Title: Advances in gallium nitride metalenses

Abstract

The rapid development of optical metasurfaces has been driven by the desire for the miniaturization of optical devices. Also, the metasurfaces realize the novel optical phenomena that are unattainable from conventional bulky and heavy optics. However, the first proposed and studied metasurfaces made of metal nano-antennas severely limit their applications because of low transmission efficiency and weak-cross polarization conversion. Thus, the all- dielectric metasurfaces have rapidly received much attraction, propelled by innovation from many groups around the world. As one of the most tremendous applications of the metasurfaces, metalenses have rapidly attracted much attention. However, highly efficient metalenses at visible wavelengths require the development of high-aspect-ratio dielectric nanostructures. Various dielectric nano- resonators have been proposed as sub-wavelength constituents for the construction of the visible metalenses. These dielectric nano-resonators can be classified according to different shapes and materials. This talk will present various dielectric materials and different kinds of nano-resonators. Then we will focus on a third-generation semiconductor named as Gallium nitride (GaN) combined with a newly developed hexagon-resonated element (HRE) to achieve metalenses of high performance in the visible. Also, well-developed fabrication techniques have been employed to realize the high-aspect-ratio metalenses working at three distinct visible wavelengths with diffraction-limited focusing efficiencies as high as 93%. The 1951 United States Air Force (USAF) test chart has been chosen to characterize the imaging capability. All of the images formed by the polarization-insensitive metalens show exceptional clear line features, and the smallest resolvable features are lines with widths of 870 nm.

Biography

Vin-Cent Su received his Ph.D. degree from the Graduate Institute of Electrical Engineering, National Taiwan University in 2013. He is currently an Associate Professor of Electrical Engineering Department, National United University. His current research interests include metasurfaces and their applications, light-emitting diodes (LEDs), optoelectronics, high-electron-mobility transistors(HEMTs) and biomedicine.