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Wire & Cable ASIA – September/October 2007 52 March/April 2013
Abstract
This article will attempt to compare mechanical perfor-
mance parameters of waveguide cables with optical
performance of both conventional fibres and reduced bend
radius fibres. The coordination of mechanical and optical
test data can point to more appropriate test criteria for
cables with reduced bend radius fibres. This will ensure a
more robust characterisation criterion appropriate to this
new class of fibre.
Introduction
The advent of both single mode and multi-mode bend
insensitive fibres has brought into question whether
existing cable test plans accurately characterise a cable
design to provide expected lifetimes.
Presently, most published test plans rely on delta
attenuation values at discrete wavelengths as pass/
fail criteria for various mechanical criteria. With the
introduction and use of new reduced bend radius fibre
types, less robust cable designs can now pass such
standardised cable tests.
This result can lead to possible substandard cable designs
that can generate future failures in the field. Long-term
stresses may be placed on the optical waveguides and
not be reflected in the delta attenuation measurement
protocols currently prescribed by standardised tests such
as Telcordia GR-409 and GR-20.
Fibre improvements
Telcordia GR-409 is the current standard of specifications
for indoor fibre cables, while Telcordia GR-20 provides
technical reference for outdoor cables.
Some companies, such as Verizon, have more
sophisticated versions that reference GR-20 and GR-409,
but also add additional qualifications. Together, this
specification documentation dictates the mechanical
performance standards agreed upon by the customer and
manufacturer. More recently, however, fibre improvements,
particularly in reduced bend radius fibres, are challenging
the industry to revisit the test standards for fibre.
With the increased performance features of reduced bend
radius fibres versus conventional fibres, existing standards
may no longer be a “one size fits all” measurement.
Several optical fibre manufacturers developed con-
ventional optical fibres in the 1970s. Over the years,
there have been few significant improvements outside
of coating developments to improve the fibre’s inherent
ability to withstand mechanical forces on its environment.
But aside from innovations during the draw process,
improving the overall empirical tensile properties of optical
waveguides, improvements to optical fibre designs have
been relatively minor until about five years ago. At that
time, several concepts emerged to improve on other fibre
characteristics, such as physical strength and bending
characteristics. This was the introduction of reduced bend
radius fibres.
Reduced bend radius fibres include several viable
technologies.
❍
❍ Figure 1: Fibre with <1% shrinkage
❍
❍ Figure 2: Fibre with >4.5% shrinkage
❍
❍ Figure 3: <5% shrinkage cable connector interface
3.0mm Jacket
3.0mm Jacket
900 Micron Tight Buffer
900 Micron Tight Buffer
Test methods for cables
incorporating reduced
bend radius fibres
By Wayne Kachmar, ADC Telecommunications, USA