The number of data points transmitted by an optical waveguide can be greatly increased by assigning one narrow wavelength region to each data point. The technique, called "wavelength or spectral multiplexing," allows hundreds of data points to be transmitted simultaneously over a few fibers. This paper outlines the concept of a two-dimensional-grating multiplexer (and demultiplexer) and includes factors governing the design, test techniques, and experimental results derived after constructing such a system. This experimental system simultaneously transmits and reconstructs 5 X 103 high quality data points from a two-dimensional object through 50 fibers in a linear array. Information concerning resolution, system efficiency, distortion, wavelength range, and the selection of components is included.