Ultrasensitive fiber optic dual parametric sensor based on harmonic Vernier effect

An ultrasensitive fiber optic dual parametric sensor based on harmonic Vernier effect is proposed and experimentally demonstrated, consisting of a fiber Sagnac interferometer (FSI) cascaded with a Fabry-Perot interferometer (FPI). The sensing interferometer FSI is fabricated by splicing a high birefringence polarization-maintaining fiber (Hi-Bi PMF) and a fiber coupler. The FPI is manufactured by splicing a segment of Hollow Core Photonic Crystal Fiber (HCPCF) between two Single Mode Fibers (SMFs). It is temperature insensitive and can be utilized as a reference interferometer. The Harmonic Vernier effect is obtained by adjusting the length of the HCPCF to change the optical path length (OPL) difference between the two interferometers, and the effect of the detuning factor on the sensitivity is verified by the experiment. The results of the experimentation reveal that the sensitivities of the proposed sensors to temperature and strain are −62.298 nm/°C and 134.97 pm/με, respectively, with low discrimination errors of ±0.0007 °C and ±0.041 με. With its high sensitivity, low cost, and simple structure, this sensor has great potential in industrial manufacturing and environmental detection applications.