Planar optical waveguides can be used for self-imaging. The formation of one-dimensional self-images in solid waveguide slabs of homogeneous refractive index is reported. The location of the self-images along the guide are shown to be dependant on the optical path of the signal wave. Reflective means are used to shorten the device size and to provide focussing so that a two-dimensional imaging device can be fabricated. The integration of a dispersive element such as a grating is proposed to permit the design of angularly dis-persive devices to the multiplexing of several optical signals at different wavelengths. Possible applications in multimode optics include branching couplers, frequency multiplexers for multimode transmission systems, fail-safe multimode switching and electro -optical modulators.