Phase correction of reference frequency signals transmitted by optical fiber link

The time and frequency reference in the three laboratories of Besancon is based on cesium clocks for absolute accuracy and long-term stability at the LAOB, on a H-maser for medium and long term stability at the LCEP, and on a liquid-He whispering gallery sapphire oscillator for best spectral purity and short-term stability at LPMO. These standards are located at three different sites, at a few hundreds meter from one another. In order to obtain the full accuracy and stability at least at one site, we combine these references using a frequency locked loop. The 100 MHz frequency reference is transferred via a two-way optical link. This article reports on measurement of the the phase noise and of the stability of the link.