Search results for " Modulation"
showing 10 items of 496 documents
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.
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…
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.
Parabolic pulse evolution in normally dispersive fiber amplifiers preceding the similariton formation regime
2006
We show analytically and numerically that parabolic pulses and similaritons are not always synonyms and that a self-phase modulation amplification regime can precede the self-similar evolution. The properties of the recompressed pulses after SPM amplification are investigated. We also demonstrate that negatively chirped parabolic pulses can exhibit a spectral recompression during amplification leading to high-power chirp-free parabolic pulses at the amplifier output.
Buffering optical topological data using passive Kerr resonators
2018
We experimentally demonstrate the existence of dissipative polarization domain walls, in a normally dispersive Kerr resonator. Through deterministic manipulation of the laser driving the resonator, we achieve systematic excitation and locking of the domain walls.
Laser Pulse Effects in Two-level Systems Driven by Coherent and Fluctuating Radiation Fields
1988
Abstract We reconsider the problem of a two-level system interacting with a radiation field in order to study some new features suggested by the actual experimental conditions. Pulse shape and duration effects are included in the formalism and the counter-rotating terms are retained. The criterion of validity of the rotating wave approximation (RWA) for pulsed fields is investigated; generalizing results well known in RWA, we establish some new formal results, including non-RWA contributions to all orders and for any pulse shape. The analysis is then carried out for fluctuating fields, by developing a method based on the theory of multiplicative stochastic differential equations. For short …
Pulse-by-pulse method to characterize partially coherent pulse propagation in instantaneous nonlinear media.
2010
We propose a numerical method for analyzing extensively the evolution of the coherence functions of nonstationary optical pulses in dispersive, instantaneous nonlinear Kerr media. Our approach deals with the individual propagation of samples from a properly selected ensemble that reproduces the coherence properties of the input pulsed light. In contrast to the usual strategy assuming Gaussian statistics, our numerical algorithm allows us to model the propagation of arbitrary partially coherent pulses in media with strong and instantaneous nonlinearities.
Acousto-optical multiple interference devices
2008
We present a new concept for waveguide acousto-optical devices based on coupled MachZehnder interferometers driven by acoustic waves. These acousto-optical multiple interference devices use the periodic refractive index modulation induced by the acoustic wave to realize functionalities such as ON/OFF switching for an arbitrary time interval, as well as for efficient light modulation at high harmonics of the acoustic frequency and pulse shaping for, e.g., integrated Q-switches. We also discuss application of the concepts to light modulation by very high acoustic frequencies, where the acoustic wavelengths become much shorter than the optical ones.