An optical fiber sensor for measurement of refractive index of liquids
Abstract
An optical fiber sensor based on the principle of cladding mode losses was configured to measure refractive index of liquids. The basic design consists of a high intensity LED source with red emission (660 nm), a U-shaped bent multimode bare silica fiber with core diameter of 100 μm and numerical aperture of 0.3, and a matched photodiode as detector. The sample liquids used have indices of refraction in the range 1.32 to 1.49, consisting of some common oils and solvents. Using the measurements obtained with an Abbe refractometer for the sample liquids, a calibration curve was obtained. Appropriate microcontroller-chip based circuitry was also designed to give a direct read-out of the refractive index.