Simultaneous measurement of refractive index and temperature with high sensitivity based on a multipath fiber Mach-Zehnder interferometer.

We present and experimentally demonstrate a highly sensitive sensor for simultaneously measuring the refractive index (RI) and temperature based on a multipath fiber Mach-Zehnder interferometer. The sensor is fabricated by sandwiching a segment of weak-coupling seven-core fiber (SCF) with two short multimode fibers, and then splicing it with lead-in and lead-out single-mode fibers, respectively. Six outer cores of the SCF are half-etched chemically for enhancing the interaction between light and matter. A high-quality transmission spectrum with 23 dB fringe visibility is obtained. Due to the strong interaction between the outer core modes and cladding modes with the surrounding medium, the proposed fiber structure exhibits not only an extremely high RI sensitivity of -1802.26  nm/RI unit from 1.427 to 1.442, but also a superior temperature sensitivity of 82 pm/°C from 10°C to 90°C. Moreover, RI and temperature can be discriminated simultaneously by measuring the central wavelength shifts of two transmission notches. This sensor has outstanding advantages of high sensitivity, easy fabrication, simple structure, and low cost, and may find applications in multiparameter highly sensitive sensing.