Patent ID: 7443897

Claim:
An optical transmitter, comprising: a semiconductor laser diode that emits an optical signal; a driver that provides a driving current for the laser diode; a photodiode configured to sense a portion of the optical signal emitted from the laser diode and to generate a sensing signal corresponding to the portion of the optical signal; and a control unit configured to provide a control signal to the driver based on the sensing signal to keep the sensing signal constant, wherein the control unit is configured to monitor the driving current at regular intervals to generate a monitoring signal corresponding to a magnitude of the driving current and a time differential of the monitoring signal, to compare the monitoring signal with a first reference and the time differential of the monitoring signal with a second reference, to set an alarm when the monitoring signal exceeds the first reference, and to set the control signal so as to stop a supply of the driving current to the laser diode when the monitoring signal exceeds the first reference and the time differential of the monitoring signal exceeds the second reference.