A Universal and Stable All-Fiber Refractive Index Sensor System

In this letter, a universal, simple, and stable all-fiber sensor system is proposed to measure the refractive index (RI) of liquids. The basic principle of the technique is based on the relative measurement of the Fresnel reflection from sensor probes. A quadruple of time-division multiplexed Fresnel reflected pulses are obtained from a single nanosecond input pulse owing to the latencies in fibers with different lengths. The measured RIs for the different liquids show that the proposed all-fiber RI sensor system enables linear and repeatable measurements. The performance of the system is compared with the previously published studies, and good agreement is observed, showing the accuracy of the measurements. The standard deviations of the measured RIs are obtained in a short-term measurement as 2.8 × 10 -6 for distilled water, and in a long-term measurement as 2.99×10 -5 for methanol, showing the high repeatability of the measurements.