Mportant – EXFO FTB -5240S/5240BP Optical Spectrum Analyzer User Manual
Page 89
Setting Up the Instrument in WDM Mode
OSA
83
Using the Commissioning Assistant
The IEC 61282-12 recommendation has not yet reached final approval
stage, and therefore the calculation might differ slightly from that
presented in this document. The standard defines OSNR as
OSNR (dB) = 10log (R) with
where:
s(
): is the time-averaged signal spectral power density, not including
ASE, expressed in W/nm.
(
) is the ASE spectral power density, independent of polarization,
expressed in W/nm.
B
r
is the reference bandwidth expressed in nm (usually 0.1 nm if not
otherwise stated) and the integration range in nm from
1
to
2
is
chosen to include the total signal spectrum.
Note: To be valid, the trace with all channels on, or all of the traces with a
channel off must come from a module onto which the commissioning
option was activated.
Note: The units and empty channel display information come from the user
preferences set in your application.
I
MPORTANT
When performing OSNR measurements using the Commissioning
Assistant, you must make sure that the noise level with the channel
shutdown is representative of the real ASE noise level. For instance,
ROADM equalization capabilities might change the noise level to
compensate for the loss of one channel in the off trace
measurement.
R
1
B
r
-----
s
-----------
d
1
2
=