Investigation of the high sensitivity RI sensor based on SMS fiber structure

A high sensitive refractive index (RI) sensor based on a Single-mode Multimode Single-mode (SMS) fiber structure was used and experimentally demonstrated. The dip in the measured spectrum signal caused by the modal interference shifted obviously when the surrounding RI changed. The approximate linear relationship between surrounding RI and spectrum dip wavelength shift was obtained experimentally. The measurement sensitivity up to 286.2 nm/RIU was showed with the surrounding RI range from 1.33 to 1.3775, which means the measurement resolution about 3.5 × 10−6 could be implemented if the wavelength shift measurement resolution of the Optical Spectrum Analyzer is 1 pm.