Coupled-resonator-induced reflection in photonic-crystal waveguide structures

We study the resonant transmission of light in a coupledresonator optical waveguide interacting with two nearly identical side cavities. We reveal and describe a novel effect of the coupled-resonatorinduced reflection (CRIR) characterized by a very high and easily tunable quality factor of the reflection line, for the case of the inter-site coupling between the cavities and the waveguide. This effect differs sharply from the coupled-resonator-induced transparency (CRIT) - an all-optical analogue of the electromagnetically-induced transparency - which has recently been studied theoretically and experimentally for the structures based on microring resonators and photonic crystal cavities. Both CRIR and CRIT effects have the same physical origin which can be attributed to the Fano-Feshbach resonances in the systems exhibiting more than one resonance. We discuss the applicability of the novel CRIR effect to the control of the slow-light propagation and low-threshold all-optical switching.