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We describe novel techniques for closed-loop control of inner and outer Mach-Zehnder (MZ) biases in a dual parallel MZ (DPMZ) optical modulator. We also present a new technique based on modulator bias dithers to monitor the optical power contribution of each RF data path. The latter is demonstrated in an I -Q power balance control loop. We show that the new control methods are extremely robust in presence of modulator non-idealities, such as finite extinction ratios and non-zero chirp. We also demonstrate these techniques to be largely independent of RF drive waveform characteristics. Mathematical derivations of control transfer curves are provided. These are supported by simulation and measurement results. Additionally, we present a simple technique for polarization power balance in a dual-polarization modulation format. Finally, we discuss some practical details related to the implementation of the control loops described in this work.