120 research outputs found
Design and Fabrication of Terahertz Metallic Gratings on a Two-Wire Waveguide
In this study, we present the design, fabrication and experimental characterization of waveguide-integrated gratings operating at THz frequencie
Skyrmion-like excitations in dynamical lattices
We construct discrete analogs of Skyrmions in nonlinear dynamical lattices.
The Skyrmion is built as a vortex soliton of a complex field, coupled to a dark
radial soliton of a real field. Adjusting the Skyrmion ansatz to the lattice
setting allows us to construct a "baby-Skyrmion" in two dimensions (2D) and
extend it into the 3D case (1D counterparts of the Skyrmions are also found).
Stability limits for these patterns are obtained analytically and verified
numerically. The dynamics of unstable discrete Skyrmions is explored, and their
stabilization by external potentials is discussed.Comment: 4 pages, 5 figure
Random quasi-phase-matched second-harmonic generation in periodically poled lithium tantalate
We observe second harmonic generation via random quasi-phase-matching in a 2.0 micron periodically poled, 1-cm-long, z-cut lithium tantalate. Away from resonance, the harmonic output profiles exhibit a characteristic pattern stemming from a stochastic domain distribution and a quadratic growth with the fundamental excitation, as well as a broadband spectral response. The results are in good agreement with a simple model and numerical simulations in the undepleted regime, assuming an anisotropic spread of the random nonlinear component
Statics and Dynamics of an Inhomogeneously-Nonlinear Lattice
We introduce an inhomogeneously-nonlinear Schr{\"o}dinger lattice, featuring
a defocusing segment, a focusing segment and a transitional interface between
the two. We illustrate that such inhomogeneous settings present vastly
different dynamical behavior than the one expected in their homogeneous
counterparts in the vicinity of the interface. We analyze the relevant
stationary states, as well as their stability by means of perturbation theory
and linear stability analysis. We find good agreement with the numerical
findings in the vicinity of the anti-continuum limit. For larger values of the
coupling, we follow the relevant branches numerically and show that they
terminate at values of the coupling strength which are larger for more extended
solutions. The dynamical development of relevant instabilities is also
monitored in the case of unstable solutions.Comment: 14 pages, 4 figure
Domain Walls in Two-Component Dynamical Lattices
We introduce domain-wall (DW) states in the bimodal discrete nonlinear
Schr{\"{o}}dinger equation, in which the modes are coupled by cross phase
modulation (XPM). By means of continuation from various initial patterns taken
in the anti-continuum (AC) limit, we find a number of different solutions of
the DW type, for which different stability scenarios are identified. In the
case of strong XPM coupling, DW configurations contain a single mode at each
end of the chain. The most fundamental solution of this type is found to be
always stable. Another solution, which is generated by a different AC pattern,
demonstrates behavior which is unusual for nonlinear dynamical lattices: it is
unstable for small values of the coupling constant (which measures the
ratio of the nonlinearity and coupling lengths), and becomes stable at larger
. Stable bound states of DWs are also found. DW configurations generated by
more sophisticated AC patterns are identified as well, but they are either
completely unstable, or are stable only at small values of . In the case of
weak XPM, a natural DW solution is the one which contains a combination of both
polarizations, with the phase difference between them 0 and at the
opposite ends of the lattice. This solution is unstable at all values of ,
but the instability is very weak for large , indicating stabilization as the
continuum limit is approached. The stability of DWs is also verified by direct
simulations, and the evolution of unstable DWs is simulated too; in particular,
it is found that, in the weak-XPM system, the instability may give rise to a
moving DW.Comment: 14 pages, 14 figures, Phys. Rev. E (in press
Accessible Light Bullets via synergetic nonlinearities
We introduce a new form of stable spatio-temporal self-trapped optical
packets stemming from the interplay of local and nonlocal nonlinearities.
Pulsed self-trapped light beams in media with both electronic and molecular
nonlinear responses are addressed to prove that spatial and temporal effects
can be decoupled, allowing for independent tuning. We numerically demonstrate
that (3+1)D light bullets and anti-bullets, i. e. bright and dark temporal
solitons embedded in stable (2+1)D nonlocal spatial solitons, can be generated
in reorientational media under experimentally feasible conditions.Comment: 17 pages, 4 figures A scale error in the index perturbation vs
average power dependence has been fixe
Spatial optical solitons in nonlinear photonic crystals
We study spatial optical solitons in a one-dimensional nonlinear photonic
crystal created by an array of thin-film nonlinear waveguides, the so-called
Dirac-comb nonlinear lattice. We analyze modulational instability of the
extended Bloch-wave modes and also investigate the existence and stability of
bright, dark, and ``twisted'' spatially localized modes in such periodic
structures. Additionally, we discuss both similarities and differences of our
general results with the simplified models of nonlinear periodic media
described by the discrete nonlinear Schrodinger equation, derived in the
tight-binding approximation, and the coupled-mode theory, valid for shallow
periodic modulations of the optical refractive index.Comment: 15 pages, 21 figure
Wavepacket reconstruction via local dynamics in a parabolic lattice
We study the dynamics of a wavepacket in a potential formed by the sum of a
periodic lattice and of a parabolic potential. The dynamics of the wavepacket
is essentially a superposition of ``local Bloch oscillations'', whose frequency
is proportional to the local slope of the parabolic potential. We show that the
amplitude and the phase of the Fourier transform of a signal characterizing
this dynamics contains information about the amplitude and the phase of the
wavepacket at a given lattice site. Hence, {\em complete} reconstruction of the
the wavepacket in the real space can be performed from the study of the
dynamics of the system.Comment: 4 pages, 3 figures, RevTex
Variational Approach to the Modulational Instability
We study the modulational stability of the nonlinear Schr\"odinger equation
(NLS) using a time-dependent variational approach. Within this framework, we
derive ordinary differential equations (ODEs) for the time evolution of the
amplitude and phase of modulational perturbations. Analyzing the ensuing ODEs,
we re-derive the classical modulational instability criterion. The case
(relevant to applications in optics and Bose-Einstein condensation) where the
coefficients of the equation are time-dependent, is also examined
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