Abstract
Optical fibres are favourable tabletop laboratories to investigate both coherent and incoherent nonlinear waves. In particular, exact solutions of the onedimensional nonlinear Schrödinger equation such as fundamental solitons or solitons on finite background can be generated by launching periodic, specifically designed coherent waves in optical fibres. It is an open fundamental question to know whether these coherent structures can emerge from the nonlinear propagation of random waves. However the typical subpicosecond timescale prevented—up to now—timeresolved observations of the awaited dynamics. Here, we report temporal ‘snapshots’ of random light using a specially designed ‘timemicroscope’. Ultrafast structures having peak powers much larger than the average optical power are generated from the propagation of partially coherent waves in optical fibre and are recorded with 250 femtoseconds resolution. Our experiment demonstrates the central role played by ‘breatherlike’ structures such as the Peregrine soliton in the emergence of heavytailed statistics in integrable turbulence.
Introduction
First studied in oceanography, rogue waves (RWs) also called freak waves are waves of giant amplitude that occur more frequently than expected from the normal law^{1,2,3}. From the pioneering optical fibre experiment performed by Solli et al in 2007 (ref. 4), optical RWs have been studied in various optical experiments such as supercontinuum generation in fibres^{4,5,6,7}, laser filamentation^{8,9}, passive cavities^{10}, lasers^{11,12,13,14} and Raman fibre amplifiers^{15}. In all these experiments, the socalled optical RWs (and more generally extreme events) correspond to a large variety of phenomena, often not comparable to ocean waves, and their generation cannot be ascribed to a unique physical mechanism^{1,3,16,17,18}.
In this context, however, the onedimensional focusing nonlinear Schrödinger equation (1DNLSE) plays a fundamental role by providing a onetoone correspondence between some unidirectional systems in hydrodynamics and in nonlinear optics^{19,20,21}. The focusing 1DNLSE indeed describes at leading order propagation of deep water waves in onedimensional tanks and also nonlinear propagation of light in singlemode fibres^{21}. Moreover it admits breathers solutions that exhibit localization and amplitude properties having some degree of compatibility with the definition of RW objects^{22,23,24,25,26}. It is conjectured by some authors that breather solutions of the 1DNLSE such as the Peregrine soliton (PS) may represent prototypes of RWs^{20,22,24,26,27,28}. This has motivated nice experiments in which these solitons on finite background (SFB) have been generated in optical fibres^{29,30,31,32} and in a onedimensional water tank^{32,33}. In these experiments, SFB are generated from coherent and deterministic (that is, nonstochastic) initial conditions that have to be carefully designed.
Alternatively, hydrodynamical and optical fields can be of a random and irregular nature. The questions related to the local emergence of coherent structures compatible with breathers solutions of the 1DNLSE are still completely open in the context where waves randomly fluctuate in space or time. The problem of random (or partially coherent) inputs in wave systems described by integrable equations such as 1DNLSE enters within the fundamental framework of the socalled ‘integrable turbulence’ introduced by V.E. Zakharov^{34,35,36,37,38,39}. As wave interactions are not resonant for the 1DNLSE^{40,41}, features characterizing integrable turbulence are of profoundly different nature than those found in conventional turbulence and they are still not well understood^{36,39,40,42}.
Partially coherent waves correspond here to random waves whose optical spectral width is finite and small in comparison with the carrier wave frequency^{43}. Assuming independent random Fourier components the statistics of the partially coherent field is Gaussian^{43}. It is now well established that heavytailed deviations from Gaussianity can occur in integrable turbulence. This phenomenon arises in particular when partially coherent waves are used as initial conditions in a wave system that is described at leading order by the focusing 1DNLSE. This has been recently shown in optical fibre experiments reported in refs 38, 42. Heavytailed deviations from Gaussianity reported in previous experiments possibly arise from the stochastic generation of SFB that are localized in space and time, such as the PS. So far, this conjecture is supported by numerical simulations of the 1DNLSE that have shown that some highamplitude coherent structures compatible with some breather solutions of the 1DNLSE like the PS can spontaneously emerge from a stochastic background^{25,28,36,38}.
However, the stochastic and local generation of SFB solutions of the 1DNLSE has never been reported so far. Moreover, the relationship between these structures and heavytailed statistics has never been experimentally demonstrated. Optical fibres represent suitable tabletop laboratory to generate deterministic solutions of 1DNLSE on the one hand^{29,31,32,44} and investigate integrable turbulence on the other hand^{38,42,45}. However, in optical fibres, typical time scale characterizing SFB or soliton solutions of 1DNLSE falls in the picosecond range. Some wellestablished methods like intensity autocorrelation or frequencyresolved optical gating have been used to measure phase and/or power profiles of breathers having this duration^{29,31}. However all those standard methods rely on the fact that the optical signal under investigation must be periodic. These methods are inherently inadequate for the precise observation of the dynamics of breatherlike coherent structures that may emerge from the nonlinear propagation of nonperiodic random waves.
From the technical point of view, it is important to note that, up to now and despite the numerous experiments devoted to optical RWs, the precise time domain observation of coherent structures embedded in random fields and compatible with 1DNLSE solutions was not possible. Contrary to the direct observation of spatial structures in experiments in which the intensity profile of a light beam is recorded with a camera^{9,46,47}, the fast time scales of fluctuations (picoseconds or less) involved in singlemode fibre experiments make singleshot recording of RWs a particularly challenging task. Pioneer works performed in optical fibres hence did not provide single shot observation of RW objects but evidence of it by using, for example, spectral filtering^{4,6,48} or statistical measurement from optical sampling techniques^{38}. In the case of modelocked laser dynamics, statistical measurement of the pulse amplitude can also been performed with standard photodetectors^{12}. However, up to now, in all these experiments, the realtime and singleshot observation of the shape of the picosecond time scale structures generated from the nonlinear propagation of random waves has never been reported.
In this article, we present direct singleshot recordings of optical RWs by using a specially designed time microscope (TM) ultrafast acquisition system^{49,50,51}. The temporal resolution of ∼250 fs of our TM (see Methods and Supplementary Note 1) allows us to investigate the fast dynamics underlying integrable turbulence arising in optical fibres. We study experimentally the changes of the dynamics and of the statistics arising from the deterministic and nonlinear propagation of partially coherent waves in optical fibre. The observations performed with our TM reveal the frequent emergence of subpicosecond structures having peak powers much larger than the average optical power. The field used as initial condition has a Gaussian statistics and coherent subpicosecond structures growing from nonlinear propagation induce heavytailed deviations from Gaussian statistics.
Results
Experimental setup and observation of rogue waves
The principle of our experiments is displayed in Fig. 1a. Partially coherent waves are launched into an optical fibre. Observations performed with the TM (see Fig. 2) at the output of the fibre immediately reveals the emergence of intense peaks, with powers frequently exceeding the average power 〈P〉 by factors of 10–50 (see Fig. 1b–d and Supplementary Movie 1). Starting from random fluctuations having typical time scale around 5–10 ps (Fig. 1a), those extreme events are also found to be extremely short, with time scales of the order of several hundreds of femtoseconds (Figs 1b–d and 3b–d).
More precisely, the random waves used as initial conditions in our experiments are partially coherent light waves emitted by a high power Amplified Spontaneous Emission (ASE) light source at a wavelength λ∼1560, nm (see Fig. 1). Using a programmable optical filter, the optical spectrum of the partially coherent light is precisely designed to assume a Gaussian shape having a full width at half maximum that is adjusted either to Δν=0.1 THz or Δν=0.05 THz. The partially coherent waves are launched into a 500 m long single mode polarization maintaining fibre at a wavelength falling into the anomalous (focusing) regime of dispersion. The light at the output of the nonlinear fibre is then directed to the TM (detailed in Fig. 2), which acquires traces (optical power versus time over a ≈20 ps long window) at a rate of 500 per second, and displays the signals in real time.
As in a standard spatial imaging microscope, the TM is composed of an objective and a tube lens (see Fig. 2b). The objective is a time lens^{49,50,51} operating from sumfrequency generation (SFG) between the 1560, nm signal and a chirped pump pulse (at 800 nm) (see Methods). The observation in the focal plane of the tube lens is achieved by a spectrum analyser (composed of a diffraction grating, a lens and a camera). The use of this TM strategy enables to easily reach extremely high dynamical ranges (up to 40 dB; see Methods), which is a crucial point for analysing extreme events embedded in moderate power fluctuations. The temporal resolution of our TM is ∼250 fs (see Methods, Supplementary Note 1 and Supplementary Figs 1–3).
Evidence of heavytailed statistical distributions
In order to quantify the emergence of high power structures, we compute statistical distributions from a large amount of data recorded with the TM at the input and at the output ends of the fibre (see Methods). As expected, the probability density function (PDF) of the optical power emitted by the ASE source is systematically very close to the exponential distribution. The exponential distribution of the power ^{2} (see Fig. 3a) corresponds to a Rayleigh distribution of  and to a Gaussian statistics for the field under the assumption of uniformly distributed random phases^{1,36,38,43} (See Supplementary Note 2 and Supplementary Fig. 4). According to the central limit theorem, the Gaussian statistics of the field used as initial condition arises from the linear superposition of numerous independent waves (that is, independent spectral components of the ASE source). On the contrary, the PDF of light power measured at the output of the nonlinear fibre is found to exhibit heavytailed deviations from the exponential distribution, thus confirming the generation of RWs (see Fig. 3a). Moreover, the PDFs demonstrate that the number of structures having high peak power increases while the mean power 〈P〉 of random optical waves (that is, the strength of nonlinearity) increases (see Fig. 3a).
Analysis of coherent structures
Experimental signals plotted in Figs 1a–d and 3b–h represent direct and accurate observations of the dynamical structures underlying these heavytailed statistics. Starting from random light propagating with a mean power of 4 W in the fibre, huge RWs having peak power that exceeds 300 W can be observed at the output of the fibre (Fig. 3d). Note that the conventional threshold of RWs in the experiments performed with 〈P〉=4 W is given by ≃9.7 (see Supplementary Note 2 and Supplementary Fig. 4).
From a careful analysis of the data, two typical shapes can be distinguished : isolated breatherlike structures (see Fig. 3b and Supplementary Movie 1) and more complicated structures composed of several peaks (see Fig. 3c and Supplementary Movie 1). It is difficult to draw clear conclusions from singleshot observation displayed in Fig. 3c: these structures might be compatible with interacting fundamental solitons or with randomly perturbed periodic Akhmediev breathers. On the contrary, some of the singleshot observations seem to correspond to different dynamical stages that are typical for the emergence of ‘breather’ solutions of 1DNLSE. In order to illustrate the process of emergence of isolated breatherlike structures, we plot in Fig. 3e–h different structures observed after the propagation of partially coherent waves having an initial spectral width Δν=0.05 THz and an average power 〈P〉=0.3 W.
The precise understanding of the mechanisms underlying these dynamical features (Fig. 3b–h) is an open question. Our experiments are performed in a strongly nonlinear regime (see Methods) and they are compatible with the emergence of ‘breatherlike’ dynamics associated to the Nsoliton solutions of 1DNLSE with zero boundary conditions^{52}. Moreover, we have selected structures displayed in Fig. 3e–h because their shapes are strikingly similar to those found in the theoretical scenario demonstrated in the semiclassical (smalldispersion) regime : the evolution of a single hump leads in a generic way to the emergence of a Peregrine breather^{53}. Partially coherent fields with narrow spectrum and having a Gaussian statistics at initial stage consist of many ‘slow’ fluctuations that are individually compatible with such humps (see Figs 1a and 4b). Remarkably, the power profile of the exact analytical PS coincides with some of the structures experimentally observed (see green dashed line in 3(h)). However note that the precise identification of the breatherlike structures (as PS or Akhmediev breather or other more complex solutions of 1DNLSE) would require a simultaneous measurement of the phase dynamics^{37}.
Numerical simulations
Behaviours observed in experiments can be well reproduced from numerical simulations of the 1DNLSE (see Methods). First of all, the PDFs of optical power (see Fig. 4a) and the optical spectra (see Supplementary Fig. 5 and Supplementary Note 3) are well reproduced by numerical simulations. Figure 4 shows a picture of typical random fluctuations of the optical power that are found at the input and output ends of the optical fibre. Taking a partially coherent light field having a bandwidth of 0.1 THz at initial stage, the typical time scale for power fluctuations is around a few picoseconds (Fig. 4b). The scenari observed in the experiments are also found in numerical simulations (see Fig. 4 and Supplementary Movie 2). In particular, either breatherlike structures appear and disappear along the propagation (see Fig. 4g), either several pulses simultaneously emerge together from the random background (see Fig. 4c). Our experiments provide snapshots randomly recorded while the numerical simulations allow to follow the dynamics of nonlinear random waves along the propagation. In this respect, the numerical simulations reveal that the breatherlike structures often emerge on the top of the initial power fluctuations (see Fig. 4d–g and Supplementary Movie 2).
Discussion
We believe that our experiments bring new and fundamental data allowing to examine model and conjectures related to nonlinear random waves and integrable turbulence. In particular, in the past few years, it has been conjectured that breather solutions of 1DNLSE such as PS or Akhmediev breathers represent prototypes of RWs^{20,24,27,28,29,30,33}. These SFB solutions have been generated in a deterministic way in optical fibres^{29,30,31} and in a onedimensional water tank^{33,54}. In ref. 54, it is also shown that the deterministic generation of the PS is robust against some additional noise. However, the relevance of the possible emergence of soliton on finite background solutions from a randomly fluctuating background is still discussed.
Our experiments with randomly fluctuating optical waves show that Peregrinelike breathers tend to emerge at the top of power fluctuations. These results may be interpreted in the light of recent mathematical results which show that PS spontaneously emerges in a generic way from an isolated hump^{53}. In the context of integrable turbulence, our experiments thus confirm the relevance of a scenario in which the RW objects that spontaneously emerge from a noisy background are indeed locally compatible with breather solutions of the 1DNLSE. Moreover and for the first time, our timeresolved observations correlate in an unambiguous way the occurrence of a heavytailed statistics with the frequent occurrence of breatherlike coherent structures. The simultaneous fast measurement of phase and amplitude fluctuations represents the next experimental bottleneck for the careful identification of optical RWs.
The conclusions which are drawn here in optical fibre experiments well described by the 1DNLSE cannot be directly extrapolated to phenomena found in the oceans. Let us emphasize however, that the principle of our experiment is identical to the one of some previous experiments performed in onedimensional deep water tank^{55}. Starting from random initial conditions, those hydrodynamical experiments have also demonstrated the formation of heavytailed statistics. Note finally that the extreme amplitudes observed in our optical fibres experiments could not be observed in water waves that are strongly limited by the wave breaking phenomenon^{1,56,57}.
The timeresolved direct observation of RWs presented in this letter opens the way to numerous other studies on fast dynamics in Optics. Integrable turbulence^{36,38,39} is a fundamental framework to study nonlinear random waves because various systems such as onedimensional deepwater waves or nonlinear optical waves are ruled at the leading order by the integrable 1DNLSE^{21,22,58}. One of the most intriguing issues of integrable turbulence is the dramatic dependence of the asymptotic statistics on the statistics of the initial condition^{36,38,39}. On the one hand, and as it is shown in this article, initial conditions made of partially coherent waves lead to the emergence of strongly heavytailed PDFs^{38}. On the other hand, the modulational instability is known to lead to a stationary state characterized by Gaussian statistics^{36}. The difference between the nature of the structures emerging in the context of random waves on one hand or in the context of modulation instability on the other hand is an open and fundamental question^{38,39}. The dynamics underlying the process of noisedriven modulational instability, of its nonlinear stage and more generally of optical turbulence represent open and fundamental questions that can now be experimentally studied by using our TM^{36,59,60}.
Methods
Partially coherent source and nonlinear propagation setup
The partially coherent light (that is, the initial condition) is generated by an Erbium fibre broadband ASE source (from Highwave), which is spectrally filtered (with programmable shape and linewidth) using a programmable optical filter (Waveshaper 1000S, from Finisar). The output is then amplified by an Erbiumdoped fibre amplifier (from Keopsys). This random light is launched into a singlemode polarization maintaining fibre (Fibercore HB1550T), with 500 m length, a dispersion β_{2}=−20 ps^{2} km^{−1} (measured). For a given spectral width, the power of the light launched inside the fibre is controlled using a half wavelength plate and a polarizing cube.
The experiments presented in the article are performed in nonlinear regimes characterized by a dispersion length L_{D} much larger than the nonlinear length L_{NL} in the initial stage. Typically, for a time scale T_{0}∼10 ps corresponding to the initial spectral width Δν=0.1 THz, km. Considering a hump with a maximum power P=5 × 〈P〉 and 〈P〉=0.5 W (Fig. 1b), the nonlinear length is km.
Timemicroscope setup and performances
For the singleshot acquisition of the subpicosecond optical signals, we realized an upconversion timemicroscope, largely based on the work of ref. 50. From the inputoutput point of view, the TM encodes the temporal shape of the optical signal onto the spectrum of a chirped pulse (that is, spectral encoding). Then the spectrum is recorded using a simple spectrometer composed of a 1800, lines mm^{−1} grating and a sCMOS camera. A region of interest (of typically 2048 × 8 pixels) is selected for recording the image (a raw image is presented in Supplementary Fig. 2).
For reaching high temporal resolution, a key element is the time lens^{49}, which is composed of a BBO crystal, pumped by a chiped 800 nm pulse. Before entering the time lens, the 1560, nm signal experiences anomalous dispersion in a classic Treacy grating compressor (see Fig. 2).
As in other time lens systems^{49,50,51} high resolution requires proper adjustment of the 1560, nm compressor (see Supplementary Note 1 for adjustment detail, and performances of the setup). Conceptually, this is exactly analogue to the tuning of the objectmicroscope objective distance in classical microscopes. For all results presented in this paper, the temporal resolution is 250 fs FWHM (see Supplementary Figs 1 and 2), and the field of view is of the order of 20 ps. Temporal calibration of the timemicroscope is obtained by recording the response to a series of two laser pulses with known delay (see Supplementary Fig. 3 and Supplementary Note 1).
As another crucial point, the timemicroscope strategy leads to an extremely high dynamical range (that is, the ratio between maximal recordable signal and dark noise). This directly stems from the choice of employing a camera for the recording. More precisely, our 16bit sCMOS camera has an RMS dark noise of ≈2 electrons and a saturation value of 30,000 electrons, leading to a ≈40 dB dynamical range.
The 800 nm pump is provided by an amplified TitaniumSapphire laser (Spectra Physics Spitfire, 2 mJ, 40 fs, a spectral bandwidth of about 25 nm), operated at 500 Hz, and only 100 nJ are typically used here. For inducing (normal) dispersion on the 800 nm pulses we simply adjusted the amplifier’s output compressor. The dispersion was fixed to 0.23 ps^{2}, leading to chirped pulses of duration of about 20 ps. The 1560, nm grating compressor uses two 600 lines mm^{−1} gratings, operated at an angle of incidence of 40 degrees, and whose planes are separated by 42 mm. The BBO crystal has 8 mm length and is cut for noncolinear typeI SFG (θ=24.2 °,==90 °, external angle between pump and signal=12.5 °). Focusing of the 800 and 1560, nm signals on the BBO crystal are performed by two lenses with 20 cm focal lengths. In order to improve the rejection of the 800 nm and the 1560, nm and to keep only the SFG at 528 nm, a 40nm bandpass filter around 531 nm (FF01 531/4025 from Semrock) is added after the crystal. The camera is a sCMOS Hamamatsu Orca flash 4.0 V2 (C1144022CU), equipped with an 60 mm lens (Nikkor Micro 60 mm f/2.8 AFD). The objective is focused at infinity and the waist of the SFG in the BBO crystal is imaged on the camera sensor. The camera is synchronized on the 800 nm laser pulses, and the integration time is adjusted to 1 ms, thus enabling singleshot operation of the timemicroscope. PDFs of optical power are computed with 75.10^{6} samples (10^{2} points taken in the centre of the temporal field of the TM from 75.10^{4} frames) for a given set of parameters.
Numerical simulations details
Numerical simulations are performed by integrating the 1DNLSE :
where is complex envelope of the electric field, normalized so that ^{2} is the optical power, z is the longitudinal coordinate in the fibre, and t is the retarded time. β_{2}=−20 ps^{2} km^{−1} is the secondorder dispersion coefficient of the fibre and γ is the Kerr coupling coefficient. From the comparison between the optical spectra measured in the experiments and the ones computed from the numerical simulations, we estimate that the Kerr coefficient is γ∼2–3 W^{−1} km^{−1}. We have chosen γ=2 W^{−1} km^{−1} in the numerical simulations displayed in Fig. 4. The PS displayed in Fig. 3h corresponds to γ=3 W^{−1} km^{−1}. All numerical integrations are performed using an adaptive stepsize pseudospectral method, using a mesh of 2048 or 8192 points, over a temporal window of ΔT=250 ps.
In numerical simulations presented in this letter, we neglect linear losses (≃0.5 dB) and stimulated Raman scattering. These approximations provide precise and quantitative agreement between experiments and numerical simulations at moderate powers (<2 W, see also Supplementary Note 3 and Supplementary Fig. 5). Additional numerical simulations show that stimulated Raman scattering has to be taken into account in order to reproduce very precisely the experimental PDFs and optical spectra at high values of the mean power (that is, 〈P〉=4 W). However the main physical results (formation of RWs, emergence of breatherlike structures and heavytailed PDFs) are not affected by stimulated Raman scattering. Note finally that we consider here the deterministic 1DNLSE (without any additional noise occurring along the propagation inside the fibre).
The random complex field (t, z=0) used as initial condition in numerical simulations is made from a discrete sum of Fourier components:
with and Δω=2π/ΔT. The Fourier modes are complex variables. We have used the socalled random phase (RP) model in which only the phases =_{m} of the Fourier modes are considered as being random^{41}. In this model, the phase of each Fourier mode is randomly and uniformly distributed between −π and π. Moreover, the phases of separate Fourier modes are not correlated so that where δ_{nm} is the Kronecker symbol (δ_{nm}=0 if n≠m and δ_{nm}=1 if n=m). With the assumptions of the RP model above described, the statistics of the initial field is stationary, which means that all statistical moments of the complex field (z=0, t) do not depend on x^{41}. In the RP model, the power spectrum n_{0}(ω) of the random field (z=0, t) reads as:
with ω_{n}=nΔω. In our simulations, we have taken a random complex field (z=0,t) having a Gaussian optical power spectrum that reads
where Δω=2πΔν is the half width at 1/e of the power spectrum. Statistical properties of the random wave have been computed from Monte Carlo simulation made with an ensemble of 10^{4} realizations of the random initial condition.
Data availability
The data that support the findings of this study are available from the corresponding author on request.
Additional information
How to cite this article: Suret P. et al. Singleshot observation of optical rogue waves in integrable turbulence using time microscopy. Nat. Commun. 7, 13136 doi: 10.1038/ncomms13136 (2016).
References
 1.
Kharif, C., Pelinovsky, E. & Slunyaev, A. Rogue waves in the ocean Springer (2009).
 2.
Onorato, M., Osborne, A. R., Serio, M. & Bertone, S. Freak waves in random oceanic sea states. Phys. Rev. Lett. 86, 5831–5834 (2001).
 3.
Onorato, M., Residori, S., Bortolozzo, U., Montina, A. & Arecchi, F. Rogue waves and their generating mechanisms in different physical contexts. Phys. Rep. 528, 47–89 (2013).
 4.
Solli, D. R., Ropers, C., Koonath, P. & Jalali, B. Optical rogue waves. Nature 450, 1054–1057 (2007).
 5.
Solli, D., Ropers, C. & Jalali, B. Active control of rogue waves for stimulated supercontinuum generation. Phys. rev. lett. 101, 233902 (2008).
 6.
Erkintalo, M., Genty, G. & Dudley, J. M. Roguewavelike characteristics in femtosecond supercontinuum generation. Opt. Lett. 34, 2468–2470 (2009).
 7.
Kibler, B., Finot, C. & Dudley, J. M. Soliton and rogue wave statistics in supercontinuum generation in photonic crystal fibre with two zero dispersion wavelengths. Eur. Phys. J. 173, 289–295 (2009).
 8.
Kasparian, J., Béjot, P., Wolf, J.P. & Dudley, J. M. Optical rogue wave statistics in laser filamentation. Opt. Express 17, 12070–12075 (2009).
 9.
Birkholz, S. et al. Spatiotemporal rogue events in optical multiple filamentation. Phys. Rev. Lett. 111, 243903 (2013).
 10.
Montina, A., Bortolozzo, U., Residori, S. & Arecchi, F. T. Nongaussian statistics and extreme waves in a nonlinear optical cavity. Phys. Rev. Lett. 103, 173901 (2009).
 11.
Bonatto, C. et al. Deterministic optical rogue waves. Phys. Rev. Lett. 107, 053901 (2011).
 12.
Kovalsky, M. G., Hnilo, A. A. & Tredicce, J. R. Extreme events in the ti:sapphire laser. Opt. Lett. 36, 4449–4451 (2011).
 13.
Lecaplain, C., Grelu, P., SotoCrespo, J. M. & Akhmediev, N. Dissipative rogue waves generated by chaotic pulse bunching in a modelocked laser. Phys. Rev. Lett. 108, 233901 (2012).
 14.
Randoux, S. & Suret, P. Experimental evidence of extreme value statistics in raman fiber lasers. Opt. Lett. 37, 500–502 (2012).
 15.
Hammani, K., Finot, C., Dudley, J. M. & Millot, G. Optical roguewavelike extreme value fluctuations in fiber raman amplifiers. Opt. Express 16, 16467–16474 (2008).
 16.
Akhmediev, N. & Pelinovsky, E. Editorial  introductory remarks on ‘discussion & debate: Rogue waves—towards a unifying concept?’. Eur. Phys. J. 185, 1–4 (2010).
 17.
Arecchi, F. T., Bortolozzo, U., Montina, A. & Residori, S. Granularity and inhomogeneity are the joint generators of optical rogue waves. Phys. Rev. Lett. 106, 153901 (2011).
 18.
Akhmediev, N. et al. Roadmap on optical rogue waves and extreme events. J. Opt. 18, 063001 (2016).
 19.
Osborne, A. Nonlinear ocean waves Academic Press (2010).
 20.
Dudley, J. M., Dias, F., Erkintalo, M. & Genty, G. Instabilities, breathers and rogue waves in optics. Nat. Photon. 8, 755 (2014).
 21.
Chabchoub, A. et al. The nonlinear schrodinger equation and the propagation of weakly nonlinear waves in optical fibers and on the water surface. Ann. Phys. 361, 490–500 (2015).
 22.
Peregrine, D. H. Water waves, nonlinear Schrödinger equations and their solutions. J. Aust. Math. Soc. Ser. B 25, 16–43 (1983).
 23.
Henderson, K., Peregrine, D. & Dold, J. Unsteady water wave modulations: fully nonlinear solutions and comparison with the nonlinear Schrödinger equation. Wave Motion 29, 341–361 (1999).
 24.
Akhmediev, N., Ankiewicz, A. & Taki, M. Waves that appear from nowhere and disappear without a trace. Phys. Lett. A 373, 675–678 (2009).
 25.
Akhmediev, N., SotoCrespo, J. & Ankiewicz, A. Extreme waves that appear from nowhere: on the nature of rogue waves. Phys. Lett. A 373, 2137–2145 (2009).
 26.
Shrira, V. I. & Geogjaev, V. V. What makes the Peregrine soliton so special as a prototype of freak waves? J. Eng. Math. 67, 11–22 (2010).
 27.
Akhmediev, N., Dudley, J. M., Solli, D. R. & Turitsyn, S. K. Recent progress in investigating optical rogue waves. J. Opt. 15, 060201 (2013).
 28.
Toenger, S. et al. Emergent rogue wave structures and statistics in spontaneous modulation instability. Sci. Rep. 5, 10380 (2015).
 29.
Kibler, B. et al. The Peregrine soliton in nonlinear fibre optics. Nat. Phys. 6, 790–795 (2010).
 30.
Kibler, B. et al. Observation of kuznetsovma soliton dynamics in optical fibre. Sci. Rep. 2, 463 (2012).
 31.
Frisquet, B., Kibler, B. & Millot, G. Collision of akhmediev breathers in nonlinear fiber optics. Phys. Rev. X 3, 041032 (2013).
 32.
Kibler, B., Chabchoub, A., Gelash, A., Akhmediev, N. & Zakharov, V. E. Superregular breathers in optics and hydrodynamics: omnipresent modulation instability beyond simple periodicity. Phys. Rev. X 5, 041026 (2015).
 33.
Chabchoub, A., Hoffmann, N. P. & Akhmediev, N. Rogue wave observation in a water wave tank. Phys. Rev. Lett. 106, 204502 (2011).
 34.
Zakharov, V. E. Turbulence in integrable systems. Stud. Appl. Math. 122, 219–234 (2009).
 35.
Zakharov, V. E. & Gelash, A. A. Nonlinear stage of modulation instability. Phys. Rev. Lett. 111, 054101 (2013).
 36.
Agafontsev, D. & Zakharov, V. E. Integrable turbulence and formation of rogue waves. Nonlinearity 28, 2791 (2015).
 37.
Randoux, S., Suret, P. & El, G. Inverse scattering transform analysis of rogue waves using local periodization procedure. Sci. Rep. 6, doi:10.1038/srep29238 (2016).
 38.
Walczak, P., Randoux, S. & Suret, P. Optical rogue waves in integrable turbulence. Phys. Rev. Lett. 114, 143903 (2015).
 39.
SotoCrespo, J. M., Devine, N. & Akhmediev, N. Integrable turbulence and rogue waves: breathers or solitons? Phys. Rev. Lett. 116, 103901 (2016).
 40.
Suret, P., Picozzi, A. & Randoux, S. Wave turbulence in integrable systems: nonlinear propagation of incoherent optical waves in singlemode fibers. Opt. Express 19, 17852–17863 (2011).
 41.
Picozzi, A. et al. Optical wave turbulence: towards a unified nonequilibrium thermodynamic formulation of statistical nonlinear optics. Phys. Rep. 542, 1–132 (2014).
 42.
Randoux, S., Walczak, P., Onorato, M. & Suret, P. Nonlinear random optical waves: integrable turbulence, rogue waves and intermittency. Physica D: Nonlinear Phenomena 333, 323–335 (2016).
 43.
Goodman, J. W. Statistical optics WileyInterscience (1985).
 44.
Fatome, J., Finot, C., Millot, G., Armaroli, A. & Trillo, S. Observation of optical undular bores in multiple fourwave mixing. Phys. Rev. X 4, 021022 (2014).
 45.
Randoux, S., Walczak, P., Onorato, M. & Suret, P. Intermittency in integrable turbulence. Phys. Rev. Lett. 113, 113902 (2014).
 46.
Bromberg, Y., Lahini, U., Small, E. & Silberberg, Y. Hanbury brown and twiss interferometry with interacting photons. Nat. Photon. 4, 721–726 (2010).
 47.
Pierangeli, D., Di Mei, F., Conti, C., Agranat, A. J. & DelRe, E. Spatial rogue waves in photorefractive ferroelectrics. Phys. Rev. Lett. 115, 093901 (2015).
 48.
Mussot, A. et al. Observation of extreme temporal events in cwpumped supercontinuum. Opt. Express 17, 17010–17015 (2009).
 49.
Kolner, B. H. & Nazarathy, M. Temporal imaging with a time lens. Opt. lett. 14, 630–632 (1989).
 50.
Bennett, C. & Kolner, B. Upconversion time microscope demonstrating 103 × magnification of femtosecond waveforms. Opt. lett. 24, 783–785 (1999).
 51.
Foster, M. A. et al. Siliconchipbased ultrafast optical oscilloscope. Nature 456, 81–84 (2008).
 52.
Yang, J. Nonlinear waves in integrable and nonintegrable systems vol. 16, SIAM (2010).
 53.
Bertola, M. & Tovbis, A. Universality for the focusing nonlinear schrödinger equation at the gradient catastrophe point: Rational breathers and poles of the tritronquée solution to painlevé i. Commun. Pure Appl. Math. 66, 678–752 (2013).
 54.
Chabchoub, A. Tracking breather dynamics in irregular sea state conditions. Preprint at arXiv:1604.06019 (2016).
 55.
Onorato, M. et al. Observation of strongly nongaussian statistics for random sea surface gravity waves in wave flume experiments. Phys. Rev. E 70, 067302 (2004).
 56.
Toffoli, A., Babanin, A., Onorato, M. & Waseda, T. Maximum steepness of oceanic waves: field and laboratory experiments. Geophys. Res. Lett. 37, 5 (2010).
 57.
Iafrati, A., Babanin, A. & Onorato, M. Modulational instability, wave breaking, and formation of largescale dipoles in the atmosphere. Phys. Rev. Lett. 110, 184504 (2013).
 58.
Dyachenko, S., Newell, A., Pushkarev, A. & Zakharov, V. Optical turbulence: weak turbulence, condensates and collapsing filaments in the nonlinear Schrödinger equation. Phys. D 57, 96–160 (1992).
 59.
Solli, D., Herink, G., Jalali, B. & Ropers, C. Fluctuations and correlations in modulation instability. Nat. Photon. 6, 463–468 (2012).
 60.
Turitsyna, E. G. et al. The laminarturbulent transition in a fibre laser. Nat. Photon. 7, 783–786 (2013).
Acknowledgements
This work has been partially supported by the Agence Nationale de la Recherche through the LABEX CEMPI project (ANR11LABX0007) and the OPTIROC project (ANR12BS040011 OPTIROC), and the EQUIPEX FLUX (ANR11EQPX0017) as well as by Lille 1 University (BQR ÉmergenceInnovation) and by the Ministry of Higher Education and Research, NordPas de Calais Regional Council and European Regional Development Fund (ERDF) through the Contrat de Projets EtatRégion (CPER Photonics for Society P4S). The authors acknowledge Miguel Onorato (Torino, Italy), Gennady El (Loughborough, UK), Tamara Grava (Trieste, Italy) and Goery Genty (Tampere University, Finland) for fruitful discussions. The authors are grateful to Francois Anquez and the Biophysics of Cellular Stress Response group of the PhLAM for the fruitful discussions, their crucial help, and for providing the sCMOS Camera. The authors are also grateful to Arnaud Mussot, Rémi Habert and the photonics group of the PhLAM for fruitful discussions, for the equipments (the ps laser), and for the measurement of the GVD of the fibre. The authors thank Nunzia Savoia for the everyday work on the femto laser and Marc Le Parquier for his crucial contribution in the development of the time lens.
Author information
Affiliations
Laboratoire de Physique des Lasers, Atomes et Molecules, UMRCNRS 8523, Université de Lille, Villeneuve d’Ascq 59655, France
 Pierre Suret
 , Rebecca El Koussaifi
 , Alexey Tikan
 , Clément Evain
 , Stéphane Randoux
 , Christophe Szwaj
 & Serge Bielawski
Centre d’Etudes et de Recherches Lasers et Applications (CERLA), Villeneuve d’Ascq 59655, France
 Pierre Suret
 , Rebecca El Koussaifi
 , Alexey Tikan
 , Clément Evain
 , Stéphane Randoux
 , Christophe Szwaj
 & Serge Bielawski
Authors
Search for Pierre Suret in:
Search for Rebecca El Koussaifi in:
Search for Alexey Tikan in:
Search for Clément Evain in:
Search for Stéphane Randoux in:
Search for Christophe Szwaj in:
Search for Serge Bielawski in:
Contributions
P.S. and S.B. have initiated the work. The design and realization of the experimental setup on rogue wave generation has been performed by S.R., P.S. and R.E.K. The timemicroscope has been designed and realized by C.S., C.E., S.B. and P.S. All authors participated to data acquisition that has been essentially performed by R.E.K. Data analysis has been performed by A.T. and P.S. Numerical simulations and code development have been performed by S.R., P.S. and C.E. P.S., S.B., S.R., C.S., C.E. have written and revised the manuscript.
Competing interests
The authors declare no competing financial interests.
Corresponding author
Correspondence to Pierre Suret.
Supplementary information
PDF files
 1.
Supplementary Information
Supplementary Figures 15, Supplementary Notes 13 and Supplementary References.
 2.
Peer Review File
Videos
 1.
Supplementary Movie 1
Singleshot experimental recordings using the time microscope (power versus time). Left: typical initial conditions at the fiber input. Right: signal after nonlinear propagation in the 500 m long fiber (see text). Average power inside the fiber is <P>=4 W. Note the occurrence of high power pulses (rogue waves), some reaching more than 160 W (at frame 24).
 2.
Supplementary Movie 2
Numerical simulation. Temporal dynamics along the propagation in the fiber. The animated frame corresponds to the intensity profile on the moving red line (spatiotemporal diagram).
Rights and permissions
This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/
About this article
Further reading

Realtime observation of dissipative soliton formation in nonlinear polarization rotation modelocked fibre lasers
Communications Physics (2018)

Machine learning analysis of extreme events in optical fibre modulation instability
Nature Communications (2018)

Realtime fullfield characterization of transient dissipative soliton dynamics in a modelocked laser
Nature Photonics (2018)

Singleshot measurement of phase and amplitude by using a heterodyne timelens system and ultrafast digital timeholography
Nature Photonics (2018)

Panoramicreconstruction temporal imaging for seamless measurements of slowlyevolved femtosecond pulse dynamics
Nature Communications (2017)
Comments
By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.