arXiv subjects
Publications and source records attributed to Yuri S. Kivshar.
We report on the first experimental observation of higher-order modes guided by soliton-induced waveguides in unbiased 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 it the mode mixing and coupling give rise to an unstable output.
We analyze numerically the thermal conductivity of carbon nanoribbons with ideal and rough edges. We demonstrate that edge disorder can lead to a suppression of thermal conductivity by several orders of magnitude. This effect is associated with the edge-induced Anderson localization and suppression of the phonon transport, and it becomes more pronounced for longer nanoribbons and low temperatures.
We demonstrate that the presence of a supporting substrate can break the symmetry of a metamaterial structure, changing the symmetry of its effective parameters, and giving rise to bianisotropy. This indicates that magneto-electric coupling will occur in all metamaterials fabricated on a substrate, including those with symmetric designs.
We analyze localization of light in honeycomb photonic lattices restricted in one dimension which can be regarded as an optical analog of (``armchair'' and ``zigzag'') graphene nanoribbons. We find the conditions for the existence of spatially localized states and discuss the effect of lattice topology on the properties of discrete solitons excited inside the lattice and at its edges. In particular, we discover a novel type of soliton bistability, the so-called geometry-induced bistability, in the lattices of a finite extent.
We study experimentally light localization at phase-slip waveguides and at the intersection of phase-slips in a two-dimensional (2D) square photonic lattice. Such system allows to observe a variety of effects, including the existence of spatially localized modes for low powers, the generation of strongly localized states in the form of discrete bulk and surface solitons, as well as a crossover between one-dimensional (1D) and 2D localization.
We analyze numerically the optical response and effective macroscopic parameters of fishnet metamaterials infiltrated with a nematic liquid crystal. We show that even a small amount of liquid crystal can provide tuning of the structures due to reorientation of the liquid crystal director. This enables switchable optical metamaterials, where the refractive index can be switched from positive to negative by an external field. This tuning is primarily determined by the shift of the cut-off wavelength of the holes, with only a small influence due to the change in plasmon dispersion
We propose a method for achieving dynamically controllable transport of highly mobile matter-wave solitons in a driven two-dimensional optical lattice. Our numerical analysis based on the mean-field model and the theory based on the time-averaging approach, demonstrate that a fast time-periodic rocking of the two-dimensional optical lattice enables efficient stabilization and manipulation of spatially localized matter wavepackets via induced reconfigurable mobility channels.
We study the propagation and localization of classical waves in one-dimensional disordered structures composed of alternating layers of left- and right-handed materials (mixed stacks) and compare them to the structures composed of different layers of the same material (homogeneous stacks). For weakly scattering layers, we have developed an effective analytical approach and have calculated the transmission length within a wide region of the input parameters. When both refractive index and layer thickness of a mixed stack are random, the transmission length in the long-wave range of the localized regime exhibits a quadratic power wavelength dependence with the coefficients different for mixed and homogeneous stacks. Moreover, the transmission length of a mixed stack differs from reciprocal of the Lyapunov exponent of the corresponding infinite stack. In both the ballistic regime of a mixed stack and in the near long-wave region of a homogeneous stack, the transmission length of a realization is a strongly fluctuating quantity. In the far long-wave part of the ballistic region, the homogeneous stack becomes effectively uniform and the transmission length fluctuations are weaker. The crossover region from the localization to the ballistic regime is relatively narrow for both mixed and homogeneous stacks. In mixed stacks with only refractive-index disorder, Anderson localization at long wavelengths is substantially suppressed, with the localization length growing with the wavelength much faster than for homogeneous stacks. The crossover region becomes essentially wider and transmission resonances appear only in much longer stacks. All theoretical predictions are in an excellent agreement with the results of numerical simulations.
We study vibrational states localized at the edges of graphene nanoribbons. Such surface oscillations can be considered as a phonon analog of Tamm states well known in the electronic theory. We consider both armchair and zigzag graphene stripes and demonstrate that surface modes correspond to phonons localized at the edges of the graphene nanoribbon, and they can be classified as in-plane and out-of-plane modes. In addition, in armchair nanoribbons anharmonic edge modes can experience longitudinal localization in the form of self-localized nonlinear modes, or surface breather solitons.
We demonstrate how to achieve reversible nonreciprocal optical response in a periodic photonic structure with a pair of defects, one of them being a nonlinear liquid crystal defect layer. The twin defect layers structure is symmetric at low intensity and becomes asymmetric above a power threshold corresponding to the optical reordering of the liquid crystal. We show that nonreciprocal effects can be reversed by changing the wavelength as a consequence of the defect mode dependent light localization inside the structure.
We study the dynamics of a pair of nonlinear split-ring resonators (a `metadimer') excited by an alternating magnetic field and coupled magnetically. Linear metadimers of this kind have been recently used as the elementary components for three-dimensional metamaterials or 'stereometamaterials' [N. Liu {\em et al}, Nature Photon. {\bf 3}, 157 (2009)]. We demonstrate that nonlinearity offers more possibilities with respect to real-time tunability and a multiplicity of states which can be reached by varying the external field. Moreover, we demonstrate almost total localization of the energy in one of the resonators in a broad range of parameters.
We demonstrate that the spatial profiles of both propagating and evanescent Bloch-modes in a periodic structure can be extracted from a single measurement of electric field at the specified optical wavelength. We develop a systematic extraction procedure by extending the concepts of high-resolution spectral methods previously developed for temporal data series to take into account the symmetry properties of Bloch-modes simultaneously at all spatial locations. We apply our method to a photonic crystal waveguide interface and confirm its robustness in the presence of noise.
We introduce a concept of the Mach-Zehnder-Fano interferometer by inserting a cavity exhibiting Fano resonance into a conventional interferometer. By employing the scattering-matrix approach, we demonstrate that the transmission is sensitive to a position of the cavity such that an asymmetric structure exhibits a series of narrow resonances with almost perfect reflection. We discuss how to implement this novel geometry in two-dimensional photonic crystals and use direct numerical simulations to demonstrate novel regimes of the resonant transmission and reflection.
Nowadays nanotechnology allows to scale-down various important devices (sensors, chips, fibres, etc), and, thus, opens up new horizon for their applications. Nevertheless, the efficiency most of them is still based on the fundamental physical phenomena, such as resonances. Thus, the understanding of the resonance phenomena will be beneficial. One of the well-known examples is the resonant enhancement of the transmission known as Breit-Wigner resonances, which can be described by a Lorentzian function. But, in many physical systems the scattering of waves involves propagation along different paths, and, as a consequence, results in interference phenomena, where constructive interference corresponds to resonant enhancement and destructive interference to resonant suppression of the transmission. Recently, a variety of experimental and theoretical work has revealed such patterns in different branches of physics. The purpose of this Review is to demonstrate that this kind of resonant scattering is related to the Fano resonances, known from atomic physics. One of the main features of the Fano resonances is the asymmetric profile. The asymmetry comes from the close coexistence of resonant transmission and resonant reflection. Fano successfully explained such a phenomenon in his seminal paper in 1961 in terms of interaction of a discrete (localized) state with a continuum of propagation modes. It allows to describe both resonant enhancement and resonant suppression in a unified manner. All of these properties can be demonstrated in the frame of a very simple model, which will be used throughout the Review to show that resonant reflections observed in different complex systems are indeed closely related to the Fano resonances.
We study experimentally the propagation dynamics and interaction of spatial optical solitons in a bias-free cell filled with nematic liquid crystals. We reveal and measure long-range effects due to the cell boundaries for a single nematicon as well as for the interacting in-phase and out-of-phase nematicons. We discuss the effect of initial beam focusing and relative input angle on the interaction of in-phase nematicons.
We study the properties of two-color nonlinear localized modes which may exist at the interfaces separating two different periodic photonic lattices in quadratic media, focussing on the impact of phase mismatch of the photonic lattices on the properties, stability, and threshold power requirements for the generation of interface localized modes. We employ both an effective discrete model and continuum model with periodic potential and find good qualitative agreement between both models. Dynamics excitation of interface modes shows that, a two-color interface twisted mode splits into two beams with different escaping angles and carrying different energies when entering a uniform medium from the quadratic photonic lattice. The output position and energy contents of each two-color interface solitons can be controlled by judicious tuning of
We study the properties of electromagnetic Bloch waves in semi-infinite periodic structures created by alternating metamaterial and dielectric layers. We derive and analyze the dispersion relations in the long-wavelength limit for both TE- and TM-polarized surface Bloch modes, for magnetic metamaterials with negative refraction and metal-dielectric plasmonic superlattices. We reveal that in the subwavelength regime the bulk modes are characterized by three different refractive indices ("tri-refringence") while the surface modes can propagate parallel to the Bloch wavevector and along the interface between superlattice and semi-infinite dielectric.
We propose and design a new type of nonlinear metamaterials exhibiting a resonant electric response at microwave frequencies. By introducing a varactor diode as a nonlinear element within each resonator, we are able to shift the frequency of the electric mode stop-band by changing the incident power, without affecting the magnetic response. These elements could be combined with the previously developed nonlinear magnetic metamaterials in order to create negative index media with control over both electric and magnetic nonlinearities.