Structurally chiral photonic crystals with magneto-optic activity: indirect photonic bandgaps, negative refraction, and superprism effects

We have theoretically investigated the general properties of photonic crystals without time-reversal and space-inversion symmetries by examining the case of one-dimensional periodic, lossless dielectric helical media (HM) with magneto-optic (MO) activity. We show that photonic bandgap formation in the absence of these two symmetry elements leads to a remarkable set of properties: indirect photonic bandgaps (edges not aligned in k space), backward wave propagating eigenroodes (which allow for negative refraction), unusual nonpropagating modes in the gap (their complex-valued wave vectors have frequency-dependent, nonzero real parts, which do not change sign for opposite decay directions), anomalous propagation, and group-velocity-based unidirectional superprism effects. Particular properties of MO HM are discussed in detail. (C) 2005 Optical Society of America.