Group velocity control in microring resonator chains in the presence of gain or loss

We analyse the effects of gain and loss on the group velocity of light propagating in microring resonator chains. These are shown to permit the nonlinear all-optical control of the transmission delay in ring resonator microstructures. In the superluminal regime, the analysis of lossy structures provides a general framework for the description of faster-than-light optical signal transmission of narrowband pulses at resonances in dissipative media.