The authors report a theoretical analysis and practical implementation
of cylindrical prisms for very efficient coupling into standard plana
r waveguides. The 90 and 92% efficiencies, respectively, measured at 6
38 and 980nm for several SiON waveguides on silicon are among the high
est performances reported to date with the prism coupling technique. S
till higher values are predicted for the case of cylindrical prisms wi
th radius of curvature larger than used.