Wide-angle filters based on nanoresonators for the visible spectrum

Design of hybrid narrow-band plasmonic absorber based on chalcogenide phase change material in the infrared spectrum

Structures absorbing electromagnetic waves in the infrared spectral region are important optical components in key areas such as biosensors, infrared images, thermal emitters, and special attention is required for reconfigurable devices. We propose a three-dimensional metal-dielectric plasmonic absorber with a layer of PCM's (Phase Change Materials). The phase shift effects of PCMs are numerically analyzed, and it is possible to obtain a shifting control of the resonant absorption peaks between the amorphous and crystalline states using the Lorentz-Lorenz relation. By using this empirical relation, we analyzed the peak absorption shift at intermediate phases between the amorphous and the crystalline. The geometric parameters of the structure with the PCM layer in the semi-crystalline state were adjusted to exhibit strong absorption for normal incidence. The effects of the oblique incidence on the absorption for the TM and TE polarization modes were also analyzed. Our results demonstrate that PCMs have great potential for reconfigurable nanophotonic devices.

Absorptive angular-selective filters consisting of dielectric multilayers combined with thin absorbing layers

We propose a concept of angular-selective filters (ASFs) that transmit the incident light in the transmitting angular ranges and mostly absorb in the blocking ranges. The absorptive ASF consists of a transparent dielectric multilayer combined with a thin absorbing layer, utilizing the change in the fringe pattern of the light intensity in the filter dependent on the incident angle. We clarified the design guide to select the suitable multilayer structure and absorbing material. Concrete structures of three types were designed using Cr for the absorbing material on the basis of ${\text{SiO}_2}/{\text{TiO}_2}$SiO₂/TiO₂ bandpass, shortpass, and longpass filters, exhibiting the absorptive ASF functions with the transmitting/blocking ranges of 0-10°/10-30°, 0-30°/30-60°, and 10-60°/0-10°, respectively. The present multilayered structures provide a great advantage for practical use: no need for two- or three-dimensional patterning using lithographic techniques.

Design of planar and wideangle resonant color absorbers for applications in the visible spectrum

We propose a design approach for color absorbers based on a tri-layer metal-dielectric-metal (MDM) planar geometry, which maintains the same color absorbed, over a range of incident angles from 0° to 80° for light with TM polarization. The dielectrics are chosen to satisfy the ideal conditions of resonance. We calculate the ideal thickness of each dielectric layer by using the planar resonance theory. The numerical results show a total absorption above 85% for all colors of the absorber. We analyzed the influence of the of the metallic top layer thickness and we demonstrated the fabrication error tolerance of the proposed absorber. Finally, we present and discuss the physical mechanisms for the coupling of the electromagnetic field and the absorbed optical power in the structure.