Optical and terahertz interactions with phase-change materials and nanostructures

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This application seeks support for research on the interactions between light and tunable media such as phase change materials (PCM's) and nanostructures. PCM's are being studied to advance knowledge in condensed-matter physics and used in optical technologies such as data storage and memory. One important PCM is vanadium dioxide (VO2), whose reversible phase transition from semiconductor to metal can be induced thermally or optically on rapid time scales. Large refractive index changes occur during the phase transition, making the material capable of modifying and controlling the flow of light. Other materials with similar properties include chalcogenides like Ge2Sb2Te5 and AgInSbTe. Building on the experience gained in recent years with PCM's, I will explore three new avenues: Terahertz (THz) radiation is important to science as a probe to study the fundamental properties of materials, and useful to industry as an imaging tool capable of penetrating materials that are opaque to visible and infrared light. The expansion of THz science has relied not only on the development of efficient detectors and powerful coherent sources, but also on the availability of basic components to manipulate the field, such as polarizers, modulators and phase-plates. To this end, one of the research goals is to explore how PCM's can modify and control the amplitude, phase and polarization of THz radiation on rapid time scales. Phase change displays have generated much interest in recent years, as ultra-thin color displays were demonstrated based on interference effects of white light in PCM films. By switching the material between its two phases, the reflected spectrum was shifted to different color coordinates. Having previously found that VO2 alters the polarization state of light, I would like to investigate polarization effects as a way to enhance the performance of phase change displays. Gold nanoparticles, with optical properties tunable with size, will be combined with PCM's to further enhance coloration control. Silicon optical components are interesting because they create an interface for photonics and electronics, and because of the many technologies available to process the material at the nanometer scale. One goal of this research proposal is to study how thin, uniform layers of PCM's interfaced to silicon can achieve some basic functions of silicon photonics, such as controlling the flow of light in and out of silicon and silicon waveguides, and controlling the amplitude, phase and polarization of the light traveling inside. The research program will benefit society by training students in research fields that are relevant to both fundamental knowledge and optical technology. Given the applied nature of the research, there is significant potential for partnerships with industry for the creation of new photonic devices.