Highly sensitive electro-optic probe incorporating an ultra-high Q-factor LiNbO₃ etalon

A highly sensitive electro-optic (EO) probe has been proposed and realized by tethering an ultra-high-quality (Q)-factor LiNbO₃ etalon to a single-mode fiber operating at around a 1550-nm wavelength. For the adopted EO etalon, the electric-field-induced refractive index modification is deemed to shift its own spectral response. An electrical modulation signal is anticipated to be produced when a probe light beam with a fixed bias wavelength impinges upon the EO etalon. The EO etalon is particularly required to exhibit a remarkably steep spectral response and thus facilitate modulation efficiency. In aiming to scrutinize the performance in terms of sensitivity, two EO probes involving profoundly different Q-factors were prepared and applied to detect the electric field emitted from a microstrip device. It was confirmed that the sensitivity could be efficiently enhanced by as much as 28 dB by boosting the Q-factor 18 times when a probe light beam operating at =∼1550  nm was properly collimated and polarized. Accordingly, the minimum detectable signal was successfully diminished.