Phased-array metamaterial systems are enabling new classes of refractive and diffractive optical elements through spatial-phase engineering. In this article, we develop design principles for reconfigurable optical antennas and metasurfaces. We theoretically demonstrate the tunability of infrared scattering phase and radiation patterns in low-loss, high-index dielectric resonators using free carrier refraction. We demonstrate reconfigurable endfire antennas based on interference between multiple elements. Within single resonators, we demonstrate reconfigurable broadside antenna radiation lobes arising from interfering electric and magnetic dipole resonances. Extending this concept to infinite arrays, we design ideal Huygens metasurfaces with spectrally overlapping electric and magnetic dipole resonances. By introducing free charge carriers into these metasurfaces, we demonstrate continuously tunable transmission phase between 0 and 2π with less than 3 dB loss in intensity. Such tunable metasurfaces may form the basis for reconfigurable metadevices that enable unprecedented control over the electromagnetic wavefront.

Phased-array metasurfaces have been extensively used for wavefront shaping of coherent incident light. Due to the incoherent nature of spontaneous emission, the ability to similarly tailor photoluminescence remains largely unexplored. Recently, unidirectional photoluminescence from InGaN/GaN quantum-well metasurfaces incorporating one-dimensional phase profiles has been shown. However, the possibility of generating arbitrary two-dimensional waveforms-such as focused beams-is not yet realized. Here, we demonstrate two-dimensional metasurface axicons and lenses that emit collimated and focused beams, respectively. First, we develop off-axis meta-axicon/metalens equations designed to redirect surface-guided waves that dominate the natural emission pattern of quantum wells. Next, we show that photoluminescence properties are well predicted by passive transmission results using suitably engineered incident light sources. Finally, we compare collimating and focusing performances across a variety of different light-emitting metasurface axicons and lenses. These generated two-dimensional phased-array photoluminescence waveforms facilitate future development of light sources with arbitrary functionalities.

III-Nitride light emitting diodes (LEDs) are the backbone of ubiquitous lighting and display applications. Imparting directional emission is an essential requirement for many LED implementations. Although optical packaging, nano-patterning and surface roughening techniques can enhance LED extraction, directing the emitted light requires bulky optical components. Optical metasurfaces provide precise control over transmitted and reflected waveforms, suggesting a new route for directing light emission. However, it is difficult to adapt metasurface concepts for incoherent light emission, due to the lack of a phase-locking incident wave. In this Letter, we demonstrate metasurface-based design of InGaN/GaN quantum-well structures that generate narrow, unidirectional transmission and emission lobes at arbitrary engineered angles. We show that the directions and polarization of emission differ significantly from transmission, in agreement with an analytical Local Density of Optical States (LDOS) model. The results presented in this Letter open a new paradigm for exploiting metasurface functionality in light emitting devices.