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

TLDR

Advances in opto‑electronics are driven by materials with unique properties, and transparent conductive oxides have recently attracted attention for on‑chip active photonic devices. This review examines how indium tin oxide can be leveraged for high‑performance, ultra‑compact electro‑optic modulation. ITO’s refractive index can change by about one unit, allowing sub‑wavelength modulation when thin films are coupled to plasmonic confinement that compresses optical modes to nanometer scales. The material shows unit‑scale refractive index shifts, enabling plasmonic modulators that outperform diffraction‑limited devices, yet the exact permittivity modulation mechanism remains to be fully clarified.

Abstract

Abstract: 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.