High-refractive index dielectric nanostructures with both electric and magnetic responses to external optical field have recently become a hot topic in nanophotonics. The resonances inside these particles at subwavelength scale are governed by the nanoparticle geometry and can be described by Mie theory. There has been many potential applications based on this concept such as: light beam focusing, bending, hologram generation, etc. Recently, lasing behavior have been realized in these systems by combining these resonance with the bound state in the continuum. In this presentation, we will show how to engineer these resonances and their strong coupling effect to create effective optical cavities for lasing with controlled emission directionality both in-plane and out-of-plane. The coupling of Mie resonances will be discussed in three different cases: 2D arrays, 1D chains and single nanoparticles. In all cases, by carefully designing the geometry and periodicity of these nanoparticles, highly localized states or so-called supercavities can be formed by strong coupling of dipole or multipole resonances of individual nanoparticles. Using GaAs – a common III-V semiconductor- as both dielectric nanoantenna and gain medium, we demonstrate experimentally unprecedented lasing behavior in these systems by optical pumping at cryogenic temperature. Our design concept will provide a guideline for nanolasers with controllable directionality for optoelectronic applications.
We numerically and experimentally demonstrate that metasurfaces can be used to control the light emission from light emitting diodes (LED). This control provides a desired wavefront and functionality of the light emission in addition to enhancing light extraction efficiency. Simply placing the metasurface on top of the LED does not work as conventional metasurface designs require plane wave excitation, which LEDs cannot provide. To overcome this challenge we implement a novel concept using internal and external resonant cavities combined with the LED. Guided by our numerical simulations, we experimentally demonstrate this concept by fabricating Si and TiO2 metasurfaces on top of the resonant cavity LED structures. The integration of these metasurfaces with commercially available GaN and GaP LED devices show full wavefront control, beam deflection and beam collimation. Both the cavity and the metasurface enhance the LED radiation. Moreover, following the proposed principle, any random light emitting sources including fluorescent molecules and quantum dots can be integrated into a similar optical device to achieve focusing, beam deflecting, vortex beam generation and other capabilities.