Abstract

A novel low-cost, compact, assembly-free and sensitive optical fiber curvature sensor is presented. This device consists of an off-axis positive refractive index modified zone (PRIMZ), induced by a direct femtosecond laser, written in a single-mode fiber (SMF) core. The PRIMZ transforms the original SMF section into a few-mode fiber (FMF). As a result, the whole fiber forms an assembly-free “SMF-FMF-SMF” sandwich Mach–Zehnder interferometer. When the device is bent, a direction-dependent spectral shift of the interference pattern is produced. The sensitivity of the sensor is up to 2.53 and $2.24\mathrm{nm}/{\mathrm{m}}^{-1}$ for the 0° and 180° orientations in a wide bend range (from 0 to $4{\mathrm{m}}^{-1}$). In addition, the device is immune to the surrounding refractive index and has a low-temperature crosstalk, which makes it very attractive for practical structural monitoring applications.

© 2018 Optical Society of America

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