Document #: GP-UM-PMD-1000-21
Page 110 of 122
PMD source for PMD compensator evaluation
A PMD source is also necessary to evaluate the performance of a PMD compensator,
whether optical or electrical, as shown in Figure 32. PMD compensator evaluation can
include several types of tests. First, the system improvement margin at different PMD
settings can be determined. Second, the PMD compensation range of the compensator
can be determined by gradually increasing the input PMD while measuring the BER of
the fiber link. 3) Third, the PMD compensator’s PMD recovery time can be determined
by performing a step PMD change and monitoring the PMD compensator’s response.
Finally, the PMD compensator’s SOP recovery time at different PMD settings can be
determined by changing the SOP rapidly at each PMD setting and monitoring the PMD
compensator’s response. Therefore, a PMD source with fast PMD variation and fast
polarization control capabilities is attractive for PMD compensator evaluation.
Figure 32 PMD compensator evaluation setup schematic. For electrical compensation, the compensator
may be inside the receiver (RX). The plots shown in Figure 31 can be generated here with PMD
compensation at different PMD settings of the PMD source.
PMD analyzer or monitor for link PMD determination
The PMD values of fiber routes generally must be measured before link deployment. This
requires PMD analyzers. In general, a PMD analyzer requires a large-bandwidth light
source, whether it is tunable-laser-based or broadband-source-based. As mentioned
previously, the PMD of fiber routes may change with time due to changes in
environmental conditions. For a ROADM network, once the fibers are lit, the wavelength
channel for each transceiver pair is determined and is confined within a 50GHz
bandwidth. Therefore, PMD analyzers requiring broadband light sources cannot be used
to characterize such a system. In addition, it is undesirable to disconnect the transceivers
and insert a PMD analyzer into the link, because this would cause a severe service
interruption. It is therefore attractive to be able to determine the PMD value of an in-
service link while both the transmitter and receiver are operational. This capability is
important for the diagnosis of fiber routes with performance issues.
TX
RX
Computer
BER tester
PMD Compensator
PMD source
PMD source
