Uniformly-distributed energy losses in photonic gratings enabled by exceptional points in band diagrams

Abstract

Non-Hermitian systems manifesting degeneracy in both eigenvectors and eigenvalues - exceptional points (EPs) - demonstrate exotic phenomena in many fields and have been used to distinguish lasing modes, control light propagation, increase the resonator sensitivity to perturbations, show loss-induced transparency and non-reciprocal light transmission and propagation [1] , [2]. By proper tuning photonic grating dimensions, EPs can be observed in band diagrams [3] , [4]. Lately, systems with EPs have been reported to show constant-intensity solutions. However, decay-free fields in systems with EPs have been experimentally demonstrated only in macro-scale acoustical waveguides [5]. We report here uniformly-distributed energy losses experimentally observed in photonic gratings with ≈ 50 % duty cycle (DC), which operate between EPs in their band diagram. The losses are accompanied by projecting a decay-free free-space beam profile, even though the photonic structure is excited only from one side. Both the finite element method (FEM) and a coupled-mode theory (CMT) strongly agree with experimental findings.