Hybrid Optical Fiber Sensor With High Resolution for Simultaneous Measurement of Temperature and Refractive Index

A high-resolution hybrid optical fiber sensor with a cascade of Fabry-Perot interferometer (FPI) and Mach–Zehnder interferometer (MZI) is proposed for simultaneous measurement of temperature and refractive index (RI), which is fabricated by Fs-Laser-Inscribed technology. FPI is formed by welding the hollow-core fiber (HCF) with the cavity completely filled with Polydimethylsiloxane (PDMS). MZI is the splicing of the single-cladding fiber (SCF) between two a pair of single-mode fibers (SMFs) with a large offset. The experimental results indicate that the sensor could achieve RI and temperature measurement with high sensitivities of -14225.79 nm/RIU and -32.76 nm/°C, and their resolution could be up to 3.5×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> RIU and 1.5×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> °C, respectively. Meanwhile, the bivariate quadratic surface fitting (BQSF) method is adopted to reduce the cross-sensitivity issue, and the RI indication error is merely 0.016 %. The proposed sensor exhibits the capacity for concurrent RI and temperature measurement, holding substantial promise for applications within biotechnology, food safety surveillance, and marine ecosystem investigations.