Influence of nonlinear conventional saturation on spatio-temporal modulational instabilities in PT-symmetric fiber Bragg grating structures

Abstract

This paper is intended to present an investigation into the impact of cubic, quintic, and saturable nonlinearity on the instability in PT-symmetric fiber Bragg grating structures (FBG) with various PT-symmetry regimes. A conventional linear stability analysis identifies the modulational instability (MI) gain, where the combinatorial influence of cubic and quintic nonlinearities on MI is carefully studied in both normal and anomalous dispersion regimes. Additionally, we investigate the characteristics of MI at the bottom and top edges of the photonic band gap. The investigation highlights the importance of non-Kerr nonlinearity in relation to the MI gain. It is shown that even in the presence of PT-symmetry, one could effectively control the MI by varying the cubic, quintic, and saturable nonlinearity for various PT-symmetric regimes. The investigation revealed a range of spectral varieties, including asymmetry, symmetry, sideband spectrum, steadily increasing gain, broad spectrum, and others. We find an anomalous spectrum that is more discrete than continuous for the few physical components. The emergence of solitary waves in nonlinear episodic structures is also examined following the use of PT-symmetry.