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The development of compact fiber-based light sources emitting over a wide wavelength range in the mid-infrared and their application to the detection of greenhouse gases and volatile organic compounds still remain of critical interest. In the present work, we make use of several dedicated infrared fibers for implementing a mid-infrared optical device pumped by a thulium doped-fiber laser around 1.965 μm that simultaneously enables a first nonlinear stage of frequency conversion and supercontinuum generation and a second linear stage of gas absorption spectroscopy. As a proof-of-principle, we carry out mid-infrared supercontinuum absorption spectroscopy of methane around 7.7 μm by means of a hollow-core fiber-based gas cell combined to a commercial Fourier-transform infrared spectrometer. Our all-fiber configuration operating in the femtosecond regime at megahertz repetition rate allows the detection of methane concentrations as low as 20 ppm. [ABSTRACT FROM AUTHOR]

The modulation instability (MI) is responsible for the disintegration of a regular nonlinear wave train and can lead to strong localizations in the form of rogue waves. This mechanism has been studied in a variety of nonlinear dispersive media, such as hydrodynamics, optics, plasma, mechanical systems, electric transmission lines, and Bose–Einstein condensates, while its impact on applied sciences is steadily growing. It is well-known that the classical MI dynamics can be triggered when a pair of small-amplitude sidebands are excited within a particular frequency range around the main peak frequency. That is, a three-wave system, consisting of the carrier wave together with a pair of unstable sidebands, is usually adopted to initiate the wave focusing process in a numerical or laboratory experiment. Breather solutions of the nonlinear Schrödinger equation (NLSE) revealed that MI can generate much more complex localized structures, beyond the three-wave system initialization approach or by means of a continuous spectrum. In this work, we report an experimental study for deep-water surface gravity waves asserting that a MI process can be triggered by a single unstable sideband only, and thus, initialized from a two-wave process when including the contribution of the peak frequency. The experimental data are validated against fully nonlinear hydrodynamic numerical wave tank simulations and show very good agreement. The long-term evolution of such unstable wave trains shows a distinct shift in the recurrent Fermi–Pasta–Ulam–Tsingou focusing cycles, which are captured by the NLSE and fully nonlinear hydrodynamic simulations with some distinctions. [ABSTRACT FROM AUTHOR]

In this study, we report the generation of multi-wavelength light sources through enhanced four-wave-mixing processes using a straightforward and adaptable dual-frequency Brillouin fiber laser. This passive optical and nonreciprocal cavity is first tested and analyzed with long fiber lengths up to 1 km in the 1.55 μm telecommunication C band and then in the 2-μm waveband. In the latter case, we demonstrate that our fiber cavity enables efficient multiple four-wave mixings, in the continuous-wave regime, which are commonly inaccessible in long silica-fibers due to increased losses. We also report on the tunable repetition rate from tens of GHz to hundreds of GHz, by simply changing the frequency spacing between the two continuous-wave pumps. The coherence limitations of our all-fiber system are discussed, along with the impact of the dispersion regime of the nonlinear fiber that forms the cavity. [ABSTRACT FROM AUTHOR]

Fifty years ago, the concept of solitons in optical fibres was proposed numerically by F. Tappert and A. Hasegawa from Bell Labs. Seven years later in 1980, experiments confirmed that dispersion and the Kerr nonlinearity could combine to yield a coherent ultrashort pulse able to propagate without distortion. The implications of this discovery go well beyond the sector of telecommunications as initially suggested, and solitons now play a major role in modern ultrafast nonlinear photonics. [ABSTRACT FROM AUTHOR]

Highly coherent frequency combs are of crucial importance for optical synthesis and metrology, spectroscopy, laser ranging, and optical communications. Kerr combs, generated via cascaded nonlinear frequency conversion in a passive optical cavity, typically offer high repetition rates, which is essential for some of these applications. Recently, new ways of generating Kerr combs combining Kerr and Brillouin effects have emerged with the aim of improving some performances, especially in the fiber cavity platform. Direct coherent pumping is replaced by lasing on specific cavity modes, offering easily adjustable repetition rates, and enhanced coherence by Brillouin purification. In this study, such a scheme is implemented and investigated in a non‐reciprocal cavity. Highly coherent combs are demonstrated by finely controlling bi‐chromatic Brillouin lasing and the Kerr comb parameters. A suitable numerical model is introduced to account for the interplay between Brillouin scattering, Kerr effect, and cavity resonant feedback. Quantitative agreements with experiments reveal the importance of the pump lasers detuning in setting the comb's properties, through the mode pulling effect. This phenomenon, along with multi‐mode lasing that impedes the coherence, is not studied in previous fiber‐based demonstrations. These limitations are discussed, and several scaling laws are devised. [ABSTRACT FROM AUTHOR]

We report on mid-infrared gas spectroscopy measurements by means of the supercontinuum (SC) absorption spectroscopy method. We developed a 80 MHz-repetition-rate mid-infrared SC light source with an average power of 40 mW generated through nonlinear propagation of 200 fs pulses in a 10 cm-long segment of step-index tellurite fiber. A compact multipass cell is used for analyzing absorption of CO2 and CH4 gases and their mixture in the 2–3.5 µm spectral range. Experimental results are compared to the HITRAN database. [ABSTRACT FROM AUTHOR]

We reviewed the tellurite glass purification studies performed over the last 20 years, in particular dealing with the mid‐infrared (mid‐IR) transmission performances. Best results are obtained under rich O2 atmosphere with platinum crucibles although Gibbs energy calculations show that other crucibles material are possible such as gold or alumina. From the point of view of the thermodynamics of involved oxidation reactions only, we identified the suitable conditions based on Gibbs energy calculations to be a synthesis temperature set above 900 K and a O2 pressure around 105 Pa. The performances of the different purification techniques were also compared. Finally, we analyzed the tellurite fibers recently optimized for mid‐IR which present low attenuation up to 4 µm allowing supercontinuum generation up to 5 µm. [ABSTRACT FROM AUTHOR]

Material characteristics and input-field specifics limit controllability of nonlinear electromagnetic-field interactions. As these nonlinear interactions could be exploited to create strongly localized bright and dark waves, such as nonlinear surface polaritons, ameliorating this limitation is important. We present our approach to amelioration, which is based on a surface-polaritonic waveguide reconfiguration that enables excitation, propagation and coherent control of coupled dark rogue waves having orthogonal polarizations. Our control mechanism is achieved by finely tuning laser-field intensities and their respective detuning at the interface between the atomic medium and the metamaterial layer. In particular, we utilize controllable electromagnetically induced transparency windows commensurate with surface-polaritonic polarization-modulation instability to create symmetric and asymmetric polaritonic frequency combs associated with dark localized waves. Our method takes advantage of an atomic self-defocusing nonlinearity and dark rogue-wave propagation to obtain a sufficient condition for generating phase singularities. Underpinning this method is our theory which incorporates dissipation and dispersion due to the atomic medium being coupled to nonlinear surface-polaritonic waves. Consequently, our waveguide configuration acts as a bimodal polaritonic frequency-comb generator and high-speed phase rotator, thereby opening prospects for phase singularities in nanophotonic and quantum communication devices. [ABSTRACT FROM AUTHOR]

Featured Application: Supercontinuum generation in novel infrared fibers from high-repetition-rate femtosecond mode-locked laser pulses provides mid-infrared radiation with very attractive features such as high coherence and spectral power density over an ultra-broad spectral range, thus opening new prospects for remote sensing applications, in particular through mid-infrared spectroscopy. Mid-infrared supercontinuum generation from 1.5 to 4.5 µm with sub-nanojoule femtosecond pump pulses is demonstrated by using a short segment of dispersion-engineered step-index tellurite fiber with very low OH content. Distinct group-velocity dispersion regimes in a simple design of step-index tellurite fiber are also reported, which allows to choose the nonlinear pulse propagation regime according to the required tailoring of the supercontinuum source. Numerical simulations based on the generalized nonlinear Schrödinger equation are used to determine optimized fiber parameters before experimental demonstrations. We also analyse the coherence properties of the resulting supercontinuum sources. [ABSTRACT FROM AUTHOR]

We report on the experimental generation of an octave-spanning supercontinuum in a 2.2 cm-long titanium dioxide optical waveguide with two zero dispersion wavelengths. The resulting on-chip supercontinuum reaches the visible wavelength range as well as the mid-infrared region by using a femtosecond fiber laser pump at 1.64 µm. [ABSTRACT FROM AUTHOR]

A combination of state-of-the-art temporal and spatial shaping techniques enables shaping pulsed laser light in all dimensions in a correlated manner, paving the way for new classes of on-demand space–time wavepackets. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to demonstrate the quasi-phase-matching of third harmonic generation process in optical fibers using refractive-index gratings. We compare conversion efficiency calculated with analytical coupled-modes theory and numerical approach employing a system of coupled generalized nonlinear Schrödinger equation. Moreover, we show that introducing the phase matching condition that takes into account the nonlinear contribution to propagation constants significantly increases the conversion efficiency by several orders of magnitude. Finally, we optimize the grating constant to maximize conversion efficiency. [ABSTRACT FROM PUBLISHER]

Parabolic pulses in optical fibers have stimulated an increasing number of applications. We review here the physics underlying the generation of such pulses as well as the results obtained in a wide range of experimental configurations. [ABSTRACT FROM AUTHOR]