Search results for "modulational instability"
showing 10 items of 65 documents
Influence of spatial delay on the modulational instability in a composite system with a controllable nonlinearity.
2017
A theoretical investigation of the modulational instability (MI) in a composite system with a nonlocal response function is presented. A composite system of silver nanoparticles in acetone is chosen, whose nonlinearity can be delicately varied by controlling the volume fraction of the constituents, thus enabling the possibility of nonlinearity management. A pump-probe counterpropagation configuration has been assumed, and the interplay between the competing nonlinearities and the nonlocalities in the MI dynamics is systematically explored. A different class of nonlocalities have been considered, and the study reveals that the nonlocality critically depends on the kind of nonlocal function. …
Modulational instability and generation of self-induced transparency solitons in resonant optical fibers
2009
International audience; We consider continuous-wave propagation through a fiber doped with two-level resonant atoms, which is described by a system of nonlinear Schrodinger-Maxwell-Bloch (NLS-MB) equations. We identify the modulational instability (MI) conditions required for the generation of ultrashort pulses, in cases of both anomalous and normal GVD (group-velocity dispersion). It is shown that the self-induced transparency (SIT) induces non-conventional MI sidebands. The main result is a prediction of the existence of both bright and dark SIT solitons in the anomalous and normal GVD regimes.
Energy localization in a nonlinear discrete system
1996
International audience; We show that, in the weak amplitude and slow time limits, the discrete equations describing the dynamics of a one-dimensional lattice can be reduced to a modified Ablowitz-Ladik equation. The stability of a continuous wave solution is then investigated without and with periodic boundary conditions; Energy localization via modulational instability is predicted. Our numerical simulations, performed on a cyclic system of six oscillators, agree with our theoretical predictions.
Modulational instability and two-dimensional dynamical structures
2008
A process of nonlinear structure formation on a two-dimensional lattice is proposed. The basic model consists of a two-dimensional lattice equipped at each node with a molecule or dipole rotating in the lattice plane. The interactions involved in the model are reduced to a periodic lattice. Such a discrete system can be applied to the problem of molecule adsorption on a substrate crystal surface, for instance. The continuum approximation of the model leads to a 2-D sine-Gordon system including nonlinear couplings, which itself can be reduced to a 2-D nonlinear Schrodinger equation in the low amplitude limit. Spatio-temporal structure formation is investigated by means of numerical simulatio…
Generation of optical domain-wall structures from modulational instability in a bimodal fiber.
1998
We study experimentally modulational instability in a normally dispersive bimodal fiber under modal group-velocity-matching conditions. In the strong pump depletion regime, higher order sideband harmonics detected in the output spectra as well as autocorrelation measurements reveal the formation of subpicosecond domain-wall structures. Across these temporal structures the electromagnetic field distribution switches abruptly between the two transverse modes of the fiber. These structures are reminiscent of the so-called domain-wall soliton. Our results constitute therefore an experimental indication of the existence of this fundamental soliton.
General approach to spatiotemporal modulational instability processes
2011
International audience; In this article, we derive the general exact solution of the modulation instability gain. The solution described here is valid for 1-D, 2-D, and 3-D cases considering any temporal response function of the medium and with possible higher order Kerr nonlinearities. In particular, we show that the gain induced by modulation instability is initial condition dependent, while the usual calculations do not lead to such a dependence. Applications for current and high-interest nonlinear propagation problems, such as 1-D optical fiber propagation with delayed Raman response and 2-D filamentation in gases, are investigated in detail. More specifically, we demonstrate that the 2-D …
Toward a wave turbulence formulation of statistical nonlinear optics
2012
International audience; During this last decade, several remarkable phenomena inherent to the nonlinear propagation of incoherent optical waves have been reported in the literature. This article is aimed at providing a generalized wave turbulence kinetic formulation of random nonlinear waves governed by the nonlinear Schrodinger equation in the presence of a nonlocal or a noninstantaneous nonlinear response function. Depending on the amount of nonlocal (noninstantaneous) nonlinear interaction and the amount of inhomogeneous (nonstationary) statistics of the incoherent wave, different types of kinetic equations are obtained. In the spatial domain, when the incoherent wave exhibits fluctuatio…
Modulational instability processes in optical isotropic fibers under dual-frequency pumping
2001
Experiments are presented showing that under dual-frequency, circular polarization pumping, a host modulational instability processes can be generated in a single isotropic fiber, by carefully tuning the frequency spacing between the pumps.
Polarization mode dispersion and vectorial modulational instability in air silica microstructure fiber
2002
The birefringence of an air-silica microstructure fiber has been studied by measurement of the fiber polarization mode dispersion (PMD) over the wavelength range 545-640 nm. The experimental results are shown to be in good agreement with vectorial numerical calculations, assuming an elliptical core with an eccentricity of 7%. We also report controlled experiments studying nonlinear vectorial modulation instability in the fiber, yielding 3.9-THz modulational instability sideband shifts that are in good agreement with theoretical predictions based on the calculated fiber dispersion and PMD characteristics.
Emergence of extreme events in fiber-based parametric processes driven by a partially incoherent pump wave
2009
Modulation instability (MI) generated by a picosecond coherent pulse has been recently identified as the key element of the generation of optical rogue-waves in supercontinuum-based systems [1]. Similar rare but highly energetic pulse structures can also appear in non-solitonic configurations such as Raman amplifiers driven by a partially incoherent pump wave propagating in fibres with low group velocity dispersion [2]. Therefore, one may wonder whether optical rogue-like event can also occur in MI-based amplifier because both Raman and parametric amplifiers benefit from a quasi-instantaneous gain. We provide here experimental evidence of rare optical events in a parametric amplifier in pre…