200 research outputs found
Fundamentals and applications of spatial dissipative solitons in photonic devices : [Chapter 6]
We review the properties of optical spatial dissipative solitons (SDS). These are stable, self‐localized optical excitations sitting on a uniform, or quasi‐uniform, background in a dissipative environment like a nonlinear optical cavity. Indeed, in optics they are often termed “cavity solitons.” We discuss their dynamics and interactions in both ideal and imperfect systems, making comparison with experiments. SDS in lasers offer important advantages for applications. We review candidate schemes and the tremendous recent progress in semiconductor‐based cavity soliton lasers. We examine SDS in periodic structures, and we show how SDS can be quantitatively related to the locking of fronts. We conclude with an assessment of potential applications of SDS in photonics, arguing that best use of their particular features is made by exploiting their mobility, for example in all‐optical delay lines
Stability of multi-hump optical solitons
We demonstrate that, in contrast with what was previously believed,
multi-hump solitary waves can be stable. By means of linear stability analysis
and numerical simulations, we investigate the stability of two- and three-hump
solitary waves governed by incoherent beam interaction in a saturable medium,
providing a theoretical background for the experimental results reported by M.
Mitchell, M. Segev, and D. Christodoulides [Phys. Rev. Lett. v. 80, p. 4657
(1998)].Comment: 4 pages, 5 figures, to appear in PR
Interaction of cavity solitons in degenerate optical parametric oscillators
Numerical studies together with asymptotic and spectral analysis establish
regimes where soliton pairs in degenerate optical parametric oscillators fuse,
repel, or form bound states. A novel bound state stabilized by coupled internal
oscillations is predicted.Comment: 3 page
Rheology of protein-stabilised emulsion gels envisioned as composite networks. 1 - Comparison of pure droplet gels and protein gels
Protein-stabilised emulsion gels can be studied in the theoretical framework
of colloidal gels, because both protein assemblies and droplets may be
considered as soft colloids. These particles differ in their nature, size and
softness, and these differences may have an influence on the rheological
properties of the gels they form. Pure gels made of milk proteins (sodium
caseinate), or of sub-micron protein-stabilised droplets, were prepared by slow
acidification of suspensions at various concentrations. Their microstructure
was characterised, their viscoelasticity, both in the linear and non-linear
regime, and their frequency dependence were measured, and the behaviour of the
two types of gels was compared. Protein gels and droplet gels were found to
have broadly similar microstructure and rheological properties when compared at
fixed volume fraction, a parameter derived from the study of the viscosity of
the suspensions formed by proteins and by droplets. The viscoelasticity
displayed a power law behaviour in concentration, as did the storage modulus in
frequency. Additionally, strain hardening was found to occur at low
concentration. These behaviours differed slightly between protein gels and
droplet gels, showing that some specific properties of the primary colloidal
particles play a role in the development of the rheological properties of the
gels.Comment: 27 pages, 6 figure
Optomechanical self-structuring in cold atomic gases
The rapidly developing field of optomechanics aims at the combined control of
optical and mechanical (solid-state or atomic) modes. In particular, laser
cooled atoms have been used to exploit optomechanical coupling for
self-organization in a variety of schemes where the accessible length scales
are constrained by a combination of pump modes and those associated to a second
imposed axis, typically a cavity axis. Here, we consider a system with many
spatial degrees of freedom around a single distinguished axis, in which two
symmetries - rotations and translations in the plane orthogonal to the pump
axis - are spontaneously broken. We observe the simultaneous spatial
structuring of the density of a cold atomic cloud and an optical pump beam. The
resulting patterns have hexagonal symmetry. The experiment demonstrates the
manipulation of matter by opto-mechanical self-assembly with adjustable length
scales and can be potentially extended to quantum degenerate gases.Comment: 20 pages, 6 figure
Instabilities of Higher-Order Parametric Solitons. Filamentation versus Coalescence
We investigate stability and dynamics of higher-order solitary waves in
quadratic media, which have a central peak and one or more surrounding rings.
We show existence of two qualitatively different behaviours. For positive phase
mismatch the rings break up into filaments which move radially to initial ring.
For sufficient negative mismatches rings are found to coalesce with central
peak, forming a single oscillating filament.Comment: 5 pages, 7 figure
Frequency selection by soliton excitation in nondegenerate intracavity downconversion
We show that soliton excitation in intracavity downconversion naturally
selects a strictly defined frequency difference between the signal and idler
fields. In particular, this phenomenon implies that if the signal has smaller
losses than the idler then its frequency is pulled away from the cavity
resonance and the idler frequency is pulled towards the resonance and {\em vice
versa}. The frequency selection is shown to be closely linked with the relative
energy balance between the idler and signal fields.Comment: 5 pages, 3 figures. To appear in Phys Rev Let
Modulational instability of bright solitary waves in incoherently coupled nonlinear Schr\"odinger equations
We present a detailed analysis of the modulational instability (MI) of
ground-state bright solitary solutions of two incoherently coupled nonlinear
Schr\"odinger equations. Varying the relative strength of cross-phase and
self-phase effects we show existence and origin of four branches of MI of the
two-wave solitary solutions. We give a physical interpretation of our results
in terms of the group velocity dispersion (GVD) induced polarization dynamics
of spatial solitary waves. In particular, we show that in media with normal GVD
spatial symmetry breaking changes to polarization symmetry breaking when the
relative strength of the cross-phase modulation exceeds a certain threshold
value. The analytical and numerical stability analyses are fully supported by
an extensive series of numerical simulations of the full model.Comment: Physical Review E, July, 199
New possibilities for research on reef fish across the continental shelf of South Africa
[From introduction] Subtidal research presents numerous challenges that restrict the ability to answer fundamental ecological questions related to reef systems. These challenges are closely associated with traditional monitoring methods and include depth restrictions (e.g. safe diving depths for underwater visual census), habitat destruction (e.g. trawling), mortality of target species (e.g. controlled angling and fish traps), and high operating costs (e.g. remotely operated vehicles and large research vessels. Whereas many of these challenges do not apply or are avoidable in the shallow subtidal environment, the difficulties grow as one attempts to sample deeper benthic habitats. This situation has resulted in a paucity of knowledge on the structure and ecology of deep water reef habitats around the coast of South Africa and in most marine areas around the world. Furthermore, the inability to effectively survey deep water benthic environments has limited the capacity of researchers to investigate connectivity between shallow and deep water habitats in a standardised and comparable fashion
Modulational instability of solitary waves in non-degenerate three-wave mixing: The role of phase symmetries
We show how the analytical approach of Zakharov and Rubenchik [Sov. Phys.
JETP {\bf 38}, 494 (1974)] to modulational instability (MI) of solitary waves
in the nonlinear Schr\"oedinger equation (NLS) can be generalised for models
with two phase symmetries. MI of three-wave parametric spatial solitons due to
group velocity dispersion (GVD) is investigated as a typical example of such
models. We reveal a new branch of neck instability, which dominates the usual
snake type MI found for normal GVD. The resultant nonlinear evolution is
thereby qualitatively different from cases with only a single phase symmetry.Comment: 4 pages with figure
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