Mode propagation and field distribution in a strip-loaded waveguide are analyzed for the case where the refractive index of the loading film is higher than that of the waveguide. It is found that the propagation constant is remarkably changed by loading the film with the thickness around the cutoff. As a result, the effect of the optical energy confinement below the strip film is large compared with the previously proposed case where the low-index film is loaded, and the use of the high refractive-index film as the loading strip is very attractive for constructing a three-dimensional waveguide structure.
© 1976 Optical Society of America
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