Etch-free dual-mode electro-optic metasurface enabled by hybrid photoresist integration

All-dielectric metasurfaces exhibit remarkable capabilities for optical wavefront manipulation; however, the growing demands of optical communication, integrated optical computing, and reconfigurable neuromorphic photonic networks have shifted research focus toward electro-optical metasurfaces, which enable active control of electromagnetic responses. Despite their effectiveness in dynamic light modulation, electro-optical metasurfaces face critical challenges in achieving low-voltage operation and fabrication simplicity. To address these limitations, we propose a novel design incorporating a photoresist-based perturbation layer and a barium titanate (BTO) localized layer, leveraging BTO's high Pockels coefficient to facilitate both quasi-bound states in the continuum (Q-BIC) and guided mode resonance (GMR). Under x-polarized illumination, a high-quality-factor continuous-spectrum quasi-bound-state (Q-BIC) resonance (Q≈6 × 10⁵) is generated at 1550 nm, facilitated by symmetry breaking in the upper-layer dimer photoresist structure. Additionally, a guided mode (GMR) resonance (Q≈1.65 × 10⁵) is induced at 1547.32 nm under y-polarized excitation, triggered by a single rectangular photoresist structure. Moreover, both modes exhibit excellent modulation effects with refractive index changes of 5 × 10^-5 and 3 × 10^-4, respectively. We also performed band structure calculations on the model, further validating the simulation results: The Q-BIC mode manifests as a dark mode at the Γ point with a resonance at 1500 nm, which can transition to a bright mode via symmetry breaking; whereas the GMR mode exhibits degeneracy at the Γ point and displays distinctly different dispersion relations along different directions. This work advances the development of etch-free, photoresist-integrated electro-optical materials while expanding the practical applicability of active metasurfaces in next-generation optical communication systems.