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If current production and waste management trends continue, it is projected that roughly 12 billion metric tons of plastic waste will be in landfills or in the natural environment by 2050. Plastics represent a significant environmental problem: They are for the most part not biodegradable, cause problems for terrestrial and aquatic life, and enter the food chain in the form of microplastics. .
Photonic sensors are ideally suited for material sorting due to the spectroscopy technique, which allows for discrimination between different polymer types by illuminating with near infrared electromagnetic fields and measuring absorption. An important development goal is to make such spectroscopy simple, affordable and energy efficient. The ElastoMETA project aims to design and fabricate functional nanostructured surfaces, known as metasurfaces, to meet these goals. These surfaces contain simple subwavelength nano-structures that can shape light which is transmitted through them. Despite their simplicity, they offer a new paradigm for advanced field manipulation due to unprecedented control of phase, polarization, amplitude and dispersion of the electromagnetic fields. The versatility of this approach is evident by the short time during which numerous realizations have been made: e.g. micro-lenses, filters, couplers, emitters and even holograms. With further development, metasurfaces are expected to have several advantages over existing optical sensor technologies for recycling applications (e.g. diffractive optics), in terms of (i) increased efficiency, (ii) relative ease of fabrication, and (iii) enhanced functionality.