Sensitivity amplification of high birefringence fiber loop mirror temperature sensor with Vernier effect

A fiber optic temperature sensor consisting of two cascaded high birefringence fiber loop mirrors (Hi-Bi FLMs) was proposed and experimentally demonstrated to enhance the temperature sensitivity and resolution by Vernier effect. The FSRs for the two Hi-Bi FLMs are designed to be slightly different to generate the Vernier effect. The working principle for the proposed sensor is analogous to Vernier-scale, one Hi-Bi FLM acts as a reference, while the other is for temperature sensing. The temperature sensitivity and resolution for the cascaded configuration are much higher than those for single Hi-Bi FLM due to the Vernier effect. A Gauss fitting algorithm is introduced to fit the Vernier spectral envelope to accurately trace the wavelength shift of the envelope peak. Experimental result shows that the temperature sensitivity and resolution can be improved from - 2.24 nm/degrees C and +/- 0.0223 degrees C (single Hi-Bi FLM) to - 23.68 nm/degrees C and +/- 0.0021 degrees C (cascaded configuration), respectively. The enhancement factors for temperature sensitivity and resolution are both 10.6, which are in good agreement with the theoretical prediction (10.7). The proposed sensor with high sensitivity, accuracy, easy fabrication and low cost is highly desirable for some applications that needs precise temperature control, such as micro-nano satellites, lasers, some chemical reaction process and enzyme reaction process.