Search results for "Modula"
showing 10 items of 1481 documents
Effects of structural irregularities on modulational instability phase matching in photonic crystal fibers
2004
International audience; The effect of structural irregularities in photonic crystal fibers on scalar and vector modulational instability (MI) processes is studied by numerical simulations and experiments. For an anomalous-dispersion regime pump, variations in core ellipticity as small as 0.5% over length scales of the order of several meters are shown to have a negligible effect on scalar MI, yet they completely suppress vector MI. In contrast, for a normal-dispersion regime pump, vector MI is shown to be robust against such fluctuations.
Experimental Study of Modulational Instability and Vector Solitons in Optical Fibers
2003
This chapter brings forth the experimental study of modulational instability and vector solitons in optical fibers.
Scaling the abruptly autofocusing beams in the direct-space
2017
International audience; We propose a simple technique to scale the abruptly autofocusing beams in the direct space by introducing a scaling factor in the phase. Analytical formulas are deduced based on optical caustics, explicitly revealing how the scaling factor controls location, peak intensity, and size of the focal spot. We demonstrate that the multiplication of a scaling factor on the phase is equivalent to the axial-scaling transformation under the paraxial approximation. Further numerical and experimental results confirm theoretical predictions. In addition, amplitude modulation using phase-only holograms is used to maintain the peak intensity level of the focal spots.
Baseband modulation instability as the origin of rogue waves
2015
International audience; We study the existence and properties of rogue-wave solutions in different nonlinear wave evolution models that are commonly used in optics and hydrodynamics. In particular, we consider the Fokas-Lenells equation, the defocusing vector nonlinear Schrödinger equation, and the long-wave-shortwave resonance equation. We show that rogue-wave solutions in all of these models exist in the subset of parameters where modulation instability is present if and only if the unstable sideband spectrum also contains cw or zero-frequency perturbations as a limiting case (baseband instability). We numerically confirm that rogue waves may only be excited from a weakly perturbed cw whe…
Higher-Order Modulation Instability in Nonlinear Fiber Optics
2011
International audience; We report theoretical, numerical, and experimental studies of higher-order modulation instability in the focusing nonlinear Schrödinger equation. This higher-order instability arises from the nonlinear superposition of elementary instabilities, associated with initial single breather evolution followed by a regime of complex, yet deterministic, pulse splitting. We analytically describe the process using the Darboux transformation and compare with experiments in optical fiber. We show how a suitably low frequency modulation on a continuous wave field induces higher-order modulation instability splitting with the pulse characteristics at different phases of evolution r…
Modulation instability, Akhmediev Breathers and continuous wave supercontinuum generation
2009
Numerical simulations of the onset phase of continuous wave supercontinuum generation from modulation instability show that the structure of the field as it develops can be interpreted in terms of the properties of Akhmediev Breathers. Numerical and analytical results are compared with experimental measurements of spectral broadening in photonic crystal fiber using nanosecond pulses
The nonlinear Schrodinger equation and the propagation of weakly nonlinear waves in optical fibres and on the water surface
2015
International audience; The dynamics of waves in weakly nonlinear dispersive media can be described by the nonlinear Schrödinger equation (NLSE). An important feature of the equation is that it can be derived in a number of different physical contexts; therefore, analogies between different fields, such as for example fiber optics, water waves, plasma waves and Bose–Einstein condensates, can be established. Here, we investigate the similarities between wave propagation in optical Kerr media and water waves. In particular, we discuss the modulation instability (MI) in both media. In analogy to the water wave problem, we derive for Kerr-media the Benjamin–Feir index, i.e. a nondimensional par…
Impact of a temporal sinusoidal phase modulation on the optical spectrum
2018
International audience; We discuss the effects of imparting a temporal sinusoidal phase modulation to a continuous wave on the frequency spectrum. While a practical analytical solution to this problem already exists, we present here a physical interpretation based on interference processes. This simple model will help the students better understand the origin of the oscillatory structure that can be observed in the resulting spectrum and that is characteristic of Bessel functions of the first kind. We illustrate our approach with an example from the field of optics.
Nonlinear parametric resonances in quasiperiodic dispersion oscillating fibers
2015
We numerically study the evolution of the spectrum of parametric resonance or modulation instability sidebands in quasiperiodic dispersion oscillating fibers. We separately consider a linear variation along the fiber of either the spatial period, the average dispersion, or the amplitude of the dispersion oscillation. We found that this linear variation of the dispersion oscillating fiber parameters may provide different novel mechanisms for the splitting of the resonance sideband spectrum, owing to coherent interference between quasi-resonant waves that are generated at different points along the fiber. (C) 2015 Elsevier B.V. All rights reserved.
Nonlinear spectrum broadening cancellation by sinusoidal phase modulation
2017
International audience; We propose and experimentally demonstrate a new approach to dramatically reduce the spectral broadening induced by self-phase modulation occurring in a Kerr medium. By using a temporal sinusoidal phase modulation, we efficiently cancel to a large extend the chirp induced by the nonlinear effect. Experimental validation carried out in a passive or amplifying fiber confirm the interest of the technic for the mitigation of spectral expansion of long pulses.