Blazed grating couplers in unibond SOI

Grating couplers can be more efficient than end-fire coupling, in coupling light into a thin film waveguide. The aim of this work is to fabricate a low cost, highly efficient silicon waveguide grating coupler which is to be use data the telecommunication wavelength of 1.3 micrometers . Silicon-on-insulator (SOI) is chosen for fabricating the gratings as it is low cost using the exiting silicon technology. Unibond wafers were used because they offer flexibility in the choice of the thickness' of both the silicon film and the buried oxide layer, and they have low optical waveguide loss. The wafers used in this work have a Si film thickness of 1.14 μm and a SiO 2 buried layer thickness of 0.67 μm. Gratings that have asymmetrical profiles, such as blazed gratings are known to have higher directionality than the symmetrical rectangular gratings, and hence a higher output efficiency. Using perturbation theory, Si blazed gratings with an optimum grating height were predicted to have a maximum output efficiency of the order of 90% towards the substrate. The design and fabrication of the blazed gratings will be discussed in this paper.