Ultra-High-Sensitivity Temperature Sensor Using a Fiber Loop Mirror Based on a Water-Filled Asymmetric Two-Hole Fiber

We present an ultra-high sensitivity fiber loop mirror temperature sensor based on an asymmetric two-hole fiber (ATHF) filled with distilled water. The design of the ATHF allows for larger interaction between the optical mode and the region with large induced birefringence. This enhanced interaction provides large changes in the sensing signal when the temperature is varied. The sensing signal can easily be tracked by following the change in the frequency of the interference signal as a function of the temperature, thus allowing for absolute temperature measurements. Experimental results show that the ATHF birefringence is modified from 1.18×10
^-5
to 3.33 × 10
^-4
when the temperature changes from 40 to 80°C; generating, in terms of frequency, a sensitivity of 6 × 10
^-3
nm
^-1
/°C. In the case of very small temperature changes, where the wavelength shift is also small, simulations were performed using experimental parameters of the ATHF and an ultra-high sensitivity of 240 nm/°C was calculated. The sensitivity of the presented sensor can also be tuned by changing the liquid infiltrated into the fiber holes.