236 research outputs found
Generation of Bragg solitons through modulation instability in a Bragg grating structure
In this article, we consider the continuous wave (cw) propagation through the nonlinear periodic structure that consists of alternating layers of both positive and negative Kerr coefficients along the propagation direction. We investigate the modulational instability (MI) conditions required for the generation of ultrashort pulses for the nonlinearity management system. We study the occurrence of MI at the top and bottom edges of the photonic band gap (PBG) where the forward and backward propagating waves are strongly coupled because of the presence of the grating structure. We also study the MI when cw is detuned from the edges of the PBG into the anomalous and normal dispersion regimes. In addition, we discuss the existence of gap solitons for the nonlinearity management system in the upper and lower branches of the dispersion curve through the MI gain spectra. We observe the generation of higher order solitons in the nonlinear periodic structure when the input power is increased beyond a certain critical level. Finally, we discuss the generation of higher order Bragg grating solitons through the intensity evolution of the forward and backward propagating fields
Study of implosion in an attractive Bose-Einstein condensate
By solving the Gross-Pitaevskii equation analytically and numerically, we
reexamine the implosion phenomena that occur beyond the critical value of the
number of atoms of an attractive Bose-Einstein condensate (BEC) with
cigar-shape trapping geometry. We theoretically calculate the critical number
of atoms in the condensate by using Ritz's variational optimization technique
and investigate the stability and collapse dynamics of the attractive BEC by
numerically solving the time dependent Gross-Pitavskii equation
Modulational instability in binary spin-orbit-coupled Bose-Einstein condensates
We study modulation instability (MI) of flat states in two-component
spin-orbit-coupled (SOC) Bose-Einstein condensates (BECs) in the framework of
coupled Gross-Pitaevskii equations for two components of the pseudospinor wave
function. The analysis is performed for equal densities of the components.
Effects of the interaction parameters, Rabi coupling, and SOC on the MI are
investigated. In particular, the results demonstrate that the SOC strongly
alters the commonly known MI (immiscibility) condition, ,
for the binary superfluid with coefficients and of the
intra- and interspecies repulsive interactions. In fact, the binary BEC is
always subject to the MI under the action of the SOC, which implies that the
ground state of the system is plausibly represented by a striped phase
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