Asymmetric guidance of multiple hybrid modes through a gain-loss-assisted planar coupled-waveguide system hosting higher-order exceptional points

The gain-loss-assisted optical systems have revealed an unconventional light manipulation tool by hosting exceptional points (EPs), which has lately a great deal of interest in the photonics community. Here, the emergence of higher-order EPs is investigated in a planar coupled-waveguide geometry, which has the potential to assemble additional degrees of freedom to explore EP-induced light dynamics. A planar form of waveguide array consisting of four high-indexed guides is designed to support multiple quasiguided hybrid modes. An inhomogeneous customized gain-loss profile to couple at least three chosen modes is introduced in such a way that the waveguide hosts an EP of order three with the simultaneous presence of two second-order EPs in the gain-loss parameter plane. We investigate the dynamical parametric encirclement schemes of embedded EPs of different orders and exclusively reveal both the chiral and nonchiral dynamics of light assisted by asymmetric conversions of hybrid modes. The implementation of our findings in discrete photonic systems hosting higher-order EPs indeed opens up a fertile platform to meet a wide range of enticing applications in the context of manipulation of modes including conversion and switching.