Fiber-amplified spontaneous emission sources incorporating spectral filters show an improvement in mean wavelength stability versus a number of operating factors, including pump wavelength, pump power, feedback, and temperature. By adjusting the spectral characteristics of the filter, the position of the filter along the length of the fiber, and the length of the rare-earth doped fiber, a stable ASE source is designed so as to provide stable operating points for the mean wavelength versus desired operating parameters. In many cases the sources show an improvement in mean wavelength stability by an order of magnitude or more over present sources.