485 research outputs found
Solitons in a medium with linear dissipation and localized gain
We present a variety of dissipative solitons and breathing modes in a medium
with localized gain and homogeneous linear dissipation. The system posses a
number of unusual properties, like exponentially localized modes in both
focusing and defocusing media, the existence of modes in focusing media at
negative propagation constant values, the simultaneous existence of stable
symmetric and anti-symmetric localized modes when the gain landscape possesses
two local maxima, as well as the existence of stable breathing solutions.Comment: 4 pages, 5 figures, to appear in Optics 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
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
Vortex solitons in large-scale waveguide arrays with adjustable discrete rotational symmetry
We consider vortex solitons in large-scale arrays composed of N elliptical
waveguides placed on a ring, which can be fabricated using fs-laser writing
technique in transparent nonlinear dielectrics. By introducing variable twist
angles between longer axes of neighboring elliptical waveguides on a ring, we
create circular arrays with adjustable discrete rotational symmetry ranging
from C_N to C_1, when the number of waveguides N on the ring remains fixed.
This allows to consider the impact of discrete rotational symmetry on the
properties of available vortex solitons without changing the number of guiding
channels in the structure, and to predict how exactly splitting of higher-order
phase singularities into sets of charge-1 singularities occurs in vortex
states, when they are forbidden by the discrete rotational symmetry of the
structure that imposes the restrictions on the maximal possible vortex charge.
It is found that separation between split charge-1 phase singularities in such
higher-order vortex states increases with increase of the order of solution. We
also study linear spectra of such arrays and show how variation of their
discrete rotational symmetry affects linear eigenmodes, whose combinations can
give rise to vortex modes. We also show that variation of discrete rotational
symmetry in arrays with fixed number of guiding channels N has strong impact on
stability of vortex solitons. Thus, only higher-charge vortex solitons are
stable in such large-scale arrays and the number of stable states typically
decreases with decrease of the order of discrete rotational symmetry of the
structure at fixed N.Comment: 8 pages, 5 figures, to appear in Chaos, Solitons and Fractal
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