Fabrication of Side-Polished Single Mode-Multimode-Single Mode Fiber and Its Characteristics of Refractive Index Sensing

This paper presents a low-cost, flexible, and highly efficient wheel polishing techniques for the fabrication of sidepolished single mode-multimode-single mode fiber (SP-SMSF). The evolution of transmission spectrum of SP-SMSF is measured, simulated, and discussed. The good linear relationship between polished depth (PD) and polish-induced loss has relatively high linear correlation at 95%, allowing us to monitor and control the critical parameter PD in line and in real time. Several desirable SPSMSF with PD = 9.6 , 15, 20.6 μm were fabricated successfully. Their characteristics of refractive index (RI) sensing are investigated experimentally. The results show that SP-SMS sensitivity increases as RI increases, approaching its maximum when the latter gets close to its core. The maximum sensitivity of the SP-SMSF with PD = 20.6 μm is 1190 nm/RIU, comparable to that of chemically etched SMSF. The dependence of the sensitivity on the PD of SP-SMSF is also measured and discussed, showing that an increase in PD can improve the sensitivity of SP-SMSF. In addition, such novel structure of SP-SMSF will provide a flat platform to implement various fiber devices.