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Why it's important to clean your fiber optic equipment

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. To illustrate this, it can be compared to a typical human hair which is between 50 and 75 micron. A dust particle can be as little as 9 micron and is pretty much impossible to see without a microscope. Despite this, it could completely block a single-mode fiber core, and if trapped between two fiber faces it can even scratch the glass, damaging the end-face. If this happens, then at best it will require the careful and time-consuming process of being polished out and, at worst, it will have to be replaced.

Furthermore, with high-power lasers now in use, if the contamination remains in place when the laser is turned on, it can actually be burned into the end-face to such an extent that it cannot be polished out. Whilst this may seem extreme, each time you disconnect and re-connect a fiber connector, problems can be re-introduced; a statement backed by a study carried out by NEMI (National Electronics Manufacturing Initiative). The study showed that mating caused loose contaminants to spread. Through connection, a significant amount of the particles were transferred from the contaminated connector to the clean reference connector in a pattern similar to that seen on the contaminated connector.

Even the use of 'dirty' dust caps can have a significant impact on the 'cleanliness' of the fiber installation. The oil from human skin can also have a dramatic effect when viewed under a microscope. A recent incident was reported claiming that fiber cable was failing after less than 10 years of use when it shouldn't degrade at all over this period of time. The first clue to the culprit of the problem was that the building and cabling infrastructure had transferred ownership on two separate occasions during this time. Each time, there was a massive opportunity to introduce contamination, which in reality is what had occurred.

The Cleaning Process

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.

A bottle of 90-percent isopropyl alcohol (IPA) and dry wipes are recommended for the cleaning process, and are included in DINTEK's ezi-FIBER Quick Install Technicians Kit. When using the bottle of IPA, it is important to note that over time it will begin to collect moisture and a technician that uses this moisture-penetrated alcohol will find that the surface of the fiber will take longer to dry, leaving it susceptible to dirt. Alcohol pads can effectively mitigate the risk of this occurring.

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 connector 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.


A suggested process for cleaning fiber connectors


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

DINTEK Fiber Optic Cleaning Box which contains superfine fiber tape and is suitable for SC/FC/MU/LC/ST/D4 and DIN connectors

DINTEK 2.5mm Connector Cleaning Pen for SC/ST/FC connectors

DINTEK 1.25mm LC Connector Cleaning Pen for LC connectors

DINTEK One Push MPO/MTP Optic Cleaner for MPO/MTP connectors

The Do's and Don'ts of Cleaning Fiber

  • Never touch the end-face of the fiber connectors - natural body oil can be a major cause of contamination.
  • Always keep a protective cap on unplugged fiber connectors - protection from both damage and contamination.
  • Do not clean bulkhead connectors without a way of inspecting them - how else will you know whether the cleaning is successful?
  • Always store unused protective caps in a sealed container - they can be a major source of contamination if not stored in a clean environment.
  • Never re-use any tissue, swab or cleaning cassette reel.
  • Never touch any portion of tissue or swab where alcohol was applied - you could be introducing both dirt and body oil.
  • Never use a wet cleaning method without a way of dry cleaning immediately afterwards - the wet process can leave a harmful residue that is hard to remove when it dries.


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