An Electrooptic Sensor with Sub-millivolt Sensitivity Using a Nonlinear Optical Disk resonator

A high sensitive electro-optic (EO) sensing technique with a nonlinear optical disk resonator made of LiNbO3was demonstrated. The high Q factor of the resonator allows strong enhancement of sensitivity. In order to apply optical heterodyne technique and downconvert EO signal to sub-MHz, the modulated light was coupled into the disk resonator. Electromagnetic-field intensity on a microstrip transmission line was measured. The strong peaks of EO signal were observed at the frequency of 6.7 GHz and 13.4 GHz for the resonator with diameter of 6.6 mm. The estimated minimum detectable signal amplitude at the optimum frequency was 0.13 mV/Hz^-1/2.