Metamaterials are artificially fabricated materials that allow for the control of light and acoustic waves in a manner that is not possible in nature. This Review covers the recent developments in the study of so-called metasurfaces, which offer the possibility of controlling light with ultrathin, planar optical components. Conventional optical components such as lenses, waveplates and holograms rely on light propagation over distances much larger than the wavelength to shape wavefronts. In this way substantial changes of the amplitude, phase or polarization of light waves are gradually accumulated along the optical path. This Review focuses on recent developments on flat, ultrathin optical components dubbed 'metasurfaces' that produce abrupt changes over the scale of the free-space wavelength in the phase, amplitude and/or polarization of a light beam. Metasurfaces are generally created by assembling arrays of miniature, anisotropic light scatterers (that is, resonators such as optical antennas). The spacing between antennas and their dimensions are much smaller than the wavelength. As a result the metasurfaces, on account of Huygens principle, are able to mould optical wavefronts into arbitrary shapes with subwavelength resolution by introducing spatial variations in the optical response of the light scatterers. Such gradient metasurfaces go beyond the well-established technology of frequency selective surfaces made of periodic structures and are extending to new spectral regions the functionalities of conventional microwave and millimetre-wave transmit-arrays and reflect-arrays. Metasurfaces can also be created by using ultrathin films of materials with large optical losses. By using the controllable abrupt phase shifts associated with reflection or transmission of light waves at the interface between lossy materials, such metasurfaces operate like optically thin cavities that strongly modify the light spectrum. Technology opportunities in various spectral regions and their potential advantages in replacing existing optical components are discussed.

Flat Optics With Designer Metasurfaces

On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160)  Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

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The Observation of Gravitational Waves from a Binary Black Hole Merger

A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Since its discovery, the asymmetric Fano resonance has been a characteristic feature of interacting quantum systems. The shape of this resonance is distinctively different from that of conventional symmetric resonance curves. Recently, the Fano resonance has been found in plasmonic nanoparticles, photonic crystals, and electromagnetic metamaterials. The steep dispersion of the Fano resonance profile promises applications in sensors, lasing, switching, and nonlinear and slow-light devices.

The Fano resonance in plasmonic nanostructures and metamaterials

Bose-Einstein condensation (BEC) has been observed in a dilute gas of sodium atoms. A Bose-Einstein condensate consists of a macroscopic population of the ground state of the system, and is a coherent state of matter. In an ideal gas, this phase transition is purely quantum-statistical. The study of BEC in weakly interacting systems which can be controlled and observed with precision holds the promise of revealing new macroscopic quantum phenomena that can be understood from first principles.

Bose-Einstein condensation in a gas of sodium atoms


 Phonon lasers, exploiting coherent amplifications of phonons, have been a cornerstone for exploring quantum phononics, imaging nanomaterial structures, and realizing force sensors or phonon frequency combs. Single-mode phonon lasers, governed by dispersive optomechanical coupling, have been recently demonstrated via levitating a nanoparticle using an optical tweezer. Such levitated optomechanical (LOM) devices, with fundamental minimum of noises in high vacuum, can flexibly control large-mass objects with no internal discrete energy levels. However, it is still elusive to realize nonlinear multi-frequency phonon lasing with levitated microscale objects, dominated instead by dissipative LOM coupling due to much stronger optical scattering loss. Here, we report such a nonlinear phonon laser by employing a Yb3+-doped active LOM system. We observe a 3-order of magnitude enhancement for the fundamental-mode phonon lasing, compared with that in its passive counterparts. Above the lasing threshold, higher-order mechanical sidebands emerge spontaneously. Coherent correlations are also identified for the phonon modes. Our gain-assisted dissipative LOM platform no longer relies on any complicated external feedback control. Our work drives LOM into a new regime where it becomes promising to study mechanical properties or quantum entanglement of typical micro-size objects, such as atmospheric particulates and living cells, and build levitated force sensors with these objects for biomedical or astronomical applications.

https://www.researchsquare.com/article/rs-1252606/latest.pdf

Nonlinear phonon laser with dissipation-governed levitated optomechanics

We observed photonic nanojet mediated back-action owing to the light concentration at the focus of the microsphere and the absorption in immersion medium. Such back-action is a competing effect of light absorption and thermal conductivity.

Back-action of dielectric microparticles mediated by photonic nanojet

A unique recipe of achieving compound spiral photonic crystals (CSPCs) in three dimensions by holography is proposed, which is composed of unit cells with double right-handed (RH) spirals of π phase shift. Interferences between side beams in the umbrella-type configurations are employed to generate CSPCs. Chirality is pronounced, and paradoxical high RH transmission peaks appear exactly in the RH polarization gap. Fano resonances, which stems from the mode interferences between left-handed propagating modes along spiral axis (direct pathway) and negative group velocity modes in the extended Brillouin zone (resonance-assisted indirect pathway), is revealed and discussed. By analyzing Fourier spectra and chirality of the photonic eigenmodes, intrinsic mechanism of such a paradox is well understood by the mode coupling theory.

Fano resonance in 3-D compound spirals: Chiral quality, extraordinary transmission and polarization gap

The creation of wave-dynamic illusion functionality is of great interests to various scientific communities, which can potentially transform an actual perception into the pre-controlled perception, thus empowering unprecedented applications in the advanced-material science, camouflage, cloaking, optical and/or microwave cognition, and defense security, etc. By using the space transformation theory and engineering capability of metamaterials, we propose and realize a functional ghost illusion device, which is capable of creating wave-dynamic virtual ghost images off the original object's position under the illumination of electromagnetic waves. The scattering signature of the object is thus ghosted and perceived as multiple ghost targets with different geometries and compositions. The ghost-illusion material, being inhomogeneous and anisotropic, was realized by thousands of varying unit cells working at non-resonance. The experimental demonstration of the ghost illusion validates our theory of scattering metamorphosis and opens a novel avenue to the wave-dynamic illusion, cognitive deception, manipulate strange light or matter behaviors, and design novel optical and microwave devices.

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Creation of Ghost Illusions Using Metamaterials in Wave Dynamics

We propose a temporal superoscillatory pulse generation method by amplitude modulation. The cross correlation using temporal superoscillatory pulse as reference pulse is proposed and validated for ultrafast pulse characterization.

Cheng-Wei Qiu

Papers

Nonlinear phonon laser with dissipation-governed levitated optomechanics

Back-action of dielectric microparticles mediated by photonic nanojet

Fano resonance in 3-D compound spirals: Chiral quality, extraordinary transmission and polarization gap

Creation of Ghost Illusions Using Metamaterials in Wave Dynamics

Characterization of Ultrafast Pulse by Temporal Superoscillatory Pulse