Analysing curved optical waveguides using the finite difference beam propagation method

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Murphy, Tommy
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University College Cork
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Photonic integrated circuits (PICs) integrate optical components on a single semiconductor chip. As time has progressed, advances have been made allowing the components of these PICs to become smaller and smaller. It is now possible to place many of these components on a single PIC. As these components can contain, or be connected by, bending waveguides, it is desirable to make these waveguide bends with as small a radius of curvature as possible to allow many components to fit on the single PIC. Unfortunately, as the radius of curvature decreases, the power loss through the bend increases due to the waveguide’s fundamental mode shifting towards the outside of the bend, causing large loss from the transition between the straight and curved waveguides. The power from the shifted mode also leaks as the fields propagate through the bend. Therefore, the aim of this thesis was to reduce the loss caused by these bends at small radii of curvature, allowing the bends to take up less space on a PIC. This involved designing the waveguide bends to have curvature profiles other than the conventional circular waveguide bend. The propagating fields through the bends were then analysed by numerical simulations using a program utilising the 3D finite difference beam propagation method, which was created and optimised over the course of the research, to investigate if the different curvature profiles could reduce the loss caused by bends in ridge waveguides. It was found that much lower loss could be achieved for curved deep-etched ridge waveguides with small radii of curvature by designing the bend to have a section where the curvature of the waveguide linearly changes.
Curved waveguides , III-V semiconductors , Beam propagation method , Linear curvature , Finite difference method , Shallow-etched , Deep-etched
Murphy, T. 2020. Analysing curved optical waveguides using the finite difference beam propagation method. MRes Thesis, University College Cork.