1,721,002 research outputs found
Light propagation through a nonlinear defect: symmetry breaking and controlled soliton emission
No full textWe investigate the emission of solitons at a nonlinear longitudinal defect. We discuss the basic physics and introduce a novel approach to achieve complete nonlinear control of the process. Theoretical results are confirmed by numerical simulations. (c) 2006 Optical Society of America
Symmetry-breaking instabilities in perturbed optical lattices: Nonlinear nonreciprocity and macroscopic self-trapping
No full textWe develop an asymptotic analysis of nonlinear energy propagation in lattices subject to slowly varying perturbations, investigating symmetry breaking and its effects. We derive a general set of evolution equations and study them by using catastrophe theory, revealing a wealth of system dynamics. Below a power threshold, symmetry breaking drives nonreciprocal oscillations; beyond that, symmetry breaking yields an effect of "macroscopic" self-trapping, which supports a self-maintained energy imbalance between Bloch bands. We numerically verify the theoretical results and discuss their possible implementation in waveguide arrays
Nonlinear adiabatic evolution and emission of coherent Bloch waves in optical lattices
No full textWe investigate energy propagation in a perturbed optical lattice, studying the nonlinear adiabatic evolution of a light beam. Through an asymptotic model, we demonstrate that: (i) energy propagating in the adiabatic regime visualizes the dispersion relation of the unperturbed lattice; (ii) the adiabatic evolution can be broken by nonlinearity, giving rise to tunneling between Bloch bands; (iii) the tunneling is accompanied by nonlinear emission of one - or more - coherent Bloch waves, the properties of which can be completely controlled by linear and/or nonlinear parameters. We verify the analytical results against numerical simulations and indicate possible experimental implementations
Governing soliton splitting in one-dimensional lattices
No full textWe investigate discrete light dynamics in the presence of a longitudinal defect of arbitrary extension, amplitude and position in a nonlinear waveguide array. We model and discuss the physics of the soliton-defect interaction, showing how to gain complete control over the system outcome for soliton-based data processing. We propose all-optical management in dye-doped liquid crystals
Dispersion spectroscopy of photonic lattices
No full textWe theoretically demonstrate how to acquire the full bandgap spectrum of a photonic lattice of arbitrary profile. Focusing on the ID case in the presence of a linear refractive index acceleration and employing a multiscale analysis, we show that each photonic band can be directly mapped by the light evolution in the lattice, whereas the size of each gap corresponds to the tunneling rate. We verify the analytical results with numerical simulations and discuss experimental realizations of this technique for dispersive spectroscopy. (c) 2006 Optical Society of Americ
Dynamic light diffusion, Anderson localization and lasing in disordered inverted opals: 3D ab-initio Maxwell-Bloch computation
No full textPhotons propagate in photonic crystals in the same way as electrons propagate in solids. The periodical refractive index induces forbidden frequency bands, which nurture a variety of novel integrated devices and several fundamental studies ranging from threshold-less lasers to quantum computing. However, these investigations have to face the unavoidable disorder of real-world structures: if on one hand it largely hampers experiments, on the other hand it opens the possibility to study three-dimensional (3D) photon strong localization. We report on 3D+1 Maxwell–Bloch simulations of light dynamics in inverted opals exhibiting a complete photonic bandgap. We show that the disorder-induced localized states strongly alter the photonic crystal's response to femtosecond optical pulses, drastically reducing the diffusion constant and trapping light. We find that an optimal amount of randomness favours the strongest localization; correspondingly, self-starting laser processes are mediated by Anderson states that prevail over spatially extended Bloch modes
All-optical Landau-Zener tunneling in waveguide arrays
No full textWe investigate Landau-Zener all-optical tunneling in a voltage-controlled waveguide array realized in undoped nematic liquid crystals. From the material governing equations we derive the original Zener model and demonstrate a novel approach to Floquet-band tunneling. (c) 2006 Optical Society of America
Discrete light localization in one-dimensional nonlinear lattices with arbitrary nonlocality
No full textWe model discrete spatial solitons in a periodic nonlinear medium encompassing any degree of transverse nonlocality. Making a convenient reference to a widely used material-nematic liquid crystals-we derive a form of the discrete nonlinear Schrodinger equation and find a family of discrete solitons. Such self-localized solutions in optical lattices can exist with an arbitrary degree of imprinted chirp and have breathing character. We verify numerically that both local and nonlocal discrete light propagation and solitons can be observed in liquid crystalline arrays
Free-energy transition in a gas of non-interacting nonlinear wave-particles.
No full textWe investigate the dynamics of a gas of noninteracting particlelike soliton waves, demonstrating that phase transitions originate from their collective behavior. This is predicted by solving exactly the nonlinear equations and by employing methods of the statistical mechanics of chaos. In particular, we show that a suitable free energy undergoes a metamorphosis as the input excitation is increased, thereby developing a first-order phase transition whose measurable manifestation is the formation of shock waves. This demonstrates that even the simplest phase-space dynamics, involving independent (uncoupled) degrees of freedom, can sustain critical phenomena
On the universal character of the Discrete Nonlinear Schroedinger Equation
No full textWe address the universal applicability of the discrete nonlinear Schrodinger equation. By employing an original but general top-down-bottom-up procedure based on symmetry analysis to the case of optical lattices, we derive the most widely applicable and simplest possible model, revealing that the discrete nonlinear Schrodinger equation is "universally" fit to describe light propagation even in discrete tensorial nonlinear systems and in the presence of nonparaxial and vectorial effects
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