Propagation-induced transition from slow to fast light in highly doped erbium fibers

Abstract

We analyze the propagation regime of an amplitude-modulated 1536 nm signal when traveling along a highly doped erbium fiber pumped at 977 nm as a function of the fiber length. A propagation-induced transition from superluminal to subluminal propagation takes place along the fiber length which allows a change in regime solely based upon increasing the signal modulation frequency. This peculiar behavior is due to the interplay between pump absorption and pump-power broadening of the spectral hole induced by coherent population oscillations. The effect of ion density on this frequency-dependent regime change has been investigated.