An inline fiber Mach-Zehnder interferometer based on core-offset and peanut-shape for refractive index sensing

An inline fiber Mach-Zehnder Interferometer (MZI) that consisted of a standard single-mode fiber sandwiched between one peanut-shape and a core-offset joints is fabricated by a fusion splicer for RI sensing purpose. After substituted a peanut shape for a core-offset in an inline fiber MZI with the core-offset pair, the influence caused by the misplaced direction of the core-offset is avoided since the peanut structure is symmetrical, and it is found that its RI sensing performance was improved as well. The inline fiber MZIs with the different arm lengths and core-offset displacement were evaluated for refractive index (RI) measurement. The RI sensitivity of -72.4 nm/RIU was achieved within the measured RI range of 1.333-1.373.