Large measurement range temperature sensor based on WGM and MMI in an offset structure fiber coupler.

• The coupler is simply made of SMF-NCF-SMF offset splicing. • The coupled structure can realize the coexistence of MMI with a large FSR and WGM with small FWHM. • The sensor can simultaneously achieve temperature detection with a large measuring range and low detection limit. • Asymmetric Fano lines can be obtained under the modulation of interference. In this paper, a coupler based on a single-mode fiber (SMF)- no-core fiber (NCF)- SMF offset structure was proposed and demonstrated, which can generate the evanescent field to excite whispering gallery mode (WGM) of a microsphere cavity. By reasonably controlling the length and offset distance of NCF, the multimode interference (MMI) and WGMs can be generated at the same time. The experimental results show that the temperature measurement with a large measurement range and low detection limit can be realized simultaneously with the assistance of the interference envelope, which solves the problem of large range measurement difficulty caused by the dense dips of WGM to some extent. In the range of 22 ℃-80 ℃, the sensitivity of WGM resonant dips is ∼10.5 pm/℃. On the other hand, symmetric Lorenz lines with a quality factor of 8.2 × 103 and asymmetric Fano lines with a slope of -21.94 dB/nm were obtained under the modulation of interference. The coupler proposed in this paper has the advantages of simple preparation and strong structural robustness, and shows good potential in applications such as sensors and filters. [ABSTRACT FROM AUTHOR]