Design, fabrication and characterization of metasurfaces for diffractive optics applications

Abstract

The goal of this PhD research proposal is to design, model, fabricate, and characterize metamaterials (in their state-of-the-art) capable of controlling the propagation of light beams with low insertion losses for diffractive optics applications, particularly binary phase holograms. More specifically, this research will focus on plasmonic diffractive optics for the design of distributed nano antennas forming a so called metasurface. These structures are capable of modulating the phase and amplitude of light in a much more efficient way than regular diffractive optics elements do. It will also be investigated strategies to mitigate truncation (finite-size) effects in the response of these elements, establish the ideal dimensions of the sub-masks, and optimize the geometry of the transition region from +p to a -p sub-matrix to mitigate undesired diffractive effects. Additionally, once obtaining low insertion losses is crucial (because metamaterials tend to produce high insertion losses, particularly when operating in the negative refraction regime), it will be investigated different substrates and appropriate configurations for the nano inclusions aiming at mitigating these losses. The metals adopted for the metasurfaces are silver and aluminum, due to their compatibility with CMOS processes. However, it is expected the metal type to influence the performance of the nano antennas. Therefore, the procedure adopted for the nano antennas' experimental characterization will be established in such a way as assess the performance of the metasurfaces. It will also be designed e fabricated metasurfaces (to be used an benchmarks) using conventional modeling techniques. The theoretical and experimental results obtained in this stage will be used for performance comparison with the optimized structures (free from unwanted diffractions). By exploring added degrees of freedom, this approach has great potential for producing high scientific impact results with new optimized designs for periodic metamaterials, with higher bandwidth and lower insertion losses. This will be achieved by means of electromagnetic simulations assisted with optimization tools aiming always at obtaining different optical functionalities with the proposed structures, such as a stringent frequency selectivity and optimized transmission patterns. Finally, it is expected that the present research demonstrates both theoretically and experimentally new concepts for binary phase holography based on the proposed metasurfaces. Additionally, the approach here proposed has great potential for applications in sensing and optical interconnects. (AU)