A comparative study of optical fiber sensors for refractive index measurement

摘要

Refractive index (RI) is one of the physical properties of material, such as boiling/ melting point, density, and elasticity. As one of the distinctive features of the material, measurement of the RI is nowadays used in many areas including the food, oil and petroleum industry, biomedical applications, and environmental analysis. In recent years, fiber optic based refractometers become highly popular thanks to the advantages they provide compared to other methods used in the above mentioned fields. Two fiber optic refractive index sensors were investigated in this study: Fresnel reflection based- and long-period fiber grating (LPFG) based-refractometers. The former uses SMF fiber tip as sensing point interrogated by an OTDR from a distant location, where the latter examines the changes in the resonance wavelength. Experimental work realised on different concentrations of glucose-water and glycerol-water solutions successfully demonstrated the capability of the proposed sensor in measuring RI of liquid chemicals with a precision of 1.7×10-4 (Fresnel-based sensor) and maximum sensitivity of 193.42 nm/RIU (LPGF based sensor).