Light trapping and releasing in side-coupled microresonator structures with asymmetric cavity–waveguide coupling

In this work we analyze the waveguiding properties of a kind of side-coupled microresonator structures with asymmetric coupling. The mismatch in the two resonator–waveguide couplings plays a similar role of loss and gain in the constituent material but offers much flexible controllability, in terms of achieving fast- and slow-light. Using a generalized transfer matrix formalism, we determine the criteria for achieving subluminal and superluminal pulse propagation in these structures. Moreover, we propose a scheme for light trapping and releasing by dynamical control of the resonator–waveguide coupling strengths. Time-domain numerical simulations with feasible physical parameters for the switching operation are presented.