Broadband Angularly Stable Polarization Conversion in Terahertz Band via Vertically Stacked Frequency Selective Surface Metasurface

Broadband Angularly Stable Polarization Conversion in Terahertz Band via Vertically Stacked Frequency Selective Surface Metasurface | 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 Research Article Broadband Angularly Stable Polarization Conversion in Terahertz Band via Vertically Stacked Frequency Selective Surface Metasurface Sara Rahdar, Mahmoud Nikoufard This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8320718/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 04 Apr, 2026 Read the published version in Optical and Quantum Electronics → Version 1 posted 11 You are reading this latest preprint version Abstract This paper introduces a compact three-layer metasurface polarization converter for efficient bidirectional transverse electric (TE) to transverse magnetic (TM) mode conversion in the terahertz (THz) regime. The design overcomes critical limitations of conventional converters—narrow bandwidth and angular sensitivity—using vertically stacked copper split-ring resonators (SRRs) on a silicon substrate. Through optimized phase and resonance tuning, the metasurface achieves > 90% polarization conversion efficiency across a broad 1–1.8 THz bandwidth while maintaining robust performance for incidence angles up to 60°. Full-wave simulations validate its angular insensitivity and bidirectional functionality, with surface current and field analyses elucidating the multi-resonance mechanism. Fabrication feasibility is ensured via standard copper/SiO₂ deposition and photolithography processes. This high-performance, readily integrable design advances THz applications requiring dynamic polarization control, including communications, imaging, and sensing systems. Terahertz metasurface Angularly stable frequency selective surface (FSS) Split-ring resonators (SRR) Broadband polarization conversion Bidirectional mode conversion polarization converter Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1 Introduction Terahertz (THz) technology—spanning 0.1–10 THz—represents a rapidly advancing field bridging microwave electronics and infrared photonics (Tonouchi 2007 ), (Siegel 2002 ). This spectral window is crucial for emerging technologies due to its coverage of molecular rotational/vibrational energy states and penetration capability through non-conductive materials (Ferguson and Zhang 2002 ). These properties enable transformative applications including ultra-high-speed wireless communications (6G and beyond) (Akyildiz et al. 2018 ; Rappaport et al. 2019 ); high-resolution medical imaging/spectroscopy for cancer detection (Li et al. 2022 ; Woodward et al. 2003 ); non-destructive material inspection (Jepsen et al. 2011 ); and stand-off security screening (Mittleman 2018 ). However, realizing these systems requires precise manipulation of THz wave properties, among which polarization control is paramount (Zheludev and Kivshar 2012 ). Efficient dynamic control of polarization states (e.g., TE/TM conversion) is essential for: enhancing communication signal-to-noise ratios (Cong et al. 2017 ); mitigating polarization-mismatch losses (He et al. 2015 ); and enabling polarization-sensitive imaging/spectroscopy to probe material anisotropy and surface textures (Rashid et al. 2023 ). Historically, polarization control relied on conventional optical components exploiting natural material properties—such as birefringence in quartz/calcite waveplates or the Faraday effect in magneto-optical materials (Goldstein 2017 ). These approaches, however, prove ineffective at THz frequencies where most natural materials exhibit weak electromagnetic responses. Consequently, devices require interaction lengths spanning tens of wavelengths to achieve sufficient phase shifts (Masson and Gallot 2006 ), resulting in bulky, expensive systems with narrow operational bandwidths (Ako et al. 2020 ). To overcome these limitations, researchers have adopted metamaterials—artificially structured media with subwavelength "meta-atoms" engineered for bespoke electromagnetic responses (Pendry et al. 1999 ; Smith et al. 2000 ). Their 2D counterparts, metasurfaces, offer unprecedented control over wave amplitude, phase, and polarization within ultrathin profiles (Kildishev et al. 2013 ; Yu et al. 2011 ), enabling compact, efficient components (Glybovski et al. 2016 ). For THz polarization conversion, metasurfaces are categorized as reflective or transmissive. Reflective designs typically achieve superior efficiency and bandwidth through simplified Fabry-Perot resonance mechanisms (Chen 2012 ). Numerous resonator geometries have been explored for unit-cell designs, including V-shaped antennas (Grady et al. 2013 ), split-ring resonators (SRRs) (Cheng et al. 2014 ), cross-shaped structures (Ahmad et al. 2022 )d shaped resonators (Xu et al. 2018 ). While demonstrating significant improvements over conventional approaches, these designs often face critical performance trade-offs. A persistent challenge remains the simultaneous achievement of high polarization conversion ratio (PCR), broad bandwidth, and angular stability across wide incidence angles (Zhang et al. 2022 ). For instance, single-layer designs typically achieve near-unity PCR at discrete resonant frequencies but exhibit rapid performance degradation under frequency detuning or oblique incidence (Yang et al. 2024 ). Multi-layer structures—proposed to broaden bandwidth through stacked resonators exciting adjacent resonances (Dong et al. 2016 ; Fei et al. 2020 )—still suffer from fabrication complexity and pronounced angular sensitivity. These limitations necessitate further innovation. This paper addresses these challenges through a novel three-layer passive metasurface polarization converter optimized for THz frequencies. The design employs vertically stacked copper ring resonators on a low-loss silicon substrate, enabling efficient bidirectional TE/TM conversion. The simple ring geometry ensures robustness, while numerical optimization of the tri-layer stack facilitates excitation of overlapping resonances. This strategy achieves > 90% polarization conversion efficiency across a 1–1.8 THz bandwidth while maintaining high performance for incidence angles up to 60°—a substantial improvement in angular stability over prior designs. Fabrication leverages established copper/SiO₂ deposition and photolithography techniques (Zhang et al. 2005 ), ensuring compact, robust, and system-integrable devices. This work provides a high-performance solution for dynamic polarization control in advanced THz communication, imaging, and sensing systems operating under variable angles. 2 FSS Structural Design The performance of the proposed FSS filter is governed by its geometric parameters and material composition. As illustrated in Fig. 1 , the structure features four vertically stacked dielectric layers (thicknesses ℎ 1 ​ to ℎ 4 ) aligned along the z -axis. The top SiO₂ layer (ℎ 1​ ) functions as both protective coating and anti-reflection element, while the underlying silicon layers (ℎ 2 ​, ℎ 3 ​, ℎ 4 ​) embed copper resonators. Unit cells are arranged periodically in the x - y plane with lattice constant p , a critical parameter controlling resonant frequency and bandwidth. Three sets of split-ring resonators (SRRs) embedded across different layers serve as the primary frequency-selective elements. Each SRR is defined by radius ( R 1 ​, R 2 ​, R 3 ​), width ( W 1 ​, W 2 ​, W 3 ​), and capacitive gap ( C 1 ​, C 2 ​, C 3 ), with the incomplete loops creating gaps essential for resonant tuning. The unit cell design, illustrated in top-down views (Fig. 1 ), positions each ring resonator at distinct depths within the stack, enabling vertical integration. This multi-layered configuration with varied ring dimensions achieves tailored frequency responses, specifically enabling broadband filtering across the THz range. Optimization of layer thicknesses (ℎ 1 ​-ℎ 4 ​), periodicity ( p ), and ring geometric parameters ( R x ​, W x ​ , C x ​ ) is critical for resonance control. We numerically optimized these parameters to position resonances at target frequencies, with final design values listed in Table 1 . Table 1 Optimized geometric parameters of the FSS unit cell enabling broadband angular-stable polarization conversion. Parameter p h 1 h 2 h 3 h 4 R 1 R 2 R 3 w 1 w 2 w 3 c 1 c 2 c 3 Value ( \(\:\varvec{\mu\:}\mathbf{m})\) 34.7 26.3 10.5 9.15 10 16.6 23 31.6 2.7 6.7 7.7 2.25 5.9 7.3 3 Theorical model and analytical framework To support the full-wave numerical simulations, we develop a comprehensive multilayer analytical model based on classical thin-film interference theory and generalized Fresnel reflection principles. This theoretical framework elucidates the physical mechanisms by which the proposed vertically stacked split-ring resonator metasurface achieves broadband polarization conversion between TE and TM modes through strategic suppression of co-polarized reflection combined with enhanced anisotropic cross-polarization coupling. The top SiO₂ layer functions as an AR coating. The quarter-wave optical thickness condition (Xiong et al. 2013 ) as \(\:\text{h}₁=\frac{m.\lambda\:}{4{\stackrel{\sim}{n}}_{\text{A}\text{R}}}\:\) where \(\:\lambda\:\) is the target wavelength and \(\:{\stackrel{\sim}{n}}_{\text{A}\text{R}}\) is the refractive index of the AR coating. The odd integer \(\:m\) enforces a π-phase difference between reflections at the air–SiO₂ and SiO₂–Si interfaces, minimizing co-polar reflectance. Such destructive interference enhances the relative strength of cross-polarized components generated by the SRRs. Transmit ( \(\:{T}_{d}^{\left(\alpha\:\right)}\left)\:\text{a}\text{n}\text{d}\:\text{R}\text{e}\text{f}\text{l}\text{e}\text{c}\text{t}\text{i}\text{v}\text{e}\:\right({R}_{d}^{\left(\alpha\:\right)}\) ) field amplitudes in layer d follow the generalized Fresnel recursion (Parratt 1954 ): $$\:\frac{{T}_{d}^{\left(\alpha\:\right)}}{{R}_{d}^{\left(\alpha\:\right)}}=\frac{{e}^{i2{k}_{lz}^{\left(\alpha\:\right)}{h}_{d}}}{{\rho\:}_{d(d+1)}^{\left(\alpha\:\right)}}+\frac{\left(1-\frac{1}{{\left({\rho\:}_{d(d+1)}^{\left(\alpha\:\right)}\right)}^{2}}\right){e}^{i2\left({k}_{d(d+1)z}^{\left(\alpha\:\right)}+{k}_{dz}^{\left(\alpha\:\right)}\right){h}_{d}}}{\frac{1}{{\rho\:}_{d(d+1)}^{\left(\alpha\:\right)}}{e}^{i2{k}_{(d+1)z}^{\left(\alpha\:\right)}{h}_{d}}+\frac{{T}_{d+1}^{\left(\alpha\:\right)}}{{R}_{d+1}^{\left(\alpha\:\right)}}}$$ 1 Where \(\:{\alpha\:}\in\:\{\text{T}\text{E},\:\text{T}\text{M}\}\) denotes the polarization of wave (TE, TM (, and \(\:{k}_{dz}^{\left(\alpha\:\right)}\) is the z component of the wavevector in layer d, and \(\:{\rho\:}_{d(d+1)}^{\left(\alpha\:\right)}\) is the Fresnel reflection coefficient at the interface between layers d and (d + 1). The boundary condition at the bottom perfectly conducting ground plane (layer N) is \(\:\frac{{\text{T}}_{N}^{\left({\alpha\:}\right)}}{{\text{R}}_{N}^{\left({\alpha\:}\right)}}=-1\) Recursively solving Eq. ( 1 ) from the bottom layer upward yields the total reflection coefficient (Zhou et al. 2010 ) as \(\:{\rho\:}^{\left(\alpha\:\right)}=\frac{{T}_{0}^{\left(\alpha\:\right)}}{{R}_{0}^{\left(\alpha\:\right)}}\) . The overall co-polar reflectance is given by the classical Airy thin-film formula (Sun et al. 2011 ): $$\:{R}_{\alpha\:\alpha\:}(\nu\:,\theta\:)={\left|\stackrel{\sim}{\rho\:}\right|}^{2}=\frac{{\left({\rho\:}_{12}^{\left(\alpha\:\right)}\right)}^{2}+{\left({\tau\:}_{12}^{\left(\alpha\:\right)}{\rho\:}_{23}^{\left(\alpha\:\right)}{\tau\:}_{21}^{\left(\alpha\:\right)}\right)}^{2}+2{\rho\:}_{12}^{\left(\alpha\:\right)}{\tau\:}_{12}^{\left(\alpha\:\right)}{\rho\:}_{23}^{\left(\alpha\:\right)}{\tau\:}_{21}^{\left(\alpha\:\right)}\text{c}\text{o}\text{s}\left({{\Phi\:}}^{\left(\alpha\:\right)}\right)}{1+{\left({\rho\:}_{12}^{\left(\alpha\:\right)}{\rho\:}_{23}^{\left(\alpha\:\right)}\right)}^{2}-2{\rho\:}_{12}^{\left(\alpha\:\right)}{\rho\:}_{23}^{\left(\alpha\:\right)}\text{c}\text{o}\text{s}\left({{\Phi\:}}_{{\Sigma\:}}^{\left(\alpha\:\right)}\right)}$$ 2 Here, \(\:{\rho\:}_{\text{i}\text{j}}^{\left(\alpha\:\right)}\) and \(\:{\tau\:}_{\text{i}\text{j}}^{\left(\alpha\:\right)}\) are the Fresnel reflection and transmission coefficients at interface \(\:\text{i}-\text{j}\) , respectively. The phase term is defined as \(\:{{\Phi\:}}^{\left(\alpha\:\right)}={\varphi\:}_{12}^{\alpha\:}-{{\psi\:}}^{{\alpha\:}},\:{{\Phi\:}}_{{\Sigma\:}}^{\alpha\:}={\varphi\:}_{12}^{\alpha\:}+{\varphi\:}_{23}^{\alpha\:}+2{{\beta\:}}^{{\alpha\:}}\) and \(\:{{\beta\:}}^{{\alpha\:}}=\sqrt{{ϵ}_{AR}}{k}_{0}\text{cos}\left({\theta\:}_{s}\right){{\Sigma\:}}_{i=1}^{4}{h}_{i}\) where \(\:{\varphi\:}_{ij}^{\alpha\:}\) are the reflection phase shift at each interface, \(\:{{\psi\:}}^{{\alpha\:}}\) accounts for transmission phase accumulation, \(\:{ϵ}_{AR}\) is the effective complex permittivity of the multilayer AR coating, \(\:{k}_{0}=\frac{2\pi\:}{\lambda\:}\) is the free space wave number, and \(\:{\theta\:}_{s}\) is the incident angle in the substrate. Co-polar reflection is minimized when: $$\:{\rho\:}_{12}^{\left(\alpha\:\right)})\:=\:{\tau\:}_{12}^{\left(\alpha\:\right)}\:{\rho\:}_{23}^{\left(\alpha\:\right)})\:\:{\tau\:}_{21}^{\left(\alpha\:\right)}$$ 3 \(\:{{\Phi\:}}^{\left(\alpha\:\right)}\) = (2N+1) π, N ∈ ℤ(4) When these conditions are met, destructive interference occurs at the dielectric interfaces, suppressing the co-polarized reflection to near zero. Consequently, the split-ring resonators (SRRs) efficiently rotate the polarization of the incident field from TE to TM (and vice versa). This conversion arises from SRR-induced resonant surface currents at the target wavelength, which generates the required cross-polarized response at the interface. Due to the circular shape of the SRRs, the surface current excited by the incident field exhibits both Jx and Jy component on the surface of the conductor (Fig. 5). Under resonant excitation, the Jx currents on the two split sections are out of phase and therefore cancel in the far field, whereas the Jy components remain in phase and add constructively. As a result, a pronounced cross-polarized response is produced, consistent with the strong polarization conversion observed in the extracted S-parameters. As can be seen in the S-parameter S11 TE-TE versus frequency, (Fig. 3 ) in certain frequencies we observe deep spectral dips. These resonance frequencies correspond to regions where the above-mentioned conditions are satisfied, and co-polar reflection component approaches to zero. The SRR layers are geometrically anisotropic (R₁<R₂<R₃, with differing capacitive gaps C i ), producing off-diagonal reflection terms \(\:{\rho\:}_{TE,TM}\:and\:{\rho\:}_{TM,TE}\) (Ahmad et al. 2022 ): $$\:\mathbf{R}=\left[\begin{array}{ll}{\rho\:}_{\text{T}\text{E},\text{T}\text{E}}&\:{\rho\:}_{\text{T}\text{E},\text{T}\text{M}}\\\:{\rho\:}_{\text{T}\text{M},\text{T}\text{E}}&\:{\rho\:}_{\text{T}\text{M},\text{T}\text{M}}\end{array}\right]$$ 5 When (2)– (4) suppress the diagonal terms ρ TE,TE and ρ TM,TM , the cross-polar terms dominate. Reciprocity gives ρ TE,TM = ρ TM,TE . This produces bidirectional \(\:TE\leftrightarrow\:\:TM\) conversion with near unity polarization conversion ratio (PCR > 0.95) and angular stability up to 60 incidence angles. 4 Simulation results Figure 3 presents CST simulation results for the polarization converter under TE- and TM-polarized plane wave illumination across varying incidence angles. As shown in Fig. 3 a, resonant dips occur in the 1–1.8 THz range for co-polarized reflections (TE/TE and TM/TM), reaching approximately − 15 dB. These minima arise from destructive interference between incident and reflected waves. Conversely, cross-polarized reflections (TE/TM and TM/TE) exhibit near-unity magnitude (approaching 0 dB) across this bandwidth (Fig. 3 a), confirming efficient polarization conversion. This demonstrates the FSS metasurface enables robust TE/TM mode conversion over 1–1.8 THz. The stacked SRR layers create multiple reflection paths for incident waves. Phase oscillations result from interference between waves reflected from the top resonator layer and also from waves penetrating deeper layers and reflecting from subsequent resonators/substrates. Phase changes linearly between resonances (e.g., smooth slopes in Fig. 3 b) represent propagation delays through dielectric layers and the slope magnitude ( dω/dϕ ) relates to the effective electrical length of the structure. Figure 4 depicts the reflection coefficient magnitude ∣S11∣ of the FSS filter as a function of frequency (0–2 THz) and incidence angle (0°–90°). Subfigures (a), (b), (c), and (d) present results for TE→TE, TE→TM, TM→TM, and TM→TE polarization conversions, respectively. Critically, within the 1–1.8 THz frequency range and incidence angles of 0°–60°, the reflection coefficient for co-polarized conversions (TE→TE and TM→TM) remains very low (approaching 0), while cross-polarized conversions (TE→TM and TM→TE) exhibit consistently high values (approaching 1). This confirms efficient polarization rotation across broad spectral and angular regimes. Figure 5 illustrates the surface current distributions across the three split-ring resonators (SRR₁, SRR₂, SRR₃) within the FSS metasurface at four resonant frequencies. At 1 THz (Fig. 5a), currents localize predominantly along SRR₃'s inner edges, indicating fundamental resonance excitation. Minimal activity occurs in SRR₁, while SRR₂ exhibits weak coupling. By 1.3 THz (Fig. 5b), the resonance shifts to SRR₂-dominant with symmetric current patterns, accompanied by diminished SRR₁/SRR₃ contributions. At 1.6 THz (Fig. 5c), strong hybrid resonance emerges between SRR₃ and SRR₁, with secondary SRR₂ excitation. Finally, at 1.8 THz (Fig. 5d), asymmetric currents intensify in SRR₂ and SRR₃, while SRR₁ participation remains negligible. These distinct modal distributions confirm that coupled SRR resonances generate destructive interference, producing the sharp reflection minima at 1.0, 1.3, 1.6, and 1.8 THz observed in Fig. 3 . This multi-resonator synergy enables precise spectral control across the 1–1.8 THz operational band. Complementary field analyses (Fig. 6) elucidate wave-matter interactions. The electric field (Figs. 6a, 6c) concentrates at unit-cell boundaries, traversing SRRs as electric dipoles. At 1 THz, strong confinement occurs at SRR₃ (Fig. 6a), shifting to SRR₂ at 1.3 THz (Fig. 6c) consistent with current distributions. Conversely, the magnetic field (Figs. 6b, 6d) circulates around resonator edges, confirming distinct polarization-dependent coupling mechanisms. 5 Discussions To model the frequency-selective response of the metasurface, an equivalent circuit was developed that accounts for both Fabry-Perot resonances in the dielectric stack and split-ring resonator interactions. The circuit (Fig. 7a) employs four cascaded transmission line segments (TLIN₁–TLIN₄) corresponding to the SiO₂ cap ( h ₁) and silicon interval-layers ( h ₂– h ₄), with electrical lengths proportional to physical layer thicknesses. Each split-ring resonator is represented by coupled LC networks where the conductive rings provide series inductance ( L ) and the capacitive gaps introduce shunt capacitance ( C ). Impedance discontinuities at dielectric interfaces are inherently modeled through transmission line impedance variations, not explicit grounding. The circuit is terminated with 377 Ω ports to emulate standard measurement conditions. Validation in Fig. 7b demonstrates reasonable agreement between circuit simulations and full-wave results across the 1–1.8 THz operating band, confirming its ability to predict: 1) Fabry-Perot resonance frequencies governed by cumulative layer thicknesses, 2) resonance quality factors controlled by SRR LC ratios, and 3) cross-polarization efficiency linked to gap capacitance asymmetry. This model enables performance tuning through parameter adjustments: Increasing SRR gap widths ( W ₁, W ₂, W ₃) reduces shunt capacitance, broadening resonance bandwidths; modifying ring radii scales inductance, shifting coupled-resonance frequencies; and varying layer thicknesses ( h ₁– h ₄) alters transmission line lengths, controlling Fabry-Perot mode spacing. Physical dimensions thereby map directly to circuit components for targeted THz spectral shaping. Fabrication feasibility guided the metasurface design, with materials selected for THz-optimized dielectric properties and microfabrication compatibility. The process, detailed in Fig. 8 , begins with a high-resistivity silicon substrate (> 10 kΩ·cm) to minimize THz absorption. A 5–10 nm chromium adhesion layer is deposited via e-beam evaporation, followed by 200 nm copper to form the base conductive plane. The first SRR layer is patterned using photolithography: photoresist spin-coating, UV exposure through a photomask defining ring geometry (radius R₁ = 16.6 µm, gap C ₁ = 2.25 µm), development, and 100 nm copper evaporation. Liftoff yields the defined SRRs. Low-pressure chemical vapor deposition (LPCVD) then grows a 10.0 µm crystalline silicon spacer ( h ₄). The sequence repeats for subsequent layers: Photolithography patterns SRR₂ ( R ₂ = 23.0 µm, C ₂ = 5.9 µm) followed by 100 nm copper evaporation and LPCVD of a 9.15 µm silicon layer ( h ₃). Precise alignment ensures functional integrity during SRR₃ patterning ( R ₃ = 31.6 µm, C ₃ = 7.3 µm), copper evaporation, and deposition of the final 10.5 µm silicon spacer ( h ₂) via LPCVD. A 26.3 µm silicon dioxide cap layer is deposited by plasma-enhanced CVD (PECVD) in staged cycles (< 5 µm/layer) with 300°C anneals to mitigate film stress. Alternatively, spin-on-glass (SOG) with pyrolysis annealing provides a stress-relieved oxide. Critical features—including subwavelength periodicity ( p = 34.7 µm) and ring widths down to W ₁=2.7 µm—are achievable through i-line photolithography or electron-beam patterning. This fabrication framework enables physical realization of the broadband polarization converter, with design parameters aligning with standard microfabrication capabilities for THz system integration. Conclusion This work demonstrates a multi-layer FSS metasurface achieving efficient, angularly stable TE-TM polarization conversion across 1–1.8 THz. By vertically stacking copper ring resonators on a silicon/silicon dioxide platform, the design enables > 90% conversion efficiency while maintaining robust performance for incidence angles up to 60°—significantly outperforming conventional single-layer converters. Three key advances underpin this breakthrough: Broadband operation stems from four coupled resonances (1.0, 1.3, 1.6, 1.8 THz) generated through Fabry-Perot modes in dielectric spacers and SRR hybridization; angular insensitivity arises from optimized periodicity (p = 34.7 µm) and substrate thicknesses; and CMOS-compatible fabrication employs lithographically patterned copper resonators (minimum feature width 2.7 µm) with LPCVD/PECVD dielectric stacking. Validated through full-wave simulations and equivalent circuit modeling, this architecture overcomes fundamental limitations of narrow bandwidth and angular sensitivity in THz polarization control. The design is readily integrable into 6G communication systems (beamforming arrays), polarization-sensitive imaging diagnostics, and material birefringence sensors. Future work will explore active tuning via vanadium dioxide interlayers and experimentally validate the staged PECVD fabrication process. Declarations Author Contribution S.R. conceived and designed the study, performed the simulations and data analysis, interpreted the results, and wrote the manuscript. M.N. supervised the work, provided scientific guidance, and contributed to the revision, editing, and final approval of the manuscript. References Ahmad, T., Rahim, A.A., Bilal, R.M.H., Noor, A., Maab, H., Naveed, M.A., Madni, A., Ali, M.M., Saeed, M.A.: Ultrawideband Cross-Polarization Converter Using Anisotropic Reflective Metasurface. Electronics. 11, 487 (2022). https://doi.org/10.3390/electronics11030487 Ako, R.T., Lee, W.S.L., Atakaramians, S., Bhaskaran, M., Sriram, S., Withayachumnankul, W.: Ultra-wideband tri-layer transmissive linear polarization converter for terahertz waves. APL Photonics. 5, 046101 (2020). https://doi.org/10.1063/1.5144115 Akyildiz, I.F., Han, C., Nie, S.: Combating the Distance Problem in the Millimeter Wave and Terahertz Frequency Bands. IEEE Commun. Mag. 56, 102–108 (2018). https://doi.org/10.1109/MCOM.2018.1700928 Chen, H.-T.: Interference theory of metamaterial perfect absorbers. Opt. Express. 20, 7165 (2012). https://doi.org/10.1364/OE.20.007165 Cheng, Y.Z., Withayachumnankul, W., Upadhyay, A., Headland, D., Nie, Y., Gong, R.Z., Bhaskaran, M., Sriram, S., Abbott, D.: Ultrabroadband reflective polarization convertor for terahertz waves. Appl. Phys. Lett. 105, 181111 (2014). https://doi.org/10.1063/1.4901272 Cong, L., Pitchappa, P., Wu, Y., Ke, L., Lee, C., Singh, N., Yang, H., Singh, R.: Active Multifunctional Microelectromechanical System Metadevices: Applications in Polarization Control, Wavefront Deflection, and Holograms. Advanced Optical Materials. 5, 1600716 (2017). https://doi.org/10.1002/adom.201600716 Dong, G.-X., Shi, H.-Y., Xia, S., Li, W., Zhang, A.-X., Xu, Z., Wei, X.-Y.: Ultra-broadband and high-efficiency polarization conversion metasurface with multiple plasmon resonance modes. Chinese Phys. B. 25, 084202 (2016). https://doi.org/10.1088/1674-1056/25/8/084202 Fei, P., Vandenbosch, G.A.E., Guo, W., Wen, X., Xiong, D., Hu, W., Zheng, Q., Chen, X.: Versatile Cross‐Polarization Conversion Chiral Metasurface for Linear and Circular Polarizations. Advanced Optical Materials. 8, 2000194 (2020). https://doi.org/10.1002/adom.202000194 Ferguson, B., Zhang, X.-C.: Materials for terahertz science and technology. Nature Mater. 1, 26–33 (2002). https://doi.org/10.1038/nmat708 Glybovski, S.B., Tretyakov, S.A., Belov, P.A., Kivshar, Y.S., Simovski, C.R.: Metasurfaces: From microwaves to visible. Physics Reports. 634, 1–72 (2016). https://doi.org/10.1016/j.physrep.2016.04.004 Goldstein, D.H.: Polarized Light. CRC Press (2017) Grady, N.K., Heyes, J.E., Chowdhury, D.R., Zeng, Y., Reiten, M.T., Azad, A.K., Taylor, A.J., Dalvit, D.A.R., Chen, H.-T.: Terahertz Metamaterials for Linear Polarization Conversion and Anomalous Refraction. Science. 340, 1304–1307 (2013). https://doi.org/10.1126/science.1235399 He, J., Xie, Z., Wang, S., Wang, X., Kan, Q., Zhang, Y.: Terahertz polarization modulator based on metasurface. J. Opt. 17, 105107 (2015). https://doi.org/10.1088/2040-8978/17/10/105107 Jepsen, P.U., Cooke, D.G., Koch, M.: Terahertz spectroscopy and imaging – Modern techniques and applications. Laser & Photonics Reviews. 5, 124–166 (2011). https://doi.org/10.1002/lpor.201000011 Kildishev, A.V., Boltasseva, A., Shalaev, V.M.: Planar Photonics with Metasurfaces. Science. 339, 1232009 (2013). https://doi.org/10.1126/science.1232009 Li, L., Wang, Y., Wang, X., Chen, M. eds: Advances in Terahertz Detection and Imaging. Frontiers Media SA (2022) Masson, J.-B., Gallot, G.: Terahertz achromatic quarter-wave plate. Opt. Lett. 31, 265 (2006). https://doi.org/10.1364/OL.31.000265 Mittleman, D.M.: Twenty years of terahertz imaging [Invited]. Opt. Express. 26, 9417 (2018). https://doi.org/10.1364/OE.26.009417 Parratt, L.G.: Surface Studies of Solids by Total Reflection of X-Rays. Phys. Rev. 95, 359–369 (1954). https://doi.org/10.1103/PhysRev.95.359 Pendry, J.B., Holden, A.J., Robbins, D.J., Stewart, W.J.: Magnetism from conductors and enhanced nonlinear phenomena. IEEE Trans. Microwave Theory Techn. 47, 2075–2084 (1999). https://doi.org/10.1109/22.798002 Rappaport, T.S., Xing, Y., Kanhere, O., Ju, S., Madanayake, A., Mandal, S., Alkhateeb, A., Trichopoulos, G.C.: Wireless Communications and Applications Above 100 GHz: Opportunities and Challenges for 6G and Beyond. IEEE Access. 7, 78729–78757 (2019). https://doi.org/10.1109/ACCESS.2019.2921522 Rashid, A., Murtaza, M., Zaidi, S.A.A., Zaki, H., Tahir, F.A.: A single-layer, wideband and angularly stable metasurface based polarization converter for linear-to-linear cross-polarization conversion. PLoS ONE. 18, e0280469 (2023). https://doi.org/10.1371/journal.pone.0280469 Siegel, P.H.: Terahertz technology. IEEE Trans. Microwave Theory Techn. 50, 910–928 (2002). https://doi.org/10.1109/22.989974 Smith, D.R., Padilla, W.J., Vier, D.C., Nemat-Nasser, S.C., Schultz, S.: Composite Medium with Simultaneously Negative Permeability and Permittivity. Phys. Rev. Lett. 84, 4184–4187 (2000). https://doi.org/10.1103/PhysRevLett.84.4184 Sun, J., Liu, L., Dong, G., Zhou, J.: An extremely broad band metamaterial absorber based on destructive interference. Opt. Express. 19, 21155 (2011). https://doi.org/10.1364/OE.19.021155 Tonouchi, M.: Cutting-edge terahertz technology. Nature Photon. 1, 97–105 (2007). https://doi.org/10.1038/nphoton.2007.3 Woodward, R.M., Wallace, V.P., Pye, R.J., Cole, B.E., Arnone, D.D., Linfield, E.H., Pepper, M.: Terahertz Pulse Imaging of ex vivo Basal Cell Carcinoma. Journal of Investigative Dermatology. 120, 72–78 (2003). https://doi.org/10.1046/j.1523-1747.2003.12013.x Xiong, H., Hong, J.-S., Luo, C.-M., Zhong, L.-L.: An ultrathin and broadband metamaterial absorber using multi-layer structures. Journal of Applied Physics. 114, 064109 (2013). https://doi.org/10.1063/1.4818318 Xu, J., Li, R., Qin, J., Wang, S., Han, T.: Ultra-broadband wide-angle linear polarization converter based on H-shaped metasurface. Opt. Express. 26, 20913 (2018). https://doi.org/10.1364/OE.26.020913 Yang, J., Li, K., Zha, X., Zhang, G., Xi, H., Deng, G., Li, Y., Yin, Z.: High-efficiency reflective terahertz cross-polarization converter with broadband and wide-angle response. Appl. Opt. 63, 3212 (2024). https://doi.org/10.1364/AO.517364 Yu, N., Genevet, P., Kats, M.A., Aieta, F., Tetienne, J.-P., Capasso, F., Gaburro, Z.: Light Propagation with Phase Discontinuities: Generalized Laws of Reflection and Refraction. Science. 334, 333–337 (2011). https://doi.org/10.1126/science.1210713 Zhang, B., Zhu, C., Zhang, R., Yang, X., Wang, Y., Liu, X.: Ultra-Broadband Angular-Stable Reflective Linear to Cross Polarization Converter. Electronics. 11, 3487 (2022). https://doi.org/10.3390/electronics11213487 Zhang, S., Fan, W., Panoiu, N.C., Malloy, K.J., Osgood, R.M., Brueck, S.R.J.: Experimental Demonstration of Near-Infrared Negative-Index Metamaterials. Phys. Rev. Lett. 95, 137404 (2005). https://doi.org/10.1103/PhysRevLett.95.137404 Zheludev, N.I., Kivshar, Y.S.: From metamaterials to metadevices. Nature Mater. 11, 917–924 (2012). https://doi.org/10.1038/nmat3431 Zhou, X., Xu, X., Chen, X., Chen, J.: Magic wavelengths for terahertz clock transitions. Phys. Rev. A. 81, 012115 (2010). https://doi.org/10.1103/PhysRevA.81.012115 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 04 Apr, 2026 Read the published version in Optical and Quantum Electronics → Version 1 posted Editorial decision: Revision requested 14 Jan, 2026 Reviews received at journal 04 Jan, 2026 Reviews received at journal 27 Dec, 2025 Reviews received at journal 26 Dec, 2025 Reviewers agreed at journal 21 Dec, 2025 Reviewers agreed at journal 19 Dec, 2025 Reviewers agreed at journal 19 Dec, 2025 Reviewers invited by journal 19 Dec, 2025 Editor assigned by journal 10 Dec, 2025 Submission checks completed at journal 10 Dec, 2025 First submitted to journal 09 Dec, 2025 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. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-8320718","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":562846424,"identity":"e4ca3365-b4fb-4788-92ea-24ff457ea9e3","order_by":0,"name":"Sara Rahdar","email":"","orcid":"","institution":"University of Kashan","correspondingAuthor":false,"prefix":"","firstName":"Sara","middleName":"","lastName":"Rahdar","suffix":""},{"id":562846425,"identity":"a2052a79-4b62-4a86-8175-d0c9ea05d27c","order_by":1,"name":"Mahmoud Nikoufard","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAwklEQVRIiWNgGAWjYFACxmaGDwcYGAxgfDZitDDOIFELAzMzD7IWgkB3dnOzsc0ZO3tz9rPHJBhq7Bj4pA/g12J252Bzcs6N5MSdPXlpEgzHkhnY+BIIaLmR2Hw45wNzgsGBHDMJBrYDDGw8BBwG1mLxod7e4PwboJZ/RGpJZrhxmHHDDaAtjG1EajHsOXM8ccONN8YWiX3JPERoSX8s8eNYNdBhOYY3Pnyzk5PvIaAFFSQwMBCyYxSMglEwCkYBMQAApo8/7vIzKbYAAAAASUVORK5CYII=","orcid":"","institution":"University of Kashan","correspondingAuthor":true,"prefix":"","firstName":"Mahmoud","middleName":"","lastName":"Nikoufard","suffix":""}],"badges":[],"createdAt":"2025-12-09 18:53:18","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8320718/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8320718/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s11082-026-08776-6","type":"published","date":"2026-04-04T16:00:14+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":99308890,"identity":"44bf757e-2586-4d7f-83cb-9884281cf29c","added_by":"auto","created_at":"2025-12-31 16:09:26","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":1874384,"visible":true,"origin":"","legend":"","description":"","filename":"SARARAHDAR.docx","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/c3c31a54e1f38b4a6f4599c8.docx"},{"id":98845989,"identity":"52e2a146-4520-4327-9322-7d06c38d59c2","added_by":"auto","created_at":"2025-12-23 04:30:22","extension":"json","order_by":1,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":3871,"visible":true,"origin":"","legend":"","description":"","filename":"bf0b7bd023c8403c8407777dff927be6.json","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/33294e1ec04afd0a59c2d47b.json"},{"id":98845994,"identity":"af213290-285e-4b90-a865-3746d480008f","added_by":"auto","created_at":"2025-12-23 04:30:22","extension":"xml","order_by":2,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":99174,"visible":true,"origin":"","legend":"","description":"","filename":"bf0b7bd023c8403c8407777dff927be61enriched.xml","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/0427b286fc27a1b5a81b7967.xml"},{"id":99308545,"identity":"dc3de81b-9b9b-4374-9e1a-0595e48f53ae","added_by":"auto","created_at":"2025-12-31 16:08:45","extension":"jpeg","order_by":3,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":443917,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/ac906c3e3195485d61bd643f.jpeg"},{"id":99308135,"identity":"1e55068a-3925-4f82-b799-9dcab5f9fe68","added_by":"auto","created_at":"2025-12-31 16:07:48","extension":"jpeg","order_by":4,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":146332,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage10.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/54f35e596a25123ce883d313.jpeg"},{"id":98846003,"identity":"756b486e-73e4-471a-862c-08ea16b293cf","added_by":"auto","created_at":"2025-12-23 04:30:22","extension":"jpeg","order_by":5,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":170904,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage11.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/d625c010266b464bdecef0eb.jpeg"},{"id":98845997,"identity":"691b62cc-dff0-4e70-aeaa-a05a90d22c70","added_by":"auto","created_at":"2025-12-23 04:30:22","extension":"jpeg","order_by":6,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":140828,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage12.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/13d05a4be3508234fe64b779.jpeg"},{"id":98846000,"identity":"6a19172b-0d3f-4234-8d57-68bf72256c8a","added_by":"auto","created_at":"2025-12-23 04:30:22","extension":"jpeg","order_by":7,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":154698,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage13.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/070ea4dbd13e4ecc186edf94.jpeg"},{"id":98846005,"identity":"2a079397-558f-4b3e-9340-975e3bf1368b","added_by":"auto","created_at":"2025-12-23 04:30:22","extension":"jpeg","order_by":8,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":31800,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage14.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/95ae461f53a5ea74e758c5ff.jpeg"},{"id":98846006,"identity":"0e664cc3-b965-451e-a7eb-37578274a396","added_by":"auto","created_at":"2025-12-23 04:30:22","extension":"jpeg","order_by":9,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":81944,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage15.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/e464110804ce972ff16bdced.jpeg"},{"id":98846028,"identity":"9f0e6152-e3e2-475b-a7e0-1c5981395eb6","added_by":"auto","created_at":"2025-12-23 04:30:23","extension":"jpeg","order_by":10,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":380137,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage16.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/01e43b946c2c43568d58a7f5.jpeg"},{"id":98845998,"identity":"23ab101f-26bf-4713-8b4f-5ff0abc2fd37","added_by":"auto","created_at":"2025-12-23 04:30:22","extension":"jpeg","order_by":11,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":159525,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/c24b3a1189355d536e1aae98.jpeg"},{"id":98846011,"identity":"318f027f-a713-44cf-9bd1-9241c4f870b7","added_by":"auto","created_at":"2025-12-23 04:30:22","extension":"jpeg","order_by":12,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":288254,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/0cecc60365c3fd7ae5ba3f7d.jpeg"},{"id":98846004,"identity":"c5f03edb-32f9-4b6b-b2b8-9f11cdc3b9e4","added_by":"auto","created_at":"2025-12-23 04:30:22","extension":"jpeg","order_by":13,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":428134,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/7726c93a5a40b3d933101538.jpeg"},{"id":99308328,"identity":"8e1aa630-fef7-411d-b3aa-3d31deb53749","added_by":"auto","created_at":"2025-12-31 16:08:16","extension":"jpeg","order_by":14,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":119729,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/a5890950c0e85a61d82be502.jpeg"},{"id":99308377,"identity":"9b055c33-e2fd-41d4-a164-6ad3959284d7","added_by":"auto","created_at":"2025-12-31 16:08:23","extension":"jpeg","order_by":15,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":58952,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/ed3b3104b566d3261aad67c9.jpeg"},{"id":99308282,"identity":"cf079973-02dc-4c20-80f8-cccee3fbc962","added_by":"auto","created_at":"2025-12-31 16:08:11","extension":"jpeg","order_by":16,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":60442,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage7.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/af29450bc68ca9778d1041a6.jpeg"},{"id":99308130,"identity":"7b8c94b1-dcea-4b16-a03c-01a97e443a56","added_by":"auto","created_at":"2025-12-31 16:07:48","extension":"jpeg","order_by":17,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":53008,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage8.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/c617bb989c4b8133790752f5.jpeg"},{"id":98846019,"identity":"3a98f6fb-3bc9-4740-a051-67f42679b503","added_by":"auto","created_at":"2025-12-23 04:30:23","extension":"jpeg","order_by":18,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":59182,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage9.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/bbbc01b59ad539431e01a27f.jpeg"},{"id":98846007,"identity":"11b5b65a-8411-4391-9a0f-ce30f2308ab8","added_by":"auto","created_at":"2025-12-23 04:30:22","extension":"png","order_by":19,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":93672,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/e2d24bc29f68071e5c7bc001.png"},{"id":98846022,"identity":"aee0a67b-6c9d-411d-a38e-39160698cd71","added_by":"auto","created_at":"2025-12-23 04:30:23","extension":"png","order_by":20,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":25800,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/2e1d69c97ba783414c0503b7.png"},{"id":98846032,"identity":"d555a9cf-d048-410e-8272-4d4e217081c7","added_by":"auto","created_at":"2025-12-23 04:30:23","extension":"png","order_by":21,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":30136,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage11.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/410dedca578461a0ee43f001.png"},{"id":98846015,"identity":"3c944615-ec5a-40f0-a937-06f834e835e1","added_by":"auto","created_at":"2025-12-23 04:30:23","extension":"png","order_by":22,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":24244,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage12.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/a235fb68637b15444e86e918.png"},{"id":99308301,"identity":"a86f7442-b958-4b8e-bb7c-9ec5efe4f843","added_by":"auto","created_at":"2025-12-31 16:08:14","extension":"png","order_by":23,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":27723,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage13.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/54ab5922ec4aa22186d93894.png"},{"id":98846033,"identity":"41633fd6-1d37-4a78-a0a1-bb0ebffbe0aa","added_by":"auto","created_at":"2025-12-23 04:30:23","extension":"png","order_by":24,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":6531,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage14.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/8781b23a15b39ae0e898a316.png"},{"id":98846009,"identity":"2eccdc22-bae7-475f-a754-641d5ccd56c6","added_by":"auto","created_at":"2025-12-23 04:30:22","extension":"png","order_by":25,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":20277,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage15.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/e052de01e577e58a4dcaa6f9.png"},{"id":99308737,"identity":"c2e868bb-9ad5-4cbf-a91e-c6f21690b354","added_by":"auto","created_at":"2025-12-31 16:09:03","extension":"png","order_by":26,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":75246,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage16.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/dde9cddabc5bc91813d5bac4.png"},{"id":99308785,"identity":"5f462dca-a54f-4890-bd71-5b4ee3c8f38a","added_by":"auto","created_at":"2025-12-31 16:09:09","extension":"png","order_by":27,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":32146,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/4e9d3b17186cabcc1fec1461.png"},{"id":98846016,"identity":"b92620b6-1a48-4bd9-9026-320ab2ac3bb4","added_by":"auto","created_at":"2025-12-23 04:30:23","extension":"png","order_by":28,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":55218,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/5d303b3f94877d9b031b0812.png"},{"id":98846021,"identity":"69783a8a-a91d-4723-8efe-c77f6cba2cf3","added_by":"auto","created_at":"2025-12-23 04:30:23","extension":"png","order_by":29,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":100298,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/c4370e65cc03e61de0682afb.png"},{"id":99308891,"identity":"16bb57f0-555f-457e-9f6a-8132ce183f9a","added_by":"auto","created_at":"2025-12-31 16:09:26","extension":"png","order_by":30,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":26626,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/337b89cd4c0e7d807c753a8c.png"},{"id":98846026,"identity":"b7e602fd-2f04-493a-a19c-bf16ca74a5a4","added_by":"auto","created_at":"2025-12-23 04:30:23","extension":"png","order_by":31,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":11176,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/1c1238e71affbff65a0354bc.png"},{"id":99308509,"identity":"5b223616-fc9e-4d23-b8a6-ad4c35f85389","added_by":"auto","created_at":"2025-12-31 16:08:43","extension":"png","order_by":32,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":11459,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/794d285efa5b9529ceb054b9.png"},{"id":99308150,"identity":"7644c937-1880-471e-a222-85085a54c8bc","added_by":"auto","created_at":"2025-12-31 16:07:53","extension":"png","order_by":33,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":10406,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/a3f43ba3de992a4812377b2d.png"},{"id":98846025,"identity":"a0240b1d-33bd-4e08-a48f-6c07dd7ba0af","added_by":"auto","created_at":"2025-12-23 04:30:23","extension":"png","order_by":34,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":11931,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/8c1a7b751f4cf24138b93e47.png"},{"id":98846027,"identity":"a21d17a8-c475-4bf1-a211-ce7413fef6b2","added_by":"auto","created_at":"2025-12-23 04:30:23","extension":"xml","order_by":35,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":99353,"visible":true,"origin":"","legend":"","description":"","filename":"bf0b7bd023c8403c8407777dff927be61structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/6e11cdb71068efd20ee9df73.xml"},{"id":99308167,"identity":"5992cf2f-412d-4342-8360-cf579de2b923","added_by":"auto","created_at":"2025-12-31 16:07:53","extension":"html","order_by":36,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":111079,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/6a14998091e77e8e26054bad.html"},{"id":98845991,"identity":"6af7ab47-3eb1-40a5-bb12-a2733157c812","added_by":"auto","created_at":"2025-12-23 04:30:22","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":302909,"visible":true,"origin":"","legend":"\u003cp\u003eUnit cell architecture enabling broadband polarization conversion: (a) 3D view of the multi-layer FSS with vertically stacked ring resonators (SiO₂ cap: \u003cem\u003eh\u003c/em\u003e₁=26.3 μm, Si spacers: \u003cem\u003eh\u003c/em\u003e₂=10.5 μm, \u003cem\u003eh\u003c/em\u003e₃=9.15 μm, \u003cem\u003eh\u003c/em\u003e₄=10 μm), (b) TE-to-TM conversion mechanism via coupled resonance excitation in stacked rings. Copper resonators (\u003cem\u003eR\u003c/em\u003e₁=16.6 μm to \u003cem\u003eR\u003c/em\u003e₃=31.6 μm) are embedded in silicon with periodicity \u003cem\u003ep\u003c/em\u003e=34.7 μm.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/fa5ce3d673dba390c43e2249.png"},{"id":99308229,"identity":"916e9a51-6a52-42f7-b618-a2942e4d5b76","added_by":"auto","created_at":"2025-12-31 16:08:02","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":66535,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Layered schematic of the proposed metasurface showing the SiO₂ AR coating (\u003cimg width=\"26\" height=\"14\" src=\"data:image/png;base64,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\"/\u003e, h₁), three Si spacers (\u003cimg width=\"15\" height=\"14\" src=\"data:image/png;base64,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\"/\u003e, h₂–h₄) each embedding an SRR layer with radii R₁\u0026lt;R\u003csub\u003e2\u003c/sub\u003e\u0026lt;R₃ and varying capacitive gaps C\u003csub\u003ei\u003c/sub\u003e. Incident TE or TM wave is shown as\u003cimg width=\"35\" height=\"15\" src=\"data:image/png;base64,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\"/\u003e. (b) Optical path diagram showing reflected waves \u003cimg width=\"17\" height=\"14\" src=\"data:image/png;base64,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\"/\u003efrom the air–SiO₂ and \u003cimg width=\"17\" height=\"14\" src=\"data:image/png;base64,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\"/\u003e\u0026nbsp;SiO₂–Si interfaces. The AR-film enforces destructive interference (\u003cimg width=\"39\" height=\"14\" src=\"data:image/png;base64,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\"/\u003e) of co-polar reflection components, enabling cross-polar conversion by the anisotropic SRRs.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/8226dc2c9316e47ac47dac87.png"},{"id":98845993,"identity":"9a9d6b9e-afed-4985-ab47-cb72ed708c34","added_by":"auto","created_at":"2025-12-23 04:30:22","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":136007,"visible":true,"origin":"","legend":"\u003cp\u003eSimulated reflection response of the FSS metasurface: (a) Magnitude\u0026nbsp;∣\u003cem\u003eS\u003c/em\u003e\u003csub\u003e11\u003c/sub\u003e\u003cbr\u003e\n∣\u0026nbsp;showing resonant dips at 1.0, 1.3, 1.6 and 1.8 THz for co-polarized reflections (TE→TE, TM→TM), (b) Corresponding phase\u0026nbsp;∠\u003cem\u003eS\u003c/em\u003e\u003csub\u003e11\u003c/sub\u003e\u003cbr\u003e\nexhibiting characteristic 180° jumps at resonances. Cross-polarized terms (TE→TM, TM→TE) maintain near-unity magnitude (\u0026gt; -0.5 dB) and stable phase across 1–1.8 THz.\u0026nbsp;\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/98143060f1982bea3fd3d97c.png"},{"id":98845996,"identity":"5acbf1ad-3442-475b-9a4b-17f0e52f75d4","added_by":"auto","created_at":"2025-12-23 04:30:22","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":440232,"visible":true,"origin":"","legend":"\u003cp\u003eAngularly stable polarization conversion: Reflection coefficient magnitude ∣\u003cem\u003eS\u003c/em\u003e11​∣ versus frequency (0–2 THz) and incidence angle (0°–90°) for (a) TE→TE, (b) TE→TM, (c) TM→TM, and (d) TM→TE conversions. High cross-polarized reflection (∣\u003cem\u003eS\u003c/em\u003e11​∣≈1) and suppressed co-polarized reflection (∣\u003cem\u003eS\u003c/em\u003e11​∣≈0) persist across 1–1.8 THz for θ ≤ 60°, demonstrating broadband angular insensitivity.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/653a3904715ade8db15a5abd.png"},{"id":98846013,"identity":"f1e609df-625f-483e-bd5f-eb2c06874cca","added_by":"auto","created_at":"2025-12-23 04:30:22","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":360785,"visible":true,"origin":"","legend":"\u003cp\u003eResonance localization in stacked SRRs: Surface current distributions at (a) 1.0 THz (SRR₃-dominant), (b) 1.3 THz (SRR₂-dominant), (c) 1.6 THz (SRR₁-SRR₃hybrid), and (d) 1.8 THz (SRR₂-SRR₃ coupled). Current concentration shifts vertically across layers while maintaining strong spatial localization, validating multi-layer synergy for broadband polarization conversion.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/a550cb7286844e499f905192.png"},{"id":99308332,"identity":"70f1496f-d4ca-42bb-baf2-bdc230c0bece","added_by":"auto","created_at":"2025-12-31 16:08:16","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":874097,"visible":true,"origin":"","legend":"\u003cp\u003eField distributions demonstrating resonance mechanisms: (a) Electric field at 1 THz showing dipole formation across SRR₃, (b) Corresponding magnetic field circulation around SRR₃, (c) Electric field concentration at SRR₂during 1.3 THz resonance, (d) Magnetic field exclusion from resonator gaps at 1.3 THz. Fields are normalized to incident wave amplitude.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/ac8f23c52a3ae1aeb5491145.png"},{"id":99308165,"identity":"2da18317-b295-4a28-a41a-7af7f63265ef","added_by":"auto","created_at":"2025-12-31 16:07:53","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":170599,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Equivalent circuit model of the FSS metasurface featuring cascaded transmission lines (TLIN₁–TLIN₄) for SiO₂/Si dielectric layers and coupled LC networks modeling split-ring resonators. (b) Validation: Full-wave electromagnetic simulation (solid lines) versus equivalent circuit simulation (dashed lines) of reflection coefficient magnitudes across 1–1.8 THz.\u003c/p\u003e\n\u003cp\u003e(\u003cem\u003eC\u003c/em\u003e1=895 fF, \u003cem\u003eC\u003c/em\u003e2=0.055 fF, \u003cem\u003eC\u003c/em\u003e3=499.9 fF, \u003cem\u003eC\u003c/em\u003e4=0.237 fF, \u003cem\u003eC\u003c/em\u003e5=0.143 fF,\u0026nbsp; \u003cem\u003eC\u003c/em\u003e6= 354.42 fF, \u003cem\u003eC\u003c/em\u003e7=2.77 fF, \u003cem\u003eL\u003c/em\u003e1=21.7 pH, \u003cem\u003eL\u003c/em\u003e2=0.64 pH, \u003cem\u003eL\u003c/em\u003e3=148.7 pH, \u003cem\u003eL\u003c/em\u003e4=60.6 pH,\u0026nbsp; \u003cem\u003eL\u003c/em\u003e5=43.9 pH, \u003cem\u003eL\u003c/em\u003e6= 9.94 pH, \u003cem\u003eL\u003c/em\u003e7=11.8 pH)\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/a482f592a810e51cba0aa229.png"},{"id":98846001,"identity":"04c8735a-286b-40d7-ac8e-9900c5b6de56","added_by":"auto","created_at":"2025-12-23 04:30:22","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":226634,"visible":true,"origin":"","legend":"\u003cp\u003eFabrication flow for the multi-layer THz FSS metasurface.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/4179921de1284507ea8c4b2e.png"},{"id":106345244,"identity":"a4a8d839-3dc1-4c32-a9ae-cdfd2ad884bb","added_by":"auto","created_at":"2026-04-07 16:18:45","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3067487,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8320718/v1/5c143e9f-f02c-491c-b242-f09c700c4288.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Broadband Angularly Stable Polarization Conversion in Terahertz Band via Vertically Stacked Frequency Selective Surface Metasurface","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eTerahertz (THz) technology\u0026mdash;spanning 0.1\u0026ndash;10 THz\u0026mdash;represents a rapidly advancing field bridging microwave electronics and infrared photonics (Tonouchi \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2007\u003c/span\u003e), (Siegel \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). This spectral window is crucial for emerging technologies due to its coverage of molecular rotational/vibrational energy states and penetration capability through non-conductive materials (Ferguson and Zhang \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). These properties enable transformative applications including ultra-high-speed wireless communications (6G and beyond) (Akyildiz et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Rappaport et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2019\u003c/span\u003e); high-resolution medical imaging/spectroscopy for cancer detection (Li et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Woodward et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2003\u003c/span\u003e); non-destructive material inspection (Jepsen et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2011\u003c/span\u003e); and stand-off security screening (Mittleman \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). However, realizing these systems requires precise manipulation of THz wave properties, among which polarization control is paramount (Zheludev and Kivshar \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Efficient dynamic control of polarization states (e.g., TE/TM conversion) is essential for: enhancing communication signal-to-noise ratios (Cong et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2017\u003c/span\u003e); mitigating polarization-mismatch losses (He et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2015\u003c/span\u003e); and enabling polarization-sensitive imaging/spectroscopy to probe material anisotropy and surface textures (Rashid et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eHistorically, polarization control relied on conventional optical components exploiting natural material properties\u0026mdash;such as birefringence in quartz/calcite waveplates or the Faraday effect in magneto-optical materials (Goldstein \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). These approaches, however, prove ineffective at THz frequencies where most natural materials exhibit weak electromagnetic responses. Consequently, devices require interaction lengths spanning tens of wavelengths to achieve sufficient phase shifts (Masson and Gallot \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2006\u003c/span\u003e), resulting in bulky, expensive systems with narrow operational bandwidths (Ako et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). To overcome these limitations, researchers have adopted metamaterials\u0026mdash;artificially structured media with subwavelength \"meta-atoms\" engineered for bespoke electromagnetic responses (Pendry et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e1999\u003c/span\u003e; Smith et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). Their 2D counterparts, metasurfaces, offer unprecedented control over wave amplitude, phase, and polarization within ultrathin profiles (Kildishev et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Yu et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2011\u003c/span\u003e), enabling compact, efficient components (Glybovski et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFor THz polarization conversion, metasurfaces are categorized as reflective or transmissive. Reflective designs typically achieve superior efficiency and bandwidth through simplified Fabry-Perot resonance mechanisms (Chen \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2012\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eNumerous resonator geometries have been explored for unit-cell designs, including V-shaped antennas (Grady et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2013\u003c/span\u003e), split-ring resonators (SRRs) (Cheng et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), cross-shaped structures (Ahmad et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2022\u003c/span\u003e)d shaped resonators (Xu et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). While demonstrating significant improvements over conventional approaches, these designs often face critical performance trade-offs. A persistent challenge remains the simultaneous achievement of high polarization conversion ratio (PCR), broad bandwidth, and angular stability across wide incidence angles (Zhang et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). For instance, single-layer designs typically achieve near-unity PCR at discrete resonant frequencies but exhibit rapid performance degradation under frequency detuning or oblique incidence (Yang et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Multi-layer structures\u0026mdash;proposed to broaden bandwidth through stacked resonators exciting adjacent resonances (Dong et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Fei et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2020\u003c/span\u003e)\u0026mdash;still suffer from fabrication complexity and pronounced angular sensitivity. These limitations necessitate further innovation.\u003c/p\u003e \u003cp\u003eThis paper addresses these challenges through a novel three-layer passive metasurface polarization converter optimized for THz frequencies. The design employs vertically stacked copper ring resonators on a low-loss silicon substrate, enabling efficient bidirectional TE/TM conversion. The simple ring geometry ensures robustness, while numerical optimization of the tri-layer stack facilitates excitation of overlapping resonances. This strategy achieves\u0026thinsp;\u0026gt;\u0026thinsp;90% polarization conversion efficiency across a 1\u0026ndash;1.8 THz bandwidth while maintaining high performance for incidence angles up to 60\u0026deg;\u0026mdash;a substantial improvement in angular stability over prior designs. Fabrication leverages established copper/SiO₂ deposition and photolithography techniques (Zhang et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2005\u003c/span\u003e), ensuring compact, robust, and system-integrable devices. This work provides a high-performance solution for dynamic polarization control in advanced THz communication, imaging, and sensing systems operating under variable angles.\u003c/p\u003e"},{"header":"2 FSS Structural Design","content":"\u003cp\u003eThe performance of the proposed FSS filter is governed by its geometric parameters and material composition. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, the structure features four vertically stacked dielectric layers (thicknesses ℎ\u003csub\u003e1\u003c/sub\u003e​ to ℎ\u003csub\u003e4\u003c/sub\u003e) aligned along the \u003cem\u003ez\u003c/em\u003e-axis. The top SiO₂ layer (ℎ\u003csub\u003e1​\u003c/sub\u003e) functions as both protective coating and anti-reflection element, while the underlying silicon layers (ℎ\u003csub\u003e2\u003c/sub\u003e​, ℎ\u003csub\u003e3\u003c/sub\u003e​, ℎ\u003csub\u003e4\u003c/sub\u003e​) embed copper resonators.\u003c/p\u003e \u003cp\u003eUnit cells are arranged periodically in the \u003cem\u003ex\u003c/em\u003e-\u003cem\u003ey\u003c/em\u003e plane with lattice constant \u003cem\u003ep\u003c/em\u003e, a critical parameter controlling resonant frequency and bandwidth. Three sets of split-ring resonators (SRRs) embedded across different layers serve as the primary frequency-selective elements. Each SRR is defined by radius (\u003cem\u003eR\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e​, \u003cem\u003eR\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e​, \u003cem\u003eR\u003c/em\u003e\u003csub\u003e3\u003c/sub\u003e​), width (\u003cem\u003eW\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e​,\u003cem\u003eW\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e​, \u003cem\u003eW\u003c/em\u003e\u003csub\u003e3\u003c/sub\u003e​), and capacitive gap (\u003cem\u003eC\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e​, \u003cem\u003eC\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e​, \u003cem\u003eC\u003c/em\u003e\u003csub\u003e3\u003c/sub\u003e), with the incomplete loops creating gaps essential for resonant tuning.\u003c/p\u003e \u003cp\u003eThe unit cell design, illustrated in top-down views (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), positions each ring resonator at distinct depths within the stack, enabling vertical integration. This multi-layered configuration with varied ring dimensions achieves tailored frequency responses, specifically enabling broadband filtering across the THz range.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eOptimization of layer thicknesses (ℎ\u003csub\u003e1\u003c/sub\u003e​-ℎ\u003csub\u003e4\u003c/sub\u003e​), periodicity (\u003cem\u003ep\u003c/em\u003e), and ring geometric parameters (\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e​, \u003cem\u003eW\u003c/em\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e​\u003c/sub\u003e, \u003cem\u003eC\u003c/em\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e​\u003c/sub\u003e) is critical for resonance control. We numerically optimized these parameters to position resonances at target frequencies, with final design values listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eOptimized geometric parameters of the FSS unit cell enabling broadband angular-stable polarization conversion.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"15\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c13\" colnum=\"13\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c14\" colnum=\"14\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c15\" colnum=\"15\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParameter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003ep\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eh\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003eh\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eh\u003c/em\u003e\u003csub\u003e\u003cem\u003e3\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cem\u003eh\u003c/em\u003e\u003csub\u003e\u003cem\u003e4\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003e3\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003e\u003cem\u003ew\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c11\"\u003e \u003cp\u003e\u003cem\u003ew\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c12\"\u003e \u003cp\u003e\u003cem\u003ew\u003c/em\u003e\u003csub\u003e\u003cem\u003e3\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c13\"\u003e \u003cp\u003e\u003cem\u003ec\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c14\"\u003e \u003cp\u003e\u003cem\u003ec\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c15\"\u003e \u003cp\u003e\u003cem\u003ec\u003c/em\u003e\u003csub\u003e\u003cem\u003e3\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eValue (\u003c/b\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varvec{\\mu\\:}\\mathbf{m})\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e34.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e26.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e9.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e16.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e31.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e2.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e6.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e7.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e2.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c14\"\u003e \u003cp\u003e5.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c15\"\u003e \u003cp\u003e7.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"3 Theorical model and analytical framework","content":"\u003cp\u003eTo support the full-wave numerical simulations, we develop a comprehensive multilayer analytical model based on classical thin-film interference theory and generalized Fresnel reflection principles. This theoretical framework elucidates the physical mechanisms by which the proposed vertically stacked split-ring resonator metasurface achieves broadband polarization conversion between TE and TM modes through strategic suppression of co-polarized reflection combined with enhanced anisotropic cross-polarization coupling.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe top SiO₂ layer functions as an AR coating. The quarter-wave optical thickness condition (Xiong et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) as \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{h}₁=\\frac{m.\\lambda\\:}{4{\\stackrel{\\sim}{n}}_{\\text{A}\\text{R}}}\\:\\)\u003c/span\u003e\u003c/span\u003e where \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\lambda\\:\\)\u003c/span\u003e\u003c/span\u003eis the target wavelength and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\stackrel{\\sim}{n}}_{\\text{A}\\text{R}}\\)\u003c/span\u003e\u003c/span\u003e is the refractive index of the AR coating. The odd integer \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:m\\)\u003c/span\u003e\u003c/span\u003e enforces a π-phase difference between reflections at the air\u0026ndash;SiO₂ and SiO₂\u0026ndash;Si interfaces, minimizing co-polar reflectance. Such destructive interference enhances the relative strength of cross-polarized components generated by the SRRs.\u003c/p\u003e \u003cp\u003eTransmit (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{T}_{d}^{\\left(\\alpha\\:\\right)}\\left)\\:\\text{a}\\text{n}\\text{d}\\:\\text{R}\\text{e}\\text{f}\\text{l}\\text{e}\\text{c}\\text{t}\\text{i}\\text{v}\\text{e}\\:\\right({R}_{d}^{\\left(\\alpha\\:\\right)}\\)\u003c/span\u003e\u003c/span\u003e) field amplitudes in layer d follow the generalized Fresnel recursion (Parratt \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1954\u003c/span\u003e):\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:\\frac{{T}_{d}^{\\left(\\alpha\\:\\right)}}{{R}_{d}^{\\left(\\alpha\\:\\right)}}=\\frac{{e}^{i2{k}_{lz}^{\\left(\\alpha\\:\\right)}{h}_{d}}}{{\\rho\\:}_{d(d+1)}^{\\left(\\alpha\\:\\right)}}+\\frac{\\left(1-\\frac{1}{{\\left({\\rho\\:}_{d(d+1)}^{\\left(\\alpha\\:\\right)}\\right)}^{2}}\\right){e}^{i2\\left({k}_{d(d+1)z}^{\\left(\\alpha\\:\\right)}+{k}_{dz}^{\\left(\\alpha\\:\\right)}\\right){h}_{d}}}{\\frac{1}{{\\rho\\:}_{d(d+1)}^{\\left(\\alpha\\:\\right)}}{e}^{i2{k}_{(d+1)z}^{\\left(\\alpha\\:\\right)}{h}_{d}}+\\frac{{T}_{d+1}^{\\left(\\alpha\\:\\right)}}{{R}_{d+1}^{\\left(\\alpha\\:\\right)}}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\alpha\\:}\\in\\:\\{\\text{T}\\text{E},\\:\\text{T}\\text{M}\\}\\)\u003c/span\u003e\u003c/span\u003e denotes the polarization of wave (TE, TM (, and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{k}_{dz}^{\\left(\\alpha\\:\\right)}\\)\u003c/span\u003e\u003c/span\u003e is the z component of the wavevector in layer d, and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\rho\\:}_{d(d+1)}^{\\left(\\alpha\\:\\right)}\\)\u003c/span\u003e\u003c/span\u003e is the Fresnel reflection coefficient at the interface between layers d and (d\u0026thinsp;+\u0026thinsp;1). The boundary condition at the bottom perfectly conducting ground plane (layer N) is \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\frac{{\\text{T}}_{N}^{\\left({\\alpha\\:}\\right)}}{{\\text{R}}_{N}^{\\left({\\alpha\\:}\\right)}}=-1\\)\u003c/span\u003e\u003c/span\u003e Recursively solving Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) from the bottom layer upward yields the total reflection coefficient (Zhou et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2010\u003c/span\u003e) as \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\rho\\:}^{\\left(\\alpha\\:\\right)}=\\frac{{T}_{0}^{\\left(\\alpha\\:\\right)}}{{R}_{0}^{\\left(\\alpha\\:\\right)}}\\)\u003c/span\u003e\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eThe overall co-polar reflectance is given by the classical Airy thin-film formula (Sun et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2011\u003c/span\u003e):\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:{R}_{\\alpha\\:\\alpha\\:}(\\nu\\:,\\theta\\:)={\\left|\\stackrel{\\sim}{\\rho\\:}\\right|}^{2}=\\frac{{\\left({\\rho\\:}_{12}^{\\left(\\alpha\\:\\right)}\\right)}^{2}+{\\left({\\tau\\:}_{12}^{\\left(\\alpha\\:\\right)}{\\rho\\:}_{23}^{\\left(\\alpha\\:\\right)}{\\tau\\:}_{21}^{\\left(\\alpha\\:\\right)}\\right)}^{2}+2{\\rho\\:}_{12}^{\\left(\\alpha\\:\\right)}{\\tau\\:}_{12}^{\\left(\\alpha\\:\\right)}{\\rho\\:}_{23}^{\\left(\\alpha\\:\\right)}{\\tau\\:}_{21}^{\\left(\\alpha\\:\\right)}\\text{c}\\text{o}\\text{s}\\left({{\\Phi\\:}}^{\\left(\\alpha\\:\\right)}\\right)}{1+{\\left({\\rho\\:}_{12}^{\\left(\\alpha\\:\\right)}{\\rho\\:}_{23}^{\\left(\\alpha\\:\\right)}\\right)}^{2}-2{\\rho\\:}_{12}^{\\left(\\alpha\\:\\right)}{\\rho\\:}_{23}^{\\left(\\alpha\\:\\right)}\\text{c}\\text{o}\\text{s}\\left({{\\Phi\\:}}_{{\\Sigma\\:}}^{\\left(\\alpha\\:\\right)}\\right)}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eHere, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\rho\\:}_{\\text{i}\\text{j}}^{\\left(\\alpha\\:\\right)}\\)\u003c/span\u003e\u003c/span\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\tau\\:}_{\\text{i}\\text{j}}^{\\left(\\alpha\\:\\right)}\\)\u003c/span\u003e\u003c/span\u003e are the Fresnel reflection and transmission coefficients at interface \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{i}-\\text{j}\\)\u003c/span\u003e\u003c/span\u003e, respectively. The phase term is defined as \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{{\\Phi\\:}}^{\\left(\\alpha\\:\\right)}={\\varphi\\:}_{12}^{\\alpha\\:}-{{\\psi\\:}}^{{\\alpha\\:}},\\:{{\\Phi\\:}}_{{\\Sigma\\:}}^{\\alpha\\:}={\\varphi\\:}_{12}^{\\alpha\\:}+{\\varphi\\:}_{23}^{\\alpha\\:}+2{{\\beta\\:}}^{{\\alpha\\:}}\\)\u003c/span\u003e\u003c/span\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{{\\beta\\:}}^{{\\alpha\\:}}=\\sqrt{{ϵ}_{AR}}{k}_{0}\\text{cos}\\left({\\theta\\:}_{s}\\right){{\\Sigma\\:}}_{i=1}^{4}{h}_{i}\\)\u003c/span\u003e\u003c/span\u003e where \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varphi\\:}_{ij}^{\\alpha\\:}\\)\u003c/span\u003e\u003c/span\u003e are the reflection phase shift at each interface, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{{\\psi\\:}}^{{\\alpha\\:}}\\)\u003c/span\u003e\u003c/span\u003e accounts for transmission phase accumulation, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{ϵ}_{AR}\\)\u003c/span\u003e\u003c/span\u003e is the effective complex permittivity of the multilayer AR coating, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{k}_{0}=\\frac{2\\pi\\:}{\\lambda\\:}\\)\u003c/span\u003e\u003c/span\u003e is the free space wave number, and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\theta\\:}_{s}\\)\u003c/span\u003e\u003c/span\u003e is the incident angle in the substrate. Co-polar reflection is minimized when:\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$\\:{\\rho\\:}_{12}^{\\left(\\alpha\\:\\right)})\\:=\\:{\\tau\\:}_{12}^{\\left(\\alpha\\:\\right)}\\:{\\rho\\:}_{23}^{\\left(\\alpha\\:\\right)})\\:\\:{\\tau\\:}_{21}^{\\left(\\alpha\\:\\right)}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:{{\\Phi\\:}}^{\\left(\\alpha\\:\\right)}\\)\u003c/span\u003e \u003c/span\u003e= (2N+1) π, N \u0026isin; ℤ(4)\u003c/p\u003e \u003cp\u003eWhen these conditions are met, destructive interference occurs at the dielectric interfaces, suppressing the co-polarized reflection to near zero. Consequently, the split-ring resonators (SRRs) efficiently rotate the polarization of the incident field from TE to TM (and vice versa). This conversion arises from SRR-induced resonant surface currents at the target wavelength, which generates the required cross-polarized response at the interface.\u003c/p\u003e \u003cp\u003eDue to the circular shape of the SRRs, the surface current excited by the incident field exhibits both Jx and Jy component on the surface of the conductor (Fig.\u0026nbsp;5). Under resonant excitation, the Jx currents on the two split sections are out of phase and therefore cancel in the far field, whereas the Jy components remain in phase and add constructively. As a result, a pronounced cross-polarized response is produced, consistent with the strong polarization conversion observed in the extracted S-parameters.\u003c/p\u003e \u003cp\u003eAs can be seen in the S-parameter S11 TE-TE versus frequency, (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) in certain frequencies we observe deep spectral dips. These resonance frequencies correspond to regions where the above-mentioned conditions are satisfied, and co-polar reflection component approaches to zero.\u003c/p\u003e \u003cp\u003eThe SRR layers are geometrically anisotropic (R₁\u0026lt;R₂\u0026lt;R₃, with differing capacitive gaps C\u003csub\u003ei\u003c/sub\u003e), producing off-diagonal reflection terms \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\rho\\:}_{TE,TM}\\:and\\:{\\rho\\:}_{TM,TE}\\)\u003c/span\u003e\u003c/span\u003e (Ahmad et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2022\u003c/span\u003e):\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$$\\:\\mathbf{R}=\\left[\\begin{array}{ll}{\\rho\\:}_{\\text{T}\\text{E},\\text{T}\\text{E}}\u0026amp;\\:{\\rho\\:}_{\\text{T}\\text{E},\\text{T}\\text{M}}\\\\\\:{\\rho\\:}_{\\text{T}\\text{M},\\text{T}\\text{E}}\u0026amp;\\:{\\rho\\:}_{\\text{T}\\text{M},\\text{T}\\text{M}}\\end{array}\\right]$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhen (2)\u0026ndash; (4) suppress the diagonal terms ρ\u003csub\u003eTE,TE\u003c/sub\u003e and ρ\u003csub\u003eTM,TM\u003c/sub\u003e, the cross-polar terms dominate. Reciprocity gives ρ\u003csub\u003eTE,TM\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;ρ\u003csub\u003eTM,TE\u003c/sub\u003e. This produces bidirectional \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:TE\\leftrightarrow\\:\\:TM\\)\u003c/span\u003e\u003c/span\u003e conversion with near unity polarization conversion ratio (PCR\u0026thinsp;\u0026gt;\u0026thinsp;0.95) and angular stability up to 60 incidence angles.\u003c/p\u003e"},{"header":"4 Simulation results","content":"\u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e presents CST simulation results for the polarization converter under TE- and TM-polarized plane wave illumination across varying incidence angles.\u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, resonant dips occur in the 1\u0026ndash;1.8 THz range for co-polarized reflections (TE/TE and TM/TM), reaching approximately \u0026minus;\u0026thinsp;15 dB. These minima arise from destructive interference between incident and reflected waves. Conversely, cross-polarized reflections (TE/TM and TM/TE) exhibit near-unity magnitude (approaching 0 dB) across this bandwidth (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea), confirming efficient polarization conversion. This demonstrates the FSS metasurface enables robust TE/TM mode conversion over 1\u0026ndash;1.8 THz.\u003c/p\u003e \u003cp\u003eThe stacked SRR layers create multiple reflection paths for incident waves. Phase oscillations result from interference between waves reflected from the top resonator layer and also from waves penetrating deeper layers and reflecting from subsequent resonators/substrates. Phase changes linearly between resonances (e.g., smooth slopes in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb) represent propagation delays through dielectric layers and the slope magnitude (\u003cem\u003edω/dϕ\u003c/em\u003e) relates to the effective electrical length of the structure.\u003c/p\u003e \u003cp\u003eFigure 4 depicts the reflection coefficient magnitude ∣S11∣ of the FSS filter as a function of frequency (0–2 THz) and incidence angle (0°–90°). Subfigures (a), (b), (c), and (d) present results for TE→TE, TE→TM, TM→TM, and TM→TE polarization conversions, respectively. Critically, within the 1–1.8 THz frequency range and incidence angles of 0°–60°, the reflection coefficient for co-polarized conversions (TE→TE and TM→TM) remains very low (approaching 0), while cross-polarized conversions (TE→TM and TM→TE) exhibit consistently high values (approaching 1). This confirms efficient polarization rotation across broad spectral and angular regimes.\u003c/p\u003e \u003cp\u003eFigure 5 illustrates the surface current distributions across the three split-ring resonators (SRR₁, SRR₂, SRR₃) within the FSS metasurface at four resonant frequencies. At 1 THz (Fig.\u0026nbsp;5a), currents localize predominantly along SRR₃'s inner edges, indicating fundamental resonance excitation. Minimal activity occurs in SRR₁, while SRR₂ exhibits weak coupling. By 1.3 THz (Fig.\u0026nbsp;5b), the resonance shifts to SRR₂-dominant with symmetric current patterns, accompanied by diminished SRR₁/SRR₃ contributions. At 1.6 THz (Fig.\u0026nbsp;5c), strong hybrid resonance emerges between SRR₃ and SRR₁, with secondary SRR₂ excitation. Finally, at 1.8 THz (Fig.\u0026nbsp;5d), asymmetric currents intensify in SRR₂ and SRR₃, while SRR₁ participation remains negligible.\u003c/p\u003e \u003cp\u003eThese distinct modal distributions confirm that coupled SRR resonances generate destructive interference, producing the sharp reflection minima at 1.0, 1.3, 1.6, and 1.8 THz observed in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. This multi-resonator synergy enables precise spectral control across the 1\u0026ndash;1.8 THz operational band.\u003c/p\u003e\u003cp\u003eComplementary field analyses (Fig.\u0026nbsp;6) elucidate wave-matter interactions. The electric field (Figs.\u0026nbsp;6a, 6c) concentrates at unit-cell boundaries, traversing SRRs as electric dipoles. At 1 THz, strong confinement occurs at SRR₃ (Fig.\u0026nbsp;6a), shifting to SRR₂ at 1.3 THz (Fig.\u0026nbsp;6c) consistent with current distributions. Conversely, the magnetic field (Figs.\u0026nbsp;6b, 6d) circulates around resonator edges, confirming distinct polarization-dependent coupling mechanisms.\u003c/p\u003e"},{"header":"5 Discussions","content":"\u003cp\u003eTo model the frequency-selective response of the metasurface, an equivalent circuit was developed that accounts for both Fabry-Perot resonances in the dielectric stack and split-ring resonator interactions. The circuit (Fig.\u0026nbsp;7a) employs four cascaded transmission line segments (TLIN₁\u0026ndash;TLIN₄) corresponding to the SiO₂ cap (\u003cem\u003eh\u003c/em\u003e₁) and silicon interval-layers (\u003cem\u003eh\u003c/em\u003e₂\u0026ndash;\u003cem\u003eh\u003c/em\u003e₄), with electrical lengths proportional to physical layer thicknesses. Each split-ring resonator is represented by coupled LC networks where the conductive rings provide series inductance (\u003cem\u003eL\u003c/em\u003e) and the capacitive gaps introduce shunt capacitance (\u003cem\u003eC\u003c/em\u003e). Impedance discontinuities at dielectric interfaces are inherently modeled through transmission line impedance variations, not explicit grounding. The circuit is terminated with 377 Ω ports to emulate standard measurement conditions.\u003c/p\u003e \u003cp\u003eValidation in Fig.\u0026nbsp;7b demonstrates reasonable agreement between circuit simulations and full-wave results across the 1\u0026ndash;1.8 THz operating band, confirming its ability to predict: 1) Fabry-Perot resonance frequencies governed by cumulative layer thicknesses, 2) resonance quality factors controlled by SRR LC ratios, and 3) cross-polarization efficiency linked to gap capacitance asymmetry. This model enables performance tuning through parameter adjustments: Increasing SRR gap widths (\u003cem\u003eW\u003c/em\u003e₁, \u003cem\u003eW\u003c/em\u003e₂, \u003cem\u003eW\u003c/em\u003e₃) reduces shunt capacitance, broadening resonance bandwidths; modifying ring radii scales inductance, shifting coupled-resonance frequencies; and varying layer thicknesses (\u003cem\u003eh\u003c/em\u003e₁\u0026ndash;\u003cem\u003eh\u003c/em\u003e₄) alters transmission line lengths, controlling Fabry-Perot mode spacing. Physical dimensions thereby map directly to circuit components for targeted THz spectral shaping.\u003c/p\u003e \u003cp\u003eFabrication feasibility guided the metasurface design, with materials selected for THz-optimized dielectric properties and microfabrication compatibility. The process, detailed in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e8\u003c/span\u003e, begins with a high-resistivity silicon substrate (\u0026gt;\u0026thinsp;10 kΩ\u0026middot;cm) to minimize THz absorption. A 5\u0026ndash;10 nm chromium adhesion layer is deposited via e-beam evaporation, followed by 200 nm copper to form the base conductive plane.\u003c/p\u003e \u003cp\u003eThe first SRR layer is patterned using photolithography: photoresist spin-coating, UV exposure through a photomask defining ring geometry (radius R₁ = 16.6 \u0026micro;m, gap \u003cem\u003eC\u003c/em\u003e₁ = 2.25 \u0026micro;m), development, and 100 nm copper evaporation. Liftoff yields the defined SRRs. Low-pressure chemical vapor deposition (LPCVD) then grows a 10.0 \u0026micro;m crystalline silicon spacer (\u003cem\u003eh\u003c/em\u003e₄).\u003c/p\u003e \u003cp\u003eThe sequence repeats for subsequent layers: Photolithography patterns SRR₂ (\u003cem\u003eR\u003c/em\u003e₂ = 23.0 \u0026micro;m, \u003cem\u003eC\u003c/em\u003e₂ = 5.9 \u0026micro;m) followed by 100 nm copper evaporation and LPCVD of a 9.15 \u0026micro;m silicon layer (\u003cem\u003eh\u003c/em\u003e₃). Precise alignment ensures functional integrity during SRR₃ patterning (\u003cem\u003eR\u003c/em\u003e₃ = 31.6 \u0026micro;m, \u003cem\u003eC\u003c/em\u003e₃ = 7.3 \u0026micro;m), copper evaporation, and deposition of the final 10.5 \u0026micro;m silicon spacer (\u003cem\u003eh\u003c/em\u003e₂) via LPCVD.\u003c/p\u003e \u003cp\u003eA 26.3 \u0026micro;m silicon dioxide cap layer is deposited by plasma-enhanced CVD (PECVD) in staged cycles (\u0026lt;\u0026thinsp;5 \u0026micro;m/layer) with 300\u0026deg;C anneals to mitigate film stress. Alternatively, spin-on-glass (SOG) with pyrolysis annealing provides a stress-relieved oxide. Critical features\u0026mdash;including subwavelength periodicity (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;34.7 \u0026micro;m) and ring widths down to \u003cem\u003eW\u003c/em\u003e₁=2.7 \u0026micro;m\u0026mdash;are achievable through i-line photolithography or electron-beam patterning.\u003c/p\u003e \u003cp\u003eThis fabrication framework enables physical realization of the broadband polarization converter, with design parameters aligning with standard microfabrication capabilities for THz system integration.\u003c/p\u003e "},{"header":"Conclusion","content":"\u003cp\u003eThis work demonstrates a multi-layer FSS metasurface achieving efficient, angularly stable TE-TM polarization conversion across 1\u0026ndash;1.8 THz. By vertically stacking copper ring resonators on a silicon/silicon dioxide platform, the design enables\u0026thinsp;\u0026gt;\u0026thinsp;90% conversion efficiency while maintaining robust performance for incidence angles up to 60\u0026deg;\u0026mdash;significantly outperforming conventional single-layer converters. Three key advances underpin this breakthrough: Broadband operation stems from four coupled resonances (1.0, 1.3, 1.6, 1.8 THz) generated through Fabry-Perot modes in dielectric spacers and SRR hybridization; angular insensitivity arises from optimized periodicity (p\u0026thinsp;=\u0026thinsp;34.7 \u0026micro;m) and substrate thicknesses; and CMOS-compatible fabrication employs lithographically patterned copper resonators (minimum feature width 2.7 \u0026micro;m) with LPCVD/PECVD dielectric stacking. Validated through full-wave simulations and equivalent circuit modeling, this architecture overcomes fundamental limitations of narrow bandwidth and angular sensitivity in THz polarization control. The design is readily integrable into 6G communication systems (beamforming arrays), polarization-sensitive imaging diagnostics, and material birefringence sensors. Future work will explore active tuning via vanadium dioxide interlayers and experimentally validate the staged PECVD fabrication process.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eS.R. conceived and designed the study, performed the simulations and data analysis, interpreted the results, and wrote the manuscript. M.N. supervised the work, provided scientific guidance, and contributed to the revision, editing, and final approval of the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAhmad, T., Rahim, A.A., Bilal, R.M.H., Noor, A., Maab, H., Naveed, M.A., Madni, A., Ali, M.M., Saeed, M.A.: Ultrawideband Cross-Polarization Converter Using Anisotropic Reflective Metasurface. Electronics. 11, 487 (2022). https://doi.org/10.3390/electronics11030487\u003c/li\u003e\n\u003cli\u003eAko, R.T., Lee, W.S.L., Atakaramians, S., Bhaskaran, M., Sriram, S., Withayachumnankul, W.: Ultra-wideband tri-layer transmissive linear polarization converter for terahertz waves. APL Photonics. 5, 046101 (2020). https://doi.org/10.1063/1.5144115\u003c/li\u003e\n\u003cli\u003eAkyildiz, I.F., Han, C., Nie, S.: Combating the Distance Problem in the Millimeter Wave and Terahertz Frequency Bands. IEEE Commun. Mag. 56, 102\u0026ndash;108 (2018). https://doi.org/10.1109/MCOM.2018.1700928\u003c/li\u003e\n\u003cli\u003eChen, H.-T.: Interference theory of metamaterial perfect absorbers. Opt. Express. 20, 7165 (2012). https://doi.org/10.1364/OE.20.007165\u003c/li\u003e\n\u003cli\u003eCheng, Y.Z., Withayachumnankul, W., Upadhyay, A., Headland, D., Nie, Y., Gong, R.Z., Bhaskaran, M., Sriram, S., Abbott, D.: Ultrabroadband reflective polarization convertor for terahertz waves. Appl. Phys. Lett. 105, 181111 (2014). https://doi.org/10.1063/1.4901272\u003c/li\u003e\n\u003cli\u003eCong, L., Pitchappa, P., Wu, Y., Ke, L., Lee, C., Singh, N., Yang, H., Singh, R.: Active Multifunctional Microelectromechanical System Metadevices: Applications in Polarization Control, Wavefront Deflection, and Holograms. Advanced Optical Materials. 5, 1600716 (2017). https://doi.org/10.1002/adom.201600716\u003c/li\u003e\n\u003cli\u003eDong, G.-X., Shi, H.-Y., Xia, S., Li, W., Zhang, A.-X., Xu, Z., Wei, X.-Y.: Ultra-broadband and high-efficiency polarization conversion metasurface with multiple plasmon resonance modes. Chinese Phys. B. 25, 084202 (2016). https://doi.org/10.1088/1674-1056/25/8/084202\u003c/li\u003e\n\u003cli\u003eFei, P., Vandenbosch, G.A.E., Guo, W., Wen, X., Xiong, D., Hu, W., Zheng, Q., Chen, X.: Versatile Cross‐Polarization Conversion Chiral Metasurface for Linear and Circular Polarizations. Advanced Optical Materials. 8, 2000194 (2020). https://doi.org/10.1002/adom.202000194\u003c/li\u003e\n\u003cli\u003eFerguson, B., Zhang, X.-C.: Materials for terahertz science and technology. Nature Mater. 1, 26\u0026ndash;33 (2002). https://doi.org/10.1038/nmat708\u003c/li\u003e\n\u003cli\u003eGlybovski, S.B., Tretyakov, S.A., Belov, P.A., Kivshar, Y.S., Simovski, C.R.: Metasurfaces: From microwaves to visible. Physics Reports. 634, 1\u0026ndash;72 (2016). https://doi.org/10.1016/j.physrep.2016.04.004\u003c/li\u003e\n\u003cli\u003eGoldstein, D.H.: Polarized Light. CRC Press (2017)\u003c/li\u003e\n\u003cli\u003eGrady, N.K., Heyes, J.E., Chowdhury, D.R., Zeng, Y., Reiten, M.T., Azad, A.K., Taylor, A.J., Dalvit, D.A.R., Chen, H.-T.: Terahertz Metamaterials for Linear Polarization Conversion and Anomalous Refraction. Science. 340, 1304\u0026ndash;1307 (2013). https://doi.org/10.1126/science.1235399\u003c/li\u003e\n\u003cli\u003eHe, J., Xie, Z., Wang, S., Wang, X., Kan, Q., Zhang, Y.: Terahertz polarization modulator based on metasurface. J. Opt. 17, 105107 (2015). https://doi.org/10.1088/2040-8978/17/10/105107\u003c/li\u003e\n\u003cli\u003eJepsen, P.U., Cooke, D.G., Koch, M.: Terahertz spectroscopy and imaging \u0026ndash; Modern techniques and applications. Laser \u0026amp;amp; Photonics Reviews. 5, 124\u0026ndash;166 (2011). https://doi.org/10.1002/lpor.201000011\u003c/li\u003e\n\u003cli\u003eKildishev, A.V., Boltasseva, A., Shalaev, V.M.: Planar Photonics with Metasurfaces. Science. 339, 1232009 (2013). https://doi.org/10.1126/science.1232009\u003c/li\u003e\n\u003cli\u003eLi, L., Wang, Y., Wang, X., Chen, M. eds: Advances in Terahertz Detection and Imaging. Frontiers Media SA (2022)\u003c/li\u003e\n\u003cli\u003eMasson, J.-B., Gallot, G.: Terahertz achromatic quarter-wave plate. Opt. Lett. 31, 265 (2006). https://doi.org/10.1364/OL.31.000265\u003c/li\u003e\n\u003cli\u003eMittleman, D.M.: Twenty years of terahertz imaging [Invited]. Opt. Express. 26, 9417 (2018). https://doi.org/10.1364/OE.26.009417\u003c/li\u003e\n\u003cli\u003eParratt, L.G.: Surface Studies of Solids by Total Reflection of X-Rays. Phys. Rev. 95, 359\u0026ndash;369 (1954). https://doi.org/10.1103/PhysRev.95.359\u003c/li\u003e\n\u003cli\u003ePendry, J.B., Holden, A.J., Robbins, D.J., Stewart, W.J.: Magnetism from conductors and enhanced nonlinear phenomena. IEEE Trans. Microwave Theory Techn. 47, 2075\u0026ndash;2084 (1999). https://doi.org/10.1109/22.798002\u003c/li\u003e\n\u003cli\u003eRappaport, T.S., Xing, Y., Kanhere, O., Ju, S., Madanayake, A., Mandal, S., Alkhateeb, A., Trichopoulos, G.C.: Wireless Communications and Applications Above 100 GHz: Opportunities and Challenges for 6G and Beyond. IEEE Access. 7, 78729\u0026ndash;78757 (2019). https://doi.org/10.1109/ACCESS.2019.2921522\u003c/li\u003e\n\u003cli\u003eRashid, A., Murtaza, M., Zaidi, S.A.A., Zaki, H., Tahir, F.A.: A single-layer, wideband and angularly stable metasurface based polarization converter for linear-to-linear cross-polarization conversion. PLoS ONE. 18, e0280469 (2023). https://doi.org/10.1371/journal.pone.0280469\u003c/li\u003e\n\u003cli\u003eSiegel, P.H.: Terahertz technology. IEEE Trans. Microwave Theory Techn. 50, 910\u0026ndash;928 (2002). https://doi.org/10.1109/22.989974\u003c/li\u003e\n\u003cli\u003eSmith, D.R., Padilla, W.J., Vier, D.C., Nemat-Nasser, S.C., Schultz, S.: Composite Medium with Simultaneously Negative Permeability and Permittivity. Phys. Rev. Lett. 84, 4184\u0026ndash;4187 (2000). https://doi.org/10.1103/PhysRevLett.84.4184\u003c/li\u003e\n\u003cli\u003eSun, J., Liu, L., Dong, G., Zhou, J.: An extremely broad band metamaterial absorber based on destructive interference. Opt. Express. 19, 21155 (2011). https://doi.org/10.1364/OE.19.021155\u003c/li\u003e\n\u003cli\u003eTonouchi, M.: Cutting-edge terahertz technology. Nature Photon. 1, 97\u0026ndash;105 (2007). https://doi.org/10.1038/nphoton.2007.3\u003c/li\u003e\n\u003cli\u003eWoodward, R.M., Wallace, V.P., Pye, R.J., Cole, B.E., Arnone, D.D., Linfield, E.H., Pepper, M.: Terahertz Pulse Imaging of ex vivo Basal Cell Carcinoma. Journal of Investigative Dermatology. 120, 72\u0026ndash;78 (2003). https://doi.org/10.1046/j.1523-1747.2003.12013.x\u003c/li\u003e\n\u003cli\u003eXiong, H., Hong, J.-S., Luo, C.-M., Zhong, L.-L.: An ultrathin and broadband metamaterial absorber using multi-layer structures. Journal of Applied Physics. 114, 064109 (2013). https://doi.org/10.1063/1.4818318\u003c/li\u003e\n\u003cli\u003eXu, J., Li, R., Qin, J., Wang, S., Han, T.: Ultra-broadband wide-angle linear polarization converter based on H-shaped metasurface. Opt. Express. 26, 20913 (2018). https://doi.org/10.1364/OE.26.020913\u003c/li\u003e\n\u003cli\u003eYang, J., Li, K., Zha, X., Zhang, G., Xi, H., Deng, G., Li, Y., Yin, Z.: High-efficiency reflective terahertz cross-polarization converter with broadband and wide-angle response. Appl. Opt. 63, 3212 (2024). https://doi.org/10.1364/AO.517364\u003c/li\u003e\n\u003cli\u003eYu, N., Genevet, P., Kats, M.A., Aieta, F., Tetienne, J.-P., Capasso, F., Gaburro, Z.: Light Propagation with Phase Discontinuities: Generalized Laws of Reflection and Refraction. Science. 334, 333\u0026ndash;337 (2011). https://doi.org/10.1126/science.1210713\u003c/li\u003e\n\u003cli\u003eZhang, B., Zhu, C., Zhang, R., Yang, X., Wang, Y., Liu, X.: Ultra-Broadband Angular-Stable Reflective Linear to Cross Polarization Converter. Electronics. 11, 3487 (2022). https://doi.org/10.3390/electronics11213487\u003c/li\u003e\n\u003cli\u003eZhang, S., Fan, W., Panoiu, N.C., Malloy, K.J., Osgood, R.M., Brueck, S.R.J.: Experimental Demonstration of Near-Infrared Negative-Index Metamaterials. Phys. Rev. Lett. 95, 137404 (2005). https://doi.org/10.1103/PhysRevLett.95.137404\u003c/li\u003e\n\u003cli\u003eZheludev, N.I., Kivshar, Y.S.: From metamaterials to metadevices. Nature Mater. 11, 917\u0026ndash;924 (2012). https://doi.org/10.1038/nmat3431\u003c/li\u003e\n\u003cli\u003eZhou, X., Xu, X., Chen, X., Chen, J.: Magic wavelengths for terahertz clock transitions. Phys. Rev. A. 81, 012115 (2010). https://doi.org/10.1103/PhysRevA.81.012115\u003c/li\u003e\n\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":"optical-and-quantum-electronics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"oqel","sideBox":"Learn more about [Optical and Quantum Electronics](https://www.springer.com/journal/11082)","snPcode":"11082","submissionUrl":"https://submission.nature.com/new-submission/11082/3","title":"Optical and Quantum Electronics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Terahertz metasurface, Angularly stable frequency selective surface (FSS), Split-ring resonators (SRR), Broadband polarization conversion, Bidirectional mode conversion, polarization converter","lastPublishedDoi":"10.21203/rs.3.rs-8320718/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8320718/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis paper introduces a compact three-layer metasurface polarization converter for efficient bidirectional transverse electric (TE) to transverse magnetic (TM) mode conversion in the terahertz (THz) regime. The design overcomes critical limitations of conventional converters\u0026mdash;narrow bandwidth and angular sensitivity\u0026mdash;using vertically stacked copper split-ring resonators (SRRs) on a silicon substrate. Through optimized phase and resonance tuning, the metasurface achieves\u0026thinsp;\u0026gt;\u0026thinsp;90% polarization conversion efficiency across a broad 1\u0026ndash;1.8 THz bandwidth while maintaining robust performance for incidence angles up to 60\u0026deg;. Full-wave simulations validate its angular insensitivity and bidirectional functionality, with surface current and field analyses elucidating the multi-resonance mechanism. Fabrication feasibility is ensured via standard copper/SiO₂ deposition and photolithography processes. This high-performance, readily integrable design advances THz applications requiring dynamic polarization control, including communications, imaging, and sensing systems.\u003c/p\u003e","manuscriptTitle":"Broadband Angularly Stable Polarization Conversion in Terahertz Band via Vertically Stacked Frequency Selective Surface Metasurface","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-23 04:30:17","doi":"10.21203/rs.3.rs-8320718/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-01-15T01:18:04+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-01-04T06:13:28+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-27T13:15:00+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-26T07:56:16+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"241926549612399800256382404308324762566","date":"2025-12-22T01:25:16+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"147675347047790249263151219744618319493","date":"2025-12-19T08:53:34+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"241264448539456620918485309455167476778","date":"2025-12-19T08:38:08+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-12-19T07:43:19+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-12-11T01:16:03+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-12-10T13:17:11+00:00","index":"","fulltext":""},{"type":"submitted","content":"Optical and Quantum Electronics","date":"2025-12-09T18:43:19+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"optical-and-quantum-electronics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"oqel","sideBox":"Learn more about [Optical and Quantum Electronics](https://www.springer.com/journal/11082)","snPcode":"11082","submissionUrl":"https://submission.nature.com/new-submission/11082/3","title":"Optical and Quantum Electronics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"8742114c-7513-46dc-a148-8117977260c1","owner":[],"postedDate":"December 23rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-04-07T16:18:03+00:00","versionOfRecord":{"articleIdentity":"rs-8320718","link":"https://doi.org/10.1007/s11082-026-08776-6","journal":{"identity":"optical-and-quantum-electronics","isVorOnly":false,"title":"Optical and Quantum Electronics"},"publishedOn":"2026-04-04 16:00:14","publishedOnDateReadable":"April 4th, 2026"},"versionCreatedAt":"2025-12-23 04:30:17","video":"","vorDoi":"10.1007/s11082-026-08776-6","vorDoiUrl":"https://doi.org/10.1007/s11082-026-08776-6","workflowStages":[]},"version":"v1","identity":"rs-8320718","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8320718","identity":"rs-8320718","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}