Wavelength-tunable infrared metasurfaces with chiral bound states in the continuum

Wavelength-tunable infrared metasurfaces with chiral bound states in the continuum | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Wavelength-tunable infrared metasurfaces with chiral bound states in the continuum Tao Zhang, Jiachen Liu, Liangliang Gu, Haifeng Hu, Qiwen Zhan This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5163501/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 02 Jan, 2025 Read the published version in Scientific Reports → Version 1 posted 10 You are reading this latest preprint version Abstract In recent years, research on chiral bound states in the continuum (BIC) has surged, leading to the development of various chiral metasurfaces with narrow bandwidths by breaking of in-plane and out-of-plane symmetries. However, the ability to dynamically tune the working band remains relatively unexplored, which is valuable for chiral sensing applications. Optical phase-change materials, with tunable dielectric constants and switchable properties during phase transition, offer the potential for dynamic control of optical metasurfaces. This work demonstrates a wavelength-tunable infrared chiral metasurface by combining the phase-change material GST with chiral BIC structures. By varying the longitudinal tilt angle of the nanostructure, an infrared chiral metasurface with an extremely narrow bandwidth of chiral resonance and a CD value of over 0.8 is designed. The phase-change properties of GST enable wavelength-tunable chiral resonance without altering the structural parameters, and the influence of key structural parameters of the metasurface on the chiral resonance wavelength and CD value is analyzed. The proposed chiral BIC metasurface with phase-change materials shows promising application prospects in filter devices, chiral thermal switches, infrared imaging, and tunable chiral photonics. Physical sciences/Optics and photonics/Optical materials and structures/Metamaterials Physical sciences/Optics and photonics/Optical materials and structures/Silicon photonics Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction Chirality is a fundamental feature of nature, referring to the geometric properties of objects lacking mirror reflection symmetry 1 . The interaction of light with these geometries can cause chiral optical effects. During this process, the chiral features of the structures can be measured. A typical technique based on optical method is circular dichroism (CD), which measures the difference in intensity and phase response between left and right circularly polarized (LCP/RCP) light illumination 2 . Although chirality plays a key role in various research fields such as drug synthesis, chiral sensing 3 and optical communication 4 , CD in natural optical materials is extremely weak due to the mismatch between light wavelength and the size of chiral molecule, which limits the applications of chiral optical techniques 5 . Meticulously designed artificial chiral structures can exhibit exceptionally strong chiral optical signals 6 – 8 . A key parameter to enhance the intensity of chiral light-matter interaction is the quality ( Q ) factor of the associated resonance. Importantly, bound states in continuous domains (BICs) provide a feasible solution to design the chiral narrow-band structure. BICs are identified as local states coexisting with extended modes within the light cone, which have attracted significant attention due to the infinite Q -factor 9 . By utilizing the decoupling between BICs and continuum states, a research team has successfully designed and fabricated the metasurface with the extreme chirality (i.e. chiral BIC) for the first time, addressing the challenge of achieving chiral metasurfaces with huge CD signal 10 . In recently years, the evolution from passive to actively tunable chiral metasurfaces has been emphasized 11 . Actively tunable chiral metasurfaces are ideal for dynamically controlling the interaction between chiral wave-matter and circularly polarized light 12 . General GST (GST-225) is a nonvolatile phase change material, which exhibits excellent dielectric constant contrast during the phase transition from amorphous to crystalline state 13 . Meanwhile, GST-based metasurfaces can be regulated by phase transition without changing the geometric parameters of the cell structure, showing great potential in applications such as biosensing 14 , thermal imaging 15 and thermal camouflage 16 . Results Design of tunable chiral metasurfaces. Chiral BIC metasurfaces have the characteristics of high CD and high Q -factor. We introduce phase change materials into the chiral BIC metasurface, and design the structure which achieves wavelength tunability of chiral resonance with high CD and high Q -factor simultaneously. This paper adopts a dual perturbation structure design and introduces the phase-change material GST as the structural medium. The out-of-plane mirror symmetry of the metasurface is broken by the method of structural tilt, and the in-plane mirror symmetry is broken by adding a trapezoidal nanopore. The key parameters of the designed structure are optimized. In addition, the optical constant of GST during the phase change process are measured experimentally in the mid-infrared range. By utilizing the variable optical properties of phase change material GST, the infrared chiral metasurface with high CD absorption and tunable resonance with narrow bandwidth is realized. The demonstrated results of tunable infrared chiral metasurfaces will pave the way for the development of dynamically controlled chiral photonic devices to advance applications such as chiral thermal switches, infrared imaging, and tunable chiral photonics. The schematic diagram presented in Fig. 1(a) illustrates the design of a chiral meta-surface based on the phase change material Ge 2 Sb 2 Te 5 . This metasurface consists of a skewed trapezoidal nano-hole array in GST film, with its upper and lower regions filled with silicon to match the refractive index. The structure evolved from vertical square hole, as shown in Fig. 1(b). It is worth noting that this structure is characterized by introducing two types of perturbations: a deformation angle α for in-plane symmetry breaking and a tilt angle β for out-of-plane symmetry breaking. The combination of these two perturbations transforms the hole into a chiral structure. When no disturbances are involved ( α = 0 and β = 0), this structure supports a continuous domain in the momentum space, with a symmetry-protected bound state. However, when the in-plane disturbance ( α ≠ 0 and β = 0) is introduced, the bound-in-continuum (BIC) states are broken and evolve into quasi-BIC ( Q -BIC). This Q -BIC exhibits far-field radiation in the form of linear polarization. When both in-plane deformation and out-of-plane tilt disturbances ( α ≠ 0 and β ≠ 0) are introduced, the eigenstate at Γ point produces chiral far-field radiation. Figure 1(c) elucidates the phase transition process of GST from amorphous to crystalline states and vice versa. When the temperature of the amorphous GST exceeds its melting point, which is approximately 160°C, the amorphous phase transforms into an unstable cubic crystal structure, akin to sodium chloride (NaCl) 17 . If the temperature is further increased, the unstable crystal structure will evolve into a stable hexagonal structure. This phase transition from amorphous to crystalline can be achieved by subjecting GST to a heating plate, using laser pulses, or applying an external voltage 18 . Conversely, by heating crystalline GST above its melting point of about 640°C, liquefying it, and then rapid cooling, amorphous GST can be formed 12 . The skewed trapezoidal nanohole arrays in GST film is designed to achieve the tunability of chiral metasurfaces and to optimize other geometric parameter for the desired operating wavelength range. The dynamic tuning of the chiral resonance wavelength can be achieved by the variable optical constant of GST during the phase transition process. Simulation of tunable chiral metasurfaces. We conduct numerical simulation analysis on the structure to understand the chiral optical response mechanism of the metasurface based on the finite element method (FEM). Figure 2(a) shows the band structure diagram and corresponding Q -factor of the structure without perturbation ( α = 0, β = 0), demonstrating that the eigenmode at the Γ point in momentum space supports a symmetry-protected bound state in the continuum. When the perturbations α and β are small, the Q -factor of the quasi-BIC is approximately proportional to the square of all perturbations 19 : Q ~ 1/( α 2 + Aβ 2 ), where A represents the different sensitivities of Q to α and β . Figure 2(b) illustrates the Q -factor under different tilt angle β when the in-plane deformation angle α is fixed at 0.052. One can see that when both in-plane and out-of-plane perturbations ( α ≠ 0, β ≠ 0) are introduced, the BIC state is broken and evolves into a Q -BIC, with the Q -factor experiencing a significant drop during the increase of β perturbation, However, even after the deformation with large β angle, the Q -BIC mode still maintain a relative high Q-factor compared with other modes. Figure 2(c) demonstrate the simulated transmission rates for LCP and RCP incidence and the CD spectrum of the metasurface after introducing both in-plane and out-of-plane perturbation angles. The inset shows the momentum-space characteristic polarization diagram of the mode. It can be observed that after breaking both in-plane and out-of-plane symmetries of the structure, the metasurface exhibits totally different response for LCP and RCP incident states, resulting in extremely high CD values. Here CD is defined as CD = (T L -T R )/(T L +T R ), where T L(R) is the normalized transmission spectra under LCP(RCP) illumination. The polarization state in reciprocal space is shown in the inset of Fig. 2(c). Near the Γ point, the eigenmode with LCP state can be solved, which is the origin of high CD. In Fig. 2(d), we illustrated the relationship between the in-plane disturbance angle β and the CD amplitude with α = 0.052. It is evident that there exists an optimal combination of in-plane and out-of-plane perturbation angles that maximizes the optical chirality of the perturbed metasurface. Subsequent investigations into other parameters of the metasurface are conducted based on this perturbation angle configuration. Beside the eigenmode analysis, the chirality of BIC in the metasurface can also be explained by the interaction between electric dipole and magnetic dipole. The intrinsic chirality of the BIC can also be explained by the general theory of chiral optics, which dictates that the optical chirality of an object, under the dipole approximation, is determined by p ⊥ · m ⊥ , where p ⊥ and m ⊥ are the projections of electric dipole p and magnetic dipole m onto the plane perpendicular to the incident wave vector k 20 . For the metasurface in this work, in the absence of any perturbations (α = β = 0), the metasurface supports symmetry-protected bound states in the continuum (BICs) at the Γ point of Brillouin zone. When the metasurface is subjected to in-plane perturbations (α ≠ 0, β = 0), the in-plane symmetry is broken, and the BIC evolves into a quasi-BIC, the magnetic fields of quasi-BICs are predominantly directed along the x axis whereas the electric fields are out-of-plane (along z direction). In this case, p ⊥ · m ⊥ is zero. However, when the metasurface experiences both in-plane and out-of-plane perturbations (α ≠ 0, β ≠ 0), the nanohole is slanted towards the x direction, resulting in an electric field component aligned with this direction. Meanwhile, the magnetic field components are predominantly maintained along x-axis, leading to non-zero value of p ⊥ · m ⊥ and optical chirality 10 . In order to investigate the influence of structural geometric parameters on the chiral optical response of metasurfaces, we perform parameter scanning calculations for the period a , the size b of the trapezoidal nanoholes, and the thickness h of the GST film in this structure. Figure 2(a) shows the chiral optical response of the metasurface when the period is varied from 1200nm to 1400nm with b = 1000 nm and h = 500 nm. It can be observed that wavelength of the chiral resonance is tuned from 4200 nm to 5200 nm by increasing the period of metasurface. During the tuning process, the peak CD value remains above 0.8. The influence of hole size is shown in Fig. 2(b), when a = 1300nm and h = 500 nm. When the parameter b varies from 850 nm to 1100 nm, the chiral optical response of the metasurface exhibits significant fluctuations, with a wavelength span of the peak CD ranging from 5000 nm to 4500 nm. Therefore, considering the fabrication of this structure, it is necessary to ensure size accuracy of the trapezoidal holes to achieve a higher chiral optical response of the metasurface. In addition, the thickness of the GST film is considered in the simulation in Fig. 3(c). The wavelength of the chiral resonance can also be tuned by the film thickness, but the peak value of the CD spectrum is significantly affected by it. According to the simulation result, the optimized value of the GST film thickness is in the range of 450 nm-550 nm. Therefore, to fabricate the chiral metasurface, film thickness is key parameter to obtain high CD signal. By utilizing the phase change property of GST material, it is possible to modify the chiral resonance of the metasurface based on the BIC effect. Unlike the volatile phase change material VO 2 , GST does not require continuous energy to maintain the crystalline state, and can retain this state when it returns to room temperature after reaching the phase change temperature 21,22 . The typical phase transition temperature of GST-225 phase change material from amorphous to crystalline state is about 160°C 23 . In order to study the dynamic tuning of chiral metasurface resonance wavelength by phase change material GST, we experimentally measured the refractive index of GST at different heating temperatures, as shown in Fig. 4(a). It can be seen that within the wavelength range from 4 µm to 5 µm, the real and imaginary parts of the refractive index of GST gradually increase with the increase of the heating temperature. If the imaginary part of refractive index is too large, it means that the energy loss of the metasurface is greater caused by GST film absorption, and the corresponding chiral dispersion (CD) response is smaller. To avoid this problem, we confine our analysis of the tunable chiral metasurface in the low loss cases, which corresponding to the heating temperature of GST film within the range from 20℃ to 200℃. As shown in Fig. 4(b), when the refractive index of GST is in the range of 4.8 to 5.0, the CD response of the designed chiral metasurface is above 0.8, and the corresponding chiral resonance wavelength is tunable within the range of 50 nm. Therefore, it can be seen that the metasurface with phase change material can dynamically tune the chiral resonance wavelength by controlling the heating temperature of GST. Discussion In conclusion, a wavelength-tunable infrared chiral metasurface based on phase-change material GST-225 with chiral perturbation has been proposed and analyzed. This metasurface introduces the out of plane tilt angle as a degree of freedom to build chiral structure, avoiding the use of a complex bilayer structure design. Combined with the phase-change material GST-225, it is able to achieve a CD value of above 0.8, and the wavelength bandwidth of the chiral resonance is only about 1nm. Moreover, the working wavelength can be tuned by varying the heating temperature, instead of the structural parameters. This work not only promotes the development of adaptive and active metasurfaces using phase-change materials but also provides an opportunity for dynamic modulation of circular polarization control in switchable metasurfaces with narrow working bandwidth. Additionally, the dynamic modulation of chiral metasurfaces induced by opto-thermally triggered GST phase transitions can reach timescales ranging from picoseconds to nanoseconds, depending on the duration and intensity of the laser pulses for heating process, as well as the thermal conductivity of the material 24 , 25 . Advancements in phase-change chiral metasurfaces will drive research in the infrared band for filter devices 26 , optical switches 27 , thermal imaging, and chiral sensing 28 . Declarations Data availability Data available on request with contacting the corresponding author. Acknowledgements This work is supported by the National Natural Science Foundation of China (Grant No: 92050202, 12434012, 1240042013, 22ZR1443100). Author Contributions T.Z. and Q.Z. were responsible for the original research concept and physical interpretation. T.Z. was responsible for the theoretical derivations and COMSOL simulations. T.Z. wrote the main manuscript with the help of J.L. and H.H. All authors reviewed the manuscript. Additional Information Competing financial interests: The authors declare no competing financial interests. References Adhikari, S. & Orrit, M. Optically Probing the Chirality of Single Plasmonic Nanostructures and of Single Molecules:Potential and Obstacles. Acs Photonics . 9 , 3486–3497 (2022). Shi, T. et al. Planar chiral metasurfaces with maximal and tunable chiroptical response driven by bound states in the continuum. Nat. Commun. 13 , 4111 (2022). Chen, Y., Yang, X. & Gao, J. Spin-controlled wavefront shaping with plasmonic chiral geometric metasurfaces. Light Sci. Appl. 7 , 86 (2018). Li, W. et al. Circularly polarized light detection with hot electrons in chiral plasmonic metamaterials. Nat. Commun. 6 , 8379 (2015). Tang, H., Stan, L., Czaplewski, D. A., Yang, X. & Gao, J. Wavelength-tunable infrared chiral metasurfaces with phase-change materials. Opt. Express . 31 , 21118–21127 (2023). Decker, M. et al. Strong optical activity from twisted-cross photonic metamaterials. Opt. Lett. 34 , 2501–2503 (2009). Hu, G., Wang, M., Mazor, Y., Qiu, C. W. & Alù, A. Tailoring Light with Layered and Moiré Metasurfaces. Trends Chem. 3 , 342–358 (2021). Mark, A. G., Gibbs, J. G., Lee, T. C. & Fischer, P. Hybrid nanocolloids with programmed three-dimensional shape and material composition. Nat. Mater. 12 , 802–807 (2013). Hsu, C. W., Zhen, B., Stone, A. D., Joannopoulos, J. D. & Soljačić, M. Bound states in the continuum. Nat. Rev. Mater. 1 , 16048 (2016). Chen, Y. et al. Observation of intrinsic chiral bound states in the continuum. Nature . 613 , 474–478 (2023). Hail, C. U., Michel, A. K. U., Poulikakos, D. & Eghlidi, H. Optical Metasurfaces: Evolving from Passive to Adaptive. Adv. Opt. Mater. 7 , 1801786 (2019). Wuttig, M., Bhaskaran, H. & Taubner, T. Phase-change materials for non-volatile photonic applications. Nat. Photonics . 11 , 465–476 (2017). Michel, A. K. U., Wuttig, M. & Taubner, T. Design Parameters for Phase-Change Materials for Nanostructure Resonance Tuning. Adv. Opt. Mater. 5 , 1700261 (2017). Cabré, A., Verdaguer, X. & Riera, A. Recent Advances in the Enantioselective Synthesis of Chiral Amines via Transition Metal-Catalyzed Asymmetric Hydrogenation. Chem. Rev. 122 , 269–339 (2021). Julian, M. N., Williams, C., Borg, S., Bartram, S. & Kim, H. J. Reversible optical tuning of GeSbTe phase-change metasurface spectral filters for mid-wave infrared imaging. Optica . 7 , 746–754 (2020). Senbua, W., Mearnchu, J. & Wichitwechkarn, J. Easy-to-use and reliable absorbance-based MPH-GST biosensor for the detection of methyl parathion pesticide. Biotechnol. Rep. 27 , e00495 (2020). Shportko, K. et al. Resonant bonding in crystalline phase-change materials. Nat. Mater. 7 , 653–658 (2008). Nevzorov, A. A. et al. Controlling optical properties of GST thin films by ultrashort laser pulses series impact. Opt. Mater. 141 , 113925 (2023). Koshelev, K., Lepeshov, S., Liu, M., Bogdanov, A. & Kivshar, Y. Asymmetric Metasurfaces with High- $ Q $ Resonances Governed by Bound States in the Continuum. Phys. Rev. Lett. 121 , 193903 (2018). Plum, E., Fedotov, V. A. & Zheludev N. I. Optical activity in extrinsically chiral metamaterial. Appl. Phys. Lett. 93 , 191911 (2008). Long, L., Taylor, S. & Wang, L. Enhanced Infrared Emission by Thermally Switching the Excitation of Magnetic Polariton with Scalable Microstructured VO2 Metasurfaces. ACS Photonics . 7 , 2219–2227 (2020). Ding, F., Zhong, S. & Bozhevolnyi, S. I. Vanadium Dioxide Integrated Metasurfaces with Switchable Functionalities at Terahertz Frequencies. Adv. Opt. Mater. 6 , 1701204 (2018). Sittner, E. R. et al. GeTe)x–(Sb2Te3)1–x phase-change thin films as potential thermoelectric materials. Phys. Status Solidi a . 210 , 147–152 (2012). Yan, W., Wang, J. Y., Qu, Y. R., Li, Q. & Qiu, M. Tunable metasurfaces based on phase-change materials. Acta Phys. Sin . 69 , 200453 (2020). Kiselev, A. V. et al. Dynamics of reversible optical properties switching of Ge2Sb2Te5 thin films at laser-induced phase transitions. Opt. Laser Technol. 147 , 107701 (2022). Williams, C., Hong, N., Julian, M., Borg, S. & Kim, H. J. Tunable mid-wave infrared Fabry-Perot bandpass filters using phase-change GeSbTe. Opt. Express . 28 , 10583–10594 (2020). He, Q. et al. Low-loss ultrafast and nonvolatile all-optical switch enabled by all-dielectric phase change materials. iScience . 25 , 104375 (2022). Khan, S. A. et al. Optical sensing by metamaterials and metasurfaces: from physics to biomolecule detection. Adv. Opt. Mater. 10 , 2200500 (2022). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 02 Jan, 2025 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 06 Dec, 2024 Reviews received at journal 24 Nov, 2024 Reviews received at journal 16 Nov, 2024 Reviewers agreed at journal 14 Nov, 2024 Reviewers agreed at journal 13 Nov, 2024 Reviewers invited by journal 11 Nov, 2024 Editor assigned by journal 20 Oct, 2024 Editor invited by journal 20 Oct, 2024 Submission checks completed at journal 15 Oct, 2024 First submitted to journal 27 Sep, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5163501","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":386985088,"identity":"f8222a1a-0af9-4465-8bc0-f45f8cf46b3b","order_by":0,"name":"Tao Zhang","email":"","orcid":"","institution":"University of Shanghai for Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Tao","middleName":"","lastName":"Zhang","suffix":""},{"id":386985089,"identity":"c62f949b-4449-4b55-9746-458fe15de24d","order_by":1,"name":"Jiachen Liu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA6ElEQVRIiWNgGAWjYBACPmYGBoMEBgYgYj4AFUvAr4UNoYUNpNSACC0Ik3kMiNTCzmNQ8KDGLo9fuueb5I8/fxj42XMMGH7uwOcwHgODhGPJxZJzzm6T5m0zYJDseWPA2HuGkBa2A4kbbuRuk2ZsMGAwuJFjwMzYRkjLvwOJ+2/kPAM6zIDBnigtiW1AWyRy2CR42IC2SBDUwlZgkNiXnDjjRpqxNW+bMY/EmWcFB3vxaOHnP7zN8Mc3u8T+GckPb/74IyfH35688cFPPFpAFhkg83hAxAG8GoAJ5QEBBaNgFIyCUTDSAQDZmUh1esiXEgAAAABJRU5ErkJggg==","orcid":"","institution":"University of Shanghai for Science and Technology","correspondingAuthor":true,"prefix":"","firstName":"Jiachen","middleName":"","lastName":"Liu","suffix":""},{"id":386985090,"identity":"66c5648e-8986-45a2-9fc9-144898f33515","order_by":2,"name":"Liangliang Gu","email":"","orcid":"","institution":"University of Shanghai for Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Liangliang","middleName":"","lastName":"Gu","suffix":""},{"id":386985091,"identity":"e10d0605-3b17-4da9-819c-4b1ea604479c","order_by":3,"name":"Haifeng Hu","email":"","orcid":"","institution":"University of Shanghai for Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Haifeng","middleName":"","lastName":"Hu","suffix":""},{"id":386985092,"identity":"10c081aa-2d0c-4399-ad22-305d86010ae5","order_by":4,"name":"Qiwen Zhan","email":"","orcid":"","institution":"University of Shanghai for Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Qiwen","middleName":"","lastName":"Zhan","suffix":""}],"badges":[],"createdAt":"2024-09-27 08:23:21","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5163501/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5163501/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-024-84587-7","type":"published","date":"2025-01-02T15:57:19+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":72333908,"identity":"69143192-3815-4f7b-9626-cdc5e4555623","added_by":"auto","created_at":"2024-12-25 15:27:15","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":41162,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Schematic of the slant-perturbation metasurface with GST-225 phase-change material. (b) Disturbance diagram of in-plane deformation Angle \u003cem\u003eα\u003c/em\u003e and out-of-plane inclination Angle \u003cem\u003eβ\u003c/em\u003e. The geometric parameters are: \u003cem\u003ea\u003c/em\u003e = 1300 nm, \u003cem\u003eb\u003c/em\u003e = 1000 nm, \u003cem\u003eh\u003c/em\u003e = 500 nm. (c) The illustration of the phase transition of GST-225 from the amorphous state to the crystalline state.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5163501/v1/a65edb438c9f66414421a201.png"},{"id":72333909,"identity":"97bb959d-3314-4dcc-ab73-6c55ebb35fa1","added_by":"auto","created_at":"2024-12-25 15:27:15","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":89326,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Simulated \u003cem\u003eQ\u003c/em\u003e-factor of characteristic modes near the \u003cem\u003eГ\u003c/em\u003e point, with the inset showing the mode band structure. (b) Function curve of the \u003cem\u003eQ\u003c/em\u003e-factor of characteristic modes after perturbation as the perturbation angle \u003cem\u003eβ \u003c/em\u003evaries. (c) Transmission spectra and corresponding CD response of the metasurface under LCP and RCP incidence with \u003cem\u003eα\u003c/em\u003e = \u003cem\u003eβ\u003c/em\u003e = 0.052. The inset displays the characteristic polarization map of the first Brillouin zone, where the polarization states are represented by ellipses and the blue and red ones representing left-handed and right-handed states, respectively. (d) Function curve of the maximum CD response of the metasurface with \u003cem\u003eα\u003c/em\u003e = 0.052 as the perturbation angle \u003cem\u003eβ \u003c/em\u003evaries.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5163501/v1/35d32ea76404b9b2e3621cc5.png"},{"id":72334250,"identity":"ff5bd646-f5c2-4182-8f4f-ccd047622569","added_by":"auto","created_at":"2024-12-25 15:35:15","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":78838,"visible":true,"origin":"","legend":"\u003cp\u003eThe chiral resonance wavelength and CD value of chiral metasurface as functions of the main geometric parameters\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5163501/v1/0b6cac32f51782facb465160.png"},{"id":72333922,"identity":"2651f332-7a05-4506-9f35-40f9fbc4f1e8","added_by":"auto","created_at":"2024-12-25 15:27:15","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":66181,"visible":true,"origin":"","legend":"\u003cp\u003e(a) The real and imaginary parts of the refractive index of GST-225 at different phase transition temperatures. (b) The influence of the refractive index of GST near the phase transition temperature of 170 °C on the chiral resonance wavelength and CD value.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5163501/v1/150c244363f1a4be6a6b7274.png"},{"id":73093277,"identity":"393cbf1d-278f-4f1d-b6a8-69a32fdb1968","added_by":"auto","created_at":"2025-01-06 16:12:41","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":588129,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5163501/v1/aaf509dc-4a60-44f6-b831-adbbfb1a74cc.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Wavelength-tunable infrared metasurfaces with chiral bound states in the continuum","fulltext":[{"header":"Introduction","content":"\u003cp\u003eChirality is a fundamental feature of nature, referring to the geometric properties of objects lacking mirror reflection symmetry\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. The interaction of light with these geometries can cause chiral optical effects. During this process, the chiral features of the structures can be measured. A typical technique based on optical method is circular dichroism (CD), which measures the difference in intensity and phase response between left and right circularly polarized (LCP/RCP) light illumination\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. Although chirality plays a key role in various research fields such as drug synthesis, chiral sensing\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e and optical communication\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e, CD in natural optical materials is extremely weak due to the mismatch between light wavelength and the size of chiral molecule, which limits the applications of chiral optical techniques \u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eMeticulously designed artificial chiral structures can exhibit exceptionally strong chiral optical signals\u003csup\u003e\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. A key parameter to enhance the intensity of chiral light-matter interaction is the quality (\u003cem\u003eQ\u003c/em\u003e) factor of the associated resonance. Importantly, bound states in continuous domains (BICs) provide a feasible solution to design the chiral narrow-band structure. BICs are identified as local states coexisting with extended modes within the light cone, which have attracted significant attention due to the infinite \u003cem\u003eQ\u003c/em\u003e-factor\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. By utilizing the decoupling between BICs and continuum states, a research team has successfully designed and fabricated the metasurface with the extreme chirality (i.e. chiral BIC) for the first time, addressing the challenge of achieving chiral metasurfaces with huge CD signal \u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn recently years, the evolution from passive to actively tunable chiral metasurfaces has been emphasized\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. Actively tunable chiral metasurfaces are ideal for dynamically controlling the interaction between chiral wave-matter and circularly polarized light\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. General GST (GST-225) is a nonvolatile phase change material, which exhibits excellent dielectric constant contrast during the phase transition from amorphous to crystalline state\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. Meanwhile, GST-based metasurfaces can be regulated by phase transition without changing the geometric parameters of the cell structure, showing great potential in applications such as biosensing\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e, thermal imaging\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e and thermal camouflage\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cstrong\u003eDesign of tunable chiral metasurfaces.\u003c/strong\u003e Chiral BIC metasurfaces have the characteristics of high CD and high \u003cem\u003eQ\u003c/em\u003e-factor. We introduce phase change materials into the chiral BIC metasurface, and design the structure which achieves wavelength tunability of chiral resonance with high CD and high \u003cem\u003eQ\u003c/em\u003e-factor simultaneously. This paper adopts a dual perturbation structure design and introduces the phase-change material GST as the structural medium. The out-of-plane mirror symmetry of the metasurface is broken by the method of structural tilt, and the in-plane mirror symmetry is broken by adding a trapezoidal nanopore. The key parameters of the designed structure are optimized. In addition, the optical constant of GST during the phase change process are measured experimentally in the mid-infrared range. By utilizing the variable optical properties of phase change material GST, the infrared chiral metasurface with high CD absorption and tunable resonance with narrow bandwidth is realized. The demonstrated results of tunable infrared chiral metasurfaces will pave the way for the development of dynamically controlled chiral photonic devices to advance applications such as chiral thermal switches, infrared imaging, and tunable chiral photonics.\u003c/p\u003e\n\u003cp\u003eThe schematic diagram presented in Fig.\u0026nbsp;1(a) illustrates the design of a chiral meta-surface based on the phase change material Ge\u003csub\u003e2\u003c/sub\u003eSb\u003csub\u003e2\u003c/sub\u003eTe\u003csub\u003e5\u003c/sub\u003e. This metasurface consists of a skewed trapezoidal nano-hole array in GST film, with its upper and lower regions filled with silicon to match the refractive index. The structure evolved from vertical square hole, as shown in Fig.\u0026nbsp;1(b). It is worth noting that this structure is characterized by introducing two types of perturbations: a deformation angle \u003cem\u003e\u0026alpha;\u003c/em\u003e for in-plane symmetry breaking and a tilt angle \u003cem\u003e\u0026beta;\u003c/em\u003e for out-of-plane symmetry breaking. The combination of these two perturbations transforms the hole into a chiral structure.\u003c/p\u003e\n\u003cp\u003eWhen no disturbances are involved (\u003cem\u003e\u0026alpha;\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0 and \u003cem\u003e\u0026beta;\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0), this structure supports a continuous domain in the momentum space, with a symmetry-protected bound state. However, when the in-plane disturbance (\u003cem\u003e\u0026alpha;\u003c/em\u003e\u0026thinsp;\u0026ne;\u0026thinsp;0 and \u003cem\u003e\u0026beta;\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0) is introduced, the bound-in-continuum (BIC) states are broken and evolve into quasi-BIC (\u003cem\u003eQ\u003c/em\u003e-BIC). This \u003cem\u003eQ\u003c/em\u003e-BIC exhibits far-field radiation in the form of linear polarization. When both in-plane deformation and out-of-plane tilt disturbances (\u003cem\u003e\u0026alpha;\u003c/em\u003e\u0026thinsp;\u0026ne;\u0026thinsp;0 and \u003cem\u003e\u0026beta;\u003c/em\u003e\u0026thinsp;\u0026ne;\u0026thinsp;0) are introduced, the eigenstate at \u0026Gamma; point produces chiral far-field radiation.\u003c/p\u003e\n\u003cp\u003eFigure\u0026nbsp;1(c) elucidates the phase transition process of GST from amorphous to crystalline states and vice versa. When the temperature of the amorphous GST exceeds its melting point, which is approximately 160\u0026deg;C, the amorphous phase transforms into an unstable cubic crystal structure, akin to sodium chloride (NaCl)\u003csup\u003e17\u003c/sup\u003e. If the temperature is further increased, the unstable crystal structure will evolve into a stable hexagonal structure. This phase transition from amorphous to crystalline can be achieved by subjecting GST to a heating plate, using laser pulses, or applying an external voltage\u003csup\u003e18\u003c/sup\u003e. Conversely, by heating crystalline GST above its melting point of about 640\u0026deg;C, liquefying it, and then rapid cooling, amorphous GST can be formed\u003csup\u003e12\u003c/sup\u003e. The skewed trapezoidal nanohole arrays in GST film is designed to achieve the tunability of chiral metasurfaces and to optimize other geometric parameter for the desired operating wavelength range. The dynamic tuning of the chiral resonance wavelength can be achieved by the variable optical constant of GST during the phase transition process.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSimulation of tunable chiral metasurfaces.\u003c/strong\u003e We conduct numerical simulation analysis on the structure to understand the chiral optical response mechanism of the metasurface based on the finite element method (FEM). Figure 2(a) shows the band structure diagram and corresponding \u003cem\u003eQ\u003c/em\u003e-factor of the structure without perturbation (\u003cem\u003e\u0026alpha;\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0, \u003cem\u003e\u0026beta;\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0), demonstrating that the eigenmode at the \u003cem\u003e\u0026Gamma;\u003c/em\u003e point in momentum space supports a symmetry-protected bound state in the continuum. When the perturbations \u003cem\u003e\u0026alpha;\u003c/em\u003e and \u003cem\u003e\u0026beta;\u003c/em\u003e are small, the \u003cem\u003eQ\u003c/em\u003e-factor of the quasi-BIC is approximately proportional to the square of all perturbations\u003csup\u003e19\u003c/sup\u003e: \u003cem\u003eQ\u003c/em\u003e\u0026thinsp;~\u0026thinsp;1/(\u003cem\u003e\u0026alpha;\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eA\u0026beta;\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e), where \u003cem\u003eA\u003c/em\u003e represents the different sensitivities of \u003cem\u003eQ\u003c/em\u003e to \u003cem\u003e\u0026alpha;\u003c/em\u003e and \u003cem\u003e\u0026beta;\u003c/em\u003e. Figure 2(b) illustrates the \u003cem\u003eQ\u003c/em\u003e-factor under different tilt angle \u003cem\u003e\u0026beta;\u003c/em\u003e when the in-plane deformation angle \u003cem\u003e\u0026alpha;\u003c/em\u003e is fixed at 0.052. One can see that when both in-plane and out-of-plane perturbations (\u003cem\u003e\u0026alpha;\u003c/em\u003e\u0026thinsp;\u0026ne;\u0026thinsp;0, \u003cem\u003e\u0026beta;\u003c/em\u003e\u0026thinsp;\u0026ne;\u0026thinsp;0) are introduced, the BIC state is broken and evolves into a \u003cem\u003eQ\u003c/em\u003e-BIC, with the \u003cem\u003eQ\u003c/em\u003e-factor experiencing a significant drop during the increase of \u003cem\u003e\u0026beta;\u003c/em\u003e perturbation, However, even after the deformation with large \u003cem\u003e\u0026beta;\u003c/em\u003e angle, the \u003cem\u003eQ\u003c/em\u003e-BIC mode still maintain a relative high Q-factor compared with other modes. Figure\u0026nbsp;2(c) demonstrate the simulated transmission rates for LCP and RCP incidence and the CD spectrum of the metasurface after introducing both in-plane and out-of-plane perturbation angles. The inset shows the momentum-space characteristic polarization diagram of the mode. It can be observed that after breaking both in-plane and out-of-plane symmetries of the structure, the metasurface exhibits totally different response for LCP and RCP incident states, resulting in extremely high CD values. Here CD is defined as CD = (T\u003csub\u003eL\u003c/sub\u003e-T\u003csub\u003eR\u003c/sub\u003e)/(T\u003csub\u003eL\u003c/sub\u003e+T\u003csub\u003eR\u003c/sub\u003e), where T\u003csub\u003eL(R)\u003c/sub\u003e is the normalized transmission spectra under LCP(RCP) illumination. The polarization state in reciprocal space is shown in the inset of Fig. 2(c). Near the \u0026Gamma; point, the eigenmode with LCP state can be solved, which is the origin of high CD. In Fig. 2(d), we illustrated the relationship between the in-plane disturbance angle \u003cem\u003e\u0026beta;\u003c/em\u003e and the CD amplitude with \u0026alpha;\u0026thinsp;=\u0026thinsp;0.052. It is evident that there exists an optimal combination of in-plane and out-of-plane perturbation angles that maximizes the optical chirality of the perturbed metasurface. Subsequent investigations into other parameters of the metasurface are conducted based on this perturbation angle configuration.\u003c/p\u003e\n\u003cp\u003eBeside the eigenmode analysis, the chirality of BIC in the metasurface can also be explained by the interaction between electric dipole and magnetic dipole. The intrinsic chirality of the BIC can also be explained by the general theory of chiral optics, which dictates that the optical chirality of an object, under the dipole approximation, is determined by \u003cstrong\u003ep\u003c/strong\u003e\u003csub\u003e\u0026perp;\u003c/sub\u003e\u0026middot;\u003cstrong\u003em\u003c/strong\u003e\u003csub\u003e\u0026perp;\u003c/sub\u003e, where \u003cstrong\u003ep\u003c/strong\u003e\u003csub\u003e\u0026perp;\u003c/sub\u003e and \u003cstrong\u003em\u003c/strong\u003e\u003csub\u003e\u0026perp;\u003c/sub\u003e are the projections of electric dipole \u003cstrong\u003ep\u003c/strong\u003e and magnetic dipole \u003cstrong\u003em\u003c/strong\u003e onto the plane perpendicular to the incident wave vector \u003cstrong\u003ek\u003c/strong\u003e\u003csup\u003e20\u003c/sup\u003e. For the metasurface in this work, in the absence of any perturbations (\u0026alpha;\u0026thinsp;=\u0026thinsp;\u0026beta;\u0026thinsp;=\u0026thinsp;0), the metasurface supports symmetry-protected bound states in the continuum (BICs) at the \u0026Gamma; point of Brillouin zone. When the metasurface is subjected to in-plane perturbations (\u0026alpha;\u0026thinsp;\u0026ne;\u0026thinsp;0, \u0026beta;\u0026thinsp;=\u0026thinsp;0), the in-plane symmetry is broken, and the BIC evolves into a quasi-BIC, the magnetic fields of quasi-BICs are predominantly directed along the \u003cem\u003ex\u003c/em\u003e axis whereas the electric fields are out-of-plane (along z direction). In this case, \u003cstrong\u003ep\u003c/strong\u003e\u003csub\u003e\u0026perp;\u003c/sub\u003e\u0026middot;\u003cstrong\u003em\u003c/strong\u003e\u003csub\u003e\u0026perp;\u003c/sub\u003e is zero. However, when the metasurface experiences both in-plane and out-of-plane perturbations (\u0026alpha;\u0026thinsp;\u0026ne;\u0026thinsp;0, \u0026beta;\u0026thinsp;\u0026ne;\u0026thinsp;0), the nanohole is slanted towards the \u003cem\u003ex\u003c/em\u003e direction, resulting in an electric field component aligned with this direction. Meanwhile, the magnetic field components are predominantly maintained along x-axis, leading to non-zero value of\u0026nbsp;\u003cstrong\u003ep\u003c/strong\u003e \u003csub\u003e\u0026perp;\u003c/sub\u003e\u0026middot;\u003cstrong\u003em\u003c/strong\u003e\u003csub\u003e\u0026perp;\u003c/sub\u003e and optical chirality\u003csup\u003e10\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eIn order to investigate the influence of structural geometric parameters on the chiral optical response of metasurfaces, we perform parameter scanning calculations for the period \u003cem\u003ea\u003c/em\u003e, the size \u003cem\u003eb\u003c/em\u003e of the trapezoidal nanoholes, and the thickness \u003cem\u003eh\u003c/em\u003e of the GST film in this structure. Figure 2(a) shows the chiral optical response of the metasurface when the period is varied from 1200nm to 1400nm with \u003cem\u003eb\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1000 nm and \u003cem\u003eh\u003c/em\u003e\u0026thinsp;=\u0026thinsp;500 nm. It can be observed that wavelength of the chiral resonance is tuned from 4200 nm to 5200 nm by increasing the period of metasurface. During the tuning process, the peak CD value remains above 0.8. The influence of hole size is shown in Fig. 2(b), when \u003cem\u003ea\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1300nm and \u003cem\u003eh\u003c/em\u003e\u0026thinsp;=\u0026thinsp;500 nm. When the parameter \u003cem\u003eb\u003c/em\u003e varies from 850 nm to 1100 nm, the chiral optical response of the metasurface exhibits significant fluctuations, with a wavelength span of the peak CD ranging from 5000 nm to 4500 nm. Therefore, considering the fabrication of this structure, it is necessary to ensure size accuracy of the trapezoidal holes to achieve a higher chiral optical response of the metasurface. In addition, the thickness of the GST film is considered in the simulation in Fig. 3(c). The wavelength of the chiral resonance can also be tuned by the film thickness, but the peak value of the CD spectrum is significantly affected by it. According to the simulation result, the optimized value of the GST film thickness is in the range of 450 nm-550 nm. Therefore, to fabricate the chiral metasurface, film thickness is key parameter to obtain high CD signal.\u003c/p\u003e\n\u003cp\u003eBy utilizing the phase change property of GST material, it is possible to modify the chiral resonance of the metasurface based on the BIC effect. Unlike the volatile phase change material VO\u003csub\u003e2\u003c/sub\u003e, GST does not require continuous energy to maintain the crystalline state, and can retain this state when it returns to room temperature after reaching the phase change temperature\u003csup\u003e21,22\u003c/sup\u003e. The typical phase transition temperature of GST-225 phase change material from amorphous to crystalline state is about 160\u0026deg;C\u003csup\u003e23\u003c/sup\u003e. In order to study the dynamic tuning of chiral metasurface resonance wavelength by phase change material GST, we experimentally measured the refractive index of GST at different heating temperatures, as shown in Fig.\u0026nbsp;4(a). It can be seen that within the wavelength range from 4 \u0026micro;m to 5 \u0026micro;m, the real and imaginary parts of the refractive index of GST gradually increase with the increase of the heating temperature. If the imaginary part of refractive index is too large, it means that the energy loss of the metasurface is greater caused by GST film absorption, and the corresponding chiral dispersion (CD) response is smaller. To avoid this problem, we confine our analysis of the tunable chiral metasurface in the low loss cases, which corresponding to the heating temperature of GST film within the range from 20℃ to 200℃. As shown in Fig.\u0026nbsp;4(b), when the refractive index of GST is in the range of 4.8 to 5.0, the CD response of the designed chiral metasurface is above 0.8, and the corresponding chiral resonance wavelength is tunable within the range of 50 nm. Therefore, it can be seen that the metasurface with phase change material can dynamically tune the chiral resonance wavelength by controlling the heating temperature of GST.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn conclusion, a wavelength-tunable infrared chiral metasurface based on phase-change material GST-225 with chiral perturbation has been proposed and analyzed. This metasurface introduces the out of plane tilt angle as a degree of freedom to build chiral structure, avoiding the use of a complex bilayer structure design. Combined with the phase-change material GST-225, it is able to achieve a CD value of above 0.8, and the wavelength bandwidth of the chiral resonance is only about 1nm. Moreover, the working wavelength can be tuned by varying the heating temperature, instead of the structural parameters. This work not only promotes the development of adaptive and active metasurfaces using phase-change materials but also provides an opportunity for dynamic modulation of circular polarization control in switchable metasurfaces with narrow working bandwidth. Additionally, the dynamic modulation of chiral metasurfaces induced by opto-thermally triggered GST phase transitions can reach timescales ranging from picoseconds to nanoseconds, depending on the duration and intensity of the laser pulses for heating process, as well as the thermal conductivity of the material\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e,\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e. Advancements in phase-change chiral metasurfaces will drive research in the infrared band for filter devices\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e, optical switches\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e, thermal imaging, and chiral sensing\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData available on request with contacting the corresponding author.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work is supported by the National Natural Science Foundation of China (Grant No: 92050202, 12434012, 1240042013, 22ZR1443100).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eT.Z. and Q.Z. were responsible for the original research concept and physical interpretation. \u0026nbsp;T.Z. was responsible for the theoretical derivations and COMSOL simulations. \u0026nbsp;T.Z. wrote the main manuscript with the help of J.L. and H.H.\u003c/p\u003e\n\u003cp\u003eAll authors reviewed the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAdditional Information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCompeting financial interests: The authors declare no competing financial interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAdhikari, S. \u0026amp; Orrit, M. Optically Probing the Chirality of Single Plasmonic Nanostructures and of Single Molecules:Potential and Obstacles. \u003cem\u003eAcs Photonics\u003c/em\u003e. \u003cb\u003e9\u003c/b\u003e, 3486\u0026ndash;3497 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShi, T. et al. Planar chiral metasurfaces with maximal and tunable chiroptical response driven by bound states in the continuum. \u003cem\u003eNat. Commun.\u003c/em\u003e \u003cb\u003e13\u003c/b\u003e, 4111 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen, Y., Yang, X. \u0026amp; Gao, J. Spin-controlled wavefront shaping with plasmonic chiral geometric metasurfaces. \u003cem\u003eLight Sci. Appl.\u003c/em\u003e \u003cb\u003e7\u003c/b\u003e, 86 (2018).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, W. et al. Circularly polarized light detection with hot electrons in chiral plasmonic metamaterials. \u003cem\u003eNat. Commun.\u003c/em\u003e \u003cb\u003e6\u003c/b\u003e, 8379 (2015).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTang, H., Stan, L., Czaplewski, D. A., Yang, X. \u0026amp; Gao, J. Wavelength-tunable infrared chiral metasurfaces with phase-change materials. \u003cem\u003eOpt. Express\u003c/em\u003e. \u003cb\u003e31\u003c/b\u003e, 21118\u0026ndash;21127 (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDecker, M. et al. Strong optical activity from twisted-cross photonic metamaterials. \u003cem\u003eOpt. Lett.\u003c/em\u003e \u003cb\u003e34\u003c/b\u003e, 2501\u0026ndash;2503 (2009).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHu, G., Wang, M., Mazor, Y., Qiu, C. W. \u0026amp; Al\u0026ugrave;, A. Tailoring Light with Layered and Moir\u0026eacute; Metasurfaces. \u003cem\u003eTrends Chem.\u003c/em\u003e \u003cb\u003e3\u003c/b\u003e, 342\u0026ndash;358 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMark, A. G., Gibbs, J. G., Lee, T. C. \u0026amp; Fischer, P. Hybrid nanocolloids with programmed three-dimensional shape and material composition. \u003cem\u003eNat. Mater.\u003c/em\u003e \u003cb\u003e12\u003c/b\u003e, 802\u0026ndash;807 (2013).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHsu, C. W., Zhen, B., Stone, A. D., Joannopoulos, J. D. \u0026amp; Soljačić, M. Bound states in the continuum. \u003cem\u003eNat. Rev. Mater.\u003c/em\u003e \u003cb\u003e1\u003c/b\u003e, 16048 (2016).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen, Y. et al. Observation of intrinsic chiral bound states in the continuum. \u003cem\u003eNature\u003c/em\u003e. \u003cb\u003e613\u003c/b\u003e, 474\u0026ndash;478 (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHail, C. U., Michel, A. K. U., Poulikakos, D. \u0026amp; Eghlidi, H. Optical Metasurfaces: Evolving from Passive to Adaptive. \u003cem\u003eAdv. Opt. Mater.\u003c/em\u003e \u003cb\u003e7\u003c/b\u003e, 1801786 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWuttig, M., Bhaskaran, H. \u0026amp; Taubner, T. Phase-change materials for non-volatile photonic applications. \u003cem\u003eNat. Photonics\u003c/em\u003e. \u003cb\u003e11\u003c/b\u003e, 465\u0026ndash;476 (2017).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMichel, A. K. U., Wuttig, M. \u0026amp; Taubner, T. Design Parameters for Phase-Change Materials for Nanostructure Resonance Tuning. \u003cem\u003eAdv. Opt. Mater.\u003c/em\u003e \u003cb\u003e5\u003c/b\u003e, 1700261 (2017).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCabr\u0026eacute;, A., Verdaguer, X. \u0026amp; Riera, A. Recent Advances in the Enantioselective Synthesis of Chiral Amines via Transition Metal-Catalyzed Asymmetric Hydrogenation. \u003cem\u003eChem. Rev.\u003c/em\u003e \u003cb\u003e122\u003c/b\u003e, 269\u0026ndash;339 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJulian, M. N., Williams, C., Borg, S., Bartram, S. \u0026amp; Kim, H. J. Reversible optical tuning of GeSbTe phase-change metasurface spectral filters for mid-wave infrared imaging. \u003cem\u003eOptica\u003c/em\u003e. \u003cb\u003e7\u003c/b\u003e, 746\u0026ndash;754 (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSenbua, W., Mearnchu, J. \u0026amp; Wichitwechkarn, J. Easy-to-use and reliable absorbance-based MPH-GST biosensor for the detection of methyl parathion pesticide. \u003cem\u003eBiotechnol. Rep.\u003c/em\u003e \u003cb\u003e27\u003c/b\u003e, e00495 (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShportko, K. et al. Resonant bonding in crystalline phase-change materials. \u003cem\u003eNat. Mater.\u003c/em\u003e \u003cb\u003e7\u003c/b\u003e, 653\u0026ndash;658 (2008).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNevzorov, A. A. et al. Controlling optical properties of GST thin films by ultrashort laser pulses series impact. \u003cem\u003eOpt. Mater.\u003c/em\u003e \u003cb\u003e141\u003c/b\u003e, 113925 (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKoshelev, K., Lepeshov, S., Liu, M., Bogdanov, A. \u0026amp; Kivshar, Y. Asymmetric Metasurfaces with High-\u003cspan\u003e$\u003c/span\u003eQ\u003cspan\u003e$\u003c/span\u003e Resonances Governed by Bound States in the Continuum. \u003cem\u003ePhys. Rev. Lett.\u003c/em\u003e \u003cb\u003e121\u003c/b\u003e, 193903 (2018).\u003c/span\u003e \u003c/li\u003e \u003cli\u003e\u003cspan\u003ePlum, E., Fedotov, V. A. \u0026amp; Zheludev N. I. Optical activity in extrinsically chiral metamaterial. \u003cem\u003eAppl. Phys. Lett.\u003c/em\u003e \u003cb\u003e93\u003c/b\u003e, 191911 (2008).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLong, L., Taylor, S. \u0026amp; Wang, L. Enhanced Infrared Emission by Thermally Switching the Excitation of Magnetic Polariton with Scalable Microstructured VO2 Metasurfaces. \u003cem\u003eACS Photonics\u003c/em\u003e. \u003cb\u003e7\u003c/b\u003e, 2219\u0026ndash;2227 (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDing, F., Zhong, S. \u0026amp; Bozhevolnyi, S. I. Vanadium Dioxide Integrated Metasurfaces with Switchable Functionalities at Terahertz Frequencies. \u003cem\u003eAdv. Opt. Mater.\u003c/em\u003e \u003cb\u003e6\u003c/b\u003e, 1701204 (2018).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSittner, E. R. et al. GeTe)x\u0026ndash;(Sb2Te3)1\u0026ndash;x phase-change thin films as potential thermoelectric materials. \u003cem\u003ePhys. Status Solidi a\u003c/em\u003e. \u003cb\u003e210\u003c/b\u003e, 147\u0026ndash;152 (2012).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYan, W., Wang, J. Y., Qu, Y. R., Li, Q. \u0026amp; Qiu, M. Tunable metasurfaces based on phase-change materials. \u003cem\u003eActa Phys. Sin\u003c/em\u003e. \u003cb\u003e69\u003c/b\u003e, 200453 (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKiselev, A. V. et al. Dynamics of reversible optical properties switching of Ge2Sb2Te5 thin films at laser-induced phase transitions. \u003cem\u003eOpt. Laser Technol.\u003c/em\u003e \u003cb\u003e147\u003c/b\u003e, 107701 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWilliams, C., Hong, N., Julian, M., Borg, S. \u0026amp; Kim, H. J. Tunable mid-wave infrared Fabry-Perot bandpass filters using phase-change GeSbTe. \u003cem\u003eOpt. Express\u003c/em\u003e. \u003cb\u003e28\u003c/b\u003e, 10583\u0026ndash;10594 (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHe, Q. et al. Low-loss ultrafast and nonvolatile all-optical switch enabled by all-dielectric phase change materials. \u003cem\u003eiScience\u003c/em\u003e. \u003cb\u003e25\u003c/b\u003e, 104375 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKhan, S. A. et al. Optical sensing by metamaterials and metasurfaces: from physics to biomolecule detection. \u003cem\u003eAdv. Opt. Mater.\u003c/em\u003e \u003cb\u003e10\u003c/b\u003e, 2200500 (2022).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-5163501/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5163501/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn recent years, research on chiral bound states in the continuum (BIC) has surged, leading to the development of various chiral metasurfaces with narrow bandwidths by breaking of in-plane and out-of-plane symmetries. However, the ability to dynamically tune the working band remains relatively unexplored, which is valuable for chiral sensing applications. Optical phase-change materials, with tunable dielectric constants and switchable properties during phase transition, offer the potential for dynamic control of optical metasurfaces. This work demonstrates a wavelength-tunable infrared chiral metasurface by combining the phase-change material GST with chiral BIC structures. By varying the longitudinal tilt angle of the nanostructure, an infrared chiral metasurface with an extremely narrow bandwidth of chiral resonance and a CD value of over 0.8 is designed. The phase-change properties of GST enable wavelength-tunable chiral resonance without altering the structural parameters, and the influence of key structural parameters of the metasurface on the chiral resonance wavelength and CD value is analyzed. The proposed chiral BIC metasurface with phase-change materials shows promising application prospects in filter devices, chiral thermal switches, infrared imaging, and tunable chiral photonics.\u003c/p\u003e","manuscriptTitle":"Wavelength-tunable infrared metasurfaces with chiral bound states in the continuum","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-12-25 15:27:10","doi":"10.21203/rs.3.rs-5163501/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-12-06T06:59:08+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-11-24T11:24:30+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-11-16T14:29:46+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"112032848966758483922923545854667986096","date":"2024-11-14T12:36:38+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"289621038957093342321720836164406416407","date":"2024-11-13T10:54:50+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-11-12T03:34:41+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-10-20T19:28:21+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2024-10-20T17:43:15+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-10-15T07:18:23+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2024-09-27T08:19:22+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"4aba1d6d-0a1b-4f5e-adb6-4ed8539245ad","owner":[],"postedDate":"December 25th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":41238387,"name":"Physical sciences/Optics and photonics/Optical materials and structures/Metamaterials"},{"id":41238388,"name":"Physical sciences/Optics and photonics/Optical materials and structures/Silicon photonics"}],"tags":[],"updatedAt":"2025-01-06T16:00:38+00:00","versionOfRecord":{"articleIdentity":"rs-5163501","link":"https://doi.org/10.1038/s41598-024-84587-7","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-01-02 15:57:19","publishedOnDateReadable":"January 2nd, 2025"},"versionCreatedAt":"2024-12-25 15:27:10","video":"","vorDoi":"10.1038/s41598-024-84587-7","vorDoiUrl":"https://doi.org/10.1038/s41598-024-84587-7","workflowStages":[]},"version":"v1","identity":"rs-5163501","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5163501","identity":"rs-5163501","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}