High-order exceptional points in non-Hermitian Moire lattices

This study proposes an approach to generate high-order exceptional points (EPs) in non-Hermitian systems. A system comprising a homogenous waveguide is considered wherein the imaginary part of the refractive index is modulated using a one-dimensional Moire profile. This gain-loss modulation couples different lossless waveguide modes, and these hybrid modes can be modeled using a non-Hermitian matrix with complex off-diagonal elements. Results indicate that third-order EPs can be produced by the coalescence of two second-order EPs. Then, the necessary requirements are analyzed using coupled-wave equations and the physical effects of the singularities are discussed.