Network integration of quantum key distribution is crucial for its future widespread deployment due to the high cost of using optical fibers dedicated for the quantum channel only. We studied the performance of a system running a simplified BB84 protocol at 2.5 GHz repetition rate, operating in the original wavelength band, the short O-band, when multiplexed with communication channels in the conventional wavelength band, and the short C-band. Our system could successfully generate secret keys over a single-mode fiber with a length of 95.5 km and with co-propagating classical signals at a launch power of 8.9 dBm. Furthermore, we discuss the performance of an ideal system under the same conditions, showing the limits of what is possible with a discrete variable system in the O-band. We also considered a short and lossy link with 51 km optical fiber resembling a real link in a metropolitan area network. In this scenario, we could exchange a secret key with a launch power up to 16.7 dBm in the classical channels.

中文翻译：

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复用量子信道和经典信道的局限性：2.5 GHz 离散可变量子密钥分发系统的案例研究

由于使用专用于量子通道的光纤成本高昂，量子密钥分发的网络集成对其未来的广泛部署至关重要。我们研究了以 2.5 GHz 重复率运行简化 BB84 协议的系统的性能，该系统在原始波段、短 O 波段、与传统波段和短 C 波段中的通信信道复用时运行。我们的系统可以在长度为 95.5 公里的单模光纤上成功生成密钥，并以 8.9 dBm 的发射功率共同传播经典信号。此外，我们讨论了理想系统在相同条件下的性能，显示了 O 波段离散变量系统可能存在的限制。我们还考虑了具有 51 公里光纤的短且有损链路，类似于城域网中的真实链路。在这种情况下，我们可以在经典信道中交换发射功率高达 16.7 dBm 的密钥。