Hi! Lalit
Samsung explained well about the use of FBG to get desired wavelength from the LED spectrum in order to realize the WDM system.I also want to add some point that set the frequency of FBG according to the wavelength you requires which directly relates to your coding scheme and how many different wavelength you are using.so please mention the coding scheme for better understanding of your topic .Moreover you can visit the links provided by Samsung from forum archives where discussion on similar topic has already been done.