It is frequently necessary to convert a larger mode, such as a fiber mode, down to the single mode of a planar lightwave circuit (PLC). A mode converter can be used to allow for an adiabatic transition between two optical modes. This example illustrates the design and simulation of a mode converter that consists of two linearly-tapered rib waveguides which transition from a wide multimode waveguide to a smaller single mode SOI waveguide. Two tapers will be used to convert between these two waveguides. The conversion efficiency of the coupler will be computed.