Fiber in-line interferometer based on air-cavity with suspended fiber-core for sensing

Abstract

We demonstrate a new type of fiber in-line Mach–Zehnder interferometer (MZI). The device is fabricated by firstly inscribing a ring structure surrounding the fiber core at the ends of two single-mode fibers using a femtosecond laser micromachining technique and then fusion-splicing the two fibers with end structures. Due to the high temperature produced in the fusion splicing process, the ring structure expands rapidly and results in an inner air-cavity with a suspended fiber-core. The incident light traveling in the fiber core is split into two parts at the edge of the inner air-cavity, one propagating through the air cavity while the other remains traveling along the suspended fiber core; both are collected by the fiber core at the air-cavity end, thus forming an in-line MZI. The device has good high-temperature sustainability up to 900 °C. Moreover, by drilling a hole on top of the air-cavity, an open micro-channel can be created for air pressure measurement with a pressure sensitivity of ~−8214.68 pm MPa−1.