Eugenia D. Eugenieva

Modulation Instability and Pattern Formation in Spatially Incoherent Light Beams

We report on the experimental observation of modulation instability of partially spatially incoherent light beams in noninstantaneous nonlinear media and show that in such systems patterns can form spontaneously from noise. Incoherent modulation instability occurs above a specific threshold that depends on the coherence properties (correlation distance) of the wave packet and leads to a periodic train of one-dimensional filaments. At a higher value of nonlinearity, the incoherent one-dimensional filaments display a two-dimensional instability and break up into self-ordered arrays of light spots. This discovery of incoherent pattern formation reflects on many other nonlinear systems beyond optics. It implies that patterns can form spontaneously (from noise) in diverse nonlinear many-body systems involving weakly correlated particles, such as atomic gases at (or near) Bose-Einstein condensation temperatures and electrons in semiconductors at the vicinity of the quantum Hall regime.

Self-trapping and flipping of double-charged vortices in optically induced photonic lattices.

We report what is believed to be the first observation of self-trapping and charge-flipping of double-charged optical vortices in two-dimensional photonic lattices. Both on- and off-site excitations lead to the formation of rotating quasi-vortex solitons, reversing the topological charges and the direction of rotation through a quadrupole-like transition state. Experimental results are corroborated with numerical simulations.

Design of switching junctions for two-dimensional discrete soliton networks

The performance of switching junctions in two-dimensional discrete-soliton networks is analyzed theoretically by coupled-mode theory. Our analysis can be used for the design of routing junctions with specified operational characteristics. Appropriately engineering the intersection site can further improve the switching efficiency of these junctions. Our analytical results are verified by numerical simulations.

Elliptic incoherent solitons in saturable nonlinear media

We identify elliptic incoherent spatial solitons in isotropic saturable nonlinear media. These solitary states are possible, provided that their correlation function is anisotropic. The propagation dynamics of this new class of solitons are investigated by use of numerical simulations. We find that, during a collision event of two such elliptic solitons, their intensity ellipse rotates, and at the same time their centers of gravity tend to revolve around each other.

Transmission of images through highly nonlinear media by gradient-index lenses formed by incoherent solitons

We experimentally demonstrate image transmission through a noninstantaneous self-focusing medium. A partially spatially incoherent soliton is used to form a multimode waveguide in a photorefractive crystal, and the modes of that waveguide are used to transmit an incoherent image through this nonlinear medium.

Minimizing bending losses in two-dimensional discrete soliton networks: errata

We show that reflection losses suffered by discrete solitons along sharp bends in two-dimensional waveguide-array networks can be almost eliminated. Analysis indicates that this can be accomplished by appropriately engineering the corner site of the bend. Our analytical results are verified by numerical simulations.

Self-trapping of bright rings.

We present experimental observations of self-trapped rings carrying zero topological charge, along with simulations that display the self-focusing dynamics of the rings and their stability features in materials with saturable nonlinearities.

Modulation instability and pattern formation of incoherent light

Summary form only given. Modulation Instability (MI) is a universal process that appears in most nonlinear wave systems in nature. Because of MI, small amplitude and phase perturbations (from noise) grow rapidly under the combined effects of nonlinearity and diffraction (or dispersion, in the temporal domain). As a result, a broad optical beam (or a quasi-CW pulse) disintegrates during propagation, leading to filamentation or to break-up into pulse trains. Modulation instability is largely considered as a precursor of solitons, because the filaments (or pulse trains) that emerge from the MI process are actually trains of almost ideal solitons. We have theoretically demonstrated that MI can also exist in relation with partially-incoherent wave-packets or beams and shows a threshold-like dependence of the involved nonlinearity.

Self-deflection of partially spatially coherent beams and solitons in photorefractive crystals

Summary form only given. Using the so-called coherent density approach, we have investigated both analytically and numerically the self-bending behavior of partially coherent beams and solitons in biased and unbiased photorefractive crystals. We found that in the case of bright incoherent soliton beams the self-bending angle increases as the degree of coherence of the optical beam decreases.

Selfdeflection of partially spatially coherent beams and solitons in photorefractive crystals

We investigate both analytically and numerically the self-bending behavior of partially coherent beams and solitons in biased and unbiased photorefractive crystals. We show that in the linear diffraction regime, the self-bending angle decreases with increasing the degree of incoherence. This is in contrast with the case of partially coherent soliton beams.