Abstract: Self-aligned aperture masks are produced using a positive-acting photoresist (18) which is developed with a liquid developer. The apertures (30) of the mask have lower levels of inter-aperture variability than masks produced using mechanical transfer of toner particles (FIGS. 4-5 and 7-8), both for the apertures of a given mask and between masks.

Abstract: The present invention relates to a coupler having one input port and 2.sup.n output ports which includes a plurality of essentially coplanar waveguides connecting the input port to one of the 2.sup.n output ports. The plurality of waveguides are arranged in two symmetrical groups in relation to the axis of the coupler and have points of inflection. Each of the waveguides includes branches connected in a tree-like manner by n levels of Y-junctions where the waveguides connecting at least two of the output ports that are located furthest from the axis of the coupler to the input port have no singularities and between the first level and the nth level of the Y-junction have points of inflection located outside the junctions. Further, the junctions located along these waveguides have axes of symmetry which are not parallel to the axis of the coupler.