Tilted Bragg grating in a glycerol-infiltrated specialty optical fiber for temperature and strain measurements

• Xuehao Hu, yang liu, Heming Wei, Chuanxin Teng, Qianqing Yu, Zhijun luo, Zhenggang Lian, Hang Qu, and Christophe Caucheteur
• received 02/20/2024; accepted 04/21/2024; posted 04/22/2024; Doc. ID 521797
• Abstract: In this Letter, we propose an in-line tilted fiber Bragg grating sensor for temperature and strain measurements. The grating is inscribed in a specialty optical fiber using tightly-focused femtosecond laser pulses and the line-by-line direct writing method. Beside the central core in which the grating is produced, a hollow channel filled with glycerol aqueous solution significantly improves the sensitivity of the fiber cladding modes due to its high thermo-optic coefficient. We show that the temperature sensitivity of the core mode is 9.8 pm/°C , while the one of the cladding modes is strongly altered and can reach ‒24.3 pm/°C, in the investigated range of 20-40 °C. For strain measurement, sensitivities of the core mode and the cladding modes are similar (~0.60 pm/με) between 0 and 2400 με. The significative difference of temperature sensitivity between the two modes facilitates the discrimination of the dual parameters in simultaneous measurements.