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Shapeshifting Metasurfaces for Chemically Selective Augmented Reality

Periodic Reporting for period 3 - METAmorphoses (Shapeshifting Metasurfaces for Chemically Selective Augmented Reality)

Reporting period: 2022-10-01 to 2024-03-31

Planar optical components, designed as optical metasurfaces or as Diffractive Optical Elements (DOEs), have now demonstrated to reach, or even overcome, the performances of refractive optical elements. While optical metasurfaces implement the desired spatial dependent modulation through variations of local geometrical parameters (shape, size, orientation) of single subwavelength nanoresonators or nanoantennas, the optical modulation is completely encoded in their three-dimensional surface profiles. In both cases, the surface geometry plays a key role in the definition of the optical functionality, making typical flat components intrinsically static devices, with operating characteristics fixed during the fabrication processes. Many efforts are now oriented toward the realization of active flat optical components, able to modify their optical functionality in response to external stimuli. Display technologies, wearables, and augmented reality are only few examples of possible application fields that would be significantly boosted by dynamically controllable planar optical elements. Besides the direct modification of relative spatial arrangement of the subwavelength resonators through mechanical actuation of stretchable substrates or the use of phase-change materials in the fabrication of index-switchable scatterers, the resonant nature of the modulation in metasurfaces has offered different strategies for tuning the optical response of flat devices. However, in several cases, complex actuation systems are required, the degree of achievable tunability is limited and it comes at the expenses of reduced optical quality and modulation efficiency, partially losing some of the key advantages that are typically attributed to the metasurfaces over the diffraction-based flat optical devices.
The ERC project METAmorphoses aims at realizing reconfigurable planar optical devices with on-demand optical functionality.
According to the project scheduled activities, the research of the first reporting period have been mainly focused on the materials characterization and the design of planar devices. In this period we introduced a new mechanism in the metasurfaces design that allows for enhanced purity of the structured light beam. This result represent a step forward in the light filtering capabilities of metasurfaces and it is a principle that applyes to any used material and spectral range.
The new design mechanism we introduce to filter out undesired light passing through a metasurface is based on engineering of the local polarization status imposed by the metasurface. So far, mainly light amplitude and phase have been considered and used. However, we design devices that impose a specific polarization mask to the light beam together with a phase mask. This allow then to combine the device with standard polarization devices to filter out undesired light components and increase the quality of the light beam.
We are currently further developing this aspect by also implementing schemes where the best suited light beam is provided by a laser, structured by means of our metasurfaces technology. This is expected to result into enhanced beam quality for our applications.
Continuing towards the end of the project, the developed experimental schemes will feed back into the modellization for output optimization in view of the other milestones of the project.
structured-light purification mechanism