Performance Analysis of Integrated Electro-Optic Phase Modulators Based on Emerging Materials

• Published in: IEEE journal of selected topics in quantum electronics Vol. 27; no. 3; pp. 1 - 11
• Main Authors: Amin, Rubab, Maiti, Rishi, Khurgin, Jacob B., Sorger, Volker J.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.05.2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Absorption; Bandwidths; Charge distribution; Data communication; Density; Electric potential; Electrical junctions; Energy bandwidth ratio; Graphene; Indexes; Indium tin oxide; Indium tin oxides; Insertion loss; integrated photonics; ITO; Lithium niobates; Modulators; Neural networks; Optical materials; Optical waveguides; Optics; Phase modulation; Photonics; Silicon; Thin films; Tradeoffs; Transition metal compounds; transition metal di chalcogenides; Voltage; WSe<named-content xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:ali="http://www.niso.org/schemas/ali/1.0/" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" content-type="math" xlink:type="simple"> <inline-formula> <tex-math notation="LaTeX"> _2</tex-math> </inline-formula> </named-content>
• ISSN: 1077-260X; 1558-4542
• DOI: 10.1109/JSTQE.2020.3041835

Electro-optic modulators are utilized ubiquitously ranging from applications in data communication to photonic neural networks. While tremendous progress has been made over the years, efficient phase-shifting modulators are challenged with fundamental tradeoffs, such as voltage-length, index change-losses or energy-bandwidth, and no single solution available checks all boxes. While voltage-driven phase modulators, such as based on lithium niobate, offer low loss and high speed operation, their footprint of 10's of cm-scale is prohibitively large, especially for density-critical applications, for example in photonic neural networks. Ignoring modulators for quantum applications, where insertion loss is critical, in this work we distinguish between current versus voltage-driven modulators. We focus on the former, since current-based schemes of emerging thin electro-optical materials have shown unity-strong index modulation suitable for heterogeneous integration into foundry waveguides. Here, we provide an in-depth ab-initio analysis of obtainable modulator performance based on heterogeneously integrating low-dimensional materials, i.e., graphene, thin films of indium tin oxide, and transition metal dichalcogenide monolayers into a plurality of optical waveguide designs atop silicon photonics. Using the fundamental modulator tradeoff of energy-bandwidth-product as a design-quality quantifier, we show that a small modal cross section, such as given by plasmonic modes, enables high-performance operation, physically realized by arguments on charge-distribution and low electrical resistance. An in-depth design understanding of phase-modulator performance, beyond doped-junctions in silicon, offers opportunities for micrometer-compact yet energy-bandwidth-ratio constrained modulators with timely opportunities to hardware-accelerate applications beyond data communication towards photonic machine intelligence, for instance; where both performance and integration-density are critical.