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Abstract

An optical data generator including a mechanism for locking the phase between clock and data signals to generate return-to-zero optically encoded data streams with low distortion. The optical data generator includes a pair of series-connected optical modulators. A clock voltage is provided to the first optical modulator and a data voltage is provided to the second optical modulator in the series. The laser light propagating through the first and second optical modulators is modulated with the respective clock and data voltages to produce a return-to-zero optical data stream. The optical data generator includes a phase shifter coupled between the clock voltage and the first optical modulator, and a synchronous demodulator coupled between the output of the optical data generator and the phase shifter. The synchronous demodulator provides DC bias and dither voltages suitable to operate the phase shifter at the quiescent point of the phase shifter transfer function, thereby controlling the phase offset of the clock voltage relative to the phase of the data voltage.

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