EoW January 2013

Technical article

expansion values need to be incorporated into specification performance precursor requirements. This article proposes to update existing standards, particularly the GR-409 specifications for required tolerance for shrinkage and fibre strain. Otherwise, it is possible for sub-par cable designs to pass existing standards as they are written and be deployed in the field. It should be recognised that conventional fibre and reduced bend radius fibre exhibit different properties and characteristics, and test criteria should be written to address the requirements of both. Therefore, the proposal is to consider adding more focused test criteria to existing standards specifications. This in effect creating a new class of GGR-409 and GGR-20 qualifications specifically identifying the fibres used and qualified in any specific cable designs. Re-purposing the current standards with new reduced bend radius fibres in mind will enable service providers to take full advantage of the unique characteristics these fibres bring to the table, particularly in today’s FTTP deployments. n Acknowledgments The author would like to acknowledge the help of Wagner Aguiar, Ken Nardone, Henry Rice, and Bill Jacobsen in obtaining data and test information for this paper.

Cleaning tool

Cutting Measuring

Master Rod

▲ ▲ Figure 6 : Fibre strain vs tensile loading

▲ ▲ Figure 7 : High precision shrinkage gauge

Although this is a requirement of some customers in their own standards, it is not part of the existing generic fibre standards. Cable shrinkage testing needs to move to a higher level of repeatability and gauges for this purpose have been designed. The range of testing and the effect of fibre extrusion from the cable core need to be determined as well. This is only a secondary effect of GR 326 the test standard for cable connectors and cable assemblies. Conclusions The introduction of reduced bend radius fibres, and their emerging popularity in fibre-to-the-premise (FTTP) architectures, is cause for concern when it comes to the current GR-409, GR-20, GR 326 and other specification standards written for conventional fibres. New tests should be proposed to accurately define their unique characteristics to better ensure long-term reliability. A cable design that takes advantage of the tighter bend radius fibre would most certainly show much higher attenuation using conventional single mode fibre. In other words, a reduced bend radius fibre would survive very well in an environment where conventional fibre would not. The cable to connector interface may create new aging models where cable shrinkage can lead to unacceptable fibre bend radii at the cable/connector interface. The results of which will only show up after loose cable assemblies are aged and then moved. This alone indicates the need for a set of revised test standards and requirements for reduced bend radius types of fibre. Cable designs tested to GR 409 or GR 20 are requirements for GR 326 testing. The need exists to use fibre strain and cable shrinkage as well as fibre extrusion from cables after aging as a more complete precursor to GR326 testing. environmental operating ranges of cables becoming the norm, thermal co-efficient of linear Also with increased

standards for conventional fibre. These existing standards should be carefully reviewed and appropriate criteria added to specifically include the unique characteristics of reduced bend radius fibres.

New testing considerations

There is a need for the addition of several new test criteria to GR-409 and GR-20 in light of the unique characteristics of reduced bend radius fibre types. For example, a means of measuring fibre strain should be added to existing test criteria. Strain or stress should be measurable on both indoor and outdoor fibre cables during tensile FOTP-33b, aging and other mechanical testing processes where this type of testing is not currently conducted. This may be difficult without introducing a new family of qualification tests for fibre strain, but the new reduced bend radius fibres demand it. A second consideration for changing testing methods may be to measure delta excess fibre length, in loose tube type cables, before and after ageing, and also in individual tubes. For instance, attenuation and excess length could be measured before ageing and temperature cycling processes, and then again following these processes. They would then be compared to established pass/fail criteria. Current specifications do not require this type of testing, nor do they require testing in a loose configuration. All testing is currently done on spools or coils. In a loose-tube configuration in a coil, you can have a great deal more excess length and relaxed length than in a straight line. Attenuation increases would be less evident without the ability to measure excess length as a mechanical test. It is worth noting that new measurements should include the very long wavelength of 1,625nm. These new measurements would propose additional qualifications for that wavelength where the microbend edge moves in as the fibre is strained.

References

TIA-455A Fiber Optic test procedures Telcordia GR-220-core Issue 3 Telcordia GR-4409-core issue 22 Telcordia GR-3326-core issue 44 ITU 652 .A-D 22009-11 ITU 657.A 200 9-11

Reliability of bend Insensitive Fibres; Willem Griffoem Draka Communications Proceedings of the 58 th IWCS pages 251- 257 2009 Macrobending Loss in Bend Insensitive Fibres: A Statistical Parameter? Susanna Cattelan, Prysmian SpA, Proceedings of the 58 th IWCS pages 258-263

ADC Telecommunications Eden Prairie, Minneapolis, USA Tel : +1 800 366 3889 Website : www.adc.com Email : info@adc.com

53

www.read-eurowire.com

January 2013