Chiral metasurface and humidity-regulated high circular dichroism chiral switching method

Abstract

The present application relates to the field of micro-nano optics and optical detection technology, and discloses a chiral super-structured surface and a method for realizing high circular dichroism chiral switching based on humidity control. The present application designs a hook-type chiral super-structured surface and lays polyvinyl alcohol hydrogel on the silicon nano-brick structure; the volume expansion and refractive index change of the hydrogel with humidity change are used to realize the regulation and control of the optical response of the super-structured surface; during the process of relative humidity from 20% to 42%, the thickness of the hydrogel film layer increases and the refractive index decreases, causing the circular dichroism to be blue-shifted, and realizing the switching of the normalized circular dichroism value from-0.8 to +0.8 in the visible light range, with a blue-shift bandwidth of about 8nm. The chiral super-structured surface structure of the present application has the characteristics of high integration, excellent reversibility and good stability, and can be applied to the fields of circular dichroism optical identification, humidity sensing and dynamic optical information storage, etc., and provides a technical approach for the design and implementation of dynamic integrated optical systems.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of micro-nano optical technology and optical detection technology, in particular to a method for realizing high circular dichroism dynamic chiral switching based on a hook-type chiral metasurface integrated with a hydrogel film layer, and aims to solve the problems of limited dynamic regulation range, high energy consumption of driving mode, low device integration, and poor repeatability of existing chiral metasurfaces. BACKGROUND

[0002] Chiral metasurfaces have become an important platform for constructing new chiral optical devices due to their ability to finely regulate the phase, polarization, and amplitude of light fields. By precisely designing the geometry and periodic arrangement of subwavelength units, metasurfaces can achieve selective coupling and differential scattering of left-handed / right-handed circularly polarized light (LCP / RCP), thus demonstrating important application value in detection, biological recognition, chiral discrimination, and information coding. However, the dynamic regulation of existing chiral metasurfaces still faces several technical challenges:

[0003] On the one hand, most efficient circular dichroism (CD) implementations rely on static geometric optimization or require external complex driving (such as electric field, thermal field, or phase transition material-induced phase state conversion). These methods, although able to achieve high static CD values in certain wavebands, often involve high energy consumption, complex driving systems, high integration difficulty, or limited cycle life. On the other hand, mechanical deformation (such as flexible stretching) and humidity response schemes based on metal-hydrogel cavities provide tuning possibilities, but the former relies on external force, device life, and batch processing limitations, while the latter still has deficiencies in amplitude and structural complexity in achieving high-amplitude, reusable CD polarity reversal. SUMMARY

[0004] To solve the problems of existing technology in realizing high circular dichroism switching, the present application provides a chiral metasurface and a high circular dichroism chiral switching method for humidity regulation. By introducing a polyvinyl alcohol (PVA) hydrogel film layer on the hook-type chiral composite nanobrick structure, the changes in volume and refractive index of the hydrogel during relative humidity changes are utilized to accurately regulate the chiral optical response of the metasurface.

[0005] According to an aspect of the present application, a chiral metasurface is provided, which can realize chiral switching of circular dichroism values from -0.8 to +0.8;

[0006] The chiral metasurface includes:

[0007] a silicon dioxide substrate layer;

[0008] A silicon nanobrick structure layer is disposed on the silicon dioxide substrate layer, and includes a plurality of hook-shaped silicon nanobrick units arranged in a rectangular periodicity, the hook-shaped silicon nanobrick unit including a first nanometer arm, a second nanometer arm and a third nanometer arm, the long axis of the first nanometer arm being perpendicular to the long axis of the second nanometer arm and the long axis of the third nanometer arm, and the long axis of the first nanometer arm being parallel to the long axis of the second nanometer arm.

[0009] A hydrogel film layer is disposed on the silicon nanobrick structure layer and the plurality of hook-shaped silicon nanobrick units, and is used for dynamically regulating the circular dichroism of the chiral superstructure surface when the ambient humidity changes.

[0010] As a further technical solution, the hydrogel is polyvinyl alcohol, the volume and the refractive index of which change with humidity, and the relative humidity is the volume after swelling / the maximum swelling volume x 100%.

[0011] As a further technical solution, under the condition of a relative humidity of 20%, the designed hydrogel film layer has a thickness of 340 nm and a refractive index of 1.51; under the condition of a relative humidity of 42%, the hydrogel film layer swells after absorbing water, and the thickness increases to 585 nm and the refractive index decreases to 1.4157.

[0012] As a further technical solution, under the condition of a relative humidity of 20%, when the designed superstructure surface is normally incident, the transmittance difference of the silicon nanobrick structure layer to left-handed circularly polarized light and right-handed circularly polarized light causes the appearance of chiral circular dichroism; the transmittance difference is characterized by a Jones matrix and is dynamically regulated by the refractive index of the hydrogel film layer.

[0013] As a further technical solution, when the relative humidity changes from 20% to 42% and the relative humidity changes from 42% to 20%, the circular dichroism generated by the superstructure surface changes in the opposite direction.

[0014] As a further technical solution, when the relative humidity changes from 20% to 42%, the circular dichroism is blue-shifted; when the relative humidity changes from 42% to 20%, the circular dichroism is red-shifted.

[0015] As a further technical solution, when the designed chiral superstructure surface is normally incident, the formation of high circular dichroism is due to the chirality introduced by the second nanometer arm and the third nanometer arm.

[0016] As a further technical solution, one or more nanometer arms remain stable in the characterization of the chiral switching of the circular dichroism peak under the same humidity regulation in the presence of ±10 nm perturbation.

[0017] According to an aspect of the present application, a humidity-controlled high-circular dichroism chiral switching method is provided, which is realized by using the chiral metasurface, and the method comprises: dynamically controlling the circular dichroism of the chiral metasurface when the environmental humidity changes, and realizing the chiral switching of the circular dichroism value from-0.8 to +0.8.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] 1. The present application designs a hook-shaped chiral metasurface structure, which combines the chiral response of the chiral metasurface to the circular dichroism light and the mechanism of the humidity-controlled PVA hydrogel film layer thickness and refractive index, and realizes the dynamic control of the circular dichroism spectrum by the humidity control.

[0020] 2. The present application designs a humidity-controlled chiral metasurface, which realizes the large-scale regulation of the normalized circular dichroism (CD) value from-0.8 to +0.8.

[0021] 3. The present application provides a novel humidity-driven chiral switching method for circular dichroism, which uses environmental humidity as a driving variable, and does not need additional power supply, heating or mechanical loading and other excitation conditions, compared with the existing phase change material or flexible stretching scheme, which significantly reduces the energy consumption and system complexity, and is suitable for integrated application.

[0022] 4. The unit structure capable of circular dichroism chiral switching provided by the present application is simple and easy to integrate. The superstructure surface structure of the present application is composed of a hydrogel film layer, a hook-shaped chiral silicon nanobrick array and a silicon dioxide substrate, which is compatible with common micro-nano processing technology, and is convenient for large-scale manufacturing and application in on-chip photonic devices.

[0023] 5. The hydrogel material used in the present application can change the volume and refractive index by humidity control, which has stable reversibility. The PVA hydrogel can still maintain stable volume and refractive index changes after multiple humidity adsorption-desorption cycles, and the device of the present application also shows stable CD switching performance in multiple humidity switching, which ensures long-term reliable operation.

[0024] 6. The chiral metasurface designed in the present application has high processing robustness. When the nanometer arm or the center brick has a ±10 nm perturbation, the CD response of the device remains stable, which significantly improves the feasibility in actual manufacturing and application process.

[0025] 7. The humidity-controllable chiral switching mechanism provided by the present application has wide application prospect, which can be applied to circular dichroism optical recognition, humidity sensing, dynamic optical information storage and security encryption, and provides a feasible path for developing a new generation of low-energy, integrable and dynamically controllable superstructure photonic devices. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the accompanying drawings used in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort.

[0027] Figure 1 is a straight line diagram of the thickness change of the hydrogel film layer on the designed chiral metasurface in embodiment 1 based on the humidity response;

[0028] Figure 2 is a schematic diagram of the geometric parameters and relative position information of the hook-shaped silicon nanobrick unit designed in embodiment 1 of the present application;

[0029] Figure 3 is a schematic diagram of the thickness change of the hydrogel film layer under different relative humidity in embodiment 1 of the present application;

[0030] Figure 4 is a simulation effect diagram of the x-y plane electric field of the chiral metasurface under different circularly polarized light incidence in embodiment 1 of the present application;

[0031] Figure 5 is a CD distribution simulation effect diagram of the scanning size of the chiral metasurface in embodiment 1 of the present application;

[0032] Figure 6 is a schematic diagram of the chiral metasurface based on humidity control realizing high circular dichroism chiral switching in the present application;

[0033] Figure 7 is a schematic diagram of the CD value corresponding to the perturbation of ±10nm of the parameter W of the third nanometer arm in the chiral metasurface of embodiment 2 of the present application;

[0034] Figure 8 is a schematic diagram of the CD value corresponding to the perturbation of ±10nm of the parameter L of the third nanometer arm in the chiral metasurface of embodiment 2 of the present application;

[0035] Figure 9 is a schematic diagram of the CD value corresponding to the perturbation of ±10nm of the parameter W of the first nanometer arm of the chiral metasurface of embodiment 2 of the present application;

[0036] Figure 10 is a schematic diagram of the CD value corresponding to the perturbation of ±10nm of the parameter L of the first nanometer arm of the chiral metasurface of embodiment 2 of the present application;

[0037] Figure 11is a schematic diagram of the corresponding CD value when the perturbation of ±10 nm exists in the parameter W of the second nano-arm in the chiral metasurface of embodiment 2 of the present application;

[0038] Figure 12 is a schematic diagram of the corresponding CD value when the perturbation of ±10 nm exists in the parameter L of the second nano-arm in the chiral metasurface of embodiment 2 of the present application;

[0039] Figure 13 is a schematic diagram of the corresponding CD when the perturbation of +10 nm exists in the parameter W of the third nano-arm in the chiral metasurface of embodiment 2 of the present application, and the size of the parameter L of the second nano-arm is changed.

[0040] Figure 14 is a schematic diagram of the corresponding CD when the perturbation of -10 nm exists in the parameter W of the third nano-arm in the chiral metasurface of embodiment 2 of the present application, and the size of the parameter L of the second nano-arm is changed. DETAILED DESCRIPTION

[0041] Although hydrogels (especially hydrophilic polymers such as polyvinyl alcohol PVA) show good thickness variability and refractive index tunability as reversible hygroscopic materials in optical modulation applications such as color tuning, structural color and holographic display, the direct use of the hygroscopic-volume-refractive index effect of hydrogels to realize a device-level design of “high amplitude, reversible and repeatable circular dichroism inversion in the visible light band” has not been fully solved in the existing disclosed technology. The existing technology lacks a dynamic chiral regulation scheme that is low in energy consumption, can be integrated on a chip, and takes into account high contrast and processing robustness.

[0042] Based on the above technical status, it is urgently needed to propose a new metasurface device system: the system should be able to achieve large, reversible CD polarity switching driven by passive (environmental) variables while maintaining high CD response, and have good cycle stability and manufacturing tolerance, so as to facilitate popularization in practical applications such as sensing, identification and information storage.

[0043] To this end, the application provides a chiral metasurface and a method for realizing high circular dichroism chiral switching through humidity regulation based on the chiral metasurface. By introducing a polyvinyl alcohol (PVA) hydrogel film layer on the hook-shaped chiral composite nanobrick structure, the volume and refractive index changes of the hydrogel during the relative humidity change process are utilized to realize accurate regulation of the chiral optical response of the metasurface. During the process of increasing the relative humidity from 20% to 42%, the PVA film layer thickness increases from about 340 nm to 585 nm, and the refractive index decreases from 1.51 to 1.4157, resulting in a total blue shift of about 8 nm of the circular dichroism spectrum, and the normalized CD value at the visible wavelength of 677 nm is switched from -0.7581 to +0.8011, with a change amplitude of up to 1.56. The application not only realizes high-contrast, reversible and stable chiral switching, but also ensures the recycling and reuse, and still maintains stable performance when the size of the nanobranch or the center brick has a ±10 nm perturbation, which embodies excellent processing robustness.

[0044] It should be noted that:

[0045] The chiral optical response of the chiral metasurface refers to the specific optical response exhibited by the chiral metasurface when interacting with light. These responses mainly manifest in the differences in absorption, transmission and reflection of circularly polarized light of different chirality. The chiral optical response of the chiral metasurface can be described by CD, i.e. circular dichroism. Circular dichroism is defined as the difference in absorption, transmittance or reflectance of LCP and RCP, and its expression is as follows:

[0046]

[0047] Wherein, K can be A, T or R, representing absorption, transmission or reflection. In order to construct a structure with high circular dichroism, Jones Matrix, i.e. Jones matrix, is used for calculation. Jones matrix is a mathematical tool for describing the change of light wave polarization state, which represents the electric field components of light wave in two orthogonal directions perpendicular to the propagation direction by a two-dimensional complex matrix. The amplitude of the scattering field related to the chiral metasurface can also be represented by the Jones matrix, and its expression is as follows:

[0048]

[0049] In formulas (2) and (3) , represents the reflected or transmitted light field component in the circularly polarized state; represents the reflection coefficient of different polarization directions; represents the transmission coefficient of different polarization directions; is the matrix involved in the calculation for participating in the transformation between different polarization states by Jones Matrix, i.e. the change of the propagation direction of light. denotes the reflection / transmission matrix, which represents the reflection and transmission coefficients in a certain direction. denotes the reflection coefficient of circularly polarized light, each subscript represents the relationship between the incident circular polarization state and the outgoing circular polarization state, such as may represent the complex amplitude coefficient of the reflected left-handed circularly polarized light (LCP) after the incident LCP; represents the complex amplitude coefficient of the reflected left-handed circularly polarized light (LCP) after the incident LCP; t denotes the transmission coefficient of circularly polarized light, and its symbol is the same as r. r and t are complex numbers, and the modulus represents the change of amplitude, and the phase represents the change of phase, which is used to describe the conversion of the polarization state of circularly polarized light in the reflection and transmission process.

[0050] Therefore, in combination with the Jones matrix, the CD can be defined as:

[0051]

[0052] The present application realizes dynamic regulation of CD by regulating the thickness and refractive index of PVA hydrogel. The hydrogel film layer material used in the present application is polyvinyl alcohol, and the water absorption degree can be represented by the volume expansion degree:

[0053]

[0054] wherein V represents the volume after expansion, represents the volume before expansion, and thus the volume expansion degree of the hydrogel is The refractive index of the hydrogel after expansion can be further obtained:

[0055]

[0056] wherein 1.51 is the refractive index of the dried hydrogel, and 1.33 is the refractive index of water. The refractive index of the hydrogel film layer expanded to a certain volume can be calculated using the refractive index formula. And polyvinyl alcohol can only expand to 5 times the original volume in general experimental environment, so the relative humidity can be defined as:

[0057]

[0058] Therefore, the relative humidity of 20% and 42% respectively represents the dry condition of the hydrogel and the water absorption expansion of the hydrogel to 2.1 times the original volume.

[0059] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. In addition, the technical features of the various embodiments or individual embodiments provided by the present invention can be arbitrarily combined to form new technical solutions. Such combinations are not bound by the order of steps and / or structural composition patterns, but must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0060] Example 1

[0061] Example 1 provides a chiral metasurface and a method for achieving circular dichroism chiral switching based on the chiral metasurface through humidity control, mainly including the following steps:

[0062] Step 1: Design chiral metasurfaces and optimize their structural parameters.

[0063] A unit structure for constructing a chiral metasurface is formed, consisting of a silica substrate layer, a silicon nanobrick structure layer, and a polyvinyl alcohol hydrogel film layer. The silicon nanobrick structure layer comprises a rectangularly periodically arranged array of hook-shaped silicon nanobrick units. The thickness of the silica substrate is... The thickness of the silicon nanobrick structure is 1000 nm. The array is 270 nm with a period of 270 nm. P = 400 nm, see Figure 1 The image shows a side view of the chiral metasurface. It should be noted that the array period can be considered as the distance between two adjacent silicon nanobrick units. Specifically, P=400nm represents that the length and width of a single hook-shaped unit structure are both 400nm.

[0064] This invention designs a hook-shaped silicon nanobrick structure. The advantages of this design are reflected in the fabrication process. Due to the shape of the hook, certain process parameters (such as etching angle or aspect ratio) may help align subsequent layers (such as PVA hydrogel layers), thereby achieving a more consistent metasurface structure. On the other hand, the hook-shaped design is conducive to enhancing the local electric field, thereby promoting the interaction between light and chiral materials, making the metasurface unit structure more sensitive to changes in the humidity of the PVA layer.

[0065] Design as Figure 2As shown, the hook-shaped silicon nanobrick is composed of three cuboid nanometer arms, and the nanobrick therein is defined as , and the structural parameters correspond to , respectively. The designed hook-shaped chiral metasurface under normal incidence, in the hook-shaped nanostructure integrated hydrogel metasurface, the formation of high circular dichroism is due to the chiralities introduced by the upper and lower nanometer arms of the hook-shaped structure. With the change of the length and width of the nanobrick in the hook-shaped structure, the selective coupling of chiral light is caused. This morphological change causes the change of the circular dichroism resonance supported by the periodic nanostructure. In order to further understand the circular dichroism response of the hook-shaped silicon structure, a scanning with a step of 5 nm is performed on .

[0066] After a series of parameter scanning and high circular dichroism chiral switching effect simulation verification process, the structure parameters selected in the simulation process in this embodiment which simultaneously satisfy higher circular dichroism and can realize chiral switching function are: 330 nm and 90 nm, respectively; 135 nm and 95 nm, respectively; 225 nm and 120 nm, respectively. For specific structural parameters and relative position information, please refer to Figure 2 .

[0067] Step 2: Chiral switching of circular dichroism is realized while ensuring higher circular dichroism by adjusting humidity.

[0068] The designed chiral metasurface in step 1 under normal incidence, by adjusting the relative humidity to change the thickness and refractive index of the hydrogel film layer, Figure 1 It is shown that the volume of the hydrogel film layer in the chiral metasurface in the present application will change when the relative humidity increases and decreases.

[0069] Figure 3 It is shown that the thickness of the hydrogel film layer changes with the relative humidity. The volume change of the hydrogel film layer integrated on the chiral metasurface can be characterized as the change of the film layer thickness, and the specific thickness calculation method is shown in the code appendix.

[0070] Specific thickness calculation method:

[0071] The volume of the silicon nanometer column ;

[0072] The thickness of the hydrogel at a relative humidity of 20% is , then the volume of the hydrogel at a relative humidity of 20% is ;

[0073] The volume of the hydrogel at a relative humidity of 42% is , then the thickness of the hydrogel at a relative humidity of 42% is .

[0074] Based on the hydrogel refractive index formula (6), the refractive index of the hydrogel decreases with the increase of the volume, so the water absorption and swelling of the hydrogel film layer generally causes the circular dichroism to blue shift. In addition, by comparing the left and right circularly polarized light (LCP, RCP) incident x-y The plane electric field simulation diagram can observe the selective coupling of the hook type to different rotating lights Figure 4 ). Figure 4 The electric field distribution of the incident left / right circularly polarized light (LCP / RCP) on the x-y plane of the super surface under different relative humidity (RH=20%, 42%) conditions, wherein a is LCP under RH 20%; b is RCP under RH 20%; c is LCP under RH 42%; d is RCP under RH 42%. The electric field changes are concentrated at the interface between the structure and the air, so it is expected that by using the changes of the thickness and refractive index of the hydrogel film layer in the simulation, the dynamic regulation of the circular dichroism can be realized, and the chiral switching of the circular dichroism can be realized.

[0075] Figure 5 The CD distribution simulation effect diagram of the scanning size in step 1 is shown, and the simulation results show that when the relative humidity is 20%, the LCP transmittance is 0.01607 at a wavelength of 677 nm, and the RCP transmittance is 0.11676, and the CD value at this place is-0.7581 obtained by using the transmission type circular dichroism calculation formula (4) combined with the Jones matrix; when the relative humidity is 42%, the LCP transmittance is 0.11709 at a wavelength of 677 nm, and the RCP transmittance is 0.01293, and the CD value is calculated to be 0.8011, which indicates that the present application can regulate the relative humidity to realize the change of the CD value at the same wavelength by about 1.56, and ensure high circular dichroism while realizing the chiral switching of the circular dichroism.

[0076] Step 3: The mechanism of realizing the chiral switching of the circular dichroism of the present application is shown in Figure 6 .

[0077] On the basis of steps 1 to 2, when the relative humidity is 20%, the transmittance of LCP is only about 1%, and the transmittance of RCP is higher than that of LCP, which shows that the designed super-structured surface is positive incident, and only RCP is coupled to exit. Correspondingly, when the relative humidity is 42%, only LCP is coupled to exit. The water absorption and swelling and the water loss and shrinkage characteristics of the hydrogel give the present application a reusable mechanism, so that the present application can be flexibly reused in the field of circular dichroism optical detection according to different experimental requirements.

[0078] Example 2

[0079] Example 2 provides the feasibility of the present application in actual production application.Figures 7 to 12 It is shown that the hook-shaped chiral metasurface designed in the application can ensure high circular dichroism at a certain wavelength and realize chiral switching of circular dichroism in the visible light range even if there is a perturbation of ±10 nm in the geometric structure parameters.

[0080] As shown in Figure 13 When the W3 parameter of the third nano arm is perturbed by -10 nm, that is, W3=110 nm, the CD value curves at relative humidity of 20% and 42% are derived by changing the size of the L2 parameter of the second nano arm. There are two curves of the same type, representing the CD value curves at relative humidity of 20% and relative humidity of 42%, respectively. As can be seen from the figure, there is a large change in CD value at about 677 nm under the condition of perturbation in the structure parameters, which shows a large chiral switching of circular dichroism. Figure 14 Similarly, when the W3 parameter of the third nano arm is perturbed by -10 nm, that is, W3=130 nm, the CD value curves at relative humidity of 20% and 42% are derived by changing the size of the L2 parameter of the second nano arm.

[0081] Through the design and simulation verification of example 1 and example 2, the hook-shaped chiral metasurface based on humidity control proposed in the application has proved to have the following remarkable features and engineering values:

[0082] Significant reversible chiral switching capability - under the condition of covering the PVA hydrogel film layer on the hook-shaped chiral nano brick array and regulating the relative humidity, the normalized circular dichroism (CD) value can be reversibly switched between about -0.8 and +0.8 in the visible band; at an example wavelength (such as 677 nm), the CD can be switched from about -0.7581 to about +0.8011, with a change amplitude close to 1.56, and accompanied by a spectral shift of about 8 nm, indicating that the structure takes into account both high amplitude and spectral controllability.

[0083] Low energy consumption and easy to drive - the application uses environmental humidity as a driving variable, without additional electrical / thermal or mechanical excitation, reducing system complexity and operating energy consumption, facilitating passive sensing or integration application in energy-limited scenarios.

[0084] Good cycle stability and reusability - based on the inherent hygroscopic-dehydration characteristics of PVA and the design of the present structure, the device can maintain the reversibility and stability of the CD response in multiple humidity cycles, meeting the reliability requirements for long-term use.

[0085] Process tolerance and manufacturing feasibility - simulation results show that when there is a perturbation of ±10 nm in the size of the nano component, the device can still maintain the target CD peak value and chiral switching function, indicating high processing robustness, which is conducive to batch implementation of existing micro-nano manufacturing processes.

[0086] Application potential - with the above advantages, the structure of the present application is suitable for circular dichroism optical recognition, humidity sensing, dynamic optical information storage and security encryption, and can be used as a low-energy, on-chip integrated dynamic chiral photonic device module to enter a larger system for application.

[0087] Embodiment 3

[0088] The present embodiment provides a humidity-controlled high circular dichroism chiral switching method, which is realized by using the chiral metasurface of any of the preceding embodiments, and the method comprises: dynamically adjusting the circular dichroism of the chiral metasurface when the ambient humidity changes, to realize chiral switching of the circular dichroism value from -0.8 to +0.8.

[0089] In summary of the above embodiments, the present application designs a hook-type chiral metasurface, and polyvinyl alcohol hydrogel is laid on the nano-brick unit structure; the volume expansion and refractive index change of the hydrogel with humidity change are used to realize the adjustment of the optical response of the metasurface; during the relative humidity changes from 20% to 42%, the thickness of the hydrogel film layer increases and the refractive index decreases, causing the circular dichroism to blue shift, and realizing the switching of the normalized circular dichroism value from -0.8 to +0.8 in the visible light range, with a blue shift bandwidth of about 8nm. The chiral metasurface structure of the present application has the characteristics of high integration, excellent reversibility and good stability, and can be applied to the fields of circular dichroism optical recognition, humidity sensing and dynamic optical information storage, and provides a technical approach for the design and implementation of a dynamic integrated optical system.

[0090] The terms "comprising" and "having" and any variations thereof in the specification and claims and above-described drawings are intended to cover not exclusively inclusive, for example, a process, method, system, product or device comprising a series of steps or units, not necessarily limited to the clearly listed steps or units, but can include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0091] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present application.

Claims

1. A chiral metasurface, characterized in that, The chiral metasurface can switch its chirality from -0.8 to +0.8 based on changes in ambient humidity; The chiral metasurface includes: Silicon dioxide substrate; A silicon nanobrick structure layer is disposed on the silicon dioxide substrate layer, comprising a plurality of hook-shaped silicon nanobrick units arranged in a rectangular periodic pattern. Each hook-shaped silicon nanobrick unit includes a first nanoarm, a second nanoarm, and a third nanoarm. The long axis of the first nanoarm is perpendicular to the long axis of the second nanoarm and the long axis of the third nanoarm, respectively, and the long axis of the second nanoarm is parallel to the long axis of the third nanoarm. A hydrogel film layer, disposed on the silicon nanobrick structure layer and multiple hook-shaped silicon nanobrick units, is used to dynamically regulate the circular dichroism of the chiral metasurface when the ambient humidity changes. The thickness and refractive index of the hydrogel film layer can change synergistically with the change of ambient humidity. By regulating the change of ambient humidity within a preset range, a blue shift or red shift in the circular dichroism spectrum is induced, thereby dynamically regulating the circular dichroism of the chiral metasurface and realizing the sign reversal of the circular dichroism value.

2. The chiral metasurface according to claim 1, characterized in that, The hydrogel is polyvinyl alcohol, and its volume and refractive index change with humidity. The relative humidity is calculated as the expanded volume / maximum expanded volume × 100%.

3. The chiral metasurface according to claim 2, characterized in that, Under a relative humidity of 20%, the designed hydrogel film has a thickness of 340 nm and a refractive index of 1.

51. Under a relative humidity of 42%, the hydrogel film absorbs water and expands, increasing its thickness to 585 nm and decreasing its refractive index to 1.4157.

4. The chiral metasurface according to claim 3, characterized in that, Under conditions of relative humidity of 20%, when the designed metasurface is incident normally, the difference in transmittance of the silicon nanobrick structure layer to left-handed and right-handed circularly polarized light results in chiral circular dichroism; the transmittance difference is characterized by Jones matrix calculation and is dynamically regulated by the refractive index of the hydrogel film layer.

5. The chiral metasurface according to claim 3, characterized in that, The circular dichroism produced by the metasurface undergoes opposite changes when the relative humidity changes from 20% to 42% and from 42% to 20%.

6. The chiral metasurface according to claim 3, characterized in that, When the relative humidity changes from 20% to 42%, the circular dichroism chromatogram shows a blue shift; when the relative humidity changes from 42% to 20%, the circular dichroism chromatogram shows a red shift.

7. The chiral metasurface according to claim 1, characterized in that, When the chiral metasurface is designed for normal incidence, the high circular dichroism is formed due to the chirality introduced by the second and third nanoarms.

8. The chiral metasurface according to claim 1, characterized in that, The characterization of the chiral switching of the circular dichroism peak remains stable in the presence of ±10 nm perturbations and under the same humidity control for one or more nanoarms.

9. A method for switching high circular dichroism chirality under humidity control, characterized in that, The chiral metasurface described in any one of claims 1 to 8 is used to achieve the chiral switching of the chiral metasurface from -0.8 to +0.8 when the ambient humidity changes.

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