EXFO PSO-200 Optical Modulation Analyzer - Manual (Page 259)

Optical Modulation Analyzer 251
E Measurement Definitions
Measurements follow the conventional measurement definitions from the
telecommunications industry. They are based on different histograms
obtained from the acquired samples of the signal under test.
For “constellation” measurements, the measurement procedure is
conducted on the time-less constellation graph, whereas for “Eye”
measurements, it is conducted on graphs displaying the acquired signal vs.
time, and is always conducted based on eye diagrams of the signal.
Data Used for Measurements
Both constellation and eye measurements rely on a selected portion of the
signal considered as the symbol center, which is defined in the Optical
Modulation Analyzer application using the data measurement window, as
explained in Distinguishing Data Points from Transitions on page 62. For
reliable measurements it is important to ensure a proper position and
width of this region.
The default center region is:

For NRZ data: between 40 % and 60 % of the symbol period

For RZ data: between 47.5 % and 52.5 % of the symbol period
All measurements are separately conducted on X and Y polarizations
tributaries of the signal under test.
Note: Statistical measurement of pattern-synchronized waveforms can be
obtained using the user-defined vertical/horizontal histograms. For details
see Viewing Signal Distribution Using Histograms on page 60.
Note: Some of the measurements are not performed in averaging mode.
Note: All X/Y polarization results come with average, minimum and maximum
values.