EoW March 2011

technical article

(Average 0.1 dB)

(Average 0.04 dB)

Attenuation change

MediumMAC values

Cycle Cycle Cycle Cycle Cycle Cycle Cycle Cycle Cycle 1 2 3 4 5 6 7 8 9 10

High MAC values

Maximum attenuation increase (dB)

Cable Type 1

Cable Type 2

Cable Type 3

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

8 References

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

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

[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 58 th International Wire & Cable and Connectivity Symposium, held in Charlotte, NC, 8 th –11 th November 2009. It is reproduced with the generous permission of the organisers.

Denise Matthews Draka Communications – USA Email : denise.matthews@draka.com Website : www.draka.com

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EuroWire – March 2011