The Importance of Clean Fiber Optic Termini

When clean fiber optic termini are undisturbed the optical path is preserved for years. However, during installation, maintenance, reconfiguration and equipment upgrades, those pristine connector end-faces risk exposure to the environment. The fiber optic termini may become contaminated. It’s estimated that connection points are the source of about 70% of the optical network failures. And 70% of those failures are a result of simple contamination of the end-face. The author explores better ways to clean and inspect fiber optic termini, saving time and money in the process.

Fiber Optic is Growing

Over the past decades, the use of fiber optics throughout industry and our daily lives has seen a remarkable increase. High power laser energy routinely travels through fiber for precision cutting, marking and etching of surfaces in conditions and places previously not possible. High definition TV, internet gaming,
medical data imaging, financial services, cloud computing, smartphones, general commerce and social networking all have dramatically increased the
demand for bandwidth. All the elements of optical networking are experiencing increased demand for bandwidth and the utility it provides. Be it long haul, back haul, FTTX, WAN or LAN. But, while the technology and reliability of optical components has improved over the past decades, there still remains predictable system vulnerability at the points of interconnect.

An interconnect is the point of mating two fiber optic connectors, or the mating of a fiber optic connector with an optical device. It’s estimated that connection points are the source of about 70% of the optical network failures. And more than 70% of those failures are a result of connector end-face contamination. This is because the interconnect is the only point in the network where the core of the glass fiber carrying the optical signal comes in contact with contamination from the external environment.

Keep Connectors Clean

When in service, connectors mate and make physical contact at their end-face within an alignment sleeve. They hold in place with springs contained within the connectors. This ensures continued physical contact and preservation of the optical path. However, during installation, maintenance, rerouting, and equipment upgrades, disconnected connector end-faces face exposure to the environment.  It’s at this time the end-face risks contamination. Either by accidental human contact, by contact with an unclean connector such as a test jumper, or by coming in contact with airborne contaminants.

Maintenance of the connector end-face is imperative for the fiber optic network to work correctly. It is an exacting job. The termini that create a connection must meet at an exact place. And the microscopic glass cores need to be perfectly aligned in order to have signal transmitted through the interconnect. In addition, the termini end-faces must be perfectly cleaned of all contaminants to ensure minimal signal loss. Thus, one of the most basic and important procedures for the maintenance of fiber optic networks is to clean the fiber optic termini.

Importance of Cleaning

Any contamination on the termini end-face can cause failure of an optical device or the network as a whole. Even microscopic particles on the end-faces can cause a variety of problems for optical connections. One of the biggest challenges of contamination is that it cannot be seen with the naked eye. One must use a specialized 200x or 400x inspection scope to determine the cleanliness of the end-face. It is critical to closely inspect the connector to confirm the particles and residue are completely eliminated. Thereby ensuring the interconnects perform to their full potential.

A dirty fiber optic end-face significantly degrades signal transmission and can even block the optical signal all together. Even if a stray particle is only on the ferrule edge of the end-face, it causes an air gap or misalignment in the termini between the glass cores. This can result in back reflections, instability in the network, signal attenuation or even a system shutdown. Another potential issue is a scratched surface as a result of dust particles trapped between two termini end-faces. What’s more, some fiber optic instruments such as those using high power Class IV lasers, generate a significant amount of heat, which, when in contact with contaminants can spark a surprisingly violent reaction or fire.

One of the biggest challenges in cleaning fiber optic termini is establishing a process that works consistently. Improvising a cleaning process will almost certainly lead to failure, as outlined above. The best advice is to inspect, clean, and inspect again. Repeat this process until you are absolutely sure both ends of the interconnect are completely clear of all contaminants. Spending time to clean it right the first time will save you time and money in the end.

Cleaning Methods

Materials used to clean the end-faces must be perfectly-clean, otherwise you can easily make the end-face worse by adding contamination. It may be intuitive to wipe the end-face on your coveralls or a spare cloth. But under a fiber optic inspection scope, those items carry a surprising variety of contaminants that will soil the connector. Even briefly touching the termini with your finger will cause it to be significantly dirtied with skin oil. To clean properly and avoid
further contamination, make sure to always use a cleaning product that has been specifically engineered for cleaning fiber optics. It’s also a good practice to always wash your hands prior to using fiber optic cleaning materials. This avoids the transfer of skin oil onto otherwise pristine cleaning products.

There are two basic methods properly clean fiber optic termini. A high purity wipe for male connectors, and a specialty swab for female connectors. It’s important to note that while wipes work on almost all configurations of male connector termini, swabs are sized specifically for the type of connector being cleaned. Beware, a swab sized to clean an SC connector will not fit in a LC connector alignment sleeve. To achieve your goal of a perfectly clean termini end-face, swabs and wipes should always be used with a high purity fluid.

Three types of Contamination

In very general terms, contamination found on termini end-faces falls into three basic categories: particulates, oils and salts. Each requires specialized methods for proper removal. Particulates are solids, usually held on the end-face by electrostatic attraction. Even experienced technicians are surprised to learn that static attraction, increased by the mechanical action of a cleaning product, creates a triboelectric charge on the non-conductive termini end-face.
That triboelectric charge will actually attract dust particles like a magnet.

The best way to clean particulates is by dissipating the static charge that both attracts and holds them in place. Use a specialty cleaning fluid that actively dissipates static charges. A well-engineered cleaning fluid selectively dissolves oils found on the fiber end-face without damaging materials used to make the connector, its housing, or surrounding components. Salts, on the other hand, are not necessarily fully removed by cleaning fluids alone. While cleaning fluids may quickly dissolve oils and rinse away particulate, they frequently dry and leave a white residue that is very difficult to remove. The absorbency and mechanical action of a wipe or swab improves with the addition of a cleaning fluid. It helps to fully eliminate oils, particulates and salts that otherwise stay on the termini end-face.

Buyer beware, some cleaning products on the market leave the end-face dirtier than when you started. To avoid this situation, look for products that combine wipes and fluids engineered to work together to rid the termini end-face of particulates, oils and salts.

Avoid Water

Avoid using aqueous (water based) cleaners or isopropyl alcohol (IPA), as both present significant limitations. Aqueous products dry slowly and, when used improperly, leave moisture on the end-face. In cold ambient temperatures, the moisture may actually freeze on the end-face or in the alignment sleeve. In extreme cases such as with high power lasers, if the moisture is not completely removed before the connectors mate in the sleeve, the laser-energized fiber instantly transforms the remaining liquid into vapor. This causes a small explosion through sudden expansion of the vapors.

IPA is typically comes in low purity grades and packaging simply not suitable for cleaning fiber. As a result IPA frequently leaves a hazy film behind when it dries. As with water-based cleaners, in extreme situations IPA may cause sudden vapor expansion problems or possibly ignite if left on a highly energized fiber end-face. Look for a fast drying, high-purity fluid formulated, packaged and labeled specifically for cleaning fiber optics.

Beware of Presaturated Wipes

High-purity cleaning fluids should always be used with both wipe and swab applications. But, beware of pre-saturated cleaning materials. Pre-saturated wipes and swabs often contain microscopic oily residues extracted from the plastic packaging. This then transfers to the end-face during the cleaning process. Instead, carefully apply a small amount of high purity cleaning fluid on a corner of a dry wipe or the tip of the swab. Then clean the fiber optic termini. A well-engineered cleaning fluid dissolves oils found on the end-face. It also helps eliminate the electrostatic charge generated as the applicator pulls out  of its packaging or draws across the fiber end-face when cleaning.

Remember, microscopic amounts of contamination causes big problems on a termini end-face. Use care to not touch the area of the wipe or swab you will be using to clean with your finger or your clothing. Should you touch the area of the wipe or the tip of the swab with your finger or drop it on the ground, discard the wipe or swab and start over. Avoid reusing cleaning swabs and wipes because they transfer contamination onto the next connector. Once the cleaning process is complete, discard the wipe or swab. Then inspect the end-face to ensure they are contaminant-free.

Bottom Line: Performance Critical Cleaning

Our reliance on fiber optics continues to grow. It is imperative to clean interconnect end-faces perfectly the first time around with the right products, the right way. Fiber optic service professionals can’t afford to leave behind end-face contamination which results in poor network performance and costly callbacks. Use the correct cleaning products and closely inspect the end-face to avoid these costly mistakes. Investing the time, energy and money into
the cleaning process at the beginning ends up saving you in the end.

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