking and are limited to the asymmetry of geometric structure, resulting in high processing difficulty, low precision, and low control dimensionality. By maintaining the approximate symmetry of the subwavelength structure partitioning structure, the refractive index of the optical medium layer is controlled to achieve an asymmetric distribution of refractive index in three-dimensional space. At the same time, the in-plane and out-of-plane symmetry is broken, realizing multi-dimensional control of quasi-BIC and obtaining a quasi-BIC state with strong chiral response. It has good compatibility, is easy to extend to other materials and different wavelengths, and introduces a variety of active control mechanisms. In addition, by changing the spatial arrangement order of the optical medium layers used, a metasurface device with opposite chirality can be obtained.

[0040] 2. The metasurface device of the present invention does not require complex processing schemes such as height difference and tilting. It can introduce a symmetry breaking factor simply by spatially arranging two or more optical medium layers with different refractive indices. It is compatible with the standardized micro-nano processing flow of most metals and dielectric materials. The longitudinal arrangement order of different optical medium layers can be adjusted by controlling the order of material growth. It can realize large-scale and high-precision device processing. At the same time, the material of the optical medium layer is not limited. Phase change materials can be introduced to realize the active tunable function of the device. In addition, the phase change material does not need to be too thick under this scheme. The degree of phase change and the uniformity of the phase change process can be effectively controlled to ensure the reliability of the metasurface device.

[0041] 3. The preparation method of this invention is simple and can be prepared using either an "EBL / UV lithography + etching" process or an "EBL / UV lithography + lift-off" process. In application, microfluidic chips can be fabricated on the surface of metasurface devices, or samples to be tested can be directly coated onto them to characterize and detect structures such as chiral molecules and chiral proteins. It can also be combined with pump light sources and laser gain media to generate chiral lasers. Furthermore, it can be used as a narrowband filter to selectively filter specific chiral polarized light. It not only has important application value in drug screening and biomarker analysis, but can also be applied to optical devices such as narrowband filters, optical polarization converters, circularly polarized lasers, chiral molecule sensors, and chiral quantum light sources. Attached Figure Description

[0042] Figure 1This is a partial top view of the metasurface device of Embodiment 1 of the present invention.

[0043] Figure 2 This is a partial three-dimensional structural schematic diagram of the metasurface device of Embodiment 1 of the present invention.

[0044] Figure 3 This is a partial top view of the metasurface device of Embodiment 2 of the present invention.

[0045] Figure 4 This is a partial top view of the metasurface device of Embodiment 3 of the present invention.

[0046] Figure 5 This is a partial top view of the metasurface device of Embodiment 4 of the present invention.

[0047] Figure 6 This is a partial top view of the metasurface device of Embodiment 5 of the present invention.

[0048] Figure 7 This is a partial top view of the metasurface device of Embodiment 6 of the present invention.

[0049] Figure 8 This is a partial top view of the metasurface device of Embodiment 7 of the present invention.

[0050] Figure 9 This is a partial top view of the metasurface device of Embodiment 8 of the present invention.

[0051] Figure 10 This is a flowchart of the preparation method provided in Embodiment 12 of the present invention.

[0052] Figure 11 This is the transmission spectrum of left-handed polarized incident light of the metasurface device of Embodiment 15 of the present invention in the GST amorphous state near a wavelength of 890 nm.

[0053] Figure 12 This is the transmission spectrum of right-handed polarized incident light of the metasurface device of Embodiment 15 of the present invention in the GST amorphous state near a wavelength of 890 nm.

[0054] Figure 13 This is the transmission spectrum of left-handed polarized incident light of the metasurface device of Embodiment 15 of the present invention in GST crystal state near 890nm wavelength.

[0055] Figure 14 This is the transmission spectrum of right-handed polarized incident light of the metasurface device of Embodiment 15 of the present invention in GST crystal state near 890nm wavelength.

[0056] Figure 15This is the circular dichroism spectrum of the metasurface device of Embodiment 15 of the present invention in the GST amorphous state near a wavelength of 890 nm.

[0057] Figure 16 This is the circular dichroism spectrum of the metasurface device of Embodiment 15 of the present invention in GST crystal state near a wavelength of 890 nm.

[0058] Figure 17 This is the transmission spectrum of left-handed polarized incident light of the metasurface device of Embodiment 15 of the present invention in the GST amorphous state near a wavelength of 920 nm.

[0059] Figure 18 This is the transmission spectrum of right-handed polarized incident light of the metasurface device of Embodiment 15 of the present invention in the GST amorphous state near a wavelength of 920 nm.

[0060] Figure 19 This is the transmission spectrum of left-handed polarized incident light of the metasurface device of Embodiment 15 of the present invention in GST crystal state near a wavelength of 920 nm.

[0061] Figure 20 This is the transmission spectrum of right-handed polarized incident light of the metasurface device of Embodiment 15 of the present invention in GST crystal state near a wavelength of 920 nm.

[0062] Figure 21 This is the circular dichroism spectrum of the metasurface device of Embodiment 15 of the present invention in the GST amorphous state near a wavelength of 920 nm.

[0063] Figure 22 This is the circular dichroism spectrum of the metasurface device of Embodiment 15 of the present invention in GST crystal state near a wavelength of 920 nm.

[0064] In the figure, 1 is the optical substrate; 2 is the subwavelength structure partition; 3 is the subwavelength structure unit; 4 is the subwavelength structure group; 5 is the subwavelength structure; and 6 is the optical dielectric layer. Detailed Implementation

[0065] To make the technical means, creative features, objectives and effects of this invention clearer and easier to understand, the invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0066] Example 1: Refer to Figure 1 and Figure 2 This invention discloses a quasi-BIC chiral metasurface device based on refractive index modulation, comprising an optical substrate 1 and multiple subwavelength structural partitions 2 disposed on the surface of the optical substrate 1 and arranged sequentially along the X-axis; wherein,

[0067] The optical substrate 1 is made of quartz glass (SiO2).

[0068] The two adjacent subwavelength structure partitions 2 are arranged in a double rotational symmetry relative to the Y-axis;

[0069] Subwavelength structure partition 2 includes multiple subwavelength structure units 3 arranged sequentially along the Y-axis, with adjacent subwavelength structures 5 arranged in parallel relative to the X-axis.

[0070] Subwavelength structural unit 3 includes a subwavelength structural group 4;

[0071] Subwavelength structure group 4 includes a subwavelength structure 5;

[0072] The subwavelength structure 5 includes two optical dielectric layers 6 stacked along the Z-axis. The subwavelength structure 5 is tilted relative to the Y-axis, and there is a refractive index difference between the two optical dielectric layers 6 in the subwavelength structure 5, so that the metasurface device can achieve intrinsic chirality.

[0073] The period P of the subwavelength structure 5 x =0.40μm, P y =0.80μm, length l=0.40μm, width w=0.15μm, the angle α between the subwavelength structure 5 and the Y-axis is 20°, the thickness of the optical dielectric layer 6 is t=0.15μm, and the materials of the two optical dielectric layers 6 are silicon (Si) and germanium antimony tellurium alloy (GST), respectively.

[0074] Example 2: Refer to Figure 3 This invention discloses a quasi-BIC chiral metasurface device based on refractive index modulation. The difference from Example 1 is that two adjacent subwavelength structures 5 are arranged in a mirror-symmetric manner relative to the X-axis.

[0075] Example 3: Reference Figure 4 This invention discloses a quasi-BIC chiral metasurface device based on refractive index modulation. The difference from Example 1 is that the two adjacent subwavelength structures 5 are arranged in a double rotational symmetry relative to the X-axis.

[0076] Example 4: Reference Figure 5 This invention discloses a quasi-BIC chiral metasurface device based on refractive index modulation. The difference from Embodiment 1 lies in that the subwavelength structural unit 3 comprises five subwavelength structure groups 4 arranged sequentially along the X and Y axes, respectively. The angle α between the subwavelength structure 5 and the Y axis between adjacent subwavelength structure groups 4, and the material of the optical dielectric layer 6, are different.

[0077] In the three subwavelength structure groups 4 arranged sequentially along the X-axis, the angle α between the subwavelength structure 5 and the Y-axis is 0°, 30°, and 0°. The optical medium layer 6 of the subwavelength structure 5 is made of silicon nitride, silicon nitride, silicon carbide, and silicon nitride. The remaining structural parameters are the same as in Example 1.

[0078] In the three subwavelength structure groups 4 arranged sequentially along the Y-axis, the angle α between the subwavelength structure 5 and the Y-axis is 0°, 5°, and 0°, respectively. The optical medium layer 6 of the subwavelength structure 5 is made of silicon carbide, silicon nitride, silicon carbide, and silicon carbide, respectively. The remaining structural parameters are the same as in Example 1.

[0079] In addition, the outermost subwavelength structure 5 of two adjacent subwavelength structural units 3 can be integrally formed.

[0080] Example 5: Refer to Figure 6 This invention discloses a quasi-BIC chiral metasurface device based on refractive index modulation. The difference from Embodiment 1 lies in that the subwavelength structure group 4 includes two subwavelength structures 5 arranged sequentially along the X-axis. The angle α between adjacent subwavelength structures 5 and the Y-axis, as well as the material of the optical dielectric layer 6, are different.

[0081] In the two subwavelength structures 5 arranged sequentially along the X-axis, the angle α between the subwavelength structure 5 and the Y-axis is 0° and 10°, respectively. The optical medium layer 6 of the subwavelength structure 5 is made of germanium-antimony-tellurium alloy, gold and germanium-antimony-tellurium alloy, respectively. The remaining structural parameters are the same as in Example 1.

[0082] Example 6: Refer to Figure 7 This invention discloses a quasi-BIC chiral metasurface device based on refractive index modulation. The difference from Embodiment 5 lies in that the subwavelength structural unit 3 includes three subwavelength structure groups 4 arranged sequentially along the Y-axis. The angle α between the subwavelength structure 5 and the Y-axis between adjacent subwavelength structure groups 4, and the material of the optical dielectric layer 6, are different.

[0083] The structural parameters of the subwavelength structure group 4 located in the middle are the same as those in Example 5;

[0084] In the two outermost subwavelength structure groups 4, the angle α between the subwavelength structure 5 and the Y-axis is 0° and 0°, respectively. The optical medium layer 6 of the subwavelength structure 5 is made of silicon dioxide and vanadium oxide, respectively. The remaining structural parameters are the same as in Example 1.

[0085] In addition, the outermost subwavelength structure 5 of two adjacent subwavelength structural units 3 can be integrally formed.

[0086] Example 7: Refer to Figure 8 This invention discloses a quasi-BIC chiral metasurface device based on refractive index modulation. The difference from Embodiment 1 is that the subwavelength structure group 4 includes two subwavelength structures 5 arranged sequentially along the X-axis. The structural parameters of these two subwavelength structures 5 are the same as those in Embodiment 1.

[0087] Example 8: Refer to Figure 9 This invention discloses a quasi-BIC chiral metasurface device based on refractive index modulation. The difference from Embodiment 7 is that the subwavelength structural unit 3 includes three subwavelength structure groups 4 arranged sequentially along the Y-axis. The angle α between the subwavelength structure 5 and the Y-axis between adjacent subwavelength structure groups 4, and the material of the optical dielectric layer 6, are different.

[0088] The structural parameters of the subwavelength structure 5 located in the middle are the same as those in Example 7;

[0089] In the two outermost subwavelength structure groups 4, the angle α between the subwavelength structure 5 and the Y-axis is 0° and 0°, respectively. The optical medium layer 6 of the subwavelength structure 5 is made of titanium dioxide and antimony sulfide, respectively. The remaining structural parameters are the same as in Example 1.

[0090] In addition, the outermost subwavelength structure 5 of two adjacent subwavelength structural units 3 can be integrally formed.

[0091] Examples 9-11: These are quasi-BIC chiral metasurface devices based on refractive index modulation disclosed in this invention. The difference from Example 1 is that in the subwavelength structure 5, the periods are respectively P... x =0.25μm, 0.75μm, 1.25μm, P y =0.50μm, 1.50μm, 2.50μm, the length*width*height of the optical dielectric layer 6 are 0.25*0.05*0.05μm, 1.00*0.50*0.25μm, 2.00*1.00*0.5μm respectively, and the optical dielectric layer 6 is made of silicon nitride and titanium dioxide, silicon and germanium antimony tellurium alloy, titanium dioxide and antimony selenide respectively.

[0092] Example 12: Refer to Figure 10 This invention discloses a method for fabricating a quasi-BIC chiral metasurface device based on refractive index modulation, which differs from Example 1 in that it includes the following steps:

[0093] S1 Prepare an optical substrate 1, and divide it into two photolithographic regions according to the preset stacked structure of the optical dielectric layer 6 of the subwavelength structure 5.

[0094] S2 first cleans the surface of optical substrate 1 using plasma. Then, a positive photoresist PMMA with a thickness of 800 nm is spin-coated onto the surface of optical substrate 1. After coating, it is baked on a hot plate at 180℃ for 1 min. Next, a conductive photoresist ARPC-5090 is spin-coated at 2000 rpm for 60 s, followed by baking on a hot plate at 90℃ for 4 min. Finally, electron beam exposure is performed on the first photolithography area, controlling the electron beam exposure voltage at 10 kV, the aperture at 30 μm, and the dose at 300 μC / cm. 2 After electron beam exposure, the conductive photoresist on the surface is washed away with ultrapure water and dried with nitrogen. Then, the sample is developed with ARP600-56 for 60 seconds and fixed with IPA for 30 seconds. Then, two optical dielectric layers 6 are grown sequentially by magnetron sputtering according to the preset stacked structure. After the end, the sample is soaked in acetone solvent to remove the photoresist and excess optical dielectric layer 6, and the subwavelength structure 5 is obtained.

[0095] S3 follows S2, changing the growth order of the two optical dielectric layers 6 to prepare a subwavelength structure 5 in the second photolithography region, thus obtaining a metasurface device.

[0096] Example 13: This invention discloses a method for fabricating a quasi-BIC chiral metasurface device based on refractive index modulation. The difference from Example 1 is that it includes the following steps:

[0097] S1 Prepare an optical substrate 1, and divide it into two photolithographic regions according to the preset stacked structure of the optical dielectric layer 6 of the subwavelength structure 5.

[0098] S2 first cleans the surface of optical substrate 1 using plasma. Then, a 200nm thick layer of positive photoresist PMMA is spin-coated onto the surface of optical substrate 1. After coating, it is baked at 180℃ for 1 minute. Next, conductive photoresist ARPC-5090 is spin-coated at 2000rpm for 60 seconds, followed by baking at 90℃ for 4 minutes. Finally, electron beam exposure is performed on the first photolithography area, controlling the electron beam exposure voltage at 10kV, the aperture at 30μm, and the dose at 50μC / cm. 2 After electron beam exposure, the conductive photoresist on the surface is washed away with ultrapure water and dried with nitrogen. Then, the sample is developed with ARP600-56 for 60 seconds and fixed with IPA for 30 seconds. Then, two optical dielectric layers 6 are grown sequentially by magnetron sputtering according to the preset stacked structure. After the end, the sample is soaked in acetone solvent to remove the photoresist and excess optical dielectric layer 6, and the subwavelength structure 5 is obtained.

[0099] S3 follows S2, changing the growth order of the two optical dielectric layers 6 to prepare a subwavelength structure 5 in the second photolithography region, thus obtaining a metasurface device.

[0100] Example 14: Refer to Figure 10 This invention discloses a method for fabricating a quasi-BIC chiral metasurface device based on refractive index modulation, which differs from Example 1 in that it includes the following steps:

[0101] S1 Prepare an optical substrate 1, and divide it into two photolithographic regions according to the preset stacked structure of the optical dielectric layer 6 of the subwavelength structure 5.

[0102] S2 first cleans the surface of optical substrate 1 using plasma, then spin-coates a 3μm thick layer of positive photoresist PMMA onto the surface of optical substrate 1. After coating, it is baked at 105℃ for 4 minutes. Then, maskless electron beam exposure is performed on the first photolithography area, controlling the electron beam exposure voltage to be 10kV, the aperture to be 1μm, and the dose to be 100μC / cm. 2 After electron beam exposure, the sample was developed for 60 seconds with a mixture of developer AR 300-26 and ultrapure water, and fixed with ultrapure water for 30 seconds. Then, two optical dielectric layers 6 were grown sequentially by magnetron sputtering according to the preset stacked structure. After the end, the sample was soaked in acetone solvent to remove the photoresist and excess optical dielectric layer 6, and the subwavelength structure 5 was obtained.

[0103] S3 follows S2, changing the growth order of the two optical dielectric layers 6 to prepare a subwavelength structure 5 in the second photolithography region, thus obtaining a metasurface device.

[0104] Example 15: This is an application of a quasi-BIC chiral metasurface device based on refractive index modulation disclosed in this invention. The difference from Example 1 is that the metasurface device is used in the fabrication of narrowband filters, optical polarization converters, circularly polarized lasers, chiral molecular sensors, and chiral quantum light sources.

[0105] To further verify that the above metasurface device can achieve tunable intrinsic chirality at multiple wavelengths, the structural parameters of Example 1 were first used, and the angle α between the subwavelength structure 5 and the Y-axis was adjusted from 0 to 20°. Then, the corresponding metasurface device was fabricated according to the preparation method of Example 12, such as... Figures 11-14 The image shows the transmission spectra of the fabricated metasurface device at a wavelength near 890 nm for left-handed and right-handed polarized light in crystalline (c-GST) and amorphous (a-GST) germanium-antimony-tellurium alloy (GST). It can be seen that in the amorphous state of GST, the transmission spectra of the two chiral types are not significantly different, both exhibiting high transmittance. However, in the crystalline state of GST, right-handed polarized light shows a very sharp transmittance trough, with the lowest transmittance approaching 0. (Refer to...) Figures 15-16The circular dichroism (CD) of crystalline and amorphous states was calculated using the following formula: CD = (TLL - TRR) / (TLL + TRR); where TLL and TRR represent the transmittance of left-handed and right-handed polarized light, respectively. In the crystalline state of GST, the highest quality factor (Q value) is approximately 1200, and the maximum CD value is approximately 0.98. Similarly, refer to... Figures 17-22 Another high Q signal with chiral characteristics was obtained near the wavelength of 920nm. When GST is in the amorphous state, the maximum Q value is about 1800 and the maximum CD value exceeds 0.99.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A quasi-BIC chiral metasurface device based on refractive index modulation, characterized in that: The super surface device comprises an optical substrate (1), a plurality of sub-wavelength structure partitions (2) arranged sequentially along the X axis on the surface of the optical substrate (1), and adjacent two sub-wavelength structure partitions (2) are arranged in rotational symmetry with respect to the Y axis, wherein the sub-wavelength structure (5) in the sub-wavelength structure partition (2) comprises at least two optical medium layers (6) arranged in layers along the Z axis, and at least one sub-wavelength structure (5) in the sub-wavelength structure partition (2) is arranged in an inclined manner with respect to the Y axis, and there is a refractive index difference between the at least two optical medium layers (6), so that the super surface device realizes intrinsic chirality.

2. The quasi-BIC chiral metasurface device based on refractive index modulation of claim 1, wherein: The sub-wavelength structure partition (2) comprises a plurality of sub-wavelength structure units (3) arranged sequentially along the Y axis, and adjacent two sub-wavelength structures (5) are arranged in parallel with respect to the X axis, in mirror symmetry, or in rotational symmetry.

3. The quasi-BIC chiral metasurface device based on refractive index modulation of claim 2, wherein: The sub-wavelength structure unit (3) comprises a plurality of sub-wavelength structure groups (4) arranged in a periodic array along the XY plane, and at least one structural parameter is different between the sub-wavelength structures (5) of adjacent two sub-wavelength structure groups (4).

4. The quasi-BIC chiral metasurface device based on refractive index modulation of claim 3, wherein: The sub-wavelength structure group (4) comprises a plurality of sub-wavelength structures (5) arranged sequentially along the X axis, and at least one structural parameter is different between adjacent two sub-wavelength structures (5).

5. The quasi-BIC chiral metasurface device based on refractive index modulation of claim 3, wherein: The sub-wavelength structure group (4) comprises a plurality of sub-wavelength structures (5) arranged sequentially along the X axis, and the structural parameters of adjacent two sub-wavelength structures (5) are different.

6. The quasi-BIC chiral metasurface device based on refractive index modulation of claim 3, wherein: The cross section of the sub-wavelength structure (5) is polygonal, annular, or circular, and the longitudinal section of the sub-wavelength structure (5) is rectangular, trapezoidal, or parallelogram.

7. The quasi-BIC chiral metasurface device based on refractive index modulation of claim 3, wherein: The structural parameters include the period P of the sub-wavelength structure (5), the length l of the sub-wavelength structure (5), the width w of the sub-wavelength structure (5), the included angle α between the sub-wavelength structure (5) and the Y axis, the thickness t of the optical medium layer (6), and the material of the optical medium layer (6).

8. The quasi-BIC chiral metasurface device based on refractive index modulation of claim 7, wherein: The period P of the sub-wavelength structure (5) is 0.25-2.50 μm; And / or, the length l of the sub-wavelength structure (5) is 0.25-2.00 μm; And / or, the width w of the sub-wavelength structure (5) is 0.05-1.00 μm; And / or, the included angle α between the sub-wavelength structure (5) arranged in an inclined manner and the Y axis is 2-30°; And / or, the thickness t of the optical medium layer (6) is 0.05-0.50 μm; And / or, the material of the optical medium layer (6) is one or a combination of silicon, silicon nitride, silicon dioxide, aluminum oxide, silicon carbide, titanium dioxide, gold, silver, aluminum, germanium antimony tellurium alloy, germanium antimony selenium tellurium alloy, germanium antimony tellurium sulfur alloy, vanadium oxide, antimony sulfide, and antimony selenide.

9. The method of claim 1-8, wherein the method comprises: The method comprises the following steps, S1: preparing an optical substrate (1), and dividing n photoetching regions according to a preset layering structure of the optical medium layer (6) of the sub-wavelength structure (5); S2 first coats photoresist on the surface of the optical substrate (1), then performs electron beam exposure and development in the first photolithography area, and then grows optical medium layers (6) according to the preset layer structure, and then removes the photoresist to obtain a subwavelength structure (5); S3 according to S2, sequentially prepares subwavelength structures (5) in the second photolithography area to the nth photolithography area to obtain a metasurface device.

10. Application of the quasi-BIC chiral metasurface device based on refractive index modulation according to any one of claims 1-8 in a narrow-band filter, an optical polarization converter, a circularly polarized laser, a chiral molecule sensor, and a chiral quantum light source.

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