Analysis of nonlinear response of anti-parity-time symmetric structure

Abstract

This paper presents a theoretical analysis of a gain and loss saturation effect in planar multilayer anti-parity-time (APT) symmetric structures for the first time. This analysis makes it possible to examine the behaviour of nonlinear APT structures when excited by incident light of known intensity and compare their properties with corresponding parity-time (PT) symmetric structures. Two types of APT structures are studied: one with both layers of the primitive cell being gain layers and the other with both layers being loss layers. The refractive indices of the individual layers satisfy the condition n(z) = ‒n*(‒z). Nonlinear analysis is performed using a modified transfer matrix method, which allows for the determination of output intensity characteristics as a function of input intensity for different levels of gain or loss saturation intensities. These characteristics demonstrate a bistable behaviour and a strong nonreciprocal response of the investigated APT structures. The results obtained for both types of APT structures are compared with corresponding PT structures, showing that APT structures reveal identical linear and nonlinear responses as corresponding PT structures.