The present invention relates to the transmission of optical signals, and more particularly to wavelength division multiplexers and demultiplexers for optical signals. A wavelength division multiplexer device for use in an optical transmission system comprises a light input, one or more lenses, a substrate, one or more holographic optical elements, and two or more light outputs. The light input, the substrate, and the one or more lenses direct a light beam through the device. The one or more holographic optical elements act as transmission diffraction gratings and spatially separate the input light beam into dispersed light beams. Each light output receives one of the dispersed light beams. Multiple holographic optical elements may be stacked upon one another or separated by a substrate. Additionally, the substrate may comprise edges or parts that are beveled. Finally, the elements of the present invention may be rigidly coupled to each other, without intervening air space.