Hello Urvi Pathak,
In my case the problem is with the demodulator, up to the demodulator everything is ok and as expected (Spectrum and signal power), but after the demodulator the constellation is also not coming (just few signal points are seen). I don’t thing so that there should be problem with the demodulator because without WDM everything is working fine. The problem may be at the WDM multiplexer and demultiplexer in the filter bandwidth, or at the transmitter laser frequency spacing. try changing these parameters.
Regards,
Dhiman