0.52 V mm ITO-based Mach-Zehnder modulator in silicon photonics

Abstract

Electro-optic modulators transform electronic signals into the optical domain and are critical components in modern telecommunication networks, RF photonics, and emerging applications in quantum photonics, neuromorphic photonics, and beam steering. All these applications require integrated and voltage-efficient modulator solutions with compact form factors that are seamlessly integrable with silicon photonics platforms and feature near-CMOS material processing synergies. However, existing integrated modulators are challenged to meet these requirements. Conversely, emerging electro-optic materials heterogeneously and monolithically integrated with Si photonics open up a new avenue for device engineering. Indium tin oxide (ITO) is one such compelling material for heterogeneous integration in Si exhibiting formidable electro-optic effect characterized by unity-order index change at telecommunication frequencies. Here we overcome these limitations and demonstrate a monolithically integrated ITO electro-optic modulator based on a Mach Zehnder interferometer featuring a high-performance half-wave voltage and active device length product of VπL = 0.52 V mm. We show that the unity-strong index change enables a 30 μm-short π-phase shifter operating ITO in the index-dominated region away from the epsilon-near-zero point for reduced losses. 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.