1,721,310 research outputs found
Nonlinear Guided Wave Optics
No full textExperiments and theory have rapidly progressed on nonlinear optical extreme waves, showing that guided wave nonlinear optics and fiber lasers provide a relatively simple, accessible and controllable test bed for the observations and accurate statistical studies of extreme wave phenomena that obey the same universal rules, which apply to a large ensemble of different physical systems. With introductory material to make the subject area accessible to non-specialists such as graduate and PhD students, and researchers working in other areas where extreme waves are relevant, this book features contributions by prominent scientists in this emerging field and is a comprehensive treatment of optical extreme wave research
Nonlinear optical waves in disordered ferroelectrics
Full text linkThis thesis describes an experimental, numerical and theoretical investigation of nonlinear optical phenomena in disordered photorefractive ferroelectrics in proximity of their phase-transition temperature. The work addresses different physical issues that find in nonlinear optics a common fertile research arena and are closely related to each other in the considered systems. Nonlinear wave dynamics in the spatial domain, where self-interaction of propagating waves generally results into non-spreading localized wavepackets such as spatial solitons, is extended in photorefractive ferroelectrics to non-equilibrium regimes characterized by stochastic instabilities and large material fluctuations. We discover the emergence of rogue waves, localized perturbations of abnormal intensity, whose understanding is challenging in various physical contexts and resides in the general problem of long-tail statistical distributions in complex systems. We identify their origin in spatiotemporal soliton dynamics in a saturable nonlinearity which can support scale-invariant waveforms. Properties and predictability of the observed extreme events are investigated, and, in particular, we demonstrate their active control through the spatial incoherence scale of the optical field. Moreover, we report how their emergence is sustained by turbulent transitions to an incoherent and disordered optical state triggered by modulational instability. The onset of strong turbulence for propagating optical waves has remained unobserved up to now and our results demonstrate a new experimental setting for its study. When the functional form of the nonlinearity is turned into a nonlocal one due
to diffusive fields, this setting also exploits photonics to address fundamental physical problems and access to otherwise hidden phenomena. The natural spreading of waves during propagation, representing the wavelength-defined ultimate limit to spatial
resolution, can be eliminated and reversed leading to diffraction cancellation and anti-diffraction of light. Since these behaviors on modifying the nature of underlying Schrödinger equation, we are the first to demonstrate how nonlinearity can make the spatial light distribution behave as the wavefunction of a quantum particle with negative mass. All these findings have roots in the nonlinear optical response of critical disordered ferroelectric crystals, which are also extremely interesting from the condensed matter point of view. In fact, competition of different microscopic structural phases and the associated polar-domain dynamics at the nanoscale results into non-ergodic dipolar-glass behaviors giving giant responses such as giant polarization, piezoelectricity and electro-optic effect. Disordered ferroelectrics crystals are investigated electro-optically across their ferroelectric phase-transition, where we report the observation of an anomalous electro-optic effect compatible with ultracold dipolar reorientation. In compounds presenting spatial inhomogeneity in their chemical composition, we discover a new ferroelectric phase of matter in which polar domains spontaneously coordinate into a mesoscopic coherent polarization super-crystals. This phase mimics standard solid-state structures but on scales that are thousands of times larger and represent the first spontaneous three-dimensional photonic crystal
Stabilization of spatiotemporal dissipative solitons in multimode fiber lasers by external phase modulation
Full text linkIn this work, we introduce a method for the stabilization of spatiotemporal (ST) solitons. These
solitons correspond to light bullets in multimode optical fiber lasers, energy-scalable waveguide
oscillators and amplifiers, localized coherent patterns in Bose–Einstein condensates, etc. We
show that a three-dimensional confinement potential, formed by a spatial transverse (radial)
parabolic graded refractive index and dissipation profile, in combination with quadratic
temporal phase modulation, may permit the generation of stable ST dissipative solitons. This
corresponds to combining phase mode-locking with the distributed Kerr-lens mode-locking.
Our study of the soliton characteristics and stability is based on analytical and numerical
solutions of the generalized dissipative Gross–Pitaevskii equation. This approach could lead to
higher energy (or condensate mass) harvesting in coherent spatio-temporal beam structures
formed in multimode fiber lasers, waveguide oscillators, and weakly-dissipative Bose–Einstein
condensates
Spatial Instability, All-Optical Limiting and Thresholding in Nonlinear Distributed Feedback Devices
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Conditions for walk-off soliton generation in a multimode fiber
Full text linkIt has been recently demonstrated that multimode solitons are unstable objects which evolve, in the range of hundreds of nonlinearity lengths, into stable single-mode solitons carried by the fundamental mode. We show experimentally and by numerical simulations that femtosecond multimode solitons composed by non-degenerate modes have unique properties: when propagating in graded-index fibers, their pulsewidth and energy do not depend on the input pulsewidth, but only on input coupling conditions and linear dispersive properties of the fiber, hence on their wavelength. Because of these properties, spatiotemporal solitons composed by non-degenerate modes with pulsewidths longer than a few hundreds of femtoseconds cannot be generated in graded-index fibers
Managing self-phase modulation in pseudo-linear multimodal and monomodal systems
Full text linkWe propose a new semi-analytical model, describing the bandwidth evolution of pulses propagating in dispersion managed (DM) transmission systems using multimodal graded-index fibers (GRIN) with parabolic index. The model also applies to monomodal fiber DM systems, representing the limit case where beam self-imaging vanishes. The model is successfully compared with the direct integration of the nonlinear Schrödinger equation for parabolic GRIN fibers, and to experimental results performed by using the transmission of femtosecond pulses over a 5 m span of GRIN fiber. At the high pulse powers that are possible in multimodal fibers, the pulse bandwidth variations produced by the interplay of cumulated dispersion and self-phase modulation can become the most detrimental effect, if not properly managed. The analytical model, numerical and experimental results all point to the existence of an optimal amount of chromatic dispersion, that must be provided to the input pulse, for obtaining a periodic evolution of its bandwidth. Results are promising for the generation of spatio-temporal DM solitons in parabolic GRIN fibers, where the stable, periodic time-bandwidth behaviour that was already observed in monomodal systems is added to the characteristic spatial beam self-imaging
Exotic Nonlinear Effects in Multimode Fibers
No full textWe experimentally and theoretically studied femtosecond laser pulse propagation with powers slightly below the breakdown threshold. In this regime, nonlinear absorption strongly affects spatio-temporal beam dynamics, and several exotic nonlinear optical effects are observed
Polarization Dependence of Modal Attraction in High Birefringence Optical Fibers
No full textWe study nonlinear mode coupling among two intense
and copropagating beams of different wavelength in bimodal and
high birefringence optical fibers. With the proper design of the
bimodal fiber, we show that this process may lead to modal attraction, where the modal distribution of light at a pump wavelength is replicated at the signal wavelength, independently of the input mode excitation conditions of the signal. We analyse the dependence of the efficiency of the modal attraction process upon the input state of polarization of both the signal and the pump beams
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