Showing papers by "Yuri S. Kivshar published in 2011"

Light propagation and localization in modulated photonic lattices and waveguides

Abstract: We review both theoretical and experimental advances in the recently emerged physics of modulated photonic lattices. Artificial periodic dielectric media, such as photonic crystals and photonic lattices, provide a powerful tool for the control of the fundamental properties of light propagation in photonic structures. Photonic lattices are arrays of coupled optical waveguides, where the light propagation becomes effectively discretized. Such photonic structures allow one to study many useful optical analogies with other fields, such as the physics of solid state and electron theory. In particular, the light propagation in periodic photonic structures resembles the motion of electrons in a crystalline lattice of semiconductor materials. The discretized nature of light propagation gives rise to many new phenomena which are not possible in homogeneous bulk media, such as discrete diffraction and diffraction management, discrete and gap solitons, and discrete surface waves. Recently, it was discovered that applying periodic modulation to a photonic lattice by varying its geometry or refractive index is very much similar to applying a bias to control the motion of electrons in a crystalline lattice. An interplay between periodicity and modulation in photonic lattices opens up unique opportunities for tailoring diffraction and dispersion properties of light as well as controlling nonlinear interactions.

Generation and Near-Field Imaging of Airy Surface Plasmons

Abstract: We demonstrate experimentally the generation and near-field imaging of nondiffracting surface waves, plasmonic Airy beams, propagating on the surface of a gold metal film. The Airy plasmons are excited by an engineered nanoscale phase grating, and demonstrate significant beam bending over their propagation. We show that the observed Airy plasmons exhibit self-healing properties, suggesting novel applications in plasmonic circuitry and surface optical manipulation.

Active and tunable metamaterials

Abstract: Metamaterial research is an extremely important global activity that promises to change our lives in many different ways. These include making objects invisible and the dramatic impact of metamaterials upon the energy and medical sectors of society. Behind all of the applications, however, lies the business of creating metamaterials that are not going to be crippled by the kind of loss that is naturally heralded by use of resonant responses in their construction. This review sets out some solutions to the management of loss and gain, coupled to controlled and nonlinear behavior, and discusses some critical consequences concerning stability. Under the general heading of active and tunable metamaterials, an international spectrum of authors collaborates here to present a set of solutions that addresses these issues in several directions. As will be appreciated, the range of possible solutions is really fascinating, and it is hoped that these discussions will act as a further stimulus to the field.

Nonlinearly PT-symmetric systems: Spontaneous symmetry breaking and transmission resonances

Abstract: We consider a class of $\mathcal{PT}$-symmetric systems which include mutually matched nonlinear loss and gain (in other words, a class of $\mathcal{PT}$-invariant Hamiltonians in which both the harmonic and anharmonic parts are non-Hermitian). For a basic system in the form of a dimer, symmetric and asymmetric eigenstates, including multistable ones, are found analytically. We demonstrate that, if coupled to a linear chain, such a nonlinear $\mathcal{PT}$-symmetric dimer generates previously unexplored types of nonlinear Fano resonances, with completely suppressed or greatly amplified transmission, as well as a regime similar to the electromagnetically induced transparency. The implementation of the systems is possible in various media admitting controllable linear and nonlinear amplification of waves.

Engineered optical nonlocality in nanostructured metamaterials

Abstract: We analyze dispersion properties of layered metal-dielectric structures, which can be considered as a simple example of nanostructured metamaterials. We demonstrate that, in sharp contrast to the results of the theory of effective media, the layered structure demonstrates strong optical nonlocality due to excitation of surface plasmon polaritons. Such nonlocality can be engineered by changing a ratio between the thicknesses of metal and dielectric layers. Importantly, the nonlocality leads to the existence of an additional extraordinary wave that manifests itself in the splitting of the transverse-magnetic polarized beam refracted at an air-metamaterial interface.

Magnetoelastic metamaterials

Abstract: We propose and demonstrate experimentally a novel type of nonlinearity in metamaterials, which is induced by mechanical deformation of the structure. The nonlinearity arises from the introduction of an extra degree of freedom in the metamaterial, which allows for elastic displacement of the strongly interacting structural elements (see Fig. 1a). This type of nonlinearity relies on the counterplay between the electromagnetic attraction and the elastic repulsion, and the induced deformation alters the electromagnetic response of the entire structure, leading to the novel nonlinear response of the metamaterial.

Magnetoelastic nonlinear metamaterials

Abstract: We introduce the concept of magnetoelastic metamaterials with electromagnetic properties depending on elastic deformation. We predict a strong nonlinear and bistable response of such metamaterials caused by their structural reshaping in response to the applied electromagnetic field. In addition, we demonstrate experimentally the feasibility of the predicted effect.

Spontaneous radiation of a finite-size dipole emitter in hyperbolic media

Abstract: We study the radiative decay and Purcell effect for a finite-size dipole emitter placed in a homogeneous uniaxial medium. We demonstrate that the radiative rate is strongly enhanced when the signs of the medium longitudinal and transverse dielectric constants are opposite, and that the isofrequency contour corresponds to a hyperbolic medium. We reveal that the Purcell enhancement factor remains finite even in the absence of losses and that it depends on the emitter size.

Plasmonic Airy beam manipulation in linear optical potentials

Abstract: We demonstrate, both theoretically and numerically, the efficient manipulation of plasmonic Airy beams in linear optical potentials produced by a wedged metal-dielectric-metal structure By varying the angle between the metallic plates, we can accelerate, compensate, or reverse the self-deflection of the plasmonic Airy beams without compromising the self-healing properties We also show that in the linear potentials the Airy plasmons of different wavelengths could be routed into different directions, creating new opportunities for optical steering and manipulation

Electromagnetic wave analogue of an electronic diode

Abstract: An electronic diode is a nonlinear semiconductor circuit component that allows conduction of electrical current in one direction only. A component with similar functionality for electromagnetic waves, an electromagnetic isolator, is based on the Faraday effect of rotation of the polarization state and is also a key component in optical and microwave systems. Here we demonstrate a chiral electromagnetic diode, which is a direct analogue of an electronic diode: its functionality is underpinned by an extraordinarily strong nonlinear wave propagation effect in the same way as the electronic diode function is provided by the nonlinear current characteristic of a semiconductor junction. The effect exploited in this new electromagnetic diode is an intensity-dependent polarization change in an artificial chiral metamolecule. This microwave effect exceeds a similar optical effect previously observed in natural crystals by more than 12 orders of magnitude and a direction-dependent transmission that differs by a factor of 65.

Nonlocal effective medium model for multilayered metal-dielectric metamaterials

Abstract: We study layered metal-dielectric structures, which can be considered as a simple example of nanostructured metamaterials. We analyze the dispersion properties of such structures and demonstrate that they show strong optical nonlocality due to excitation of surface plasmon polaritons. We derive a model of a nonlocal effective medium for describing the effects of strong spatial dispersion in the multilayered metal-dielectric metamaterials. We obtain analytical expressions for the components of the effective permittivity tensor which depend on the wave vector and reveal that spatial dispersion effects exist in both directions across and along the layers.

Huygens optical elements and Yagi—Uda nanoantennas based on dielectric nanoparticles

Abstract: A new class of optical nanoantennas based on dielectric nanoparticles has been proposed and their main characteristics have been analyzed. It has been shown that one dielectric nanoparticle can have the properties of a Huygens element in the optical wavelength range. A Yagi-Uda nanoantenna based on dielectric nano-particles has been studied analytically and numerically.

Solitons in a chain of parity-time-invariant dimers.

Abstract: Dynamics of a chain of interacting parity-time-invariant nonlinear dimers is investigated. A dimer is built as a pair of coupled elements with equal gain and loss. A relation between stationary soliton solutions of the model and solitons of the discrete nonlinear Schrodinger (DNLS) equation is demonstrated. Approximate solutions for solitons whose width is large in comparison to the lattice spacing are derived, using a continuum counterpart of the discrete equations. These solitons are mobile, featuring nearly elastic collisions. Stationary solutions for narrow solitons, which are immobile due to the pinning by the effective Peierls-Nabarro potential, are constructed numerically, starting from the anticontinuum limit. The solitons with the amplitude exceeding a certain critical value suffer an instability leading to blowup, which is a specific feature of the nonlinear parity-time-symmetric chain, making it dynamically different from DNLS lattices. A qualitative explanation of this feature is proposed. The instability threshold drops with the increase of the gain-loss coefficient, but it does not depend on the lattice coupling constant, nor on the soliton's velocity.

Discrete breathers in deformed graphene

Abstract: The linear and nonlinear dynamics of elastically deformed graphene have been studied. The region of the stability of a planar graphene sheet has been represented in the space of the two-dimensional strain (ɛ xx , ɛ yy ) with the x and y axes oriented in the zigzag and armchair directions, respectively. It has been shown that the gap in the phonon spectrum appears in graphene under uniaxial deformation in the zigzag or armchair direction, while the gap is not formed under a hydrostatic load. It has been found that graphene deformed uniaxially in the zigzag direction supports the existence of spatially localized nonlinear modes in the form of discrete breathers, the frequency of which decreases with an increase in the amplitude. This indicates soft nonlinearity in the system. It is unusual that discrete breather has frequency within the phonon spectrum of graphene. This is explained by the fact that the oscillation of the discrete breather is polarized in the plane of the graphene sheet, while the phonon spectral band where the discrete breather frequency is located contains phonons oscillating out of plane. The stability of the discrete breather with respect to the small out-of-plane perturbation of the graphene sheet has been demonstrated.

Near-field interaction of twisted split-ring resonators

Abstract: We experimentally observe the tuning of metamaterials through the relative rotation of the elements about their common axis. In contrast to previous results we observe a crossing of resonances, where the symmetric and anti-symmetric modes become degenerate. We associate this effect with an interplay between the magnetic and electric near-field interactions and verify this by calculations based on the interaction energy between resonators.

Metamaterials and metaoptics

Abstract: We discuss the topics of metamaterials—electromagnetic composites off ering simultaneous control of electric and magnetic fi elds through structuring on a fi ne scale compared with the wavelength of light—and metaoptics, including striking optical eff ects achieved using metamaterial-based systems such as backward wave propagation and negative refraction. We survey fabrication methods and past achievements for systems working at long wavelengths and near-visible wavelengths, with emphasis on the recent development of this fi eld in Australia. We select several striking conceptual and technological advances made in this rapidly developing fi eld, such as cloaking, nonlinear metamaterials and drawable fi ber-based metamaterials.

Metamaterials with conformational nonlinearity

Abstract: Within a decade of fruitful development, metamaterials became a prominent area of research, bridging theoretical and applied electrodynamics, electrical engineering and material science. Being man-made structures, metamaterials offer a particularly useful playground to develop interdisciplinary concepts. Here we demonstrate a novel principle in metamaterial assembly which integrates electromagnetic, mechanical, and thermal responses within their elements. Through these mechanisms, the conformation of the meta-molecules changes, providing a dual mechanism for nonlinearity and offering nonlinear chirality. Our proposal opens a wide road towards further developments of nonlinear metamaterials and photonic structures, adding extra flexibility to their design and control.

An arrayed nanoantenna for broadband light emission and detection

Abstract: We suggest a broadband optical unidirectional arrayed nanoantenna consisting of equally spaced nanorods of gradually varying length Each nanorod can be driven by near-field quantum emitters radiating at different frequencies or, according to the reciprocity principle, by an incident light at the same frequency Broadband unidirectional emission and reception characteristics of the nanoantenna open up novel opportunities for subwavelength light manipulation and quantum communication, as well as for enhancing the performance of photoactive devices such as photovoltaic detectors, light-emitting diodes, and solar cells

Dipole azimuthons and vortex charge flipping in nematic liquid crystals.

Abstract: We demonstrate self-trapped laser beams carrying phase singularities in nematic liquid crystals. We experimentally observe the astigmatic transformation of vortex beams into spiraling dipole azimuthons accompanied by power-dependent charge-flipping of the on-axis phase singularity. The latter topological reactions involve triplets of vortex lines and resemble pitchfork bifurcations.

Scattering of linear and nonlinear waves in a waveguide array with a PT-symmetric defect

Abstract: We study the scattering of linear and nonlinear waves in a long waveguide array with a parity-time ($\mathrm{PT}$)-symmetric defect created by two waveguides with balanced gain and loss. We present exact solutions for the scattering of linear waves on such a defect, and then demonstrate numerically that the linear theory can describe, with a good accuracy, the soliton scattering in the case of weak nonlinearity. We reveal that the reflected and transmitted linear and nonlinear waves can be amplified substantially after interaction with the $\mathrm{PT}$-symmetric defect thus allowing an active control of the wave scattering in the array.

Interface modes in nanostructured metal-dielectric metamaterials

Abstract: We study surface modes at an interface separating two different layered metal-dielectric metamaterials. We demonstrate that, in a sharp contrast to the effective-medium approach predicting a single interface mode with the surface-plasmon dispersion, the transfer-matrix method reveals the existence of three types of localized interface modes, including a backward interface mode. These results confirm that metal-dielectric nanostructured metamaterials can demonstrate strong optical nonlocality due to the excitation of surface plasmon polaritons.

Anderson localization of light near boundaries of disordered photonic lattices

Abstract: We study numerically the effect of boundaries on Anderson localization of light in truncated two-dimensional photonic lattices in a nonlinear medium. We demonstrate suppression of Anderson localization at the edges and corners, so that stronger disorder is needed near the boundaries to obtain the same localization as in the bulk. We find that the level of suppression depends on the location in the lattice (edge vs corner), as well as on the strength of disorder. We also discuss the effect of nonlinearity on various regimes of Anderson localization.

Controlling split-ring resonators with light

Abstract: We propose an original approach for creating tunable electromagnetic metamaterials. We demonstrate experimentally that magnetic resonance of a split-ring resonator (“meta-atom” of a composite material) with a photodiode operated in photovoltaic mode can be tuned by changing the intensity of an external light source. Moreover, for two coupled resonators, we show that we can achieve light-induced switching between dark- and bright-mode responses.

Enhanced emission and light control with tapered plasmonic nanoantennas

Abstract: We introduce a design of Yagi-Uda plasmonic nanoantennas for enhancing the directive gain and achieving control over the angular emission of light. We demonstrate that tapering of nanoantenna elements allows to decrease the inter-element spacing tenfold also enhancing the emission directivity. We find the optimal tapering angle that provides the maximum directivity enhancement and the minimum end-fire beamwidth.

Comparative Study of FDTD-Adopted Numerical Algorithms for Kerr Nonlinearities

Abstract: Accurate finite-difference time-domain (FDTD) modeling of optical pulse propagation in nonlinear media usually implies the use of auxiliary differential equation (ADE) techniques. The updating of electric field in full-vectorial 3-D ADE FDTD modeling of the optical Kerr effect and two-photon absorption in optical media is proceeded conventionally through the iterative solution of nonlinear algebraic equations. Here, we study three approaches for the field update including simple noniterative explicit schemes. By comparing them to the analytical results for optical pulse propagation in long nonlinear media (nonlinear phase incursion for the pump wave of about π radians), we demonstrate convincingly that simple noniterative FDTD updating schemes, which are commonly believed to be inaccurate and unstable, produce accurate results and drastically speed up the computation as compared to ADE approaches. Such schemes can significantly reduce the CPU time for nonlinear computations, especially in 3-D models.

Laser Pulse Heating of Spherical Metal Particles

Abstract: We consider the general problem of laser pulse heating of spherical metal particles with the sizes ranging from nanometers to millimeters. We employ the exact Mie solution of the diffraction problem and solve the heat-transfer equation to determine the maximum temperature rise at the particle surface as a function of optical and thermometric parameters of the problem. Primary attention is paid to the case when the thermal diffusivity of the particle is much larger than that of the environment, as it is in the case of metal particles in fluids. We show that, in this case, for any given duration of the laser pulse, the maximum temperature rise as a function of the particle size reaches a maximum at a certain finite size of the particle. We suggest simple approximate analytical expressions for this dependence, which cover the entire parameter range of the problem and agree well with direct numerical simulations.

Multimode nematicon waveguides.

Abstract: We report on the first (to our knowledge) experimental observation of higher-order modes guided by soliton-induced waveguides in nematic liquid crystals. We find that the nematicon waveguides operate in a bounded power region specific to each guided mode. Below this region, the guided beams diffract; above this region, the mode mixing and coupling give rise to an unstable output.

Cascaded third harmonic generation in lithium niobate nanowaveguides

Abstract: We predict highly efficient third harmonic generation through simultaneous phase-matching of second-harmonic generation and sum-frequency generation in lithium niobate nanowaveguides, enabled due to strong modal dispersion. We demonstrate that the waveguide size which corresponds to phase-matching is also optimal for highest mode confinement and therefore for strongly enhanced conversion efficiency.

Stability range for a flat graphene sheet subjected to in-plane deformation

Abstract: The effects of the elastic deformation on the mechanical and physical properties of graphene are a subject of intensive current studies. Nevertheless, the stability range for a flat graphene sheet subjected to in-plane deformation is still unknown. Here, this problem is solved by atomistic simulations. In the three-dimensional space corresponding to the ɛ xx , ɛ yy , and ɛ xy components of the planar strain tensor, the surface bounding the stability range for a flat graphene sheet has been constructed disregarding the thermal vibrations and the effects of boundary conditions. For the points of this surface, force components T x , T y , and T xy have been calculated. It is shown that graphene is structurally stable up to strains on the order of 0.3–0.4, but it is unstable with respect to the shear in the absence of stretching forces. In addition, graphene cannot preserve its flat shape under the effect of a compressive force since it has zero flexural stiffness.

Counterpropagating optical beams and solitons

Abstract: Physics of counterpropagating optical beams and spatial optical solitons is reviewed, including the formation of stationary states and spatiotemporal instabilities. First, several models describing the evolution and interactions between optical beams and spatial solitons are discussed, that propagate in opposite directions in nonlinear media. It is shown that coherent collisions between counterpropagating beams give rise to an interesting focusing mechanism resulting from the interference between the beams, and that interactions between such beams are insensitive to the relative phase between them. Second, recent experimental observations of the counterpropagation effects and instabilities in waveguides and bulk geometries, as well as in one- and two-dimensional photonic lattices are discussed. A variety of different generalizations of this concept are summarized, including the counterpropagating beams of complex structures, such as multipole beams and optical vortices, as well as the beams in different media, such as photorefractive materials and liquid crystals.