Electrical field sensing in an etchless lithium niobate heterostructure with Low driving voltage based on quasi-bound states in the continuum

Abstract

Realizing lithium niobate-based electric eld (E-eld) sensor for low driving voltage has been attractive extensive attention in eld of extremely weak electric eld detection, wireless communications, and even astronomical observations. However, lithium niobate (LN) is di cult to be etched with high accuracy.Here, we theoretically proposed a heterostructure E-eld sensor consisted of etchless LN thin lm 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 con ne electromagnetic eld inside the LN layer leading to an optical eld enhancement factor to 14.2 times normalized to unpatterned thin lm LN. And this resonance also boosts the strong interaction among optical eld, EO material and applied electric eld. Numerical simulations are carried out to demonstrate the Fabry-Perotlike 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 eld 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-eld 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-eld sensors.