Coherent Passive Optical Networks: Why, When, and How

While the capacity of the next-generation access network is expected to be 100 Gb/s and beyond, coherent optics is going to be a logical choice for the physical layer as the currently used intensity-modulation/ direct-detection technology will fail to meet the required power budget of such high line-rate systems. In this article, we present an overview of necessities, timeframe, and technological challenges for the future passive optical network utilizing coherent technology.