Optical properties of natural materials have been numerically and experimentally characterized in order to understand their function in living organisms and, furtherly, to exploit them in bio-based and bio-inspired photonic devices. In particular, lot of effort has been devoted to the study of diatoms. Diatoms, monocellular microalgae responsible for about 20-25% of the global primary production, are characterized by a porous siliceous shell, the frustule, which is covered by regular patterns of micro/nanometric perforations thus resembling an artificial photonic crystal; it allows to optimize light harvesting in environments where sunlight is not easiliy accesible. Optical properties of frustules comprise, among others, light confinement and focusing (whose efficiency is strongly dependent by wavelength), light-guided mode coupling, and photoluminescence. Optical, mechanical and structural properties of diatom frustules can be exploited in several applications: design and development of highly efficient solar cells; plasmonics and SERS; sub-diffractive optics; photoluminescence-based sensors and biosensors; molding in micro- and nano- devices fabrications.
Numerical simulations based con Beam Propagation Method (BPM), Finite Difference Time Domain (FDTD) and Finite Integration Technique (FIT) algorithms are used to study the propagation of optical fields in the intricate ultra-structures of the frustule; transmission imaging and digital holography allows to study the spatial distribution of light after interaction with frustules; a photoluminescence set-up is used to study the emission spectra of frustules after UV/blue excitation.
The expertise gained in these years with diatom photonics can be applied in the study of other living organisms photonic structures (butterfly scales; beetle cuticles; fly eyes etc.).