- The Elegant Optical Network
Advanced optical fiber and components will help make optical networks simpler.
Consumer technologies with which we are accustomed, such as the personal computer, have become
more complex in their internal workings, while the interfaces have become much more
elegant in their simplicity. This dual trend is reflected in optical networks as
Highly dense optical circuit packs, multiple network
layers, optical switches with thousands of micromachines and more intense network
monitoring all will make the networks more complex. On the other hand, weblike interfaces,
common control electronics and outside-plant technologies will make networks seem
simpler to those who install the fiber and equipment and to those who operate it.
In the past, networks were optimized
for specific applications because access, metropolitan, regional and long-haul systems
tended to have their own array of technologies and architectures. Today, operators
can implement functions more inexpensively across all networks, thanks to several
disruptive technologies ranging from novel modulation formats to new methods of
amplifying signals employing stimulated Raman scattering.
Another technology, forward error correction,
was developed for radio communications from deep-space probes, but in fiber networks
it can add several decibels of gain at little cost. In access and metro networks,
new electro-absorption and directly modulated laser technologies continue to raise
performance and lower costs and, combined with high-speed optics, will help drive
the emergence of 40-Gb/s Internet protocol ports.
With these tools at hand, network designers
will push for more integrated architectures that will allow simpler operations,
fewer spare parts, less training and reduced costs overall. Their networks will
be able to move massive amounts of data quickly and easily — necessary because
the margins for transporting data are so much less than those for moving switched
The past three years have been a wild ride in
the optical fiber industry. Most of the excitement has been in the long-haul market
as a “land grab” mentality of fiber build-outs that began in North America
in 1998 was followed by the pan-European builds in 2000. These built-out regions
will experience a continued meshing of optical path topologies as well as installation
of new technologies that will help stabilize long-haul fiber deployment growth.
A number of other projects were sprinkled
throughout Latin America, the Asia/Pacific region and Eastern Europe, but the focus
of recent months has been on China as new entrants and recently divided incumbents
have begun the daunting task of installing high-fiber-count cables along the eastern
seaboard and into the central provinces.
In the near term, operators deciding
which optical fiber to deploy will turn to diverse sets of solutions.
In one, optimized performance required
by specific sections of the network will determine the fiber type. Enhanced multimode
fibers will continue to be deployed at the premises level, for example, where low-cost
vertical-cavity surface-emitting lasers are the primary driver. In the ultralong-haul
area, where data traffic is aggregated into cost-efficient bit rates and channel
counts, fiber selection will be based on achieving the highest-performance, most
cost-effective and upgradable optical solutions.
If performance, cost-efficiency and upgradability drive fiber selection
in ultralong-haul applications, the criteria for fiber in access, metropolitan and
regional networks will be low attenuation, good splicing capability, excellent handling
and a dispersion profile suitable for multiple applications.
Meanwhile, submarine networks have
moved dispersion management — that is, managing the slope of dispersion —
into the fiber plant itself. Elegant dispersion-managed fiber technology is proving
itself there, and it is only a matter of time before it is deployed in the high-data-rate
segments of the long-haul network.
A separate set of fiber solutions will
find application in access, metro and regional networks — the largest growth
segments. To maintain a simple, single network across all of these segments, outside-plant
personnel will require equipment that is easy to install, maintain and operate.
The technologists will demand high-performance fiber and components that will deliver
greater capacity and enable simple upgrades and low transport costs.
The major criteria for fiber in access,
metro and regional networks will be low attenuation, good splicing capability, excellent
handling and a dispersion profile (with dispersion compensation) designed for multiple
It is difficult to predict trends beyond
these imminent fiber network advances, but deployment of some technologies clearly
will not happen in the near future. For example, although much research has been
focused on photonic crystal, or “holey” fibers, they will not be transmitting
signals in commercial networks for at least five years. Nor will newer materials
begin to replace silica-based optical fibers. Lastly, the debates on transport rates
and protocols will probably continue beyond 2006.
Although we have completed an exciting
time in optical network build-outs, there is good evidence that much more excitement
is ahead. Refinements in the technology thus far have only scratched the surface.
Clearly, designers and suppliers alike must be prepared to spend the time and energy
necessary to deliver the right selection of components in the right combination
and packaging to enable the next generation of elegant optical networks.
Meet the author
Alan Dowdell is new products manager for Corning
Inc. in Corning, N.Y.
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