Slow-light dispersion in coupled periodic waveguides

Periodic waveguides bring a new twist to the typical waveguiding problems of the intermediate case between photonic crystal waveguides and photonic wires or ridge waveguides. We develop an asymptotic theory applicable for a broad class of coupled periodic waveguide structures and use the analytical expressions to identify the generic types of dispersion in the vicinity of a photonic band edge, where the group velocity of light is reduced. We show that the dispersion can be controlled by the longitudinal shift between the waveguides. We also demonstrate through finite-difference time-domain simulations examples of spatial and temporal pulse dynamics in association with different types of slow-light dispersion.