Optical signals are dispersed according to their wavelength by an optical path length difference generator (26) that couples a single pathway (12) conveying a plurality of different wavelength signals to multiple pathways (52, 54, 56, 58) separately conveying the different wavelength signals. The optical path length generator (26) can be formed by a reflective stack having a plurality of partially reflective surfaces for reflecting successive portions of the energy of each of the different wavelength signals along different length optical paths.