728 research outputs found
Ultrasonic cavity solitons
We report on a new type of localized structure, an ultrasonic cavity soliton,
supported by large aspect-ratio acoustic resonators containing viscous media.
The spatio-temporal dynamics of this system is analyzed on the basis of a
generalized Swift-Hohenberg equation, derived from the microscopic equations
under conditions close to nascent bistability. These states of the acoustic and
thermal fields are robust structures, existing whenever a spatially uniform
solution and a periodic pattern coexist. An analytical solution for the
ultrasonic cavity soliton is also presented
Interaction of two modulational instabilities in a semiconductor resonator
The interaction of two neighboring modulational instabilities in a coherently driven semiconductor cavity is investigated. First, an asymptotic reduction of the general equations is performed in the limit of a nearly vertical input-output characteristic. Next, a normal form is derived in the limit where the two instabilities are close to one other. An infinity of branches of periodic solutions are found to emerge from the unstable portion of the homogeneous branch. These branches have a nontrivial envelope in the bifurcation diagram that can either smoothly join the two instability points or form an isolated branch of solutions
Phase-Locked Spatial Domains and Bloch Domain Walls in Type-II Optical Parametric Oscillators
We study the role of transverse spatial degrees of freedom in the dynamics of
signal-idler phase locked states in type-II Optical Parametric Oscillators.
Phase locking stems from signal-idler polarization coupling which arises if the
cavity birefringence and/or dichroism is not matched to the nonlinear crystal
birefringence. Spontaneous Bloch domain wall formation is theoretically
predicted and numerically studied. Bloch walls connect, by means of a
polarization transformation, homogeneous regions of self-phase locked
solutions. The parameter range for their existence is analytically found. The
polarization properties and the dynamics of walls in one- and two transverse
spatial dimensions is explained. Transition from Bloch to Ising walls is
characterized, the control parameter being the linear coupling strength. Wall
dynamics governs spatiotemporal dynamical states of the system, which include
transient curvature driven domain growth, persistent dynamics dominated by
spiraling defects for Bloch walls, and labyrinthine pattern formation for Ising
walls.Comment: 27 pages, 16 figure
Polarization coupling and pattern selection in a type-II optical parametric oscillator
We study the role of a direct intracavity polarization coupling in the
dynamics of transverse pattern formation in type-II optical parametric
oscillators. Transverse intensity patterns are predicted from a stability
analysis, numerically observed, and described in terms of amplitude equations.
Standing wave intensity patterns for the two polarization components of the
field arise from the nonlinear competition between two concentric rings of
unstable modes in the far field. Close to threshold a wavelength is selected
leading to standing waves with the same wavelength for the two polarization
components. Far from threshold the competition stabilizes patterns in which two
different wavelengths coexist.Comment: 14 figure
Stabilization of Spatial Solitons by Gain Diffusion
It is shown, that diffusion of saturated gain (e.g. diffusion of population
inversion in lasers) causes, and/or enhances a modulational instability of
generated light field. In case of a subcritical system (e.g. a laser with
saturable absorber) the enhancement of the modulational instability stabilizes
spatial solitons. These predictions are made for general nonlinear optical
systems, and are illustrated by numerical simulation of lasers with saturable
absorber.Comment: 10 pages, 4 figures, submitted to Phys.Rev.
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