Automatic bias stabilization of dual-polarization in-phase and quadrature optical modulator

摘要

Embodiments include a method and apparatus used for automatic bias stabilization of a DP IQM based on MZM for transmitting DP-QPSK optical data and/or DP-16QAM optical data. The apparatus simultaneously dithers DC-bias voltages of in-phase child, quadrature-phase child, and parent MZMs with three different dither patterns in time-domain which are mutually orthogonal to each other in the frequency-domain for X and Y polarization IQ modulators. Tap monitor photodiodes detect an interference term between these three dither patterns for each polarization. The interference term is sampled using an ADC in the time domain. The time-synchronous detection method may solve a set of three simultaneous linear partial differential equations with three unknowns to compute controlled DC-bias voltages to set on the respective MZM with a solution set which may iteratively converge to a unique solution, thereby biasing the child MZM in dual-polarization IQM to transmission minimum and parent MZM in quadrature transmission.

主权项

1. A method of automatic bias stabilization, the method comprising:
simultaneously dithering DC-bias voltage of each of an X polarization in-phase child Mach-Zehnder modulator (MZM), an X polarization quadrature-phase child MZM, and an X polarization parent MZM included in an X polarization arm of a dual-polarization in-phase and quadrature optical modulator (IQM) according to three first dither patterns that are different from each other; detecting, at a first tap monitor photodiode coupled to an output of the X polarization arm, an X polarization interference term between the three first dither patterns; sampling an output of the first tap monitor photodiode to generate an X polarization interference signal indicative of the X polarization interference term; calculating an in-phase child MZM error signal, based on the interference signal between a quadrature-phase child MZM error signal and an X polarization parent MZM error signal; updating an in-phase child MZM DC-bias set point to minimize the in-phase child MZM error signal; calculating the quadrature-phase child MZM error signal, based on the interference signal between the in-phase child MZM error signal and the X polarization parent MZM error signal; updating a quadrature-phase child MZM DC-bias set point to minimize the quadrature-phase child MZ error signal; calculating the X polarization parent MZM error signal, based on the interference signal between the in-phase child MZM error signal and the quadrature-phase child MZM error signal; and updating a parent MZM DC-bias set point to minimize the X polarization parent MZM error signal.