A clean sweep

Best practices with fibre often start with the basics of proper inspection and effective cleaning. Doug Vandenberg, product marketing manager for Fluke's Fibre installation products writes on the things to look for when laying out fibre connections.

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By  Doug Vandenberg Published  January 16, 2008

Fibre optic cabling systems has resulted in special importance being given to optical care and cleanliness. While inspecting and cleaning fibre connectors is not new, it is growing in importance as links with increasingly higher data rates are driving decreasingly small loss budgets. With less tolerance for overall light loss, the attenuation through adapters must get lower and lower. This is achieved by properly inspecting and cleaning when necessary. Yet there is no reason to feel intimidated by these tighter loss budgets because inspecting and cleaning connections is straightforward and easy.

Fibre basics

Fibre optic cabling carries pulses of light between transmitters and receivers. These pulses represent the data being sent across the cable. In order 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.

Among key sources of loss that can bring a fibre network down, dirty and damanged end-faces are the most underestimated threat.

In lower data rate networks with shorter lengths, loss budgets may be generous enough to allow for significant attenuation throughout the link and still the link will function properly. However, there is one perpetual trend in structured cabling: 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 threat most underestimated. In a survey commissioned by Fluke Networks, dirty end-faces were found to be the number one cause of fibre link failure for both installers and private network owners. Contaminated end-faces were the cause of fibre links failing 85% of the time. It's astounding and yet easy to prevent. Nevertheless, there continues to be a lack of appreciation for this crucial issue and lots of misinformation about proper techniques.

The problem

There are two types of problems that will cause loss as light leaves one end-face and enters another inside an adapter: contamination and damage.

Contamination

Contamination comes in many forms from dust to oils to buffer gel. Simply touching the ferrule will immediately 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. This can be especially true in facilities undergoing construction or renovation. In new installations, buffer gel and pulling lube can easily find its way onto the fibre's end-face.

Ironically, 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 mold release compound that will contaminate end-faces on contact. Further, as the plastic cap ages the plasticizers deteriorate resulting in an outgas residue. Last, airborne dust itself will 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 very common mistake to assume that end-faces are clean when patch cords or pre-terminated pigtails are removed from a sealed bag with protective caps in place.

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