processing, and storage and indicates key directions for the future for optics in these fields.

Communications

Optical communications networks provide the underlying high-capacity, ubiquitous connectivity that underpins the global Internet. Figure 3.1 characterizes the growth of communication and computing between 1986 and 2007, based on a broad collection of data.2 Approximately 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 Figure 3.1, 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.3 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

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2 Hilbert, M., and P. Lopez. 2011. The world’s technological capacity to store, communicate, and compute information. Science 332(6025):60-65.

3 Alferness, R.C. 2008. “Optical Communications—A View to the Future.” 24th European Conference on Optical Communications, Brussels, Belgium, September 22. Available at http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=4729111&tag=1. Accessed June 26, 2012.



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