| 摘要 |
Laser modulation control apparatus and methods which provide direct control of the transmitted optical extinction ratio of a semiconductor laser. A relatively low frequency and low amplitude pilot tone is superimposed on the signal used to drive the laser. Setting the amplitude of the pilot tone to a fixed fraction of the laser modulation current causes the transmitted optical power to vary a fixed fraction of the optical data amplitude at the pilot tone frequency. By using feedback to control the laser modulation current, the amplitude of the variation can be maintained at a desired value, which in turn maintains the transmitted optical data amplitude at a constant value, regardless of variations due to operating temperature or laser aging. A separate control loop is employed to maintain the average optical power at a fixed value. Since the optical data amplitude and the average optical power remain constant, the optical extinction ratio is also constant. Alternate embodiments are disclosed.
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