Anomalous interactions of spatial gap solitons in optically induced photonic lattices

We demonstrate coherent interactions between spatial gap solitons in optically induced photonic lattices. Because of the "staggered" phase structures, two in-phase (out-of-phase) bright gap solitons can repel (attract) each other at close proximity, in contrast to soliton interaction in homogeneous media. A reversal of energy transfer direction and a transition between attractive and repulsive interaction forces can be obtained solely by changing the initial soliton separation relative to the lattice spacing.     

Backward-wave propagation and discrete solitons in a left-handed electrical lattice

We study experimentally, analytically and numerically the backward-wave propagation, and formation of discrete bright and dark solitons in a nonlinear electrical lattice. We observe experimentally that a focusing (defocusing) effect occurs above (below) a certain carrier frequency threshold, and backward-propagating bright (dark) discrete solitons are formed. We develop a discrete model emulating the relevant circuit and benchmark its linear properties against the experimental dispersion relation. Using a perturbation method, we derive a nonlinear Schrödinger equation, that predicts accurately the carrier frequency threshold. Finally, we use numerical simulations to corroborate our findings and monitor the space-time evolution of the discrete solitons.     

Dynamics of bright discrete staggered solitons in photovoltaic photorefractive media

Theoretical results on spatial optical bright solitons excited in arrays of nonlinear defocusing waveguides, that result from the photovoltaic effect in a photorefractive material, are presented. The existence of four types of stationary discrete bright staggered solitons, on-site, inter-site, twisted inter-site, and twisted on-site solitons, is shown both analytically and numerically, and their stability properties are investigated. The maximum Hamiltonian of staggered solitons with the same total power corresponds to stable modes. It is shown that for low total power the on-site mode is stable while in the high power regime the inter-site mode is stable. These results are confirmed numerically. In addition, steering properties of localized modes are investigated by introducing a transversal translational shift. Because of the translational symmetry between on-site and inter-site localized modes they are considered as two dynamical realizations of the same moving mode, and the formalism of the Peierls-Nabarro effective potential is applied to interpret the exchange between trapping and steering of these modes. This critically depends on the mode’s total power and the introduced phase difference. On the other hand, steering of twisted inter-site and on-site localized modes is not numerically observed. Instead, transversal perturbation leads to a transformation of twisted modes either into a trapped on-site mode of smaller power and radiation, or into two trapped on-site modes.     

Observation of discrete vortex solitons in optically induced photonic lattices

We report on the first experimental observation of discrete vortex solitons in two-dimensional optically induced photonic lattices. We demonstrate strong stabilization of an optical vortex by the lattice in a self-focusing nonlinear medium and study the generation of the discrete vortices from a broad class of singular beams.     

Necklacelike solitons in optically induced photonic lattices

We report the first observation of stationary necklacelike solitons. Such necklace structures were realized when a high-order vortex beam was launched appropriately into a two-dimensional optically induced photonic lattice. Our theoretical results obtained with continuous and discrete models show that the necklace solitons resulting from a charge-4 vortex have a pi phase difference between adjacent "pearls" and are formed in an octagon shape. Their stability region is identified.     

Subdiffractive discrete cavity solitons

We describe what we believe to be novel types of discrete cavity solitons in nonlinear waveguide arrays that are driven by an external holding beam. We demonstrate that a holding beam with a definite inclination drives the system in a subdiffractive regime and allows the formation of stable discrete cavity solitons. We predict the existence of both bright and dark moving midband discrete cavity solitons for an identical set of system parameters for both focusing and defocusing Kerr nonlinearities.     

Observation of surface gap solitons in semi-infinite waveguide arrays

We report on the observation of surface gap solitons found to exist at the interface between uniform and periodic dielectric media with defocusing nonlinearity. We demonstrate strong self-trapping at the edge of a LiNbO3 waveguide array and the formation of staggered surface solitons with propagation constant inside the first photonic band gap. We study the crossover between linear repulsion and nonlinear attraction at the surface, revealing the mechanism of nonlinearity-mediated stabilization of the surface gap modes.     

Observation of second-band vortex solitons in 2D photonic lattices

We demonstrate second-band bright vortex-array solitons in photonic lattices. This constitutes the first experimental observation of higher-band solitons in any 2D periodic system. These solitons possess complex intensity and phase structures, yet they can be excited by a simple highly localized vortex-ring beam. Finally, we show that the linear diffraction of such beams exhibits preferential transport along the lattice axes.     

Dark-bright discrete solitons: A numerical study of existence, stability and dynamics

In the present work, we numerically explore the existence and stability properties of different types of configurations of dark-bright solitons, dark-bright soliton pairs and pairs of dark-bright and dark solitons in discrete settings, starting from the anti-continuum limit. We find that while single discrete dark-bright solitons have similar stability properties to discrete dark solitons, their pairs may only be stable if the bright components are in phase and are always unstable if the bright components are out of phase. Pairs of dark-bright solitons with dark ones have similar stability properties as individual dark or dark-bright ones. Lastly, we consider collisions between dark-bright solitons and between a dark-bright one and a dark one. Especially in the latter and in the regime where the underlying lattice structure matters, we find a wide range of potential dynamical outcomes depending on the initial soliton speed.     

Bright Bose-Einstein gap solitons of atoms with repulsive interaction

We report on the first experimental observation of bright matter wave solitons for 87Rb atoms with repulsive atom-atom interaction. This counterintuitive situation arises inside a weak periodic potential, where anomalous dispersion can be realized at the Brillouin zone boundary. If the coherent atomic wave packet is prepared at the corresponding band edge, a bright soliton is formed inside the gap. The strength of our system is the precise control of preparation and real time manipulation, allowing the systematic investigation of gap solitons.     

DNA adsorption on graphene

We study analytically the properties of the optical absorption and the spatial weak-light solitons in a quantum dot molecule system with the interdot tunneling coupling (ITC). It is shown that, for the linear case, there exists tunneling induced transparency (TIT) in the context of a weak ITC, while the TIT can be replaced by Autler-Townes splitting in the presence of a strong ITC. For the nonlinear case, it is probable to realize the spatial optical solitons even under weak light intensity. Interestingly, we find that there appears transformation behavior between the bright and dark solitons by properly turning both the ITC strength and the detuning of the probe field. Meanwhile, the transformation condition of the bright and dark solitons is obtained. Additionally it is also found that the amplitude of the solitons first descends and then rises with the increasing of ITC strength. Our results may have potential applications for nonlinear optical experiments and optical telecommunication engineering in solid systems.     

Bright spatial solitons on a partially incoherent background

We present the first observation of incoherent antidark spatial solitons in noninstantaneous nonlinear media. This new class of soliton states involves bright solitons on a partially incoherent background of infinite extent. In the case where the nonlinearity is of the Kerr type, their existence is demonstrated analytically by means of an exact solution. Computer simulations and experiments indicate that these incoherent antidark solitons can propagate in a stable fashion provided that the spatial coherence of their background is reduced below the incoherent modulation instability threshold.     

Two-dimensional multipole solitons in nonlocal nonlinear media

We present the experimental observation of scalar multipole solitons in highly nonlocal nonlinear media, including dipole, tripole, quadrupole, and necklace-type solitons, organized as arrays of out-of-phase bright spots. These complex solitons are metastable, but with a large parameters range where the instability is weak, permitting their experimental observation.     

Compression of Bright Bound Solitons in the Bose-Einstein Condensates with Exponentially Time-Dependent Atomic Scattering Length by the Feshbach Resonance

We investigate compression of the bright bound solitons in the Bose-Einstein condensates (BECs) by exponentially increasing the absolute value of the atomic scattering length. Similarity transformation and Hirota bilinear method are used to symbolically solve the one-dimensional nonlinear Schrödinger equation with the time-dependent coefficients. We present types of the bright bound solitons in compression through manipulating their initial coherence. Results show that the improved quantity of the atomic density peaks can be observed before the collapse of the solitons when their coherence is increased. Furthermore, we discuss how those compressed bound solitons are influenced by the adjacent solitons. The bound structures in our study are illustrated to exist with the parameters within the current experimental capacity (the spatial and temporal ranges of the bound solitons are less than 56 μm and 50 ms in our investigation), which suggests a future observation in the BECs experiments.     

Matching group velocity of bright and/or dark solitons via double-dark resonances

We propose a scheme which can generate group velocity matching bright and/or dark solitons in a four-level tripod configuration atomic system via double-dark resonances. It is shown that the linear absorption properties can be controlled by the controlling fields. For the nonlinear case, the optical soliton can form in the first and second electromagnetically induced transparency windows and their group velocities can be matched under the condition of equal half Rabi frequencies of the two controlling fields. We also show that adjusting the amplitude and group velocity of the soliton as well as the bright and dark solitons conversion can be realized.     

Controlled generation and steering of spatial gap solitons

We demonstrate the first fully controlled generation of immobile and slow spatial gap solitons in nonlinear periodic systems with band-gap spectra, and observe the key features of gap solitons that distinguish them from discrete solitons, including a dynamical transformation of gap solitons due to nonlinear interband coupling. We also describe theoretically and confirm experimentally the effect of the anomalous steering of gap solitons in optically induced photonic lattices.     

Dark solitons in ferromagnetic chains with first- and second-neighbor interactions

We present a study of the ferromagnetic spin chain with both first- and second-neighbor interactions. We obtain the condition for the appearance and stability of bright and dark solitons for arbitrary wave number in the Brillouin zone. The influence of the second-neighbor interaction and the anisotropy on the soliton properties is considered. The scattering of dark solitons from point defects in the discrete spin chain is investigated numerically.     

The linear and nonlinear optical effects of white light

An overview of our research group’s experimental and theoretical developments is provided on the linear and nonlinear optical effects of white light since 2003. Their work includes the experimental researches on the white light one-dimensional photovoltaic dark spatial solitons and the waveguides and directional couplers induced by them, the circular and elliptic white-light dark spatial solitons and the white-light photorefractive phase masks, two-dimensional white-light photonic lattices and the applicati...     

Modulation instability of bright photovoltaic solitons on a partially incoherent background

We present the observation of incoherent anti-dark photovoltaic solitons in LiNbO₃:Fe crystal. This new class of soliton states involves bright photovoltaic solitons on a background beam meeting ?? > 1, where ?? is the ratio of background illumination photovoltaic constant to that of soliton beam. For ?? < 1, dark photovoltaic solitons are generated. Furthermore, this novel type solitons are investigated experimentally by injecting coherent light and partially coherent background of infinite extent. In case of spatial coherence of the background lower than the threshold of incoherent modulation instability, these results indicate that bright photovoltaic solitons can propagate in a stable fashion.     

光诱导光子晶格结构中新型的离散空间光孤子

离散孤子标志着从线性到非线性，从连续到非连续，从相干到非相干，人们对孤子认识的一个飞越．文章简要回顾了近期在二维光致光子晶格结构中有关空间离散光孤子的研究，包括基模离散孤子、类矢量离散孤子、离散偶极孤子、离散涡旋孤子和离散孤子串等．在非线性光折变晶体里用部分相干光诱导的波导阵列中，对每一种离散孤子，都清楚地观测到光从二维的离散衍射状态到自囚禁形成离散孤子的转变过程，获得的结果将对其他离散非线性系统中类似现象的研究有所启发．