Role of higher order nonlinearities in the instability spectra of two core oppositely directed saturated coupler

Abstract

We theoretically investigate the impact of modified form of saturable nonlinearity in the modulational instability (MI) spectra of an opposite directed two core coupler with a negative index material channel. Particularly, our emphasize is on the interplay between the nonlinear saturation and the higher order nonlinear effects in fibers such as self-steepening and intrapulse Raman scattering. Using the modified nonlinear Schrödinger equation we appropriately model the light propagation in the two core opposite coupler with saturation of nonlinearity. A standard approach like the linear stability analysis was used to derive the dispersion relation pertaining to the MI. For a comprehensive picture, we consider both the normal and the anomalous dispersion regimes and special attention is paid to understand the influence of system parameters such as the power, coupling coefficient, saturation parameter, and nonlinear coefficient on the MI. Effect of different combinations of self-steepening as well as the contribution of intrapulse Raman scattering are discussed and its role on the instability bands are highlighted. Thus we report new ways to generate and manipulate the MI in two core oppositely directed couplers with the effect of saturation of nonlinearity.