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Fiber Optic Fundamentals - Installation Best Practices Part Two

Here in part two of our series on the best practices for installing fiber optic cable, we highlight some often-overlooked practices which can be critical in maintaining a fiber run's signal integrity, and how you can prevent them from happening.

HOW CLEAN ARE YOUR CONNECTORS?

According to the textbook by Bill Woodward, titled Cabling: The Complete Guide to Copper and Fiber-Optic Networking, dirty fiber end-faces account for 85 percent of attenuation loss issues. The impurities come in many forms, including dust particles attracted to the connector surface by moisture ingress (e.g. moisture-laden isopropyl alcohol); dust particles attracted to the connector surface by static electricity; dust particles rubbed into the connector surface causing permanent scratching; and fingerprint oil.

It is important to clean both connectors before testing a cable regardless of whether or not dust caps were placed on them during storage. The tiny fiber core is easily obstructed with dirt particles, finger oils, and various types of mishandling. This can obstruct the light source (or sensor) or force the two end-faces apart, generating scattering, dispersion, and ultimately, intermittent connections and network down-time. During testing, dirty endfaces are often the culprit for inconsistent results after multiple measurements. Dirty reference cables can also cause faulty readings with test equipment such as gain or unusually high loss. Not only is the possibility of dirt readily entering the connector very high to begin with, but so is the risk of pushing around dirt creating scratches and grooves, causing permanent damage.

DINTEK have a comprehensive range of fiber optic cleaning products each individually designed to clean specific connector types. The range includes:


CONNECTOR POLISHING

Most often, the main point of failure in fiber terminations is an improperly polished connector. Connector polishing is a task that takes a bit of finesse and therefore has an associated learning curve, with the end goal of 1) shaping the end tip until the desired shape is accomplished; 2) smoothening the shape to minimize light refraction.

Common polish topologies include physical contact (PC); ultra physical contact (UPC) and angled physical contact (APC). PC connectors end faces are polished with a slight curvature. That convex shape locates the fibers at the highest point of the surface, which reduces air gaps between them. Typical return loss in these connectors in single mode applications is -40 dB. 

An extended polishing is given to the UPC connector end face, which results in a better surface finish. The curvature makes them look dome-shaped. Their optical return loss is about -50 dB or higher.

An APC ferrule is polished with an 8-degree angle that brings the fibers tighter and reflects light at an angle into the cladding instead of reflecting directly to the light sources, which causes its Optical Return Loss to be -60dB or higher, being the better performance connector.

There are a number of tools available to terminate with a prepolished connector and DINTEK's ezi-FIBER Quick Install Technicians Kit has all that you need, including a fiber optic cleaver, a fiber optic stripper, Kevlar scissors and a jacket stripper.

This fully-equipped kit is designed to provide the installer everything that is required for an easy fit-off, eliminating most of the steps and labor associated with traditional fiber optic terminations, and following the above guidelines, will ensure optimal fiber integrity.

DINTEK's ezi-FIBER Quick Install Technicians Kit

After terminating a cable, there are two main assessments that can be made to judge the integrity of the connector head: a visual inspection and a method to measure reflectance. The reflectance (or back reflection) of the connector measures the amount of light that is reflected back to the source due to the imperfections in the polished interface. A poor polish will send many reflections back, causing a higher loss in the connector and ultimately, the entire installation. A good visual inspection of the connector will likely yield a good reflectance. However, less-experienced technicians may not be able to adequately visually discern an acceptable fiber connector so an additional test may be a helpful redundancy. Power meters, visual fault locators and continuity testers are therefore helpful not only for large installations, but on a case-by-case basis to reduce scrap rates in training new installers.

KEEP IT SAFE 

Mishandling thin pieces of glass can have serious side effects, so it is imperative that precautions are taken when handling fiber cabling. When terminating a cable, an installer would benefit from wearing goggles and protective clothing such as an apron. Additionally, it is recommended to wash the hands before rubbing eyes or touching any food as a precaution. Black rollup mats that hold polishing plates in place can also help identify fiber splinters. These splinters should be disposed of in a scrap trash can with tweezers. The goal is to mitigate the risk of getting glass shards into sensitive areas, and because these shards can be hard to detect, it might be better to operate as though they will inevitably occur.

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