Conical diffraction, pseudospin, and nonlinear wave dynamics in photonic Lieb lattices

Band structure singularities occur in 2D photonic lattices when two or more bands intersect at a point. At this degenerate point, the wave group velocity is undefined. These singularities are associated with unusual wave dynamics such as conical diffraction [1], Klein tunnelling [2], and pseudo-diffusive wave transmission [3]. Conical diffraction and nonlinear wave propagation near such an intersection were first observed in a honeycomb lattice created using the optical induction technique [4]. More recently, other singular lattices generalising the Dirac point of the honeycomb lattice have been found [5, 6].