Small-signal amplification in short, Yb3+-sensitized, Er3+-doped alumina (Al2O3) channel optical waveguides with high Er3+ concentrations is analyzed. Taking into account uniform up-conversion, excited state absorption (ESA) from the Er3+ metastable level (4I13/2), and Yb3+ -> Er3+ energy transfer by cross relaxation, the obtainable gain improvements compared to Yb3+-free Er3+-doped Al2O3 optical waveguides are investigated. The amplifier model is based on propagation and population rate equations and is solved numerically by combining finite elements and the Runge-Kutta algorithm. The analysis predicts that 5-cm long Yb3+/Er3+ co-doped Al2O3 waveguides show 13-dB net signal gain for 100 mW pump power at p = 980nm.
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