Tran Vinh Son’s research while affiliated with Concordia University and other places

The propagation of surface-plasmon-polariton (SPP) waves at the planar interface of a metal and a dielectric material was investigated for a dielectric material with strongly temperature-dependent constitutive properties. The metal was silver and the dielectric material was vanadium multioxide impregnated with a combination of active dyes. Depending upon the volume fraction of vanadium multioxide, either attenuation or amplification of the SPP waves may be achieved; the degree of attenuation or amplification is strongly dependent on both the temperature and whether the temperature is increasing or decreasing. At intermediate volume fractions of vanadium multioxide, for a fixed temperature, a SPP wave may experience attenuation if the temperature is increasing but experience amplification if the temperature is decreasing.

The propagation of surface-plasmon-polariton (SPP) waves at the planar interface of a metal and a dielectric material was investigated for a dielectric material with strongly temperature-dependent constitutive properties. The metal was silver and the dielectric material was vanadium multioxide impregnated with a combination of active dyes. Depending upon the volume fraction of vanadium multioxide, either attenuation or amplification of the SPP waves may be achieved; the degree of attenuation or amplification is strongly dependent on both the temperature and whether the temperature is increasing or decreasing. At intermediate volume fractions of vanadium multioxide, for a fixed temperature, a SPP wave may experience attenuation if the temperature is increasing but experience amplification if the temperature is decreasing.

Thermal hysteresis in the optical and electrical properties of VO2 when cycling the temperature through insulator-to-metal states is well known. Here we show that no hysteresis is observed in the co-evolution of the real and imaginary parts of the refractive index, or equivalently, in the evolution of the polarization state of light reflected from a film. Using models for the effective optical properties of inhomogeneous materials, we show that this observation is consistent with a two-phase composition having similar depolarization factors during the temperature cycling. Absence of hysteresis also rules out the possibility of light acquiring different polarization states when interacting with the material during a full cycle of the phase transition. Such considerations are important to understand the functioning of VO2-based photonic devices.

Thin layers of phase change materials are investigated theoretically and experimentally as way to modulate the properties of light interacting with silicon at a planar interface. By inducing a phase transition in vanadium dioxide films, the resulting changes in refractive index modulate the injection of light into silicon and the ejection out of it. Internal reflection of light propagating inside silicon causes the polarization state to be altered during the phase transition. Possible applications to silicon photonics are discussed.

Wavelength and polarization-dependent phase shifts on light interacting with a phase change material can lead to coloration shifts. By exploiting polarization selective effects, the range of attainable colors during switching of a phase-change layer is widened. Theoretical and experimental results are shown for the case of VO2, a reversible phase change material that can be excited thermally, electrically or optically.

Optical effects are measured during the phase transition of vanadium dioxide (VO2) exposed to friction, thereby opening new possibilities for friction measurements and detection. Exposure to periodic cycles of kinetic friction yield measurable, repeatable and reversible changes in optical properties of the films. Changes in reflectance are detected with thermal flux intensities as low as 1 mW/cm². Characteristic response and recovery times are studied and modelled, as well as the effect of operating temperature, friction speed, pressure, friction coefficient and the thermal properties of the substrate.