  We propose and analyze novel surface-state-based waveguides in bandgap
photonic crystals. We discuss surface mode band structure, field localization
and effect of imperfections on the waveguiding properties of the surface modes.
We demonstrate that surface-state-based waveguides can be used to achieve
directional emission out of the waveguide. We also discuss the application of
the surface-state waveguides as efficient light couplers for conventional
photonic crystal waveguides.
