Transfer efficiencies in guided wave electrooptic filters/mode converters

The influence of a spatially nonuniform electric field on the polarization Conversion efficiency of single- and multimode guided wave electrooptic filters is analyzed quantitatively, using coupled-mode theory. A single-mode graded-index surface waveguide filter is capable of essentially 100-percent transfer efficiency, with overlap integrals of field and a single TE, TM mode pair approaching 0.6 in Ti: LiNbO3. The thicker multi-mode slab waveguides require that spatial periods of applied field be considerably greater than the guide thickness to achieve high transfer efficiency, though never quite 100 percent; The best performance also requires focused coupling into the lowest order mode only. Experimental results with a LiTaO3slab waveguide filter show reasonable agreement with a multiple-coupled-mode solution.