Drift-Free Characterization of Electro-Optic Tuning Efficiency in Lithium Niobate Photonic Nanocavities

Abstract

Lithium niobate photonic crystal nanobeam cavity (PCNBC) provides a promising platform for integrated electro-optics, offering deep subwavelength mode confinement, enhanced light-matter interactions, and ultralow power consumption. However, accurate characterization of the electro-optic (EO) tuning efficiency in such high-Q devices is fundamentally impeded by DC drift, a time-dependent spectral instability arising from charge redistribution, surface screening, or buffer-layer relaxation under sustained electric fields. Here, we report the systematic analysis of DC drift dynamics in lithium niobate nanocavities and demonstrate that conventional quasi-static DC voltage scanning introduces substantial uncertainty into the extracted EO tuning efficiency. To circumvent this limitation, we introduce a drift-free, dynamic measurement methodology that employs high-frequency triangular-wave voltage sweeps to effectively decouple the instantaneous electronic Pockels response from slow charge relaxation processes. Validated across 35 devices with varying electrode geometries, our method delivers a reproducible tuning efficiency of 4.3–4.5 pm/V with a low coefficient of variation of 1.1%, showing excellent quantitative agreement with three-dimensional finite-element simulations. This robust, drift-free measurement technique establishes a reliable methodology for the characterization and optimization of resonant cavity electro-optics, accelerating the development of high-performance thin-film lithium niobate photonic integrated circuits.