Hello Hanan,
The Lasers’ wavelength and WDM MUX/DEMUX have to match. The BW is related to the user modulated signal bandwidth, which you need to consider in the MUX/DEMUX bandwidth.
Please refer to the examples on OCDMA in the Example library located at the following location.
C:\Users\USER NAME\Documents\OptiSystem 18.0 Samples\Metro and access systems\PON and CDMA systems
Regards,
Ahmad