Temperature and refractive index sensor based on a spherical-structure Mach-Zehnder interferometer combined with a long-period fiber grating

The majority of biology and chemistry takes place in solution, in which temperature and refractive index sensing underlie molecular detection and profiling. All-in-fiber integrated devices are uniquely suited to detect the properties of samples. In this paper, a novel, to the best of our knowledge, spherical-structure Mach-Zehnder interferometer (MZI) combined with a two-mode long-period fiber grating (TM-LPFG) for temperature and refractive index sensing is presented and experimentally investigated. Because the two dips caused by MZI and TM-LPFG have different responses to temperature and surrounding refractive index, the simultaneous measurements of temperature and surrounding refractive index can be achieved by monitoring wavelength shifts of the two dips. The effectiveness of the method has been verified by simulations and experiments. The experimental results show that the temperature sensitivity is 828.09 pm/°C, and the refractive index sensitivity is -188.83nm/RIU. The sensor is outstanding among the reported results, especially at temperature, and it provides an economical method for many applications that require simultaneous measurement of temperature and refractive index.