arXiv subjects

Fangwei Ye

Publications and source records attributed to Fangwei Ye.

At least 73 records · Page 4Linked to original sources

arXiv2014

PT-symmetry in optics beyond the paraxial approximation

The concept of the PT-symmetry, originating from the quantum field theory, has been intensively investigated in optics, stimulated by the similarity between the Schrödinger equation and the paraxial wave equation that governs the propagation of light in a guiding structure. We go beyond the bounds of the paraxial approximation and demonstrate, using the solution of the Maxwell's equations for light beams propagating in deeply subwavelength waveguides and periodic lattices with "balanced" gain and loss, that the PT symmetry may stay unbroken in this setting. Moreover, the PT-symmetry in subwavelength optical structures may be restored after being initially broken upon the increase of gain and loss. Critical gain/loss levels, at which the breakup and subsequent restoration of the PT symmetry occur, strongly depend on the scale of the structure.

physics.optics↗

arXiv2014

Anderson Localization at the Subwavelength Scale and Loss Compensation for Surface-Plasmon Polaritons in Disordered Arrays of Metallic Nanowires

Using a random array of coupled metallic nanowires as a generic example of disordered plasmonic systems, we demonstrate that the structural disorder induces localization of light in these nanostructures at a deep-subwavelength scale. The ab initio analysis is based on solving the complete set of 3D Maxwell equations. We find that random variations of the radius of coupled plasmonic nanowires are sufficient to induce the Anderson localization (AL) of surface-plasmon polaritons (SPPs), the size of these trapped modes being significantly smaller than the wavelength. Remarkably, the optical-gain coefficient, needed to compensate losses in the plasmonic components of the system, is much smaller than the loss coefficient of the metal, which is obviously beneficial for the realization of the AL in plasmonic nanostructures. The dynamics of excitation and propagation of the Anderson-localized SPPs are addressed too.

physics.optics↗

arXiv2013

Tunneling inhibition for subwavelength light

We show that light tunneling inhibition may take place in suitable dynamically modulated waveguide arrays for light spots whose features are remarkably smaller than the wavelength of light. We found that tunneling between neighboring waveguides can be suppressed for specific frequencies of the out-of-phase refractive index modulation, affording undistorted propagation of the input subwavelength light spots over hundreds of Rayleigh lengths. Tunneling inhibition turns out to be effective only when the waveguide separation in the array is above a critical threshold. Inclusion of a weak focusing nonlinearity is shown to improve localization. We analyze the phenomenon in purely dielectric structures and also in arrays containing periodically spaced metallic layers.

physics.optics↗

arXiv2013

Solitary vortices supported by localized parametric gain

We demonstrate the existence and stability of bright vortex solitons sustained by a ring-shaped parametric gain, for both focusing and defocusing Kerr nonlinearities in lossy optical media. With the defocusing nonlinearity, the vortices are stable at all values of the detuning parameter, while under the focusing nonlinearity their stability region is limited to some positive values of the detuning. Unstable vortices in the focusing medium transform into stable rotating azimuthons.

nlin.PS↗

arXiv2013

Multiband Vector Plasmonic Lattice Solitons

We predict multiband vector Plasmonic Lattice Solitons (PLSs) in metal-dielectric waveguide arrays, in both focusing and defocusing nonlinearities. Such vector solitons consist of two components originating from different transmission bands. By simulating the full nonlinear Maxwell equations (MEs), we demonstrate the diffractionless propagation of vector PLSs and their discrete diffraction when only one component is present. Their subwavelength size characteristics and the influences of metallic losses are also studied.

physics.optics↗

arXiv2013

Solitons supported by localized parametric gain

We address the existence and properties of one-dimensional solitons maintained by localized parameter gain in focusing and defocusing lossy nonlinear media. Localized parametric gain supports both fundamental and multipole solitons. We found that the family of fundamental solitons is partly stable in focusing nonlinear medium, and completely stable in defocusing medium, while all higher-order solitons are unstable. In addition to numerical results, the existence threshold for the solitons, and a particular stable exact solution are obtained in an exact analytical form.

physics.optics↗

arXiv2012

Surface Plasmonic Lattice Solitons

We reveal the existence of the surface plasmonic lattice solitons (surface PLSs) at the boundary of a semi-infinite metallic-dielectric periodic nano-structure. We find that the truncation of the periodic structure imposes a threshold power for the existence of surface PLSs, and enhances significantly the modal localization. The propagation and excitation of surface PLSs as well as their potential application in the all-optical subwavelength switching are also demonstrated.

physics.optics↗

arXiv2012

Symmetric and asymmetric solitons in a nonlocal nonlinear coupler

We study effects of nonlocality of the cubic self-focusing nonlinearity on the stability and symmetry-breaking bifurcation (SBB) of solitons in the model of a planar dual-core optical waveg- uide with nonlocal (thermal) nonlinearity. In comparison with the well-known coupled systems with the local nonlinearity, the present setting is affected by the competition of different spatial scales, viz., the coupling length and correlation radius of the nonlocality, $\sqrt{d}$. By means of numer- ical methods and variational approximation (VA, which is relevant for small d), we find that, with the increase of the correlation radius, the SBB changes from subcritical into supercritical, which makes all the asymmetric solitons stable. On the other hand, the nonlocality has little influence on the stability of antisymmetric solitons. Analytical results for the SBB are also obtained (actually, for antisymmetric "accessible solitons") in the opposite limit of the ultra-nonlocal nonlinearity, using a coupler based on the Snyder-Mitchell model. The results help to grasp the general picture of the symmetry breaking in nonlocal couplers.

nlin.PS↗

arXiv2010

Nonlinearity-mediated soliton ejection from trapping potentials in nonlocal media

We address the properties of optical solitons in thermal nonlinear media with a local refractive index defect that is capable to trap solitons launched even close to the sample boundary despite the boundary-mediated forces that tend to deflect all beams toward the center of the sample. We show that while such forces become more pronounced with increasing the input beam power the defect can trap only light below a critical power above which solitons are ejected. The dynamics of soliton ejection and the subsequent propagation may be controlled.

nlin.PS↗

arXiv2010

Subwavelength Plasmonic Lattice Solitons in Arrays of Metallic Nanowires

We predict theoretically that stable subwavelength plasmonic lattice solitons (PLSs) are formed in arrays of metallic nanowires embedded in a nonlinear medium. The tight confinement of the guiding modes of the metallic nanowires, combined with the strong nonlinearity induced by the enhanced field at the metal surface, provide the main physical mechanisms for balancing the wave diffraction and the formation of PLSs. As the conditions required for the formation of PLSs are satisfied in a variety of plasmonic systems, we expect these nonlinear modes to have important applications to subwavelength nanophotonics. In particular, we show that the subwavelength PLSs can be used to optically manipulate with nanometer accuracy the power flow in ultracompact photonic systems.

physics.optics↗

arXiv2010

Collapse suppression and stabilization of dipole solitons in two-dimensional media with anisotropic semi-local nonlinearity

We consider the impact of anisotropic nonlocality on the arrest of the collapse and stabilization of dipole-mode (DM) solitons in two-dimensional (2D) models of optical media with the diffusive nonlinearity. The nonlocal nonlinearity is made anisotropic through elliptic diffusivity. The medium becomes semi-local in the limit case of 1D diffusivity. Families of fundamental and DM solitons are found by means of the variational approximation (VA) and in a numerical form. We demonstrate that the collapse of 2D beams is arrested even in the semi-local system. The anisotropic nonlocality readily stabilizes the DM solitons, which are completely unstable in the isotropic medium.

physics.optics↗

arXiv2010

Twin-vortex solitons in nonlocal nonlinear media

We consider soliton formation in thermal nonlinear media bounded by rectangular cross-sections and uncover a new class of nonlinear stationary topological state. Specifically, we find that stationary higher-order vortex states in standard shapes do not exist, but rather they take the form of multiple, spatially separated single-charge singularities nested in an elliptical beam. Double-charge states are found to be remarkably robust despite their shape asymmetry and the phase-singularity splitting. States with higher topological charges are found to be unstable.

physics.optics↗

arXiv2010

Stability of Multipole-mode Solitons in Thermal Nonlinear Media

We study the stability of multipole-mode solitons in one-dimensional thermal nonlinear media. We show how the sample geometry impacts the stability of mutlipole-mode solitons and reveal that the tripole and quadrupole can be made stable in their whole domain of existence, provided that the sample width exceeds a critical value. In spite of such geometry-dependent soliton stability, we find that the maximal number of peaks in stable multipole-mode solitons in thermal media is the same as that in nonlinear materials with finite-range nonlocality.

nlin.PS↗

arXiv2009

Power-dependent soliton steering in thermal nonlinear media

We address the existence and properties of optical solitons excited in thermal nonlinear media with a transverse refractive index gradient. We show that in such a geometry one can generate controllable switching from surface soliton propagating near the sample edges to bulk solitons. Beam steering associated to the different soliton output locations can be achieved by varying the input light intensity.

physics.optics↗

arXiv2009

Light bullets in Bessel optical lattices with spatially modulated nonlinearity

We address the stability of light bullets supported by Bessel optical lattices with out-of-phase modulation of the linear and nonlinear refractive indices. We show that spatial modulation of the nonlinearity significantly modifies the shapes and stability domains of the light bullets. The addressed bullets can be stable, provided that the peak intensity does not exceed a critical value. We show that the width of the stability domain in terms of the propagation constant may be controlled by varying the nonlinearity modulation depth. In particular, we show that the maximum energy of the stable bullets grows with increasing nonlinearity modulation depth.

nlin.PS↗

arXiv2009

Elliptic Vortices in Composite Mathieu Lattices

We address the elliptically shaped vortex solitons in defocusing nonlinear media imprinted with a composite Mathieu lattice. Elliptic vortices feature anisotropic patterns both in intensity and phase, and can only exist when their energy flow exceed some certain threshold. Single-charged elliptic vortices are found to arise via bifurcation from dipole modes, which, to the best of our knowledge is the first example in the context of optics studies of symmetry breaking bifurcations for the phase dislocations of different dimensionalities. Higher-order elliptic vortices with topological charge could exhibit spatially separated single-charged phase singularities, leading to their stabilization. The salient features of reported elliptic vortices qualitatively hold for other elliptic shaped confining potentials.

nlin.PS↗

arXiv2008

Nonlinear switching of low-index defect modes in photonic lattices

We address nonlinear signal switching between two low-index defect channels induced in periodic optical lattices. In contrast to conventional directional couplers, where the guiding mechanism is total internal reflection or refraction, in such Bragg-type coupler, the guidance is of a photonic-bandgap origin. The coupling length in the low-index coupler is controlled by the lattice parameters and by the channel spacing. In the nonlinear regime the Bragg-type coupler behaves as an all-optical switch, exhibiting a remarkable difference of switching power for focusing versus defocusing nonlinearity.

physics.optics↗

arXiv2008

Bragg guiding of domain-like nonlinear modes and kink arrays in lower-index core structures

We introduce a novel class of stable nonlinear modes trapped in a lower-index film core sandwiched between two optical lattices, or in the cylindrical core of a radial lattice, imprinted in defocusing media. Such family of nonlinear modes transforms into defect lattice solitons when the core width is sufficiently small or into an array of kinks when the width is large enough. We find that higher-order modes with multiple zeros inside the guiding core can be stable in one-dimensional settings.

physics.optics↗