Integrated microcavity optomechanics with a suspended photonic crystal mirror above a distributed Bragg reflector

Increasing the interaction between light and mechanical resonators is an ongoing endeavor in the field of cavity optomechanics. Optical microcavities allow for boosting the interaction strength through their strong spatial confinement of the optical field. In this work, we follow this approach by realizing a sub-wavelength-long, free-space optomechanical microcavity on-chip fabricated from an (Al,Ga)As heterostructure. A suspended GaAs photonic crystal mirror is acting as a highly reflective mechanical resonator, which together with a distributed Bragg reflector forms an optomechanical microcavity. We demonstrate precise control over the microcavity resonance by change of the photonic crystal parameters. The interplay between the microcavity mode and a guided resonance of the photonic crystal modifies the cavity response and results in a stronger dynamical backaction on the mechanical resonator compared to conventional optomechanical dynamics.Comment: 11 pages, 6 figures + Supplementary Material with 10 pages, 12 figures, 2 table

Etude des propriétés optiques de revêtements thermochromes nanostructurés à base de dioxyde de vanadium

Vanadium dioxide (VO2) encounters a phase transition from semiconducting to metallic at a certain transition temperature, which results in a change of its physical properties, in particular its optical properties, making it a promising material for applications like energy efficient coating for windows, buildings, satellites and camouflage. The optical behavior of a polymer opal photonic crystal containing VO2 nanoparticles is studied through an optical model based on the Fourier modal method adapted to 3D photonic crystals. The introduced periodicity generates a reflectance peak related to a photonic bandgap (PBG) which depends on various parameters like the materials refractive indexes, the opal spheres size and the VO2 concentration. In response to the target applications, the material optical properties are studied from the visible to the mid-infrared spectral range, in order to calculate the luminous and solar transmittance on one hand, and the emissivity on the other hand. The structure impact is limited due to the transparency condition linked to the glazing application. However, a stronger PBG effect is observed in the case of opaque materials, especially at low temperatures. This PBG causes a 27% decrease of the emissivity modulation at the VO2 phase transition which translates into a 3 °C rise of the material surface temperature in cold conditions. This property is interesting for applications as energy efficient coating for buildings and satellites. Finally, in order to mimic the behavior of real materials, structural disorder is introduced in the model.Le dioxyde de vanadium (VO2) subit une transition de phase de semi-conducteur vers métallique à une certaine température de transition. Ceci se traduit par des changements de ses propriétés physiques, en particulier optiques, faisant de lui un matériau prometteur pour des applications comme revêtement pour les vitres, bâtiments et satellites, à fort rendement énergétique, ainsi que pour du camouflage. Le comportement optique d’une opale contenant des nanoparticules de VO2 est étudié à travers un modèle optique basé sur la méthode modale de Fourier (FMM) adaptée aux cristaux photoniques 3D. La périodicité introduite génère un pic de réflectance lié à une bande interdite photonique (PBG) qui dépend de différents paramètres tels que l’indice de réfraction des matériaux, la taille des sphères de l’opale et la concentration de VO2. Pour répondre aux différentes applications ciblées, les propriétés optiques du matériau sont étudiées du visible au mid-infrarouge, afin de calculer les transmittances lumineuse et solaire d’une part, et l’émissivité d’autre part. L’impact de la structure est limité par la condition de transparence liée à l’application vitres. Un plus fort effet de PBG est observé dans le cas de matériaux opaques, principalement à faibles températures. Il permet une diminution de 27% de la différence d’émissivité entre les cas chaud et froid, ce qui se traduit par une hausse de 3°C de la température de surface du matériau dans le cas froid, résultat intéressant pour les applications bâtiments et satellites. Enfin, afin de mieux modéliser le comportement de matériaux réels, du désordre dans la structure est apportée au modèle

Numerical study of the thermally adaptive emissivity of VO2-polymer nanostructured coatings

The emissivity of an opal photonic crystal loaded with thermochromic VO2 nanoparticles is studied through optical calculations, highlighting the influence of the structure by comparison with a homogenized model. Parameters are first set to maximize the structure influence on material emissivity. Then, a full study of the influence of the VO2 concentration is made to identify, on one hand, cases with the highest structure impact, and on the other hand, interesting cases for applications such as energy-efficient coatings for buildings, satellites, and camouflage applications