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/°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.