  Surface modes are generally believed to be an undesirable feature of finite
photonic crystals (PC), unlike point or line defect modes. However, it is
possible to make the surface mode radiate by appropriate corrugation of the PC
interface. In this paper we show theoretically that the coherent action of
these surface indentations can be engineered to collimate within a few degrees
the light exiting a PC waveguide, or to funnel light coming from free space
into the waveguide.
