Controllable propagation of light pulses in Er-doped fibers with saturable absorption.

We report controllable (slow or fast) propagation of low-intensity probe-light pulses through erbium-doped fiber periodically saturated by the synchronized master-pulse sequence. These two pulse sequences could have significantly different carrier wavelengths within the fundamental absorption spectrum 1470-1570 nm of Er(+3) ions. The effect of fractional delay or advancement grew with the fiber optical absorption at the probe wavelength and could be significantly stronger than that at the saturating wavelength. The probe-pulse advancement was observed in the case when the saturating and probe waves were modulated approximately in antiphase. The observed effects are explained in the framework of a simple model of a periodically saturated homogeneously broadened absorption line.