Manifestation of super chiral exceptional point in plasmonic metasurface

The exceptional point (EP), a degenerate point within non-Hermitian parametric space, has attracted considerable attention, especially for its chiral responses. However, achieving ideal circular dichroism (CD) remains challenging due to the existence of parallel components at the EP. Here, we delve into the theoretical condition required to attain a zero-transmission parallel component. This condition, together with the chiral EP condition, leads to a point characterized by near-unity CD, termed the super chiral EP (SCEP). To illustrate our theoretical framework, we introduce a parity-time symmetric metasurface with gain and loss. The observation of SCEP is demonstrated by tuning both the coupling strength and gain–loss ratio. Furthermore, we explore distinctive properties of SCEP, including phase flip and unidirectional invisibility. Leveraging SCEP and the topological phase transition point, we achieve polarization states across the entire Poincaré surface. This work opens avenues for potential applications in polarizing optical elements, holography, logic gates, chiral molecular detection, ultrasensitive sensing, and polarization-sensitive imaging.