Secure High-Speed Optical Communication Systems

Abstract

Optical communications have been widely deployed all over the world. In state-of-the-art optical communication systems, security and high capacity are the most important factors to be considered. As the rapid development of quantum computing, traditional computational complexity based encryption faces unprecedented challenges. To guarantee the unconditional security, quantum key distribution (QKD) has been proposed and now is attracting increasing attentions. Classical optical communications have been exponentially growing for decades. The telecommunications industry is always in favor of high-speed, long-haul, and cost-efficient optical transports. Lots of advanced techniques have been applied to meet the requirements, e.g., multi-dimensional multiplexing, advanced modulation formats, coherent detection, forward error correction (FEC) coding, constellation shaping, and adaptive coding. In this dissertation, I will investigate continuous-variable QKD (CV-QKD) protocols to enable unconditional security and study the reliable classical advanced optical transmission systems. In a dynamic fiber-optic transmission system, the system performance can be improved by the proposed self-adaptive coding approach. We also experimentally and numerically compare the mutual information (MI) performances of regular/probabilistically shaped/geometrically shaped (PS/GS)-8/16/32 quadrature amplitude modulation (QAM) formats. Therefore, the industry can select the best shaping scheme accordingly in a specific situation. Furthermore, we propose a novel hybrid PS/GS scheme, which can minimize non-Gray mapping penalty as well as be tolerant to the implementation penalty. In addition, free-space optical (FSO) communication systems are also studied here. We emulate the outdoor atmospheric turbulence by indoor turbulence emulator, which is based on split-step beam propagation method (SSBPM). Turbulence mitigation methods, including adaptive optics (AO), channel coding, spatial offset, and Huffman coding, are proposed and experimentally demonstrated to enable high-speed FSO communications. At the end, we propose novel four-state and eight-state CV-QKD systems, where the phase noise can be effectively mitigated, and power fluctuation caused by turbulence can be accurately monitored. Thereafter, beyond 1 Gb/s CV- QKD systems can be realized by controlling phase noise, leveraging reconciliation efficiency, monitoring power fluctuation, and multiplexing quantum channels.