Rahmouni A, Shrestha P, Li-Baboud Y S, Richards A M, Shi Y, Merzouki M, Ma L, Migdall A, Battou A, Slattery O, Gerrits T
Opt Express. 2025 Jul 28;33(15):32594-32602. doi: 10.1364/OE.560153.
Leveraging pre-existing classical fiber optic infrastructure, particularly optical fibers, and their associated component technologies, is essential for the practical realization of future quantum networks. However, when adapting such infrastructure for quantum communication, optical crosstalk from sub-milliwatt classical-channel power into quantum channels presents a significant challenge in quantum network development, introducing substantial noise that limits the network's performance, scalability, and fidelity. Crosstalk can occur between fibers at multiple points, such as connector interfaces at patch panels, within optical devices due to inadequate optical isolation, and in other fiber-related components. Crosstalk also occurs between channels with different frequencies within a single optical fiber, as Raman scattering converts classical light to photons at frequencies that may interfere with the quantum signal. While Raman scattering in optical fibers has been widely studied, crosstalk occurring between separate fibers at their connection locations, typically at network components such as transparent switches and patch panels, in quantum networks has not received sufficient attention. Here we report a demonstration using photon-counting optical time-domain reflectometry (ν-OTDR) to precisely identify and localize crosstalk between separate channels within the same fiber and between separate fibers. The coexistence of classical and quantum signals in the same network necessitates the use of optical switches for efficient routing and control. Crosstalk characterization of an optical switch reveals a strong dependence on the cross-connect configuration. Higher crosstalk levels were observed in certain specific configurations, while no measurable crosstalk was detected in others. Additionally, we found that crosstalk exhibits a pronounced wavelength dependence, increasing over tenfold at longer wavelengths. These findings demonstrate the value of ν-OTDR in diagnosing and mitigating crosstalk in quantum networks. They highlight the importance of optimizing optical switch configurations and wavelength management to minimize noise, ultimately enhancing the scalability, fidelity, and overall performance of quantum networks. This work establishes a foundational approach to addressing crosstalk, paving the way for more robust and efficient quantum network designs.
利用现有的经典光纤基础设施，特别是光纤及其相关组件技术，对于未来量子网络的实际实现至关重要。然而，在将此类基础设施应用于量子通信时，从亚毫瓦级经典信道功率到量子信道的光学串扰在量子网络发展中构成了重大挑战，引入了大量噪声，限制了网络的性能、可扩展性和保真度。串扰可在多个点的光纤之间发生，例如配线架处的连接器接口、由于光学隔离不足在光学设备内部以及其他与光纤相关的组件中。串扰也会在单根光纤内不同频率的信道之间发生，因为拉曼散射会将经典光转换为可能干扰量子信号频率的光子。虽然光纤中的拉曼散射已得到广泛研究，但在量子网络中，单独光纤在其连接位置（通常在诸如透明交换机和配线架等网络组件处）之间发生的串扰尚未得到足够关注。在此，我们报告了一项利用光子计数光学时域反射仪（ν - OTDR）精确识别和定位同一光纤内不同信道之间以及单独光纤之间串扰的演示。同一网络中经典和量子信号的共存使得必须使用光开关进行高效路由和控制。光开关的串扰特性表明其强烈依赖于交叉连接配置。在某些特定配置中观察到更高的串扰水平，而在其他配置中未检测到可测量的串扰。此外，我们发现串扰呈现出明显的波长依赖性，在较长波长下增加超过十倍。这些发现证明了ν - OTDR在诊断和减轻量子网络串扰方面的价值。它们强调了优化光开关配置和波长管理以最小化噪声的重要性，最终提高量子网络的可扩展性、保真度和整体性能。这项工作建立了一种解决串扰的基础方法，为更强大、高效的量子网络设计铺平了道路。
