Apparatus and method for linearizing the operation of an external optical modulator
AssigneeGeneral Instrument Corporation
InventorYudhi Trisno
Life of this patent
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Abstract
A modulating signal is predistorted to linearize the output of an optical intensity modulator. The modulating signal is split into first and second paths. In the first path, the signal is phase shifted. In the second path, distortion components are introduced. The phase shifted signal from the first path is then combined with the distorted signal from the second path to provide a predistorted signal for use in modulating a light source. The distortion generator can comprise a diode pair coupled with opposite polarities in parallel. Both diodes are forward biased, and the pair is coupled in series with the input signal to provide the desired predistortion.
Claims17
External optical intensity modulator apparatus having reduced third order distortion products comprising:
- means for splitting an analog input signal into first and second paths;
- phase shift means coupled to said first path for shifting the input signal phase;
- distortion generator means coupled to said second path for introducing distortion components into said input signal;
- means for combining the phase shifted input signal from said first path with the distorted input signal from said second path to provide a predistorted analog modulation signal;
- and
- an external optical intensity modulator having an input for receiving said predistorted analog modulation signal for use in modulating a light source.
A method for linearizing the output of an external analog optical modulator comprising the steps of:
- providing an analog modulating signal for use in modulating an external optical modulator;
- adjusting the phase of said modulating signal in a first path to compensate for a phase shift introduced by said modulator;
- predistorting said modulation signal in a second path with odd order distortion components similar to but opposite in polarity than distortion components introduced by said modulator;
- combining the phase adjusted modulating signal from said first path with the predistorted modulation signal from said second path to provide a predistorted, phase shifted signal;
- and
- coupling said predistorted, phase shifted signal to a modulating signal input of said modulator.
Dependencies are inferred from the claim text.