Indium‐Tin‐Oxide for High‐performance Electro‐optic Modulation

Advances in opto‐electronics are often led by discovery and development of materials featuring unique properties. Recently, the material class of transparent conductive oxides (TCO) has attracted attention for active photonic devices on‐chip. In particular, indium tin oxide (ITO) is found to have refractive index changes on the order of unity. This property makes it possible to achieve electrooptic modulation of sub‐wavelength device scales, when thin ITO films are interfaced with optical light confinement techniques such as found in plasmonics; optical modes are compressed to nanometer scale to create strong light‐matter interactions. Here we review efforts towards utilizing this novel material for high performance and ultra‐compact modulation. While high performance metrics are achieved experimentally, there are open questions pertaining to the permittivity modulation mechanism of ITO. Finally, we review a variety of optical and electrical properties of ITO for different processing conditions, and show that ITO‐based plasmonic electro‐optic modulators have the potential to significantly outperform diffractionlimited devices.