Experimental Study on Dual-Parameter Sensing Based on Cascaded Sagnac Interferometers With Two PANDA Fibers

A sensitivity-amplifying optical fiber sensor using cascaded Sagnac interferometers (CSIs) was designed and experimentally demonstrated for the dual-parameter measurement of strain and temperature. The proposed CSIs sensor consisted of two Sagnac interferometers (SIs) in which two identical PANDA polarization-maintaining fibers (PMFs) for just slightly different lengths were inserted. An envelope with a period of 123.6 nm, which was amplified more than 10 times than the single SI, was observed in the interference spectrum. Experimental results showed that the strain sensitivity increased from 32.91 pm/μϵ for the single SI to 336 pm/μϵ for the CSIs, while the temperature sensitivity increased from −1.38 nm/°C for the single SI to −14.86 nm/°C for the CSIs, correspondingly. We also found that the envelope of the CSIs shifted in opposite directions when the longer or shorter PMF was selected as the sensing arm. Higher sensitivity could be realized by selecting longer PMF as the sensing arm. Our proposed CSIs sensor possesses the merits of simple structure, high sensitivity, low cost, and low hysteresis effect, which make it a competitive candidate for strain and temperature monitoring.