Optofluidic Photonic Crystal Fiber Coupler for Measuring the Refractive Index of Liquids

We report a novel optical sensing device capable of measuring the refractive index of liquids based on evanescent field coupling between a photonic crystal fiber (PCF) that is side-polished and coupled to a side-polished single-mode fiber (SMF). The PCF is used for liquid analyte transport, while the SMF is used for light ingress and egress. The optical coupling efficiency in this device is sensitive to the refractive index of the PCF which varies with the presence of analytes in the holes of the PCF. The fabrication process of the coupler and its performance as a refractive-index sensor are presented. Due to its compact size and features for interactions between the light and the analyte, the sensor can operate as a highly responsive optofluidic device. The results show that this kind of sensing device provides a promising platform for refractive index measurements with an estimated accuracy of 10
^-5
refractive index unit.