Tracking DDS for coherent optical links

We report on the design and the realization of a digital architecture based on a tracking direct digital synthesizer (DDS) driven by a Field Programmable Gate Array (FPGA) for the implementation of a coherent optical link for time and frequency dissemination. The realized digital system has been implemented and characterized on a real fiber link on a 47 km metropolitan optical telecommunication network using a Dense Wavelength Division Multiplexing, that is shared with the internet data traffic. We describe the technique, the hardware and the characterization of the link, and we compare the new digital system with the analogic one, that uses common fiber links electronics.