An S-Shaped Core M-Z Interferometer Induced by Arc-Discharging for Strain Sensing

In this study, a kind of in-fiber Mach–Zehnder interferometer (MZI) is designed and experimentally examined. The MZI is composed of two in-fiber S-shaped cores (SSCs), which enhance strain sensitivity. To prepare the SSCs, a high-frequency CO2 laser is first utilized to polish grooves on the symmetrical surface of a single-mode fiber (SMF). The polished area is then subjected to arc-discharging by a commercial fusion splicer, and the core of the fiber bends towards the polished grooves due to the self-roundness of the cladding and the heating effect of discharge. The results of the experiments demonstrate that the sensor achieves high strain sensitivities of −66.5 pm/με and −40.1 pm/με within the strain range of 0 με to 350 με. By solving the matrix equation, simultaneous online measurements of temperature and strain can be performed. With the advantages of easy fabrication, low cost, high sensitivity, and compactness, the proposed sensor is a competitive candidate in strain sensing.