Modeling of high-index coating lensed fibers for silicon nanophotonic device coupling

Two types of high-index coated lensed fibers are numerically investigated for optical coupling from Si-based nanowire waveguides to the lensed fibers. One is with a layer of high-index film coated on tip of conventional lensed single-mode fiber (SMF) and the other is with an additional coreless fiber section inserted in between. The simulation results show that, for nanowires with mode size diameters ranging from 0.6 μm to 1.3 μm, the coupling efficiency as high as 80% can be obtained with the former type of fiber when the radius of curvature is around 10 μm and coated with a 5-10 μm thick high-index film. As for the latter design of fiber, an improved working distance is calculated to be as long as 36.8 μm by inserting a coreless fiber section. Both high-index coating lensed SMF designs show potential application for coupling with Si-based nanophotonics.