On the role of evanescent modes and group index tapering in slow light photonic crystal waveguide coupling efficiency
We investigate effects of different mechanisms on coupling efficiency between strip waveguides and the slow light mode in photonic crystal waveguides (PCWs). Both numerical simulations and experimental results show that group index (𝑛𝑔)(ng) tapering improves strip-PCW butt-coupling efficiency when compared to a direct coupling between a strip waveguide and a high-𝑛𝑔ng PCW. However, coupling efficiency is even higher when an intermediate low-𝑛𝑔ng PCW is used to couple from a strip waveguide to a high-𝑛𝑔ng PCW without an 𝑛𝑔ng tapering. Our results suggest that the role of evanescent mode is more dominant in efficient coupling between two PCWs with large 𝑛𝑔ng mismatch.
This research was supported by the AFOSR Multi Disciplinary University Research Initiative (MURI) under Grant No. FA9550-08-1-0394 and AFOSR Small Business Technology Transfer (STTR) under Grant No. FA9550-11-C-0014.
