  Proper operation of electro-optic I/Q modulators rely on precise adjustment
and control of the relative phase biases between the modulator's internal
interferometer arms. We present an all-analog phase bias locking scheme where
error signals are obtained from the beat between the optical carrier and
optical tones generated by an auxiliary 2 MHz RF-tone to lock the phases of all
three involved interferometers for operation up to 10 GHz. With the developed
method, we demonstrate an I/Q modulator in carrier-suppressed single-sideband
mode, where the suppressed carrier and sideband are locked at optical power
levels $< -27 dB$ relative to the transmitted sideband. We describe a simple
analytical model for calculating the error signals, and detail the
implementation of the electronic circuitry for the implementation of the
method.
