High Sensitivity Strain MZI Based on Spiral Core Fiber

Fiber optic Mach–Zehnder interferometer (MZI) strain sensors are widely used in many fields, but their sensitivity needs further improvement. This article proposes a new method of strain sensitization by simultaneously increasing the effective refractive index difference and the difference in sensing path length between the fiber core and cladding to increase the change in optical path difference. By replacing the single-mode fiber in the middle part of the multimode-single mode-multimode (MSM) structure with spiral core fiber fabricated by the eccentric fiber, the separation of the core sensing length and the cladding sensing length of the sensing fiber was achieved, and the length difference of the fiber core and cladding sensing path was increased. However, due to twisting processing of the eccentric fiber, the higher order cladding modes were excited, thereby increasing the effective refractive index difference of the fiber core and cladding. By experimental testing, the highest strain sensing sensitivity of −72.9 pm/ $\mu \varepsilon $ was achieved, providing a new idea for the further development of fiber optic integrated MZI strain sensing.