Investigation of refractive index sensors based on side-polished plastic optical fibers

A side-polished plastic optical fiber (POF) was proposed for liquid's refractive index (RI) measurement. The POF was polished into an arc shape on the surface of the fiber for increasing its RI sensitivity. The experiment shows that the straight side-polished POFs are not sensitive enough as the RI probes. After the straight side-polished POFs were bent into the U-shaped probes, the sensitivities were markedly increased. By changing the structural parameters, the RI sensing performance of the U-shaped probe was optimized, a sensitivity of 864%/RIU with a resolution of 3.3 × 10−4/RIU in the RI range of 1.33-1.44 was obtained. In addition, the characteristic of the temperature dependence of the sensor was presented. The sensor is a low cost solution for RI sensing applications which has the features of simple structure, compact size, and intensity modulation at visible wavelength.