Kristian Motzek

Transverse modulational instabilities of counterpropagating solitons in photorefractive crystals

We study numerically the counterpropagating vector solitons in SBN:60 photorefractive crystals. A simple theory is provided for explaining the symmetry-breaking transverse instability of these solitons. Phase diagram is produced that depicts the transition from stable counterpropagating solitons to bidirectional waveguides to unstable optical structures. Numerical simulations are performed that predict novel dynamical beam structures, such as the standing-wave and rotating multipole vector solitonic clusters. For larger coupling strengths and/or thicker crystals the beams form unstable self-trapped optical structures that have no counterparts in the copropagating geometry.

Multicomponent dipole-mode spatial solitons

We study (2+1) -dimensional multicomponent spatial vector solitons with a nontrivial topological structure of their constituents and demonstrate that these solitary waves exhibit a symmetry-breaking instability, provided their total topological charge is nonzero. We describe a novel type of stable multicomponent dipole-mode solitons with intriguing swinging dynamics.

Polychromatic interface solitons in nonlinear photonic lattices

We demonstrate that interfaces between two nonlinear periodic photonic lattices offer unique possibilities for controlling the nonlinear interaction between different spectral components of polychromatic light, and a change in the light spectrum can have a dramatic effect on the propagation along the interface. We predict the existence of polychromatic surface solitons that differ fundamentally from their counterparts in infinite lattices.

Counterpropagating self-trapped beams in photorefractive crystals

A time-dependent model for the formation of self-trapped optical beams in photorefractive media by counterpropagating laser beams is analysed. It is shown that dynamically the beams may form stable steady-state structures or display periodic and irregular temporal behaviour. Steady-state solutions of non-uniform cross section are found, representing a general class of self-trapped waveguides, that include counterpropagating spatial vector solitons as a particular case. Two critical curves are identified in the plane of parameters, the first one separating vector solitons from the stable bidirectional waveguides and the second one separating stable waveguides from the unstable ones. Dynamically stable rotating beam structures are discovered that have no analogues in the usual steady-state theory of spatial solitons.

Self-trapping of polychromatic light in nonlinear periodic photonic structures

We study dynamical reshaping of polychromatic beams due to collective nonlinear self-action of multiple-frequency components in periodic and semi-infinite photonic lattices and predict the formation of polychromatic gap solitons and polychromatic surface solitons due to light localization in spectral gaps. We show that the self-trapping efficiency and structure of emerging polychromatic solitons depend on the input spectrum due to the lattice-enhanced dispersion, including the effect of crossover from localization to diffraction in media with defocusing nonlinearity.

Incoherent multi-gap optical solitons in nonlinear photonic lattices

We demonstrate numerically that partially incoherent light can be trapped in the spectral band gaps of a photonic lattice, creating partially incoherent multi-component spatial optical solitons in a self-defocusing nonlinear periodic medium. We find numerically such incoherent multi-gap optical solitons and discuss how to generate them in experiment by interfering incoherent light beams at the input of a nonlinear periodic medium.

Stabilization and breakup of coupled dipole-mode beams in an anisotropic nonlinear medium

We study the mutual trapping of two dipole-mode light beams in a medium with a nonlocal anisotropic saturable nonlinearity. It is shown that the incoherent attraction of perpendicularly aligned dipole-mode beams leads to the stabilization of their composite structure. Our numerical analysis gives a stationary solution that is stable only with respect to small amplitude modulations. The coupled solitary structure disintegrates in a well-defined way when the numerical perturbations or the experimental propagation length exceeds a certain limit. In this case a new and more robust, multicomponent solitary transverse light structure consisting of two dipole-mode vector solitons will be generated.

Dipole-mode vector solitons in anisotropic photorefractive media

Stable dipole-mode vector solitons in photorefractive (PR) crystals are studied, both in numerical simulations and in experimental investigation. Numerically exact multi-humped solitary solutions to the propagation equations of two incoherently coupled beams in PR media with an anisotropic nonlocal material response are found. A continuous set of dipole-mode vector solitons, ranging from the solitons with negligible dipole-mode contribution to the solitons with negligible ground mode contribution, is identified. The results are compared with experimental data.

Multi-component vector solitons in photorefractive crystals

We study the existence and stability of multi-component spatial optical solitons in anisotropic nonlocal photorefractive media. For the case of three components, we find numerically the whole family of composite solitons with two perpendicular dipole components, and show their stability for a wide range of parameters. We confirm our theoretical results by an experimental observation of these novel types of composite optical solitons in a photorefractive strontium barium niobate crystal.

Soliton transverse instabilities in anisotropic nonlocal self-focusing media.

We study, both numerically and experimentally, the transverse modulational instability of spatial stripe solitons in anisotropic nonlocal photorefractive media. We demonstrate that the instability scenarios depend strongly on the stripe orientation, but the anisotropy-induced features are largely suppressed for spatial solitons created by self-trapping of partially incoherent light.