Hi Swapandeep,
I believe the explanation I have formerly made about SAC OCDMA with MD codes would help you understand how the codes are made and how the FBG wavelengths are chosen. Please read my comment below and take a look at the paper I have introduced if needed. If you had further questions about my reply, feel free to ask. Here’s the link:
http://staging.optiwave.com/forums/topic/sac-ocdma-with-md-code/#post-22736
And the name of the paper is “Development of a new code family based on SAC-OCDMA system with large cardinality for OCDMA network”.
Regards