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1 July 2004 Compact grating coupler between vertically stacked silicon-on-insulator waveguides
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The area of integrated optical circuits has been undergoing rapid development due to the important applications of fiber communication systems and optical interconnects. A significant challenge of photonic circuits is to increase circuit density and to miniaturize these devices. The vertical integration of stacked waveguides for photonic circuits onto a single substrate is a promising configuration to enable the dense monolithic integration of three-dimensional photonic devices. Application of high-index-contrast waveguides, such as silicon-on-insulator waveguides, is another important way to increase the density of optical circuits due to their small sizes. These waveguides produce high confinement in the guiding layers and have the advantages of compactness and immunity of cross-talk between different waveguides. It is thus expected that efficient coupling of light between vertically integrated waveguides where no direct field-overlap of guided modes exists is a key issue. We propose a compact double-grating coupler to realize efficient coupling through radiation modes between two vertically stacked SOI waveguides. The grating is strong enough to be considered as a onedimensional photonic bandgap structure which facilitates a very short coupling length. Simulations suggest that a 22% efficiency is achievable in coupling light from one waveguide to another with a 12.9μm long grating. We find that the coupling efficiency is enhanced by Fabry-Perot resonance between two gratings. Coupling efficiency can be dramatically increased by incorporating a reflective under-layer structure or using blazed grating.
© (2004) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Po Dong and Andrew G. Kirk "Compact grating coupler between vertically stacked silicon-on-insulator waveguides", Proc. SPIE 5357, Optoelectronic Integration on Silicon, (1 July 2004);

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