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Shaping Ultraviolet Light with Dielectric Metasurfaces
1  Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), Singapore


Metasurfaces are comprised of two-dimensional (2D) subwavelength metal/dielectric structures produced in a planer fashion to be able to introduce abrupt changes in optical properties, enabling users’ independence of propagation effect in contrast to the heavy dependence of conventional bulky optical elements. Based on optimization algorithm, metasurfaces can be rigorously engineered to tailor their the amplitude and phase responses to achieve a variety of manipulations, such as wavefronts control of incident beams, beam focusing and steering, polarization conversion and angular momentum manipulation. It opens a new avenue in the context of photonic miniaturization to scale traditional bulky optical items down to ultrathin and ultracompact components, which has been a rapidly growing research fields in recent years.       


Typically metasurfaces can be realized by two different strategies from the materials perspectives. It can be made of plasmonic materials being of a negative permittivity such as metals, doped semiconductors, transition metal oxides and nitrides. However, their efficiency is greatly limited due to intrinsic absorption losses across a wide spectrum from THz to visible wavelengths. The other way is to employ high refractive index and low loss dielectrics to achieve high efficiency. Recently, relatively high aspect-ratio nano-pillars without resonances of unit cells have been demonstrated to achieve high efficiency of 80%-90% in the transmission mode. Silicon (amorphous, poly- & single crystalline) and titanium dioxide have been overwhelmingly utilized for the spectrum spanning the infrared to visible regime. Unfortunately, these materials exhibit relatively high loss in the ultraviolet (UV) range while high efficiency UV light metasurfaces hasn’t been demonstrated yet for exploitation of this essential optical domain. To address it, in this talk, I will introduce our latest achievement in the development of high aspect ratio nanostructured dielectric metasurfaces with high efficiency in the UV range and metasurfaces devices have been fabricated to demonstrate focusing and hologram. This work facilitates metasurfaces to find applications in optical nanolithography and anticounterfeiting and extend the operating wavelength of high efficiency metasurfaces from infrared, visible to the UV regime.