Light coupling for single-mode photonic crystal waveguides

We use a transfer-matrix method (TMM) to investigate light coupling into and out of single-end single-mode photonic crystal waveguides. Without multi-reflection complexity, we give clearly the unambiguous quantitative determination of the coupling efficiency of external light into guided mode and the transition among guided modes. It is shown that the waveguide with a line defect along ΓJ direction exhibits a much better coupling efficiency than that with a line-defect orientation along ΓM direction.