EXFO FTB-5600 Distributed PMD Analyzer - Manual (Page 127)

Distributed PMD Analyzer 121
D Optimizing Measurements
Firstly the FTB-5600 measures the cumulative PMD as a function of
distance. According to the square law of PMD statistics nature, a small PMD
after a high PMD may be hardly distinguished if a measurement uncertainty
is too high.
For example, if a 3 ps section is followed by a 10 ps high PMD fiber section,
an additional increased PMD value after 3 ps fiber section is only of
~0,44 ps (that is,
). This requires that the instrument
must be able to have a measurement uncertainty better than a few
percents.
Secondly according to the PMD theory, a measured PMD (defined as RMS
DGD in a given wavelength range) may be varied from one measurement
to another because of a PMD theoretical uncertainty due to a finite
wavelength range being used; thereby a better accurate measurement
may be achieved by using a maximum available wavelength range from
the instrument as well as to average over time.
The Advanced testing mode will allow you to improve the measurement.
Basic Verification Steps
Here are some basic verification steps to make sure that your
measurement is optimized:
³
Make sure that there is not a strong loss at the instrument connector.
³
Verify the link length. EXFO recommends optimizing the link length to
speed up the acquisition process and make files smaller.
³
Verify that there are no big losses along the link. In good conditions, the
dynamic of the instrument is around 15 dB. Therefore, do not expect to
measure after 15 dB of link loss.
³
Verify the scale of the PMD curve, adjust the scale if required.
10
2
3
2
+ 10 – 0 44 , ≈