Final Report Summary - HYPHONE (Hybrid Photonic Metamaterials at the Multiscale) The scientific goal of the project is to bridge the gap between photonic structures and metamaterials, and to design hybrid photonic devices that have a mix of miniature (wavelength-scale) and ultra-miniature (subwavelength-scale) structuring. The primary project activities consisted in developing a theoretical model of wave propagation and light-matter interaction in inhomogeneous media with multiple scales of feature sizes and wide variety of geometrical structures. The key step involved determining the critical parameters defining the structure geometries on both scales of structuring. Elaborating computational methods suitable for hybrid multiscale photonic simulations in order to complement the analytical models was also within the project scope. Much of the project work has focused on wave propagation in hybrid multiscale multilayers based on hyperbolic metamaterials. In this way, we have succeeded in implementing the multiscale principles to the simplest, one-dimensional type of hybrid photonic structures. First, plasmonic monolayers as constructing cells for photonic structures were studied. Then, the building principles of hybrid multilayer devices were identified, and photonic devices based on these principles have been proposed. The building strategy has included application of periodic and deterministically aperiodic structural blocks. Finally, variations of the canonical multilayer design involving layers with interface roughness and layers made of self-organized assemblies of nanoparticles have been explored as candidates for multiscale hyperbolic metamaterials. Experimental methods for realizing multiscale hyperbolic metamaterials are under development.These results form a solid methodological basis for important applications that are directly relevant to society. One example is the proposed design of a metamaterial structure (the "dark-field hyperlens") that brings about a possibility of label-free biological imaging and manipulation with nanoscopic resolution, which would be enabling in modern biology and chemistry.The principles confirmed for one-dimensional geometry have been extended to two-dimensional structuring based on nanoparticle lattices and microslot patterned membranes. In both kinds of structures, the multiscale approach has been put to use to enhance the photoelectric and polarization conversion effects present in the individual elements. New photoelectric effects, such as transition absorption and giant plasmonic photogalvanic effect, have been discovered in nanoparticle lattices. These effects make way for the design of new-type photodetectors and solar cells, as well as open up new perspective in photocatalysis, photochemistry, and photoelectrochemistry.Polarization control properties of microslot membranes have been confirmed in experiments carried out in the THz range, thus experimentally validating the multiscale approach. Membrane-based THz optics can be enabling in compact-sized steering and manipulation of all applications involving THz radiation, from spectroscopy to medical imaging to security screening.All the findings of the project can also be used as design principles for functional photonic/metamaterial devices with integrated optical applications. Examples include on-chip frequency and polarization filtering, on-chip label-free sensing, and on-chip engineering of the device-enhanced light-matter interactions. Didactically, the project results have increased the overlap between photonics and metamaterials research communities. This will both advance the research in the general field of optical physics and increase the field's visibility, promoting its interest to the general public and furthering the interest of society to modern physics.