After the Glass Rush: The Fiber Optics Upgrade Problem

After the Glass Rush

The fiber optic industry really began taking off about 30 years ago. Fiber’s bandwidth and distance superiority over copper wires or radio links—and the financial advantages those technical advantages provided—prompted a rapid growth in fiber use, a “glass rush” so to speak. Telcos led the rush to replace aging copper cables that had limited capability to begin with, troublesome microwave links, and expensive and annoying satellites.

The real boom era came in the late 1990s when many companies built new fiber networks, speculating on the growth of the internet. Of course, that market bubble burst in 2001. Later it was reported that 92 percent of all installed fiber was unused “dark fiber.” It took years for it to be used up and the installation of new fiber to grow again.

Most of that fiber was plain old single-mode, what we call G.652 today. It was optimized for 1,310-nanometer (nm) transmission but worked OK for 1,550 nm—in fact, with lower loss that allowed longer links. Networks using it started at speeds under 150 megabits per second and operated at around 1 gigabit per second (Gbps) by the end of the first 10 years of use.

Much of that fiber is still in use. However, networking speeds have skyrocketed. Today, 2.5 Gbps is slow, 10–40 Gbps is normal, serious users are at 100 Gbps, and some are doing field trials at 400 Gbps. Modern networks almost always use wavelength division multiplexing (WDM), creating up to 128 channels per fiber.

At the Fiber Optic Association, we get many calls from owners of older fiber networks who want to know if they can upgrade to faster speeds or WDM. We explain the bandwidth limitations of older fiber, chromatic and polarization mode dispersion, and how they can have the fiber tested to determine its potential.

Much of this 20–30-year-old fiber is past its prime. The manufacturing processes for both the fiber and cable have improved tremendously. The older fiber usually doesn’t have the necessary capacity, and often, the cable has deteriorated, making the fiber brittle and hard to handle.

Deciding to replace the fiber is not easy for many network owners, but at least the cost of fiber and cable have decreased enough that cable can be considered cheap—cheaper than kite string and monofilament fishing line, according to a market researcher I know. The cost of installation has not declined as much, but some innovative new products and techniques make installation easier.

Much underground cable still is installed in conduit buried in trenches. If the route allows, new cable can be plowed directly in the ground. Directional boring is being used to avoid digging trenches when crossing roads or creeks. New techniques such as microtrenching and blowing cables into microducts are faster and cheaper than conventional trenching.

There are also innovative ways of installing aerial cable. All-dielectric self-supporting (ADSS) cable is much easier to install than lashing cable to a messenger. Techniques now exist to wrap cable around current cables, including electrical power and ground wire cables, leaving the current cable in place. That is a big issue for electrical utilities that need more fiber capacity but are unable to shut down electrical transmission lines to replace optical ground wire.

But what do you do if you have no space in ducts or obsolete cables in ducts you want to replace? Or, even worse, what if you have small, low fiber count cables in innerduct in current conduit that you need to use until it is replaced? Some creative solutions exist.

Microcables available today are half the diameter of regular loose tube cables. A traditional duct pulled into 4-inch conduit can be replaced by a microduct with room for six cables of up to 288 fibers each. Sometimes microducts can be pulled into conduit that already contains a cable, expanding capacity.

Another solution replaces traditional plastic fiber innerduct with fabric ducts. If you have new construction, you can put a dozen or more cables in a 4-inch conduit where you were limited to four cables in innerduct. You can even use a machine to pull out the old innerduct and pull in multiple fabric ducts while leaving the current cables in place, further expanding conduit capacity.

Another option for CATV companies involves pulling the center conductor and insulation out of hardline CATV coaxial and then blowing in a fiber optic cable. If you really want to be different, you can use robots to install fiber optic cables in sewers, water pipes and gas pipes.

About the Author

Jim Hayes

Fiber Optics Columnist and Contributing Editor
Jim Hayes is a VDV writer and trainer and the president of The Fiber Optic Association. Find him at www.JimHayes.com .

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