Long Term PMD Monitor:
This function is designed for live monitoring of PMD in a system. The PMD effect in a
system is a dynamic phenomenon. It changes over time with changes in input polarization
or environmental conditions. Whereas the other PMDC functions provide a snapshot
measurement of the PMD of the system at the time the measurement was taken, this
function allows the user to monitor the PMD effect over an extended period to
characterize the behavior of the actual system. It uses the lookup table DGD
measurement function described in the previous section.
TCA-1000
Link with PMD
WDM
MUX
WDM
DeMUX
Figure 26 System setup using TCA-1000 as signal emulator
Figure 26 illustrates a system setup for PMD monitoring using General Photonics
Tunable Channelized ASE Source (TCA-1000) in conjunction with the PMDPro. The
TCA-1000 is used as the input to one frequency channel before multiplexing. After
demultiplexing, that frequency channel is sent to the PMDPro, which performs DGD
measurements at user-specified intervals.
Since the PMD effect varies with input polarization, it is possible to obtain spurious
results if the input polarization happens to be aligned to the effective fast or slow axis
of the device or link under test. To counter this possibility, the TCA-1000 can be
instructed to periodically rotate its output polarization state by 45°.
TX
Link with PMD
WDM
MUX
WDM
DeMUX
RX
Tunable filter
Figure 27 System setup for long-term monitoring of in-service link
Document #: GP-UM-PMD-1000-21
Page 86 of 122