Dynamically reconfigurable metasurfaces (Presentation Recording)

Abstract

Recently, the use of phased array metasurfaces to control the phase and amplitude of electromagnetic waves at subwavelength dimensions have led to large number of devices ranging from flat optical elements to holographic projections. Here we analytically (and numerically using FDTD techniques) develop a design principle to form reconfigurable metasurfaces that control the phase of transmitted beam between 0 and 2π in a lossless manner. For a linearly polarized plane wave incident on a sub-wavelength array of dielectric resonators, we engineer the size of the individual resonators and the array periodicity such that the fundamental Electric and Magnetic dipole resonances of the device cross each other. This mode crossing caused by coupling of individual resonator modes with the surface lattice resonances, constructively interferes with the incident plane wave enabling us to form lossless metasurfaces. By optically pumping charge carriers into the resonators, we can tune the refractive index of the individual resonators leading to arbitrary control over the phase of the transmitted beam between 0 and 2π with less than 3dB loss in intensity. Further, we extend these strategies by redesigning the resonator elements by forming core-shell (metal-dielectric) resonators to cause the resonance matching within each resonator. This enables the mode crossing to be independent of the periodicity of the resonator elements while preserving the arbitrary control over the phase through charge carrier modulation. Such metasurfaces with spectrally overlapping electric and magnetic dipole modes may form the basis for a range of metadevices with unprecedented control over the Electromagnetic wave front.