PMD and CD Testing

 PMD plot interferogramPolarisation Mode Dispersion (PMD) testing is now often a routine requirement for telecoms fibres, and especially where dark fibre contracts require measurement results from the fibre supplier. Lucid can tailor PMD courses to exact requirements, but we have the following standard courses:

  • Advanced PMD and chromatic dispersion course (OA level 3 Certificate)
  • PMD and chromatic dispersion evaluation and interpretation

Advanced PMD and CD Testing Course – level 3 Qualification

Our advanced PMD and CD (Chromatic Dispersion) training course is a 3-day Open Awards (OA) certified course covering the principles of PMD and chromatic dispersion, and the theory, techniques and practice of testing these optical fibre limitations. Trace interpretation and measurement analysis is covered, along with mathematical curve fitting such as 3 and 5-term Sellmeier curve fits to chromatic dispersion phase shift data points.
This course is primarily aimed at field dispersion testing specialists, but many of the techniques and principles are equally employed in fibre, cable and component test laboratories.
The OA level 3 PMD and CD testing award is accredited by the Fibre-optics Industry Association (FIA) as part of their qualification scheme for fibre optics professionals.
This course also forms an essential part of the knowledge required to characterise a telecommunications fibre network. Full network characterisation would also require a good knowledge of OTDR and LSPM testing and measurement techniques and interpretation, as taught on our Advanced OTDR Measurements training course (OA level 3 certificate)

PMD and Chromatic Dispersion measurement evaluation and interpretation

Chromatic dispersion curveThis is a shorter 1-day course for managers who need to check and interpret PMD and Chromatic Dispersion measurement plots and test results. A longer 2-day version is recommended for those with little or no previous fibre optics training.

We also develop bespoke Polarisation Mode Dispersion (PMD) and Chromatic Dispersion (CD) training courses for clients with particular requirements. Please phone or email with any special dispersion testing or measurement analysis training requirements.

Field PMD Measurements using TINTY and GINTY

There has been much discussion recently on the relative merits of various
PMD measurement techniques, with the interferometric technique favoured
for field measurments being shown to be a little imprecise in certain circumstances.
In order to improve on the reliability of the PMD measurement result from
the white light interferometer with a wider range of PMD measurement results,
the ‘General Interferometry’ or GINTY techniques was developed and championed
by EXFO as an improvement over the ‘Traditional Interferometry’ or TINTY.

The difference in PMD measurement results between TINTY and GINTY values is typically around 10%, although it can be from 0% to 25%. For most people these accuracy values are not critical for PMD where some variability is expected anyway, but the improved GINTY measurement technique has been shown to agree better with other PMD measurement techniques such as those using polaimeters in laboratories.

Curve Fitting to Chromatic Dispersion Measurements of Fibre Networks

Whether the chromatic dispersion of fibre optic networks is tested using the phase-shift method or the differential phase shift method there is a curve fit to appy to the data in order to yield values at all of the wavelengths of interest. On the one hand curve fitting is an important part of Chromatic Dispersion network testing as it gives a lot of information on the quality of the measurement points and can have a very significant affect on measurement results that are extrapolated from the curve fit and hence calculated rather than truly measured.

At Lucid we explain why there are different curve fits and which are best for various situations. We can explain the mathematics of the curve fits if required, but most trainees do not want or need this. The good news with chromatic dispersion curve fitting is that even if the wrong fit (that is a poor or inappropiate curve fit) is applied to the chromatic dispersion measurement data this is not final. So long as the measurement has been saved, then the correct, or a more appropriate, curve fit can be applied retrospectively. This means that if Sellmeier versus quadratic is confusing you, you can call us to resolve your chromatic dispersion measurement issues.

Taking the zzz out of Polarization Mode Dispersion and Network Characterization

Throughout this website we have used the UK spelling of ‘polarisation’ and ‘characterisation’ using the letter ‘s’ instead of the US spelling of ‘polarization’ and ‘characterization’. With todays software spelling checkers commonly switching even UK nationals onto US spelling this can be confusing.
At Lucid we believe in being flexible and we have delivered training courses in the US where we have gone all through our training course manuals and used US spellings thoughout.

As standard, however, our philosphy is to ensure our training courses are informative and interesting – without the zzz factor.