Soliton Emission Research Articles

Widely varying giant Goos–Hänchen shifts from Airy beams at nonlinear interfaces

We present a numerical study of the giant Goos-Hänchen shifts (GHSs) obtained from an Airy beam impinging on a nonlinear interface. To avoid any angular restriction associated with the paraxial approximation, the analysis is based on the nonlinear Helmholtz equation. We report the existence of nonstandard nonlinear GHSs displaying an extreme sensitivity to the input intensity and the existence of multiple critical values. These intermittent and oscillatory regimes can be explained in terms of competition between critical coupling to a surface mode and soliton emission from the refracted beam component and how this interplay varies with localization of the initial Airy beam.

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.

Multimode ultrafast nonlinear optics in optical waveguides: numerical modeling and experiments in kagomé photonic-crystal fiber

We introduce a general full-field propagation equation for optical waveguides, including both fundamental and higher order modes, and apply it to the investigation of spatial nonlinear effects of ultrafast and extremely broadband nonlinear processes in hollow-core optical fibers. The model is used to describe pulse propagation in gas-filled hollow-core waveguides including the full dispersion, Kerr, and ionization effects. We study third-harmonic generation into higher order modes, soliton emission of resonant dispersive waves into higher order modes, intermodal four-wave mixing, and Kerr-driven transverse self-focusing and plasma-defocusing, all in a gas-filled kagome photonic crystal fiber system. In the latter case a form of waveguide-based filamentation is numerically predicted.

Quasi-periodicity of vector solitons in a graphene mode-locked fiber laser

We report on the experimental observation of quasi-periodic dynamics of vector solitons in an erbium-doped fiber laser passively mode-locked with atomic layer graphene. Apart from the stable polarization-locked vector soliton emission, it was found that under certain conditions the fiber laser could also emit vector solitons with quasi-periodic pulse energy variation and polarization rotation during the cavity roundtrips. We show that the physical mechanism for the quasi-periodic vector soliton evolution is cavity-induced soliton modulation instability. Quasi-periodic evolution of multiple vector solitons was also observed in the same laser.

Dynamical generation of interwoven soliton trains by nonlinear emission in binary Bose-Einstein condensates

We propose a method for the generation of trains of alternating bright solitons in two-component Bose-Einstein condensates, using controlled emission of nonlinear matter-waves in the uncoupled regime with spatially-varying intra-species interaction and out-of-phase oscillations of the ground states in the trap. Under this scheme, solitons are sequentially launched from the different components, and interact with each other through phase-independent cross-coupling. We obtain an analytical estimation of the critical condition for soliton emission using a geometric guiding model, in analogy with integrated optical systems. In addition, we show how strong initial perturbations in the system can trigger the spontaneous generation of supersolitons, i.e. localized phonon-like excitations of the soliton trains. Finally, we demonstrate the controllable generation of slow and fast supersolitons by adding external localized potentials in the nonlinear region.

Controllable stretched pulse and dissipative soliton emission using non‐linear polarisation rotation and cavity loss tuning mechanism

The authors demonstrate a controllable generation of a stretched pulse and dissipative soliton in a normal dispersion erbium-doped fibre laser (EDFL) based on non-linear polarisation rotation technique. It is found that the mode-locking could self-start in the EDFL even without inserting a polariser in the cavity because of the large residual polarisation-dependent loss of a cavity component. By slightly adjusting a polarisation controller, a stretched pulse can be switchable to the dissipative soliton, while maintaining the repetition rate of 2.5 MHz. The stretched pulse has a pulse width of 0.35 ps with energy of 127.6 pJ, whereas the dissipative soliton has a pulse width of 0.60 ps with energy of 208.4 pJ.

Continuous emission of fundamental solitons from vortices in dissipative media by a radial-azimuthal potential

We report novel dynamical regimes of dissipative vortices supported by a radial-azimuthal potential (RAP) in the 2D complex Ginzburg-Landau (CGL) equation with the cubic-quintic nonlinearity. First, the stable solutions of vortices with intrinsic vorticity S = 1 and 2 are obtained in the CGL equation without potential. The RAP is a model of an active optical medium with respective expanding anti-waveguiding structures with m (integer) annularly periodic modulation. If the potential is strong enough, m jets fundamental of solitons are continuously emitted from the vortices. The influence of m, diffusivity term (viscosity) β, and cubic-gain coefficient ε on the dynamic region is studied. For a weak potential, the shape of vortices are stretched into the polygon, such as square for m = 4. But for a stronger potential, the vortices will be broke into m fundamental solitons.

Controllable dissipative soliton and Q-switched pulse emission in a normal dispersion fiber laser using SESAM and cavity loss tuning mechanism

We report on the controllable generation of the dissipative soliton and the Q-switched pulse in a normal dispersion fiber ring laser. The hybrid saturable absorber is used to obtain the dissipative soliton or the Q-switched pulse by slightly adjusting the polarization controller. Based on the experimental results and theoretical analysis, the controllable dissipative soliton and Q-switched pulse emission can be induced by the cavity loss tuning mechanism of the fiber laser.

Evidence of dissipative solitons in Yb^3+:CaYAlO_4

Operation of an end-pumped Yb³⁺:CaYAlO₄ laser operating in the positive dispersion regime is experimentally investigated. The laser emitted strongly chirped pulses with extremely steep spectral edges, resembling the characteristics of dissipative solitons observed in fiber lasers. The results show that dissipative soliton emission constitutes another operating regime for mode locked Yb³⁺-doped solid state lasers, which can be explored for the generation of stable large energy femtosecond pulses.

Bound states of solitons in a fiber laser mode locked with carbon nanotube saturable absorber

We report on the experimental observation of bound states of solitons in an erbium-doped fiber laser passively mode-locked by the carbon nanotube saturable absorber. Bound states of solitons with various pulse separations are obtained. While the tightly bound solitons always exhibit the same set of fixed discrete pulse separations with π or π/2 phase difference, the feature becomes less obvious for the loosely bound solitons. The result that various states of the bound solitons were obtained in the same fiber laser makes a systematic experimental study on them and a comparison of their properties possible. Our results once again show that the bound soliton emission is an intrinsic feature of the mode-locked soliton fiber lasers.

Resonant emission of solitons from impurity-induced localized waves in nonlinear lattices

We propose a mechanism for soliton creation from resonantly excited localized waves via supratransmission in band gaps of nonlinear lattices. A nonlinear localized wave, which is formed by and vibrates around an impurity with an intrinsic frequency, is found to undergo a local resonance when subject to an external forcing. Under the resonance, an instability develops that leads to the efficient emission of solitons at a much lower rate than that in uniform lattices with no impurity.

Bi-directional spatial soliton emission at engineered nonlinear waveguide interfaces

We observed tunable bi-directional emission of spatial solitons at a quadratically nonlinear interface in periodically poled lithium niobate planar waveguides. The interface consists of the boundary between two quasi-phase-matched regions with a different poling period. We show the intensity and phase-mismatch (temperature or wavelength) dependence of the phenomena.

Transcritical flow of a Bose-Einstein condensate through a penetrable barrier

The problem of the transcritical flow of a Bose-Einstein condensate through a wide repulsive penetrable barrier is studied analytically using the combination of the localized "hydraulic" solution of the 1D Gross-Pitaevskii equation and the solutions of the Whitham modulation equations describing the resolution of the upstream and downstream discontinuities through dispersive shocks. It is shown that within the physically reasonable range of parameters the downstream dispersive shock is attached to the barrier and effectively represents the train of very slow dark solitons, which can be observed in experiments. The rate of the soliton emission, the amplitudes of the solitons in the train and the drag force are determined in terms of the BEC oncoming flow velocity and the strength of the potential barrier. A good agreement with direct numerical solutions is demonstrated. Connection with recent experiments is discussed.

Soliton Generation in a Semiconductor Circular Ring Laser with a Y-Junction Coupler

We report the observation of the emission of solitons from a semiconductor circular ridge waveguide ring laser with a Y-junction coupler. The light–current (L–I) characteristics of the soliton emission through the nonwaveguide region, which refers to the photovoltaic solitons, has a low threshold value and a high quantum efficiency compare to the emission from the Y-junction coupler, and the spectrum of the soliton emission is similar to that of a linear strip laser with multimode emission. The feedback light from the end facet of the Y-junction coupling section continuously enhances the excitation of the photovoltaic solitons through the nonwaveguide region until the lasing condition is reached. It is suggested that the circular ring laser can be an alternative channel to light wave control in integrated optoelectronic system.

Passive harmonic mode locking of soliton bunches in a fiber ring laser

We report on the experimental observation of passive harmonic mode locking of bunches of single-pulse solitons or twin-pulse solitons in an Erbium-doped fiber ring laser. Experimental investigations on the phenomenon revealed that, although the soliton interaction between the adjacent single-/twin-pulse solitons in a bunch is weaker than that of the pulse interaction in the twin-pulse solitons, a soliton bunch could also function as a unit and form the state of passively harmonic mode-locking. Harmonic mode-locking is one of the intrinsic characteristics of soliton emission in passively mode-locked fiber ring lasers. It can be formed based on the single-pulse soliton, twin-pulse soliton, or bunch of solitons.

Effects of the Film Index on the Fields of Nonlinear-Cladding Optical Waveguides With Butt-Coupled Linear Waveguides

Effects of the film index of nonlinear-cladding optical waveguides on the evolution of fields at medium power levels are investigated numerically. The analysis method is based on mode matching of local normal modes of bounded waveguides. For waveguides with a film whose refractive index is greater than or nearly equal to the linear part of the index of the nonlinear cladding, the path of a beam winds between the film and the nonlinear cladding or in the film. In the case of a film index that is to some extent less than the linear part index of the nonlinear cladding, a beam is emitted to the nonlinear cladding, i.e., spatial soliton emission occurs. The lateral shift of a butt-coupled linear waveguide toward the substrate makes a beam emit to the nonlinear cladding with increased angles. Saturation and linear absorption weakens the winding of a path or decreases the angle of emission.

Effects of the Film Thickness on the Fields of Nonlinear-Cladding Optical Waveguides With Butt-Coupled Linear Waveguides

Effects of the film index of nonlinear-cladding optical waveguides on the evolution of fields at medium power levels are investigated numerically. The analysis method is based on mode matching of local normal modes of bounded waveguides. For waveguides with a film whose refractive index is greater than or nearly equal to the linear part of the index of the nonlinear cladding, the path of a beam winds between the film and the nonlinear cladding or in the film. In the case of a film index that is to some extent less than the linear part index of the nonlinear cladding, a beam is emitted to the nonlinear cladding, i.e., spatial soliton emission occurs. The lateral shift of a butt-coupled linear waveguide toward the substrate makes a beam emit to the nonlinear cladding with increased angles. Saturation and linear absorption weakens the winding of a path or decreases the angle of emission.

Soliton emission in amplifying lattice surfaces

We address surface solitons supported by the interface of optical lattices imprinted in saturable media with surface-localized gain. The nonlinearity saturation puts restrictions on the maximal energy flow carried by surface solitons. As a consequence, the presence of a thin amplifying layer near the surface results in the controllable emission of solitons toward the lattice at angles depending on the amplification rate and lattice depth.

Soliton trains and vortex streets as a form of Cerenkov radiation in trapped Bose–Einstein condensates

We numerically study the nucleation of gray solitons and vortex–antivortex pairs created by a moving impurity in, respectively, 1D and 2D Bose–Einstein condensates (BECs) confined by a parabolic potential. The simulations emulate the motion of a localized laser-beam spot through the trapped condensate. Our results for the 1D case indicate that, due to the inhomogeneity of the BEC density, the critical speed for nucleation, as a function of the condensate density displays two distinct dependences. In particular, the square root of the critical density for nucleation as a function of speed displays two different linear regimes corresponding to small and large velocities. Effectively, the emission of gray solitons and vortex–antivortex pairs occurs for any velocity of the impurity, as any given velocity will be supercritical in a region with a sufficiently small density. At longer times, the first nucleation is followed by generation of an array of solitons in 1D (“soliton train”) or vortex pairs in 2D (“vortex street”) by the moving object.

Spectral transformation of femtosecond Cr:forsterite laser pulses in a flint-glass photonic-crystal fiber

Nonlinear-optical performance of photonic-crystal fibers (PCFs) made of highly nonlinear TF10 glass is studied and compared with the general tendencies of nonlinear-optical interactions in fused-silica PCFs. The loss of TF10 glass PCFs prevents the generation of supercontinuum emission with a broad and flat spectrum, which typically requires propagation lengths comparable with or exceeding the attenuation length of the fiber. However, dispersive-wave emission of solitons, induced by high-order dispersion, phase-matched four-wave-mixing processes, and self-phase-modulation-induced spectral broadening are substantially enhanced in TF10 glass PCFs due to the high material nonlinearity, providing a high efficiency of frequency conversion of Cr:forsterite laser pulses.