Transparent conducting oxides for electro-optical plasmonic modulators

The ongoing quest for ultra-compact opticaldevices has reached a bottleneck due to the diffractionlimit in conventional photonics. New approaches that providesubwavelength optical elements, and therefore leadto miniaturization of the entire photonic circuit, are urgentlyrequired. Plasmonics, which combines nanoscalelight confinement and optical-speed processing of signals,has the potential to enable the next generation of hybridinformation-processing devices, which are superiorto the current photonic dielectric components in terms ofspeed and compactness. New plasmonic materials (otherthan metals), or optical materials with metal-like behavior,have recently attracted a lot of attention due to thepromise they hold to enable low-loss, tunable, CMOScompatibledevices for photonic technologies. In this review,we provide a systematic overview of various compactoptical modulator designs that utilize a class of themost promising new materials as the active layer or core—namely, transparent conducting oxides. Such modulatorscan be made low-loss, compact, and exhibit high tunabilitywhile offering low cost and compatibility with existingsemiconductor technologies. A detailed analysis of differentconfigurations and their working characteristics, suchas their extinction ratio, compactness, bandwidth, andlosses, is performed identifying the most promising designs.