Investigation of a cascading core-offset in-line fiber Mach-Zehnder interferometer for refractive index measurement

A cascading core-offset in-line fiber Mach-Zehnder interferometer (MZI) was proposed to improve the RI sensitivity and eliminate the cross sensitivity between RI and temperature. The sensor was fabricated by cascading a small core-offset inline fiber MZI (the offset displacement is 6μm and interference arm length is 30mm) with a large core-offset in-line fiber MZI (the offset displacement is 40μm and interference arm length is 30mm). By enlarging the offset displacement, the RI sensitivity was improved from -9.177 to 108.326nm/RIU. And the MZIs with two offset displacement offer interference dips with different RI response, by utilizing the interference dips, the simultaneously measurement can be realized to eliminate the cross sensitivity.