New Fiber Advances Bring More Options, Lower Cost
x-changemag.com
By Patrick Emery and Virginia Maxwell
By Choosing A Fiber That Has Been Specifically Optimized For
Their Networks, Local Carriers Can Gain The Added Flexibility
And Capacity Necessary To Stay Ahead Of The Demand Curve.
Until recently, all fiber optic networks were composed of standard single
mode fiber. Regardless of whether a carrier was building a long distance
or metropolitan network, when it came time to pick the fiber, the choice
was simple. With transmission systems moving to higher speeds, more
wavelengths, longer lengths and greater powers, optical fiber has had to
evolve to keep pace. No longer do carriers have to settle for a
"one-fiber-fits-all" solution.
New breakthroughs in optical fiber design and technology have resulted
in new types of fibers with carefully optimized characteristics. And, while
carriers would rather not have to manage multiple fiber types in their
networks, they also don't want to limit themselves--either in terms of
capacity or evolvability. As such, local carriers need to take a closer look
at the types of fiber and transport technologies now available to ensure
they deploy an infrastructure that will allow growth well into the future as
demand changes.
Take, for example, how networks today are scrambling to adapt to the
rapid shift in consumer demand from voice to more data types of
services. This has led to the incorporation of new techniques such as
dense wave division multiplexing (DWDM) and all-optical
networking/management. Will these new advances be enough to
accommodate the unprecedented--and still unpredictable--bandwidth
needs of the 21st century? It's anybody's guess.
Who could have predicted the Internet explosion and the demands it has
placed on networks worldwide? While the future may be somewhat
uncertain, one thing is not: exponential traffic growth and new
opportunities for local carriers to own and lease bandwidth has led to the
need for a new breed of optical fiber known as metropolitan optimized
fiber.
Opening Up a Window of Opportunity
When a local carrier deploys a conventional single mode fiber optic
system, it either can operate in the 1310 nanometer (nm) window
(1280nm to 1325nm) or the 1550nm window (1530nm to 1565nm) of
the fiber's spectrum. The wavelength region between 1350nm and
1450nm historically has not been used because of high attenuation. In
fact, conventional fiber has as much as one decibel/kilometer of loss in
this 1400nm band, limiting transmission distances to just a few
kilometers. That all changes with metro optimized fiber, which makes
available for the first time ever the entire wavelength region--from
1280nm to 1625nm.
The higher attenuation of conventional fiber is the result of an intrinsic
characteristic of silica glass to absorb light in the 1385nm region due to
the presence of hydroxyl ions (the so-called "water peak"). Lucent
Technologies Inc. has developed a manufacturing process in which the
incorporation of hydroxyl ions into the glass has been virtually eliminated,
resulting in a new metro optimized fiber in which the loss is limited only
by the intrinsic properties of pure glass.
The performance of metro optimized fiber is identical to that of single
mode fiber in the 1310nm and 1550 nm regions. They are both matched
clad fibers with identical splicing and operational characteristics.
However, by opening up that previously unusable window in the fiber
spectrum, metro optimized fiber offers local carriers several significant
advantages over conventional single mode fiber:
More usable wavelengths. Optical networking in even moderately sized
metro areas could generate the need for fiber to carry hundreds of
wavelengths. Metro optimized fiber increases the fiber spectrum usable
for DWDM transmission by up to 100nm or three times the spectrum
used today. Because this can translate into 150 or more new wavelengths
(at 100 gigahertz (gHz) spacing) for DWDM applications, the usability of
the fiber in the field can be greatly extended. (See article entitled, "How
Much is Enough?" X-CHANGE, May 15, page 38.)
Enhanced distance capabilities. The window opened by metro
optimized fiber offers unique transmission options. First, the dispersion in
the 1400 region of metro optimized fiber is about 50 percent lower than
conventional fiber's dispersion in the 1550nm region. Second, its
attenuation in the 1400 region is about one-third less than conventional
fiber's attenuation in the 1310nm band. As a result, metro optimized fiber
will support longer uncompensated distances for higher bit rate (10
gigabits per second or gbps) transmission, an important attribute since
optical networking can create the need for direct or protection
wavelengths distances up to 200 kilo-meters (km) in metro networks.
Conventional fiber using 10gbps DWDM operation at 1550nm requires
compensation at 50km to 100km.
When operating in the 1400nm band of the fiber spectrum, metro
optimized fiber allows optical signals to travel more than one-third farther
than signals in the 1310 band on conventional fiber without amplification.
One application in which this enhanced distance capability can prove
important is in the transport of video signals to subscribers. These signals
could be transmitted from remote headend locations via metro optimized
fiber directly to customers in disperse geographical areas without
amplification.
Increased service capabilities. The additional spectrum and unique
qualities of the 1350 to 1450 region enable a "banding" approach to
network management. In short, service types can be grouped together
and allocated to certain wavelength bands where they are most suited.
For example, one fiber might carry WDM analog video in the 1310
region, high-bit-rate data traffic (up to 10gbps) in the 1350nm to
1450nm region, and lower speed DWDM traffic (up to 2.5gbps) in the
region above 1450nm.
Reduced Equipment Costs. The additional spectrum provided by metro
optimized fiber could lead to the use of less expensive lasers and other
components in a local carrier's network. DWDM signals, for example,
could be spaced more widely over a broader range of wavelengths,
thereby allowing the use of less-costly directly modulated lasers. Cost
reductions in other component areas such as multiplexers, demultiplexers
and wavelength add/drop devices also can be expected when metro
optimized fiber is used.
Reuse of existing transmission equipment. Because metro optimized
fiber has the same dispersion and loss as conventional fiber in the
1310nm and 1550nm regions, all existing transmission equipment can be
used with this new class of fiber.
One of the primary concerns of local carriers building new metropolitan
fiber optic networks is capacity future-proofing. The goal of optical
networking is to establish a cost-effective foundation today that gives
carriers the flexibility to solve their evolving capacity needs in an
economical way--even when future demands are greater than could have
been predicted. Optical networking systems such as DWDM, for
example, easily can deliver the capacity expansion carriers require now
and, at the same time, allow carriers to take the incremental growth steps
necessary to reduce their first costs while building toward a future-proof
network infrastructure.
For optical networking to reach its full potential, however, it should be
coupled with a fiber that has been specifically optimized for a carrier's
particular network application. Only then will the promise of high
capacity, flexible growth and compatibility with several new generations
of transmission technology be fully realized. And, with all the economic
advantages metro optimized fiber enjoys over conventional fiber, any
added premium for the new fiber may be quickly recouped in any
number of ways.
Metro optimized fiber gives local carriers a clean sheet of paper on which
to build their business. How they use it to build--and differentiate--their
brand is up to them. That's the real strength behind this new class of fiber.
With an infrastructure that can readily support whatever service is thrown
at it, local carriers are better prepared to respond quickly and efficiently
to their customers' demands. Thanks to metro optimized fiber, local
carriers worry less about future capacity needs and begin concentrating
on being first to market with affordable, revenue-generating services.
Patrick Emery is technical manager, Fiber Optic Systems
Engineering, and Virginia Maxwell is a distinguished member of
technical staff, Optical Networking, at Lucent Technologies' Bell
Laboratories.
Copyright c 1998 by Virgo Publishing, Inc.
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