K. Lee, Y. Xu, and A. Yariv, 11 This choice is due to the sixfold symmetry of the triangular lattice, which should display quite isotropic behavior and constitute a first step towards omnidirectional extraction, J. Opt. Soc. Am. B, vol.17, 1438.

N. Hagberg, A. Erikkson, and . Larsson, 16 More precisely, the light is diffracted in the left half space, with an azimuthal direction depending on the small incident angle of the guided mode with respect to the M direction. Angular measurements slightly off the M direction reveal similar results as those reported, IEEE J. Quantum Electron, vol.32, 15961996.