The core component of ROADM is a wavelength selective switch (WSS).

The core component of a ROADM (Reconfigurable Optical Add-Drop Multiplexer) is indeed the Wavelength Selective Switch (WSS). The WSS enables dynamic selection and routing of optical wavelengths without converting them to electrical signals. It provides the flexibility to add, drop, or pass through wavelengths, allowing on-demand network reconfiguration. This capability supports agile wavelength management, crucial for modern elastic and automated optical networks. HCIP-Transmission documents emphasize that the WSS is the essential element that makes ROADMs programmable and adaptive, forming the backbone of flexible optical layer management.