Temperature and Surrounding Refractive Index Insensitive Bending Sensor Based on a Novel Cascaded All-Fiber Structure

Abstract

We have proposed a fiber-optic bending sensor based on cascading seven-core fiber (SCF)–twin-hole dual-core fiber (THDCF)–SCF structure. Several dips are generated by the Mach–Zehnder interference. The THDCF Section acts as a bending unit, exhibiting high bending sensitivity. As the applied bending increases from 0 to 8.51 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{-{1}}$ </tex-math></inline-formula> , the dip wavelength exhibits the highest sensitivity of 12.15 nm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{-{1}}$ </tex-math></inline-formula> . With the benefit of the asymmetric structure of the THDCF, the dip shows different obvious responses for different bending directions. Besides, through the temperature and the surrounding refractive index (SRI) sensing experiments, it is proved that our sensor shows low-temperature sensitivity (0.01 nm/°C) and low SRI sensitivity (2.38 nm/RIU). Simple structure, low cost, and high sensitivity make the sensor more competitive in the applications of structural conventional health monitoring and human posture detection.