EXFO PSO-200 Optical Modulation Analyzer - Manual (Page 101)

Bit Pattern Analysis and the Gearbox
Optical Modulation Analyzer 93
Performing Detailed Bit Pattern Analysis with the Gearbox
Definition Section
This section describes the type of Gearbox this file addresses. The possible
values of the “Type” field are:

OneGlobalStream

NIndividualStreams

DualXYStreams (only required and supported for dual-polarization
modulation schemes)
There is one file per Gearbox streaming type and per modulation scheme.
For example, DP-QPSK has three Gearbox configuration files.
The third type (dual X-Y streams) is different from the other two. For a
same modulation format, the “SYMBOLWORDCOORDINATES” section
content has to be seen as two single-polarization configurations. As an
example, see the dual X-Y stream configuration for DP-QPSK (left)
compared to the one global stream configuration for QPSK (right).
As these examples show, the dual X-Y streams configuration represents the
same configuration as twice the single-polarization “one global stream”.
In dual X-Y streams, the “SYMBOLWORDCOORDINATES” section does not
seem to contain all possible bit combinations, but it does. In the example,
the word “0000” is, in fact, “00” of polarization “X” and “00” of polarization
“Y”. With two bits per polarization, there are only four possible words.
For details about the Gearbox types, see Gearbox Streaming Types on
page 88.