Polarization-dependent gain in bismuth-doped phospho- and germanosilicate fiber amplifiers.

Polarization-dependent gain (PDG) effect was studied in a conventional core-pumping configuration of bismuth-doped fiber amplifiers (BDFAs) based on PANDA-type phospho- and germanosilicate core fibers. The PDG value was determined as the gain difference between the orthogonal signal polarizations, which was found to be in range of 2.5-3 dB at total gain of >20 dB in such BDFAs. This effect is more pronounced for BDFA with a germanosilicate fiber. The experimental results are in a good agreement with the calculated data derived from the simulation model, relying on the anisotropy parameter of bismuth active centers (BACs) obtained from the degree of luminescence polarization, which ranges between 9 and 12% for BACs-Si and 18 and 22% for BACs-P. The obtained data can be useful for the optimization of performance of BDFAs and studying structural peculiarities of BACs.