Thermo-Optic Tuning in an Optical Fiber Ring Laser With a Nematic Liquid Crystal Film-Embedded Sagnac Interferometer

Nematic liquid crystal (NLC) has been widely researched in temperature sensors because of its large negative temperature coefficient and unique optical anisotropy. In this article, a tunable temperature sensor based on an optical fiber ring laser (FRL) with an NLC film-embedded Sagnac interferometer (SI) was experimentally studied. By filling NLC film into a gap with hundreds of microns thick in the SI, a tunable and high spacial resolution temperature sensor was achieved. Compared to the traditional SI, the resultant sensor based on FRL with an NLC film-embedded SI in it showed a narrow 3 dB bandwidth and an ultrahigh resolution ( ${R}{)}$ . At the NLC film thickness of $288.21 ~\mu \text{m}$ , the temperature sensitivity [ ${S}{(}{t}{)}$ ], detection limit (DL), and quality factor ( ${Q}{)}$ of the resultant sensor were −3.16 nm/°C, $- 5.38\times 10^{-{3}}\,\,^{\circ }\text{C}$ , and $6.99\times 10^{{3}}$ , respectively. Experimental results also indicated that the temperature sensing characteristic could be further improved by shortening the thickness of the NLC film. This kind of sensor, which shows high ${R}$ and DL has great application potential in temperature monitoring in biomedicine, environmental monitoring, agricultural engineering, health monitoring, and aerospace.