We report on a five-channel wavelength-division demultiplexer using substrate-guided waves in conjunction with a polymer-based Littrow hologram operating at 700, 710, 720, 730, and 740 nm. An average cross talk of -40 dB between adjacent channels is measured. Diffraction efficiencies of 69%, 78%, 83%, 77%, and 69% are both experimentally and theoretically confirmed for the five-channel device. We also present further study aimed at reducing the wavelength channel separation to 1 nm and find that achieving such a goal requires a device length of 6.4 cm corresponding to a propagation distance of 9.05 cm.