Photonic and plasmonic modulators based on optical switching in VO2

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 (VO2) 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 VO2 is also accompanied by a structural phase transition (SPT) from the M1 (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 VO2 in silicon photonics and plasmonic modulators, enabling the construction of ultrafast optical switches, modulators and memory elements.