| 摘要 |
Compensation for variation of a semiconductor laser threshold position is based on the utilization of the rectifying property of such lasers near threshold. A small amplitude test signal is applied to the laser close to threshold and a distortion component at a harmonic of the test signal frequency is isolated from a voltage or current analog generated from the laser light output. Depending on the order of the harmonic, the characteristic of this distortion component has a maximum value (even harmonic) or is zero valued (odd harmonic) when the threshold current is applied to the laser. If the laser threshold position changes, a feedback circuit resets the bias current applied to the laser to a value close to but just below, the threshold position. The test signal can also be used to compensate for change in laser slope efficiency to avoid any variation in signal power output at a fixed modulation level.
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