One thing you should notice is that 100 GHz is not equal to 2nm. So there is no reason why signal should be there at 1590.2 when you haven’t set the channel spacing as 2nm. In my attached file, please take a look at the ONU 1_1 signal which is there for 1590.2nm . That is because I have set channel spacing as 2 nm (and not 100 GHz). If you don’t find my explanation clear, please tell me.
Regards