Femtosecond laser processing for a high sensitivity fiber MZI microcavity

An ultra-compact fiber inline Mach-Zehnder interferometer sensor based on femtosecond laser micromachining technology is demonstrated. It is found that the microstructure has an ultra-high refractive index sensitivity of 16660 nm/RIU when a femtosecond pulsed laser is used to remove the upper cladding and part of the core of a standard single-mode fiber. However, its temperature sensitivity is not much different from that of most pure quartz fibers and can be as high as 7.934 nm/degrees C when the microcavity is coated with a low-refractive-index ultraviolet adhesive, which was originally used for bonding glass. With this coating, however, it demonstrates excellent robustness. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement