Transparent conducting oxides for electro-optical plasmonic modulators

The ongoing quest for ultra-compact optical devices has reached a bottleneck due to the diffraction limit in conventional photonics. New approaches that provide subwavelength optical elements, and therefore lead to miniaturization of the entire photonic circuit, are urgently required. Plasmonics, which combines nanoscale light confinement and optical-speed processing of signals, has the potential to enable the next generation of hybrid information-processing devices, which are superior to the current photonic dielectric components in terms of speed and compactness. New plasmonic materials (other than metals), or optical materials with metal-like behavior, have recently attracted a lot of attention due to the promise they hold to enable low-loss, tunable, CMOScompatible devices for photonic technologies. In this review, we provide a systematic overview of various compact optical modulator designs that utilize a class of the most promising new materials as the active layer or core— namely, transparent conducting oxides. Such modulators can be made low-loss, compact, and exhibit high tunability while offering low cost and compatibility with existing semiconductor technologies. A detailed analysis of different configurations and their working characteristics, such as their extinction ratio, compactness, bandwidth, and losses, is performed identifying the most promising designs.