With increasingly higher data rates driving decreasingly small loss budgets, inspecting and cleaning fibre connectors is more important than ever before.

For centuries, optics have been inspected and cleaned to ensure the proper passage of light. The advent of fibre optic cabling systems meant there was one more application where optical care and cleanliness were important.

Now, the increasing popularity of virtualisation in data centres means there are more fibre connectors being used. And, even one dirty connector can significantly impact the performance of applications running over that link. With less tolerance for overall light loss, the attenuation through adapters must get lower. This can be achieved through proper inspection and cleaning.

WHAT’S THE PROBLEM?

Fibre optic cabling carries pulses of light between transmitters and receivers. These pulses represent the data being sent across the cable. For the data to be transmitted successfully, the light must arrive at the far end of the cable with enough power to be measured.

Light loss between the ends of a fibre link comes from multiple sources such as the attenuation of the fibre itself, fusion splices, macrobends and loss through adapter couplings where end-faces meet.

In lower data rate networks with shorter lengths, loss budgets may be generous enough to cater for significant attenuation throughout the link. However, the one perpetual trend in structured cabling is the constant push for greater bandwidth. As fibre links are pushed to carry higher data rates, loss budgets get correspondingly smaller, requiring all loss events to be minimised.

Among key sources of loss that can bring a fibre network down, dirty and damaged end faces are the most underestimated threat. Despite being easy to prevent, contaminated end-faces are the cause of links failing in the majority of cases.

WHAT TO LOOK FOR AND WHEN

Network professionals need to know what to look for when evaluating end-face conditions. There are two types of problems that will cause loss as light leaves one endface and enters another inside an adapter.

Contamination

Contamination comes in many forms – from dust to oils to buffer gel. Simply touching the ferrule will deposit an unacceptable amount of body oil on the end-face. Dust and small static-charged particles float through the air and can land on any exposed termination.

Paradoxically, protective caps – also called “dust caps” – are one of the most common contributors to contamination. These caps are made in high-speed production processes that use a mould release compound that will contaminate end-faces on contact. Furthermore, as the plastic cap
ages, the plasticisers deteriorate, resulting in an outgas residue.

Lastly, airborne dust can find its way into the protective cap and will move to the end-face when the cap is pushed onto a ferrule. It’s a common mistake to assume that end-faces are clean when patch cords or preterminated pigtails are removed from a sealed bag with protective caps in place.

Inspection of the end-face should verify that no contaminants are within the field of view. The most crucial area to clean is the core of the fibre, followed by the cladding.

Contamination on the ferrule – outside of the end-face – could also slide towards to core as the fibre is mated or handled. Therefore, all visible contamination should be removed wherever possible.

Damage

Deciding to mate every connection first and then inspecting only those that fail is a dangerous approach. The physical contact of mated contaminants can cause permanent damage, which requires more costly and time consuming retermination or replacement of
pre-terminated links.

Damage will appear as scratches, pits, cracks or chips. These end-face surface defects could be the result of poor termination or mated contamination.

Regardless of the cause, damage must be evaluated to determine if action is required or whether it can be ignored or remedied.

Chips on the core are unacceptable. If scratches or excess epoxy bleed is found, repolishing with fine lapping paper can eliminate the problem. If the end-face is cracked or shattered, then the fibre must always be reterminated.

End-faces should always be inspected before insertion. If a connector is being mated to a port, then the port should be inspected as well.

Inspecting one side of a connection is ineffective as contamination inside a port can not only cause damage but also migrate to the connector being inserted.

HOW TO INSPECT

Fibre microscope choices

Optical microscopes incorporate an objective lens and an eyepiece lens to let you view the end-face directly through the device. Today, the barrel
shaped microscopes are commonplace in termination kits and used to inspect patch cords during troubleshooting. Optical microscopes are the least expensive way to see end-face details but they are unable to view end-faces through bulkheads or inside equipment. As a result, you will sometimes hear these microscopes referred to as “patch cord scopes.”

Video microscopes incorporate both an optical probe and a display for viewing the probe’s image. Probes are designed to be small so that they can reach ports in hardto-access places. The screens let images be expanded for easier identification of contaminants and damage. Because the endface
is viewed on a screen instead of directly, probes eliminate the chance of harmful laser light reaching the eye.

Microscope evaluation

What matters most about a microscope is what it shows the user. In the case of fibre optic inspection, the goal is to identify all contaminants and damage of a minimum size, within a critical area. Users must first identify the appropriate minimum size contaminant or defect that will affect their system. The smallest-sized item that a microscope can detect is referred to as its detection capability.

Next, look for the microscope that has the largest field of view while also maintaining the necessary detection capability. It is preferable to see as much of the surface area as possible while maintaining requisite detection capability. Detection capability and field of view require a trade-off as
improving on one dimension tends to require a detriment to the other.

If detection capability and field of view are the most appropriate measurements of a microscope, then why is magnification the prevalent metric?

Magnification is applicable to optical microscopes, as performance is a direct function of the objective and eyepiece lens inside the device. Where magnification becomes less applicable is in video microscopes where the size of the image is a function of both the magnification of the lens
as well as the size of the screen.

Complicating matters further is the effect of contrast on the ultimate goal of detection capability. Though magnification is directly related to detection capability, it is a less precise measure of a fibre microscope’s capabilities than detection capability and field of view.

HOW TO CLEAN

Beware of bad habits

Because cleaning has been part of fibre maintenance for years, most people have their own approaches for cleaning end-faces.

However, beware of bad habits that have developed in the industry over time. One common approach to cleaning end-faces is to blast them with canned air, either on a connector or inside a port. Canned air is only eff ective on large dust particles. Canned air is ineffective not only on oils and residues but also on smaller, charged dust particles.

Canned air will also tend to blow large particles around inside ports rather than carefully remove them.

Dry cleaning

Traditionally, dry cleaning is proven to be only partially eff ective in eliminating contaminants from fibre end-face and connectors. Technological advancements and better dry cleaning materials however, mean there is now a new class of fibre cleaning tools that are cost effective and efficient in cleaning more than 50% of contaminants from fibre. These tools become a perfect complement to the fibre wet cleaning solution to cover the cleaning needs in almost all situations and environments.

Use of solvent

Some contaminants, like greasy and sticky materials, are difficult to uplift without the use of a solvent. Solvents provide multiple benefits, the most significant being their ability to dissolve dried contaminants that adhere to the end-face. In addition, solvents will envelop particles and debris to effectively lift them from the ferrule surface so that they can be carried away without damaging the end-face. Lastly, solvents will prevent a static
charge from developing during cleaning with a dry wipe or reel that are not optimised for dry cleaning.

Solvent selection

Isopropyl alcohol (IPA) has been used for years in the fibre cabling industry to successfully clean end-faces and continues to be used today. But there are now solvents specially formulated for fibre end-face cleaning that are far superior to IPA. These new solvents are more effective at dissolving virtually every contaminant. Further, these custom solvents will dissolve non-ionic compounds such as pulling lube and buffer gel that IPA will not. With a specified lower surface tension, the specialised solvents will do a better job of enveloping debris for removal. When cleaning inside ports, evaporation rates become important as lingering solvents can become trapped during mating, resulting in a harmful residue. Fibre-specifi c solvents have tailored evaporation rates that give them time to work yet disappear before mating.

Lastly, IPA is highly hygroscopic, which means it will draw water moisture from the air and onto the end-face. This water mixes with the IPA and leaves a residue if it dries on the end-face.

Cleaning tools

There are a wide variety of tools available to clean end-faces. The most basic tools are wipes and swabs used to clean patch cords and inside ports, respectively. More involved approaches include mechanical, hand-held contraptions designed to make easier work of cleaning. The most complex devices incorporate blasted solvents or ultrasound in water to achieve the best result. While the more complex systems may achieve
better results, they cost far more. Individuals should determine the best approach for their application and budget. The one key criterion
for wiping materials is that they be lint-free.

BEST PRACTICES

Whatever approach is selected, there are certain rules which must be followed. Inspection must occur not only before but also after cleaning to ensure a good result. If a post-cleaning inspection shows remaining contamination, then a second cleaning must follow. Both sides of any connection need to be inspected as every mating involves two surfaces coming into contact.

Lastly, it is almost always easier and cheaper to inspect and clean as a preventative measure than as reactive response. Consistent inspection and
cleaning up front will avoid unexpected and costly downtime in the future.