A High Sensitivity Curvature Sensor Based on Microfiber Mach-Zehnder Interferometer With Tapered Seven-Core Fiber

A Microfiber Mach-Zehnder interferometer (MMZI) based on tapered seven-core fiber (SCF) for curvature measurement has been reported and demonstrated. The tapered SCF promoted the light coupling efficiency from the single-mode fiber (SMF) to the SCF, which results in the transmission spectrum with a low loss and high extinction ratio. In the process of curvature measurement, the sensitivity can reach up to 174.02957 nm/m⁻¹, which is the highest curvature sensitivity in the MZI with SCF as best as we have known. Furthermore, the maximum temperature sensitivity is 0.00956 nm/°C when the temperature changes from 30 °C to 140 °C. It shows that this sensor is naturally insensitive to temperature, which has a good performance in avoiding the cross-sensitivity effect between the temperature and curvature.

I. Introduction

In recent years, the accurate measurement of object curvature plays a critical role in many applications, such as medical devices, engineering structure monitoring, and aerospace engineering [1]. A variety of optical fiber curvature sensors with anti-electromagnetic interference, simple structure, and low price achieved by various approaches such as Mach-Zehnder interferometer (MZI), Sagnac interferometer, fiber Bragg grating (FBG), long-period grating (LPFG), and anti-resonant reflecting optical waveguide (ARROW) guidance [2]–[6]. Unfortunately, sensors based on the Sagnac interferometer, FBG, and LPFG are complex and challenging to fabricate. Comparatively, the sensors based on MZI have attracted more attention due to their small size, simple preparation, and high sensitivity [7]–[9].