Simple guidelines to predict self-phase modulation patterns

We present a simple approach to predict the main features of optical spectra affected by self-phase modulation (SPM), which is based on regarding the spectral modification as an interference effect. A two-wave interference model is found sufficient to describe the SPM-broadened spectra of initially transform-limited or up-chirped pulses, whereas a third wave should be included in the model for initially down-chirped pulses. Simple analytical formulas are derived, which accurately predict the positions of the outermost peaks of the spectra

Characterisation and mitigation of self-phase modulation in optical fibres

International audienc

Impact of initial pulse shape on the nonlinear spectral compression in optical fibre

We theoretically study the effects of the temporal intensity profile of the initial pulse on the nonlinear propagation spectral compression process arising from nonlinear propagation in an optical fibre. Various linearly chirped input pulse profiles are considered, and their dynamics is explained with the aid of time-frequency representations. While initially parabolic-shaped pulses show enhanced spectral compression compared to Gaussian pulses, no significant spectral narrowing occurs when initially super-Gaussian pulses are used. Triangular pulses lead to a spectral interference phenomenon similar to the Fresnel bi-prism experiment

Extracorporeal Membrane Oxygenation for Severe Acute Respiratory Distress Syndrome associated with COVID-19: An Emulated Target Trial Analysis.

RATIONALE: Whether COVID patients may benefit from extracorporeal membrane oxygenation (ECMO) compared with conventional invasive mechanical ventilation (IMV) remains unknown. OBJECTIVES: To estimate the effect of ECMO on 90-Day mortality vs IMV only Methods: Among 4,244 critically ill adult patients with COVID-19 included in a multicenter cohort study, we emulated a target trial comparing the treatment strategies of initiating ECMO vs. no ECMO within 7 days of IMV in patients with severe acute respiratory distress syndrome (PaO2/FiO2 <80 or PaCO2 ≥60 mmHg). We controlled for confounding using a multivariable Cox model based on predefined variables. MAIN RESULTS: 1,235 patients met the full eligibility criteria for the emulated trial, among whom 164 patients initiated ECMO. The ECMO strategy had a higher survival probability at Day-7 from the onset of eligibility criteria (87% vs 83%, risk difference: 4%, 95% CI 0;9%) which decreased during follow-up (survival at Day-90: 63% vs 65%, risk difference: -2%, 95% CI -10;5%). However, ECMO was associated with higher survival when performed in high-volume ECMO centers or in regions where a specific ECMO network organization was set up to handle high demand, and when initiated within the first 4 days of MV and in profoundly hypoxemic patients. CONCLUSIONS: In an emulated trial based on a nationwide COVID-19 cohort, we found differential survival over time of an ECMO compared with a no-ECMO strategy. However, ECMO was consistently associated with better outcomes when performed in high-volume centers and in regions with ECMO capacities specifically organized to handle high demand. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Mise en place des prothèses totales du genou assistée par ordinateur (comparaison avec la technique conventionnelle)

GRENOBLE1-BU Médecine pharm. (385162101) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Simple model of self-phase modulation spectral patterns in optical fibres

Self-phase modulation (SPM) has been extensively studied for several decades in optical fibers. This phenomenon manifests itself by a change of the frequency spectrum of a pulse, owing to the nonlinear index variation that follows the temporal evolution of the pulse. In the general case, the spectrum of the transmitted pulse cannot be calculated analytically and only approximate or rms expressions giving the bandwidth of the transmitted spectrum are used. In this paper, we present a novel theoretical treatment of SPM based on a spectral interference model. We show that a two-wave interference process is sufficient to describe the main features of the SPM-broadened spectra of initially Fourier-transform limited pulses or pulses with an initial positive linear chirp, and to accurately predict the extreme values of the spectra. The latter provide a more plausible measure of the spectrum extent than the rms width. Simplified but fully tractable closed formulae are derived for the positions of the outermost peaks of the spectra, which are particularly relevant to several recent applications of SPM. In the case of negatively chirped input pulses, the description of the SPM spectral patterns requires the inclusion of a third wave in the interference model. Our spectral interference approach can also help better understand qualitatively the genesis of peculiar spectrum shapes of laser pulses, such as the batman ear spectra observed in all-normal dispersion lasers or Mamyshev oscillators. While the present discussion focuses on SPM, the concept can also be applied to other nonlinear modulations of the phase of a pulse, such as the modulation generated by cross-phase modulation or an external modulator

Impact of a temporal sinusoidal phase modulation on the optical spectrum

International audienceWe 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

Two-wave interferences space-time duality: Young slits, Fresnel biprism and Billet bilens

International audienceTaking advantage of the analogy that can be drawn between the spatial and temporal propagations, we explore two-wave temporal interference in textbook cases such as Young's double slits, Fresnel's biprism and Billet's bilens. We illustrate our approach by numerical simulations for short pulses propagating in dispersive optical fibers with parameters typical of those found in modern optical telecommunications

Dualité temps-espace dans la propagation de la lumière

National audienceL’optique ondulatoire est souvent enseignée à travers ses manifestations dans le domaine spatial : motifs d’interférence, figures de diffraction, propagation en espace libre... En exploitant le domaine de Fourier, il est possible de dresser une analogie formelle entre la diffraction 1D de la lumière et la dispersion subie par impulsion ultrabrève. Cela a permis la transposition de solutions connues de l’optique spatiale à l’optique temporelle. Ainsi, régie par une phase quadratique, la lentille temporelle copie la lentille traditionnelle et a permis ainsi d’imaginer expérimentalement de nouvelles approches de caractérisation d’impulsions ultrabrèves.Dans cette contribution, nous présenterons d’autres configurations où cette analogie peut être mise à profit en se basant sur l’utilisation de fibres optiques. Ainsi, à partir de modèles simples, nous discuterons d’interféromètres temporels de Fresnel ou de Billet [1], d’un analogue temporel à la tâche d’Arago [2], de lentilles temporelles lenticulaires [3] ou bien encore de réseaux temporels dispersifs [4]. Ces différents exemples seront illustrés par différentes expériences menées dans un laboratoire de télécommunications optiques.[1] F. Chaussard, H. Rigneault, and C. Finot, Opt. Commun. 397, 31-38 (2017).[2] C. Finot and H. Rigneault, ArXiv:1902.06138 [3] J. Nuno, C. Finot, and J. Fatome, Opt. Fiber Technol. 36, 125-129 (2017).[4] C. Finot and H. Rigneault, J. Opt. Soc. Am. B 34, 1511-1517 (2017)