Transparent conductive oxides (TCO) like Indium tin oxide (ITO) are extensively adopted in high-tech industry such as in touchscreen displays of smartphones or contacts for solar cells. Until recently, ITO has been explored for electro-optic modulation using its free-carrier dispersive effect. Electro-optic modulators largely determine the transmission rate and are an important part of photonic communication systems. Thus, gigahertz (GHz)-fast modulation capability using ITO must be demonstrated.
GW researchers have developed a novel Mach–Zehnder interferometer (MZI)-based modulator to demonstrate a comprehensive platform of heterogeneous integration of ITO-based opto-electronics into silicon photonic integrated circuits (PIC). The Mach-Zehnder interferometer features a high-performance half-wave voltage and active device length product of VπL = 0.52 V mm. The TCO material indium tin oxide (ITO) exhibits unity-strong index change and epsilon-near-zero behavior. This device experimentally confirms electrical phase shifting in ITO enabling its use in applications such as compact phase shifters, nonlinear activation functions in photonic neural networks, and phased array applications for LiDAR.
Figure 1. Schematic of the ITO-based Mach Zehnder Interferometer (MZI) showcasing the active gating region and contacts.
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