An optical transmitter for generating a modulated optical signal for transmission over dispersive fiber optic links in which a broadband radio frequency signal input is applied to first and second RF inputs of an external modulator for modulating the output of a semiconductor laser. The transmitter includes a digital signal processor coupled to the output of the modulator for independently adjusting the DC bias of the first and second RF inputs to control a characteristic of the optical signal, such as noise associated with composite second order (CSO) distortion as a remote receiver.