Screw-Shaped Plastic Optical Fibers for Refractive Index Sensing

A screw-shape is fabricated on a commercial plastic optical fiber (POF) by a heat pressing and twisting method. The screw-shaped POF is proposed as a refractive index (RI) sensor. By changing the structural parameters of the screw-shaped POFs both with and without claddings, the RI sensing performances are studied. When the screw-shaped POF is fabricated by twisting a thin flat-shaped POF with a thickness of 600~\mu \text{m} and with a screw pitch of 2mm, the highest sensitivities of 2277%/RIU, 4318%/RIU, and 4399%/RIU with the resolutions of 3.10\times 10^{\mathbf {-4}} RIU, 1.63\times 10^{\mathbf {-4}} RIU, and 1.60\times 10^{\mathbf {-4}} RIU are obtained in the RI ranges of 1.33-1.37, 1.37-1.40, and 1.41-1.45, respectively. The results demonstrate that simply making the POF into a screw-shape, its RI sensing performance can be enhanced markedly. As a low-cost solution for RI measurement, the proposed sensor has the merits of high sensitivity, simple structure, easy fabrication, and intensity modulation at visible wavelengths.