Abstract: An optical transmitter for transmission of data signals includes a laser diode producing optical radiation and a photodiode which in response thereto produces a photocurrent the mean value of which corresponds to the mean optical power of the radiation. Based on the photocurrent a control circuit derives parameters for controlling the laser current so as to compensate for changes in the characteristic line thereof, which line is the relation between optical power and laser current. Such parameters include a modulation current setting parameter U.sub.mod and a bias current setting parameter U.sub.0. The bias current is controlled to remain at or above the dip in the characteristic line at relatively low current levels.