White light cavity formation and superluminal lasing near exceptional points

We study theoretically a superluminal laser system comprising active and passive (lossy) coupled micro-resonators with equal gain/loss. It is shown that when the system satisfies the white light cavity (WLC) condition, corresponding to zero group index, it also forms a PT-symmetric system (PTSS) at its exceptional point (EP). Slightly above lasing threshold, in the broken symmetry regime near the EP, the system exhibits “superluminal” lasing – a unique lasing condition which is highly attractive for sensing and precision metrology applications. It is also shown that some of the latest experimental studies involving PTSSs have indirectly demonstrated such superluminal lasing.