Parabolic pulse generation with active or passive dispersion decreasing optical fibers

We experimentally demonstrate the possibility to generate parabolic pulses via a single dispersion decreasing optical fiber with normal dispersion. We numerically and experimentally investigate the influence of the dispersion profile, and we show that a hybrid configuration combining dispersion decrease and gain has several benefits on the parabolic generated pulses

Simple Method for Measuring the Zero-Dispersion Wavelength in Optical Fibers

We propose a very simple method for measuring the zero-dispersion wavelength of an optical fiber as well as the ratio between the third- and fourth-order dispersion terms. The method is based on the four wave mixing process when pumping the fiber in the normal dispersion region, and only requires the measurement of two spectra, provided that a source tunable near the zero-dispersion wavelength is available. We provide an experimental demonstration of the method in a photonic crystal fiber and we show that the measured zero-dispersion wavelength is in good agreement with a low-coherence interferometry measurement.Comment: 6 pages, 4 figures; IEEE Photonics Technology Letters, VOL. 23, NO. 10, MAY 15, 201

Dynamics of cascaded resonant radiations in a dispersion-varying optical fiber

International audienceWe use a dispersion-varying optical fiber to experimentally explore the dynamics of resonant radiations emitted from Raman-shifting solitons in the vicinity of the second zero-dispersion. The evolving zero-dispersion wavelength with fiber length allows to observe unprecedented processes such as a cascade of resonant radiations, the emission of multiple resonant radiations from a single soli-ton and the generation of a 500 nm continuum exclusively composed of resonant radiations. All experiments are interpreted using numerical simulations of the generalized nonlinear Schrödinger equation which are in excellent agreement

PLIF Measurements of Nitric Oxide and Hydroxyl Radicals Distributions in Swirled Stratified Premixed Flames

Environmental and economic concerns have pushed aeronautical authorities to set stringent environmental regulations on fuel consumption, noise production, and pollutant emission. Engine manufacturers are developing novel staged injection concepts to ensure their respect. The injection staging creates a fuel-air mixture stratification involving new combustion processes not fully understood. This paper presents the experimental investigation of NO production for known swirled and / or stratified lean premixed flames. The fuel staging parameter defined as the stratification ratio is studied for values of 1, 2, and 3, while the swirl fractions are 0, 25 and 33%, changing the flowfield from non-swirling cond itions to high swirl numbers (up to 0.55). The implementation of simultaneous OH- and NOPLIF imaging techniques is achieved using high energy pulsed laser systems, able, for instance, to deliver 30 mJ/ pulse around the 226-nm UV wavelength for NO excitation. OH-PLIF is used to characterize the flame structure through the commonly extracted curvature, and also through the measurement of the flame thickness. These results show to be more accurate than thickness obtained from temperature profiles measured by Raman/ Rayleigh laser diagnostics. NO-PLIF is used to quantify the pollutant concentration. To this end, preliminary work was done to select the Q1 (29.5) transition as it the least temperature dependent excitation scheme with high fluorescence levels. After realizing a specific calibration of the NO-PLIF technique, the stud ied flames presented concentrations ranging from traces (20 ppm) to high levels (230 ppm). Further analysis of these results reveals that for high stratification ratios the prompt NO is favored and is responsible for the elevated level of NO pollutant

Modulation instability, Akhmediev Breathers and continuous wave supercontinuum generation

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 pulsesComment: 22 pages, 6 figure

DRASC 1kHz mono-coup à sonde à dérive de fréquence : étude dynamique d'une flamme de diffusion à structures cohérentes

International audienceDepuis les années 2000, la présence sur le marché de sources femtoseconde commerciales haute puissance et haute cadence a permis de développer le diagnostic DRASC (Diffusion Raman anti-Stokes Cohérente) de mesure de température dans ce régime d’interaction. L’énergie par impulsion atteignant plusieurs mJ ainsi que la puissance crête élevée du laser femtoseconde permet de réaliser des mesures instantanées à une cadence de répétition élevée pouvant atteindre la dizaine de kHz. Dans la présente étude, le développement d’une méthodologie numérique et expérimentale a permis de réaliser mesurer la température de flamme avec une précision de l’ordre du pourcent. Combiné à cette précision, le dispositif de mesure DRASC permet d’analyser des processus dynamiques de flamme comme le développement de structures tourbillonnaires périodiques où des variations élevées de température sont présentes ainsi que de faire la démonstration de l’aptitude du système à capturer la dynamique d’une flamme présentant des structures tourbillonnaires périodiques sur une amplitude importante de valeur de température

On the statistical interpretation of optical rogue waves

Numerical simulations are used to discuss various aspects of "optical rogue wave" statistics observed in noise-driven fiber supercontinuum generation associated with highly incoherent spectra. In particular, we consider how long wavelength spectral filtering influences the characteristics of the statistical distribution of peak power, and we contrast the statistics of the spectrally filtered SC with the statistics of both the peak power of the most red-shifted soliton in the SC and the maximum peak power across the full temporal field with no spectral selection. For the latter case, we show that the unfiltered statistical distribution can still exhibit a long-tail, but the extreme-events in this case correspond to collisions between solitons of different frequencies. These results confirm the importance of collision dynamics in supercontinuum generation. We also show that the collision-induced events satisfy an extended hydrodynamic definition of "rogue wave" characteristics.Comment: Paper accepted for publication in the European Physical Journal ST, Special Topics. Discussion and Debate: Rogue Waves - towards a unifying concept? To appear 201

Fiber-based broadband black-light source

International audienceBlack-Light or Wood's lamp refers to sources that emit long-wavelength ultraviolet radiation (UV-A) from 315 nm and little visible light till 410 nm (blue). In this paper, we present a new fibre-based source of "black light", a source that emits broadband ultraviolet radiation but only small amounts of visible light and no infrared light. We made this source by pumping a specially designed silica photonic crystal fibre (PCF) with 355 nm light pulses from a Q-switched frequency-tripled Nd:YAG laser. Four-wave mixing and cascaded Raman generation combine in the fibre to provide a supercontinuum output that spans from around 350 nm to 390-470 nm, with the exact spectral width dependent on the pump power, as shown in Fig. 1. This broadband black-light source can find potential applications for diagnostic and therapeutic uses in medicine and in dermatology, for the detection of substances tagged with fluorescents and minerals, for counterfeit money, for absorption spectroscopy, and for military application

Supercontinuum generation in silicon waveguides relying on wave-breaking

Four-wave-mixing processes enabled during optical wave-breaking (OWB) are exploited in this paper for supercontinuum generation. Unlike conventional approaches based on OWB, phase-matching is achieved here for these nonlinear interactions, and, consequently, new frequency production becomes more efficient. We take advantage of this kind of pulse propagation to obtain numerically a coherent octave-spanning mid-infrared supercontinuum generation in a silicon waveguide pumping at telecom wavelengths in the normal dispersion regime. This scheme shows a feasible path to overcome limits imposed by two-photon absorption on spectral broadening in silicon waveguide