As telecoms systems and dark fibre contracts become more complex, the real performance of the installed fibre link becomes critical.
Optical networking systems are becoming ever more complex with higher data rates per channel and more channels in DWDM systems. CWDM systems may operate at wide wavelength ranges that span across the S, C and L-bands or even all the way from 1311nm up to 1611nm. For 10Gb/s systems optical dispersion management will be required for most long distance links. Coherent systems for 100Gb/s and above may be optimized for the particular characteristics of the route they'll be operating over. Raman amplifiers may be used to give extended reach, extended wavelength range or lower noise (or some combination of these). All of these things mean that knowing the detail of all the characteristics of the fibre infrastructure is more important than ever before.
When a dark fibre deal is done it may be some time since the installation was originally carried out and so it is necessary to verify that the performance has not degraded, due to bends or dirty connectors for example, since the fibre was installed. A dark fibre contract may run for many years, so it is important that the fibre should support the requirements of future systems as well as today's systems.
This is why fibre characterisation has become so essential. Based on the results of the fibre characterisation exercise, decisions will need to be made about equipment choices, whether remedial works are required, or even whether to accept or reject the fibres. Often, the systems supplier will also use the characterisation data to help configure their equipment for optimal performance and/or cost. For example, chromatic dispersion parameters allow the correct amount of dispersion compensation to be applied, while loss measurement may indicate that it's possible to use lower power and lower cost optical transceiver modules.