NEXT GENERATION CW REFERENCE CLOCK TRANSFER SYSTEM WITH FEMTOSECOND STABILITY

Present and future fourth generation light sources, such as the Swiss FEL, are placing strict requirements on current CW reference clock transfer systems. Both the added jitter and the long-term stability criteria need to be in the range of a few femtoseconds. In order to meet these requirements, the existing Libera Sync CW transfer system has been redesigned. All of the aspects of the system design have been revised and improved, from new measuring methods and better evaluation of components to careful pre-design testing and simulation. New fiber link topology, new approaches in thermal stabilization, improved power supply distribution and interconnection of carefully selected electrical and state-of-the-art optical components has led to a significant reduction in added jitter and excellent long-term stability of the system. Measurements repeatedly show the jitter performance to be below 6 fsrms, integrated over the frequency range of 10 Hz to 10 MHz. Preliminary measurements of the longterm stability place the system in the range of a few tens of femtoseconds peak-to-peak of drift per day.