Performing Osnr Test In Wdm/Osnr Mode - Viavi 8100 V2 Series User Manual

Chapter 9 OSCA-710 Optical Spectrum Measurement
Measuring POL-MUX (polarization mulitplexed ) channels
Manual Settings: Reference Correlation
As each transmitter system is a sophisticated complex optical device, the unit is not
perfect. Therefore the characteristics of the transmitting laser will vary over various
types, manufacturers, configurations etc. The differences will have influences on the
quality of the transmission system.
The OSNR is calculated from the difference between the correlation of the combination
of signal and noise and the correlation of the pure signal without noise.
However, the correlation of the pure signal is smaller than 100% for all transmitters.
Therefore, the correlation of the pure signal is called Reference Correlation and can be
set manually for best accuracy. A typical reference correlation value is 98.5%.
Manual Settings: Symbol rate
The spectral correlation method depends on the knowledge of the Symbol rate the
carrier uses, because the symbol rate defines the distance for the optimal correlation for
two spectral components in the channel. Although the instrument will have a certain
tolerance, when given wrong numbers for the Symbol rate (typ. 4-5%), it is advised to
input the exact Symbol rate.
Manual Settings: PDL compensation
The accuracy of the measurement depends on spectral symmetry which could be
degraded due to polarization effects (polarization depend loss and/or polarization mode
dispersion). The analysis will gain accuracy if the effects are post-compensated by algo-
rithms when PDL compensation is set to „Yes". This is mandatory in distorted and
optional in distortion-free systems.

Performing OSNR test in WDM/OSNR mode

In the WDM/OSNR mode the instrument performs one measurement. The signal is eval-
uated with standard (out-of-band) ITU OSNR method.
Start the measurement by pushing the S
A green on top of the WDM table will show the progress of the measurement.
When the measurement is finished the green bar disappears and the result is
shown in the table.
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/S button.
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