Temperature sensors based on multimode chalcogenide fibre Bragg gratings

In this work, a theoretical study was conducted on temperature sensing in Ge–Sb–Se multimode fibre Bragg grating (MM-FBG). The sensing characteristics of the designed MM-FBGs with different fibre parameters and operating wavelengths were calculated using a coupled model method. The temperature sensitivity of this MM-FBG was found to improve significantly by shifting the operating wavelength from telecom range to mid-infrared (MIR) and utilizing the wide transmission range of Ge–Sb–Se glasses. The temperature sensitivity of the proposed Ge–Sb–Se MM-FBG was calculated to be 0.0758 nm/°C at 1550 nm, which is 7.58 times higher than silica FBGs at 1550 nm, and the temperature sensitivity was calculated to be more than 0.16 nm/°C at 3390 nm, which is 2.2 times higher than that at 1550 nm. In addition, the proposed MM-FBGs provided multi-peak information, and the sensitivity of each peak was calculated to be comparable to the single-mode FBG. The proposed Ge–Sb–Se MM-FBG has great potential for temperature sensing in MIR because of its advantages of simple preparation, high coupling efficiency, multi-peak information and wide working window.