Curvature Sensor Based on In-Fiber Mach–Zehnder Interferometer Inscribed With Femtosecond Laser

• Published in: Journal of lightwave technology 2017-11, Vol.35 (21), p.4624-4628
• Main Authors: Pallares-Aldeiturriaga, David, Rodriguez-Cobo, Luis, Quintela, Antonio, Lopez-Higuera, Jose M.
• Format: Article
• Language: English
• Subjects: Indexes; Optical fiber devices; optical fiber interference; Optical interferometry; Optical waveguides; Refractive index; Sensitivity; Ultrafast optics; Waveguide lasers
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/JLT.2017.2756103

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 1.1 × 10 -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 9.49 nm/m -1 for curvature ranges from 0 to 14 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) m -1 /°C up to 180 °C.