Silicon lithium niobate electro-optic waveguide modulator structures in the parallel-plate configuration.
Waveguide modulators incorporating paralle-plate electrodes are investigated by computer modeling. Metal-electrode structures differ from severe optical losses that are due to surface plasmons. Siliconelectrode structures exhibit lower losses. Bandwidth is limited by the resistivity and the proximity of the electrodes. Doping the silicon improves conductivity but incireases optical absorption. Device optimization involves a trade-off between bandwidth and optical loss. Devices are fabricated by the use of substrates of silicon on sapphire, with rf sputtered lithium niobate films and plasma-enhanced chemical vapor-deposited hydrogenated amorphous silicon for the upper electrodes. The electro-optic coefficient of these lithium niobate films is ~50% of the value for bulk material. The results indicate the possibility of using these devices for combining silicon integrated circuits with waveguide modulators on a common substrate.
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