A control circuit (10) controls the operation of a laser diode (1) for controlling the average power output (P.sub.av) and the extinction ratio. A state machine (21) controls the control circuit (10) which reads the current from a monitor photo diode (2) which is coupled to the laser dio
A resistive DAC (1) comprises a digital input port (2) and an analog output port (3) on which analog resistance output values are outputted in response to corresponding digital input codes on the input port (2). A decoding and control circuit (4) selects appropriate resistors (R1) to
