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CLEAN AS A WHISTLE: The impact of primary and secondary contamination on fibre optic connection surfaces.

Fibre optic cleaning techniques are based on the removal of types of dust or oily matter. 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 attention 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 350[micro]m of limited existing characterisation, compared with the total horizontal surface area of 2,500[micro]m. 90 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 350[micro]m surface area as primary contamination.

The 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. These surfaces may have secondary contamination. Consideration of primary and secondary contamination as essential will maximise existing and future deployment.

There 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. The 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. The phase-out tacitly included 99.9 per cent (reagent-grade) isopropanol, a low-performing cleaner and contributor to atmospheric ozone contamination. The newer generation cleaners required re-training, this included understanding that some evaporated very fast, leaving residual contamination more difficult to remove than the original debris. More significantly, new-generation cleaners worked in smaller amounts than before. Precision cleaners include proprietary hydrocarbons, HFE, HFC, aqueous formulations derived from high-value precision cleaning applications, with new designs on the horizon.

Wiping materials have evolved--100 per cent cellulose (paper) is never acceptable to clean these precision surfaces. Cleanroom or medical grade foam swab tools and hydroentangled poly/cellulose are ideal to clean zone-5 and alignment sleeves. Your cleaning tool likely has these materials and should be moistened every time.

The swab or probe tip is placed in the solvent patch for a count of one to five, enabling a minute amount of cleaner to solvent-transfer into the wiping material. Tools may be 'clicked-twice' to remove and dry. The end face is drawn from wet to dry, moving the end face away from contaminated initial point of contact. Precision cleaning is a process change, requiring less time to reduce costs.

Ed Forrest is a researcher and the founder of training company, Fibre Optic Precision Cleaning
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Author:Forrest, Ed
Publication:Fibre Systems
Date:Sep 3, 2019
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