Dynamically Encircling Multiple Exceptional Points in Waveguides System: Asymmetric–symmetric Multimode Switching

Dynamically encircling exceptional points in non-Hermitian systems leads to counterintuitive chiral mode conversions, which provides a new platform for implementing information processing. Previous research has shown that the position of the starting point determines whether the dynamics are chiral or non-chiral. Photonic devices that simultaneously realize chiral and non-chiral mode converters are yet to be investigated. In this letter, a four-state non-Hermitian waveguide array with two exceptional points is presented and the dynamical encirclement of each exceptional point and double exceptional points, which possess chiral and non-chiral dynamics is studied. Encircling a single exceptional point and both exceptional points gives the same outcome but a different encircling process. During non-chiral dynamics, the initial states are not on the Riemann sheet that forms the EPs, encircling both exceptional points produces more branch cuts than encircling a single exceptional point. An asymmetric–symmetric multimode switch at telecommunication wavelengths is demonstrated. Chiral mode converter and non-chiral mode converter can be implemented simultaneously on one photonic device. The research enriches the exploration of the physics associated with multiple exceptional points in non-Hermitian multistate systems and inspires wide applications in on-chip optical systems.