Dipole azimuthons and vortex charge flipping in nematic liquid crystals

Optothermal vortex-solitons in liquid crystals

We report on vortex-solitons generated in dye-doped nematic liquid crystals by a purely optothermal nonlocal nonlinearity. This response not only supports stable doughnut-shaped ordinary-wave beams with orbital angular momentum, but also provides self-confined solitary waves with excellent trajectory and profile stability over time. Using an interferometric technique, we also investigate the role of nonlocal nonlinearity in the non-illuminated axial region.

Vortex nematicons in planar cells

We provide experimental evidence that stable vortex-solitons in nematic liquid crystals, termed vortex nematicons, can be generated in planar cells without any external biases, neither electric nor magnetic. We report on nonlinear vortices with extraordinary-wave beams in various undoped samples, pin-pointing how material nonlocality and birefringence aid their stable propagation. Finally, we also demonstrate confinement and waveguiding of an incoherent co-polarized probe signal by the nonlinear vortex.

Particlelike Behavior of Topological Defects in Linear Wave Packets in Photonic Graphene

Topological defects, such as quantum vortices, determine the properties of quantum fluids. Their study has been at the center of activity in solid state and BEC communities. In parallel, the nontrivial behavior of linear wave packets with complex phase patterns was investigated by singular optics. Here, we study the formation, evolution, and interaction of optical vortices in wave packets at the Dirac point in photonic graphene. We show that while their exact behavior goes beyond the Dirac equation and requires a full account of the lattice properties, it can be still approximately described by an effective theory considering the phase singularities as "particles". These particles are capable of mutual interaction, with their trajectory obeying the laws of dynamics.

Generation of structured light by multilevel orbital angular momentum holograms

Structured light has been created by a myriad of near-and far-field techniques and has found both classical and quantum applications. In the case of orbital angular momentum (OAM), continuous spiral phase patterns in dynamic or geometric phase are often employed with the phase patterns existing across the entire transverse plane. Here, we exploit the uncertain relationship between OAM and angle in order to create structured OAM fields by using multilevel OAM holograms. We show theoretically and experimentally that only a multilevel angular phase contour in the near-field is needed to create structured OAM light in the far-field, exploiting the reciprocal nature of angular momentum and angle. We use this approach to demonstrate exotic 3D structured light control to show the Poynting vector's evolution in such fields and to highlight the physics underlying this phenomenon.

Stable vortex soliton in nonlocal media with orientational nonlinearity

We report on the first experimental observation of stable vortex solitons in nematic liquid crystals with nonlocal nonlinear reorientational response. We show how these nonlinear vortex beams can be formed and confined in extraordinary optical waves by employing the cell with no lateral boundary conditions and the application of an external magnetic field that effectively controls the molecular direction and propagation of the self-trapped beams. We also find that these vortex solitons can be generated in certain ranges of the input beam power.

Observation of stable-vector vortex solitons

We report on the first experimental observation of stable-vector vortex solitons in nonlocal nonlinear media with a reorientational response, such as nematic liquid crystals. These solitons consist of two co-polarized, mutually trapped beams of different colors, a bright fundamental spatial soliton, and a nonlinear optical vortex. The nonlinear vortex component, which is normally unstable in nonlinear media, is stabilized and confined here by the highly nonlocal refractive potential induced by the soliton.

Power-induced evolution and increased dimensionality of nonlinear modes in reorientational soft matter

We demonstrate the evolution of higher order one-dimensional guided modes into two-dimensional solitary waves in a reorientational medium. The observations, carried out at two different wavelengths in chiral nematic liquid crystals, are in good agreement with a simple nonlocal nonlinear model.

Accessible solitons in diffusive media

We investigate spatial solitons in nonlocal media with a nonlinear index well modeled by a diffusive equation. We address the role of nonlocality and its interplay with boundary conditions, shedding light on the behavior of accessible solitons in real samples and discussing the accuracy of the highly nonlocal approximation. We find that symmetric solitons exist only above a power threshold, with an existence region that grows larger and larger with nonlocality in the plane width power.

Vortex confinement and bending with nonlocal solitons

We investigate the routing of vortex beams in nonlocal media by means of coaxial, co-propagating spatial optical solitons. By introducing a refractive index perturbation in the form of a localized defect or a dielectric interface, the soliton waveguide can be curved and, therefore, can deviate the collinear vortex, effectively routing it, while preventing its destabilization and breakup.

Self-induced mode transformation in nonlocal nonlinear media

We report on the first experimental observation of self-induced optical mode transformations in nonlocal nonlinear media. We show that the quadrupole Hermite-Gaussian mode experiences complex nonlinear dynamics in a nematic liquid crystal, including power-dependent conversion into a radially symmetric Laguerre-Gaussian mode. The physical mechanism responsible for self-induced transformation is the excitation of internal modes of a metastable quadrupole nonlocal soliton and its subsequent transmutation into a robust soliton with a bright peak surrounded by a bright ring. We also observe the onset of transformations of higher-order modes, proving the generic character of this nonlinear phenomenon.

Optical vortices in antiguides

We address the question of whether an optical vortex can be trapped in a dielectric structure with a core of a lower refractive index than the cladding--namely an antiguide. Extensive numerical simulations seem to indicate that this inverse trapping of a vortex is not possible, at least in straightforward implementations. Yet, the interaction of a vortex beam with a curved antiguide produces interesting effects, namely a small but finite displacement of the optical energy center-of-mass and the creation of a symmetrical vortex-antivortex pair on the exterior of the antiguide.

Observation of multi-component spatial vector solitons of four-wave mixing

We report the observation of multi-component dipole and vortex vector solitons composed of eight coexisting four-wave mixing (FWM) signals in two-level atomic system. The formation and stability of the multi-component dipole and vortex vector solitons are observed via changing the experiment parameters, including the frequency detuning, powers, and spatial configuration of the involved beams and the temperature of the medium. The transformation between modulated vortex solitons and rotating dipole solitons is observed at different frequency detunings. The interaction forces between different components of vector solitons are also investigated.

Observation of vector solitons with hidden vorticity

This letter reports the first experimental observation, to our knowledge, of optical vector solitons composed of two incoherently coupled vortex components. We employ nematic liquid crystal to generate stable vector solitons with counterrotating vortices and hidden vorticity. In contrast, the solitons with explicit vorticity and corotating vortex components show azimuthal splitting.