Nonlinearity-induced band gap transmission in dispersive and flat-band photonic lattices

Nonlinear interactions in photonic nondispersive (flat) bands remain largely unexplored, despite their potential to yield exotic phenomena. Here, we demonstrate the nonlinearity-induced transport of light from a boundary waveguide into photonic lattices with dispersive and flat-bands. For the one-dimensional lattice supporting a dispersive band, self-focusing Kerr nonlinearity effectively makes the boundary waveguide phase-matched with the lattice modes, enabling efficient energy transfer above a threshold input power. In contrast, such nonlinear transmission to the flat-band modes is inhibited, as demonstrated in a rhombic lattice supporting an isolated flat-band. Instead, as the nonlinearity increases, light couples periodically to the lattice edge mode and then gradually spreads into the lattice due to the excitation of the lower dispersive band.