Apparatus and method for linearizing an external optical modulator
AssigneeGeneral Instrument Corporation
InventorDavid R. Huber
Life of this patent
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Abstract
An external optical modulator is linearized to reduce second order distortion. An optical carrier is modulated in the modulator by a pilot signal. The modulated optical carrier is sampled 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 to the modulator 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 are operated in series, each is provided with a feedback loop to minimize the second order distortions produced therein.
Claims20
A method for linearizing the operation of an external optical modulator comprising the steps of:
- modulating an optical carrier in said modulator by a pilot signal;
- sampling said modulated optical carrier from said modulator;
- generating an error signal indicative of a phase difference between a second harmonic of said pilot signal and second order harmonics of said pilot signal present in said sampled modulated optical carrier;
- and
- feeding said error signal back to said modulator to adjust a bias thereof to minimize said phase difference and thereby minimize second order distortions produced by said modulator.
Linearized external optical modulator apparatus comprising:
- means for modulating an optical carrier signal by an information signal and a pilot signal;
- means for sampling the modulated optical carrier signal from said modulating means;
- means for generating an error signal indicative of a phase difference between a second harmonic of said pilot signal and second order harmonics of said pilot signal present in said sampled modulated optical carrier signal;
- and
- means for feeding said error signal back to said modulating means to adjust a bias thereof to minimize said phase difference and thereby minimize second order distortions produced by said modulating means.
Dependencies are inferred from the claim text.