Electric Field Sensing of Etchless Lithium Niobate Heterostructure with Low Driving Voltage based on Quasibound States in the Continuum

Abstract

Abstract Realizing lithium niobate-based electric field (E-field) sensor for low driving voltage has been attractive extensive attention in field of extremely weak electric field detection, wireless communications, and even astronomical observations. However, lithium niobate (LN) is difficult to be etched with high accuracy. Here, we theoretically proposed a heterostructure E-field sensor consisted of etchless LN thin film and metagratings to support Fabry-Perot-like BIC mode, which has not only ultrahigh quality (Q) factor but also large extinction ratio. Due to the loss of electrodes, the BIC mode transitions into quasi-BIC resonance with Q factor of 2050. This quasi-BIC resonance is utilized to confine electromagnetic field inside the LN layer leading to an optical field enhancement factor to 14.2 times normalized to unpatterned thin film LN. And this resonance also boosts the strong interaction among optical field, EO material and applied electric field. Numerical simulations are carried out to demonstrate the Fabry-Perot-like quasi-BIC resonance is sensitive to the refractive index change Δn of LN material. As a result, we construct the relationship between the Δn and the applied electric field and successfully obtained a tuning sensitivity of 40.8 nm/V and low driving voltage of 18.9 mV with wavelength resolution of 0.38 nm. Meanwhile, we estimate the 3dB bandwidth of the E-field sensor should exceed 154 GHz after considering the low parasitic capacitance of LN material and high conductivity of electrodes. And we believe that the LN-based heterostructure has potential applications in ultralow driving voltage E-field sensors.