Electro-optic modulator having gated-dither bias control

An electro-optic modulator system which receives an optical signal from an optical source, and an electrical data carrying input signal, and modulates the optical signal to encode the optical signal with the data content of the electrical data carrying input signal, said system comprising:

• an electro-optic modulator which receives the electrical data carrying input signal and modulates the optical signal with the data carrying input signal to provide an optical data carrying output signal;
• means for biasing said electro-optic modulator to maintain the operating point of said modulator at the half-power point, comprising
• means for providing a time varying electrical signal;
• means for providing a modulation signal and for modulating said time varying electrical signal with said modulation signal to provide a dither test tone signal;
• means for detecting said optical data carrying output signal within said electro-optic modulator and for providing a detected electrical signal indicative thereof, and
• means for demodulating said detected electrical signal with said modulation signal to provide a signal V.sub.error, for integrating over time said signal V.sub.error and providing a signal V.sub.bias indicative of the integrated value, and for summing said signal V.sub.bias with said dither test tone signal and applying the resultant summed signal to said electro-optic modulator to maintain said modulator at its half-power point.

An electro-optic modulator system, which receives an optical signal from an optical source, and an electrical data carrying input signal, and modulates the optical signal to encode the optical signal with the data content of the electrical data carrying input signal, said system comprising:

• a biased electro-optic modulator which receives the data carrying input signal and modulates the optical signal with the data carrying input signal to provide an optical data carrying output signal;
• a first signal source which provides a time varying electrical signal;
• a second signal source which provides a modulation signal;
• a closed loop bias control system including, means for maintaining said electro-optic modulator at its half-power point by modulating said time varying electrical signal with said modulation signal to create a dither test tone signal, such that, the frequency spectrum of the optical data carrying output signal contains energy within the frequency spectrum of said modulation signal and provides a signal V.sub.error indicative thereof when said modulator is not operating at the half-power point, means for integrating said signal V.sub.error and providing a signal value V.sub.bias indicative of the integrated value, means for summing said signal value V.sub.bias with said dither test tone signal and means for applying the resultant summed signal to said modulator to maintain the operating point of said modulator at the half-power point.

A bias controlled electro-optic modulator system which receives an electrical data carrying input signal, and an optical signal from a light source, and provides an optical data carrying output signal, comprising:

• an electro-optic modulator which modulates the optical signal with both the data carrying input signal and a biased dither test tone signal to provide said optical data carrying output signal;
• a bias control system including
• a first signal generator which provides a time varying electrical signal;
• a second signal generator which provides a modulation signal;
• a modulator which modulates said time varying electrical signal with said modulation signal to provide a dither test tone signal;
• an optical detector which detects said optical data carrying output signal and provides a detected electrical signal indicative thereof;
• a demodulator which demodulates said detected electrical signal with said modulation signal and provides a signal V.sub.error indicative of the demodulated signal;
• an integrator which integrates said signal V.sub.error over time and provides a signal V.sub.bias indicative of the integrated value of said signal V.sub.error ;
• and
• a summer which sums said signal V.sub.bias with said dither test tone signal and provides said biased dither test tone signal value indicative of the summed value to said electro-modulator to drive said electro-optic modulator to its half-power point.

A bias controlled electro-optic modulator system which receives an electrical data carrying input signal, and an optical signal from a light source, and modulates the optical signal to encode the optical signal with the data within the electrical data carrying input signal to provide an optical data carrying output signal;

• said system comprising:
• an electro-optic modulator including waveguides through which the optical signal propagates and a set of input signal electrodes formed across a portion of said waveguide to which the electrical data carrying input signal is applied to modulate the optical signal within said waveguide, and a set of bias signal electrodes also formed across said waveguide and to which a biased dither test tone signal received from a closed loop bias control system is applied to maintain the operating point of said electro-optic modulator at its half-power point, wherein the resultant electro-optic modulator output signal is said optical data carrying output signal;
• said closed loop bias control system includes
• an optical detector which detects said optical data carrying output signal and provides a detected electrical signal indicative thereof,
• a first signal generator which generates a time varying electrical signal;
• a second signal generator which generates a modulation signal f.sub.m ;
• a modulator which modulates said time varying electrical signal with said modulation signal f.sub.m to provide a dither test tone signal;
• a demodulator which demodulates said detected electrical signal with said modulation signal f.sub.m and provides a signal V.sub.error indicative of the demodulated signal;
• an integrator which integrates said signal V.sub.error over time and provides a signal value V.sub.bias indicative of the integrated value of said signal V.sub.error ;
• and
• a summer which sums said signal V.sub.bias with said dither test tone signal and provides said biased dither test tone signal value indicative of the summed value to said second set of electrodes to drive said electro-optic modulator to its half-power point.