Enhanced lensed fiber for Si-nanowire coupling

We propose a lensed fiber design exhibiting good coupling efficiency together with a long working distance for the coupling of silicon based nanophotonic waveguides to a single mode optical fiber. The lensed fiber consists of a coreless fiber tip coated with a high refractive index material. Numerical simulations show that the coupling loss as low as -0.5 dB can be achieved with a working distance of ~37 μm for coupling from a nanowire waveguide with a mode field diameter of 700 nm to our lensed fiber. This optimized fiber design has a radius of curvature of 60 μm, a 800 μm-long coreless fiber section, and a 10 μm-thick coating layer with an index of 3.7.