All-Optical Networking—Evolution, Benefits, Challenges, and Future Vision

While all-optical networking had its origins in the research community a quarter of a century ago, the realization of the vision has not had a straight trajectory. The original goal of the all-optical network was based on keeping the data signals entirely in the optical domain from source to destination to eliminate the so-called electronic bottleneck, and to allow arbitrary signal formats, bitrates, and protocols to be transported. The latter property is referred to as transparency. When all-optical networks were finally commercialized around the turn of the century, however, a modified reality emerged; the quest for transparency was replaced by the more pragmatic objective of reducing the network cost and energy consumption. Moreover, especially for networks of large geographical extent, electronics were still present at some (relatively few) points along the data path, for signal regeneration and traffic grooming. This modified vision captures the state of today's networks, though terms like all-optical and transparent are still used to describe this technology. However, continued advancements are bringing back some aspects of the original transparency vision. In this paper, we review the evolution of all-optical networking, from the early vision to its present vibrant state, which was made possible by great advances in optical transmission and all-optical switching technologies. We describe the numerous benefits afforded by the technology, and its relative merits and drawbacks compared to competing technologies, sometimes referred to as opaque. We also discuss the remaining challenges and future directions of all-optical networking. While all-optical solutions permeate today's access, metro, and core networks, this paper focuses on the core.