Despite years of research and development, integrated laser sources remain a bottleneck for silicon photonics (SiPh). Integration of lasers into SiPh can be categorized as hybrid, heterogeneous, or monolithic. Hybrid approaches are the most mature. One example is the co-packaging of lasers with micro-optics and subsequent coupling of laser light to silicon waveguides. More scalable hybrid approaches include butt coupling of lasers and silicon waveguides without the use of micro-optics. This could be accomplished with two chips mounted side by side on a common carrier or by flip-chip bonding of laser chips into recesses adjacent to silicon waveguides. Heterogeneous approaches involve the intimate merging of traditionally incompatible materials and subsequent co-fabrication of these materials to form devices. This approach allows for best-in-class materials selection, however, co-fabrication requires complex fabrication processes. The term monolithic ordinarily refers to a single substrate and materials compatible with the substrate material. Germanium on silicon could be considered a monolithic approach, as could growth of III-V materials (such as indium phosphide (InP) and gallium arsenide) on silicon. This paper summarizes a novel 3D hybrid integration approach that is scalable, low cost, reliable, and that demonstrates superior thermal performance. The approach is based on flip-chip bonding and vertical coupling between InP and silicon waveguides. For the InP waveguide, vertical emission is achieved with a total internal reflection turning mirror. For the silicon waveguide, vertical coupling is achieved with a grating coupler. The InP chip is flip-chip bonded directly to the silicon substrate providing an effective heat sink.
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