How Dual port WDM analyser calculate the Noise Figure

[Chhayou Te]

Hi all,

As an attachment below, I just wonder how the Dual Port WDM analyzer calculate the Noise Figure, since NF (dB)= OSNR (dB)in- OSNR (dB)out
but when I calculated the value of OSNR from WDM analyzer from the same Input and Output port as the Dual Port WDM analyzer I got the difference value of NF. and in my long haul transmission I got negative value of NF(dB), so is it ok to get a negative value of NF?

*note: (In the attachment photo) on the left is OSNR (dB)in and on the right is OSNR (dB)out

Regards

Attachments:

1. 

   2017-02-23_004237.png
   

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