The goal of this proposal is to implement broadband giant refraction (n>10) to achieve a basic building block in what could be termed a white-light photonics, an all-purpose achromatic white-light transducer. The white-light transducer will be able to transfer with maximum efficiency light from any angle of incidence to a photosensitive sensor, irrespective of the input angle, achieving, for example, a self-aligning imaging system or a self-aligning solar panel.
Materials with a high index of refraction in the visible spectrum of electromagnetic field are strongly sought for their potentially revolutionary impact on optical devices. In microscopy, the minimum resolution of an optical microscope scales with index of refraction, so that a giant index of refraction makes even a rudimentary table-top microscope capable of directly observing nanoscale objects. In solar-panel technology, the higher the index of refraction, the stronger the focusing of solar light and the more efficient the energy harvesting. In optical quantum technology, giant indexes of refraction promise stronger localisation and the opportunity of achieving photon-to-photon interaction. In image transmission, a giant index of refraction effectively halts distortions associated to diffraction.
To date, GR has only been observed in the microwave and at Terahertz frequencies, while the maximum reported broadband refraction in the visible is less than 5.
In a recent set of experiments, we have demonstrated that a nanodisordered ferroelectric perovskite (KTN:Li) can manifest a giant index of refraction (n>26) for the whole visible spectrum (F. Di Mei et al., Nature Photonics, 2018). With n>26 the material is able to project visible light, of any colour, and even white incoherent light, from its input to its output, without diffraction and chromatic dispersion, irrespective of beam size, numerical aperture, wavelength (400-700 nm), coherence (from single-mode laser to white projector lamp light), intensity, and input direction (input angles up to -40 to 40 degrees to the normal). The giant index causes the material to become an ideal imaging device: for light, it is as if the input and output facets of the material coincide. The phenomenon occurs at the Critical room-temperature Tc, specifically 15 degrees Celsius, in which a strongly correlated three-dimensional ordered mosaic of spontaneous polarisation, called Super-Crystal (D. Pierangeli et al. ’Super-crystals in composite ferroelectrics,’ Nature Communications 7, 10674, 2016), emerges and causes the huge increase in dielectric susceptibility required to observe the giant index of refraction.
Specific offsprings of our proposal would then be, from a fundamental perspective, the emergence of a wavelength-independent optics, while from the applicative standpoint, the ability to develop highly integrated and miniaturised photonics for incoherent light, such as light from a LED or directly from the Sun.