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ABSTRACT: We explore experimentally the effect of nonlinearity on resonant coupling between high-symmetry momentum states in hexagonal photonic lattices. We observe nonlinear Pendellösung oscillations with the power-dependent excitation of additional critical points of the same symmetry in the reciprocal cells closest to the excitation point. In contrast, the nonlinear Landau-Zener tunneling in biased lattices exhibits a sharp transition to the modulational instability with an increase of the input optical power.
Phys. Rev. A. 07/2012; 86(1).
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ABSTRACT: We fabricate computer generated holograms for the generation of phase singularities at extreme ultraviolet (EUV) wavelengths using electron beam lithography and demonstrate their ability to generate optical vortices in the nonzero diffraction orders. To this end, we observe the characteristic intensity distribution of the vortex beam and verify the helical phase structure interferometrically. The presented method forms the basis for further studies on singular light fields in the EUV frequency range, i.e., in EUV interference lithography. Since the method is purely achromatic, it may also find applications in various fields of x ray optics.
Optics Letters 11/2011; 36(21):4143-5. · 3.40 Impact Factor
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ABSTRACT: We reveal a direct link between two fundamental wave phenomena in periodic media, Pendellösung oscillations and resonant coupling between spectral bands. We experimentally measure the power transfer between laser beams associated with the high-symmetry points in periodic and biased hexagonal photonic lattices. As a result, we demonstrate that Pendellösung oscillations dominate the dynamics of resonant interband transitions on a short propagation scale.
Physical Review Letters 02/2011; 106(8):083902. · 7.37 Impact Factor
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09/2010: pages 427 - 450; , ISBN: 9783527629374
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ABSTRACT: Nonlinear periodic structures have become an active area of research due to many exciting possibilities of controlling wave
propagation, steering and trapping. Periodicity changes the wave bandgap spectrum and therefore strongly affects propagation
and localization, leading to the formation of discrete and gap solitons which have already been studied in several branches
of science [1–4]. In optics, a periodic modulation of the refractive index can either be prefabricated as in photonic crystals
[5] or optically induced in photorefractive materials [6–9]. Until now, several different approaches for the fabrication of
photonic crystals exist [10–12]. Although these mechanisms enable a precise material structuring with periodicities adequate
for optical waves, they do not allow for flexible changes of structural parameters (e.g., lattice period or modulation depth).
In contrast, the optical induction in photorefractive crystals provides highly reconfigurable, wavelength-sensitive nonlinear
structures which can be induced at very low power levels. When dealing with optically induced photonic lattices in these photorefractive
materials, it is crucially important to consider the anisotropic properties of photorefractive crystals. The light-induced
refractive index change strongly depends on orientation as well as polarization of the lattice wave [13, 14]. In particular,
its orientation with respect to the c-axis of the crystal determines the symmetry of the induced pattern [15]. The shape of the induced refractive index pattern
also changes with increasing lattice strength depending on the saturation of the photorefractive nonlinearity. For instance,
an ordinarily polarized light pattern created by several interfering plane waves induces a change of the refractive index
while propagating linearly along the crystal. The lattice wave does not ‘feel’ the periodic modulated refractive index during
propagation. If the lattice is weak, i.e. it is not affected by the saturation of the photorefractive nonlinearity, the light-induced
refractive index follows the light intensity distribution and forms a two-dimensional photonic lattice, being uniform in the
direction of propagation. Many exciting features of non-linear light propagation have been investigated in these lattices
and have been presented in chapter 5.
03/2010: pages 101-126;
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ABSTRACT: We realize an experimental control over the topological stability of three-lobe discrete vortex solitons by modifying the symmetry of a hexagonal photonic lattice optically induced in a photorefractive crystal. By continuously deforming the lattice wave in one transverse direction, we manipulate the coupling between lattice sites and induce or inhibit the reversal of soliton vorticity.
Optics Letters 02/2010; 35(4):604-6. · 3.40 Impact Factor
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ABSTRACT: We experimentally investigate the formation of reconfigurable three-dimensional (3D) nonlinear photonic lattices in an externally biased cerium doped strontium barium niobate photorefractive crystal by a spatial light modulator-assisted versatile simplified single step optical induction approach. The analysis of the generated 3D nonlinear photonic lattices by plane wave guiding, momentum space spectroscopy, and far field diffraction pattern imaging is presented, which points to the embedded potential of these 3D structures as reconfigurable platform to investigate advanced nonlinear light-matter interaction in periodic structures.
Optics Letters 10/2009; 34(17):2625-7. · 3.40 Impact Factor
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Bernd Terhalle,
Tobias Richter,
Kody J. H. Law,
Dennis Göries,
Patrick Rose,
Tristram J. Alexander,
Panayotis G. Kevrekidis,
Anton S. Desyatnikov,
Wieslaw Krolikowski,
Friedemann Kaiser,
Cornelia Denz,
Yuri S. Kivshar
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ABSTRACT: We report on the experimental observation of stable double-charge discrete vortex solitons generated in hexagonal photonic lattices created optically in self-focusing nonlinear media and show that single-charge vortex solitons are unstable in analogous conditions. Subsequently, we study, both theoretically and experimentally, the existence and stability of spatial vortex solitons in two-dimensional hexagonal photonic lattices. We demonstrate that the stability of the double-charge vortices is a consequence of the intersite power exchange in the vortex soliton, and we provide a simple stability criterion on the basis of the analysis of the corresponding discrete nonlinear model. We extend our analysis to the case of defocusing nonlinearity and show the inversion of the vortex stability properties resulting in the fact that single-charge vortices become stable while their double-charge counterparts are unstable.
Phys. Rev. A. 04/2009; 79(4).
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ABSTRACT: We control the emission properties of a broad-area vertical-cavity surface emitting laser by coupling it to an external feedback cavity containing a photorefractive crystal with an optically induced photonic lattice. The periodic modulation of the refractive index serves as a tunable filter and enables the dynamic suppression of unwanted spatial instabilities and modes, as originally suggested by
Gomila et al. [Phys. Rev. Lett. 92, 253904 (2004)].
Applied Physics Letters 10/2008; 93(15):151114-151114-3. · 3.84 Impact Factor
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ABSTRACT: We report on the first observation of topologically stable spatially localized multivortex solitons generated in optically induced hexagonal photonic lattices. We demonstrate that topological stabilization of such nonlinear localized states can be achieved through self-trapping of truncated two-dimensional Bloch waves and confirm our experimental results by numerical simulations of the beam propagation in weakly deformed lattice potentials in anisotropic photorefractive media.
Physical Review Letters 08/2008; 101(1):013903. · 7.37 Impact Factor
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ABSTRACT: We present an efficient method for optical induction of photonic superlattices in photorefractive media via holographic multiplexing. By superimposing phase engineered periodic waves of different periodicities, incremental recording of one-and two-dimensional multiperiodic lattices is demonstrated. The induced structures are subsequently analysed in Fourier space as well as in real space to verify the existence of multiple band gaps in the linear transmission spectrum.
J. Phys. D: Appl. Phys. 01/2008; 41:224004-4.
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ABSTRACT: We experimentally generate different types of two-dimensional self-trapped photonic lattices in a photorefractive medium and analyze the induced refractive index change using two different methods. One method gives the first experimental Fourier space analysis of both linear and nonlinear self-trapped photonic lattices with periodic phase modulation using partially spatially incoherent multiband excitation of the lattice modes. The other method utilizes the waveguiding properties of the lattice to achieve a real space analysis of the induced refractive index change. The results of both methods are compared.
Physical Review E 12/2006; 74(5 Pt 2):057601. · 2.26 Impact Factor
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ABSTRACT: We predict theoretically and generate in a photorefractive crystal two-dimensional self-trapped periodic waves of different symmetries, including vortex lattices-patterns of phase dislocations with internal energy flows. We demonstrate that these nonlinear waves exist even with anisotropic nonlocal nonlinearity when the optically-induced periodic refractive index becomes highly anisotropic, and it depends on the orientation of the two-dimensional lattice relative to the crystallographic c-axis.
Optics Express 05/2006; 14(7):2851-63. · 3.59 Impact Factor
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ABSTRACT: We predict theoretically and generate experimentally in photorefractive crystal two-dimensional self-trapped periodic waves of different symmetries, including vortex lattices – patterns of phase dislocations with internal energy flows. We demonstrate that these nonlinear waves exist with nonlocal nonlinearity even when the optically-induced periodic refractive index becomes highly anisotropic, and it depends on the orientation of the two-dimensional lattice relative to the crystallographic c-axis. Article written under name Denis Träger
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