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When good fiber goes bad

Troubleshooting Fiber Optic Cables

By Richard Arneson

Fiber optics brings to mind a number of things, all of them great: speed, reliability, high bandwidth, long distance transmission, immune to electromagnetic interference (EMI), and strength and durability. Fiber optics is comprised of fine glass, which might not sound durable, but flip the words fiber and glass and you’ve got a different story.
Fiberglass, as the name not so subtly suggests, is made up of glass fibers―at least partially. It achieves its incredible strength once it is combined with plastic. Originally used as insulation, the fiberglass train gained considerable steam in the 1970’s after asbestos, which had been widely used for insulation for over fifty (50) years, was found to cause cancer. But that’s enough about insulation.

How Fiber goes bad

As is often the case with good things, fiber optics doesn’t last forever. Or, it should be said, it doesn’t perform ideally forever. There are several issues that prevent it from delivering its intended goals.


Data transmission over fiber optics involves shooting light between input and output locations, and if the light intensity degrades, or loses its power, it’s known as attenuation. High attenuation is bad; low is good. There’s actually a mathematical equation that calculates the degree of attenuation, and this sum of all losses can be caused by a degradation in the fiber itself, poor splice points, or any point or junction where it’s connected.


When you shine a flashlight, the beam of light disperses over distance. This is dispersion. It’s expected, usually needed, when using a flashlight, but not your friend when it occurs in fiber optics. In fiber, dispersion occurs as a result of distance; the farther it’s transmitted, the weaker, or more degraded, the signal becomes. It must propagate enough light to achieve the bare minimum required by the receiving electronics.


Signal loss or degradation can exist when there are microscopic variations in the fiber, which, well, scatters the light. Scattering can be caused by fluctuations in the fiber’s composition or density, and are most often due to issues in manufacturing.


When fiber optic cables are bent too much (and yes, there’s a mathematical formula for that), there can be a loss or degradation in data delivery. Bending can cause the light to be reflected at odd angles, and can be due to bending of the outer cladding (Macroscopic bending), or bending within it (Microscopic bending).

To the rescue―the Fiber Optic Characterization Study

Thankfully, determining the health of fiber optics doesn’t rely on a Plug it in and see if it works approach. It’s a good thing, considering there is an estimated 113,000 miles of fiber optic cable traversing the United States. And that number just represents “long haul” fiber, and doesn’t include fiber networks built within cities or metro areas.
Fiber Characterization studies determine the overall health of a fiber network. The study consists of a series of tests that ultimately determine if the fiber in question can deliver its targeted bandwidth. As part of the study, connectors are tested (which cause the vast majority of issues), and the types and degrees of signal loss are calculated, such as core asymmetry, polarization, insertion and optical return loss, backscattering, reflection and several types of dispersion.
As you probably guessed, Fiber Characterization studies aren’t conducted in-house, unless your house maintains the engineering skill sets and equipment to carry it out.

Questions about Fiber Characterization studies? Turn to the experts

Yes, fiber optics is glass, but that doesn’t mean it will last forever, even if it never tangles with its arch nemesis―the backhoe. If it’s buried underground, or is strung aerially, it does have a shelf life. And while its shelf life is far longer than its copper or coax counterparts, it will degrade, then fail, over time. Whether you’re a service provider or utilize your own enterprise fiber optic network, success relies on the three (3) D’s―dependable delivery of data. A Fiber Characterization Study will help you achieve those.
If you have questions about optical networking, including Fiber Characterization studies, contact The GDT Optical Transport Team at They’re highly experienced optical engineers and architects who support some of the largest enterprises and service providers in the world. They’d love to hear from you.


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