An All Fiber Mach-Zehnder Interferometer Based on Tapering Core-Offset Joint for Strain Sensing

A Mach-Zehnder interferometer, composed of two core-offset tapered joints (COTJ-MZI), is proposed and experimentally verified for high sensitivity strain sensing. The COTJ-MZI is handily fabricated by core-offset fusion splicing and tapering based on all single-mode fiber (SMF). The fiber cores form stepped cores within the COTJs. The transmission spectra with different core-offset values and interference lengths are obtained and theoretically analyzed. Benefitting from the stepped cores in the COTJ structure, the mode coupling points are able to be modulated easily by the applied strain. A strain sensitivity of −108.0 pm/$\mu \varepsilon $(0-$400~\mu \varepsilon$) and −47.6 pm/$\mu \varepsilon $(400-1200$\mu \varepsilon$) is achieved. In addition, the temperature response is also characterized as low as 23.3 pm/°C. With the advantages of low cost and high sensitivity, the COTJ-MZI sensor is competitive candidates in the field of strain measurement.