Why is it difficult?

The increasing number of devices connected to the internet demands high-capacity and robust backhaul links, which mainly consist of a network of optical fibers. The load on the optical backhaul links is expected to increase over the next decade. This brings the challenge of expanding the capacity of optical links to meet the increasing demand. The fundamental limitation on the capacity of optical links is deeply rooted in the underlying physics. There are five physical dimensions— time, frequency, space, quadrature, and polarization— that we can utilize to improve link capacity. Out of these five, only two– frequency and space—can scale by a factor of thousands. We can have large bandwidth on one side, and on the other side, we can create multiple parallel streams using space parallelism. Looking closer into these dimensions, we see that the bandwidth cannot be infinite, and high-frequency bands such as X-rays suffer from a fundamental limitation due to considerable energy harmful to the life form. This leads to the only scalable solution to lay down thousands of parallel optical fibers to increase capacity. The underlying challenge comes from the auxiliary electronics such as amplifiers, repeaters, and terminators connected to each parallel fiber. These electronics consume large power, increasing energy per-bit and leading to a major bottleneck in increasing optical link capacity.

What is the impact?

High capacity optical backhaul network has a huge potential to meet the demand of increasing network traffic. Most internet traffic comes from the end-user devices connected to the network via WiFi or LTE link. As the wireless technology improves to 5G and beyond, there will be an intensive increase in high bandwidth applications such as video streaming, virtual reality, gaming, vehicular communication, etc. These applications would rely upon a high-capacity and robust backhaul network of optical fibers.