Pump-induced Nonlinear Refractive-index Change in Erbium- and Ytterbium-doped Fibers: Theory and Experiment

摘要

A 980-nm pump-induced nonlinear refractive-index (n_2) change in erbium-doped (20-m) and ytterbiumdoped (20-m) fibers has been measured at 1064 nm by time-delayed photorefractive beam coupling in a copropagating and counterpropagating geometry. It was found that nZ decreases at the wavelength of the probe beam when the pump beam is present. We present a semiclassical theory based on a four-state system that accounts for the pump-induced change of n2. Both theoretical and experimental results show that a significant index change, of the order of 10percent, can be obtained for cw pump powers as small as 10 mW.