Recently, our company’s engineers are discussing the most common ROADM systems in the market. After discussions, they agreed that when the relevant technology matures, this ROADM system will become the most competitive solution in the market. The structure is shown in the figure, and its UNI side is M×N port adWSS. adWSS is the abbreviation of upload/download wavelength selection switch, it has M input ports and N output ports, all input ports are DWDM ports, and all output ports are single-wavelength ports. adWSS can switch any wavelength from any input port to any output port. In this ROADM system, adWSS is needed on the UNI side. A typical adWSS has 8×128 ports, which means that two adWSSs are enough for an 8-dimensional ROADM node. However, adWSS technology is not yet mature and is still far from commercial use.