Ultrasensitive RI and temperature sensor based on cascaded microfiber MZIs with Vernier effect

A sensitivity amplified optical fiber sensor based on Vernier effect by cascaded microfiber Mach-Zehnder interferometers (MZIs) is proposed and demonstrated for the simultaneous measurement of refractive index (RI) and temperature. The traditional single mode fiber is tapered into micrometer near the dispersion turning point to constitute MZI, and then cascaded to generate Vernier effect for the sensitivity enhancement. A novel phenomenon that the envelope of Vernier effect shifted in opposite directions decided by the free spectral ranges of the sensing and reference arms is clarified and demonstrated for the first time. Experimental results show that the RI sensitivity can be improved from 944 nm/RIU of single MZI to 18504 nm/RIU of Vernier effect, while the temperature sensitivity can be improved from −0.53 nm/℃ of single MZI to 9.49 nm/℃ of Vernier effect. Moreover, the proposed sensor with the merits of low hysteresis effect, good repeatability, high stability and good reliability, making it of great potential for biochemical trace detections without temperature-induced cross-sensitivity.