302 research outputs found
Dynamical light control in longitudinally modulated segmented waveguide arrays
We address light propagation in segmented waveguide arrays where the
refractive index is longitudinally modulated with an out-of-phase modulation in
adjacent waveguides, so that the coupling strength varies along propagation
direction. Thus in resonant segments coupling may be inhibited hence light
remains localized, while in detuned segments coupling results in complex
switching scenarios that may be controlled by stacking several resonant and
nonresonant segments. By tuning the modulation frequency and lengths of
waveguide segments one may control the distribution of light among the output
guides, including loca-lizing all light in the selected output channel.Comment: 12 pages, 4 figures, to appear in Europhysics Letter
Resonant mode conversion in the waveguides with an unbroken and broken PT-symmetry
We study resonant mode conversion in the PT-symmetric multimode waveguides,
where symmetry breaking manifests itself in sequential destabilization
(appearance of the complex eigenvalues) of the pairs of adjacent guided modes.
We show that the efficient mode conversion is possible even in the presence of
the resonant longitudinal modulation of the complex refractive index. The
distinguishing feature of the resonant mode conversion in the PT-symmetric
structure is a drastic growth of the width of the resonance curve when the
gain/losses coefficient approaches a critical value, at which symmetry breaking
occurs. We found that in the system with broken symmetry the resonant coupling
between exponentially growing mode with stable higher-order one effectively
stabilizes dynamically coupled pair of modes and remarkably diminishes the
average rate of the total power growth.Comment: 4 pages, 6 figure
Highly-asymmetric soliton complexes in parabolic optical lattices
We introduce multipole soliton complexes in optical lattices induced by
nondiffracting parabolic beams. Despite the symmetry-breaking dictated by the
curvature of the lattice channels, we find that complex, asymmetric
higher-order states can be stable. The unique topology of parabolic lattices
affords new types of soliton motion: single solitons launched into the lattice
with nonzero transverse momentum perform periodic oscillations along parabolic
paths.Comment: 12 pages, 4 figures, to appear in Optics Letter
Symmetry breaking and multi-hump solitons in inhomogeneous gain landscapes
We address one-dimensional soliton formation in the cubic nonlinear medium
with two-photon absorption and transversally inhomogeneous gain landscape
consisting of a single or several amplifying channels. Existence of the
solitons requires certain threshold gain while the properties of solitons
strongly depend on whether the number of the amplifying channels is odd or
even. In the former case an increase of the gain leads to a symmetry breaking,
which occurs through the pitchfork bifurcation, and to emergence of a single or
several co-existing stable asymmetric modes. In the case of even number of
amplifying channels we have found only asymmetric stable states.Comment: 4 pages, 4 figures, to appear in Physical Review
Soliton percolation in random optical lattices
We introduce soliton percolation phenomena in the nonlinear transport of
light packets in suitable optical lattices with random properties.
Specifically, we address lattices with a gradient of the refractive index in
the transverse plane, featuring stochastic phase or amplitude fluctuations, and
we discover the existence of a disorder-induced transition between
soliton-insu-lator and soliton-conductor regimes. The soliton current is found
to reach its maximal value at intermediate disorder levels and to drastically
decrease in both, almost regular and strongly disordered lattices.Comment: 9 pages, 4 figures, to appear in Optics Expres
Bragg-type soliton mirror
We study soliton reflection/transmission at the interface between uniform
medium and the optical lattice with focusing Kerr nonlinearity. We reveal that
such interfaces afford rich new opportunities for controlling the reflection
and transmission coefficients and nonlinear Snell law, the key control
parameters being the spatial frequency and depth of the lattice.Comment: 6 pages, 2 figures, to appear in Optics Expres
Light beam dynamics in materials with radially-inhomogeneous thermal conductivity
We study the properties of bright and vortex solitons in thermal media with
nonuniform thermal conductivity and homogeneous refractive index, whereby the
local modulation of the thermal conductivity strongly affects the entire
refractive index distribution. While regions where the thermal conductivity is
increased effectively expel light, self-trapping may occur in the regions with
reduced thermal conductivity, even if such regions are located close to the
material boundary. As a result, strongly asymmetric self-trapped beams may form
inside a ring with reduced thermal conductivity and perform persistent rotary
motion. Also, such rings are shown to support stable vortex solitons, which may
feature strongly non-canonical shapes.Comment: 4 pages, 5 figures, to appear in Optics Letter
Rotating surface solitons
We introduce a novel type of surface waves that form at the edge of guiding
structures consisting of several concentric rings. Such surface waves rotate
steadily upon propagation and, in contrast to nonrotating waves, for high
rotation frequencies they do not exhibit power thresholds for their existence.
There exists an upper limit for the surface wave ro-tation frequency, which
depends on the radius of the outer guiding ring and on its depth.Comment: 13 pages, 4 figures, to appear in Optics Letter
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