398 research outputs found
Digital enhancement of flow field images
Most photographs of experimentally generated fluid flow fields have inherently poor photographic quality, specifically low contrast. Thus, there is a need to establish a process for quickly and accurately enhancing these photographs to provide improved versions for physical interpretation, analysis, and publication. A sequence of digital image processing techniques which have been demonstrated to effectively enhance such photographs is described
Parametric excitation of multiple resonant radiations from localized wavepackets
Fundamental physical phenomena such as laser-induced ionization, driven
quantum tunneling, Faraday waves, Bogoliubov quasiparticle excitations, and the
control of new states of matter rely on time-periodic driving of the system. A
remarkable property of such driving is that it can induce the localized (bound)
states to resonantly couple to the continuum. Therefore experiments that allow
for enlightening and controlling the mechanisms underlying such coupling are of
paramount importance. We implement such an experiment in a special fiber optics
system characterized by a dispersion oscillating along the propagation
coordinate, which mimics "time". The quasi-momentum associated with such
periodic perturbation is responsible for the efficient coupling of energy from
the localized wave-packets sustained by the fiber nonlinearity into
free-running linear dispersive waves (continuum), at multiple resonant
frequencies. Remarkably, the observed resonances can be explained by means of a
unified approach, regardless of the fact that the localized state is a
soliton-like pulse or a shock front
Modulational instability in dispersion oscillating fiber ring cavities
We show that the use of a dispersion oscillating fiber in passive cavities
significantly extend modulational instability to novel high-frequency bands,
which also destabilize the branches of the steady response which are stable
with homogeneous dispersion. By means of Floquet theory, we obtain exact
explicit expression for the sideband gain, and a simple analytical estimate for
the frequencies of maximum gain. Numerical simulations show that stable
stationary trains of pulses can be excited in the cavity
Fast and accurate modelling of nonlinear pulse propagation in graded-index multimode fibers
We develop a model for the description of nonlinear pulse propagation in
multimode optical fibers with a parabolic refractive index profile. It consists
in a 1+1D generalized nonlinear Schr\"odinger equation with a periodic
nonlinear coefficient, which can be solved in an extremely fast and efficient
way. The model is able to quantitatively reproduce recently observed phenomena
like geometric parametric instability and broadband dispersive wave emission.
We envisage that our equation will represent a valuable tool for the study of
spatiotemporal nonlinear dynamics in the growing field of multimode fiber
optics
Dispersive dam-break flow of a photon fluid
We investigate the temporal photonic analogue of the dam-break phenomenon for
shallow water by exploiting a fiber optics setup. We clearly observe the decay
of the step-like input (photonic dam) into a pair of oppositely propagating
rarefaction wave and dispersive shock wave. Our results show evidence for a
critical transition of the dispersive shock into a self-cavitating state. The
detailed observation of the cavitating state dynamics allows for a fully
quantitative test of the Whitham modulation theory applied to the universal
defocusing nonlinear Schroedinger equation
Spectral wings of the fiber supercontinuum and the dark-bright soliton interaction
We present experimental and numerical data on the supercontinuum generation
in an optical fiber pumped in the normal dispersion range where the seeded dark
and the spontaneously generated bright solitons contribute to the spectral
broadening. We report the dispersive radiation arising from the interaction of
the bright and dark solitons. This radiation consists of the two weak
dispersing pulses that continuously shift their frequencies and shape the short
and long wavelength wings of the supercontinuum spectrum.Comment: supercontinuum, soliton, fiber; 6 page
Competing Turing and Faraday instabilities in longitudinally modulated passive resonators
We experimentally investigate the interplay of Turing and Faraday
(modulational) instabilities in a bistable passive nonlinear resonator. The
Faraday branch is induced via parametric resonance owing to a periodic
modulation of the resonator dispersion. We show that the bistable switching
dynamics is dramatically affected by the competition between the two
instability mechanisms, which dictates two completely novel scenarios. At low
detunings from resonance switching occurs between the stable stationary lower
branch and the Faraday-unstable upper branch, whereas at high detunings we
observe the crossover between the Turing and Faraday periodic structures. The
results are well explained in terms of the universal Lugiato-Lefever model
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