High-Sensitivity Optical Fiber Mach-Zehnder Interferometer Sensor Based on Eight-Core Fiber

A high-sensitivity optical fiber curvature sensor based on eight-core fiber (ECF) is proposed and demonstrated. The sensor is fabricated by directly fusing a segment of ECF between two single-mode fibers (SMFs), forming a Mach-Zehnder interferometer (MZI) in an SMF-ECF-SMF structure. Due to the mode field mismatch between ECF and SMF modes, the fundamental mode of SMF is excited to higher-order modes and coupled into ECF to detect the external environment. The cores of the ECF present a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times 4$ </tex-math></inline-formula> arrangement, which can play the role of multipath MZI due to the existence of multiple cores. In the curvature detection, the maximum curvature sensitivity of the sensor can be up to −53.32 dB/m−1 within the curvature range of 0.3006 m−1–0.5483 m−1. A wavelength dip with a maximum extinction ratio of 22 dB is obtained in the transmission spectrum, which indicates that the ECF effectively equalizes light energy. In addition, the strain response is also measured. When the strain range changes from 0 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$900~\mu \varepsilon $ </tex-math></inline-formula>, the maximum strain sensitivity is −1.83 pm/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula>. The proposed sensor, with high sensitivity, simple structure, and good repeatability, has potential applications in many fields, such as medical devices and aerospace.