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

Apparatus for controlling bias current of a laser, comprising:

• means for operating said laser in an on state and an off state in response to particular data signals;
• photodiode means for receiving at least a portion of the radiation of said laser and for passing a photodiode current corresponding to the intensity of incident laser radiation;
• and
• means for processing said photodiode current when the laser is operated in said DIFF. state to control said bias current for said laser wherein said means for processing includes:
• first fixed current source means for supplying a fixed current;
• and second switched current source means for supplying a second fixed current in dependence on said data signals;
• means for connecting said sources to a node, and to said photodiode means;
• said processing means including means responsive to a sum of currents derived from said current sources and said photodiode means for controlling said bias current.