Patent ID: 7046414

Claim:
An optical modulation system including: an optical modulator generating an intensity-modulated output optical signal; an operating point detecting unit for receiving said intensity-modulated output optical signal from said optical modulator and detecting at least one of a direction and a magnitude of a variation of an operating point from an intended operating point, based on a low frequency signal component included in said intensity-modulated output optical signal, and said operating point detecting unit generating a direct current error signal which represents said at least one of said direction and said magnitude of said variation of said operating point from said intended operating point; and a signal supplying unit being functionally coupled to said operating point detecting unit for receiving said error signal and generating an output signal which includes a stationary direct current bias voltage, said direct current error signal and a low frequency signal having a first frequency; wherein a first signal electrode of said optical modulator is coupled to said signal supplying unit for causing that at said first signal electrode, said output signal is superimposed to an input driving signal having a second frequency higher than said first frequency, in order to generate, at said first signal electrode, an amplitude-modulated input driving signal waveform, which has a pair of same phase envelope lines, and which has a full width smaller than a potential difference between adjacent two of bias voltages at which an optical intensity of said intensity-modulated output optical signal takes a minimum value or between adjacent two of other bias voltages at which said optical intensity takes a maximum value.