EFFICIENT COUPLING INTO TAPERED PROTON-EXCHANGED LINBO3 WAVE-GUIDES FABRICATED BY VERTICALLY CONTROLLED IMMERSION

Planar LiNbO3 waveguides with a 5-mm tapered region and a 10-mm homoge neous slab waveguide region were fabricated by a double proton-exchang e process. The 4-mu m waveguide entrance gives rise to a coupling effi ciency as high as 93%; the precise control of the depth profile of the tapered region results in a low 1-dB power transfer loss from the tap ered region to the 0.4-mu m-depth working region. The techniques devel oped provide an alternative to prism coupling into planar waveguides i n Cerenkov second-harmonic generation applications. (C) 1996 Optical S ociety of America