Bend Sensor Based on Mach-Zehnder Interferometer Using Single-Mode Fiber With Helical Structure

Abstract

An all-fiber bend sensor based on Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated. The fiber interferometer consists of two helical structures in single mode fiber (SMF) and is fabricated by continuous arc discharge technique. The first helical structure forms a twisted long-period fiber grating (LPFG) to excite the higher-order cladding modes and acts as a beam splitter. The LPFG arrangement is adopted to improve the bending sensitivity. The second helical structure only contains two turns and can recouple the light in the cladding back into the core. The bending characteristics of the MZI are discussed. The experimental results show that high curvature sensitivities of 24.06 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> and −7.524 dB/ <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> are obtained in the curvature range of 0-0.422m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> . Due to its low cost, small size, simple preparation, less time consuming, it could be a competitive candidate in many bending sensing applications.