Distributed PMD measuring

Measuring the PMD distribution along optical lines.

SITEL is the only company in the Czech Republic that owns a completely unique FTB-5600 measuring device which can measure the size of the PMD along the entire optical line. Most "classical" devices and measuring methods will only give one number as the final PMD value, representing the entire line. It is not possible to find out whether the whole line or just a certain section of it is faulty. In the case of a PMD over-limit value measured by the classical method (numerical value per line), PMD growth points can be determined using the FTB-5600 distributed measuring device. This will make it possible to find a segment with the above-limit PMD parameters. Repairing only this segment brings a considerable advantage in saving the funds that would be spent on repairing the entire line, as well as significantly reducing the time needed to put the whole line into operation.

When is it appropriate to use this measuring method?

Polarizing Mode Dispersion begins to influence transmission quality at 10 Gbit / s and higher. The importance of "knowledge" of this parameter is also important when WDM and analogue televisions are deployed on older optical lines. PMD is also measured to check the newly installed lines.

What is the Polarizing Mode Dispersion (PMD)?

Attenuation and dispersion are important parameters of each optical fiber. The attenuation reflects the loss of light energy and can be measured by a direct method or by a reflectometric method (OTDR). The dispersion itself causes distortion of the transmitted signal. The dispersion can be divided into a chromatic, which is always given by the way of production of each optical fiber and polarization, which cannot be guaranteed in production, but can also be changed by manipulation with the optical fiber and the cable. The PMD represents the state of spreading of individual "modes" through the optical fiber. With an ideal and simplified progress, both horizontal and vertical components arrive at the same time and position. For real fiber, both components are always shifted to each other - this is the PMD phenomenon:

What affects the PMD?

  • line installation
  • temperature (depending on the properties of the material used)
  • mechanical stresses in production, installation and operation
  • fiber quality during production
  • vibration

Illustration of measured PMD values on a self-supporting optical cable: