All-fiber intermodal Mach–Zehnder interferometer based on a long-period fiber grating combined with a fiber bitaper

We report a novel all-fiber narrow-bandwidth intermodal Mach–Zehnder interferometer (MZI) based on a long-period fiber grating (LPFG) combined with a fiber bitaper, and the MZI has no special limit for the resonant wavelength of the LPFG. Its responses to temperature and axial strain are studied theoretically and experimentally. Experimental results indicate that the temperature sensitivity is 0.0585 nm/°C within the temperature range from 30 °C to 90 °C and the axial strain sensitivity of 0.00013 nm/με can be neglected. Furthermore, as only the common single-mode fiber (SMF) is required during the fabrication process, the proposed device is cost effective and has good practicability in the optical sensing systems.