Propagation Of Light Beams Research Articles

Toward efficient light diffraction and intensity variations by using wide bandwidth surface acoustic wave

We have developed acoustic-optic (AO) based display units for implementing a handheld hologram display by modulating light deflection through wide bandwidth surface acoustic wave (SAW). The developed AO device consists of a metal layer, a ZnS waveguide layer, SAW inter digital transducers (IDTs), and a screen for display. When RF power with a particular resonant frequency was applied to IDTs, SAW was radiated and interfered with confined beam propagating along ZnS waveguide layer. The AO interacted beam was deflected laterally toward a certain direction depending on Bragg diffraction condition, exited out of the waveguide layer and then directed to the viewing screen placed at a certain distance from the device to form a single pixel. The deflected angles was adjusted by modulating the center frequency of the SAW IDT (SAW grating), the RF power of SAW, and the angles between propagating light beam path along waveguide and radiating SAW. The diffraction efficiency was also characterized in terms of waveguide thickness, SAW RF input power, and aperture length. Coupling of mode (COM) modeling was fulfilled to find optimal device parameters prior to fabrication. All the parameters affecting the deflection angle and efficiency to form a pixel for a three-dimensional (3D) hologram image were characterized and then discussed.

Self-Organization of Light in Optical Media with Competing Nonlinearities.

We study the propagation of light beams through optical media with competing nonlocal nonlinearities. We demonstrate that the nonlocality of competing focusing and defocusing nonlinearities gives rise to self-organization and stationary states with stable hexagonal intensity patterns, akin to transverse crystals of light filaments. Signatures of this long-range ordering are shown to be observable in the propagation of light in optical waveguides and even in free space. We consider a specific form of the nonlinear response that arises in atomic vapor upon proper light coupling. Yet, the general phenomenon of self-organization is a generic consequence of competing nonlocal nonlinearities, and may, hence, also be observed in other settings.

Linear and nonlinear light beam propagation in chiral nematic liquid crystal waveguides

We employ a thick layer of chiral nematic liquid crystals to demonstrate the evolution of a one-dimensional (1D) higher-order guided mode into a beam self-confined in both transverse dimensions at various wavelengths. We also report the experimental observation of higher-order modes guided by soliton-induced waveguides in chiral nematic liquid crystals. Full Text: PDF References M. Peccianti, A. Dyadyusha, M. Kaczmarek, G. Assanto, "Tunable refraction and reflection of self-confined light beams", Nature Phys. 2, 737 (2006). CrossRef G. Assanto, M.A. Karpierz, "Nematicons: self-localised beams in nematic liquid crystals", Liq. Cryst. 36, 1161 (2009). CrossRef M. Peccianti, G. Assanto, "Nematicons", Phys. Rep. 516, 147 (2012). CrossRef A. Piccardi, G. Assanto, L. Lucchetti, F. Simoni, "All-optical steering of soliton waveguides in dye-doped liquid crystals", Appl. Phys. Lett. 93 (17), 171104 (2008). CrossRef A. Pasquazi, A. Alberucci, M. Peccianti, G. Assanto, "Signal processing by opto-optical interactions between self-localized and free propagating beams in liquid crystals", Appl. Phys. Lett. 87 (26), 261104 (2005). CrossRef M.-F. Shih, M. Segev, G. Salamo, "Circular waveguides induced by two-dimensional bright steady-state photorefractive spatial screening solitons", Opt. Lett. 21, 931 (1996). CrossRef M. Peccianti, G. Assanto, A. De Luca, C. Umeton, I. C. Khoo, "Electrically assisted self-confinement and waveguiding in planar nematic liquid crystal cells", Appl. Phys. Lett. 77, 7 (2000). CrossRef J. Petter, C. Denz, "Guiding and dividing waves with photorefractive solitons", Opt. Commun. 188, 55 (2001). CrossRef M. Peccianti, G. Assanto, "Signal readdressing by steering of spatial solitons in bulk nematic liquid crystals", Opt. Lett. 26 (21), 1690 (2001) CrossRef Y.V. Isdebskaya, A.S. Desyatnikov, G. Assanto, Y. Kivshar, "Multimode nematicon waveguides", Opt. Lett. 36, 184 (2011). CrossRef P. Oswald, P. Pieranski, Nematic and Cholesteric Liquid Crystals (Taylor & Francis 2005). CrossRef A. Laudyn, M. Kwasny, M.A. Karpierz, "Nematicons in chiral nematic liquid crystals", Appl. Phys. Lett. 94, 091110 (2009). CrossRef U.A. Laudyn, P. Jung, K.B. Zegadło, M.A. Karpierz, G. Assanto, "Power-induced evolution and increased dimensionality of nonlinear modes in reorientational soft matter", Opt. Lett. 39 (22), 6399 (2014). CrossRef F. Sala, M.A. Karpierz, "Modeling of molecular reorientation and beam propagation in chiral and non-chiral nematic liquid crystals", Opt. Expr. 20(13), 13923 (2012). CrossRef U. Laudyn, P. Jung, M.A. Karpierz, G. Assanto, "Quasi two-dimensional astigmatic solitons in soft chiral metastructures", Sci. Rep. 6, 22923 (2016). CrossRef

Radiating dispersive shock waves in non-local optical media.

We consider the step Riemann problem for the system of equations describing the propagation of a coherent light beam in nematic liquid crystals, which is a general system describing nonlinear wave propagation in a number of different physical applications. While the equation governing the light beam is of defocusing nonlinear Schrödinger (NLS) equation type, the dispersive shock wave (DSW) generated from this initial condition has major differences from the standard DSW solution of the defocusing NLS equation. In particular, it is found that the DSW has positive polarity and generates resonant radiation which propagates ahead of it. Remarkably, the velocity of the lead soliton of the DSW is determined by the classical shock velocity. The solution for the radiative wavetrain is obtained using the Wentzel-Kramers-Brillouin approximation. It is shown that for sufficiently small initial jumps the nematic DSW is asymptotically governed by a Korteweg-de Vries equation with the fifth-order dispersion, which explicitly shows the resonance generating the radiation ahead of the DSW. The constructed asymptotic theory is shown to be in good agreement with the results of direct numerical simulations.

Diffraction control inPT-symmetric photonic lattices: From beam rectification to dynamic localization

We address the propagation of light beams in longitudinally modulated PT-symmetric lattices, built as arrays of couplers with periodically varying separation between their channels, and show a number of possibilities for efficient diffraction control available in such non-conservative structures. The dynamics of light in such lattices crucially depends on the ratio of the switching length for the straight segments of each coupler and the longitudinal lattice period. Depending on the longitudinal period, one can achieve either beam rectification, when the input light propagates at a fixed angle across the structure without diffractive broadening, or dynamic localization, when the initial intensity distribution is periodically restored after each longitudinal period. Importantly, the transition between these two different propagation regimes can be achieved by tuning only gain and losses acting in the system, provided that the PT-symmetry remains unbroken. The impact of Kerr nonlinearity is also discussed.

Non-one-dimensional optical solitons and ideal fluid dynamics

Influence of transverse effects on the propagation of light beams in gradient glass fiber and on the pulsed mode of the second harmonic generation is investigated. Within the approaches under consideration the equations for the pulse or beam field envelopes are reduced to a system of hydrodynamictype equations for amplitudes and eikonals. These equations are used to describe the vortex and non-vortex beam channeling modes and the propagation of light bullets.

The influence of nonlinear and linear defects on the light propagation through linear one-dimensional photonic lattice

In this paper, the light beam propagation through one-dimensional photonic lattice, possessing one nonlinear defect and one linear defect, has been investigated numerically. Different dynamical regimes have been identified in terms of the distance between the two defects, position of the incident light beam, the width of linear defect, the values of nonlinearity and presence of the transverse kick. Strong localized modes on the defects, breathing and zig-zag modes in the area between defects have been observed. It has been concluded that the width of the linear defect placed next to the nonlinear one influences localization of the beam at the nonlinear waveguide. On the other hand, the nonlinear defect, regardless of the values of nonlinearity, have a small influence on the beam propagation in photonic lattice. It has been observed that the transverse kick of the initial beam leads to the distortion of localized structures. By launching the light beam towards defects, the reflection of light has been noticed. Presented results can be useful for different applications, such as blocking, filtering and routing of light beam through optical media.

The theory of stochastic cosmological lensing

On the scale of the light beams subtended by small sources, e.g. supernovae, matter cannot be accurately described as a fluid, which questions the applicability of standard cosmic lensing to those cases. In this article, we propose a new formalism to deal with small-scale lensing as a diffusion process: the Sachs and Jacobi equations governing the propagation of narrow light beams are treated as Langevin equations. We derive the associated Fokker-Planck-Kolmogorov equations, and use them to deduce general analytical results on the mean and dispersion of the angular distance. This formalism is applied to random Einstein-Straus Swiss-cheese models, allowing us to: (1) show an explicit example of the involved calculations; (2) check the validity of the method against both ray-tracing simulations and direct numerical integration of the Langevin equation. As a byproduct, we obtain a post-Kantowski-Dyer-Roeder approximation, accounting for the effect of tidal distortions on the angular distance, in excellent agreement with numerical results. Besides, the dispersion of the angular distance is correctly reproduced in some regimes.

Automatic Fourier transform and self-Fourier beams due to parabolic potential

We investigate the propagation of light beams including Hermite–Gauss, Bessel–Gauss and finite energy Airy beams in a linear medium with parabolic potential. Expectedly, the beams undergo oscillation during propagation, but quite unexpectedly they also perform automatic Fourier transform, that is, periodic change from the beam to its Fourier transform and back. In addition to oscillation, the finite-energy Airy beams exhibit periodic inversion during propagation. The oscillating period of parity-asymmetric beams is twice that of the parity-symmetric beams. Based on the propagation in parabolic potential, we introduce a class of optically-interesting beams that are self-Fourier beams—that is, the beams whose Fourier transforms are the beams themselves.

Soliton enhancement of spontaneous symmetry breaking

Spontaneous symmetry breaking (SSB) occurs when noise triggers an initially symmetric system to evolve toward one of its nonsymmetric states. Topological and optical SSB involve material reconfiguration/transition and light propagation/distribution in time or space, respectively. In anisotropic optical media, light beam propagation and distribution of the optic axis can be linked, thereby connecting topological and optical SSB. Using nonlinear soft matter, namely uniaxial liquid crystals, we report on simultaneous topological and optical SSB, showing that spatial solitons enhance the noise-driven transition of the medium from a symmetric to an asymmetric configuration, while acquiring a power-dependent transverse velocity in either of two specular directions with respect to the initial wavevector. Solitons enhance SSB by further distorting the optic axis distribution through nonlinear reorientation, resulting in power-tunable walk-off as well as hysteresis in beam refraction versus angle of incidence.

Optical switch based on the electrically controlled liquid crystal interface.

The peculiarities of the linearly polarized light beam reflection at the interface within the bulk of a nematic liquid crystal (NLC) cell with different orientations of the director are analyzed. Two methods to create the interface are considered. Combination of the planar and homeotropic orientations of the NLC director is realized by means of a spatially structured electrode under the applied voltage. In-plane patterned azimuthal alignment of the NLC director is created by the patterned rubbing alignment technique. All possible orthogonal orientations of the LC director are considered; the configurations for realization of total internal reflection are determined. The revealed relationship between the propagation of optical beams in a liquid crystal material and polarization of laser radiation has enabled realization of the spatial separation for the orthogonally polarized light beams at the interface between two regions of NLC with different director orientations (domains). Owing to variations in the applied voltage and, hence, in the refractive index gradient, the light beam propagation directions may be controlled electrically.

Beam splitter and combiner based on Bloch oscillation in a spatially modulated waveguide array

We theoretically and numerically investigate light beam propagation in a periodic waveguide array that is spatially modulated with a certain structure which brings novel functionalities to the array. We find that a light beam may split, coalesce, deflect, and be localized during propagation in a simply modulated waveguide array. The phenomena described originate from the Bloch oscillation and supply a convenient method for fabricating on-chip beam splitters and beam combiners.

Light propagation in a homogeneous and anisotropic universe

This article proposes a comprehensive analysis of light propagation in an anisotropic and spatially homogeneous Bianchi I universe. After recalling that null geodesics are easily determined in such a spacetime, we derive the expressions of the redshift and direction drifts of light sources; by solving analytically the Sachs equation, we then obtain an explicit expression of the Jacobi matrix describing the propagation of narrow light beams. As a byproduct, we recover the old formula by Saunders for the angular diameter distance in a Bianchi I spacetime, but our derivation goes further since it also provides the optical shear and rotation. These results pave the way to the analysis of both supernovae data and weak lensing by the large-scale structure in Bianchi universes.

Defect induced wave-packet dynamics in linear one-dimensional photonic lattices

We study numerically light beam propagation across uniform, linear, one-dimensional photonic lattice possessing one nonlinear defect. Depending on the strength of nonlinear defect, input beam position and phase shift, different dynamical regimes have been identified. We distinguish input parameters set for which a regime of light propagation blockade by the nonlinear defect appears. Obtained results may be useful for all-optical control of transmission of waves in interferometry.

Effect of a geometric defect on light propagation through a composite linear photonic lattice

In this paper we investigated numerically light beam propagation through a one-dimensional composite photonic lattice composed of two structurally different lattices, with a geometric defect emerging at the interface between the two of them. Depending on the initial light beam position with respect to the geometric defect and the transverse tilt of the input beam, different dynamical regimes have been identified. Presented results may be useful for different applications, such as blocking, filtering and transporting light beams through optical media.

Photoluminescence and nonlinear optical phenomena in plasmonic random media—A review of recent works

Photoluminescence properties and nonlinear optical response of metal–dielectric nanocomposites (MDNCs)—germanate glasses, bio-cellulose membranes and colloids containing either silver (Ag) or gold (Au) nanoparticles (NPs)—are reviewed. The phenomena discussed are: i. the photoluminescence enhancement observed from rare-earth doped PbO–GeO2 glass containing Ag NPs; ii. optical amplification at 1530nm in RIB waveguides made with PbO–GeO2 thin films covered with Au NPs; iii. Random Laser emission from a bio-cellulose membrane infiltrated with Rhodamine 6G and containing Ag NPs; iv. the nonlinearity management of high-order processes in colloids containing Ag NPs suspended in acetone. In all discussed cases the influence of the metallic NPs is clearly demonstrated and a procedure to control the nonlinear propagation of light beams in heterogeneous media is presented.

Manipulation of light beam propagation in one-dimensional photonic lattices with linear refractive index profile

We use Bloch oscillations to demonstrate potential light beam propagation control in photonic lattices with linear refractive index change in transverse direction. It is qualitatively investigated how composite photonic lattice systems with varied values of refractive index gradient and nonlinearity strength along the propagation direction can be used to perform different functions, such as beam splitting and switching, in future components of all-optical networks. Additionally, we demonstrate the robustness of Bloch oscillations to nonlinearity and disorder in the proposed setup.

Flat focusing mirror.

The control of spatial propagation properties of narrow light beams such as divergence, focusing or imaging are main objectives in optics and photonics. In this letter, we propose and demonstrate experimentally a flat focusing mirror, based on an especially designed dielectric structure without any optical axis. More generally, it also enables imaging any light pattern in reflection. The flat focusing mirror with a transversal invariance can largely increase the applicability of structured photonic materials for light beam propagation control in small-dimension photonic circuits.

Localized surface modes in parity-time-symmetric potentials.

We investigate light-beam propagation along the interface between linear and nonlinear media with parity-time symmetry. A novel class of two-dimensional localized surface modes (LSMs) is found analytically and numerically. If the potential is parity-time invariant along the direction parallel to the interface between the two media, stable LSMs can exist. Otherwise, if the potential is parity-time invariant along the direction perpendicular to the interface between the two media, there are no stable LSMs.

Dielectric gradient metasurface optical elements.

Gradient metasurfaces are two-dimensional optical elements capable of manipulating light by imparting local, space-variant phase changes on an incident electromagnetic wave. These surfaces have thus far been constructed from nanometallic optical antennas, and high diffraction efficiencies have been limited to operation in reflection mode. We describe the experimental realization and operation of dielectric gradient metasurface optical elements capable of also achieving high efficiencies in transmission mode in the visible spectrum. Ultrathin gratings, lenses, and axicons have been realized by patterning a 100-nanometer-thick Si layer into a dense arrangement of Si nanobeam antennas. The use of semiconductors can broaden the general applicability of gradient metasurfaces, as they offer facile integration with electronics and can be realized by mature semiconductor fabrication technologies.