TECH FOCUS: CLEANING
CLEAN AS A WHISTLE
The impact of primary and secondary contamination on fibre optic connection surfaces
ED FORREST F
ibre optic cleaning techniques are based on the removal of types of dust or oily mater. Single soils are relatively easy to remove compared with ‘combination soils’
that might be dust, combined with human body oil or hand lotion. Understanding the inter-dynamic of location
of debris and its physical type is critical to removal. As speeds and capacities increase, and as deployments proliferate, there is a need to consider not only future, but also, heritage installations. Designers, installers and trainers face updates and backdates. Common understanding is that each
fibre requires a pristine level of precision cleaning, but, arguably, less atention is focused on alignment ports impacted with dust, that can cause misalignment of mated pairs. Misalignment induces insertion loss or reflectance, and debris on inter-surfaces can migrate. Contamination can trick auto-detect to give a
‘pass’ reading. Imagine 250 to 350µm of limited existing characterisation, compared with the total horizontal surface area of 2,500µm. 90
36 FiBRE SYSTEMS n Issue 25 n Autumn 2019
per cent of the horizontal and 100 per cent of the vertical surface of this connector are not characterised by existing standards and could be unclean. A higher understanding accepts 30-year standards and characterises the 250 to 350µm surface area as primary contamination. Te remaining surface horizontal becomes
zone-4 and vertical surfaces, inter-surfaces, and connector adapters are zone-5. Unseen alignment sleeve contamination can transfer from the jumper side to the backplane. Tese surfaces may have secondary contamination. Consideration of primary and secondary contamination as essential will maximise existing and future deployment. Tere is an inextricable interaction between
type of debris, location and means of removal. As requirements for surface cleaning evolve (clothing to fibre optics), we are challenged by concerns for high performance, environmental safety, costs and well-being of end users. New ultra-fast drying solvents, high-performance precision hydrocarbons and aqueous cleaners are used in a wide range of applications and wiping materials have evolved from cellulose
to complement these solvents. Best practice understands these new dynamics. Precision cleaning is not new, and it is ever
evolving. In 2014, a vendor-neutral examination of 10 commonly used cleaning tools and various debris was conducted. 90 per cent of the cleaning tools worked to remove various dust, oily soils, and combinations of the two using alternative techniques. For example, ‘dry cleaning’ is a mopping action that works on fluidic debris, while ‘wet-to-dry cleaning’ works best on dry debris to break surface tension, or dissipate static field contamination. Te third technique is termed solvent transfer. Beginning in the early 1990s and continuing
to this day, solvents considered environmental hazards were exchanged for safer and higher performance alternatives. Te phase-out tacitly included 99.9 per cent (reagent- grade) isopropanol, a low-performing cleaner and contributor to atmospheric ozone contamination. Te newer generation cleaners required re-training, this included understanding that some evaporated very fast, leaving residual contamination more difficult
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