Ultrasensitive fiber-optic temperature sensor based on cascaded Sagnac interferometers with a nematic liquid crystal film

We demonstrated an ultrasensitive fiber-optic temperature sensor based on cascaded Sagnac interferometers (CSIs). One of the Sagnac interferometers (SIs) consisted of a panda polarization-maintaining fiber (PMF) as the reference arm, while the other one contained two single-mode patch cables in a ferrule matching sleeve as the sensing arm, where a nematic liquid crystal (NLC) film was infiltrated into the micron-scale gap of the sleeve. In the sensing SI, the orientation of NLC film was induced by just rotating the two single-mode patch cables without any orientation agent, electric, or magnetic devices. Vernier effect was acquired by adjusting the thickness of NLC film. Experimental results revealed that the temperature sensitivity of the CSIs was up to 43.13 nm/°C, which was enhanced about 5 times compared to the single NLC SI. The designed optical fiber temperature sensor possessed the merits of compact structure, high stability, ultrahigh sensitivity, low hysteresis effect and high resolution, showing a promising application prospect in some scientific filed requiring accurate temperature measurement, such as biomolecules, medicine and other filed.