An optical fibre interferometric refractometer

Abstract

A new type of optical fibre interferometric refractometer has been made. A double interferometer consists of an optical fibre Mach–Zehnder interferometer and a Michelson interferometer. The first one measures the optical path length difference of the moving sample, while the second one measures the liquid sample displacement in air. A fringe count technique was used on both interferometers in order to obtain the refractive indices of different liquids. The described optical fibre interferometric refractometer was tested by measuring the refractive indices of different liquids, and the achieved results were compared to the results found in the literature. In addition, the refractive index of different concentrations of NaCl in water was measured and compared with the calculated calibration curve. The advantage of the proposed refractometer is high accuracy measurements including the simple construction of the optical fibre Mach–Zehnder interferometer and the commercially available Michelson interferometer.