Abstract: Improved illumination of edge illuminated signs is achieved by use of light guides of transparent material to match the aperture of an edge of a sign panel to the aperture of a light source which may be located remotely. The light guide is typically of ribbon section at the panel end and of compact section at the other. It may be formed by dividing a continuation of one edge of the panel into individual fibres. The compact end of the guide may be fitted with a ferrule for coupling to further light guide elements. The sign panel is preferably covered with internally reflective or phosphorescent material except in the regions of indicia formed on the surface of the panel by masking, abrasion or hot stamping.

Abstract: Optical fibre couplers are formed by selectively etching the cladding layer of portions of the fibres forming the coupler to provide them with an undulating profile, converging a group of fibres so that the undulating profiles interlock, and fusing the interlocking portions without drawing the fibres, so as to form a fused coupling zone of blended core and cladding glass. The fused zone is inserted in a ferrule, or a cladding layer is applied having a numerical aperture selected to maintain a more or less constant numerical aperture through the coupler. Such couplers may be cut in half and the halves optically coupled to each other by applying lenses to the cut ends and inserting the halves from opposite directions into a housing containing refractive index matching fluid so that the focuses of the lenses coincide.