Temperature-Insensitive Optical Fiber Curvature Sensor Based on SMF-MMF-TCSMF-MMF-SMF Structure

A new optical fiber curvature sensor dominated by three-core single mode fiber (TCSMF) is proposed and demonstrated. The sensing structure is formed by cascading multimode fiber (MMF), TCSMF and MMF together, namely, the SMF-MMF-TCSMF-MMF-SMF structure. Three core modes in the TCSMF interfere with each other and then form the interference spectrum. The interference phase difference is changed due to the elastic-optic effect as bending deformation inflicted on the fiber. Thus the spectrum can be shifted accordingly. The two short segments of MMF can significantly improve the coupling efficiency between the fundamental mode and three core modes, and get high fringe visibility. Experiments show that the highest curvature sensitivity of -28.29 nm/m ^-1 is achieved in the range of 2.79-3.24 m ^-1 . Moreover, this sensor possesses the temperature-insensitive characteristic on account of the similar thermo-optic coefficient among three cores.