Multi-stability and polariton solitons in microcavity wires.

Nonlinear polaritons in microcavity wires are demonstrated to exhibit multi-stable behavior and rich dynamics, including filamentation and soliton formation. We find that the multi-stability originates from co-existence of different transverse cavity modes. Modulational stability and conditions for multi-mode polariton solitons are studied. Soliton propagation in tilted, relative to the pump momentum, microcavity wires is demonstrated, and a critical tilt angle for the soliton propagation is found.

Spatial Patterns of Dissipative Polariton Solitons in Semiconductor Microcavities.

We report propagating bound microcavity polariton soliton arrays consisting of multipeak structures either along (x) or perpendicular (y) to the direction of propagation. Soliton arrays of up to five solitons are observed, with the number of solitons controlled by the size and power of the triggering laser pulse. The breakup along the x direction occurs when the effective area of the trigger pulse exceeds the characteristic soliton size determined by polariton-polariton interactions. Narrowing of soliton emission in energy-momentum space indicates phase locking between adjacent solitons, consistent with numerical modeling which predicts stable multihump soliton solutions. In the y direction, the breakup originates from inhomogeneity across the wave front in the transverse direction which develops into a stable array only in the solitonic regime via phase-dependent interactions of propagating fronts.

Effects of spin-dependent interactions on polarization of bright polariton solitons.

We report on the spin properties of bright polariton solitons supported by an external pump to compensate losses. We observe robust circularly polarized solitons when a circularly polarized pump is applied, a result attributed to phase synchronization between nondegenerate TE and TM polarized polariton modes at high momenta. For the case of a linearly polarized pump, either σ+ or σ- circularly polarized bright solitons can be switched on in a controlled way by a σ+ or σ- writing beam, respectively. This feature arises directly from the widely differing interaction strengths between co- and cross-circularly polarized polaritons. In the case of orthogonally linearly polarized pump and writing beams, the soliton emission on average is found to be unpolarized, suggesting strong spatial evolution of the soliton polarization. The observed results are in agreement with theory, which predicts stable circularly polarized solitons and unstable linearly polarized solitons.

Graphene-clad tapered fiber: effective nonlinearity and propagation losses.

We derive a pulse propagation equation for a graphene-clad optical fiber, treating the optical response of the graphene and nonlinearity of the dielectric fiber core as perturbations in asymptotic expansion of Maxwell equations. We analyze the effective nonlinear and attenuation coefficients due to the graphene layer. Based on the recent experimental measurements of the nonlinear graphene conductivity, we predict considerable enhancement of the effective nonlinearity for subwavelength fiber core diameters.

Modulational instability in a silicon-on-insulator directional coupler: role of the coupling-induced group velocity dispersion.

We report frequency conversion experiments in silicon-on-insulator (SOI) directional couplers. We demonstrate that the evanescent coupling between two subwavelength SOI waveguides is strongly dispersive and significantly modifies modulational instability (MI) spectra through the coupling induced group velocity dispersion (GVD). As the separation between two 380-nm-wide silicon photonic wires decreases, the increasing dispersion of the coupling makes the GVD in the symmetric supermode more normal and suppresses the bandwidth of the MI gain observed for larger separations.

Dispersion of nonlinearity and modulation instability in subwavelength semiconductor waveguides.

Tight confinement of light in subwavelength waveguides induces substantial dispersion of their nonlinear response. We demonstrate that this dispersion of nonlinearity can lead to the modulational instability in the regime of normal group velocity dispersion through the mechanism independent from higher order dispersions of linear waves. A simple phenomenological model describing this effect is the nonlinear Schrödinger equation with the intensity dependent group velocity dispersion.

Time and frequency domain measurements of solitons in subwavelength silicon waveguides using a cross-correlation technique.

We report time domain measurements of the group-velocity-dispersion-induced and nonlinearity-induced chirping of femtosecond pulses in subwavelength silicon-on-insulator waveguides. We observe that at a critical input power level, these two effects compensate each other leading to soliton formation. Formation of the fundamental optical soliton is observed at a peak power of a few Watts inside the waveguide. Interferometric cross-correlation traces reveal compression of the soliton pulses, while spectral measurements show pronounced dispersive waves emitted by solitons into the wavelength range of normal group velocity dispersion.

Coupled-mode approach to surface plasmon polaritons in nonlinear periodic structures.

We present a coupled-mode theory describing light propagation in an array of nonlinear plasmonic waveguides. Our model predicts a two-band dependence of the propagation constant versus transverse quasi-momentum and existence of discrete and gap plasmon solitons.

Vortex lattices in coherently pumped polariton microcavities.

We propose a new class of vortex lattices supported by the parametric conversion of polaritons in wide aperture semiconductor microcavities operating in the strong coupling regime and pumped by a coherent beam. We present numerical and analytical results confirming the existence and robustness of the polaritonic vortex lattices in practically relevant settings and discuss their melting scenarios.

Two-dimensional localization of exciton polaritons in microcavities.

We report two-dimensional localization of exciton polaritons in a coherently pumped planar semiconductor microcavity operating in the strong-coupling regime. Two-dimensional polariton solitons exist despite the opposite dispersion signs along the orthogonal in plane directions. Nonlinearities compensating the opposing dispersions have different physical origins and are due to the repulsion of polaritons on one side and due to parametric four-wave mixing on the other. Both of these nonlinearities can support their respective families of one-dimensional solitons, which coexist with each other and with the two-dimensional solitons.

Amplification of surface plasmon polaritons in the presence of nonlinearity and spectral signatures of threshold crossover.

We describe the effects of nonlinearity on propagation of surface plasmon polaritons (SPPs) at an interface between a metal and an amplifying medium of the externally pumped two-level atoms. Using Maxwell equations we derive the nonlinear dispersion law and demonstrate that the nonlinear saturation of the linear gain leads to formation of stationary SPP modes with the intensities independent from the propagation distance. Transition to the regime of stationary propagation is similar to the threshold crossover in lasers and leads to narrowing of the SPP spectrum.

Solitons and spectral broadening in long silicon-on- insulator photonic wires.

We report measurements and numerical modeling of spectral broadening and soliton propagation regimes in silicon-on-insulator photonic wire waveguides of 3 to 4 dispersion lengths using 100fs pump pulses. We also present accurate measurements of the group index and dispersion of the photonic wire.

Bouncing of a dispersive pulse on an accelerating soliton and stepwise frequency conversion in optical fibers.

We demonstrate that a short pulse with spectrum in the range of normal group velocity dispersion can experience periodic reflections on a refractive index maximum created by a co-propagating with it soliton, providing the latter is continuously decelerated by the intrapulse Raman scattering. After each reflection the intensity profile and phase of the pulse are almost perfectly reconstructed, while its frequency is stepwise converted. This phenomenon has direct analogy with the effect of 'quantum bouncing' known for cold atoms.

Four-wave mixing of solitons with radiation and quasi-nondispersive wave packets at the short-wavelength edge of a supercontinuum.

We apply the recently developed theory of frequency generation by mixing of solitons and dispersive waves [Phys. Rev. E 72, 016619 (2005)] to explain the observed formation, quasi-trapping and frequency shift of the spectral peaks at the blue edge of supercontinua generated in silica-core photonic crystal fibers.

Compactlike discrete breathers in systems with nonlinear and nonlocal dispersive terms.

Discrete breathers with purely anharmonic short-range interaction potentials localize superexponentially becoming compactlike. We analyze their spatial localization properties and their dynamical stability. Several branches of solutions are identified. One of them connects to the well-known Page and Sievers-Takeno lattice modes, another one connects with the compacton solutions of Rosenau. The absence of linear dispersion allows for extremely long-lived time-quasiperiodic localized excitations. Adding long-range anharmonic interactions leads to an extreme case of competition between length scales defining the spatial breather localization. We show that short- and long-range interaction terms competition results in the appearance of several characteristic crossover lengths and essentially breaks the concept of compactness of the corresponding discrete breathers.

Tissue factor and atherothrombosis.

Tissue factor (TF) is known to be the key element in the initiation of the extrinsic pathway of the coagulation cascade and appears to be a critical determinant of atherosclerotic plaque thrombogenicity. TF is needed to produce thrombin from prothrombin. In the extrinsic pathway, TF activates factor Vll. TF is expressed mainly on subendothelial tissues, but TF expression may be induced on endothelial cells by inflammatory mediators such as tumor necrosis factor-alpha (TNF-alpha). Subendothelial TF is responsible for initiating fibrin formation at sites of vascular injury, bloodborne TF may be an important contributor to propagation of the developing thrombus. It has been postulated that the blood-borne TF initiates the thrombogenic stimulus, leading to the formation of larger and more stable thrombus. TF may attach to cellular receptors, which in turn affect the production and release of inflammatory mediators. Baseline plasma TF activity has been demonstrated as an independent predictor for cardiovascular death in patients with acute myocardial infarction. TF is expressed by macrophage-derived foam cells in atherosclerotic plaques. TF levels were higher in atheroma from patients with unstable angina than with stable angina. These results suggest that high levels of TF exposed upon plaque rupture trigger atherothrombosis. Inhibition of TF would be expected to reduce thrombosis associated with a variety of diseases. TF pathway is a potential target for new therapeutic agents that can decrease TF activity, such as active site-inactivated factor VIIa, recombinant TF inhibitor and antibodies against TF or peptides interfering with TF-FVIIa complex activity. Significant clinical forms of atherosclerosis, such as sudden death, myocardial infarction, and stroke have common pathogenesis. The occlusion of the vessel lumen is the result from atherosclerotic plaque rupture/erosion that initiate thrombus formation. This thrombus has complex structure and contains predominantly fibrin in addition to platelets, suggesting an important role for the coagulation cascade in plaque thrombus formation. Tissue factor (TF) is known to be the key element in the initiation of the extrinsic pathway of the coagulation cascade and appears to be a critical determinant of atherosclerotic plaque thrombogenicity.

Cascaded generation of multiply charged optical vortices and spatiotemporal helical beams in a Raman medium.

Using an example of a Raman active medium we describe how a common nonlinear process of four-wave mixing can be used to induce strong coupling between the spatial and temporal degrees of freedom in optical waves. This coupling produces several unexpected effects. Amongst those are cascaded excitation of multiply charged optical vortices, spatial focusing in a nonlinearly defocusing medium, and generation of helically shaped spatiotemporal optical solitons.

Spectral-discrete solitons and localization in frequency space.

We report families of discrete optical solitons in frequency space, or spectral-discrete solitons existing in a dispersive Raman medium, where individual sidebands are coupled by coherence. The associated time-domain patterns correspond either to trains of ultrashort pulses or to weakly modulated waves. We describe the physics behind the spectral localization and study soliton bifurcations, stability, and dynamics.

Energy flow of moving dissipative topological solitons.

We study the energy flow due to the motion of topological solitons in nonlinear extended systems in the presence of damping and driving. The total field momentum contribution to the energy flux, which reduces the soliton motion to that of a point particle, is insufficient. We identify an additional exchange energy flux channel mediated by the spatial and temporal inhomogeneity of the system state. In the well-known case of a dc external force the corresponding exchange current is shown to be small but nonzero. For the case of ac driving forces, which lead to a soliton ratchet, the exchange energy flux mediates the complete energy flow of the system. We also consider the case of combination of ac and dc external forces, as well as spatial discretization effects.

Resonant light scattering by optical solitons.

We consider the process of light scattering by optical solitons in a planar waveguide with homogeneous and inhomogeneous refractive index cores. We observe resonant reflection (Fano resonances) as well as resonant transmission of light by optical solitons. All resonant effects can be controlled in experiment by changing the soliton intensity.