The longitudinal magnetooptic effect can be used in a unique way to mix TE and TM modes of a planar dielectric waveguide where the strength of mixing is dependent upon propagation direction (forwards or reverse). A detailed study of Faraday effect circulators in optical dielectric waveguides is presented and accurate design data for a practical version are offered. At this writing, experimental confirmation has been hampered by lack of success optically contacting two dissimilar materials.