Electro-Optic Lithium Niobate Metasurface Enabling Dynamic Polarization Control

Compact electro-optical (EO) polarization modulators are essential for diverse applications in optical communication, quantum information processing, and sensing. To meet the demand for miniaturized and tunable photonic elements, metasurfaces offer a promising solution. Here, we demonstrate an EO-lithium niobate (LN) metasurface that enables dynamic polarization modulation in the transmission geometry. By applying in-plane electric fields along the optic axis, the resonance-enhanced birefringence of the LN metasurface is modulated, enabling voltage-controlled tuning of both the polarization azimuth and the ellipticity. Numerical simulations reveal that the anisotropic EO response enables resonance-assisted polarization control accompanied by polarization-dependent intensity and phase modulation. A full 90° polarization azimuth rotation and handedness reversal are achieved under an alternating positive and negative bias. Experimentally, under a ±50 V drive, we observe clear modulation of both polarization orientation and ellipticity, with measured maximum responses of 0.016°/V and 0.017°/V, respectively. These results establish EO-LN metasurfaces as a compact and reconfigurable platform for ultracompact polarization control and dynamically tunable photonic devices.