The effect of ion pairs in high-concentration erbium doped fibers on slow and fast light propagation enabled by coherent population oscillations at room temperature has been experimentally investigated.
We perform a study of extremely slow pulse propagation speed in densely-doped erbium fibers by using a detuned signal. A quantum coherence effect, coherent population oscillations, produces a very narrow spectral "hole" in the homogeneous broadened absorption profile of the erbium-doped fiber. The resulting rapid spectral variation of the refractive index leads to a large value of the group index. The interparticle interaction between the nearest neighboring active particles due to the high density of erbium ions is considered. The result shows that the nonlinear refractive index can be greatly increased which leads to the smaller group velocity and the larger time delay.