Coloration and its reduction in phosphorus-doped low-loss optical fibres

Coloration and its reduction in phosphorus-doped low-loss optical fibres have been investigated. The absorption loss at 0.53¿m is as high as 60 to 100 dB/km when measured immediately after the drawing process. The coloration, however, can be almost completely reduced by annealing at 100°C for 48 h.