Digital Doppler-cancellation servo for ultra-stable optical frequency dissemination over fiber

• Published in: IEEE transactions on ultrasonics, ferroelectrics, and frequency control Vol. 69; no. 2
• Main Authors: Mukherjee, Shambo, Millo, Jacques, Marechal, Baptiste, Denis, Séverine, Goavec-Mérou, Gwenhaël, Friedt, Jean-Michel, Kersalé, Yann, Lacroûte, Clément
• Format: Journal Article
• Language: English
• Published: Institute of Electrical and Electronics Engineers 01.02.2022
• Subjects: General Physics; Instrumentation and Detectors; Physics
• ISSN: 0885-3010; 1525-8955
• DOI: 10.1109/TUFFC.2021.3125066

Progress made in optical references, including ultra-stable Fabry-Perot cavities, optical frequency combs and optical atomic clocks, have driven the need for ultra-stable optical fiber networks. Telecom-wavelength ultra-pure optical signal transport has been demonstrated on distances ranging from the laboratory scale to the continental scale. In this manuscript, we present a Doppler-cancellation setup based on a digital phase-locked loop for ultra-stable optical signal dissemination over fiber. The optical phase stabilization setup is based on a usual heterodyne Michelson-interferometer setup, while the Software Defined Radio (SDR) implementation of the phase-locked loop is based on a compact commercial board embedding a field programmable gate array, analog-to-digital and digital-to-analog converters. Using three different configurations including an undersampling method, we demonstrate a 20 m long fiber link with residual fractional frequency instability as low as $10^{-18}$ at 1000 s, and an optical phase noise of $-70$ dBc/Hz at 1 Hz with a telecom frequency carrier.