Summary form only given. Erbium-ytterbium (Er/sup 3+/-Yb/sup 3+/) codoped glass is an attractive system for short, efficient lasers and amplifiers operating in the long-haul telecommunications range. The pump absorption near 980 nm is increased, and efficient energy transfer between the Yb/sup 3+/ and Er/sup 3+/ ions enables the operation of compact laser devices with low erbium concentrations. We present simple methods that can be used to model the Er/sup 3+/-Yb/sup 3+/ codoped glass system and predict laser performance. Experimental results for fabricated waveguide laser devices are discussed.