Metasurfaces are ultra-thin man-made materials made of periodically arranged subwavelength building blocks. They hold the promise of revolutionizing the interaction of electromagnetic radiation with matter, by offering novel properties unattainable with natural materials (anomalous refraction, near-zero permittivity, artificial magnetism), enabled by the resonant nature of their building blocks. At the same time, they are extremely thin with respect to the wavelength and amenable to standard planar manufacturing techniques.

However, there are specific physical limitations that restrict the potential of metasurfaces: (i) their response is typically narrowband and (ii) the phase delay that can be imparted on the incident wave is limited (less than 2π). PHOTOSURF aims to break free from these longstanding limitations by proposing broadband multiresonant metasurfaces that combine the advantages of strong resonant response (phase delay, energy storage, field enhancement) with an arbitrarily-broad spectral bandwidth controlled by the number of resonances. This is achieved by implementing a very specific combination of multiple electric and magnetic resonances which arise from meta-atoms properly arranged in the unit cell.

Having the broadband response as a common baseline, PHOTOSURF will address in a unified approach different physical problems, targeting the control of different aspects of the electromagnetic wave (temporal and spatial wavepacket profile, polarization, frequency). The broader scope of PHOTOSURF is to replace conventional dispersive, diffractive, polarization-converting, and nonlinear bulk components with ultra-thin counterparts, offering significant technological advantages (size, weight, fabrication, integration). The envisioned breakthroughs will open metasurfaces to real-world photonic applications, where signals are rarely narrowband (monochromatic).