EXFO FTB -5240S/5240BP Optical Spectrum Analyzer - Manual (Page 279)

Managing Results
OSA 273
Managing WDM Test Results
Note: This information is available for polarized signals only.

Carved noise: When the ASE noise is filtered so that the noise level
affecting the peak at the center is higher than the noise level at either
channel edge, this usually indicates the presence of filters/ROADMs on
the link.
Four levels of information are given for channel characteristics
diagnostics.
Impairment diagnostics check for the presence of several types of
impairments and give an assessment of their severity. There are four
impairment types:

PMD Pulse Spreading: This impairment shows the presence of
Polarization Mode Dispersion (PMD) in a channel. When PMD is
present on the path of the signal, depending on the polarization
axis of the signal injected, the signal may suffer from pulse
spreading which, in turn, leads to polarization dependent spectral
deformations. These deformations can be analyzed to determine
how much polarization pulse broadening the signal has
experienced during the measurement.
Symbol Meaning
Not present
Present
Inconclusive
No symbol (blank) Not analyzed (empty channel)