Reverse-chiral response of two T -symmetric optical systems hosting conjugate exceptional points

Abstract

Exceptional points (EPs) are a special kind of singularity that appear as topological defects in parameter-dependent open systems. Here we propose the concept of conjugate EPs, where a level-repulsion phenomenon between two coupled complex states can occur in the vicinity of a square-root branch point, which is analytically associated with the presence of two complex conjugate EPs. Depending on the iteration parameter, two corresponding levels are analytically connected via one of two conjugate EPs. Here, we report the hosting of two conjugate EPs in two complementary equivalent systems connected with time-reversal ($\mathcal{T}$) symmetry by using the framework of a gain-loss assisted dual-mode planar optical waveguide. We establish that if the complex potential of any system hosts an EP, then the $\mathcal{T}$-symmetric potential of the same system can host the associated conjugate EP. Owing to the EP-aided nonadiabatic population transfer based on device chirality, the reverse-chiral responses of two $\mathcal{T}$-symmetric devices have been explored in the context of an asymmetric-mode-conversion process. The proposed scheme has the potential to open up a credible platform to study the physics of EPs in $\mathcal{T}$-symmetric systems.