Coherent wavelength division multiplexing (WDM) technologies have leveraged the optical communication systems in core networks, increasing the fiber capacity by transmission with advanced modulation formats and mitigation of impairments with digital signal processing. However, these solutions are too expensive for access networks, where cost, power budget, and footprint are limited. Hence, the key technology will be developing low-cost coherent transceivers providing an excellent selectivity and giving high sensitivity, which allows high splitting ratios. This paper reports an experimental design of a low-cost coherent ultra-dense WDM passive optical network (UDWDM-PON) with 6.25 GHz channel spacing. The users’ optical network unit (ONU) is built employing coherent transceivers with two paired low-cost distributed feedback (DFB) lasers, one as the local oscillator and another as the transmitter, offering simplicity and low-cost hardware; likewise, the optical line terminal (OLT) at the central office can profit from the same design. The ONU DFB lasers have wavelengths with limited thermal tunability, controlled by a thermo-electric cooler, which is used to allocate the wavelengths. A medium access control (MAC) at the OLT manages the spectrum channel allocation for ONUs, demanding connection when activation is requested: the OLT furnishes an optical carrier wavelength for the ONU to obtain connection by a control algorithm, assigning a down-channel and another paired up-channel assigned to the ONU DFB transmitter. The MAC can reassign the channels because of interference or collision in a dynamic wavelength allocation. Measures in an activation process and in channel reassignment have been performed in environmental conditions, including control signals and the physical parameters of DFB lasers, demonstrating the practical viability of the PON scaling from 32 up to 256 wavelength channels.

中文翻译：

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灵活的相干UDWDM-PON，具有基于有限可调激光器的动态用户分配

相干波分复用（WDM）技术利用了核心网络中的光通信系统，通过使用高级调制格式进行传输来增加光纤容量，并通过数字信号处理来减轻损害。但是，这些解决方案对于接入网来说太昂贵了，因为接入网的成本，功率预算和占地面积有限。因此，关键技术将是开发低成本相干收发器，该收发器具有出色的选择性并具有高灵敏度，从而可以实现高分光比。本文报告了具有6.25 GHz信道间隔的低成本相干超密集WDM无源光网络（UDWDM-PON）的实验设计。用户的光网络单元（ONU）采用相干收发器和两个成对的低成本分布式反馈（DFB）激光器构成，一个作为本地振荡器，另一个作为发送器，提供了简单且低成本的硬件；同样，中心局的光线路终端（OLT）也可以从相同的设计中受益。ONU DFB激光器的波长具有有限的热可调性，由可用于分配波长的热电冷却器控制。OLT上的媒体访问控制（MAC）管理ONU的频谱信道分配，在请求激活时要求连接：OLT为ONU提供光载波波长，以通过控制算法获得连接，分配下行信道和其他分配给ONU DFB发射机的成对上行通道。由于动态波长分配中的干扰或冲突，MAC可以重新分配信道。