Study of an in-line fiber Mach-Zehnder interferometer with peanut-shape structure for refractive index sensing

A peanut-shape structure based in-line fiber Mach–Zehnder interferometer (MZI) was fabricated by commercial available fusion splicer. The power distribution of the modes in the device was calculated and measured experimentally. The in-line fiber MZIs with the different arm lengths (30 and 100mm) were exploited for refractive index (RI) measurement. The highest RI sensitivity of 67.953 nm/RIU was achieved within the measured RI range of 1.33–1.36.