Impact of higher order dispersions and nonlinearities on instability criterion of oppositely directed coupler in the presence of negative index material channel

Abstract

This paper intends to investigate the modulational instability (MI) criterion of two core positive-negative index coupler channel setup from the obtained analytical dispersion relation for MI gain profile. The governing equation, the modified nonlinear Schrodinger equation (MNLSE) is studied for the role of higher order dispersion (HOD) and higher order nonlinearity (HON) on instability spectra of two core positive indexed coupler (PIM) and negative indexed coupler (NIM) arrangement. The HOD comprises of the second, third, fourth and fifth order linear dispersion terms and HON is inclusive of cubic, quintic, septic, cubic-quintic-septic-self-steepening (SS), and cubic-quintic-septic-intrapulse Raman scattering (IRS). Our study reveals that it is the 6th order linear dispersion term which brings in the considerable changes of MI gain spectrum in both normal and anomalous dispersion regimes. In particular, the combined effect of septic SS and IRS in two core directional coupler with NIM channel proves to be very crucial in the generation of instability gain spectra. This study has higher prospects in generation of solitary wave in two core directional system for optical fiber communication.