Interaction Of Optical Beams Research Articles

Soliton pairs in two-dimensional nonlocal media.

We study the interaction of optical beams of different wavelengths, described by a two-component, two-dimensional (2D) nonlocal nonlinear Schrödinger (NLS) model. Using a multiscale expansion method the NLS model is asymptotically reduced to the completely integrable 2D Mel'nikov system, the soliton solutions of which are used to construct approximate dark-bright and antidark-bright soliton solutions of the original NLS model; the latter being unique to the nonlocal NLS system with no relevant counterparts in the local case. Direct numerical simulations show that, for sufficiently small amplitudes, both these types of soliton stripes do exist and propagate undistorted, in excellent agreement with the analytical predictions. Larger amplitude of these soliton stripes, when perturbed along the transverse direction, disintegrate either to filled vortex structures (the dark-bright solitons) or to radiation (the antidark-bright solitons).

Two-dimensional control of light with light on metasurfaces.

The ability to control the wavefront of light is fundamental to focusing and redistribution of light, enabling many applications from imaging to spectroscopy. Wave interaction on highly nonlinear photorefractive materials is essentially the only established technology allowing the dynamic control of the wavefront of a light beam with another beam of light, but it is slow and requires large optical power. Here we report a proof-of-principle demonstration of a new technology for two-dimensional (2D) control of light with light based on the coherent interaction of optical beams on highly absorbing plasmonic metasurfaces. We illustrate this by performing 2D all-optical logical operations (AND, XOR and OR) and image processing. Our approach offers diffraction-limited resolution, potentially at arbitrarily-low intensity levels and with 100 THz bandwidth, thus promising new applications in space-division multiplexing, adaptive optics, image correction, processing and recognition, 2D binary optical data processing and reconfigurable optical devices.

Optical beam interactions with a periodic array of Fresnel zone plates

The interactions of first-order elegant Laguerre–Gaussian beams (ELG) with a two-dimensional periodic array are analysed theoretically and numerically. The structure consists of a periodic composition of two-zone Fresnel plates engraved in a silver film. The beam field is composed of periodic sequences of beams of circular or polar polarization incidence upon the structure. The beam axes coincide with the symmetry axes of every fourth Fresnel zone plate placed periodically along two orthogonal coordinates of a horizontal plane of the structure. It is shown that the beam-structure interaction results in substantial cross-polarization coupling, higher-order mode excitation, strong focussing and the extraordinary transmission of the optical field. An interpretation of the results is given per an analogy to the beam-structure interactions observed at planar, homogeneous and isotropic dielectric interfaces and layers.

Interactions between self-channeled optical beams in soft-matter systems with artificial nonlinearities

We demonstrate optical interactions between stable self-trapped optical beams in soft-matter systems with pre-engineered saturable self-focusing optical nonlinearities. Our experiments, carried out in dilute suspensions of particles with negative polarizabilities, show that optical beam interactions can vary from attractive to repulsive, or can display an energy exchange depending on the initial relative phases. The corresponding observations are in good agreement with theoretical predictions.

Cross-polarized normal mode patterns at a dielectric interface

Basic features of narrow optical beam interactions with a dielectric interface are analysed. As it was recently shown, two types of paraxial beams – elegant Hermite-Gaussians of linear polarization and elegant Laguerre-Gaussians of circular polarization – can be treated as vector normal modes of the interface [1]. In this contribution the problem of normal modes is discussed with special attention paid for the case of beam oblique incidence. Excitation of higher-order modes by cross-polarization coupling is described and it is shown that this process critically depends on a propagation direction of the incident beam. Besides the expected changes of mode indices induced by generalised transmission and reflection matrices, the new phenomenon of optical vortex spectral splitting at the interface is revealed and off-axis spectral placements of the splitted vortices are determined. Results of numerical simulations given here for beam reflection entirely confirm theoretical predictions even for beams beyond the range of paraxial approximation.

Nonlinear interaction of optical beams in a Bose-Einstein condensate

The results of simulation of the interaction of optical beams with different frequencies in an inhomogeneous Bose-Einstein condensate are given. The potential well has a parabolic profile, and the nonlinearity belongs to a defocusing class. The total reflection of a signal wave induced by a pump beam at a negative inhomogeneity during the wave capture in the potential well is considered.

Optical matching of single-mode fibers with different cross sections in a photopolymerizable composition

The possibility of optical matching in a photopolymerizable composition of a pair of single-mode fibers with significantly different core diameters is studied. It is shown that a polymer connector that is formed during self-channelling and interaction of optical beams at 0.63 µm in the photopolymerizable medium ensures an efficient connection of single-mode fibers at a wavelength of 1.55 µm. Results of experiments on the optical formation of matching polymer elements between SMF-28 and CS-980 and between SMF-28 and Ge-507sm single-mode fibers are presented.

Spatiotemporal interaction of optical beams in bidispersive media

The interaction of optical beams in bi-dispersive nonlinear media with self-focusing nonlinearity is numerically investigated. Under proper conditions, the interaction of spatially separated beams can lead to the creation of two prominent filaments along the other spatial or temporal dimension and, thus to an effective beam exchange. This X-wave generation-based effect could potentially be exploited in optical realizations of spatial or spatio-temporal filtering.

Visible radiation-induced connection of single-mode IR fibres in a photopolymerising composition

The properties of the optical connection of single-mode fibres by laser beams counterpropagating from the ends of these fibres are considered numerically and experimentally. It is shown that effective connection of single-mode fibres at the wavelength of 1.55 μm is possible during self-channelling and interaction of optical beams at 0.63 μm in a photopolymerising medium. In this case, the long exposure can lead to a decrease in the transmission coefficient, especially when the ends of the fibres being connected are positioned off-axially. It is obtained experimentally that for the 1–2-mm-long polymer connector and the ∼15-μm radial displacement, the efficiency of the optical connection of the SMF-28 and CS-980 single-mode fibres in a OCM-2 photopolymerising composition can achieve 80%—90% and 50%—60%, respectively.

Nonlinear optical beam interactions in waveguide arrays.

We report our investigation of Kerr nonlinear beam interactions in discrete systems. The influence of power and the relative phase between two Gaussian shaped beams was investigated in detail by performing numerical simulations of the discrete nonlinear Schrödinger equation and comparing the results with experiments done in AlGaAs waveguide arrays. Good agreement between theory and experiment was obtained.

Modification of the exchange of energy in BSO at equal optimized coupling constant

It is known that the interaction of optical beams incident upon a photorefractive crystal can produce higher order waves. Using a four-wave interaction model based on Kukhtarev’s equations and the wave equation, and considering the imaginary part of the coupling constants as a function of the period of the grating, external field and fringe velocity of optimization, it is shown that there are different ways to modify the exchange of energy with the two nearest higher order waves +1 and +2 without altering the value of the optimized imaginary part of the respective coupling constant.

Thermally induced self-focusing and optical beam interactions in planar strontium barium niobate waveguides

We present an experimental study of thermally induced self-focusing effects and interactions of incoherent light beams in strontium barium niobate waveguides. Depending on the input power, a single parallel beam is strongly focused inside the sample up to diameters of several micrometers. For higher input power we observe the splitting of the beam in a sequence of several spots. We demonstrate that these thermally induced refractive-index patterns can be used to focus and deflect an incoherent guided probe beam in the waveguide with time constants below 1 ms.

Photorefractive effects and light-induced charge migration in barium titanate

We propose a new theoretical model for the light-induced migration of charges which mediates the ’’photorefractive effect’’ (light-induced refractive index change) in barium titanate and other crystals. We also present experimental results of various effects of this light-induced charge migration in a single-domain crystal of barium titanate, specifically, (1) energy transfer between two intersecting optical beams, (2) optical four-wave mixing and optical-beam phase conjugation, (3) erasure of spatial patterns of photorefractive index variations, and (4) photoconductivity. The theoretical model predicts the observed dependences of these effects on (1) beam intensities, directions, and polarizations, (2) crystal orientation, and (3) on an externally applied dc electric field. Time dependences of transients as well as steady-state magnitudes are predicted. In this model, identical charges migrate by hopping between adjacent sites, with a hopping rate proportional to the total light intensity at the starting site. The net hopping rate varies with the local electric potential that is calculated self-consistently from the charge migration pattern. In barium titanate the charges are positive with a density of (1.90.2) ×1016 cm−3 at 514 nm. The origin of the charges and sites is at present unknown. The hopping rate constant determined from optical beam interactions is used to predict the observed photoconductivity of 1.3×10−10 cm Ω−1 W−1 at 514 nm.