Complex nonlinear multimode fiber systems

We describe the complex beam evolution that originates from purely spatial nonlinear effects in multimode optical fibers. Specifically, we focus on the spatial self-imaging effect that occurs in graded-index fibers and its impact on dissipative nonlinearities which take place at power close to the fiber damage threshold. Theoretical models are compared with recent experimental results involving nonlinear optical losses, the luminescence of the fiber defects induced by the multiphoton absorption of femtosecond pulses, as well as multiphoton ionization effects which lead to the formation of plasma filaments