Temperature measurement utilizing tilted Bragg gratings in solution-filled specialty optical fiber

In this work, we propose a tilted fiber Bragg grating (TFBG) sensor for temperature measurements. The grating is inscribed using a femtosecond laser and the line-by-line (LbL) direct writing technique in the central core of a specialty optical fiber. The channel filled with glycerol aqueous solution beside the central core significantly improves the temperature sensitivity of the TFBG cladding modes due to its high thermo-optic coefficient (TOC). We show that the temperature sensitivity of the core mode is $9.59 \mathrm{pm} /{ }^{\circ} \mathrm{C}$, while the counterparts of the cladding modes reach up to $-29.45 \mathrm{pm} /{ }^{\circ} \mathrm{C}$ in the range of $20-40^{\circ} \mathrm{C}$.