Redefining the limits of real-time noise cancellation in optical fiber links
National Institute of Standards and Technology（美国国家标准与技术研究院）；Temporis Solutio LLC（Temporis Solutio有限责任公司）；University of Colorado Denver（科罗拉多大学丹佛分校）；University of Colorado Boulder（科罗拉多大学博尔德分校）；University of L’Aquila（拉奎拉大学）
Charles A. McLemore, Marco Pomponio, Takuma Nakamura, Yifan Liu, Nazanin Hoghooghi, Antonio Mecozzi, Franklyn Quinlan
A broad and growing array of applications rely on the faithful transmission of ultrastable optical signals over noisy paths, requiring cancellation of environmentally induced noise. A generally accepted limit constrains how well the path length noise can be suppressed in real time. Here, we show that this standard limit is not fundamental and can be improved upon. By considering the temporal correlations between the round-trip and one-way signals, we develop a new framework for optimizing the noise cancellation feedback signal for any spatial distribution of noise along the signal path. We use this framework to surpass the standard limit in two sets of experiments. First, we demonstrate noise cancellation in a deployed urban optical fiber, where we achieve noise suppression approximately 6 dB beyond the standard limit. Then, in a reconfigurable lab-based fiber-optic testbed, we show that, for certain spatial distributions of noise, suppression of well over 10 dB beyond the standard limit is readily achievable. With the use of digital signal processing to generate the correction signal, our new technique requires no new electro-optic hardware relative to the field-standard noise cancellation scheme. This will allow for widespread adoption of these improved limits in existing systems, with applications in optical clock distribution, optical clock comparisons for fundamental physics and geodesy, and quantum networking.
International Optical Clock Comparison Using the European Optical Fiber Network
Istituto Nazionale di Ricerca Metrologica (INRIM)（意大利国家计量研究所）；Laboratoire Temps Espace (LNE-OP), Observatoire de Paris, Université PSL, Sorbonne Université, Université de Lille, LNE, CNRS（巴黎天文台时间空间实验室（LNE-OP））；Laboratoire de Physique des Lasers (LPL), Université Sorbonne Paris Nord, CNRS（索邦巴黎北大学激光物理实验室（LPL））；Physikalisch-Technische Bundesanstalt (PTB)（德国联邦物理技术研究院）
E-21 Level Instability Frequency Dissemination over 2067 km noisy Telecommunication Infrastructure
Hefei National Laboratory, University of Science and Technology of China（合肥国家实验室，中国科学技术大学）；Jinan Institute of Quantum Technology and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China（济南量子技术研究院和中国科学院量子信息与量子物理学前沿卓越中心，中国科学技术大学）；Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China（合肥微尺度物质科学国家研究中心和物理科学学院，中国科学技术大学）
