Influence of a dielectric overlay layer on integrated optics phase modulators

Performance of external electrooptical modulators and switches is enhanced by introducing a dielectric overlay covering the modulating electrodes. These are in the configuration of two coupled traveling-wave microstrips, and the bandwidth is evaluated by combining the orthonormal even and odd modes pertaining to the microwave waveguide. The modulation efficiency is compared in Y- and Z-cut lithium niobate substrates. The optical waveguide is investigated via the refractive effective index method, while the microwave structure is analyzed by the conformal mapping, multiple image, and finite element methods. The Y-cut configuration gives the best overall performance.<>