Abstract: An optical transmitter comprising a control loop for stabilizing the bias current which sets a bias level of the amount of light emitted by a laser diode 6. A cascade circuit 5 which includes the laser diode 6, a photodiode 7 and a variable gain control amplifier 8 is connected in the negative feedback path of the control loop. To prevent amplitude modulation of the bias current when a modulation signal occurs at the input of the gain control amplifier, the control loop produces a cancelling signal of a magnitude which cancels the mean value of such modulation signal. The cancelling signal is derived from the modulation signal in a fixed manner, by fixing the transfer factor of the negative feedback path as measured by transmission of an auxiliary signal through such path and adjusting the gain of amplifier 8 in accordance with the result of such measurements.