Managing the damage: The effect of static on fibre optics

Technical Features

Fibre optics play an important part in our everyday lives, writes Liam Taylor, European Business Manager, Fibre Optics, MicroCare UK Ltd. It keeps us engaged with the modern world by quickly carrying vast amounts of information across its connections to our businesses, healthcare facilities, military operations, transportation hubs and homes. Reliable, fast connectivity is vital to these functions. Therefore, any threat to a network’s operation or bandwidth capabilities must be managed to help prevent poor performance, latent speeds or complete network shutdown. Contamination on fiber optical interconnects is one of the most common threats to a fibre optic network. There are several sources of contamination, but one of the most challenging to manage is dust. Add electrostatic charges (ES) and it exasperates the dust problem further.

WHAT IS ELECTROSTATIC CHARGE?
ES attracts dust and traps it on ceramic and composite ferrule end faces. The ferrules and the glass fibres within are dielectric and act like an electrical insulator that can hold that static charge for months. As a result, charged dust particles are attracted to the oppositely charged connectors. In many cases, dust sticks not only to the outer areas of the connector, but also to the ferrule apex in the contact zone, where it does the most harm.

Contact friction is one of the most common ways electrostatic charges are generated on end faces or ferrules. Contact friction typically happens when end faces are mated or their protective end caps are removed. Because fibre end faces are made of non-conductive materials such as plastic, ceramic, glass, or epoxies, the static charge, also known as a triboelectric charge, does not have a path to dissipate. The dust, attracted and trapped by the ES, can change the light’s index of refraction, or the route of the signal through the fibre. This may result in insertion loss which weakens the signal, slowing down the network speed. There is also the possibility of a complete system shut down if the refraction angle is altered enough that no signal can be transmitted at all.

The ES problem is heightened with  the use of higher fibre count cable. In recent years, cables are being tightly packed with higher counts of fibres to increase bandwidth capacity and transmission speeds while maintaining a smaller footprint. As a result, typical fibre counts of 5,184, and UHCF (ultrahigh- count fibre) cables of 6,912 fibres are becoming the norm. But, the higher the fibre count, the more vulnerable the fibre cable and its connections are to contamination.

Connector construction and its material composition can also increase the chance of electrostatic charge problems. A good example is multi-fibre connectors. Newer 16-fibre arrays are replacing traditional 12-fibre arrays but still use the same 2.5-mm x 6.4-mm standard MT ferrule footprint. These connectors are not only denser, but they are also made from 80% glass, making the removal of dust problematic. Although glass helps improve thermal expansion control, it also retains more static than other types of connectors. To further complicate matters, most fibre end faces are designed with convex geometry to reduce back reflection. Although it works well for the intended job, it encourages static charge to concentrate at the contact region of the mated connector pair.

WET TO DRY WIPING
When cleaning a fibre optic end face, some technicians use a dry wipe or cleaning stick, but this dry wiping action typically causes more of triboelectric charge build-up and attracts airborne dust to the connector end face. In addition, the friction of the dry wiping can also encourage the shedding of fibre particles from the wipe or stick. This will immediately bond to the area being cleaned, increasing the problem further.
One of the best ways to combat ES buildup and remove the dust contamination from a charged end face is to replace dry wiping with the ‘wet to dry’ cleaning method. Not only is wet to dry cleaning effective, it meets the strict industry standards upheld by industry bodies like the IEC (International Electrotechnical Commission) and iNEMI (International Electronics Manufacturing Initiative) which every technician should be encouraged to follow.

FLUID ENGINEERED FOR CLEANING
When carrying out the wet to dry cleaning method, a specially engineered fibre optic cleaning fluid is of paramount importance. It will quickly dissipate any static charge making it easier to wipe away end face contamination.

Engineered cleaning fluid will also be ultra-fast drying, non-flammable and non-hazardous, meaning it is safe to use on any surface, safe to store and easy to transport, even by air.
Look for products packaged in hermetically sealed containers as this will keep the fluid ultra-pure, regardless of the working environment. The sealed container also prevents the fluid from absorbing airborne contaminants such as moisture, microscopic dust particles, exhaust particles from traffic or pollen from plants, all of which can degrade the cleaning process.

HOW TO WET-TO-DRY CLEAN

Wipe the connector end face in one motion, starting at the damp area of the wipe, and move towards the dry area to remove contamination and eliminate electrostatic charge.
To use the wet-to-dry cleaning process, with the fibre optic cleaning fluid. Wipe the connector end face in one motion, starting at the damp area of the wipe, and moving towards the dry area. This removes any contamination and eliminates any electrostatic charge.

It is important to choose your cleaning wipe carefully. Check that it is a highgrade, lint-free fabric wipe. Although a less expensive, lower-quality paper wipe may make sense when it comes to your budget, it is counterproductive. Lower-quality wipes can tear easily, leaving debris behind. Also, paper wipes generate the high static charges which trap and lock the contaminants onto the end faces.

CONTROL STATIC WITH CLEANING STICKS

To clean, first dampen the stick with cleaning fluid before inserting into the connector. If the tool of choice is a cleaning stick, the same cleaning rules apply. Opt for a high-quality stick and use it with an optical-grade static-dissipating cleaning fluid. The cleaning stick should be engineered to be non-linting and fit the end face configuration without needing to disassemble the connector or adapter.
To clean, first dampen the stick with cleaning fluid before inserting into the connector. Rotate in a clockwise direction, six to eight rotations. It is important to use one stick per end face to avoid cross-contamination.

CLICK-TO-CLEAN TOOLS
Cleaning sticks are ideal for low fibre counts or when cleaning highly contaminated end faces. If a technician is cleaning high-density fibre, a ‘click-toclean’ tool might be the better option. Click-to-clean tools are fast, effective and engineered to clean connectors with uneven geometries.

When using a click-to-clean tool, apply a small amount of cleaning fluid to a wipe first, then touch the tool to the dampened area. Finally, insert the tool into the port and push the handle until you feel and hear it fully engage. Do not spray the cleaning fluid directly onto the end face or onto the tool itself. What is important to remember with any of these cleaning tools, whether a wipe, stick or click-to-clean, is to always inspect, clean and reinspect both ends of a connector pair before mating to avoid cross-contaminating the end faces.

CLEAN NEW CONNECTORS
Electrostatic charges can also come from simply removing the protective caps from the new connector end faces.
Although the end faces passed cleanliness inspection at the factory, removing the end caps can generate static and attract contamination. Removing protective end caps is a common cause of static and dust-based contamination, so it is important to clean even brand-new fibre jumpers and connectors straight out of the pack before installation. Even testing can be a source of friction and static generation on end faces.
Inserting an inspection scope, power meter, or light source can turn the contact area of the end face into a dust magnet, attracting dust to the centre.
As these inspection tools are often used many times without cleaning between uses, they are usually dirty and can readily cross-contaminate end faces. It is recommended to always clean inspection tools with a static-dissipative optical grade cleaning fluid and wipe before use.

DON’T LET THE DUST SETTLE

Dust contamination on fibre optical interconnects is one of the most common threats to a fibre optic network. Dust contamination is one of the primary causes of fibre network failure.
Whether it’s airborne dust from dead skin, plant pollen, lint from cheap wipes or connector wear debris, it interferes with end-face connections resulting in back reflection, signal attenuation, and network instability. When you add electrostatic charge into the mix the problem significantly increases.

To ensure a reliable and robust network, fibre cleaning must be performed using proven tools and processes. Modern cleaning and inspecting processes, along with tools and fluids engineered specifically for fibre optic applications, should always be used to dissipate static and remove contamination. This will help ensure the fibre network maintains seamless connectivity and performs reliably at all times.

Liam Taylor, European Business Manager, Fibre Optics, MicroCare UK Ltd. He is also a member of the IEC/SC 86B Working Group 4. MicroCare manufactures the Sticklers™ brand of specialist fibre cleaning tools.
For more information, visit www.microcare.com.