  We report on the analysis and prototype-characterization of a dual-electrode
electro-optic modulator that can generate both amplitude and phase modulations
with a selectable relative phase, termed a universally tunable modulator (UTM).
All modulation states can be reached by tuning only the electrical inputs,
facilitating real-time tuning, and the device is shown to have good suppression
and stability properties. A mathematical analysis is presented, including the
development of a geometric phase representation for modulation. The
experimental characterization of the device shows that relative suppressions of
38 dB, 39 dB and 30 dB for phase, single-sideband and carrier-suppressed
modulations, respectively, can be obtained, as well as showing the device is
well-behaved when scanning continuously through the parameter space of
modulations. Uses for the device are discussed, including the tuning of lock
points in optical locking schemes, single sideband applications, modulation
fast-switching applications, and applications requiring combined modulations.

General Relativity and Quantum Cosmology