Method and system for the monolithic integration of circuits for monitoring and control of RF signals

A QPSK modulator for an optical communication system, comprising:

• an input light source,
• first and second Mach-Zehnder modulators that receive light from the input light source, and apply respective first and second pseudorandom data streams, to generate respective first and second Mach-Zehnder modulator outputs,
• a third Mach-Zehnder modulator formed by combining the first and second Mach-Zehnder modulator outputs and a phase bias, to generate a third Mach-Zehnder modulator output,
• a splitter coupled with the third Mach-Zehnder modulator output, and
• a photodiode coupled with the splitter, such that the splitter provides a portion of the third Mach-Zehnder modulator output to the photodiode, to generate a photodiode output;
• an analog circuit that detects broadband power in the photodiode output,
• wherein the broadband power is correlated to phase error in relation to the quadrature bias in the third Mach-Zehnder modulator, and
• wherein the analog circuit comprises:
• a first capacitor for AC coupling the photodiode output,
• a transistor for squaring the AC coupled photodiode output, and
• a second capacitor for coupling an AC component of the AC coupled, squared photodiode output to ground, to low pass filter the AC coupled, squared photodiode output;
• the QPSK modulator further comprising thermal control means for adjusting the phase bias to minimize the detected broadband power in the photodiode output, to optimize the quadrature bias.

A QPSK modulator for an optical communication system, comprising:

• an input light source,
• first and second Mach-Zehnder modulators that receive light from the input light source, and apply respective first and second pseudorandom data streams, to generate respective first and second Mach-Zehnder modulator outputs,
• a third Mach-Zehnder modulator formed by combining the first and second Mach-Zehnder modulator outputs and a phase bias, to generate a third Mach-Zehnder modulator output,
• a splitter coupled with the third Mach-Zehnder modulator output, and
• a photodiode coupled with the splitter, such that the splitter provides a portion of the third Mach-Zehnder modulator output to the photodiode, to generate a photodiode output;
• an analog circuit that detects broadband power in the photodiode output, wherein the broadband power is correlated to phase error in relation to the quadrature bias in the third Mach-Zehnder modulator;
• and
• thermal control means for adjusting the phase bias to minimize the detected broadband power in the photodiode output, to optimize the quadrature bias, wherein the thermal control means comprises a heater integrated with at least one arm of the third Mach-Zehnder modulator.