177 research outputs found
Generalized modulational instability in multimode fibers: wideband multimode parametric amplification
In this paper intermodal modulational instability (IM-MI) is analyzed in a
multimode fiber where several spatial and polarization modes propagate. The
coupled nonlinear Schr\"{o}dinger equations describing the modal evolution in
the fiber are linearized and reduced to an eigenvalue problem. As a result, the
amplification of each mode can be described by means of the eigenvalues and
eigenvectors of a matrix that stores the information about the dispersion
properties of the modes and the modal power distribution of the pump. Some
useful analytical formulas are also provided that estimate the modal
amplification as function of the system parameters. Finally, the impact of
third-order dispersion and of absorbtion losses is evaluated, which reveals
some surprising phenomena into the IM-MI dynamics. These outcomes generalize
previous studies on bimodal-MI, related to the interaction between 2 spatial or
polarization modes, to the most general case of interacting modes.
Moreover, they pave the way towards the realization of wideband multimode
parametric amplifier
Novel Fiber Design for Wideband Conversion and Amplification in Multimode Fibers
We propose an operating principle to achieve broadband and highly tunable
mode conversion and amplification exploiting inter-modal four wave mixing in a
multimode fiber. A bandwidth of 30 nanometers is demonstrated by properly
designing a simple step-index silica fiber.Comment: Ecoc conference 201
Analytical approximations of the dispersion relation of a linear chain ofmetal nanoparticles
We find some useful analytical approximations of the dispersion relation of a linear chain of metal nanoparticles in the subwavelength limit where the dipolar approximation can be used. We also approximate the group velocity without a direct estimation of the derivative of the dispersion relation, that carries unavoidable error amplifications. In the end we use these results in order to get some simple recipes that evaluate the sensitivity of the dispersion relation and the propagation losses with respect to the main
parameters of the chain
Theory of modal attraction in bimodal birefringent optical fibers
Nonlinear mode coupling among two beams of different wavelength that copropagate in a bimodal highly birefringent
optical fiber may lead to the effect of modal attraction. Under such circumstances, the modal distribution of
light at a pump wavelength is replicated at the signal wavelength, nearly irrespective of the input mode excitation
conditions of the signal
Intensity noise-driven nonlinear fiber polarization scrambler
We propose and analyze a novel all-optical fiber optic polarization scrambler, based on the transfer via the Kerr
effect of the intensity fluctuations of an incoherent pump beam into polarization fluctuations of a copropagating,
frequency shifted signal beam in a randomly birefringent telecom fiber. Optimal signal polarization scrambling
results whenever the input signal and pump beams have nearly orthogonal states of polarizations. The nonlinear
polarization scrambler may operate on either cw or high-bit-rate pulsed signals
All-optical sampling and magnification based on XPM-induced focusing
International audienceWe theoretically and experimentally investigate the design of an all-optical noiseless magnification and sampling function free from any active gain medium and associated high-power continuous wave pump source. The proposed technique is based on the co-propagation of an arbitrary shaped signal together with an orthogonally polarized intense fast sinusoidal beating within a normally dispersive optical fiber. Basically, the strong nonlinear phase shift induced by the sinusoidal pump beam on the orthogonal weak signal through cross-phase modulation turns the defocusing regime into localized temporal focusing effects. This periodic focusing is then responsible for the generation of a high-repetition-rate temporal comb upon the incident signal whose amplitude is directly proportional to its initial shape. This internal redistribution of energy leads to a simultaneous sampling and magnification of the signal intensity profile. This process allows us to experimentally demonstrate a 40-GHz sampling operation as well as an 8-dB magnification of an arbitrary shaped nanosecond signal around 1550 nm in a 5-km long normally dispersive fiber. The experimental observations are in quantitative agreement with numerical and theoretical analysis
Near to short wave infrared light generation through AlGaAs-on-insulator nanoantennas
AlGaAs-on-insulator (AlGaAs-OI) has recently emerged as a promising platform for nonlinear optics at the nanoscale. Among the most remarkable outcomes, second-harmonic generation (SHG) in the visible/near infrared spectral region has been demonstrated in AlGaAs-OI nanoantennas (NAs). In order to extend the nonlinear frequency generation towards the short wave infrared window, in this work we propose and demonstrate via numerical simulations difference frequency generation (DFG) in AlGaAs-OI NAs. The NA geometry is finely adjusted in order to obtain simultaneous optical resonances at the pump, signal and idler wavelengths, which results in an efficient DFG with conversion efficiencies up to 0.01%. Our investigation includes the study of the robustness against random variations of the NA geometry that may occur at fabrication stage. Overall, these outcomes identify what we believe to be a new potential and yet unexplored application of AlGaAs-OI NAs as compact devices for the generation and control of the radiation pattern in the near to short infrared spectral region
Observation of a Modulational Instability in Bose-Einstein condensates
We observe the breakup dynamics of an elongated cloud of condensed Rb
atoms placed in an optical waveguide. The number of localized spatial
components observed in the breakup is compared with the number of solitons
predicted by a plane-wave stability analysis of the nonpolynomial nonlinear
Schr\"odinger equation, an effective one-dimensional approximation of the
Gross-Pitaevskii equation for cigar-shaped condensates. It is shown that the
numbers predicted from the fastest growing sidebands are consistent with the
experimental data, suggesting that modulational instability is the key
underlying physical mechanism driving the breakup.Comment: 6 pages, 5 figure
Temporal spying and concealing process in fibre-optic data transmission systems through polarization bypass
International audienceRecent research has been focused on the ability to manipulate a light beam in such a way to hide, namely to cloak, an event over a finite time or localization in space. The main idea is to create a hole or a gap in the spatial or time domain so as to allow for an object or data to be kept hidden for a while and then to be restored. By enlarging the field of applications of this concept to telecommunications, researchers have recently reported the possibility to hide transmitted data in an optical fibre. Here we report the first experimental demonstration of perpetual temporal spying and blinding process of optical data in fibre-optic transmission line based on polarization bypass. We successfully characterize the performance of our system by alternatively copying and then concealing 100% of a 10-Gbit s-1 transmitted signal.
Stochastic evolution equations driven by Liouville fractional Brownian motion
Let H be a Hilbert space and E a Banach space. We set up a theory of
stochastic integration of L(H,E)-valued functions with respect to H-cylindrical
Liouville fractional Brownian motions (fBm) with arbitrary Hurst parameter in
the interval (0,1). For Hurst parameters in (0,1/2) we show that a function
F:(0,T)\to L(H,E) is stochastically integrable with respect to an H-cylindrical
Liouville fBm if and only if it is stochastically integrable with respect to an
H-cylindrical fBm with the same Hurst parameter. As an application we show that
second-order parabolic SPDEs on bounded domains in \mathbb{R}^d, driven by
space-time noise which is white in space and Liouville fractional in time with
Hurst parameter in (d/4,1) admit mild solution which are H\"older continuous
both and space.Comment: To appear in Czech. Math.
- âŠ