A method of PLL detection applied in fiber optic evanescent wave temperature sensor

A method of phase-lock loop (PLL) detection applied in fiber optic evanescent wave temperature sensor is presented in this paper. The fiber optic evanescent wave sensor is fabricated by a fiber optic coupler whose cladding of waist is replaced by temperature sensitive material. In order to demonstrate its sensitivity to temperature with high stability, the PLL detection circuit to measure the temperature variety with high accuracy is be described in detail. Compared with conventional DC signal detection, the PLL detection technique has great improvement on denoise, which is able to detect weak signal buried in noise. Experiments demonstrated that the resolution to temperature could reach 0.091degC with such temperature sensor system.