Modulational Instability in Generalized Nonlinear Schrödinger Equation for Constant Intensity Wave Propagation

We analyze the modulation instability of constant intensity solution of nonlinear Schrödinger equation with $$\mathcal{P}\mathcal{T}$$ symmetric potential and external source. The governing equation models the wave propagation in a tapered graded-index waveguide. We examined the effect of source amplitude on modulation instability of constant intensity solutions. It is observed that by controlling the external source, which can be modulated through the graded-index profile, the occurrence of modulation instability can be enhanced or suppressed.