Two-way, pulsed laser clock synchronization

Abstract

Free-space, optical time-transfer can synchronize two spatially distant clocks. Currently, Global Positioning System (GPS)-based clock synchronization is a common technique to adjust clocks around the globe to a time standard. GPS-based clock measurements utilize radio signals that travel from GPS satellites to receivers. Electromagnetic signals, like radio waves, that travel through the ionosphere interact with the free electrons that causes signal propagation delay proportional to 1=f2 and the total electron content, where f is the signal frequency. Uncertainty in the in propagation delay correlates to synchronization uncertainty. Radio frequency (1 GHz) clock synchronizations use atmospheric models and long integration times to correct for propagation delay uncertainty, however it is challenging to model the ionosphere. By utilizing optical frequencies (100 THz) for clock synchronization, the uncertainty in the propagation delay is reduced by a factor of 1010 enabling high-performing synchronization without ionosphere corrections. This paper introduces and evaluates the performance of free-space, pulsed laser clock synchronization in a laboratory setting. The pulsed laser synchronization technique is directly compared to a cable and frequency counter-based clock discrepancy measurement. This presentation evaluates the short and long term stability of time transfer between chip scale atomic clocks (CSAC) and compares them to a more stable oscillator.