A driver circuit for a laser diode or other optical source includes a differential circuit having first and second inputs for receiving differential input data, a current generator circuit for generating modulation current for the optical source in response to the input data, and a variable bias circuit for applying a variable bias to the differential circuit. The current generator is preferably adapted to establish the modulation current for application to one of a first output and a second output of the driver circuit in accordance with the differential data applied to the first and second inputs of the differential circuit. The variable bias circuit may be configured such that the variable bias current generated thereby for application to the differential circuit is a function of the modulation current, thereby controlling an output overshoot of the driver circuit.