Optical field distribution in a waveguide loaded with high refractive-index film; modulation efficiency improvement...

The change of optical field distribution by loading a high refractive-index film on a slab waveguide has been analyzed. It is found that the optical field is remarkably pulled to the film-waveguide boundary when the thickness of the loading film is close to the cutoff thickness. The optical energy content in the loading film has been calculated, and we have found that the energy existing in the film is easily made to be little (e.g., less than 10%) by the appropriate choice of the refractive index of the loading film. The effect is well utilized for the improvement of modulation efficiency in the waveguide modulator with planar-type electrodes.