Feedback circuit for controlling the peak optical output power of an injection laser

Claim 1

Apparatus for controlling a bias current of a laser at an appropriate operating point, comprising: means for operating a laser either in an ON state or an OFF state in response to corresponding data signals, photodiode means for receiving at least a portion of radiation emitted by a laser to be so controlled and for passing a photodiode current corresponding to incident radiation, a current node coupled to said photodiode means, a fixed source of current of magnitude I ON , said magnitude I ON corresponding to a photodiode current produced by a laser in said ON state and biased at an appropriate operating point, said fixed source of current also coupled to said node, current source means for generating a current of magnitude of zero or I DIFF , where I DIFF is a difference between I ON and I OFF , where I OFF is a photodiode current produced by a laser to be so controlled in an OFF state operating at an appropriate bias point, said current source means also connected to said node, and processing means responsive to a net current coupled to said node for deriving said bias current for said laser to be so controlled, wherein said processing means includes an integrator for integrating said net current and producing a signal corresponding to said net integrated current, and means responsive to said net integrated current for producing a bias current inversely proportional thereto.