Fresnel-reflection-based fiber sensor for on-line measurement of solute concentration in solutions

A fiber sensor with a simple structure for measuring solute concentration in solutions is presented. The sensor uses only a diode laser as light source, three couplers, two sensing fiber ends with protective cladding, and two photodetectors. The measurement principle is based on relative Fresnel reflective intensity. Various concentrations of salt solution and sugar solution are measured in the setup. The measured data are fitted to linear equation very well and the values of R2 are more than 0.995. Applying the relative technique, the errors resulted from fluctuation of light source and influences of environment are effectively eliminated, and the stability for long time measurement can be improved.