The volume of data traffic traversing the world’s optical fibre networks is growing by more than 40 percent per year as data-hungry services like streaming audio and video become ever more popular. So that future networks have the capacity to cope with this ever-swelling traffic, and also handle emerging applications that will boost it still more—from connected cars to mobile HD video and the Internet of Things—the technologies that power long-haul optical networks are going to need a major upgrade in the mid-2020s.