In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths (i. To begin with, we assume that we have the element parameters from a known process design kit (PDK). Each signal is carried on a different wavelength of light, and. Wavelength division multiplexers are fundamental to the functioning and performance of integrated photonic circuits, with applications ranging from optical interconnects to sensing and quantum technologies. WDM allows communication in both the directions in the fiber cable.