Modified nonlinear saturable effects on instability characteristics in three-core oppositely directed coupler with Kerr nonlinearity

Abstract

This work shows that it is possible to observe the modulational instability (MI) zones caused by the modified form of nonlinear saturation effect in triangular design of a three-core oppositely directed coupler. In this design, the first and third channels are made of a material with a low (negative) refractive index, while the second one is made of a high (positive) index. The governing equations are modified coupled nonlinear Schrödinger equations with saturable nonlinearity terms and coupling terms. In the presence of modified saturable nonlinearity, we can determine the dispersion relation for the optical coupler. We use a linear stability approach to investigate the modulation instability characteristic gain in the normal and anomalous group-velocity dispersion regimes. We greatly widened the spectrum of physical system parameters to consider various contingencies. Using nonlinear and power factors, MI can be controlled. Nonlinear saturation effect normally can suppress the MI gain and bandwidth in optical fiber system. But, as compared to conventional saturable nonlinearity, the modified saturation nonlinearity more significantly changes the MI dynamical behaviour. The analytical results show that new instability bands are created in a system parameter's normal and anomalous dispersion regimes. As a result of the effects of modified nonlinear saturation, we describe new methods for creating and managing the soliton through MI in three-core oppositely directed couplers with two negative index material channels.