This invention provides a novel wavelength-separating-routing (WSR) apparatus that uses a diffraction grating to separate a multi-wavelength optical signal by wavelength into multiple spectral channels, which are then focused onto an array of corresponding channel micromirrors. The channel micromirrors are individually controllable and continuously pivotable to reflect the spectral channels into selected output ports. As such, the inventive WSR apparatus is capable of routing the spectral channels on a channel-by-channel basis and coupling any spectral channel into any one of the output ports, thereby constituting a dynamic optical drop module (RODM). By operating an RODM in reverse, a dynamic optical add module (ROAM) is also provided. The RODM (or ROAM) of the present invention may be further equipped with servo-control and power-management capabilities. Such RODMs and ROAMs can be used as building blocks to construct dynamically reconfigurable optical add-drop multiplexers (OADMs) and other WDM optical networking systems.