Switchable materials with nanoplasmonics for optical applications

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The proposal is in the area of optical beams interacting with switchable and adjustable materials such as vanadium dioxide (VO2) and plasmonic nanoparticles. Parts of my research combine these materials with nanoparticles or uses nanometer-scale patterns to modify the properties. Among the studied materials, VO2 is especially interesting for its ability to change from a dielectric state to a metallic state when heated by only tens of degrees centigrade. This phase transition is accompanied with large changes in refractive indices and absorption coefficients, making optical control possible, with potential applications to photonic devices and metamaterials. This research is not aimed at understanding the growth, fabrication and other such material science aspects of these compounds, but rather understanding their interaction with lasers and other optical beams to exploit these effects for various photonic applications. One of the lead projects aims at controlling accurately the phase of a laser beam that is interacting with a thin film of VO2: the material shows promises for phase modulating devices as thin as 100 nanometers or less. Optical phase control, modulation and shifting is one of the central goals of photonics, with widespread applications in areas like interferometry, optical pulse delay/advance and fast/slow light. We have recently observed that films of VO2 grown under certain conditions in our laboratory exhibit an interesting property at specific wavelengths in the 800-1600 nm range: during phase transition, the phase of the optical beam is changed while keeping the other properties of the beam intact, including polarization and amplitude. Recently, we used a highly sensitive phase measurement technique (developed by our group) to see evidences of accurate phase adjustability through the film. Studies and applications of this effect will be for us a topic of research in the next few years, because it suggests the possibility of phase control over extremely short distances. The phase shift per unit of distance travelled is orders of magnitudes larger than what is typically achieved with eletro-optic materials (e.g. Pockels cells) and liquid crystals. It opens the possibility of highly miniaturized devices for integrated optics, among others. However, there are still many aspects of the problem we need to investigate before these applications are made possible. For example, the wavelength adjustability of the effect and the influence of input polarization have to be theoretically modeled and verified experimentally. Another axis of research involves the enhancement and tailoring of the properties of switchable materials by incorporating metal nanoparticles into them. Gold nanoparticles exhibit plasmon resonances that increase optical absorption at wavelengths that can be tuned by adjusting the size of these particles. With respect to VO2, gold nanoparticles are especially interesting because their resonances occur in the visible spectrum: their absoption in the near infrared is weak compared to that of the VO2 in its metallic state. As a result, nanoparticles can be used to enhance optical pumping and optically-induced switching of the material using visible laser beams. With collaborators, experts in material science, we intend to create hybrid materials with such properties and fully characterize them for photonic applications.For Canada, this research program will have a positive impact by training highly qualified personnel in the economically important areas of optics and photonics. Morover, partnership with industry will be possible because of the applied nature of the project, with potential for new device commercialization.