The authors observed a spectral burning hole and slowdown of light propagation by population oscillation technique in an Erbium-doped optical fiber. Measured bandwidth of the hole was about 55 Hz. Group velocity was 2.186×103m/s.
We investigate the reduction of the group velocity propagation resulting from the steep change of the refractive index by the coherent population oscillation in erbium-doped optical fibre. The largest delay is measured to be about 8.75ms corresponding to a group index of 1.312 × 10 6 . The time delay or advancement depends on the pump intensity. Influences of the ion density on the fractional delay and the group velocity reduction of light propagation are studied. Based on our discussion the optimization parameters should be selected in order to obtain more appropriate time delay and the slowdown of group velocity.
\n\nSpectral hole-burning in an erbium-doped silica fibre at room temperature has been experimentally demonstrated. This demonstration can be considered as a clear experimental evidence of the relationship between slow light and coherent population oscillations in erbium-doped fibres. In a 3.5 m erbium-doped silica fibre, spectral holes with a depth up to 1.5textm−1 were obtained by coupling a strong and narrow saturating power and measuring changes in the spectral absorption coefficient for a weak and wide probe power. A tuneable ring-cavity erbium-doped fibre laser was employed as saturating source. To obtain a higher saturating power, laser emission was amplified by means of a second fibre amplifier.\n
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.
The homogeneous linewidth of the transition I15/24−I13/24 in highly doped erbium fibers and its dependence with temperature in the range from 10 to 50 K are experimentally characterized using spectral hole burning. The homogeneous linewidth dependence with temperature is quadratic above 20 K where homogeneous broadening is dominated by two-phonon Raman processes, and linear at lower temperatures where direct phonon processes occur. This characteristic power-law dependence was also derived from transmittance measurements. The solution of nonlinear field equations using the results obtained from our experiments predicts that Gaussian probe pulses propagate at subluminal speed through the narrow spectral holes burned in erbium-doped fibers. For gigahertz pulses in the telecommunication window, a fractional delay as high as 0.6 is predicted.