A novel wavelength routing apparatus is disclosed, which uses a diffraction grating to separate a multi-wavelength optical signal from an input port into multiple spectral channels; a channel-interleaving assembly (e.g., an array of prisms) to interleave the spectral channels into two channel groups; and an "augmented relay system" to relay the interleaved channel groups onto two separate arrays of channel micromirrors, respectively. The channel micromirrors are individually controllable and pivotable to reflect the spectral channels into multiple output ports. As such, the inventive wavelength routing 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. Further, the channel-interleaving scheme thus devised effectively "enlarges" the channel spacing and thereby allows the channel micromirrors in each array to be made considerably larger and more reliable, thereby significantly improving the channel filtering characteristics and ensuring more robust performance.