VANISHING OPTICAL ISOLATION BARRIER IN DOUBLE ION-IMPLANTED LITHIUM-NIOBATE WAVE-GUIDE

Isolation properties at different propagation directions have been stu died for an optical barrier between two superposed planar waveguides p roduced by MeV He+ implantation in LiNbO3. The barrier exists while th e modes of the double structure propagate along the optic axis. The sp acing between the modes measured with a prism coupler features efficie ntly isolated waveguides. The barrier ''vanishes'' when the directiona l angle between an extraordinary wave and the optic axis exceeds 50 de grees. In this case the mode spacing shows strong coupling between the waveguides that makes the double structure similar to a single wavegu ide with double thickness. (C) 1996 American Institute of Physics.