Optical modulation in vanadium dioxide-based nanophotonic devices

Abstract

The material of vanadium dioxide (VO2) possesses a metal-insulator transition at approximately 68 ℃, and drastic changes in its optical and electrical properties accompany this phase transition. In recent years, benefiting from rapid advances in nanofabrication and characterisation technologies, VO2-based nanophotonic devices have attracted a lot of research attention. In terms of phase and power modulation of near-infrared lights, VO2-enabled devices present a wide range of applications such as optical imaging sensors for portable platforms and energy-control solar units. Currently there are two main challenges in applications of phase-change materials: the precise prediction of changes in their physical characteristics to improve the reliability of device designs, and how to apply the characteristic data extracted from both experiments and analytical methods to versatile designs. This thesis reports my research on these two specific challenges about the optical modulation based on VO2 phase transition through introducing two pieces of separate but highly correlated work.In my first work, I propose vertical growth models for analysing the VO2 phase transition, which assumes that during the thermally driven phase transition of VO2, the transformation of components in the mixture from the insulating phase to the metallic phase exhibits directional preference. The vertical growth models are established analytically, which assumes different regulations in changes of physical parameters from effective medium models by introducing more interfaces in the nanostructure. By comparing the temperature-dependent reflection change derived from theoretical models, the vertical growth model shows better matching to the experimental benchmark than commonly used effective medium models. It provides a potential tool to predict the behaviour of switchable devices enabled by phase transition materials.

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Identifiers

ORCID for Xu Fang: orcid.org/0000-0003-1735-2654

ORCID for Kees De Groot: orcid.org/0000-0002-3850-7101

ORCID for Kai Sun: orcid.org/0000-0001-6807-6253

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