Backscattering-Induced Chiral Absorption in Optical Microresonators

Chirality in micro- and nanophotonic structures is crucial for both fundamental research and applied technology. Here, we experimentally demonstrate chiral absorption via backscattering in a single whispering-gallery microresonator under simultaneous excitation from both ports. Remarkably, this scheme does not rely on any nonlinear effects or the breaking of parity or time-reversal symmetry. These intriguing phenomena occur due to the interference between the clockwise- and counterclockwise-propagating light fields induced by the backscattering. Furthermore, we also achieve the chiral optical states in a coupled-microresonator system, which can be utilized to manipulate the electromagnetically induced transparency or absorption effect. Our work proposes a linear and all-optical scheme to realize chiral optical states, which can help control the light flow in photonic systems with a high operation rate.