EXFO FTB -5240S/5240BP Optical Spectrum Analyzer - Manual (Page 64)

Setting Up the Instrument in WDM Mode
58 FTB-5240S/S-P/BP
Setting Up WDM Analysis Parameters

Noise for OSNR: indicates which calculation method to use for
OSNR value.
Fixed range IEC based (IEC): The IEC method uses the
interpolation of noise measured on both sides of the signal to
estimate the noise level. The position at which the noise is
estimated from the center wavelength is given by the OSNR
distance.
InBand (InB): The InBand method uses a series of scans having
different polarization states to calculate the noise level under the
peak (InBand).
InBand narrow filter (InB nf): The InBand narrow filter method
uses additional processing to provide an accurate OSNR value for
the narrow carved noise. This is because with narrow filters, the
noise level under the peak is not uniform and the OSNR value
depends on the processing width selected.