Refractive index sensor based on wavelength shift analysis in MSM optical fiber structure

A refractive index (RI) fiber optic sensor is fabricated and characterized. The structure of this sensor is multimode-single-mode-multimode (MSM) fiber, and to fabricate it, two multimode fiber (MMF) pigtails are connected to ends of a 40mm long segment of a single-mode fiber (SMF). The core mode and exited high-order cladding modes of the SMF form a Mach-Zehnder interferometer (MZI) configuration. This optical fiber sensor exhibits its sensitivity to the surrounding refractive index (SRI) by dip wavelength shift when it is submerged in solutions which contain different concentrations of glycerol. Remarkably, the obtained sensitivity of this sensor in the RI range of 1.39 to 1.47 (50% to 100% of glycerol concentration in the water-glycerol solution) is 580.89 nm/RIU.