Method and apparatus for monitoring performance of a laser transmitter

A method for monitoring an output level of a laser, the method comprising the steps of:

• selectively generating at least first threshold voltage and second threshold voltage values;
• setting a threshold voltage value to a first of the at least first and second threshold voltage values, said first threshold voltage value representing a first operational output state of said laser, and said second threshold voltage value representing a second operational output state of said laser;
• generating an output signal representative of said output level of said laser;
• comparing a value of said output signal representative of said output level with said first threshold voltage value;
• and
• selectively generating said second threshold voltage value when said value of said output signal representative of said output level of said laser is less than or equal to said first threshold voltage value.

An apparatus for use in monitoring an optical output power level of a laser, comprising

• a photodiode adapted to receive laser light from said laser to generate an electrical current which is proportional to the optical output power level of said laser;
• a resistor in series circuit relationship with the photodiode and being supplied with the electrical current to generate a monitor voltage;
• a window comparator having a plurality of input ports and a plurality of output ports, said monitor voltage being supplied to two of said input ports, wherein the window comparator compares said monitor voltage to a threshold voltage value supplied from a variable voltage source to a third input port, and supplying as an output an alarm signal in response to said comparison;
• and
• a variable voltage source having an output in circuit with said third input port and being responsive to an output from the window comparator to supply a plurality of threshold voltage values to said third input port of said window comparator.