Laser transmitter

Abstract

In a fiber optic laser controller for use in digital transmission a digital data stream and a DC bias are applied to the laser. During a monitoring period, the DC bias is stepped from a zero to a peak current. At a first threshold current, lasing occurs in response to digital `1` modulating current but not in response to digital `0` modulating current. At a second higher threshold current lasing occurs in response to both digital `1` and `0`. The threshold currents are identifiable as peaks in the second derivative d.sup.2 L/dI.sup.2 where L is the light output for an applied bias current I. A feedback circuit including a photodiode, D/A and A/D converters and a microprocessor controller are used to maintain the bias current at the second threshold current in spite of changes in the laser characteristics caused by device aging or temperature change.

Dependencies are inferred from the claim text.