Noise and drift characterization of direct laser to RF conversion scheme for the laser based synchronization system for FLASH at DESY

Next generation FELs (Free Electron Lasers) require a long and short term stable synchronization of RF reference signals with an accuracy of 10 fs. To overcome the limitations of a coaxial cable based system, an optical synchronization system is being developed for FLASH at DESY. It is based on the distribution of sub-ps optical pulses, where the timing information is encoded in the precise repetition rate. The optical pulse train has to be converted into an RF signal to provide a local reference for calibration and operation of RF based devices. The drift and jitter performance of the optical to RF converter influences directly the phase stability of the accelerator. Three different methods for optical to RF converters, namely the direct detection using a photodiode, injection locking of a DRO, and a sagnac-loop interferometer are currently under investigation. In this paper we concentrate on the jitter and drift performance of the direct photodiode conversion and show its limitations.