Optical Clock Technologies for Global Navigation Satellite Systems

Future generations of global navigation satellite systems (GNSS) can benefit from optical technologies. Especially optical clocks could back-up or replace the currently used microwave clocks, having the potential to improve GNSS position determination enabled by their lower frequency instabilities. Furthermore, optical clock technologies - in combination with optical inter-satellite links - enable new GNSS architectures, e.g. by synchronization of distant optical frequency references within the constellation using time and frequency transfer techniques. Optical frequency references based on Doppler-free spectroscopy of molecular iodine are seen as a promising candidate for a future GNSS optical clock. Compact and ruggedized setups have been developed, showing frequency instabilities at the 10^(-15) level for averaging times between 1s and 10.000s. In this paper, we introduce optical clock technologies for applications in future GNSS and present the current status of our developments of iodine-based optical frequency references.