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Topic A: With the recent advances in micro and nanofabrication methods it is possible to control the flow of light in a way that was not possible before. In particular, metasurfaces have aroused wide interest because they allow to build devices with responses to light that are unattainable with naturally available materials. Metasurfaces are represented by a patterned metal-dielectric layer that is very thin compared with the wavelength of the incident light and is typically deposited on a supporting substrate. The propagation of electromagnetic waves in these structures can be defined by the spatial and spectral dispersion of the effective dielectric properties, so it is possible to tune the composition and morphology of the nanostructure in order to achieve new desired functionalities. Moreover, thanks to their bidimensionality, they are compatible with on-chip nanophotonics devices, which is of critical importance for future applications in opto-electronics, microscopy, imaging and sensing. This could lead to a variety of devices enabling extraordinary light modulation and control: by engineering a phase discontinuity along an interface it’s possible to fully steer light. In this area, one of the most interesting application for metasurfaces can be related to the realization of ultrathin, deeply subwavelength spatial light modulators, which can also provide ultrafast and dynamically controlled responses. (P.I. Emanuela Esposito)

Topic B: Metallic structures are not the only way to achieve light control and confinement. Strong electromagnetic-field enhancement is achievable also in dielectric structures, such as photonic crystal cavity or slab, by exploiting resonance phenomena, allowing the light guiding and trapping. In general when an incident beam impinges on a lattice the reflected beam can have anomalous variation of the reflected signal. Specifically, it has been demonstrated that perfect light confinement can be achieved because of a particular type of localized state, named Bound state in the continuum. When a bound state in continuum occurs, the electromagnetic field is trapped by the structure for an infinite time and, experimentally, this implies very narrow resonances with an high Q-value coupled in an open structure. In order to experimentally detect and then apply this phenomenon, silicon nitride photonic crystals are designed, fabricated and characterized. Starting from the interesting results that we found, we are going to test some appealing applications, such as the realization of high-sensitive biosensors and enhancing Raman spectroscopy substrates. In order to manage this activity, strong collaborations are established with different research groups. (P.I. Vito Mocella)

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