It will be shown in this paper, that the mode conversion factor (MCF) as defined for Y-junctions, can be profitably the three lowest-order modes of a channel waveguide. Accordingly, these so-called mode-splitting Q-junctions were designed for implementation in PECVD SiON-technology. Propagation calculations point to crosstalk levels well below-20 dB at 10-20 mm junction length. The produced q-junctions show crosstalk Of at a desired crosstalk level. We have realized several modesplitting junctions in SiON-technology using this strategy. butions over the branches, intensity profiles in the multimodal branch and the beat-pattern of light scattered out of that branch. The characterizations show that a @-junction with a intermodal crosstalk of less than-17 dB has been realized. TO the best applied for the design of three branch junctions for These junctions were characterized by analyzing power distri-I. INTRODUCTION 11. DEVICE PRINCIPLES ULTIBRANCH junctions like the well-known Yjunction (1 + 2) or the less-known Q-junction (1 The mode-splitting behavior of multibranch junctions [2]

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Abstract-The concept of device equivalence is introduced. In equivalent devices, the light propagation can be described by identically evolving modal expansions, resulting in identical power transfer ratios. By first applying this concept to a zinvariant structure with a low refractive-index contrast it is shown how a normalized coordinate space can be defined in which equivalent structures have exactly the same geometry. Subsequently it is shown how this normalized coordinate space can be defined for t-variant integrated optical devices, again provided that the lateral refractive-index contrast is small. This normalization makes it possible to perform numerical device simulations in normalized coordinate space, the results being applicable to a large set of equivalent devices. Furthermore, starting from a known design, it simplifies redesigning that device for use at another wavelength or using other materials significantly, the resulting device being equivalent to the original one.