Self-bending photorefractive solitons

Solitary wave formation under the interplay between spatial inhomogeneity and nonlocality

The presence of spatial inhomogeneity in a nonlinear medium restricts the formation of solitary waves (SW) on a discrete set of positions, whereas a nonlocal nonlinearity tends to smooth the medium response by averaging over neighboring points. The interplay of these antagonistic effects is studied in terms of SW formation and propagation. Formation dynamics is analyzed under a phase-space approach and analytical conditions for the existence of either discrete families of bright SW or continuous families of kink SW are obtained in terms of Melinikov's method. Propagation dynamics are studied numerically and cases of stable and oscillatory propagation as well as dynamical transformation between different types of SW are shown. The existence of different types and families of SW in the same configuration, under appropriate relations between their spatial width and power with the inhomogeneity and the nonlocality parameters, suggests an advanced functionality of such structures that is quite promising for applications.

Observation of electro-activated localized structures in broad area VCSELs

We demonstrate experimentally the electro-activation of a localized optical structure in a coherently driven broad-area vertical-cavity surface-emitting laser (VCSEL) operated below threshold. Control is achieved by electro-optically steering a writing beam through a pre-programmable switch based on a photorefractive funnel waveguide.

Soliton generation by counteracting gain-guiding and self-bending

We introduce a concept for stable spatial soliton formation, mediated by the competition between self-bending induced by a strongly asymmetric nonlocal nonlinearity and spatially localized gain superimposed on a wide pedestal with linear losses. When acting separately both effects seriously prevent stable localization of light, but under suitable conditions they counteract each other, forming robust soliton states that are attractors for a wide range of material and input light conditions.

Localization of light in a parabolically bending waveguide array in thermal nonlinear media

A parabolically longitudinally bending waveguide array imprinted into thermal nonlinear media is found to support the localized stationary solitons. The localization results from the suppression of a curvature effect by the nonlinearity with an infinite-range nonlocality. The localization criterion is given analytically. Solitons propagate stably along a curved trajectory without bending loss, and their locations are significantly influenced by the waveguide curvature. These solitons represent the first example of stationary localized solitons encountered in curved waveguides.

Information throughput of photorefractive spatial solitons in the telecommunication range

Photorefractive spatial solitons are attractive elements because they can be used as controllable optical interconnectors for all-optical devices. To our knowledge, until now their properties were investigated in terms of energy transportation. We suggest considering photorefractive spatial solitons as optically induced information channels. The experimental technique to measure the information throughput of photorefractive spatial solitons in accordance with Shannon's definition was developed and demonstrated by us. We experimentally demonstrated that in the wavelength range of 1520-1630 nm it can be estimated as large as approximately 90 Tbits/s. We also experimentally demonstrate a measurement of the group-velocity dispersion and show the limitation of the pulse transfer rate of the induced waveguides to approximately 6.2 THz.

Gap solitons supported by optical lattices in photorefractive crystals with asymmetric nonlocality

We address the impact of the asymmetric nonlocal diffusion nonlinearity of gap solitons supported by photorefractive crystals with an imprinted optical lattice. We reveal how the asymmetric nonlocal response alters the domains of existence and the stability of solitons originating from different gaps. We find that in such media gap solitons cease to exist above a threshold of the nonlocality degree. We discuss how the interplay between nonlocality and lattice strength modifies the gap soliton mobility.

Mechanisms supporting long propagation regimes of photorefractive solitons

We extend investigation of one-dimensional solitons in biased photorefractive crystals to long propagation regimes, where self-trapping over a large number of linear diffraction lengths combines with the progressive growth of generally distortive spatially nonlocal components. Results indicate that saturation halts the radiative misshaping of the soliton, which follows that specific bending trajectory along which its evolution is governed by the same local screening nonlinearity that intervenes in short propagation conditions, where spatial nonlocality has a negligible effect. This finding not only allows the prediction of the curvature and of the relative role of charge displacement and diffusion, but implies a set of interesting observable effects, such as boomerangs, counterpropagating and cavity geometries, quasirectilinear and anomalous collisions, along with specific consequences on soliton arrays and on coupling to bulk gratings.

Tunable soliton self-bending in optical lattices with nonlocal nonlinearity

We address the phenomenon of soliton self-bending in Kerr-type nonlocal nonlinear media with an imprinted transverse periodic modulation of the linear refractive index. We show that the imprinted optical lattice makes possible to control the mobility of soliton by varying the depth and the frequency of the linear refractive index modulation.

Stability of screening solitons in photorefractive media

Normal mode stability of both rectilinear and self-bending photorefractive screening solitons is considered. In each case, the Evans function procedure is used to investigate stability and to search for internal modes. For the rectilinear case, a standard Evans function procedure is applied. However, in the self-bending case the asymptotic form of the eigenvalue problem is a system of Airy equations, instead of the usual system of constant coefficient differential equations. To overcome this difference, a modified version of the Evans function method, using Airy functions rather than exponentials, is implemented and applied. The results confirm stability and give an internal mode pattern in good agreement with full numerical integration.

Self-bending of the coupled spatial soliton pairs in a photorefractive medium with drift and diffusion nonlinearity

The propagation of two incoherently coupled laser beams (coupled soliton pairs) in the photorefractive crystal with drift and diffusion components of nonlinear response is investigated. By the effective particles method we have shown that not only the well-known Manakov's soliton pairs but also asymmetric pairs can propagate undistorted in photorefractive crystal with diffusion nonlinearity along the parabolic trajectory for the definite relations of propagation constants. We numerically found the exact profiles of the specific multihump soliton solutions that are possible only in the photorefractive medium with nonlocal diffusion response. The stability properties and specific features of pair collisions are analyzed.

Analytical solution for photorefractive screening solitons

We study formation and interaction of one-dimensional screening solitons in a photorefractive medium with sublinear dependence of the photoconductivity on light intensity. We find an exact analytical solution to the corresponding nonlinear Schrodinger equation. We show that these solitons are stable in propagation and their interaction is generic for solitons of saturable nonlinearity. In particular, they may fuse or "give birth" to new solitons upon collision.

Dynamics of formation and interaction of photorefractive screening solitons

An experimental and numerical investigation of the dynamical, time-dependent effects accompanying the formation and interaction of two-dimensional spatial screening solitons in a photorefractive strontium barium niobate crystal is performed. These effects include initial diffraction, collapse to the soliton shape, the oscillation of beam diameters, beam bending, and the rotation, twisting, and turning of soliton pairs. The dynamics of complex spiraling of two incoherent solitons is considered in more detail.

Fusion and birth of spatial solitons upon collision

We study experimentally the collision of photorefractive screening solitons in a strontium barium niobate crystal. Depending on the relative phase of the solitons and their intersecting angle, such effects as soliton birth, energy exchange, and soliton fusion have been observed.