The role of tungsten oxide in Er-doped bismuth-germanate glasses for optical amplification in L-band.

A series of novel Er-doped bismuth-germanate glasses containing different tungsten concentrations with a molar composition of 97.5[(75 - x)GeO-25BiO-(x)WO]-2SbO-0.5ErO (x = 5, 10, 15, 20, and 25 mol%) were fabricated. Their thermal properties are measured by differential scanning calorimetry. A structural investigation by Raman spectroscopy suggested that changes occurred in the glass network by WO incorporation. By laser excitation at 980 nm, a strong emission from Er ions at 1532 nm is observed, while the WO addition caused changes in the emission spectra. The emission cross-section spectra of Er are calculated by both McCumber and Füchtbauer-Ladenburg theories and their comparison showed these theories yielded slightly different results, but in both cases, the calculations showed that a gain signal in L-band can be achieved when 30% of the Er ions are at the excited state. This study proves that the Er-doped bismuth-germanate glasses are suitable for optical fiber amplifier applications operating at C- and L-band.