A Long Cylindrical Optical Fiber Sensor Based on Multiple Total Internal Reflections in Heterodyne Interferometry

Abstract

In this paper, a long cylindrical multimode optical fiber sensor (OFS) based on multiple total internal reflections in heterodyne interferometry is proposed. The cladding of the sensing portions of the fiber sensors is removed, but dont be coated with any metal films. With the OFS the phase shift difference due to the multiple total internal reflections (MTIRs) effect between the p-and s-polarizations can be measured by using the heterodyne interferometry. Substituting the phase shift difference into Fresnels equations, the refractive index for the tested medium can be calculated. According to numerical simulations and experimental results, the long cylindrical OFS is with the best resolution of 0.0000028 refractive index unit (RIU). However, the OFS could be valuable for chemical, biological and biochemical sensing. It has some merits, such as, high sensitivity, high resolution, stability, small size and in real-time measurement.