WDM stands for wavelength division multiplexing. It is a method for combining multiple data signals onto a single optical fiber by assigning each data stream a distinct light wavelength. What is Wavelength Division Multiplexing (WDM)? What is WDM used for? What is. Briefly speaking, WDM is a technique in fiber optic transmission for using multiple light wavelengths to send data over the same medium. This guide delves into the principles, types, applications, and future trends of WDM. Read on to learn the fundamentals of this useful technology.