Optical chaos communication and key distribution have been extensively demonstrated with high-speed advantage but only within the metropolitan-area network range of which the transmission distance is restricted to around 300 km. For secure-transmission requirement of the backbone fiber link, the critical threshold is to realize long-reach chaos synchronization. Here, we propose and demonstrate a scheme of long-reach chaos synchronization using fiber relay transmission with hybrid amplification of an erbium-doped fiber amplifier (EDFA) and a distributed fiber Raman amplifier (DFRA). Experiments and simulations show that the hybrid amplification extends the chaos-fidelity transmission distance thanks to that the low-noise DFRA suppresses the amplified spontaneous emission noise and self-phase modulation. Optimizations of the hybrid-relay conditions are studied, including launching power, gain ratio of DFRA to EDFA, single-span fiber length, and number of fiber span. A 1040-km chaos synchronization with a synchronization coefficient beyond 0.90 is experimentally achieved, which underlies the backbone network-oriented optical chaos communication and key distribution.

中文翻译：

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混合放大1040km光纤中继传输半导体激光器混沌同步

光混沌通信和密钥分发以高速优势得到广泛展示，但仅限于传输距离限制在300公里左右的城域网范围内。对于骨干光纤链路的安全传输需求，关键的门槛是实现长距离混沌同步。在这里，我们提出并演示了一种使用掺铒光纤放大器 (EDFA) 和分布式光纤拉曼放大器 (DFRA) 混合放大的光纤中继传输的长距离混沌同步方案。实验和仿真表明，由于低噪声DFRA抑制了放大的自发辐射噪声和自相位调制，混合放大延长了混沌保真传输距离。研究了混合中继条件的优化，包括发射功率、DFRA与EDFA的增益比、单跨光纤长度和光纤跨距数。实验实现了同步系数超过0.90的1040公里混沌同步，这是面向骨干网的光混沌通信和密钥分发的基础。