Hi Burhan ma’m
You should check out the CW laser power as being suggested by Dhiman by increasing the laser power to few dbm.
You should Check for Wdm mux bandwidth , filter order if you are not using ideal mux.
You should also vary the channel spacing by varying the frequency of laser, because according to TIU-T, the standard channel spacing are for WDM system are 25 ghz, 50 ghz, 75 ghz and 100 ghz, 200 ghz, 1 thz .
Check the output at different ports in the design.
You could also Vary no. loops of fiber because for small laser power WDM system gives no results at very large transmission length.
Seeking your response.
Thanks and regards
Rajguru