Saturation Characteristics of Gain Guiding in Index-Antiguided Waveguides

We investigate numerically and analytically the effects of gain saturation on the propagation of the fundamental mode in a gain-guided index-antiguided slab waveguide. The propagating mode adapts to gain saturation by becoming less confined, while at the same time its peak intensity increases more slowly. The modal gain coefficient is shown to scale linearly with the modal confinement in the cladding. At steady state, both the mode shape and power remain constant. We show that, at large index antiguiding, the field profile inside the core remains nearly constant during propagation, which allows an analytical description of the evolution of the optical power inside the core.