ABSTRACT Grating couplers can be more efficient than end-fire coupling, in coupling light into a thin film waveguide (thickness of — I im and below). The aim of this work is to fabricate a low cost, highly efficient silicon waveguide grating coupler whichis to be used at the telecommunication wavelength of 1.3 tim. Silicon-on-insulator (SOl) is chosen for fabricating thegratings as it is low cost using the existing silicon technology. Unibond wafers were used because they offer flexibility inthe 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 I . 14 im and a 5i07 buried layer thickness of 0.67 jim. Gratingsthat have asymmetrical profiles, such as blazed gratings are known to have higher directionality than the symmetricalrectangular gratings, and hence a higher output efficiency. Using perturbation theory, Si blazed gratings with an optimumgrating height were predicted to have a maximum output efficiency of the order of 90 % towards the substrate. The designand fabrication of the blazed gratings will be discussed in this paper.Key words: Unibond, silicon-on-insulators, blazed gratings, waveguide grating couplers, ion beam milling.