Viavi 8100 V2 Series User Manual page 365

NOTE
The preset min channel spacing is 50GHz, which works for most of the sys-
tems. For other systems, the operator needs to enter the effective minimum
system channel spacing of the WDM system. This is important for a correct
approximation of the noise distribution inside the transmission band of the
WDM channels.
Example 1: every second channel is loaded, system looks like 100GHz channel spacing
It might be that the system has a visible channel spacing of 100GHz but the min
channel spacing is 50GHz as only every second channel is loaded. This could
also be the case when 50GHz optical interleavers are used to multiplex two
100GHz spaced WDM signals (even and odd channels) together into a 50GHz
spaced system
=> min-ch-spacing needs to be set to 50GHz
Example 2: submarine links
Submarine links often pack 3 channels into the ITU-T 100GHz grid
=> min-channel spacing needs to be set to 33GHz
Manual Settings: OSNR method
The OSNR method can be set according to the application.
Chapter 9 OSCA-710 Optical Spectrum Measurement
Measuring POL-MUX (polarization mulitplexed ) channels
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