Embodiments of the present disclosure are directed to a semiconductor optical amplifier including a semiconductor-based gain medium configured to receive a drive current and a variable-width waveguide coupled to the in the semiconductor-based gain medium, the variable-width waveguide including a plurality of narrow width regions and a plurality of wide width regions positioned alternately along a longitudinal axis of the waveguide. The variable-width waveguide further includes a plurality of transition regions having an adiabatically varying widths. Each transition region connects adjacent ones of the plurality of narrow width and width regions and the waveguide has a reduced drive current density in the plurality of wide width regions relative to the drive current density in the plurality of narrow width regions.