Fabrication and Characterization of Single-Step Optical Microfiber Mach–Zehnder Interferometer Refractive Index Sensors

In this paper, exploiting a new single-step process, in-line Mach-Zehnder interferometers (M-MZIs) on microfibers of different diameters are fabricated and their refractive-index (RI) sensitivities and temperature stabilities are characterized. The M-MZI comprises a microfiber with two functionalizing miniature down-tapers inscribed along its longitudinal direction. It is fabricated exploiting a selectively modulated arc-discharge assisted fiber heating and pulling one-step process. In this new technique, inserted short time off-switches in the heating arc signal, while the fiber ends are pulled, induce additional microtapers on the thinned fiber is being fabricated. The resultant one-step M-MZIs show extremely high interference visibilities up to ~34 dB and high RI sensitivities up to 2271.3 nm/RI-unit around RI = 1.368. The results show that, with reducing the diameter of the structures, in addition to the higher RI sensitivity, very low temperature coefficient (~5.2 pm/°C for 8 μm sample) will be achieved. These M-MZIs have high stability, flexibility, reproducibility, and low fabrication cost.