EXFO PSO-100 Series Optical Sampling Oscilloscopes - Manual (Page 115)

Burst Mode Measurements
Optical Sampling Oscilloscope 107
The yellow samples are then visualized in an eye diagram in the lower
window, while the white samples are removed, according to the figure
below.
In this way, you can determine whether the burst parameters are set
correctly or not. For example, if the rise time parameter is too low, you will
observe samples in the middle of the eye, and if the trigger level is too high,
the refresh rate will become very low since it does not trig until the trigger
timeout value is reached. Depending on the burst period, you may need to
increase the number of samples/layers in the Display menu.
If the loop length is much longer, that is if the burst is longer than 1 ms, and
fills a whole batch entirely, you can use the internal clock instead of the
external clock to make measurements.