Testing times


The change from boom times to the current economic climate in the telecommunications industry is challenging in many different ways. The fall in revenues, along with the number of organizations under Chapter 11 protection, has led to a spate of disputes over contracts or deals that no longer suit the times. When disputes involve hundreds of drums of cable, leased fiber on a long-haul route, or even complete fiber-optic infrastructures, then millions of dollars may be at stake with potentially serious or fatal consequences for one of the parties.

So what has that got to do with training? It has brought a whole new dimension to the role of the test engineer and the importance of accurate and reliable test results. Test results may now be scrutinized closely for evidence of the tiniest defects that may provide leverage for challenging the payment terms or even rejecting a system that may now be surplus to requirements. Also, the standards referred to, the test methods used, and the competence of the people carrying out the testing may be called into question—and results may be declared invalid.

Optical-time-domain-reflectometer traces can convey an awful lot of information, or even a lot of awful information, depending on the motivations of the analyst who is looking at them. Problems with connector insertion and return loss may be uncovered. Tight bends can be identified that may compromise L-band operation. Unacceptable variations in mode field diameters can be highlighted as well as problems with fiber and splice losses.

All of these details may have been glossed over, ignored, or not even specified in better times, just so long as the system worked on day one when it was switched on! Many installation contractors took advantage of this situation, using untrained staff and cutting corners rather than providing comprehensive, well-documented test results. In those days, no one had the time to look at them—let alone analyze them in detail and consider the viability of future system upgrades.

Of course, if you are looking at taking delivery of a long-haul-cable infrastructure or signing up to a 25-year lease on dark fiber, then it is important that the infrastructure be capable of supporting more than just today's systems—typically operating at 10 Gbits/sec, with perhaps only a few channels lit in the C-band. The growth in bandwidth demand continues unabated, despite everything, so future systems will have to support 40-Gbit/sec transmission over many channels spanning the C- and L-bands. That means accurate measurements of the chromatic dispersion characteristics will be critical for effective dispersion management and that the polarization-mode dispersion properties of the system will need to be known and documented.

These new test disciplines require new skills and an understanding of the test methods and their applicability. Onsite, test engineers must be able to validate the data being acquired, and they should know the anticipated results and what can go wrong with the measurement. It is important to define pass/fail criteria for these parameters. Unfortunately, in many incidences, expensive test equipment has been put into the hands of those who clearly have not been trained to understand what they are testing. The result has been incorrect setup of the instrument for measuring fibers—and the results are therefore worthless.

A return visit to the site to retest can be expensive enough, but the outcome of incorrectly carried out tests may be much worse. Credibility is easily lost through bad test results, and the competence of the test engineer or the entire company could be called into question. In a court of law, that could mean all the tests that had been carried out are rendered invalid. The loss of credibility could mean no more testing business for the installation company. If the telecommunications operator was planning to lease some of those fibers, it could be faced with big losses or a big bill for a complete retest. Considering these potential long-term consequences therefore might help justify the training budget.


Richard Ednay is technical director of Optical Technology Training (OTT—Skipton, North Yorkshire, UK). He can be reached at Richard@ott.co.uk or via www.ott.co.uk.

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