Reconfigurable Semiconductor Phased-Array Metasurfaces

Abstract

Phased array metamaterial systems are enabling new classes of refractive and diffractive optical elements through spatial-phase engineering. In this letter, we develop design principles for reconfigurable optical antennas and metasurfaces. We theoretically demonstrate 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 2ߨ with less than 3dB loss in intensity. Such tunable metasurfaces may form the basis for reconfigurable metadevices that enable unprecedented control over the electromagnetic wave front.Antenna and metamaterial systems that can dynamically steer optical frequency beams is a pivotal area of research with applications ranging from Lidar technologies 1 , sensors 2,3 , to interand intra-chip communication 4 in nano-photonic circuits. Steering beams with metamaterials requires the ability to continuously tune the phase of scattered, reflected, or transmitted waves between 0 and 2π. Thus, there has been extensive research to construct devices which control the phase of scattered waves in a low loss manner. 5 Metamaterial devices that exploit phase engineering include flat optical elements, 6 polarization converters, 7-9 holographic projectors, 10 and optical vortex beam generators. 11 Arbitrary control of the wavelength dependent phase enables the miniaturization of bulk refractive (linear) and diffractive (interference based) optical elements to metamaterial based devices. [12][13][14] Phased array metamaterials and metasurfaces comprise assemblies of engineered optical antennas. Optical antenna systems that control the phase of transmitted, reflected, or scattered fields have mainly been built from metallic elements. Researchers have demonstrated numerous metallic optical antennas based on scaled-down bow-tie, 15 patch, 16 and split-ring 17 RF design principles for extreme concentration of light. 18 These single-element antennas typically emit dipolar radiation patterns. By exploiting phased-array concepts, multi-element optical antenna systems can support directional radiation patterns. transimitting 12 or reflecting 21-24 infrared metasurfaces, wherein the optical phase is engineered through antenna shape and size. 25 A broader challenge is to achieve such metamaterial phased arrays in a reconfigurable manner. To achieve reconfigurable properties, researchers have considered electromechanically tuning the dimensions of the resonators, 26 phase change media based antennas, 27 graphene based mod...

A review of metasurfaces: physics and applications

“…It was shown that the electric resonance has a larger tuning range because of the extending fringing field outside the resonators, while the magnetic resonance has minimal tuning capability because of the well-confined field distribution within the dielectric resonators. Reconfigurable directional scattering can be also accomplished using metasurfaces comprised of semiconducting resonator arrays through injection of free charge carriers by optical excitation [144].…”

Electrically Reconfigurable Metasurfaces Using Heterojunction Resonators

“…Our design ultimately requires suffi cient width to incorporate metallic electrodes in these side regions of low E-fi eld intensity; throughout this paper we use 3 μm wide resonators. Since introducing free-carriers causes a resonance blueshift, [ 36 ] we design the initial resonance wavelength (13.5 μm) red shifted with respect to the operating wavelength (11.35 μm) by selecting a resonator height of 1 μm.…”

“…spherical InSb Mie resonators [ 36 ] showed that the index change (Δ n ≈ 2 based on Drude model) from a doping concentration of 1.5 × 10 18 cm −3 was suffi cient to obtain 2π phase shifts. We use a worst-case Drude scattering rate of 2 THz, reported for highly doped InSb, [ 32 ] for all carrier densities.…”

“…InSb [31][32][33] or InAs [ 27,34,35 ] support free-carrier index shifts of this magnitude due to their high mobility and low electron effective mass. In our previous theory work, [ 36 ] we demonstrated full 2π tuning of the transmission phase of semiconductor metasurface by modulating the carrier concentration in InSb resonators between 10 17 -10 18 cm −3 . However, we did not consider how to achieve such modulation.…”

All-Dielectric Nanophotonics: Fundamentals, Fabrication, and Applications

“…Therefore, implementation of plasmonic principles for developing of all-dielectric nonlinear nanodevices looks tempting. Recently, the enhancement of optical nonlinearities in resonant Si nanostructures has been demonstrated theoretically and experimentally at the scale of single nanoparticles [58][59][60][61][194][195][196][197].…”