An arrangement for coupling between a free-space propagating optical signal and an ultrathin silicon waveguide formed in an upper silicon layer (SOI layer) of a silicon-an-insulator (SOI) structure includes a silicon nanotaper structure formed in the (SOI layer) and coupled to the ultrathin silicon waveguide. A dielectric waveguide coupling layer is disposed so as to overly a portion of a dielectric insulating layer in a region where an associated portion of the SOI layer has been removed. An end portion of the dielectric waveguide coupling layer is disposed to overlap an end section of the silicon nanotaper to form a mode conversion region between the free-space signal and the ultrathin silicon waveguide. A free-space optical coupling arrangement is disposed over the dielectric waveguide coupling layer and used to couple between free space and the dielectric waveguide coupling layer and thereafter into the ultrathin silicon waveguide.