Report on the redesign of the fibre link stabilisation units at FLASH

Recently, the fibre link stabilisation unit of the optical synchronisation system at FLASH has been subject to several design changes involving some major issues. Enhancements of the optical design have led to improvements in the efficiency of the free space optics and a new optical delay line allows for a more than two times longer adjustment range. The amplitude noise, encountered previously at the remote station of the links, was drastically decreased by a new beam splitting configuration. In future, this new link design will not only be used for the planned additional fibre links at FLASH, but it will also replace the already installed ones. In this paper we report on the changes of opto-mechanical design and we present first results from the recently commissioned links.