Abstract: Embodiments of the present invention are sulfur rich glass compositions comprising germanium, gallium and sulfur, which glass compositions have a low energy phonon spectrum and which glass compositions serve as a host for active materials in fabricating light sources such as fiber laser oscillators, light amplifiers, and superluminescent sources. In particular, such a laser oscillator, light amplifier or superluminescent source is comprised of an inventive glass composition which is doped with rare earth ions such as Pr.sup.3+ or Dy.sup.3+ for producing light output at wavelengths, among others, substantially at 1.3 um. Further embodiments of the present invention are light sources such as laser oscillators, light amplifiers and superluminescent sources which have emissions substantially at 1.3 um and which are comprised of an inventive glass composition which is doped with Dy.sup.3+ and Yb3+ ions, wherein Dy.sup.3+ ions are pumped by energy transfer from Yb3+ ions.