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Modelocked ultrafast lasers producing picosecond and sub-picosecond pulses are well known to exhibit a very rich landscape of nonlinear dynamics that are of tremendous interest from both fundamental and applied perspectives. Although such instabilities from ultrafast laser have been studied for many decades, the recent development of advanced photonic measurement techniques has opened up new perspectives into their analysis. In this thesis, we report a detailed experimental study of the complex dynamical regimes of two different optical fibre laser systems operating around 1550 nm: a soliton-similariton laser, and a Mamyshev oscillator. In both cases, we use the time-frequency technique of frequency resolved optical gating for complete intensity and chirp characterisation in stable regimes of operation, and the real-time dispersive Fourier transform method to characterize shot-to-shot spectral fluctuations. For the particular case of the soliton-similariton laser, stable operation yields from 7 to 10 ps pulses of 30~nm spectral width and 0,32 mW average output power at 9,5 MHz. Instabilities seen in the soliton-similariton laser include novel startup, the generation of coupled soliton molecules, the emergence of complex intermittence and chaos, and the appearance of multipulse states. For the case of the Mamyshev oscillator, stable operation yields from 3 to 5 ps pulses of 90 à 100 nm spectral width and ~4 mW average output power at 6,37 MHz. We also present results on the characterization of the Noise-Like Pulse regime of the soliton-similariton laser with the addition of highly nonlinear fiber in the cavity, which generates broadband output spanning 1000 nm. As well as presenting a range of experimental results, numerical simulations are used to gain insight into the operation of the laser systems studied., Les lasers ultrarapides produisant des impulsions picosecondes et sub-picosecondes sont connus pour présenter un riche éventail de dynamiques non linéaires qui sont d'un grand intérêt tant du point de vue fondamental qu'appliqué. Bien que les instabilités dans les lasers ultrarapides aient été étudiées depuis plusieurs décennies, le développement récent de techniques de mesure avancées a ouvert de nouvelles perspectives dans leur analyse. Dans cette thèse, nous présentons une étude expérimentale des régimes de dynamiques complexes appliquée à deux différentes classes de lasers à fibre impulsionnels fonctionnant autour de 1550 nm : un laser soliton-similariton, et un oscillateur de Mamyshev. Dans les deux cas lors du régime stable, notre caractérisation se base sur la technique d'autocorrélation résolue en fréquence (FROG) qui fournit l’accès aux mesures complètes de l'intensité et du chirp. En présence d’instabilités, nous appliquons la technique de transformée de Fourier dispersive qui nous permet d’enregistrer en temps réel les fluctuations spectrales tour par tour. Pour le laser soliton-similariton, le fonctionnement stable est associé à des impulsions de 7 à 10 ps de largeur spectrale de 30 nm et de puissance de sortie moyenne de 0,32 mW à 9,5 MHz. Les instabilités observées dans le laser à soliton-similariton comprennent des molécules solitons, de l'intermittence complexe, et des états multi-impulsionnels. Pour l'oscillateur de Mamyshev, le fonctionnement stable est associé à des impulsions de 3 à 5 ps de largeur spectrale de 90 à 100 nm et à une puissance de sortie moyenne de ~4 mW à 6,37 MHz. Nous présentons également des résultats sur la caractérisation du régime "noise-like pulse" avec l'ajout d'une fibre hautement non linéaire dans la cavité soliton-similariton associé à un spectre large bande couvrant 1000 nm. En plus de présenter une série de résultats expérimentaux, des simulations numériques ont également été utilisées afin de faciliter la compréhension du fonctionnement des systèmes étudiés.

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International audience; Ultrafast mode-locked lasers are well-known to display a rich variety of unstable dissipative soliton dynamics resulting from the interplay of nonlinearity, dispersion and dissipation. Although laser instabilities have been known and studied in depth for many years, their properties have recently received greatly renewed attention because of the development of time and frequency domain techniques that allow laser dynamics and instabilities to be measured in real-time. This has allowed the variations in circulating pulse characteristics to be examined on a roundtrip to roundtrip basis, providing a new window into understanding these instabilities and how they develop based on the cavity configuration being used. A technique of this kind that has proven both straightforward to implement and powerful is the photonic time stretch or dispersive Fourier transform (DFT) which has been used in a number of important applications including the measurement of soliton rogue waves, modulation instability and supercontinuum noise. The DFT allows direct access to shot-to-shot measurement of the mode-locked fibre laser spectrum and, via computation of the associated autocorrelation function, can also provide complementary time-domain information in cases where multiple pulse states are observed. In this paper, we report results of DFT measurements which have been used to reveal previously unreported behavior in a mode-locked fiber laser designed to operate with soliton-similariton dynamics. In particular, we observe instabilities including soliton explosions, chaotic evolution and oscillation in the relative phase of bound-state multi-pulse molecules, and what we believe to be a previously-unobserved regime of operation associated with the intermittent appearance of short-lived stable single pulses within of otherwise chaotic dynamics. Our results - obtained in a laser believed to be a particularly stable design - suggest that instabilities such as soliton explosions and intermittence are a universal feature of dissipative soliton systems transitioning from noise to stability.

International audience; Supercontinuum generation in the long pulse regime exhibits large shot-to-shot spectral variation and chaotic time domain consisting of soliton peaks emerging with random statistics. Under particular conditions, the noise-seeded dynamics may lead to the generation of a small number of extreme red-shifted rogue solitons that are associated with highly skewed “rogue wave” statistics. To overcome the restrictions in the experimental measurements, we here use the techniques of machine learning to predict the peak power and temporal shift of extreme red-shifted rogue solitons from single-shot spectral intensity profiles of supercontinuum without any phase information. The possibility to combine machine learning approaches with real-time spectral measurements to obtain temporal characteristics information without direct time-domain measurements which are often complex and limited to specific regimes of operations offers completely new avenues for the study of ultrafast dynamics in general.

We use the dispersive Fourier transform to spectrally characterize “multipulse soliton complexes” in a dissipative soliton fiber laser operating in the soliton-similariton regime. These multipulse complexes consist of two or more circulating dissipative solitons of picosecond duration, but with temporal separations of ∼5–40 ns, three orders of magnitude greater than the individual pulse durations. The results we present include a multipulse complex of 9 distinct single soliton pulses with ∼10 ns separation, as well as a multipulse complex where a soliton molecule of two bound pulses separated by ∼40 ps coexists with multiple single pulses with separations of ∼30 ns. We also use the dispersive Fourier transform to characterize breathing and transition dynamics in this multipulse regime, and our results add further to the experimental characterization of the diverse range of nonlinear structures in dissipative soliton systems. publishedVersion

International audience; We will review our recent work in real-time measurements of nonlinear instabilities including the use machine learning, as well as the observation of a range of instability processes in novel dissipative systems such as the soliton-similariton laser.

International audience; Recent years have seen renewed interest in the study of nonlinear fibre laser and propagation dynamics through the use of real-time measurement techniques for non-repetitive ultrafast optical signals. In this paper we review our recent work in this field using dispersive Fourier Transform and Time Lens techniques.