Analysis of directional emission via surface modes on photonic crystals

Directional emission of light exiting a photonic crystal waveguide by a coherent action of radiative surface modes was recently demonstrated [E. Moreno et al., Phys. Rev. B 69 (2004) 121402], and subsequently the substantial enhancement of the directional emission was achieved by engineering the surface and adjusting relevant parameters [S.K. Morrison et al., Appl. Phys. Lett. 86 (2005) 081110]. Here we present the analysis of surface modes causing directional emission by the plane wave expansion method and the finite-difference time-domain method. Then we numerically investigate the effects of surface termination on directional emission. We find another surface termination condition with a positive surface displacement. Our surface termination is more effective than the original structure, and nearly as effective as the termination for the enhancement. Besides, our termination is simpler than that for the enhancement. We confirm its effectiveness in the far-field beam profile and radiation intensity distribution of directional emission from our termination.