Light propagation via coupled defects in photonic crystals

Summary form only given. Low-loss waveguiding around sharp bends is a key task in microoptics. A coupled-defect waveguide is able to perform much better at sharp bends than a channel waveguide. It also can enhance considerably the efficiency of second harmonic generation due to the low effective group velocity. Coupled-defect optical waveguides are a superlattice or superstructure consisting of original and modified unit cells of the underlying photonic crystal. A tight-binding description of a chain of defects in a linear medium was derived in leading to a dispersion relation which is quadratic with respect to the frequency. Recently the validity of the tight-binding approximation of the defects in a two-dimensional superstructure was investigated by means of direct transmission calculations using a transfer-matrix method.