Modeling of Loss-Induced Superluminal and Negative Group Velocity in Two-Port Ring-Resonator Circuits

The group velocity v_g of light in two-port ring- resonator (TPRR) circuits with loss is theoretically studied. We point out four possible operation regimes, i.e., "slow" light with positive v_g, "slow" light with negative v_g, "fast" light with negative v_g, and "fast" light with positive v_g, where "slow" means |v_g| < c and "fast" means |v_g| > c, with c denoting the velocity of light in vacuum. The temporal behavior of pulses passing through the TPRR for the four operation regimes and the potential of "slow" light TPRR either with positive or negative v_g for sensing applications are also discussed.