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Testing dark fibre

What is fibre characterisation?

Fibre characterisation needed iconQuality control approved icon OTT

Fibre characterisation is defined as conducting a comprehensive suite of tests on an installed link in order to assess its general quality and its specific ability to support a particular application or applications. Fibre characterisation reveals how well the fibre will perform. This is important because, as data rates increase and systems become more complex, there are many factors that can impair system performance. Full fibre characterisation is recommended for any dark fibre contract.

ITU-T-G-650-3 standard

Fibre characterisation is defined in ITU G.650.3

A comprehensive suite of measurements that is carried out on an optical fibre cable link to determine the key performance attributes of that link which may affect current or future applications that operate over that link. Fibre characterization also allows the quality of the optical fibre cable link to be assessed, including the identification of the type and grade of fibre installed. Full fibre characterization includes connector end face inspection, insertion loss measurements, return loss measurements, OTDR testing, chromatic dispersion testing, polarization mode dispersion measurement, and spectral attenuation.

Certified Fibre Characterisation Engineer CFCE course logo

Fibre characterisation should be carried out by professionals

Performing all the fibre characterisation measurements to produce accurate and reliable results is a skilled task. The analysis and interpretation of the test results in order to report on the quality of the fibre infrastructure and the ability of the link to support different applications and technologies, requires a lot of detailed knowledge and understanding.

You can learn how to carry out that testing on the Certified Fibre Characterisation Engineer course. On the CFCE course you’ll learn about these 7 measurements, how to do them, validate the results, and analyze the data to report on the quality of the fibre infrastructure and the ability of the link to support a range of applications and technologies.

Richard Ednay, OTT technical Director and developer of the globally recognised Certified Fibre Characterisation Engineer (CFCE) course, wrote the definition of fibre characterisation that is in ITU G.650.3. Beware of imitation courses that attempt to trade off of the same description. The real CFCE course is only available from OTT partners. Check with us if you are unsure.

How is ‘fibre characterisation’ different from just testing fibres?

Well historically, when long distance singlemode fibre links were commissioned it was common practice just to be concerned with the losses of the installed links usually at just two wavelengths: 1310nm and 1550nm. However, with DWDM optical networking systems and CWDM optical networking systems operating over wider wavelength ranges then the ability of the infrastructure to support these over wavelengths also needs to be verified. In addition, as data rates have increased to 10Gb/s, and for non-coherent 100G delivered as 4x25G WDM, then the dispersion characteristics of the fibre have become much more critical and additional tests are required including chromatic dispersion and polarisation mode dispersion (PMD). With PMD the performance of the fibre can vary significantly from fibre to fibre within the same cable and so it is often necessary to measure every fibre and keep detailed records of which fibres can support which date rates.

With the advent of coherent technology for 40G, 100G and beyond, then there is usually electronic dispersion compensation of CD and PMD, so the limits on CD and PMD are more relaxed. However, there have been a number of reported problems with some coherent systems that show all the signs of sensitivity to high levels of PMD that are likely to result in rapid fluctuations in the State of Polarisation, so avoiding high PMD fibres is still a good idea. The performance of these advanced systems often depends upon many characteristics of the installed link, and the design of the link is optimised based on the information from the fibre characterisation exercise. So most equipment vendors will still insist on fibre characterisation being done before they connect up their equipment. Some aspects of these advanced systems are also highly dependent upon the quality of the infrastructure, this is particularly the case for Raman amplifiers, so on the CFCE course you’ll also learn about what to look out for to make sure that Raman amplifiers will work effectively and give the required amount of gain.

Tell me more about the CFCE programme

The CFCE certification programme is delivered under license by OTT’s partners in the UK, Ireland and the USA. Public courses are available in some locations but company specific courses are also available if you have a team of engineers that would benefit from this certification and would like a course delivered on your own premises. Please complete the form to be put in touch with your nearest partner.

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