In the modem world, we can access information in ways that could only be dreamt about just 50 years ago. Information can travel around the world via television, radio, telephone and computer networks, all of them connected by satellite or cable links. Modern communication systems, or media, allow almost anyone to transmit and receive verbal, visual and written information wherever they are in the world.
Optical communications networks provide the underlying high-capacity, ubiquitous connectivity that underpins the global Internet Characterizes the growth of communication and computing between 1986 and 2007, based on a broad collection of data. Around the year 2000, Internet traffic took over from voice telephone as the single largest communication format for information. Now Internet traffic dominates completely. All of the long-distance communications on the Internet are over optical fiber.
Major advances in transmission techniques and technologies have allowed network providers to provide extremely cost-effective network upgrades that have kept pace with the extraordinary appetite for broadband Internet services. That growth, as exemplified in has driven network bandwidth demands by a factor of 100 over the last 10 years. That increase has been enabled by realizing the full potential of wavelength division multiplexing (WDM) that has resulted in fibers carrying as many as 100 separate wavelengths. In addition, the capacity per wavelength in commercially deployed terrestrial networks has increased from a maximum of 10 gigabits per second (Gb/s) per wavelength when the first edition of Harnessing Light was published in 1998, to 100 Gb/s today. As a result, per fiber transmission capacities in terrestrial systems today as high as 5-10 terabits per second (Tb/s) are possible. Transoceanic capacities have lagged somewhat behind terrestrial values because the long amplifier-only distances and the desire to extend the amplifier spacing have made upgrading to per wavelength capacities above 10 Gb/s problematic. Nevertheless, transoceanic per fiber capacities of approximately 1 Tb/s are typical. For the future there are expectations that this growth will continue as more video content calls for bandwidth and that there is a need for another factor-of-100 growth in the coming 10 years as well.
Major advances have also been achieved in both cost-effectively managing the large capacity in today’s WDM optical networks and in leveraging the value proposition of optical amplifiers to provide multi-wavelength amplification over network mesh and ring architectures. Reconfigurable, wavelength-routed networks—in which wavelength-defined units of capacity can be added, dropped, or switched from one fiber route to another fiber route directly in the optical domain without the need for conversion to electronics—are now heavily deployed in long-haul terrestrial networks as well as metropolitan networks. Wavelength-routed networks provide cost-effective solutions because they allow data on wavelengths passing through a node at a multi-route network node to remain in the optical domain and benefit from the cost-effective multi-wavelength amplification enabled by optical amplifiers, rather than needing to be individually electronically regenerated. The large increase in capacity demand has ensured that a prerequisite for the economic viability of such networks—namely, that the capacity demand between any two node pairs on the network be at least as large as that which can be carried by a single wavelength—is met.
WDM optical networks require reconfigurable optical add/drop multiplexers (ROADMs) to, under network electrical control, drop or add wavelength channels at a node and to switch wavelength channels from one fiber route to another. ROADMs are key enablers that have evolved significantly in their functionality, providing increasing levels of flexibility, and in their capacity, or number of fiber ports and wavelengths per fiber, over the last decade. Further progress in these network elements and their enabling technologies will be essential to addressing the growing demand for capacity.
Ultimately, networks are no better than the access capacity that they provide to the end user, whether that customer is a business or a residence. Increasingly that access is through an optical link. The last decade has seen significant increase in the deployment of fiber in the access network, initially to the curb, but increasingly also directly to the business or home.