Efficient excitation of self-collimated beams and single Bloch modes in planar photonic crystals.

Using finite-difference time-domain calculations, we investigate out-of-plane coupling between a square-lattice planar photonic crystal and a conventional waveguide located above the photonic crystal. We couple a waveguide oriented in the gamma(chi) direction to a photonic crystal mode in the second band and show that anticrossing takes place. In this way, a self-collimated beam is launched in the planar photonic crystal, with full power transfer. Furthermore, we investigate the coupling between a waveguide oriented in the gamma(mu) direction and a photonic crystal and show that single photonic crystal modes can be selectively excited.