Simultaneous refractive index and temperature sensing system realized by hybrid interferometer structures-based microwave photonic filter

A sensing system that simultaneously measures refractive index (RI) and temperature using a hybrid fiber interferometers-based microwave photonic filter (MPF) has been proposed and experimentally demonstrated. An extrinsic Fabry-Perot interferometer (EFPI) based on single-mode fibers (SMFs) is employed for RI sensing and the temperature can be measured by using a Sagnac interferometer (SI) fabricated with a section of polarization maintaining fiber (PMF). By tracking the MPF's dual-passband at the different central frequencies, the proposed sensor can effectively achieve dual-parameter sensing. Compared with the wavelength interrogation in optical domain, the proposed sensing system using the frequency interrogation in electrical domain, has an unlimited measurement range in principle. The experimental results indicate that the proposed sensing system realizes an RI sensitivity of 1197.604 MHz/RIU in the range from 1.332-1.412 RIU and a temperature sensitivity of 0.934 MHz/°C in the range from 20-50 °C. Moreover, the proposed system, possessing advantages such as high resolution, the ease of fabrication, and good stability, has great potential for applications in the field of multi-parameter sensing, such as biochemical detection, environmental monitoring, and industrial production.