| 摘要 |
<p>An external optical modulator (18, 64, 120, 150) is linearized to reduce second order distortion. An optical carrier is modulated in the modulator by a pilot signal (38). The modulated optical carrier is sampled (26) and an error signal is generated indicative of a phase difference between a second harmonic of the pilot signal and second order harmonics thereof present in the sampled modulated optical carrier. The error signal is fed back (42, 56) to the modulator (18) to adjust the bias thereof to minimize the phase difference and thereby minimize second order distortions produced by the modulator. Where a plurality of external modulators (65, 67) are operated in series, each is provided with a feedback loop (76-82, 84-90) to minimize the second order distortions produced therein. <IMAGE></p> |
