Saturable higher nonlinearity effects on the modulational instabilities in three-core triangular configuration couplers

Abstract

This paper demonstrates the possibility to observe the modulational instability (MI) regions due to modified nonlinear saturability over and above other high-order nonlinearities for the triangular configuration of a three-core oppositely directed coupler. In this configuration, two channels are positive-refractive-index material, and one is a negative-index material. The governing equations are the modified coupled nonlinear Schrödinger equations, to which we add the higher-order nonlinearity terms and coupling terms. This equation is further modified with the saturable nonlinearity term. In the presence of several nonlinearities, we derive the dispersion relation for the optical coupler under consideration. We use a linear stability analysis to study the modulation stability characteristic gain in both the normal and anomalous group-velocity dispersion regimes. We have widely varied the parameter range of the physical system parameters to accommodate different possibilities. In the normal region, the saturable nonlinearity aids in increasing the bandwidth of the MI region, while in the anomalous regime, the bandwidth reduces. In the normal dispersion case, the simultaneous presence of all nonlinearities in the optical coupler does not provide a suitable scope for pulse propagation. On the other hand, in the anomalous regime, these nonlinearities favor for pulse propagation.