Mode conversion of various solitons in parabolic and cross-phase potential wells.

We numerically establish the controllable conversion between Laguerre-Gaussian and Hermite-Gaussian solitons in nonlinear media featuring parabolic and cross-phase potential wells. The parabolic potential maintains the stability of Laguerre-Gaussian and Hermite-Gaussian beams, while the actual conversion between the two modes is facilitated by the cross-phase potential, which induces an additional phase shift. By flexibly engineering the range of the cross-phase potential well, various higher-mode solitons can be generated at desired distances. Beams carrying orbital angular momentum can also be efficiently controlled by this method. In addition, other types of beams, such as sine complex-various-function Gaussian and hypergeometric-Gaussian vortex beams, can be periodically transformed and manipulated in a similar manner. Our approach allows the intricate internal relationships between different modes of beams to be conveniently revealed.

Surface gap solitons in the Schrödinger equation with quintic nonlinearity and a lattice potential.

We demonstrate the existence of surface gap solitons, a special type of asymmetric solitons, in the one-dimensional nonlinear Schrödinger equation with quintic nonlinearity and a periodic linear potential. The nonlinearity is suddenly switched in a step-like fashion in the middle of the transverse spatial region, while the periodic linear potential is chosen in the form of a simple sin 2 lattice. The asymmetric nonlinearities in this work can be realized by the Feshbach resonance in Bose-Einstein condensates or by the photorefractive effect in optics. The major peaks in the gap soliton families are asymmetric and they are located at the position of the jump in nonlinearity (at x = 0). In addition, the major peaks of the two-peak and multi-peak solitons at the position x = 0 are higher than those after that position, at x > 0. And such phenomena are more obvious when the value of chemical potential is large, or when the difference of nonlinearity values across the jump is big. Along the way, linear stability analysis of the surface gap solitons is performed and the stability domains are identified. It is found that in this model, the solitons in the first band gap are mostly stable (excepting narrow domains of instability at the edges of the gap), while those in the second band gap are mostly unstable (excepting extremely narrow domains of stability for fundamental solitons). These findings are also corroborated by direct numerical simulations.

Mapping the Direction of Nucleocytoplasmic Transport of Glucocorticoid Receptor (GR) in Live Cells Using Two-Foci Cross-Correlation in Massively Parallel Fluorescence Correlation Spectroscopy (mpFCS).

Nucleocytoplasmic transport of transcription factors is vital for normal cellular function, and its breakdown is a major contributing factor in many diseases. The glucocorticoid receptor (GR) is an evolutionarily conserved, ligand-dependent transcription factor that regulates homeostasis and response to stress and is an important target for therapeutics in inflammation and cancer. In unstimulated cells, the GR resides in the cytoplasm bound to other molecules in a large multiprotein complex. Upon stimulation with endogenous or synthetic ligands, GR translocation to the cell nucleus occurs, where the GR regulates the transcription of numerous genes by direct binding to glucocorticoid response elements or by physically associating with other transcription factors. While much is known about molecular mechanisms underlying GR function, the spatial organization of directionality of GR nucleocytoplasmic transport remains less well characterized, and it is not well understood how the bidirectional nucleocytoplasmic flow of GR is coordinated in stimulated cells. Here, we use two-foci cross-correlation in a massively parallel fluorescence correlation spectroscopy (mpFCS) system to map in live cells the directionality of GR translocation at different positions along the nuclear envelope. We show theoretically and experimentally that cross-correlation of signals from two nearby observation volume elements (OVEs) in an mpFCS setup presents a sharp peak when the OVEs are positioned along the trajectory of molecular motion and that the time position of the peak corresponds to the average time of flight of the molecule between the two OVEs. Hence, the direction and velocity of nucleocytoplasmic transport can be determined simultaneously at several locations along the nuclear envelope. We reveal that under ligand-induced GR translocation, nucleocytoplasmic import/export of GR proceeds simultaneously but at different locations in the cell nucleus. Our data show that mpFCS can characterize in detail the heterogeneity of directional nucleocytoplasmic transport in a live cell and may be invaluable for studies aiming to understand how the bidirectional flow of macromolecules through the nuclear pore complex (NPC) is coordinated to avoid intranuclear transcription factor accretion/abatement.

Interdimensional radial discrete diffraction in Mathieu photonic lattices.

We demonstrate transitional dimensionality of discrete diffraction in radial-elliptical photonic lattices. Varying the order, characteristic structure size, and ellipticity of the Mathieu beams used for the photonic lattices generation, we control the shape of discrete diffraction distribution over the combination of the radial direction with the circular, elliptic, or hyperbolic. We also investigate the transition from one-dimensional to two-dimensional discrete diffraction by varying the input probe beam position. The most pronounced discrete diffraction is observed along the crystal anisotropy direction.

Spiraling Laguerre-Gaussian solitons and arrays in parabolic potential wells.

Controllable trajectories of beams are one of the main themes in optical science. Here, we investigate the propagation dynamics of Laguerre-Gaussian (LG) solitons in parabolic potential wells and introduce off-axis and chirp parameters (which represent the displacement and the initial angle of beams) to make solitons sinusoidally oscillate in the x and y directions and undergo elliptically or circularly spiraling trajectories during propagation. Additionally, LG solitons with different orders and powers can be combined into soliton arrays of various shapes, depending on the off-axis parameter. Moreover, the soliton arrays can exhibit periodic converging, rotating, and other evolution behaviors, by the proper choice of the chirp parameter. A series of interesting examples demonstrate typical propagation scenarios. Our results may provide a new perspective on and stimulate further investigations of multisoliton interactions in potential wells and may find applications in optical communication and particle control.

Vector valley Hall edge solitons in distorted type-II Dirac photonic lattices.

Topological edge states have recently garnered a lot of attention across various fields of physics. The topological edge soliton is a hybrid edge state that is both topologically protected and immune to defects or disorders, and a localized bound state that is diffraction-free, owing to the self-balance of diffraction by nonlinearity. Topological edge solitons hold great potential for on-chip optical functional device fabrication. In this report, we present the discovery of vector valley Hall edge (VHE) solitons in type-II Dirac photonic lattices, formed by breaking lattice inversion symmetry with distortion operations. The distorted lattice features a two-layer domain wall that supports both in-phase and out-of-phase VHE states, appearing in two different band gaps. Superposing soliton envelopes onto VHE states generates bright-bright and bright-dipole vector VHE solitons. The propagation dynamics of such vector solitons reveal a periodic change in their profiles, accompanied by the energy periodically transferring between the layers of the domain wall. The reported vector VHE solitons are found to be metastable.

Triangular bright solitons in nonlinear optics and Bose-Einstein condensates.

We demonstrate what we believe to be novel triangular bright solitons that can be supported by the nonlinear Schrödinger equation with inhomogeneous Kerr-like nonlinearity and external harmonic potential, which can be realized in nonlinear optics and Bose-Einstein condensates. The profiles of these solitons are quite different from the common Gaussian or sech envelope beams, as their tops and bottoms are similar to the triangle and inverted triangle functions, respectively. The self-defocusing nonlinearity gives rise to the triangle-up solitons, while the self-focusing nonlinearity supports the triangle-down solitons. Here, we restrict our attention only to the lowest-order fundamental triangular solitons. All such solitons are stable, which is demonstrated by the linear stability analysis and also clarified by direct numerical simulations. In addition, the modulated propagation of both types of triangular solitons, with the modulated parameter being the strength of nonlinearity, is also presented. We find that such propagation is strongly affected by the form of the modulation of the nonlinearity. For example, the sudden change of the modulated parameter causes instabilities in the solitons, whereas the gradual variation generates stable solitons. Also, a periodic variation of the parameter causes the regular oscillation of solitons, with the same period. Interestingly, the triangle-up and triangle-down solitons can change into each other, when the parameter changes the sign.

Soliton transformation between different potential wells.

This paper presents a novel, to the best of our knowledge, method for realizing soliton transformation between different potential wells by gradually manipulating their depths in the propagation direction. The only requirements for such a transformation are that the gradient of the manipulated depth is smooth enough and the solitons in different potential wells are both in the regions of stability. The comparison of transformed solitons with the iterative ones obtained by the accelerated imaginary-time evolution method proves that our method is efficient and reliable. An interesting consequence is that in some complex potential wells in which it is difficult to find solitons by iterative numerical methods, stable solitons can be obtained by the transformation method. The controllable soliton transformation provides an excellent opportunity for all-optical switching, optical information processing, and other applications.

Vortex chaoticons in thermal nonlocal nonlinear media.

This paper numerically investigates the propagation of Laguerre-Gaussian vortex beams launched in nonlocal nonlinear media, such as lead glass. Our results show that the propagation properties depend on the selection of beam parameters m and p, which represent the azimuthal and radial mode numbers. When p=0, these profiles can be stable solitons for m≤2, or break up and then form a set of single-hump profiles for m≥3, which are unbounded states with scattered remnants of the energy. However, for p≥1, the broken beams can evolve into vortex chaoticons, which exhibit both chaotic and solitonlike properties. The chaotic properties are determined by the positive Lyapunov exponents and spatial decoherence, while the solitonlike properties are demonstrated by the invariance of beam width and the interaction of beams in the form of quasielastic collisions. In addition, the power and orbital angular momentum of unbounded beam states both decay in propagation, while those of the chaoticons maintain their values well.

Controllable propagation paths of gap solitons.

This paper numerically investigates the evolution of solitons in an optical lattice with gradual longitudinal manipulation. We find that the stationary solutions (with added noise to the amplitude) keep their width, profile, and intensity very well, although the propagation path is continuously changing during the modulated propagation. Discontinuities in the modulation functions cause the scattering of the beam that may end the stable propagation. Our results reveal a method to control the trajectory of solitons by designed variation of the optical lattice waveguides. Interesting examples presented include the snakelike and spiraling solitons that both can be adaptively induced in sinusoidally and helically shaped optical lattices. The controlled propagation paths provide an excellent opportunity for various applications, including optical switches and signal transmission, among others.

Solitions in magneto-optic waveguides with anti-cubic nonlinearity.

Optical soliton solutions are recovered for magneto-optic waveguides that maintains anti-cubic form of nonlinear refractive index. The analytical scheme is Jacobi's elliptic function approach. Once the solutions to the governing model are obtained in terms of Jacobi's elliptic functions, the limiting value to it's modulus of ellipticity reveals the complete spectrum of soliton solutions.

Computational investigation of cobalt and copper bis (oxothiolene) complexes as an alternative for olefin purification.

Considering that olefins present a large volume feedstock, it is reasonable to expect that their purification is industrially critical. After the discovery of the nickel bis (dithiolene) complex Ni(S2C2(CF3)2)2 that exhibits electro-catalytic activity with olefins but tends to decompose by a competitive reaction route, related complexes have been explored experimentally and theoretically. In this paper, a computational examination is performed on differently charged cobalt and copper bis (oxothiolene) complexes [M (OSC2(CN)2)2] to test their potential applicability as the catalysts for olefin purification, using the simplest olefin, ethylene. Possible reaction pathways for ethylene addition on these complexes were explored, to determine whether some of these candidates can avoid the reaction route that leads to decomposition, which is distinctive from the nickel complex, and to form stable adducts that can subsequently release ethylene by reduction. Our calculations suggest that the neutral cobalt complex might be an alternative catalyst, because all its forms can bind ethylene to produce stable interligand adducts with moderate to low activation barriers, rather than to form intraligand adducts that lead to decomposition. The calculations also predict that these interligand adducts are capable of releasing ethylene upon reduction. In addition, it can produce the desired interligand adducts following two different reaction pathways, assigned as the direct and the indirect, with no need for anion species as co-catalysts, which is crucial for the nickel complex. Thus, the olefin purification process could be much simpler by using this catalyst.

Parity-time symmetry light bullets in a cold Rydberg atomic gas.

A scheme is proposed to generate stable light bullets (LBs) in a cold Rydberg atomic system with a parity-time (PT) symmetric potential, by utilizing electromagnetically induced transparency (EIT). Using an incoherent population pumping between two low-lying levels and spatial modulations of control and auxiliary laser fields, we obtain a two-dimensional (2D) periodic optical potential with PT symmetry. Based on PT symmetry potential and the long-range Rydberg-Rydberg atomic interaction, the system may support slow LBs with low light intensity. Further, it is found that the local and non-local nonlinear coefficients and PT-symmetric potential can be tuned and used to manipulate the behavior of LBs.

Cubic-quartic bright optical solitons with improved Adomian decomposition method.

This paper numerically retrieves cubic-quartic solitons having power law of nonlinearity refractive index. An improvement of the Adomian decomposition scheme is the adopted algorithm of this work. The results are displayed along with the established error analysis.

Asymmetric conical diffraction in dislocated edge-centered square lattices: erratum.

Equations (1) and (2) in [Opt. Express27, 6300 (2019)10.1364/OE.27.006300] contain typos which are corrected in this erratum.

Asymmetric conical diffraction in dislocated edge-centered square lattices.

We investigate linear and nonlinear evolution dynamics of light beams propagating along a dislocated edge-centered square lattice. The band structure and Brillouin zones of this novel lattice are analyzed analytically and numerically. Asymmetric Dirac cones as well as the corresponding Bloch modes of the lattice are obtained. By adopting the tight-binding approximation, we give an explanation of the asymmetry of Dirac cones. By utilizing the appropriate Bloch modes, linear and nonlinear asymmetric conical diffraction are demonstrated. We find that both the focusing and defocusing nonlinearities can enhance the asymmetry of the conical diffractions.

Controllable optical rogue waves via nonlinearity management.

Using a similarity transformation, we obtain analytical solutions to a class of nonlinear Schrödinger (NLS) equations with variable coefficients in inhomogeneous Kerr media, which are related to the optical rogue waves of the standard NLS equation. We discuss the dynamics of such optical rogue waves via nonlinearity management, i.e., by selecting the appropriate nonlinearity coefficients and integration constants, and presenting the solutions. In addition, we investigate higher-order rogue waves by suitably adjusting the nonlinearity coefficient and the rogue wave parameters, which could help in realizing complex but controllable optical rogue waves in properly engineered fibers and other photonic materials.

Publisher Correction: Tamm plasmon modes on semi-infinite metallodielectric superlattices.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Insight into the Interactions of Amyloid ß-Sheets with Graphene Flakes: Scrutinizing the Role of Aromatic Residues in Amyloids that Interact with Graphene.

The interaction of amyloid ß-sheet segments with graphene-flake models is investigated by using DFT calculations. The structure of ß-sheets of selected amyloid segments is based on crystal structures obtained from the Protein Data Bank. Our study, based on DFT calculations for model systems, indicates that the interaction in amyloid-graphene aggregates can be stronger than the interaction in the respective amyloid-amyloid aggregates. The results also indicate an important specific role of aromatic sidechains in amyloid-graphene interactions. This work confirms recent experimental evidence that graphene and its modifications inhibit the aggregation of ß-amyloid peptides.

Optical Bloch oscillation and Zener tunneling in the fractional Schrödinger equation.

We demonstrate optical Bloch oscillation (OBO) and optical Zener tunneling (OZT) in the fractional Schrödinger equation (FSE) with periodic and linear potentials, numerically and theoretically. We investigate in parallel the regular Schrödinger equation and the FSE, by adjusting the Lévy index, and expound the differences between the two. We find that the spreading of the OBO decreases in the fractional case, due to the diminishing band width. Increasing the transverse force, due to the linear potential, leads to the appearance of OZT, but this process is suppressed in the FSE. Our results indicate that the adjustment of the Lévy index can effectively control the emergence of OBO and OZT, which can inspire new ideas in the design of optical switches and interconnects.