The effect of wavefront tilt on mode conversion in asymmetrical Y-branch waveguides

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Abstract
Step approximation models provide a simple method of studying mode propagation and mode conversion in planar Y-branch optical waveguides. They are, however, only applicable to small branching angles since they neglect the wavefront tilt of the separating waveguides. A phasefront tilt approximation which can be used in conjunction with the local normal mode profile of the five-layer structure is introduced. By rotating the Y-branch about the branching point, a symmetrical branching angle is defined so that the phasefront approximation can be used not only for symmetrical Y-branches, but also for Y-branches which have an asymmetrical branching angle or have a change in branching angle along the longitudinal axis of the Y-branch.