Femtosecond laser-fabricated Mach-Zehnder interferometer for magnetic field sensing

Abstract This paper presents a miniaturized Mach–Zehnder interferometer (MZI) sensor fabricated using femtosecond laser micromachining technology, which is used to couple light into the cladding of a single mode fiber (SMF). This sensor exhibits excellent refractive index sensing performance, with a refractive index sensitivity of 21.8 nm RIU −1 . Based on this, the sensor was encapsulated in a magnetic fluid (MF), and its potential as a magnetic - field sensor was verified through experiments. Experimental results indicate that the sensor has good magnetic field response characteristics. In the magnetic - field strength range of 100–180 Oe, the sensitivities for the positive and negative gradients are 17.8 pm Oe −1 and −16.5 pm Oe −1 respectively, demonstrating favorable sensitivity and repeatability. In addition to its high magnetic field sensitivity, the sensor can also be used as a vector sensor. It not only responds to the magnitude of the magnetic field but can also characterize the magnetic - field direction within the measurement range of 0–360°. The sensor features a small size, simple structure, and ease of fabrication, making it suitable for applications in fields such as medical devices and aerospace.