All-in-fiber multiscan Mach-Zehnder interferometer assisted by core FBG for simultaneous multi-parameter sensing

In this work, a hybrid cladding waveguide (CWG) Mach-Zehnder interferometer (MZI) sensor inscribed by femtosecond laser is demonstrated. The CWG has been inscribed using adaptive optics and multiscan technique. It has been discovered that these waveguides exhibit a phase change dependent of the number of scans performed, allowing free spectral range (FSR) control. Temperature characterization reveals a refractive index change (RIC) proportional and lower than previously reported CWG MZIs, indicating a lower degradation with high temperatures. The CWG proximity to the cladding/air boundary allows good refractive index (RI) sensitivity. Thanks to the FBG inscribed in the reference arm with the point-by-point (PbP) technique, the interferometer can measure curvature and strain simultaneously without being affected by cross-sensitivity.