Space communication for deep-space missions, inter-satellite data transfer and Earth monitoring requires high-speed data connectivity. The reach is fundamentally dictated by the available transmission power, the aperture size, and the receiver sensitivity. A transition from radio-frequency links to optical links is now seriously being considered, as this greatly reduces the channel loss caused by diffraction. A widely studied approach uses power-efficient formats along with nanowire-based photon-counting receivers cooled to a few Kelvins operating at speeds below 1 Gb/s. However, to achieve the multi-Gb/s data rates that will be required in the future, systems relying on pre-amplified receivers together with advanced signal generation and processing techniques from fibre communications are also considered. The sensitivity of such systems is largely determined by the noise figure (NF) of the pre-amplifier, which is theoretically 3 dB for almost all amplifiers. Phase-sensitive optical amplifiers (PSAs) with their uniquely low NF of 0 dB promise to provide the best possible sensitivity for Gb/s-rate long-haul free-space links. Here, we demonstrate a novel approach using a PSA-based receiver in a free-space transmission experiment with an unprecedented bit-error-free, black-box sensitivity of 1 photon-per-information-bit (PPB) at an information rate of 10.5 Gb/s. The system adopts a simple modulation format (quadrature-phase-shift keying, QPSK), standard digital signal processing for signal recovery and forward-error correction and is straightforwardly scalable to higher data rates.

深空任务、卫星间数据传输和地球监测的空间通信需要高速数据连接。覆盖范围从根本上取决于可用传输功率、孔径大小和接收器灵敏度。现在正在认真考虑从射频链路到光链路的过渡，因为这大大减少了由衍射引起的信道损耗。一种广泛研究的方法使用节能格式以及基于纳米线的光子计数接收器，该接收器冷却到几个开尔文，以低于 1 Gb/s 的速度运行。然而，为了实现未来所需的多 Gb/s 数据速率，还需要考虑依赖预放大接收器以及来自光纤通信的先进信号生成和处理技术的系统。此类系统的灵敏度很大程度上取决于前置放大器的噪声系数 (NF)，理论上几乎所有放大器的噪声系数均为 3 dB。相敏光放大器 (PSA) 具有 0 dB 独特的低 NF，有望为 Gb/s 速率的长距离自由空间链路提供最佳的灵敏度。在这里，我们展示了一种在自由空间传输实验中使用基于 PSA 的接收器的新颖方法，该方法具有前所未有的无误码、每信息位 1 个光子 (PPB) 的黑盒灵敏度，信息速率为10.5 GB/秒。该系统采用简单的调制格式（正交相移键控，QPSK）、用于信号恢复和前向纠错的标准数字信号处理，并且可以直接扩展到更高的数据速率。