Future passive optical networks (PONs) for 200Gb/s/λ${200}\;{\rm Gb/s/}\lambda$, and beyond, pose a significant technological challenge. The use of coherent technology in access networks provides a great solution based on concepts from mature technologies to achieve the speeds needed for very-high-speed PON (VHSP). In this paper, we provide an overview of the currently demonstrated technologies and propose a possible simplified optical network unit (ONU) for time division multiplex PON (TDM-PON). The proposed ONU uses a single polarization heterodyne receiver, using either a balanced photodiode or a single-ended one and an electro-absorption modulated laser (EML)-based transmitter. The experimental demonstration using the proposed ONU in a bidirectional, symmetrical transmission over fiber distances of 20 km and 40 km shows the viability of the technology. The downstream direction achieves a power budget of 34.3/29.3 dB for 20 km and 33.9/29 dB for 40 km, for a balanced/single-ended receiver, whereas the upstream transmission achieves 29.3 dB for both scenarios.

中文翻译：

---

用于超高速无源光网络的简化相干光网络单元

未来200 个无源光网络 (PON)G b / s / λ${200}\;{\rm Gb/s/}\lambda$及以上构成了重大的技术挑战。在接入网络中使用相干技术提供了一种基于成熟技术概念的出色解决方案，可实现超高速 PON (VHSP) 所需的速度。在本文中，我们概述了当前演示的技术，并提出了一种可能的时分复用 PON (TDM-PON) 简化光网络单元 (ONU)。所提出的 ONU 使用单偏振外差接收器，使用平衡光电二极管或单端光电二极管以及基于电吸收调制激光 (EML) 的发射器。使用所提出的 ONU 在 20 公里和 40 公里光纤距离上进行双向对称传输的实验演示表明了该技术的可行性。对于平衡/单端接收器，下行方向的功率预算为 20 公里 34.3/29.3 dB 和 40 公里 33.9/29 dB，而上行传输在这两种情况下均达到 29.3 dB。