Polarization of the fluorescence excited in erbium-doped fibers in 1490-1570Â nm spectral range

We present data on the polarization degree of the fluorescence, excited in erbium-doped fibers (EDF) by linearly polarized light at three essentially different wavelengths in the spectral range of the fundamental absorption of Er3+ (1492, 1526, and 1568 nm). Experiments were performed in otherwise similar single-mode fibers with a broad range of erbium concentration (≈640-5600 wt ppm). The polarization degree of the fluorescence demonstrated expected decay with the incident light power and proved to be significantly weaker for the central excitation wavelength of 1526 nm. The maximum value of the experimentally observed effect (≤0.3%) is significantly lower than it is predicted by model of the randomly oriented non-interacting dipoles. This discrepancy is explained by the reduced anisotropy (to the value 0.7-0.8) of the erbium ions absorption/emission, the effect which was utilized to explain the experimentally observed weak polarization hole burning in EDF earlier. Additional reduction in the fluorescence polarization degree and accelerated depolarization relaxation which were experimentally observed in fibers with high erbium concentration are attributed to the spatial migration of the excited state.