Slow and fast light via two-wave mixing in erbium-doped fibers with saturable absorption

Abstract

We report experimental observation of slow or fast light in configuration of counterpropagating saturating and probe waves in erbium-doped fibers with saturable absorption. The delayed or accelerated probe light propagation is shown to be associated with two-wave mixing (TWM) between these two waves via dynamic population grating. As compared with recording at 1526 nm from the central region of ${\text{Er}}^{3+}$ fundamental absorption spectrum, at 1485 nm, the population grating has significant admixture of the refractive index component. This results in a significant asymmetry of the TWM-induced transmittance of the probe wave as a function of the frequency offset $\ensuremath{\Delta}\ensuremath{\Omega}$ between the waves and shifts position of the maximum group delay from zero $\ensuremath{\Delta}\ensuremath{\Omega}$. The same reason ensures appearance of a significant group advancement for the frequency offset of the opposite sign.