Compact coupling of light from conventional photonic wire to slow light waveguides

In this study, efficient input and output power coupling schemes for transition regions at the interface of conventional and slow light waveguides are investigated. By optimizing the tapered nano-tip of the input and output slab waveguides that support a group index of 3.58, we achieved 97% coupling efficiency to a square-lattice based slow light photonic crystal waveguide with a group index of 1200. The complementary slow waveguide structure based on triangular-lattice is also designed to support same order of magnitude slow light mode and targeted to alleviate the severity of the coupling loss. An acceptable efficiency value is recorded for the second type of slow waveguide mode. For the sake of targeting only input and output coupling losses, we made an assumption that other loss mechanisms are absent in the structure. The successful demonstration of effective and compact slow light couplers will assist the deployment of slow light devices in important applications, such as nonlinear optics, optical buffers, and optical delay lines.