It is two decades since the first reports that the insulator-to-metal transition (IMT) in vanadium dioxide (VO2) occurred on an ultrafast time scale, followed by growing interest in the potential use of this strongly correlated oxide in a variety of switching schemes. At first glance, VO2 would seem to be ideally suited to a variety of applications in electro-optics and all optical switching: The IMT occurs on a sub-picosecond time scale; it is fully reversible and has a large dielectric contrast at wavelengths in the near- to mid-infrared; and the material itself is fully compatible with many optical and electronic materials of interest. However, there are also well-known difficulties, chief among them the fact that the IMT, if fully completed, is accompanied by a structural phase transition (SPT) that requires nanoseconds to return from the rutile, metallic state to the monoclinic insulating ground state – thus essentially limiting switching speeds to time scales similar to those in amorphous-to-crystalline transitions in chalcogenide glasses. Here we discuss the ways in which the very considerable advantages of VO2 as a modulating or threshold switch can be amplified by deploying it appropriately in silicon photonic modulators, switchable metasurfaces, plasmonic heterostructures, and two-dimensional materials that can support phonon polariton optics. We focus particularly on ways of tailoring the physical properties of the VO2 component of a system to meet the requirements of operating in particular wavelength regions, meeting specific threshold requirements and choosing electrical or optical initiation of the IMT.
Vanadium Dioxide is an optically dense phase change material that has been applied to modulating the resonances of plasmonic structures resonant in the THz, infrared and optical ranges. It has been shown previously that fabrication of optical antennas on thin films of Vanadium Dioxide can result in a resonance shift of more than 10% across the phase change. This post-fabrication, dynamic tuning mechanism has the potential to significantly increase the possible applications of plasmonic devices.
Here, we show that optical antenna arrays fabricated on differing thicknesses of Vanadium Dioxide supported by a silicon substrate show a dependence of their resonant wavelengths on this thickness. Along with the geometry of the antennas in the arrays this constitutes an additional degree of freedom in the design of the tuning range of these devices, offering further potential for optimisation of this mechanism. The potential extra blue-shift provided by optimising this thickness may be used, for example, in lieu of reducing antenna dimensions to avoid increasing antenna absorption and the additional plasmonic heating that can result.