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. This technique enables bidirectional communications over a. 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. WDM allows communication in both the directions in the fiber cable.