EXFO FTB -5240S/5240BP Optical Spectrum Analyzer - Manual (Page 280)

Managing Results
274 FTB-5240S/S-P/BP
Managing WDM Test Results

Interchannel Crosstalk: In densely-filled channel plans,
neighboring channels may have a non-negligible portion of their
spectrum that extends within the channel bandpass of a given
signal.

Non Linear Depolarization: Fast changing power levels in
multichannel systems (10 G and 40 G) may induced local
polarization dependent changes in the refraction index of the fiber.
This, sometimes, leads to inter-channel nonlinear effects (for
example cross-phase modulation) which, in turn, lead to partial
depolarization of neighboring channels.

Carrier leakage: In a phase-modulated transmission, a CW carrier
wave is modulated using external modulators which are generally
polarization dependent. When the CW source polarization axis is
not optimally aligned with the modulator, a portion of the CW
signal passes through unmodulated and gets transmitted as such
along the path. When this CW residual signal is present, it may be
detected as carrier leakage using advanced polarization analysis to
provide a useful diagnostic.
The symbols that are used to illustrate the diagnostics are the same,
regardless of the type of impairment. The global diagnostic status is shown
in the status bar at the bottom of the window according to the severity
displayed in the table below. The most severe status takes precedence
over the others for all tested channels.