A phosphate glass 1-.mu.m fiber ASE source provides high power and broadband emission that covers wavelengths on the short side of Yb-doped silica. A single-mode fiber formed from phosphate glass is doped with highly elevated concentrations of Yb dopants 0.5-30 wt. % and typically 2-10 wt. %, far higher than either silica or germano-silicate. The high concentration of Yb dopant absorbs the pump in a short length, typically 10-150 cm instead of tens of meters, to provide high saturated output power and a shifted emission spectrum. The excess power allows the fiber ASE source to be configured to provide the output powers, emission bandwidth and stability desired by many applications. Furthermore, the ASE can be configured to emit a nearly Gaussian spectral profile without sacrificing power or bandwidth. The backward emission spectrum of Yb-doped phosphate glass is centered near 1020 nm instead of 1060, which allows the ASE source to cover wavelength on the short side of Yb-doped silica, which may be important in certain applications such as ophthalmic OCT where water absorption has a transparency window.