Answer:
3.WDM
Step-by-step explanation:
WDM ( wavelength division multiplexing ) involves signals composed of light beams WDM is used in communication where fibers are used it is used for multiplexing of number of carrier signals which are made of optical fibers by using different wavelength of laser light it has different wavelength so this WDM is used for signals composed of light beams it has property of multiplexing of signal