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We deploy a supervised machine-learning model based on a neural network to predict the temporal and spectral reshaping of a simple sinusoidal modulation into a pulse train having a comb structure in the frequency domain, which occurs upon nonlinear propagation in an optical fibre. Both normal and anomalous second-order dispersion regimes of the fibre are studied, and the speed of the neural network is leveraged to probe the space of input parameters for the generation of custom combs or the occurrence of significant temporal or spectral focusing.

The four-wave mixing process is a fundamental nonlinear interaction in Kerr media that can be described by a closed trajectory in the associated phase plane. We show here that it is possible to manipulate these trajectories and to connect two points that are not part of the same orbit. Our approach is based on a localized abrupt modification of the average power of the system. This mechanism is confirmed using different experimental realizations where iterative propagation in a short fiber segments mimics propagation in an idealized optical fiber.

The study of temporal solitons has revolutionized fiber optics, yielded new classes of ultrafast laser and opened multiple interdisciplinary applications.

Neural networks have been recently shown to be highly effective in predicting time-domain properties of optical fiber instabilities based only on analyzing spectral intensity profiles. Specifically, from only spectral intensity data, a suitably trained neural network can predict temporal soliton characteristics in supercontinuum generation, as well as the presence of temporal peaks in modulation instability satisfying rogue wave criteria. Here, we extend these previous studies of machine learning prediction for single-pass fiber propagation instabilities to the more complex case of noise-like pulse dynamics in a dissipative soliton laser. Using numerical simulations of highly chaotic behaviour in a noise-like pulse laser operating around 1550 nm, we generate large ensembles of spectral and temporal data for different regimes of operation, from relatively narrowband laser spectra of 70 nm bandwidth at the -20 dB level, to broadband supercontinuum spectra spanning 200 nm at the -20 dB level and with dispersive wave and long wavelength Raman extension spanning from 1150–1700 nm. Using supervised learning techniques, a trained neural network is shown to be able to accurately correlate spectral intensity profiles with time-domain intensity peaks and to reproduce the associated temporal intensity probability distributions. publishedVersion

International audience; Fiber-based supercontinuum (SC) generation has been a subject of intense interest over the last decade, with a significant impact on both basic science and industry. New uses for SC fiber sources are constantly emerging due to their unique properties that combine high brightness, visible to mid-infrared (MIR) wavelength coverage, fiber delivery, and single-mode output. Recent years have seen significant progress in overcoming the current shortcomings of SC sources in terms of wavelength coverage towards the 2 to 20 mu molecular fingerprint mid-infrared (MIR) region and in the ultraviolet (UV) down to 100 nm, while also improving stability, noise, coherence, power density, and robustness. In this talk, we will review all the recent advances in supercontinuum generation in a range of specialty optical fibers including: fluoride, chalcogenide, telluride, and silicon-core fibers for the MIR; UV-grade silica fibers and gas-filled hollow-core fibers for the UV range; and all-normal dispersion fibers for ultra-low noise coherent SC generation. Significant developments have been made in reaching target UV and MIR wavelength ranges, and the fiber SC has matured considerably to become a truly disruptive technology able to meet a range of societal and industrial challenges.

We present an erratum to our Letter [Opt. Lett. 47, 802 (2022)10.1364/OL.448571]. This erratum corrects an error in the sign of one of the higher-order dispersion coefficient used in the simulations of Figs. 2 and 4, as well as in Figs. S1 and S3. The simulations in the original Letter were performed using the correct value, and therefore this correction does not affect any of the results and conclusions of the original Letter.

Intensity fluctuations in supercontinuum generation are studied in polarization-maintaining (PM) and non-PM all-normal dispersion tellurite photonic crystal fibers. Dispersive Fourier transformation is used to resolve the shot-to-shot spectra generated using 225 fs pump pulses at 1.55 {\mu}m, with experimental results well reproduced by vector and scalar numerical simulations. By comparing the relative intensity noise for the PM and non-PM cases, supported by simulations, we demonstrate the advantage of the polarization-maintaining property of the PM fibers in preserving low-noise dynamics. We associate the low-noise in the PM case with the suppression of polarization modulation instability., Comment: Shreesha Rao D. S., Tanvi Karpate, Amar Nath Ghosh, Iv\'an B. Gonzalo, Mariusz Klimczak, Dariusz Pysz, Ryszard Buczy\'nski, Cyril Billet, Ole Bang, John M. Dudley, and Thibaut Sylvestre, "Noise in supercontinuum generated using PM and non-PM tellurite glass all-normal dispersion fibers". Optics Letters 47.10 (May 2022), pp. 2550-2553

We combine a programmable spectral filter and machine learning via a genetic algorithm to optimize nonlinear fiber propagation dynamics to generate an on-demand target spectrum.

We teach a feed-forward neural network the differential propagation dynamics of the generalized nonlinear Schrödinger equation, allowing for fast and memory-efficient emulation of nonlinear propagation scenarios in optical fibers from pulse compression to supercontinuum generation.

We demonstrate broadband supercontinuum generation with self-cleaning dynamics in a non-silica multimode graded-index fiber with enhanced nonlinearity and trans-parency window compared to silica.

The discovery of optical transverse orbital angular momentum (OAM) has broadened our understanding of light and is expected to promote optics and other physics. However, some fundamental questions concerning the nature of such OAM remain, particularly whether they can survive from observed mode degradation and hold OAM values higher than 1. Here, we show that the strong degradation actually origins from inappropriate time-delayed kx–ω modulation, instead, for transverse OAM having inherent space-time coupling, immediate modulation is necessary. Thus, using immediate x–ω modulation, we demonstrate theoretically and experimentally degradation-free spatiotemporal Bessel (STB) vortices with transverse OAM even beyond 102. Remarkably, we observe a time-symmetrical evolution, verifying pure time diffraction on transverse OAM beams. More importantly, we quantify such nontrivial evolution as an intrinsic dispersion factor, opening the door towards time diffraction-free STB vortices via dispersion engineering. Our results may find analogues in other physical systems, such as surface plasmon-polaritons, superfluids, and Bose-Einstein condensates.

The generation of a two-octave supercontinuum from the visible to mid-infrared (700–2800 nm) in a non-silica graded-index multimode fiber is reported. The fiber design is based on a nanostructured core comprised of two types of drawn lead-bismuth-gallate glass rods with different refractive indices. This yields an effective parabolic index profile and ten times increased nonlinearity when compared to silica fibers. Using femtosecond pulse pumping at wavelengths in both normal and anomalous dispersion regimes, a detailed study is carried out into the supercontinuum generating mechanisms and instabilities seeded by periodic self-imaging. Significantly, suitable injection conditions in the high power regime are found to result in the output beam profile showing clear signatures of beam self-cleaning from nonlinear mode mixing. Experimental observations are interpreted using spatio-temporal 3+1D numerical simulations of the generalized nonlinear Schrödinger equation, and simulated spectra are in excellent agreement with experiment over the full two-octave spectral bandwidth. Experimental comparison with the generation of supercontinuum in a silica graded-index multimode fiber shows that the enhanced nonlinear refractive index of the lead-bismuth-gallate fiber yields a spectrum with a significantly larger bandwidth. These results demonstrate a new pathway towards the generation of bright, ultrabroadband light sources in the mid-infrared.

Join the chairs and speakers from the conference on Emerging Topics in Artificial Intelligence for a Panel Discussion on Opportunities for Young Researchers.

The real-time characterization of ultrafast dynamics is essential to the understanding of the underlying physics and in recent years there has been major interest into the measurement of complex instabilities. One important example of instability is associated with modulation instability, a key physical process underlying the emergence of localized structures such as the Peregrine soliton. It is only very recently that it has been possible to precisely characterize these dynamics in the laboratory with the development of real-time measurement techniques. All previous experimental studies have been made for the case of ideal modulation instability excited by a near continuous wave input but it is in fact much more common for modulation instability to develop under non-ideal conditions in a regime where the dynamics present mixed multiscale features of both nonlinear envelope evolution and modulation instability dynamics on the pulse envelope itself. Here, combining a broadband reference phase-stable field generated by self-phase modulation with Fourier-transform spectral interferometry (FTSI) [1] , [2] we characterize for the first time modulation instability dynamics of an ultrafast pulse leading to fission into its fundamental soliton constituents. Our experiments can characterize the associated complex field in real-time with 20 fs resolution, allowing to resolve the individual soliton structures emerging from the initial stage of modulation instability.

The ultrabroadband supercontinuum (SC) source possesses a number of unique characteristics which have had a major impact in many research fields, ranging from precision metrology to high resolution imaging and ultrafast spectroscopy [1] . The generation of a supercontinuum is a highly complex process resulting from the propagation of intense light pulses in a nonlinear medium such as an optical fibre or waveguide. As a result of the very rich landscape of nonlinear dynamics, the input pulses injected into the fibre experience massive spectral broadening that can expand an initially narrowband input field to an output spanning from the visible to infrared [1] .

Ultrafast broadband sources based on the Mamyshev regeneration concept are a new class of oscillator that exploit cascaded reshaping and regeneration via offset filtering to sustain mode-locked operation [1] . The use of regeneration as a saturable absorber introduces new design degrees of freedom, and has led to many impressive results [2] . However, the intracavity evolution in a Mamyshev oscillator is associated with large variations in temporal and spectral characteristics, raising questions concerning the basic intracavity dynamics, and the degree to which instabilities seen in other dissipative soliton systems are also present in the Mamyshev system [3] .

Dissipative soliton lasers are widely used to generate stable ultrashort pulses, but they are also known to exhibit complex instabilities of great interest from a nonlinear dynamics perspective. A particular example is the "noise-like pulse" laser emitting sub-ps pulses that randomly evolve under a longer envelope. However, although this operation was first observed more than 20 years ago, it remains poorly understood. Here, we fill this gap and report experiments and modelling that reveal the underlying physics of broadband noise-like pulse operation in a cavity including highly nonlinear fibre. Our simulations reveal the key role of supercontinuum dynamics, and are in quantitative agreement with experiments using both real-time and time-averaged characterization techniques.

Supercontinuum (SC) generation in all-normal dispersion (ANDi) photonic crystal fibers (PCFs) has recently been investigated due to its ability to generate a low-noise broadband coherent spectrum, with a noise level much lower than typical SC sources based on anomalous dispersion fibers [1] , [2] . Several recent works have however reported some limitations on the input pulse duration due to both stimulated Raman scattering (SRS) and polarization modulation instability (PMI) [2] . Here, using a polarization-maintaining (PM) ANDi PCF pumped by a compact ytterbium-doped femtosecond laser at 1049 nm, we overcome these limitations and demonstrate an ultra-flat octave-spanning (670 nm-1390 nm) coherent SC with excellent low noise (RIN 17 dB) properties. This highly-stable broadband PM-fiber based source could find strong potential applications in biomedical imaging and microscopy where improved signal to noise ratio is essential.

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