Opt Express. 2023 Feb 13;31(4):6076-6087. doi: 10.1364/OE.477156.
The full time-jitter response of a single-photon detector can make a significant contribution to the quantum bit error rate (QBER) of high repetition rate quantum key distribution (QKD) implementations. Although there have been studies into understanding the contribution for single-mode optical fiber coupled single-photon detectors, the contribution of larger, multimode core diameters to the QBER have not been explored in detail. With the growing importance of free-space QKD, which typically use multimode fibers to reduce coupling loss, it is vitally important to understand how the multimode fiber coupling will impact the total QBER. This work studies the impact of the time-jitter contribution to QBER when coupling a commercial off-the-shelf silicon single-photon avalanche diode with various multimode fibers while simulating operating at 1 GHz with empirical measurements taken at 1 MHz repetition rate. It was found that step-index multimode fibers can significantly increase the QBER, while graded-index fibers can provide an QBER contribution similar to a single-mode fiber. The results highlight that there is a significant benefit in using graded index multimode fibers for a free-space QKD receiver, particularly for high repetition rate applications.
单光子探测器的全时间抖动响应会对高重复率量子密钥分发（QKD）实现的量子比特误码率（QBER）产生重大影响。虽然已经有研究试图了解单模光纤耦合单光子探测器的影响，但对于更大的多模芯径对 QBER 的贡献，尚未进行详细探讨。随着自由空间 QKD 的重要性日益增加，自由空间 QKD 通常使用多模光纤来降低耦合损耗，因此了解多模光纤耦合将如何影响总 QBER 至关重要。本工作研究了在以 1MHz 重复率进行实际测量的同时，以 1GHz 的速率进行模拟时，将商业现货硅雪崩光电二极管与各种多模光纤耦合时，时间抖动对 QBER 的影响。结果表明，阶跃折射率多模光纤会显著增加 QBER，而梯度折射率光纤则可提供类似于单模光纤的 QBER 贡献。这些结果表明，对于自由空间 QKD 接收器，使用梯度折射率多模光纤具有显著的优势，特别是对于高重复率应用。
