Abstract: Disclosed are bias control methods for Mach-Zehnder modulators for the generation of optical QAM signals while ensuring correct I/Q polarity of the generated optical QAM signal. One exemplary method involves temporarily offsetting I and Q biases from ideal transmission null bias points while another illustrative method temporarily makes I and Q data streams identical.

Abstract: Disclosed are bias control methods for Mach-Zehnder modulators for the generation of optical QAM signals while ensuring correct I/Q polarity of the generated optical QAM signal. One exemplary method involves temporarily offsetting I and Q biases from ideal transmission null bias points while another illustrative method temporarily makes I and Q data streams identical.

Abstract: Disclosed are bias control methods for Mach-Zehnder modulators for the generation of optical QAM signals while ensuring correct I/Q polarity of the generated optical QAM signal. One exemplary method involves temporarily offsetting I and Q biases from ideal transmission null bias points while another illustrative method temporarily makes I and Q data streams identical.

Abstract: Disclosed are bias control methods for Mach-Zehnder modulators for the generation of optical QAM signals while ensuring correct I/Q polarity of the generated optical QAM signal. One exemplary method involves temporarily offsetting I and Q biases from ideal transmission null bias points while another illustrative method temporarily makes I and Q data streams identical.

Abstract: An optical receiver circuit includes a differential limiter amplifier receiving a binary electrical waveform generated by an optical-to-electrical converter receiving an optical communications signal. Low-pass filter circuits are coupled to differential outputs of the limiter amplifier to obtain the average DC values of the mirror-image output signals. The outputs of the low-pass filter circuits are provided to a differential amplifier to obtain the difference between these average DC values. The output of the differential amplifier is provided to an integrator circuit whose slowly-varying output is provided to the limiter amplifier to establish a switching threshold for distinguishing logic “0”s from logic “1”s in the received data signal. The switching threshold is automatically adjusted in response to varying operation conditions such as changes in the received optical signal power.

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.

Abstract: An optical data generator for generating a return-to-zero optical data stream. The optical data generator includes a single optical modulator for receiving an input optical signal, an electrical data generator for generating a return-to-zero electrical data stream, and a driver amplifier for receiving the return-to-zero electrical data stream and providing a modulation signal representing the return-to-zero electrical data stream to the optical modulator. The optical modulator is configured to modulate the modulation signal onto the input optical signal to generate a return-to-zero optical data stream at an output port of the optical data generator.