Abstract

In this paper, an in-fiber Mach–Zehnder interferometer inscribed by femtosecond laser for curvature sensing has been designed and manufactured. Its operating principle consists of a secondary waveguide inscription working as a sensing arm. This waveguide has been manufactured using asymmetric structures with an average refractive index change of $\text{1.1}\times \text{10}^{-\text{2}}$ in its guiding section measured by refracted near-field profilometry. The overall arm/cladding index difference is higher than its core/cladding counterpart, which is a suggested condition for device operation following preliminary simulations. The manufactured Mach–Zehnder interferometer exhibits a linear response to bending radius that is also dependent on an established bending axis. Sensitivity has been measured up to $\text{9.49}\,\text{nm/m}^{-1}$ for curvature ranges from 0 to 14 $\text{m}^{-1}$ . Simulation results using the beam propagation method and conformal mapping transformation to convert bending action into a tilt refractive index agree with experimental results for the same index parameters. Preliminary temperature test shows a remarkable cross sensitivity of $0.0024(3)\,\text{m}^{-1}/^\circ$ C up to 180 $^\circ$ C.

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