Double-clad and Yb:Er codoped fiber lasers emitting at eye-safe wavelengths
(>1.5 mum) have been investigated by varying the codopant concentrations,
core modifiers, fiber length, and the spectrum of the diode pump. With a pr
oper composition, the laser output contains only one lasing wavelength, at
1.6 mum. Highest slope efficiency greater than 60% for this three-level sys
tem, emitting only at 1.6 mum, has been obtained by using a 20-m-long, doub
le-clad and codoped fiber with the core and clad diameters of 6.3 and 300 m
um, respectively. By tradeoff of slope efficiency for higher output power,
a 30-m-long fiber is considered to be the best choice.