Abstract: A wavelength division method and system employing a radiation transmissive planar waveguide provided with collimating and focusing lenses and with a periodic radiation transmissive diffraction grating incorporating radiation reflecting elements in spaced array, preselected, in demultiplexing service, to separate into individual entities an optical signal input constituting a multiplicity of coherent radiation signals of different characteristic wavelengths transmitted simultaneously via the waveguide and, in multiplexing service, to consolidate a multiplicity of coherent radiation signals individually introduced to the grating via the waveguide along angular courses substantially coincident with the angular courses taken by individual radiation signals of corresponding wavelengths exiting the grating during demultiplexing service, and means directing the signals to dedicated receptors.