Sensitivity to termination morphology of light coupling in photonic-crystal waveguides

We use a transfer-matrix method to investigate light coupling problem in single-end photonic-crystal (PC) waveguides. We find that the coupling efficiency is sensitive to the surface termination morphology of the waveguide. A slightly tapering geometry can lead to an order of magnitude difference in the coupling efficiency of an external extended wave into the waveguide. However, this tapering geometry does not necessarily lead to enhanced coupling of a guided wave out of the PC waveguide. We have attributed this strong asymmetric coupling characteristic to the significant difference in the scattering behavior of an extended wave and a localized wave by the complex surface microstructure of a PC waveguide.