Hello,
OCDMA should normally be executed with Power Splitters and Combiners. A power splitter will only effect the power of an input signal by dividing it by the number of output ports. WDM work differently by SELECTING signals centered at different wavelengths, basically acting as multiple bandpass filters.
In SAC-OCDMA, the signal selecting and unselecting (coding I guess is a better term!), is done by the Fiber Bragg gratings.