Photonic and plasmonic modulators based on optical switching in VO_2

摘要

Researchers all over the world are competing in a technology-driven quest to develop the next generation of ultrasmall, low-power photonic and plasmonic devices. One route to this objective involves hybrid structures that incorporate a phase-changing material into the structure, creating a nanocomposite material in which the optical response of a plasmonic or photonic structure is modulated by a change in phase, crystallinity or dielectric function induced by thermal, optical or electrical stimulus. Vanadium dioxide (VO_2) has been considered as a potential electro-optic switching material for electronic and photonic applications ever since its semiconductor-to-metal transition (SMT) was first described half a century ago. This review describes the application of vanadium dioxide as the switching element in (ⅰ) a hybrid silicon ring resonator and (ⅱ) a polarization-sensitive, multifunctional plasmonic modulator in the form of a nanoscale heterodimer. As is now widely known, the SMT in VO_2 is also accompanied by a structural phase transition (SPT) from the Ml (monoclinic) to a rutile (tetragonal, R) crystalline form that was believed to prevent a fast recovery after switching. However, recent research has shown that this picture is oversimplified, and that there is a monoclinic metallic state that enables true ultrafast switching. That understanding, in turn, is leading to new concepts in developing hybrid nanocomposites that incorporate VO_2 in silicon photonics and plasmonic modulators, enabling the construction of ultrafast optical switches, modulators and memory elements.