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Using this criterion, the example given in Table 1 can be
simplified as follows:
• 0.69 GPa fibre at 20 per cent long-term load will
provide reliable performance
• 0.69 GPa fibre at 40 per cent long-term load will not
provide reliable performance
• 1.38 GPa fibre at 20 per cent long-term load will not
provide reliable performance
Though it is apparent that proof-testing at higher levels
greatly improves the performance of the cables, the value
commonly used in cabling standards – 20 per cent of the
proof test level – can lead to false expectations about the
long-term reliability of the optical cables.
6 Recommendations
The information described in this document indicates
that, though 20 per cent of the proof-test load for a
long-term load on optical fibre may be a reasonable
criterion for optical fibre proof-tested at 0.69 GPa or less,
it may produce optimistic estimations for optical fibre
proof-tested at higher levels.
Currently, most major optical fibre standards, including
those in ITU-T, IEC, and TIA, require the fibre to be
proof-tested at 0.69 GPa. Cable standards in IEC,
ICEA and IEEE should align with this criterion. It is thus
recommended that the documents be modified to simply
require maximum long-term load of 0.14 GPa (20 kpsi) on
the cabled optical fibre after deployment, regardless of the
proof-test level. A note could be added to the requirement
stating that when optical fibre with proof-test levels higher
than 0.69 GPa is deployed, higher strains on the optical
fibre will affect reliability and should be agreed to by the
cable supplier and end user, and that more precise fibre
reliability models should be considered.
7 Conclusions
This paper has shown that modern cable designs are
pushing the design limits for allowable long-term strain
in optical cables. Under these new boundary conditions,
the old rule of thumb allowing up to 20 per cent of the
proof-test level as a long-term strain may no longer be
appropriate.
A new recommendation requiring the long-term load be
limited to 0.14 GPa is proposed as an alternative criterion.
This new criterion should be included in upcoming
revisions of fibre cable standards. Particularly critical
designs are high-strain cable types such as drop cable,
and overhead cables including OPGW and ADSS cables.
8 Acknowledgments
Special thanks to Peter Hasløv (OFS), Hiroshi Nakamura
(Furukawa) and Peter Pondillo (Corning) for their helpful
discussions on fibre lifetime.
9 References
[1] Steven R Schmid, et. al, ‘Development and Characterisation of
a Superior Class of Micro bend Resistant Coatings for Today’s
Networks’, Proceedings of the 58th IWCS, (2009), 72-78
[2] Glaesemann, G S, and Gulati, S T, ‘Design Methodology for the
mechanical reliability of optical fibre’, Optical Engineering, June 1991,
Vol 30 No 6, 709-715
[3] Castilone, Glaesemann G S, and Hanson, T, NFOEC-2000, 1-9 (August
2000)
[4] IEC TR 62048 Power Law Reliability
Paper courtesy of the 62nd International Wire and Cable
Symposium, North Carolina, USA, 10th to 13th November
2013.
OFS
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Norcross, Georgia
USA
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