Encircling an exceptional point in a multiwaveguide anti–parity-time-symmetry system

Abstract

Encircling exceptional points in an anti--parity-time- (anti--PT) symmetry system is known to provide a new platform to realize information processing. Dynamically enclosing an exceptional point can lead to chiral mode switching, where eventual modes are determined by the direction of the path. Dynamical chiral mode conversion of multiwaveguide systems has been lacking in the literature. Here, we propose an approach to study the dynamical process and discover a chiral mode conversion in multiwaveguide system. We demonstrate that if the number of waveguides is more than or equal to three, then the system can be simplified to a two-level anti--PT symmetric system by adding given gain or loss. Besides, for the particularity of asymmetrical loop in actual waveguide systems, modes switching are related to the direction and the starting points of the trajectory, thus exhibiting another chiral form. Our research not only provides a mechanism to control the mode evolution dynamics but also offers a method towards designing photonic devices to realize telematics.