Wideband trapping of light by edge states in honeycomb photonic crystals
  We study theoretically light propagations at the zigzag edge of a honeycomb photonic crystal consisting of dielectric rods in air, analogous to graphene. Within the photonic band gap of the honeycomb photonic crystal, a unimodal edge state may exist with a sharp confinement of optical fields. Its dispersion can be tuned simply by adjusting the radius of the edge rods. For the edge rods with a graded variation in radius along the edge direction, we show numerically that light beams of different frequencies can be trapped sharply in different spatial locations, rendering wideband trapping of light. 
Chunfang Ouyang, Dezhuan Han, Fangyuan Zhao, Xinhua Hu, Xiaohan Liu   and Jian Zi
cond-mat.mes-hall physics.optics