Achromatic super-oscillatory lenses with subwavelength focusing

Lenses are crucial to light-enabled technologies.Conventional lenses have been perfected to achieve near-diffraction-limited resolution and minimal chromatic aberrations.However,such lenses are bulky and cannot focus light into a hotspot smaller than a half-wavelength of light.Pupil filters,initially suggested by Toraldo di Francia,can overcome the resolution constraints of conventional lenses but are not intrinsically chromatically corrected.Here we report single-element planar lenses that not only deliver sub-wavelength focusing,thus beating the diffraction limit of conventional refractive lenses,but also focus light of different colors into the same hotspot.Using the principle of super-oscillations,we designed and fabricated a range of binary dielectric and metallic lenses for visible and infrared parts of the spectrum that are manufactured on silicon wafers,silica substrates and optical fiber tips.Such low-cost,compact lenses could be useful in mobile devices,data storage,surveillance,robotics,space applications,imaging,manufacturing with light and spatially resolved nonlinear microscopies.

The magnetic response of graphene split-ring metamaterials

Graphene has emerged as a promising platform for THz plasmonics,allowing high confinement,long lifetimes and fast electrical tunability.Here,we predict a strong magnetic dipole response by graphene split nanorings at THz frequencies,allowing the attainment of metamaterials with a high degree of field confinement(approximately one hundredth of the excitation wavelength)that is not reachable with conventional noble metals.The magnetic response of highly doped graphene split-rings in the far-infrared is much stronger than that displayed by gold structures of similar thicknesses.We further explored stacked graphene layers as a practical way of producing high-frequency magnetism in thin,electrically tunable metamaterials.Our results support the great potential of using graphene to achieve electrically tunable magnetic metamaterials.

Two-dimensional control of light with light on metasurfaces

The ability to control the wavefront of light is fundamental to focusing and redistribution of light,enabling many applications from imaging to spectroscopy.Wave interaction on highly nonlinear photorefractive materials is essentially the only established technology allowing the dynamic control of the wavefront of a light beam with another beam of light,but it is slow and requires large optical power.Here we report a proof-of-principle demonstration of a new technology for two-dimensional(2D)control of light with light based on the coherent interaction of optical beams on highly absorbing plasmonic metasurfaces.We illustrate this by performing 2D all-optical logical operations(AND,XOR and OR)and image processing.Our approach offers diffractionlimited resolution,potentially at arbitrarily-low intensity levels and with 100 THz bandwidth,thus promising new applications in space-division multiplexing,adaptive optics,image correction,processing and recognition,2D binary optical data processing and reconfigurable optical devices.

Controlling light with light using coherent metadevices: all-optical transistor, summator and invertor

Although vast amounts of information are conveyed by photons in optical fibers,the majority of data processing is performed electronically,creating the infamous‘information bottleneck’and consuming energy at an increasingly unsustainable rate.The potential for photonic devices to directly manipulate light remains unfulfilled due largely to a lack of materials with strong,fast optical nonlinearities.In this paper,we show that small-signal amplifier,summator and invertor functions for optical signals may be realized using a four-port device that exploits the coherent interaction of beams on a planar plasmonic metamaterial,assuming no intrinsic nonlinearity.The redistribution of energy among ports can provide nonlinear input-output signal dependencies and may be coherently controlled at very low intensity levels,with multi-THz bandwidth and without introducing signal distortion,thereby presenting powerful opportunities for novel optical data processing architectures,complexity oracles and the locally coherent networks that are becoming part of the mainstream telecommunications agenda.

Controlling light-with-light without nonlinearity

According to the fundamental Huygens superposition principle,light beams traveling in a linear medium will pass though one another without mutual disturbance.Indeed,the field of photonics is based on the premise that controlling light signals with light requires intense laser fields to facilitate beam interactions in nonlinear media,where the superposition principle can be broken.Here we challenge this wisdom and demonstrate that two coherent beams of light of arbitrarily low intensity can interact on a metamaterial layer of nanoscale thickness in such a way that one beam modulates the intensity of the other.We show that the interference of beams can eliminate the plasmonic Joule losses of light energy in the metamaterial or,in contrast,can lead to almost total absorption of light.Applications of this phenomenon may lie in ultrafast all-optical pulse-recovery devices,coherence filters and terahertz-bandwidth light-by-light modulators.

Nonlinear dielectric optomechanical metamaterials

We introduce a dielectric photonic metamaterial presenting a giant nonlinear optical response driven by resonant optomechanical forces.Being inherently free of Joule losses,it exhibits optical bistability at intensity levels of less than 0.2 mW mm22 and,furthermore,manifests nonlinear asymmetric transmission with a forward:backward optical extinction ratio of more than 30 dB.

Wavevector Selective Metasurfaces and Tunnel Vision Filters

Metasurfaces offer unprecedented flexibility in the design and control of light propagation,replacing bulk optical components and exhibiting exotic optical effects.One of the basic properties of the metasurfaces,which renders them as frequency selective surfaces,is the ability to transmit or reflect radiation within a narrow frequency band that can be engineered on demand.Here we introduce and demonstrate experimentally in the THz domain the concept of wavevector selective surfaces–metasurfaces transparent only within a narrow range of light propagation directions operating effectively as tunnel vision filters.Practical implementations of the new concept include applications in wavefront manipulation,observational instruments,vision and free-space communication in light-scattering environments.

Quantum super-oscillation of a single photon

Super-oscillation is a counterintuitive phenomenon describing localized fast variations of functions and fields that happen at frequencies higher than the highest Fourier component of their spectra.The physical implications of this effect have been studied in information theory and optics of classical fields,and have been used in super-resolution imaging.As a general phenomenon of wave dynamics,super-oscillations have also been predicted to exist in quantum wavefunctions.Here we report the experimental demonstration of super-oscillatory behavior of a single-quantum object,a photon.The super-oscillatory behavior is demonstrated by tight localization of the photon wavefunction after focusing with an appropriately designed slit mask to create an interference pattern with a sub-diffraction hotspot(~0.45λ).Such quantum super-oscillation can be used for low-intensity far-field super-resolution imaging techniques even down to single-photon counting regime,which would be of interest to quantum physics and non-invasive and label-free biological studies.

All-optical dynamic focusing of light via coherent absorption in a plasmonic metasurface

Vision,microscopy,imaging,optical data projection and storage all depend on focusing of light.Dynamic focusing is conventionally achieved with mechanically reconfigurable lenses,spatial light modulators or microfluidics.Here we demonstrate that dynamic control of focusing can be achieved through coherent interaction of optical waves on a thin beam splitter.We use a nanostructured plasmonic metasurface of subwavelength thickness as the beam splitter,allowing operation in the regimes of coherent absorption and coherent transparency.Focusing of light resulting from illumination of the plasmonic metasurface with a Fresnel zone pattern is controlled by another patterned beam projected on the same metasurface.By altering the control pattern,its phase,or its intensity,we switch the lens function on and off,and alter the focal spot’s depth,diameter and intensity.Switching occurs as fast as the control beam is modulated and therefore tens of gigahertz modulation bandwidth is possible with electro-optical modulators,which is orders of magnitude faster than conventional dynamic focusing technologies.

An optical fiber network oracle for NP-complete problems

The modern information society is enabled by photonic fiber networks characterized by huge coverage and great complexity and ranging in size from transcontinental submarine telecommunication cables to fiber to the home and local segments.This world-wide network has yet to match the complexity of the human brain,which contains a hundred billion neurons,each with thousands of synaptic connections on average.However,it already exceeds the complexity of brains from primitive organisms,i.e.,the honey bee,which has a brain containing approximately one million neurons.In this study,we present a discussion of the computing potential of optical networks as information carriers.Using a simple fiber network,we provide a proof-of-principle demonstration that this network can be treated as an optical oracle for the Hamiltonian path problem,the famous mathematical complexity problem of finding whether a set of towns can be travelled via a path in which each town is visited only once.Pronouncement of a Hamiltonian path is achieved by monitoring the delay of an optical pulse that interrogates the network,and this delay will be equal to the sum of the travel times needed to visit all of the nodes(towns).We argue that the optical oracle could solve this NP-complete problem hundreds of times faster than brute-force computing.Additionally,we discuss secure communication applications for the optical oracle and propose possible implementation in silicon photonics and plasmonic networks.