Design and Simulation of an Integrated Fiber-to-Chip Coupler for Silicon-on-Insulator Waveguides

We report a novel design for a monolithically integrated fiber to silicon-on-insulator (SOI) waveguide coupler. The structure consists of a relatively large silicon block on top of a sub-micrometer dimensional silicon rib waveguide. The block and the waveguide are separated by a thin oxide layer, which acts as an efficient etch stop during fabrication. The optical facet is $5\times 5\ \mu \mathrm{m}$ (the cross-sectional area of the block at the device edge) and hence provides an efficient overlap with the optical mode of commercially available tapered fiber. By matching the effective index of the block and the underlying rib waveguide we show that efficient coupling of optical signal can be achieved. Simulations using the beam propagation technique suggest that $> 90\%$ efficiency can be maintained for all reasonable manufacturing tolerances.