Exotic light dynamics around an exceptional point of order four associated with three connecting second-order exceptional points

The physics of exceptional point (EP) singularities has been a key to a wide range of unique physical applications in open systems. In this context, the mutual interactions among four coupled states around a fourth-order EP (EP4) in a physical system is yet to be explored. Here we investigate the unique features of an EP4 in a fabrication feasible planar optical waveguide with a multilayer gain-loss profile based on only two tunable parameters. Following a quasistatic gain-loss around the embedded EP4, a unique fourth-order successive switching phenomenon among the propagation constants (β values) of four coupled modes has been explored. An exclusive chiral light dynamic following the dynamical variation of the gain-loss profile has been reported for the first time, which enables a special type of asymmetric higher-order mode conversion scheme. Here all the coupled modes associated with an EP4 are fully converted into different specific higher-order modes based on the choice of encirclement directions. The proposed scheme would present EP4 as a new light manipulation tool for integrated photonic devices.