Digital electronics based on red pitaya platform for coherent fiber links

Abstract

Recent improvements and continuous research on accurate clocks and frequency standards require the study of suitable tools and techniques for frequency transfer that minimize the added noise and allow fully exploiting these clocks in metrology applications. Different experiments performed during the last decade validated fiber links as the most performing tool for frequency transfer, reaching a statistical uncertainty of 10−20 for thousands kilometers links [1]. Recently, digital implementations have been used for metrological applications due to the flexibility, cost effective and compact solutions that can be achieved. In this paper, we propose a digital implementation for the detection and compensation of the phase noise induced by the fiber link. The beat note, representing the fiber length variations, is acquired directly with a fast Analog to Digital Converter (ADC) followed by a Tracking Numerical Controlled Oscillator (NCO). This reduces the component's latency and the communication delay between different blocks, increasing the tracking bandwidth. In addition, we report the characterization of the main components that allows foreseeing which are the limiting aspects and the expected performance of the complete implementation. The proposed system is being implemented on Red Pitaya, an open source platform driven by a Zynq, System on Chip (SoC) of Xilinx that contains a FPGA and an ARM processor embedded on the same chip.