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In order for optical transmission systems to compete successfully with other techniques, the circuits must be comparably small, comparably rugged, and comparably priced. The avenue to achieving these characteristics is via miniature guided-wave structures in contrast to beam-mode propagation via lenses and mirrors. Passive miniature transmission lines with satisfactory losses have been formed in glass and fused silica using ion bombardment and reactive sputtering. Certain crystalline systems seem well adapted to thin-film non-linear interactions at low absolute-power levels. Nonlinear liquids in hollow glass fibers can be used to achieve interaction lengths of a meter or more with the field concentrated to a few wavelengths width in the transverse direction. Photolithographic techniques based on visible or ultraviolet exposure of the photoresist yield waveguide-edge roughness greater than that needed for optical circuitry. However, electron beam exposure of the photoresist seems capable of yielding satisfactory results.