Search results for "FREQUENCY"
showing 10 items of 2158 documents
Even harmonics generation in plasma as a new tool of current evolution diagnostics
2005
It is shown that using even harmonics of a test wave it is possible to diagnose the fast time evolution of the current density.
High-frequency even harmonics generation in a plasma with electron heat flux
2004
It is shown that in a weakly nonuniform plasma with electron heat flux the generation of odd and even harmonics of high frequency radiation is possible. The even harmonics properties qualitatively differ as compared to those of odd harmonics and depend in an essential way on the heat flux value and orientation with respect to the fundamental wave polarization and propagation directions.
On the correlation between phase-locking modes and Vibrational Resonance in a neuronal model
2018
International audience; We numerically and experimentally investigate the underlying mechanism leading to multiple resonances in the FitzHugh-Nagumo model driven by a bichromatic excitation. Using a FitzHugh-Nagumo circuit, we first analyze the number of spikes triggered by the system in response to a single sinusoidal wave forcing. We build an encoding diagram where different phase-locking modes are identified according to the amplitude and frequency of the sinusoidal excitation. Next, we consider the bichromatic driving which consists in a low frequency sinusoidal wave perturbed by an additive high frequency signal. Beside the classical Vibrational Resonance phenomenon, we show in real ex…
All-fiber incoherent frequency-to-time mapping method for microwave signal generation with baseband transmission and multicasting support
2008
We present a proof-of-principle experiment for achieving simultaneous distribution of baseband radio-frequency data and up-conversion with broadcasting support over a passive optical network. The technique is based on an incoherent frequency-to-time mapping method for pulse shaping. Specifically, we synthesize the spectral density function of sliced ASE noise from an EDFA with a periodic Mach-Zehnder fiber interferometer optical filter. By using external intensity modulation combined with propagation in an optical fiber, after photodetection, the resultant averaged temporal pulse profile resembles the shape of the incoherent source. The photodetected signal contains both the baseband data a…
Continuously Variable Periodic Test Target
1987
CONTINUOUSLY VARIABLE PERIODIC TEST TARGETP. ANDRES*, J. OJEDA- CASTANEDAt, and J.C. BARREIRO*tINAOE, Apartado Postal 216, 72000 Puebla, Pue., Mexico*Departamento de Optica, Universidad de Valencia, 46100 Burjasot, Spain1. INTRODUCTIONThe modulus of the optical transfer function (MTF) of the eye or any other optical system is usuallyevaluated by imaging either several gratings each with different spatial frequency, or a single test tar-get having patterns with different frequencies (USAF resolution chart). In any of these two usual proce-dures, the measurement of the MTF is made at discrete values of the spatial frequency.Here we describe a method based on the self -imaging phenomenon for p…
Complete characterization of terahertz pulse trains generated from nonlinear processes in optical fibers
2001
The measurement technique of frequency-resolved optical gating (FROG) is used to characterize the intensity and phase of terahertz pulse trains generated from nonlinear and dispersive interactions in optical fibers. We show that existing FROG retrieval algorithms are easily adapted to allow the retrieval of periodic pulse characteristics and, using synthetic pulse trains generated from numerical simulations, we demonstrate how FROG can differentiate between periodic pulse trains with fundamentally different intensity and phase characteristics, yet qualitatively similar autocorrelation functions and spectra. Experimental results are presented for the FROG characterization of a 0.3-THz sinuso…
Spectral incoherent solitons: a localized soliton behavior in the frequency domain
2008
We show both theoretically and experimentally in an optical fiber system that a noninstantaneous nonlinear environment supports the existence of spectral incoherent solitons. Contrary to conventional solitons, spectral incoherent solitons do not exhibit a confinement in the spatiotemporal domain, but exclusively in the frequency domain. The theory reveals that the causality condition inherent to the nonlinear response function is the key property underlying the existence of spectral incoherent solitons. These solitons constitute nonequilibrium stable states of the incoherent field and are shown to be robust with respect to binary collisions.
Higher-order modulation instability in fiber optics
2012
We report on analytical, numerical and experimental studies of higher-order modulation instability in fiber optics. This new form of instability arises from the nonlinear superposition of elementary instabilities and manifests as complex, yet deterministic temporal pulse break-up dynamics. We use the Darboux transformation to analytically describe the process and compare with experiments. In particular, we show how suitably low frequency modulation on a continuous wave field allows for the excitation of higher-order modulation instability through cascaded four-wave mixing.
Theory of Raman effect on solitons in optical fibre systems: impact and control processes for high-speed long-distance transmission lines
2004
We examine the effects of stimulated Raman scattering on ultra-short pulses propagating in optical fibre systems. We demonstrate that the existing theories for the Raman-induced soliton self-frequency shift give consistent results in a restricted domain of pulse width which excludes important practical applications to high-speed soliton transmission systems. We present a general theory for the soliton self-frequency shift (SSFS), which applies to any pulse whose spectral bandwidth lies within the third-order telecommunication window. We also show that the harmful impact of the SSFS in high-speed long-distance transmission lines can be suppressed by use of filters whose central frequency is …
Unambiguous phase retrieval in fiber-based interferometers
2020
A scheme for fiber interferometers, exploiting frequency-multiplexing in orthogonal fiber polarization modes, enables unambiguous phase retrieval. This allows for arbitrary phase tuning, providing a precise tool for time-bin qubit manipulation.