Erbium-ytterbium co-doped is an attractive system for short, efficient lasers and amplifiers operating in the 1.5 micron band. Co-doping permits a cooperative cross-relaxation process to transfer energy from excited ytterbium ions to the erbium system. This process can be used as a transfer energy from excited ytterbium ions to the erbium system. This process can be used as a pumping mechanism at 980 nanometers to significantly increase the absorbed pump power.Efficient energy transfer between the ytterbium and erbium ions enables the operation of compact laser devices with low erbium concentration, thus avoiding parasitic effects. The material parameters of a co-doped glass, including the cross-relaxation coefficient, are measured. A rate equation analysis of the co-doped system is developed, and approximate analytic expressions are derived for the lasing threshold, slope efficiency, and maximum output power. Short, ion-exchanged, waveguide lasers are fabricated in co-doped erbium-ytterbium glass. Lasing is achieved around 1537 nanometers with a launch power threshold and slope efficiency of approximately 15 milliwatts and 5.5 percent, respectively.