Plasmonic, photonic, or hybrid? Reviewing waveguide geometries for electro-optic modulators

Electro-optic modulators are key elements in high-speed optical telecommunication links and preferably rely on materials with a linear electro-optic effect. Choosing adequate waveguide geometries is a key challenge in the design of electro-optic modulators. While all-dielectric geometries promise high-speed modulation with low propagation loss, their modulation efficiency suffers from low confinement and weak electrical fields, resulting in lengthy devices. Plasmonic geometries, on the other hand, allow for most compact devices featuring highest electro-optical bandwidths, but at the cost of higher losses. Alternatively, hybrid photonic–plasmonic solutions open a sweet spot for high-speed modulators with moderate loss. In this review, we discuss the three waveguide types by analyzing and comparing their performance and their sensitivity to variations in geometry with respect to a choice of the electro-optical Pockels-effect material.