Hi Prarthana,
Based on what I know about the optical interleaver application, I can say that optical interleaver and WDM interleaver MUX are the same. Conversely. optical de-interleaver and WDM interleaver DEMUX are supposed to do the same task, which is separating the two sets of DWDM signals. So whenever optical interleaver can be used, you can use interleaver MUX.
Regards