CW tunable laser emission between the F-2(5/2) and F-2(7/2) levels of
trivalent ytterbium has been studied in single mode ZBLAN fibres. Diff
erential quantum efficiency of more than 60%, 100 mW output power and
tunability range between 975 and 1055 nm were obtained with various ca
vity configurations and ytterbium concentrations.