High-Sensitivity Bending Sensor Based on Supermode Interference in Coupled Four-Core Sapphire-Derived Fiber

A Mach-Zehnder interferometer (MZI) sensor based on a four-core sapphire-derived fiber (FSDF) for bending sensing is proposed and demonstrated. The MZI is formed by splicing a coupled FSDF between two single-mode fibers, delivering supermode interference among four LP01-like supermodes (LP01s modes) and eight LP11-like supermodes (LP11s modes). Benefiting from the different response of the field distribution of each supermode to curvature changes, MZI sensors with a variety of bending properties can be fabricated based on the interference of different supermodes in the FSDF. The experimental results show that the sensitivity of the FSDF-MZI sensor I based on the interference between the LP01s and the LP11s modes is about 4.5 dB/m-1 in the curvature range from 0.4 m-1 to 2.5 m-1. The FSDF-MZI sensor II based on the interference of two LP11s modes can realize bending sensing in ± Y directions. The sensitivity of FSDF-MZI sensor II in the curvature range of -10.0 m-1 - 5.0 m-1 in the Y direction is about -24.526 nm/m-1. It suggests that the proposed FSDF-MZI sensor has potential application in the field of structure health detection.