Fiber Optics - Troubleshooting Those Dirty Little Fibers

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Fiber Optics - Troubleshooting Those Dirty Little Fibers

With its greater bandwidth capacity and ability to transmit signals over long distances with very little power loss, fiber has become the hands-down favorite for the future of

 Broadband. Fiber’s resistance to magnetic interference makes transmissions nearly noise free, and it has the advantage of better signal quality and less plant maintenance.

But while there are fewer problems associated with fiber deployments, there are still issues that need to be addressed. Many of these problems can make troubleshooting long, expensive, and frustrating. Therefore, field technicians need a best practices routine to determine the positions and causes of fails.

Troubleshooting and Best Practices for Fiber Cable

When troubleshooting, there can be several causes of a poor transmission or no transmission to the subscriber. Problems with the ONT equipment, with one of the splitters or a fault in the fiber link between the two splitters are examples. And just running fiber around a corner can put too much bend in the fiber and cause problems with the signal.

In addition to those bends and breaks in the fiber, signal loss can result because of bad or contaminated connectors, faulty connections at the patch, poor quality splices, or too many connectors or splices in the fiber run. Finally, there is the possibility that there is insufficient signal strength from the transmitter. But what you really need to know is…

The Number One Cause

Installers have established that the number one cause of issues or failed transmissions is dirty connections. Fiber is smaller and thinner than a human hair and unfortunately you can’t just look at a fiber strand with the naked eye and tell if it’s clean. If the strands become dirty, it can affect the transmission to the point where it stops working altogether.

So how do they get dirty? When installing and connecting the fiber, natural oil from the installer’s fingers will contaminate the fiber, and dust will cling to that oil. A brush of clothing will put static charged particles or tiny traces of debris in the air and those can settle on the end faces of the fibers when they’re connected. These nearly invisible specks of dust on the fiber strand will block the delivery of light through the fiber.

Think of the dust motes you sometimes see floating in a band of sunlight beaming through a window. These same dust specks are heading toward your fiber and you won’t see these on the fiber strands just by looking. And dust and specks on that box of fiber connectors can lead to damage to the end faces and contaminate the other connections. This adds to the problem and makes troubleshooting even more challenging. Keep the unused fiber cabling connectors covered at all times, even when not in use, to avoid this complication.

Keeping It Clean

Save yourself some headaches by cleaning fibers every time you connect them. Whenever fiber is being handled, following a “keep it clean” mantra will limit the problems that crop up. With this cleaning and inspection routine, you won’t have to put in as much time searching for issues later.dirtclean

To ensure a clean connection, it’s a good practice to clean the end faces to get rid of oil and dust particles. A package of lint-free wipes and a bottle of rubbing alcohol will work well. This process will clean the oils and residue and eliminate static charge. When cleaning the end faces don’t use canned air or blowers. These just blow particles around and add more dust to what’s already there.

And if you’re making a repair and a patch is unavoidable, the leads can easily become scratched or dirty during the handling. Patch leads should be cleaned every time.
Once cleaned, you can use a scope to verify the fiber end faces are clean. A fiber optic microscope is designed specifically for inspecting fiber optics. A scope with a high magnification level will show you more detail when inspecting the cable.

Next, running a quick test with an inexpensive fiber optic tracer can verify if the fiber is clean and transmitting light. If only one fiber isn’t transmitting light, this usually means a bad connector. Using the optic microscope to look at the fiber at the connector, look for dirt, dust or cracks in  the fiber and clean if required. After cleaning, check the scope again. If both connectors now look good, the problem is most likely internal. At that point you'll need additional testing equipment such as a visual fault locator (VFL) or optical domain reflectometer (OTDR).

Things to Remember When Installing Fiber

Improper cleaning of fiber optic cable connections will come back to haunt you.

Dirty fiber optic cable connections are the number one cause for network failures and truck roll call-backs. Installers claim that contamination is the root cause of most network failures.

You can’t determine if it’s clean with the naked eye.

You just can’t look at the fiber and tell if it’s clean or not, even if it appears to be. A dust particle so small you can’t see it without a scope, can completely block transmitted light through the cable. Using a fiber optic microscope capable of at least 200 times magnification and preferably 400 times will show you those particles.

You can count on fiber optic contamination to occur.

It’s almost impossible to prevent contamination of fiber connections. No matter how careful you are the common sources of fiber contamination are all around you, even on those covered and capped connectors. Oils and dust, fingerprints, clothing fibers, packaging material and other debris at the work site are guaranteed to be present. Rubbing alcohol as a sealed alcohol wipe can be used for contaminates on the connectors and the fiber surfaces. Always clean and inspect before connecting.

Clean physical contact of the fiber components is critical.

Even the most microscopic trace of contamination will prevent good physical contact. These invisible contaminates on the connector end-face can move when making connections. This will cause scratches and pitting that lead to permanent damage of your fiber optic cable. This lack of good contact prevents the glass-to-glass contact necessary to achieve a low reflection or low loss connection. Any scratch, pitting, film or debris can cause an air gap on the surface of the glass and increases the loss and the reflections.

Dust attracts dust.

Statically charged dust particles attract even more particles. Contaminated connector end faces will continue to accumulate more and more dust and debris. Use the microscope religiously to avoid damage to the core. Clean fiber will appear spotless under the microscope.

Zeroing In On the Problem

To read more about narrowing down and zeroing in on problems and how diagnostics applications will help you before you roll a truck, download this free paper here or contact us with any questions.

About the Author: Marsha Hemmerich

Marsha brings thirteen years of experience in the broadband industry as a Marketing Specialist and Technical Writer.

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