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We expand our previous analysis of nonlinear pulse shaping in optical fibres using machine learning [Opt. Laser Technol., 131 (2020) 106439] to the case of pulse propagation in the presence of gain/loss, with a special focus on the generation of self-similar parabolic pulses. We use a supervised feedforward neural network paradigm to solve the direct and inverse problems relating to the pulse shaping, bypassing the need for direct numerical solution of the governing propagation model., arXiv admin note: text overlap with arXiv:2002.08815

We report an octave-spanning coherent supercontinuum (SC) fiber laser with excellent noise and polarization properties. This was achieved by pumping a highly birefringent all-normal dispersion photonic crystal fiber with a compact high-power ytterbium femtosecond laser at 1049 nm. This system generates an ultra-flat SC spectrum from 670 to 1390 nm with a power spectral density higher than 0.4 mW/nm and a polarization extinction ratio of 17 dB across the entire bandwidth. An average pulse-to-pulse relative intensity noise down to 0.54% from 700 to 1100 nm was measured and found to be in good agreement with numerical simulations. This highly stable broadband source could find strong potential applications in biomedical imaging and spectroscopy where an improved signal-to-noise ratio is essential.

Understanding dynamical complexity is one of the most important challenges in science. Significant progress has recently been made in optics through the study of dissipative soliton laser systems, where dynamics are governed by a complex balance between nonlinearity, dispersion, and energy exchange. A particularly complex regime of such systems is associated with noise-like pulse multiscale instabilities, where sub-picosecond pulses with random characteristics evolve chaotically underneath a much longer envelope. However, although observed for decades in experiments, the physics of this regime remains poorly understood, especially for highly-nonlinear cavities generating broadband spectra. Here, we address this question directly with a combined numerical and experimental study that reveals the physical origin of instability as nonlinear soliton dynamics and supercontinuum turbulence. Real-time characterisation reveals intracavity extreme events satisfying statistical rogue wave criteria, and both real-time and time-averaged measurements are in quantitative agreement with modelling., In this work the authors perform a combined numerical and experimental study of noise-like pulse multiscale instabilities in dissipative laser systems. They reveal an underlying multiscale dynamics and report the observation of rogue wave events.

International audience; Kerr comb generation is usually based on the nonlinear dynamics of the intracavity field in a whispering-gallery-mode resonator pumped by a continuous-wave laser. However, using a pulsed instead of a continuous-wave pump opens an alternative research avenue from both the theoretical and experimental viewpoints, as it permits us to tailor the spectral properties of ultrashort pulse trains with a single passive nonlinear element. In this article we study the dynamics of Kerr optical frequency combs when the whispering-gallery-mode resonator is pumped by a synchronous pulse train. We propose a model that is based on an extension of the Lugiato-Lefever equation, which accounts for both the pulsed nature of the pump and the mismatch between the free-spectral range of the resonator and the repetition rate of the pulse train. We lay a particular emphasis on the effect of pump-cavity desynchronization on the spectral shape of the output combs. The numerical simulations are successfully compared with experimental measurements where the optical pulses are generated via time-lens soliton compression, and the resonator is a millimeter-size magnesium fluoride resonator with a billion quality factor at the pump wavelength.

Solitons are coherent structures that describe the nonlinear evolution of wave localizations in hydrodynamics, optics, plasma and Bose-Einstein condensates. While the Peregrine breather is known to amplify a single localized perturbation of a carrier wave of finite amplitude by a factor of three, there is a counterpart solution on zero background known as the degenerate two-soliton which also leads to high amplitude maxima. In this study, we report several observations of such multi-soliton with doubly-localized peaks in a water wave flume. The data collected in this experiment confirm the distinctive attainment of wave amplification by a factor of two in good agreement with the dynamics of the nonlinear Schrödinger equation solution. Advanced numerical simulations solving the problem of nonlinear free water surface boundary conditions of an ideal fluid quantify the physical limitations of the degenerate two-soliton in hydrodynamics. Laboratory of Dynamical Systems and Applications NRU HSE, of the Ministry of Science and Higher Education of the Russian Federation Russian Foundation for Basic Research French National Research Agency European Research Council

Recent years have seen the rapid growth and development of the field of smart photonics, where machine-learning algorithms are being matched to optical systems to add new functionalities and to enhance performance. An area where machine learning shows particular potential to accelerate technology is the field of ultrafast photonics — the generation and characterization of light pulses, the study of light–matter interactions on short timescales, and high-speed optical measurements. Our aim here is to highlight a number of specific areas where the promise of machine learning in ultrafast photonics has already been realized, including the design and operation of pulsed lasers, and the characterization and control of ultrafast propagation dynamics. We also consider challenges and future areas of research. The potential of machine-learning application to the field of ultrafast photonics is reviewed, with key examples including pulsed lasers, and control and characterization of ultrafast propagation dynamics.

International audience; We review recent progress in the generation of broadband supercontinuum light sources using soft-glass based optical fibers.

International audience; We compare real-time noise measured using dispersive Fourier transform spectroscopy in supercontinuum generated in PM and non-PM all-normal dispersion tellurite fibers and show that PM fiber provides better stability and higher coherence.

International audience; We use machine learning techniques to predict the peak intensity and temporal shift of extreme red-shifted rogue solitons in supercontinuum generation from simulated single-shot spectral intensity profiles without any phase information.

International audience; Numerical modelling based on purely scalar nonlinear Schröodinger equation propagation is applied to a dissipative soliton laser operating in the soliton-similariton regime and generating parabolic pulses. The model is shown to reproduce a range of instabilities that have been reported in recent experiments. Here, we study in detail the laser stability characteristics as a function of the parameters of the gain medium and the saturable absorber, allowing us to readily identify clear regimes where stable single solitons and soliton molecules are observed. Outside these regimes, we reproduce a wide range of instabilities linked with soliton molecule internal motion, soliton explosions and intermittence.

International audience; Numerical simulations of a dissipative soliton-similariton laser are shown to reproduce a range of instabilities seen in recent experiments. The model uses a scalar nonlinear Schrödinger equation map, and regions of stability and instability are readily identified as a function of gain and saturable absorber parameters. Studying evolution over multiple round trips reveals spectral instabilities linked with soliton molecule internal motion, soliton explosions, chaos, and intermittence. For the case of soliton molecules, the relative phase variation in the spectrum is shown to be due to differences in nonlinear phase evolution between the molecule components over multiple round trips.

Femtosecond pulses from an ultrafast mode-locked fiber laser can be optimized in real time by combining single-shot spectral measurements with a smart genetic algorithm to actively control and drive the intracavity dynamics.

International audience; We report a small-core UV-grade silica multimode photonic crystal fiber for nonlinear frequency conversion in the ultraviolet spectral region. The fiber has been fabricated using F110 UV-Grade glass from Heraeus, which features excellent transmission and low solarization in the UV window. Pumping the fiber core at 355 nm with picosecond laser pulses, we observe the appearance of parametric sidebands in several spatial modes up to 380 nm. We modelled this process using intermodal phase-matching conditions and obtained excellent agreement between calculations and the measured data. We further report frequency conversion pumping into the fiber microstructured cladding where broadband cascaded Raman scattering spanning up to 391 nm is observed. These results represent a significant step towards the efficient and stable generation of UV supercontinuum spectra in an all-silica fiber platform.

International audience; The Advanced Photonics special issue celebrating the 60-year laser anniversary is an ideal opportunity to review some highlights from its history, at the same time taking us on a tour of over a century of Nobel Prizes.

We use recurrent neural network to successfully predict the spectral evolution of cohererent supercontinuum along propagation in an optical fiber. The network performs particularly well for a wide range of input pulse parameters.

International audience; We demonstrate surprising effects of technical pump laser fluctuations on the noise of a normal-dispersion fs-pumped supercontinuum and how the noise varies with power in fibers with a zero-dispersion at longer wavelengths.

The study of dissipative solitons in mode-locked lasers reveals a rich landscape of interaction dynamics resulting from the interplay of nonlinearity, dispersion and dissipation. Here, we characterize a range of instabilities in a dissipative soliton fibre laser in a regime where both conventional soliton and similariton propagation play significant roles in the intracavity pulse shaping. Specifically, we use the Dispersive Fourier Transform technique to perform real-time spectral measurements of buildup dynamics from noise to the generation of stable single pulses, phase evolution dynamics of bound state “similariton molecules”, and several examples of intermittent instability and explosion dynamics. These results show that the instabilities previously seen in other classes of passively mode-locked fibre lasers are also observed in the presence of strong nonlinear attraction of similariton evolution in an optical fibre amplifier.

Ghost imaging is a non-direct measurement technique that uses the correlation between multiple probing patterns and the integrated signal measured after transmission (or reflection) through an object. [1] The resolution of the technique is determined by the characteristic length scale of the probing patterns fluctuations and/or the resolution with which they can be measured. Originally demonstrated in the spatial domain to reconstruct images of real physical objects, ghost imaging has been recently extended to the time-domain to measure ultrafast signals at telecom wavelengths [2]. In this work, we experimentally demonstrate ultrafast ghost imaging in the time-domain where the correlated intensities have completely different wavelengths. This wavelength-conversion temporal ghost-imaging scheme exploits fully the benefit of ghost imaging opening up new possibilities for ultrafast imaging in spectral regions where sensitive and/or fast detectors are not available and in particular the mid-infrared or THz range.

In contrast with direct measurement methods, correlation imaging measures the correlation function between the intensity emitted by a light source and the total (integrated) intensity transmitted (or reflected) by an object, such that the image can be reconstructed without the object to be actually seen. The essential nature of such "ghost imaging" [1] lies in the mutual correlation of the two non-interacting beams, and the image is obtained by summing over the different probing patterns weighted by the integrated signal from the detector [2]. Here, we demonstrate for the first time broadband ghost imaging in the spectral domain using a supercontinuum source [3]. We demonstrate the approach by using a gas cell filled with pure methane as the object in the test arm and reconstruct its absorption spectrum. The advantage of the correlation approach is that it detects the total integrated signal after the object and is thus very sensitive even in low light conditions or in spectral regions where no fast detector exists. It is also inherently insensitive to any perturbation occurring between the object and the detector.

International audience; Supercontinuum (SC) generation via femtosecond (fs) pumping in all-normal-dispersion (ANDi) fiber is predicted to offer completely coherent broadening mechanisms, potentially allowing for substantially reduced noise levels in comparison to those obtained when operating in the anomalous dispersion regime. However, previous studies of SC noise typically treat only the quantum noise, typically in the form of one-photon-per-mode noise, and do not consider other technical noise contributions, such as the stability of the pump laser, which become important when the broadening mechanism itself is coherent. In this work, we discuss the influence of the amplitude and pulse length noise of the pump laser, both added separately and combined. We show that for a typical mode-locked laser, in which the peak power and pulse duration are anticorrelated, their combined impact on the SC noise is generally smaller than in isolation. This means that the supercontinuum noise is smaller than the noise of the mode-locked pump laser itself, a fact that was recently observed in experiments but not explained. Our detailed numerical analysis shows that the coherence of ANDi SC generation is considerably reduced on the spectral edges when realistic pump laser noise levels are taken into account.

Optical fiber systems are well-known to provide convenient platforms in which one may investigate a large variety of fascinating fundamental nonlinear coherent structures such as solitons or self-similar patterns. Interestingly, one of the major conclusions of the studies dealing with extreme-value fluctuations is that the temporal and spectral characteristics of localization processes can be well described in terms of solitons over finite background and in particular in terms of Peregrine soliton (PS) [1]. Whereas the longitudinal evolution of the temporal and spectral intensity of the PS have been characterized in detail [2], much less attention has been experimentally devoted to the evolution of its phase properties. We report here a study that complements the analysis of the nonlinear dynamics of this coherent structure: by exploring the longitudinal evolution of the temporal phase profile and the phase difference Δϕ between the central part of the pulse and the continuous background, we experimentally confirm some important features of the PS [3].

International audience; The concepts of Fourier optics were established in France in the 1940s by Pierre-Michel Duffieux, and laid the foundations of an extensive series of activities in the French research community that have touched on nearly every aspect of contemporary optics and photonics. In this paper, we review a selection of results where applications of the Fourier transform and transfer functions in optics have been applied to yield significant advances in unexpected areas of optics, including the spatial shaping of complex laser beams in amplitude and in phase, real-time ultrafast measurements, novel ghost imaging techniques, and the development of parallel processing methodologies for photonic artificial intelligence.

International audience; Diffraction-free Bessel beams have attracted major interest because of their stability even in regimes of nonlinear propagation and filamentation. However, Kerr nonlinear couplings are known to induce significant longitudinal intensity modulation, detrimental to the generation of uniform plasma or for applications in the processing of transparent materials. These nonlinear instabilities arise from the generation of new spatiospectral components through an initial stage of continuous spectral broadening followed by four-wave mixing. In this paper, we investigate these processes analytically and numerically and show that nonlinear instabilities can be controlled through shaping the spatial spectral phase of the input beam. This opens new routes for suppressing the nonlinear growth of new frequencies and controlling ultrashort pulse propagation in dielectrics.

International audience; We report on interferometric autocorrelation measurements of broadband supercontinuum light in the anomalous dispersion regime using two-photon absorption in a GaP photodetector. The method is simple and low-cost and provides a direct measure of second-order coherence properties, including quantitative information on coherence time and average duration of the supercontinuum pulses as well as on the presence of temporally coherent sub-structures. We report measurements in regimes where the supercontinuum is coherent and incoherent. In the former case, the interferometric measurements are similar to what is observed for mode-locked laser pulses, while in the latter case, the interferometric measurements and coherence properties are shown to have characteristics similar to those of a stationary chaotic light source.

We report the spectral distribution of the parametric process generated in a photonic crystal fiber pumped by a chirped pulse. The spectral correlation of four-wave mixing has been measured using the dispersive Fourier transform method. From statistical analysis of multiple shot-to-shot spectral measurements, the spectral correlation between the signal and idler photons reveals physical insights into the particular portion of the pump spectrum responsible for generating the four-wave mixing. Therefore, the shape of the correlation map indicates directly the temporal and spectral links between the signal and the pump, which are highly important to design a four-wave mixing based amplifier.

International audience; We investigate in detail the qualitative similarities between the pulse localization characteristics observed using sinusoidal phase modulation during linear propagation and those seen during the evolution of Akhmediev breathers during propagation in a system governed by the nonlinear Schrödinger equation. The profiles obtained at the point of maximum focusing indeed present very close temporal and spectral features. If the respective linear and nonlinear longitudinal evolutions of those profiles are similar in the vicinity of the point of maximum focusing, they may diverge significantly for longer propagation distance. Our analysis and numerical simulations are confirmed by experiments performed in optical fiber.

International audience; Mid-infrared supercontinuum (mid-IR SC) sources in the 2-20 mu m molecular fingerprint region are in high demand for a wide range of applications including optical coherence tomography, remote sensing, molecular spectroscopy, and hyperspectral imaging. Herein, mid-IR SC generation is investigated in a cascaded silica-ZBLAN-chalcogenide fiber system directly pumped with a commercially available pulsed fiber laser operating in the telecommunications window at 1.55 mu m. This fiber-based system is shown to generate a flat broadband mid-IR SC covering the entire range from 2 to 10 mu m with several tens of mW of output power. This technique paves the way for low cost, practical, and robust broadband SC sources in the mid-IR without the requirement of mid-infrared pump sources or Thulium-doped fiber amplifiers. A fully realistic numerical model used to simulate the nonlinear pulse propagation through the cascaded fiber system is also described and the numerical results are used to discuss the physical processes underlying the spectral broadening in the cascaded system. Finally, recommendations are provided for optimizing the current cascaded system based on the simulation results.

We present a simultaneous study of the phase properties of rational breather waves generated in a water wave tank and in an optical fiber platform, namely, the Peregrine soliton and related second-order solution. Our analysis of experimental wave measurements makes use of standard demodulation and filtering techniques in hydrodynamics and more complex phase retrieval techniques in optics to quantitatively confirm analytical and numerical predictions. We clearly highlight a characteristic phase shift that is a multiple of π between the central pulsed part and the continuous background of rational breathers at their maximum compression. Moreover, we reveal a large longitudinal phase shift across the point of maximum compression.

International audience; We report the first experimental study of the longitudinal evolution of breather pulses during nonlinear fiber propagation. Gerchberg-Saxton phase retrieval reveals a large phase shift across the point of maximum compression.

A central research area in nonlinear science is the study of instabilities that drive extreme events. Unfortunately, techniques for measuring such phenomena often provide only partial characterisation. For example, real-time studies of instabilities in nonlinear optics frequently use only spectral data, limiting knowledge of associated temporal properties. Here, we show how machine learning can overcome this restriction to study time-domain properties of optical fibre modulation instability based only on spectral intensity measurements. Specifically, a supervised neural network is trained to correlate the spectral and temporal properties of modulation instability using simulations, and then applied to analyse high dynamic range experimental spectra to yield the probability distribution for the highest temporal peaks in the instability field. We also use unsupervised learning to classify noisy modulation instability spectra into subsets associated with distinct temporal dynamic structures. These results open novel perspectives in all systems exhibiting instability where direct time-domain observations are difficult., Real-time characterisation of nonlinear processes in the time domain is challenging. Here, Närhi et al. show that machine learning techniques can help overcome this limitation and use them to infer time-domain properties of optical fibre modulation instability from spectral intensity measurements.

In this paper we investigate supercontinuum (SC) generation in several suspended-core soft-glass photonic crystal fibers (PCFs) pumped by an optical parametric oscillator (OPO) tunable around 1550 nm. The fibers were drawn from leadbismuth- gallium-cadmium-oxide glass (PBG81) featuring a wide transmission window from 0.5 μm till 2.7 μm and a high nonlinear refractive index up to 43×10 -20 m 2 /W. They have been specifically designed with a microscale suspended hexagonal core for efficient pumping around 1550 nm. This microstructure geometry also prevents from glass recrystallization and provides higher mechanical durability. We experimentally demonstrate two SC spectra spanning from 1.07 μm to 2.31 μm and 0.89 μm to 2.46 μm by pumping two PCFs in both normal and anomalous dispersion regimes at 1550 nm and 1580 nm, respectively. We further show a number of nonlinear phenomena such as spectral broadening due to self-phase modulation, soliton generation, and Raman soliton self-frequency shift in the fiber at the pumping wavelengths. We also numerically simulate the group velocity dispersion curves for these fibers from their scanning electron microscope (SEM) images.

International audience; This work shows that step-index few-mode fibers can be combined with a simple microchip picosecond laser to give a multi-octave spanning supercontinuum output by cascaded Raman scattering and intermodal FWM.

Dissipative solitons are remarkably localized states of a physical system that arise from the dynamical balance between nonlinearity, dispersion and environmental energy exchange. They are the most universal form of soliton that can exist, and are seen in far-from-equilibrium systems in many fields, including chemistry, biology and physics. There has been particular interest in studying their properties in mode-locked lasers, but experiments have been limited by the inability to track the dynamical soliton evolution in real time. Here, we use simultaneous dispersive Fourier transform and time-lens measurements to completely characterize the spectral and temporal evolution of ultrashort dissipative solitons as their dynamics pass through a transient unstable regime with complex break-up and collisions before stabilization. Further insight is obtained from reconstruction of the soliton amplitude and phase and calculation of the corresponding complex-valued eigenvalue spectrum. These findings show how real-time measurements provide new insights into ultrafast transient dynamics in optics. The simultaneous use of dispersive Fourier transform and time-lens measurements allows complete characterization of the unstable spectral and temporal evolution of ultrashort dissipative solitons, providing further insight into ultrafast transient dynamics in optics.

International audience; In this paper we investigate supercontinuum generation in several suspended-core soft-glass photonic crystal fibers pumped by an optical parametric oscillator tunable around 1550 nm. The fibers were drawn from lead-bismuth-gallium-cadmium-oxide glass (PBG-81) featuring a wide transmission window from 0.5 to 2.7 μm and a high nonlinear refractive index up to 4.3·1019 m2/W. They have been specifically designed with a microscale suspended hexagonal core for efficient supercontinuum generation around 1550 nm. We experimentally demonstrate two supercontinuum spectra spanning from 1.07 to 2.31 μm and 0.89 to 2.46 μm by pumping two PCFs in both normal and anomalous dispersion regimes, respectively. We also numerically model the group velocity dispersion curves for these fibers from their scanning electron microscope images. The results are in good agreement with numerical simulations based on the generalized nonlinear Schrödinger equation including the pump frequency chirp.

International audience; The complex spatiotemporal dynamics of nonlinear light propagation in multimode fibers (MMFs) has recently witnessed a renewed interest because of their experimental realization in emerging key areas of laser physics and fiber optics [1]. Specifically, MMFs have a number of linear and nonlinear optical properties that make them very attractive to investigate new spatiotemporal effects fundamentally different from standard single-mode fibers. These include the observation of multimode solitons [2], intermodal four-wave mixing (FWM) [3], geometric parametric instabilities [4], spatial beam self-cleaning [5], and the generation of supercontinuum (SC) light when pumping in the strong normal dispersion regime [6,7]. However, to date most of these recent works have been performed using graded-index MMFs featuring weak modal dispersion. Here we show that step-index few-mode fibers also allows for the achievement of far-detuned intermodal FWM and supercontinuum generation. We demonstrate in particular broadband SC generation from 560 nm up to 2350 nm by coupling a Q-switched picosecond microchip laser at 1064 nm into a 15 µm-core step-index germanium-doped silica fiber, designed to support five spatial modes at 1064 nm. It is further shown that multiple cascaded intermodal FWM and Raman processes take place in the fiber with large frequency detuning up to 150 THz. The multimode properties of this fiber yield a number of intermodal nonlinear coupling terms and the parametric sideband wavelengths have been obtained from the phase-matching condition for intermodal FWM. A further investigation with another microchip pump laser at 532 nm reveals the observation of many parametric sidebands due to intermodal FWM involving more than eight spatial modes. The very good agreement between theory and experiment at 532 nm confirms our fiber step-index model, which allows us to simulate the modal eigenvalue solutions of Helmholtz equation to get the effective index for all modes at any wavelength as well as their modal dispersion.

We report experimental confirmation of the universal emergence of the Peregrine soliton predicted to occur during pulse propagation in the semiclassical limit of the focusing nonlinear Schrödinger equation. Using an optical fiber based system, measurements of temporal focusing of high power pulses reveal both intensity and phase signatures of the Peregrine soliton during the initial nonlinear evolution stage. Experimental and numerical results are in very good agreement, and show that the universal mechanism that yields the Peregrine soliton structure is highly robust and can be observed over a broad range of parameters. publishedVersion

International audience; We investigate high-speed glass cleaving with ultrafast laser beams with engineered transverse intensity profile. We achieve accuracy of ~ 1 µm at 25 mm/s and drastically enhance cleavability compared to standard Bessel beams.

International audience; Bessel beams exploit conical energy flow to yield near-uniform intensity along a line focus which has been shown to be extremely attractive for laser processing in dielectrics. At high power, however, the nonlinear Kerr effect is known to induce significant oscillations of the on-axis intensity which is deleterious for machining applications. Here, we show through theory and numerical modelling how this problem can be understood and overcome by appropriate spatial phase shaping of the input profile. Our results also solve the longstanding problem related to the nonlinear Bessel beam dynamics seen at an air-dielectric interface.

The dispersive Fourier transform (DFT) [1] uses optical fibre dispersion to separate the spectral components of a noisy incident signal to allow real-times spectral measurement using a photodetector and oscilloscope. DFT has now become a standard tool in ultrafast laboratories to study ultrafast dynamics of complex transient phenomena including optical rogue waves [1] and Kerr-lens mode-locking [2]. The dynamic range of DFT, however, is limited to typically only 20 dB due to the usual 8-bit analog-to-digital converter of the oscilloscope. Here, we demonstrate an unbalanced dual path mechanical streak camera capable of resolving single shot spectra with 60 dB dynamic range. We use this technique to detect spectrally, for the first time, the collision of breathers in noise-seeded modulation instability (MI) whose spectral signature is manifested in the wings of the spectrum below the 30 dB level, and which are not captured by the standard DFT technique.

Ghost imaging is a novel imaging technique based on correlation measurements between a structured illumination pattern (the reference) and the total intensity transmitted or reflected by an object [1]. The reference illumination patterns may be either randomly generated by a spatially incoherent light source, or pre-programmed e.g. with a spatial light modulator. Light transmitted (or reflected) by the object is measured by a single-pixel “bucket” detector with null spatial resolution. A unique feature associated with ghost imaging is that (i) neither the bucket detector nor the reference measurement caries enough information to retrieve the object shape and (ii) it is insensitive to distortions placed after the object.

The field of nonlinear guided wave optics has steadily expanded in the last decade, as a rich variety of novel nonlinear phenomena have been demonstrated in a wide range of different systems. Looking back on the rapid expansion of this field with hindsight, it is clear that much of this progress has occurred because of parallel developments in two technological areas. Firstly, picosecond and femtosecond lasers have evolved from complex and sensitive systems usable only under controlled laboratory conditions to robust turnkey tools that allow the generation of high power optical radiation over wavelength ranges from the visible to the infrared, and indeed extending into new wavelength ranges on either side [1]. Secondly, the invention of new classes of optical waveguide based on artificially structured materials provide new degrees of freedom to control light, because their optical properties can be tailored through appropriate material choices and precise structural design and engineering. When designed to guide light with enhanced optical confinement impossible to achieve with standard optical fibres, such emerging — sometimes hybrid — waveguide structures open up fundamentally new regimes of nonlinear guided wave optics [2].

Bessel beams are a class of non-diffracting solution to the propagation equation. They exhibit a constant size of their main lobe over propagation distances that are much longer than the Rayleigh range of Gaussian beams with identical lobe size [1]. Such beam have been widely used for, femto-laser ablation [2], microscopy and optical coherence tomography [3-5].

During ultrafast laser pulse propagation in dielectrics, the nonlinear generation of new spatial frequencies can be deleterious to reach high intensities and to generate uniform plasma channels. In this context, diffraction-free Bessel beams have attracted major recent interest because of their enhanced stability when compared to conventional Gaussian beams. However, Bessel beams can still suffer from significant modulation instability arising from noise-induced nonlinear four-wave mixing. In this Letter, we report control of the nonlinear instability growth by shaping the longitudinal intensity profile of the incident field. Our results show that tailored longitudinal intensity shaping of a non-diffracting Bessel beam can strongly reduce four wave mixing induced oscillations and stabilize nonlinear propagation at ablation-level intensities.&nbsp

The material processing technique of “stealth” nanomachining is based on translating a longitudinally extended beam such as a Bessel beam into a transparent sample to generate extended nanochannels, which leads to subsequent internal stress that facilitates high quality cleaving. In this letter, we compare the quality of such cleaving in glass samples obtained using Bessel beams with both circularly symmetric and elliptical transverse profiles. We find that the use of an elliptical Bessel beam generates elliptical nanochannels, which greatly improves the cleavage quality and cuts material strength by aligning the centre of the cleavage plane with the centre of the machined channels. These results are interpreted using numerical simulations that show how elliptical nanochannels enhance the intensity and localization of the tensile stress distribution in glass under bending when compared to channels with circular cross-sections.

Ultrafast lasers have revolutionized material processing, opening a wealth of new applications in many areas of science. A recent technology that allows the cleaving of transparent materials via non-ablative processes is based on focusing and translating a high-intensity laser beam within a material to induce a well-defined internal stress plane. This then enables material separation without debris generation. Here, we use a non-diffracting beam engineered to have a transverse elliptical spatial profile to generate high aspect ratio elliptical channels in glass of dimension 350 nm x 710 nm, and subsequent cleaved surface uniformity at the sub-micron level., Comment: 5 pages, 4 figures

Ghost imaging allows the imaging of an object without directly seeing this object. Originally demonstrated in the spatial domain, it was recently shown that ghost imaging can be transposed into the time domain to detect ultrafast signals, even in the presence of distortion. We propose and experimentally demonstrate a temporal ghost imaging scheme which generates a 5× magnified ghost image of an ultrafast waveform. Inspired by shadow imaging in the spatial domain and building on the dispersive Fourier transform of an incoherent supercontinuum in an optical fiber, the approach overcomes the resolution limit of standard time-domain ghost imaging generally imposed by the detectors speed. The method can be scaled up to higher magnification factors using longer fiber lengths and light source with shorter duration., published version, peerReviewed

Modulation instability is a fundamental process of nonlinear science, leading to the unstable breakup of a constant amplitude solution of a physical system. There has been particular interest in studying modulation instability in the cubic nonlinear Schrödinger equation, a generic model for a host of nonlinear systems including superfluids, fibre optics, plasmas and Bose–Einstein condensates. Modulation instability is also a significant area of study in the context of understanding the emergence of high amplitude events that satisfy rogue wave statistical criteria. Here, exploiting advances in ultrafast optical metrology, we perform real-time measurements in an optical fibre system of the unstable breakup of a continuous wave field, simultaneously characterizing emergent modulation instability breather pulses and their associated statistics. Our results allow quantitative comparison between experiment, modelling and theory, and are expected to open new perspectives on studies of instability dynamics in physics., Low amplitude noise on an otherwise constant-intensity wave can grow exponentially and induce nonlinear dynamical behaviour. Here, the authors present time-domain measurements of a phenomenon arising from such modulation instability: the emergence of highly localised breathers in an optical fibre.

In this paper, we report the design and fabrication of a highly birefringent polarization-maintaining photonic crystal fiber (PM-PCF) made from chalcogenide glass, and its application to linearly-polarized supercontinuum (SC) generation in the mid-infrared region. The PM fiber was drawn using the casting method from As38Se62 glass which features a transmission window from 2 to 10 $\mu m$ and a high nonlinear index of 1.13.10$^{-17}$m$^{2}$W$^{-1}$. It has a zero-dispersion wavelength around 4.5 $\mu m$ and, at this wavelength, a large birefringence of 6.10$^{-4}$ and consequently strong polarization maintaining properties are expected. Using this fiber, we experimentally demonstrate supercontinuum generation spanning from 3.1-6.02 $\mu m$ and 3.33-5.78 $\mu m$ using femtosecond pumping at 4 $\mu m$ and 4.53 $\mu m$, respectively. We further investigate the supercontinuum bandwidth versus the input pump polarization angle and we show very good agreement with numerical simulations of the two-polarization model based on two coupled generalized nonlinear Schr\"odinger equations., Comment: 13 pages, 8 figures

Wave impact and run-up onto vertical obstacles are among the most important phenomena which must be taken into account in the design of coastal structures. From linear wave theory, we know that the wave amplitude on a vertical wall is twice the incident wave amplitude with weakly nonlinear theories bringing small corrections to this result. In this present study, however, we show that certain simple wave groups may produce much higher run-ups than previously predicted, with particular incident wave frequencies resulting in run up heights exceeding the initial wave amplitude by a factor of 5, suggesting that the notion of the design wave used in coastal structure design may need to be revisited. The results presented in this study can be considered as a note of caution for practitioners, on one side, and as a challenging novel material for theoreticians who work in the field of extreme wave - coastal structure interaction.

International audience; We report on the first demonstration of computational ghost imaging in the time domain using wavelength multiplexing. The wavelength-multiplexed Hadamard patterns used to probe a time-varying waveform enables image reconstruction in real time.