  Electric field detection has been widely utilized in many fields such as
scientific research and integrated circuits. To enhance the tuning sensitivity
of E-field sensor, in this paper, we theoretically proposed a highly sensitive
E-field sensor composed of etchless lithium niobate (LN) material and hybrid
coupling-grating systems in the visible near-infrared regime. Such
configuration supports high-quality factor quasi-BIC resonance, which generates
strong localized field confinement. Due to the large electro-optic coefficient
of LN material, one can shift the wavelength and reflection ratio of resonance
by tuning the refractive index of LN material. An analytical theory is carried
out to explain the relationship between the refractive index variations and the
applied voltages, so we successfully obtained a tuning sensitivity of 40.8 nm/V
and a minimum detectable electric field amplitude of 24.5 mV with wavelength
resolution of 1 nm. Due to the low parasitic capacitance of LN material and
high conductivity of gold film and ITO layer which are utilized as the
electrodes, the 3dB bandwidth of the devices should exceed 154 GHz. And we
believe that such a surface-normal E-field sensor has extensive potential for
the extremely weak electric field detection.
