Dynamically Encircling Exceptional Points in Different Riemann Sheets for Orbital Angular Momentum Topological Charge Conversion

Orbital angular momentum (OAM) provides an additional degree of freedom for optical communication systems, and manipulating on-chip OAM is important in integrated photonics. However, there is no effective method to realize OAM topological charge conversion on chip. In this Letter, we propose a way to convert OAM by encircling two groups of exceptional points in different Riemann sheets. In our framework, any OAM conversion can be achieved on demand just by manipulating adiabatic and nonadiabatic evolution of modes in two on-chip waveguides. More importantly, the chiral OAM conversion is realized, which is of great significance since the path direction can determine the final topological charge order. Our Letter presents a special chiral behavior and provides a new method to manipulate OAM on the chip.