Refractive Index Sensing Based on a Side-Polished Macrobending Plastic Optical Fiber

In this paper, a plastic optical fiber (POF) probe with a side-polished macrobending structure is proposed for the refractive index (RI) sensing. The principle of operation is based on the macrobending loss and evanescent field, which are introduced by the side-polished macrobending structure on the fiber, and modulated by the environmental RI. A thermal setting method is used to solve the problem of the mechanical stability of the probe with smaller curvature radius after side-polishing process. By changing the curvature radius, the polished depth, and the polished position (angle), the sensing performance of the probe is optimized. In addition, we obtain the maximum sensitivity reaches 154 dB/RIU in the RI range of 1.33-1.44 when the curvature radius, the polished depth, and the polished position are 5 mm, 500 μm, and 60°, respectively. The POF probe is a low cost solution for RI sensing applications, which has the features of simple structure, compact, and intensity modulation at visible wavelengths.