Temperature sensing characteristics based on coreless- few mode-coreless optical fiber structure

A temperature sensor based on coreless-few mode-coreless optical fiber structure was proposed for theoretical analysis and experimental study. The coreless fiber (CLF) and the few-mode fiber (FMF) were fused together to form a coreless-few mode-coreless optical fiber structure, and the single-mode fiber (SMF) was fused at both ends of the structure as input and output fiber. The mode mismatch between the first section of coreless fiber and single-mode fiber could excite higher-order modes. The two modes of LP01 and LP11 in the few-mode fiber were transmitted along the core of the few-mode fiber. Under the action of the second section coreless fiber, the two modes were recoupled back to the single-mode fiber, and the two modes interfered to form an interference spectrum. When the outside temperature changed, the optical path difference between the two modes also changed, and the interference troughs of the interference spectrum were shifted. Two different interference troughs were selected as the characteristic wavelengths for experimental analysis. The experimental results show that the interference troughs with wavelength around 1 550 nm and 1 534 nm both have red shift, and the corresponding temperature sensitivity is 68 pm/ and 44.5 pm/ respectively. The sensing structure has the advantages of simple fabrication, high sensitivity and good application prospects.