Measurement of high photodarkening resistance in heavily yb31-doped phosphate fibres

The measurement of record-high photodarkening resistance in single- mode phosphate fibres doped with 12 and 6 wt.% Yb₂O₃ is reported. After pumping for 10 000 min at a high population inversion (~47%), the fibre exhibited no photodarkening at 660 nm. Silica fibres pumped to the same inversion did show photodarkening, indicating that the phosphate fibre can be doped with at least six times as much Yb and still show no photodarkening.