Laser diode driving circuit with safety feature

A driving circuit for driving a laser diode comprising:

• an optical power monitor for generating a monitor current indicative of output optical power from the laser diode;
• a set resistor for generating a set voltage based on the monitor current;
• an operational amplifier having a first input coupled to a main reference voltage and a second input for receiving the set voltage, the operational amplifier for generating an output signal indicative of a comparison between the first and second inputs;
• a variable current source coupled to an output of said operational amplifier, and coupled to said laser diode for biasing said laser diode, whereby the operational amplifier adjusts the output signal thereof to ensure that the set voltage and the main reference voltage are substantially equal;
• first comparator means for comparing the set voltage with a first safety reference voltage, whereby when the set voltage is substantially less than the first safety reference voltage a first fault signal is generated;
• a monitor diode comparator for comparing voltage across the monitor diode with a monitor diode safety reference voltage, whereby when the voltage on the monitor diode's anode is substantially greater than the monitor diode safety reference voltage a monitor diode fault signal is generated for shutting off the laser diode;
• shut down means for shutting down the laser diode in response to receiving the first fault signal or the monitor diode fault signal;
• and
• logic means for sending a signal to the shut down means for shutting down the laser diode if either of the first or the mointor diode fault signals is generated.