Hello Nghia,
You may use the “ideal Dispersion Compensation FBG” component in OptiSystem after or before the fiber depending on your design to compensate the DWDM signal. You need to make sure that the “Bandwidth” parameter of the FBG includes all DWDM channels. After the compensation you place the DEMUX to separate the DWDM channels and detect each separately.
There is an example on post compensation in OptiSystem example library at
C:\Users\xxxxxxxx\Documents\OptiSystem 15.2 Samples\Dispersion compensation\
Regards,
Ahmad