Relationship between gain and Yb3+ concentration in Er3+-Yb3+ doped waveguide amplifiers

We have used a rate equation propagation model of an Er3+/Yb3+ doped Al2O3 waveguide amplifier with copropagating pump at 980 nm to investigate the de pendence of gain on Yb3+ concentration. The model includes excited state ab sorption and energy transfer upconversion processes within the Er3+ as well as the relevant energy transfer processes between Yb3+ and Er3+. The resul ts of the calculations indicate a close relationship of the parameters gain , launched pump power, waveguide length, and Yb3+ concentration. Codoping w ith a well-chosen Yb3+ concentration is shown to increase the gain around 1 530 nm for all combinations of these parameters. The gain is improved most by Yb3+ codoping at pump powers around the amplifier threshold. At high pum p powers the increase in gain of an Er3+/Yb3+ doped waveguide is insignific ant compared to that of its Er3+ doped counterpart. Furthermore for each la unched pump power, a nonzero Yb3+ concentration can be determined, which ma ximizes the gain. (C) 2001 American Institute of Physics.