Temperature-insensitive curvature sensor with few-mode-fiber based hybrid structure

An in-fiber interferometric curvature sensor based on few-mode fiber (FMF) with high sensitivity and broad measurement range has been proposed, and the simulation analysis and experimental verification have been accomplished. The interference of the SMF-MMF-FMF-MMF-SMF(SMFMS) hybrid structure predominantly arises between the core modes and the low-order cladding modes of the sensing fiber. Four sensors with varied lengths of FMF have been constructed, and in-depth study has been carried out from three aspects: curvature sensing, stability and temperature sensing. The experimental results have revealed that when utilizing a 7 mm MMF and an 8 mm FMF, the sensor has the maximum curvature sensitivity of −16.33 nm/m−1 from 0.881 m−1 to 3.065 m−1. The proposed curvature sensor exhibits the advantages of good stability, miniaturization and ability to solve temperature cross sensitivity problems without any additional means, thus provides a new solution for cost-effective and performance enhanced curvature measurement in practical applications.