Phase readout for satellite interferometry

This thesis describes the development of digital phase readout systems, so-called phasemeters, required for performing precise length measurements in and between satellites with laser interferometry at frequencies below 1 Hz. These technologies have been studied in the scope of the planned space-borne gravitational wave detector LISA (Laser Interferometer Space Antenna and of future satellite geodesy missions such as GRACE (Gravity Recovery and Climate Experiment) Follow-On. The studies presented here were conducted between 2010 and 2013 at the Albert Einstein Institute in Hannover, Germany. The first part of this thesis provides a comprehensive overview of the basic concepts of inter-satellite interferometry. The analogue and digital parts of the phase measurement chain are described, with a focus on the design elements that are critical for achieving urad/sqrt(Hz) performance levels under the extreme conditions of the inter-satellite link. Digital signal simulations, as well as performance tests in analogue and optical set-ups with phasemeter prototypes are presented, which were used to determine the limiting effects with realistic signals. This includes tests of a precise angular readout technique, which were performed in the scope of GRACE Follow-On breadboarding activities. The developments presented culminate in the design, implementation and testing of an elegant breadboard model of the LISA phasemeter, which has been developed in the scope of an ESA (European Space Agency) technology development activity. The second part of this thesis describes investigations for new interferometry techniques using state-of-the-art digital signal processing. These allow the simplification of optical designs and are therefore candidates for performing the local interferometry in future satellite missions. A real time phasemeter was developed for deep phase modulation, a readout scheme that uses strong phase modulations in a homodyne/heterodyne hybrid architecture to deduce the interferometric phase. Additionally, a new interferometry technique called Digital Interferometry was experimentally investigated in collaboration with the Australian National University. This scheme allows interferometric signals to be multiplexed through a single measurement chain, allowing fundamentally new interferometer architectures to be constructed. A dedicated phasemeter system and an optical set-up have been used to study its limitations and performance. Finally, these new schemes were compared to existing technologies.