Long period gratings as solution concentration sensors

The on-line concentration measurement of solutions is of great interest in many industrial processes as a means of quality production control, in order to measure concentrations of harmful solutions or solutions that cannot be reached by the operator. An optical fiber long-period grating (LPG), tested for the refractometry of sodium chloride, calcium chloride and ethylene glycol aqueous solutions, is presented. Resolution values comparable to or even better than those offered by an Abbe refractometer, that is typically used in these types of measurements, are obtained.