In telecommunications technology, such arrangements are integrated in 1.times.N, for example, 1.times.16, branching structures on individual chips having a length of approximately 30 mm. Minimum power losses and a high degree of uniformity in the power distribution to the various outlets are required, on the one hand, and, on the other hand, a high level of integration within a small area is necessary. The latter requires the smallest possible radii of curvature of the waveguides and a large number of curved junctions, both being factors which increase power losses. To achieve uniformity of power distribution, the elementary Y-branches, including the preceding conductor section, must conventionally be structured as symmetrically as possible, which makes curvature conditions even more difficult.
German patent publication 2,916,961 describes a branch for multimode light-guiding fibers having a typical diameter of 80 .mu.m where light-guiding fibers are mutually abutting. The geometrical transmission coefficients from the incoming fiber to the continuing fiber and the branching fiber are obtained as a ratio of the overlapping areas of the fiber cores to the entire core surface of the incoming fiber (FIG. 4). Wave-optical effects are of no significance in thick multimode fibers and the possible curvature of the incoming fiber is likewise of no significance. The offset is provided at the branching location and not at a preceding junction between an input waveguide (especially a curved input waveguide) and the branching component.
It is known from German Patent 3,107,112 and the article entitled "Curved dielectric optical waveguides with reduced transition losses" by E. Neumann, IEE Proc., Vol. 129, Pt. H., No. 5, October 1982, pages 278 to 280, that the losses in the junctions between waveguides with different curvatures can be reduced by lateral offset. This is explained by the fact that the maximum of the fundamental mode of a wave travelling in a waveguide moves to the periphery when the radius in the waveguide decreases. The offset of the waveguides permits compensation of the resulting mode mismatch in the junctions between waveguides of different curvatures. Slab waveguides, strip waveguides and fibers are given as examples.
The foregoing is also described in Japanese patent publication 4-131806 where a contactless 2.times.2 coupler with etched, sharp-cornered strip waveguides is used as an example. This is also shown in FIG. 20 of U.S. Pat. No. 5,247,594. U.S. Pat. No. 5,247,594 also makes reference to ion-diffused glass waveguides.
USPTO Backgrounds
USPTO Backgrounds