Optical transmitter comprising a laser diode

Claim 1

In an optical transmitter comprising a laser diode and, optically coupled to the laser diode a photo diode operating as a monitor diode, whose photoelectric current is used for adjusting the light power of the laser diode, and including modulators used for modulating the laser diode current by a first signal (b n ) and a second signal (B k ), wherein the improvement comprises: a) means for multiplying a control current (Is) by the first signal (b n ), the control current (Is) being a d.c. current modulated by the second signal (B k ), b) filter means coupled to the output of the monitor diode, isolating the amplitude of the component of the photoelectric current, whose frequency corresponds to the fundamental frequency of the second signal (B k ), c) means connected to the output of the monitor diode for adjusting the amplitude of the a.c. component of the control current (Is) in a manner such that the amplitude of the fundamental frequency component of the photoelectric current of the monitor diode remains constant, d) means for maintaining the modulation factor of the control current (Is) at a constant level, e) filter means connected to the output of the monitor diode, for determining the d.c. component of the photoelectric current of the monitor diode, and f) bias adjustment means coupled to the laser diode for adjusting the bias current (Iv) of the laser diode in a manner such that the d.c. component of the photoelectric current remains constant.