EoW March 2011

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EuroWire – March 2011 121
technical article
Denise Matthews
Draka Communications – USA
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tested to the PE-90 standard. These three
cables were tested with five additional
temperature extreme cycles, for a total of
ten cycles.
The resulting fibre attenuation trends for
the ten cycles are shown in Figures 3 and 4.
Figure 3 presents the average attenuation
increases for each of the ten cycles at the
–40˚C temperature extreme and Figure 4
shows the maximum attenuation increases
for each cycle at –40˚C.
It is important to note that the current
PE-90 requirement specifies at “least five
cycles”. This leaves room for additional
cycles to be completed and only the last
of the cycles to be evaluated against the
specification.
The graphs in Figure 4 shows that fibre
attenuation loss can, at times, slightly
improve with additional cycles.
6 The effect of fibre
MAC values
The MAC value of a fibre strongly affects
the magnitude of attenuation change in
mid-span testing. The MAC number of a
fibre is defined as its mode field diameter
measured at 1,550nm divided by its cut-
off wavelength.
This value is an indicator of a fibre’s
macro-bending sensitivity. Figure 5
presents the individual fibre attenuation
measurements in multiple tubes and
multiple cables for mid-span testing.
Each tube tested contained three high
MAC value fibres, three mediumMAC value
fibres and six scrap fibres to fill the twelve
fibre maximum capacity of the tubes.
Reviewing the maximums, averages and
spread of each of the fibre types (Figure 5)
it can be seen that the higher MAC value
fibres perform poorly in cold temperature
mid-span testing; high MAC value fibres
need to be taken into account when
qualifying a cable design.
7 Conclusions
It has been shown that the length of tube
expressed for mid-span access testing
affects the attenuation more so than the
difference in the test methods PE-90 and
FOTP-244. The 20-ft test requirement is
consistently more severe then the 14-ft
requirement.
It has also been shown that when
mid-span testing 20ft of expressed tube,
the results show similar losses between
the two methods. Identical cable samples
generally exhibit either passing or failing
results regardless of the method.
When multiple cycles are defined in
mid-span testing, the greatest attenuation
losses may not occur during the last cycle,
where mandatory measurements are
made.
There is a general trend up in attenuation
increase as the cycles are increased, but
not necessarily increasing at each cycle.
Fibre MAC values have been shown to
significantly affect the attenuation loss in
mid-span testing.
It is important to evaluate the higher
MAC value fibres when qualifying a cable
design, as the results may appear better
than a “worst case” scenario if this is not
taken into account. n
8 References
[1] Rural Utilities Service (RUS) 7 CRF Part 1755.902
(PE-90) Federal Register
[2] Telcordia Technologies generic requirements
GR-20-CORE issue 3
[3] TIA-455-244/FOTP-244 draft “Methods for
measuring the change in transmittance of optical
fibres in expressed buffer tubes when subjected
to temperature cycling”
[4] TIA-455-3B/FOTP-3 “Procedure to measure
temperature cycling effects on optical fibre units,
optical cable, and other passive fibre components”
[5] Ray Lovie, “Loose buffer tube construction for
mid-span access” IWCS (2007)
[6] Ray Lovie and Bob Overton, “Reliability
considerations for mid-span access points in
FTTH optical fibre systems: cable termination and
expressed buffer tube storage” IWCS (2008)
This paper was first presented at the
58th International Wire & Cable and
Connectivity Symposium, held in Charlotte,
NC, 8th–11th November 2009. It is reproduced
with the generous permission of the
organisers.
Maximum attenuation increase (dB)
Attenuation change
Cable Type 1 Cable Type 2 Cable Type 3
Cycle Cycle Cycle Cycle Cycle Cycle Cycle Cycle Cycle
1 2 3 4 5 6 7 8 9 10
High MAC values MediumMAC values
(Average 0.1 dB)
Figure 4 ▲ ▲ : 20-ft PE-90 mid-span test with five additional cycles – maximum
attenuation increase
Figure 5 ▲ ▲ : Attenuation change in high and mediumMAC value fibres
(Average
0.04 dB)