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. This makes it possible to scale capacity cost-effectively by using existing infrastructure more efficiently. The key concept behind WDM is that different signals can be transmitted simultaneously, each at its own unique wavelength. The initial. 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. Current solutions are limited by trade-offs between channel spacing, crosstalk, insertion.