Fiber-optic temperature sensor interrogation technique based on an optoelectronic oscillator

Abstract

We have proposed and experimentally demonstrated a fiber-optic temperature sensing system based on an optoelectronic oscillator (OEO). A part of the fiber in the oscillator loop is used as the sensing fiber. As the free spectrum range (FSR) of the OEO is determined by the length of the oscillator loop, when the temperature of the sensing fiber is changed, the refractive index of the fiber varies; thus, the optical path length changes as well as the FSR of the OEO. By tracking one peak of the OEO harmonics, the temperature variation can be monitored. Therefore, the temperature variation can be converted to the frequency shift of the radio frequency signals. In the experiment, we have measured the spectra of the OEO with different temperatures, which show good sensing linearity. We have also measured the relationship between the sensing responsivity and the tracked frequency (1.0, 1.5, 2.0, and 3.0 GHz) in the experiment, which shows that the harmonics at a higher frequency produce a higher sensing responsivity. The proposed temperature sensing system exhibits good tunability, stability, linearity tailorable sensing responsivity, and ease of implementation, thus it shows good application potential in remote fiber-optical temperature sensing and monitoring.