March 2001

The Future of WDM (OPN Trends Supplement)

Wavelength-division multiplexing, which is simply the technique of communicating multiple data streams on separate wavelengths, has emerged as a powerful communications technology. Rapid progress leads us to wonder what its future might be and how far it may progress. Will it one day be possible for everybody on the planet to have their own wavelength?

Developing Efficient, High-Capacity Metropolitan Area Networks (OPN Trends Supplement)

Optical-fiber communications owes much of its success to two complementary conditions: one, a staggering in-crease in demand for bandwidth between distant points, and two, an inherent capability within fiber optics to provide such bandwidth. Two ubiquitous applications of optical-fiber communications, undersea systems and long-haul networks, directly leverage this relationship. Both highly developed applications realize tremendous gains by partnering with optical communications. However, the insatiable demand for bandwidth extends beyond long-haul networks—access and aggregation networks must scale to meet demand as well. Metropolitan area net- works (MANs), which bridge the gap between long-haul networks and access networks, have enjoyed much attention as optical technologies enable novel MAN designs.

Ultrahigh-speed optical time-division multiplexing transmission (OPN Trends Supplement)

All indicators are that the rapid growth in data traffic will continue. One particularly important trend is the increase in transmission speed of local area networks (LANs); the speed of the next generation Ethernet is 10 Gbit/s, the same as that of today’s backbone transmission systems. We are now living in what is substantially a distance-free world, in which connection with anyone on Earth can be achieved by means of optical communication networks. International commerce will generate greater interconnection between high-speed LANs, as well as more extensive use of the Internet. Indeed, Internet access is now so pervasive that the latest Internet-enabled devices include not only cellular phones but appliances such as refrigerators and microwave ovens. Society is becoming ever more dependent on the free flow of data. Backbone networks with huge capacity are essential to maintain our way of life. We have been able to increase the transmission capacity of digital communication networks by adopting and enhancing the technique of time-division multiplexing (TDM). With TDM, the binary signals associated with different channels are interleaved to form a higher-speed multiplexed signal.

Interview with Donald Keck:The of Fiber Optics (OPN Trends Supplement)

By the 1960s, it had become clear that the copper wires that carried all telephone traffic were not going to be able to handle increasing demand forever. A few years before Keck’s whoopee moment, Charles K. Kao, a researcher at Standard Telecommunications Laboratory in England, had determined that for optical communications to be practical, the fiber had to lose light at no more than 20 decibels per kilometer. To achieve this result, various labs were working on making glass fiber that was optically pure.

Putting Fiber to the Test: The Early Days of Lightwave Systems

In the mid-1970s, Jacobs’ team performed a number of system experiments that would lead to the first commercial applications of fiber optics, including the historic transmission of the 1980 Olympic competitions in Lake Placid, New York.

Global Undersea Cable Network

Both the planning and the construction of optical telecommunications networks are now being conducted global scale. Phase one of the TyCom Global Network (TGN) will use 250,000 km of cable (and over 2,000,000 km of op- tical fiber) to connect the majority of the earth’s population centers with primary ca- ble landings in the Atlantic, Pacific, and Mediterranean oceans (see Fig. 1). The transmission capacity of these next-genera- tion links will far exceed 1 Tbit/s, a level once considered exclusively the realm of laboratory experiments.

The Roles of Semiconductor Optical Amplifiers in Optical Networks

Optical amplifiers have played a leading role in the evolution of telecommunications over the course of the past decade. What would the world of telecommunications look like if optical amplifier technology had not been developed? For a start, wavelength-division multiplexing (WDM) would be impractical: At every repeating station the signal would have to be demultiplexed, electronically regenerated, and retransmitted. In this scenario, multiple fibers—rather than multiple wavelengths—would probably be the most economical way to increase transmission system capacity. Cost per bit would be much higher than is the case for WDM systems. This added expense would most certainly have limited the growth of the Internet, since its market penetration is primarily due to transmission bandwidth availability and low connection costs.

Optical Metrology for Wavelength-Division-Mulitplexed Fiber Communications

In response to rapid changes in fiber-optic technology, the Optoelectronics Division of the National Institute of Standards and Technology has been developing techniques and standards to support the measurement of optical components and subsystems used in wavelength-division-multiplexed optical fiber communication systems. Current projects include the development of wavelength calibration transfer standards and the accurate measurement of spectral response, dispersion, and polarization dependence of optical fiber and components.

Wavelength Division multiplexing: Terabit technologies with high spectral efficiency

Dense wavelength-division-multiplexing (DWDM) systems meet the growing demand for transmission capacity of optical fiber trunk lines. Recent research activities on DWDM moved on to multiterabit/s transmission. To increase the total capacity and transmission distance in DWDM systems, we have to investigate technologies to overcome various limitations.

Lightwave Micromachines for Optical Networks

As data-networking interfaces approach the per-wavelength line rate, while core-transport line rates steadily rise, there is an emerging need for reconfigurable networking at the granularity of an individual wavelength, currently 2.5-10 Gbit/s. This need places severe strains on an already-war-weary arsenal of conventional optoelectronics and thus offers striking opportunities for lightwave micromachines, or micro-electromechanical systems (MEMS), that were implausible only a year or two ago.

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