Mechanically Tunable High‐Q Terahertz Fabry‐Perot Resonances in a Symmetric Misalignment‐Tolerant Metasurface Cavity

ABSTRACT Developing electromagnetic platforms that can overcome the trade‐off between high Q‐factors and low insertion loss remains a challenge for terahertz (THz) platforms. By coupling Fabry‐Perot (FP) resonance with a symmetric bilayer metasurface architecture, this study develops a copper‐based cruciform aperture cavity that transcends the performance bottlenecks of conventional structures. Simulation results demonstrate that the device achieves FP‐mode resonance at 0.228 THz, 0.252 THz, and 0.277 THz, with Q‐factors of 207 (transmittance > 94%), 537 (transmittance > 92%) and 1153 (transmittance > 88%), respectively. Its inherent structural symmetry ensures a polarization‐insensitive response, while the cavity interference mechanism provides exceptionally robust filtering performance with high tolerance against lateral offsets along the x ‐ and y ‐directions and mutual layer rotations. The cavity exhibits structural robustness in the lower frequency bands, while higher‐order resonance modes with Q‐factors reaching several thousand are excited at higher frequencies. Furthermore, continuous broadband tuning of the resonant frequency is achievable by modulating the interlayer spacing. Experimental results demonstrate a FP resonance at 0.228 THz with a Q‐factor over 191 and transmittance of 58%. This work establishes a mechanically tunable and misalignment‐tolerant metasurface cavity platform for robust THz spectral control, paving the way toward non‐destructive material characterization and high‐performance filtering devices.