Theoretical investigation of modulation instability in a three-core coupler with negative index material channel

We investigate the modulation instability (MI) in a three-core oppositely-directed coupler with a particular emphasis on a negative index material (NIM) channel. In order to give a comprehensive picture, we consider the normal and the anomalous dispersion regimes. Special attention is paid to investigation of the influence of system parameters such as the power and the coupling coefficient on the MI. We also analyze the impact of different nonlinear configurations of coupler channels on MI. •We investigate the MI in three-core oppositely directed coupler with NIM channel.•We analyze impact of power and coupling coefficient in the instability spectrum.•Different nonlinear configuration of coupler channels considerably influences MI.•In normal dispersion regime, a threshold condition exists for certain configuration.•MI spectrum behaves differently in the two dispersion regime.