Techniques are disclosed for providing modulation current that includes output impedance compensation with a feed-forward bandwidth enhancement and pre-distortion modulation to control waveform transition symmetry. A feedback circuit senses output node voltage and increases the overdrive voltage of a current source. This offsets the loss of current due to channel length modulation and increases the effective output impedance of the source. A feed-forward circuit enhances the bandwidth of the impedance compensation feedback loop. Waveform transition symmetry is improved by pre-distorting a laser modulation current by introducing an undershoot current on the falling edge of the modulating current.