COMMENT
The importance of end-face inspection Cleanliness is Next to... By Mike Gilmore, Technical Director, Fibreoptic Industry Association
The traditional Yorkshire saying “where there’s muck, there’s brass” does not carry across into optical fibre communications. In a world where the tolerance of connection loss has reduced as data rates have increased and where the need to obtain increasingly accurate measurements of those low losses has become paramount, the issue of contamination has become a critical issue for installers and users. The most common scenario results
Mike Gilmore considers the critical importance of end-face inspection.
from the partial use of installed cabling plant. Perhaps only two or four optical fibres are used within a panel - the others being left unused for a significant period. Although end-caps are useful for protecting the optical fibre end- faces from physical damage, they may not be much of a barrier to airborne contamination. This may be somewhat contra-intuitive and the unsuspecting user who simply connects his new equipment to the un-used ports may find that the newly created channel does not function as expected. This is more common now than in the past since low data rate networks were much more tolerant than the 1+ Gigabit networks of today. The FIA Technical Directorate is
often contacted by users who have been recommended to replace their installed cabling because it will not support the next-generation network due to higher than expected losses having been measured by installers. Hopefully, there were not FIA members because it is not uncommon for further investigation to show that the end-faces of the links are simply contaminated and that no effort has been made to either inspect them or clean them before any measurements were undertaken. While this does not bode well for the quality of the test cord end-faces (and any installations subsequently tested with them, assuming no further inspection or cleaning is undertaken) it is usual for a little bit of careful cleaning to reclaim the supposedly failed links to an adequate, if not perfect, condition. Of course, both installers and users
can remain blissfully unaware of the existence of contamination on optical fibre end-faces – right up until the moment it all goes horribly wrong. To reflect this increased focus on operational issues in relation to
10 NETCOMMS europe Volume II Issue 4 2012
connector cleanliness and damage prevention, the FIA has established its ‘Contamination, Inspection and Cleaning’ project team, known as PT CIC. The purpose of the Project Team is develop and promote documentation and other tools which emphasise the procedures with respect to contamination control that should be adopted to ensure effective quality assurance during new installations or the assessment/re-working of legacy installations and even more importantly, the need to maintain clean conditions during operation.
So Misunderstood PT CIC is trying to bring clarity to an area which is misunderstood, even by experienced practitioners. At the centre of this misunderstanding is a comparatively new standard, BS EN 61300-3-35, which defines the requirements for inspection of optical fibre end-faces at connectors. While this standard is a very good tool with which to specify the quality of supplied products such as cords or pigtails, it focuses on defects on the end- faces which affect specific aspects of transmission performance. The standard does not consider any impact of defects that affect insertion loss and it also assumes that all contamination (grease, particulate material) has been removed before any inspection is undertaken. There is no reason, provided that the end-faces of the optical fibre are kept in a clean condition, why the inspection criteria of BS EN 61300-3-35 cannot be maintained throughout the lifetime of an optical fibre end-face in a panel or on a cord. Unfortunately, the real world
frequently intrudes and introduces contamination on unconnected end- faces. If that contamination is not removed before mating two interfaces, it can become destructive not only for the optical performance of the connection but can also create defects in one or both of the end-faces - which will permanently prevent one or both of them ever meeting the requirements of BS EN 61300-3-35. The defects could be relatively minor in optical transmission terms but could be more significant.
This combination of risks generates
a need for different working practices for users, installers and trouble-shooters. Obviously users are subject to the most difficult task of all: to maintain the end-face quality by a regimented series of inspection and cleaning procedures before each mating. Installers have a more limited set of responsibilities. However, many installers are required
to act as trouble-shooters, going to a site only when problems occur. How should they act? Well they certainly should not dive straight in and start testing links, channels or cords without undertaking end-face inspection. Strangely enough, this lesson should have been learnt twenty five years ago and if an end-face inspection could have been employed, and an image recorded, then one of the most significant contractual disputes of that time could have been avoided. In 2012, the financial importance of optical fibre infrastructures (both in terms of the cost of transmission equipment and the value of the data transmitted) coupled with the demand for optical fibre connection performance make good practice more critical than ever.
Under the Microscope Contamination can be assessed with the human eye using a end-face optical microscope. However, the value of CCD microscopes linked to software capable of both storing and assessing the image cannot be underestimated. So, in the coming months the FIA will
issue White Papers which are targeted on different groups: users, installers and trouble-shooters to name but three. We will host suppliers’ White Papers and video clips of different inspection and cleaning products. Finally we will develop a technical database to allow the development of future standards for inspection while supporting documents such as PD TR 62627-05 (IEC TR 62627-05) on cleaning.
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