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ABSTRACT: We report the first experimental demonstration of the so-called three-Airy beams. Such beams represent a two-dimensional field that is a product (rather than simple superposition) of three Airy beams. Our experiments show that, in contrast to conventional Airy beams, this new family of Airy beams can be realized even without the use of truncation by finite apertures. Furthermore, we study linear and nonlinear propagation of the three-Airy beams in a photorefractive medium. It is found that a three-Airy beam tends to linearly diffract into a super-Gaussian-like beam, while under nonlinear propagation it either turns into three intensity spots with a self-defocusing nonlinearity or evolves into a self-trapped channel with a self-focusing nonlinearity.
Optics Express 01/2013; 21(2):1615-22. · 3.59 Impact Factor
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Mikael C. Rechtsman,
Yonatan Plotnik, Daohong Song,
Matthias Heinrich,
Julia M. Zeuner,
Stefan Nolte,
Natalia Malkova,
Jingjun Xu,
Alexander Szameit,
Zhigang Chen,
Mordechai Segev
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ABSTRACT: The intriguing properties of graphene, a two-dimensional material composed of
a honeycomb lattice of carbon atoms, have attracted a great deal of interest in
recent years. Specifically, the fact that electrons in graphene behave as
massless relativistic particles gives rise to unconventional phenomena such as
Klein tunneling, the anomalous quantum Hall effect, and strain-induced
pseudo-magnetic fields. Graphene edge states play a crucial role in the
understanding and use of these electronic properties. However, the coarse or
impure nature of the edges hampers the ability to directly probe the edge
states and their band structure. Perhaps the best example is the edge states on
the bearded edge (also called the Klein edge) that have thus far never been
observed - because such an edge is unstable in graphene. Here, we use the
optical equivalent of graphene - a photonic honeycomb lattice - to
experimentally and theoretically study edge states and their properties. We
directly image the edge states on both the zig-zag and bearded edges of this
photonic graphene, measure their dispersion properties, and most importantly,
find a new type of edge state: one residing on the bearded edge which was
unknown and cannot be explained through conventional tight-binding theory. Such
a new edge state lies near the van-Hove singularity in the edge band structure
and can be classified as a Tamm state lacking any surface defect. Our photonic
system offers the opportunity to probe new graphene-related phenomena that are
difficult or impossible to access in conventional carbon-based graphene. Edge
states in graphene-type structures play the central role in achieving photonic
topological insulation, in which light can propagate along the edges of
photonic structures without any parasitic scattering whatsoever.
10/2012;
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ABSTRACT: We demonstrate theoretically and experimentally that a finite Airy beam changes its trajectory while maintaining its acceleration in nonlinear photorefractive media. During this process, the spatial spectrum reshapes dramatically, leading to negative (or positive) spectral defects on the initial spectral distribution under a self-focusing (or defocusing) nonlinearity.
Optics Letters 08/2012; 37(15):3201-3. · 3.40 Impact Factor
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ABSTRACT: We study controllable self-shifting Bloch modes in anisotropic hexagonal photonic lattices. The shifting results from a deformed band structure due to deformation of the index distribution in each unit cell. By reconfiguration of the index profile of the unit cell, the direction in which the Bloch modes move can be controlled. Our theoretical predictions are experimentally demonstrated in hexagonal lattices optically induced in an anisotropic nonlinear crystal.
Optics Letters 06/2012; 37(12):2184-6. · 3.40 Impact Factor
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ABSTRACT: We demonstrate both experimentally and theoretically controlled acceleration of one- and two-dimensional Airy beams in optically induced refractive-index potentials. Enhancement as well as reduction of beam acceleration are realized by changing the index gradient, while the beam shape is maintained during propagation through the linear optical potential. Our results of active acceleration manipulation in graded media are pertinent to Airy-type beam propagation in various environments.
Optics Letters 08/2011; 36(16):3230-2. · 3.40 Impact Factor
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ABSTRACT: We study symmetry-breaking of the multi-vortex Bloch modes in optically induced hexagonal lattices. Such symmetry-breaking results from either exciting with an anisotropic beam or inducing an anisotropic photonic lattice.
Lasers and Electro-Optics (CLEO), 2011 Conference on; 06/2011
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ABSTRACT: We demonstrate an induction technique to generate honeycomb photonic lattices with equal and unequal sites in each unit-cell. We show light localization as nonlinear solitons and linear Shockley surface states in lattices with unequal sites.
Lasers and Electro-Optics (CLEO), 2011 Conference on; 06/2011
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ABSTRACT: In the present work, we consider the dynamics of dark solitons as one mode of
a defocusing photorefractive lattice coupled with bright solitons as a second
mode of the lattice. Our investigation is motivated by an experiment which
illustrates that such coupled states can exist with both components in the
first gap of the linear band spectrum. This finding is further extended by the
examination of different possibilities from a theoretical perspective, such as
symbiotic ones where the bright component is supported by states of the dark
component in the first or second gap, or non-symbiotic ones where the bright
soliton is also a first-gap state coupled to a first or second gap state of the
dark component. While the obtained states are generally unstable, these
instabilities typically bear fairly small growth rates which enable their
observation for experimentally relevant propagation distances.
04/2011;
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ABSTRACT: We demonstrate coherent interactions between spatial gap solitons in optically induced photonic lattices. Because of the "staggered" phase structures, two in-phase (out-of-phase) bright gap solitons can repel (attract) each other at close proximity, in contrast to soliton interaction in homogeneous media. A reversal of energy transfer direction and a transition between attractive and repulsive interaction forces can be obtained solely by changing the initial soliton separation relative to the lattice spacing.
Optics Letters 04/2011; 36(7):1167-9. · 3.40 Impact Factor
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ABSTRACT: We experimentally observe the formation of spatial dark gap solitons in higher bands in one-dimensional waveguide arrays possessing a saturable defocusing nonlinearity. By using the prism-coupler scheme, pure Floquet-Bloch modes of higher bands are excited and dark gap solitons are formed due to the counteraction of normal diffraction and the defocusing nature of the photovoltaic nonlinearity. The modulation of refractive index induced by the soliton formation is demonstrated by the guidance of a low-power probe beam in the waveguide array sample. Additionally, the phase structure of dark solitons formed in the second band is discussed.
Optics Express 12/2010; 18(26):27493-8. · 3.59 Impact Factor
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ABSTRACT: We experimentally demonstrate linear bandgap guidance of optical vortices as high-gap defect modes (DMs) in two-dimensional induced photonic lattices. We show that donut-shaped vortex beams can be guided in a tunable negative (lower-index) defect, provided that the defect strength is set at an appropriate level. Such vortex DMs have fine features in the "tails" associated with the lattice anisotropy and can be considered as a superposition of dipole DMs. Our numerical results find good agreement with experimental observations.
Optics Letters 06/2010; 35(12):2106-8. · 3.40 Impact Factor
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ABSTRACT: We demonstrate self-trapping of singly-charged vortices at the surface of an optically induced two-dimensional photonic lattice. Under appropriate conditions of self-focusing nonlinearity, a singly-charged vortex beam can self-trap into a stable semi-infinite gap surface vortex soliton through a four-site excitation. However, a single-site excitation leads to a quasi-localized state in the first photonic gap, and our theoretical analysis illustrates that such a bandgap surface vortex soliton is always unstable. Our experimental results of stable and unstable topological surface solitons are corroborated by direct numerical simulations and linear stability analysis.
Optics Express 03/2010; 18(6):5873-8. · 3.59 Impact Factor
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Daohong Song,
Cibo Lou,
Liqin Tang,
Xiaosheng Wang,
Wei Li,
Xingyu Chen,
Kody J H Law,
Hadi Susanto,
P G Kevrekidis,
Jingjun Xu,
Zhigang Chen
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ABSTRACT: We demonstrate the self-trapping of single- and double-charged optical vortices in waveguide lattices induced with a self-defocusing nonlinearity. Under appropriate conditions, a donut-shaped single-charged vortex evolves into a stable discrete gap vortex soliton, but a double-charged vortex turns into a self-trapped quadrupole-like structure. Spectrum measurement and numerical analysis suggest that the gap vortex soliton does not bifurcate from the edge of the Bloch band, quite different from previously observed gap spatial solitons. Our numerical findings are in good agreement with experimental observations.
Optics Express 08/2008; 16(14):10110-6. · 3.59 Impact Factor
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ABSTRACT: We observe dipole-like gap solitons in two-dimensional waveguide lattices optically induced with a self-defocusing nonlinearity. Under appropriate conditions, two mutually coherent input beams excited in neighboring lattice sites evolve into a self-trapped state, whose spatial power spectrum and stability depend strongly on the initial excitation conditions. Our experimental observations are compared with numerical simulations.
Optics Letters 11/2007; 32(20):3011-3. · 3.40 Impact Factor
