Erbium-doped multicomponent phosphate glass waveguides were deposited by rf sputtering techniques. The Er concentration was5.3×1020 cm−3.By pumping the waveguide at 980 nm with a power of∼21 mW,a net optical gain of 4.1 dB at 1.535 &mgr;m was achieved. This high gain per unit length at low pump power could be achieved because the Er–Er cooperative upconversion interactions in this heavily Er-doped phosphate glass are very weak [the upconversion coefficient is(2.0±0.5)×10−18 cm3/s], presumably due to the homogeneous distribution of Er in the glass and due to the high optical mode confinement in the waveguide which leads to high pump power density at low pump power. ©1997 American Institute of Physics.