In this paper, we study basic properties of gain and loss guiding propagation modes in a cylindrical optical fiber with nonlinear effects simulated by a complex-valued refractive index. For this purpose we numerically solve the wave equation using the generalized Douglas scheme applied to the time-domain finite-difference beam propagation method. We compare the nonlinear numerically results with the linear case (real-valued refractive index) and with analytical results.
Key words: Nonlinear optical fiber, complex-valued refractive index, propagation modes