Simple low-cost refractometer using a disposable optical fiber tip for measurements

Abstract

A simple but accurate fiber-optic refractometer based on Fresnel reflection in the tip of a single-mode optical fiber is reported. The refractometer can be easily assembled using a distributed feedback laser as a light source and standard low-cost fiber-optic components. The short section of an optical fiber cleaved at right-angle in both tips is used as a disposable needle-type sensor head. The sensing fiber being connected with the angle-cleaved lead fiber forms a stable reflector used for light intensity reference. Signals from the sensing and reference fiber tips, generated by modulating the laser optical frequency with a sawtooth-wave form, are demultiplexed using methods of optical frequency-modulated continuous-wave interferometry. Despite the simplicity of the device, a repeatability and reproducibility of 6×10−4 RIU and 3×10−4 RIU, respectively, were demonstrated in dip-and-read experiments using replaceable disposable fiber tips.