Exceptional points in extraordinary optical transmission through dual subwavelength metallic gratings

Complex metamaterials with multiple optical resonances in constituent elements possess many similarities with open quantum systems that can be described by non-Hermitian Hamiltonian. By analogy with a two-state open quantum system, we show that a classic analogue of exceptional points can be observed in the transmission spectra of dual subwavelength metallic gratings. Anti-crossing (crossing) between the two branches λ(R) of extraordinary optical transmission, with crossing (anti-crossing) of the corresponding widths Γ(R), is observed in the parameter space spanned by the lateral displacement L and the angle of incidence φ0. Exchanges of field patterns and phases, and the variation of field profile when circling the exceptional point are discussed. This work highlights the potential to transfer the concepts and applications from open quantum systems to optical metamaterials.