Dynamics of carrier heating and sweepout in waveguide saturable absorbers

Pump-probe measurements in reverse-biased GaAs-GaAlAs waveguide saturable absorbers used in mode-locked diode lasers reveal an ultrafast transient in the absorption recovery dynamics, and a second slower signal before the final recovery. In this paper, we present a numerical model of the absorption and carrier dynamics in these saturable absorbers. The model includes high-field and space-charge effects, in addition to the spectral hole burning and carrier heating typically considered in semiconductor laser amplifiers. The results of the model indicate that field-induced carrier heating strongly influences the absorption dynamics in saturable absorbers. Screening of the electric field by drifting photogenerated charges affects the sweepout of carriers from the absorbing region, and thus, influences the absorption dynamics as well