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Optical fibers mid-infrared (mid-IR) supercontinuum (SC) generation for sources covering the 1–20 μm range are of great interest for many applications in optics, spectroscopy, sensing for environmental monitoring or medical diagnosis and treatment. We present here our work regarding two low phonon energy glasses families, leading to highly nonlinear optical fibers for SC generation: tellurites and seleno-telluride glasses. Tellurite fibers are suitable for working in the 1-5 μm range, when seleno-telluride ones are intended to the 2-16 μm range. For tellurites, we focus on the definition of glass pairs suitable for the drawing of step index fibers with a controlled chromatic dispersion for a femto-second (fs) pumping around 2 μm. In the case of chalcogenide glasses, we focus on the Ge-Se-Te ternary system, which offers the advantage of allowing the drawing of step index or micro-structured fibers avoiding the usage of toxic arsenic. Depending on the fiber geometry the management of the chromatic dispersion is quite different. Suspended core fibers allow to shift deeply the unique zero dispersion wavelength (ZDW) towards short wavelengths for fs pumping around 2- 3 μm. For step index fibers, it is possible to design waveguides with no, one or two ZDW. Various pumping schemes are available between 3 and 9 μm, with a fs tunable source. As a result, SC generation experiments in these different fibers allows to reach wide spanning spectra, between 1 and more than 5 μm for tellurite fibers, and between 2 and more than 14 μm in the case of chalcogenides ones.

Tellurite glasses are good candidates for the development of broadband supercontinuum (SC) laser sources in the 1–5 µm range. At the moment, beside very few exceptions, SC generation in TeO2-based microstructured optical fibers (MOFs) is limited to 3 µm in the mid-infrared (MIR). We present here an observation of an optical aging occurring in six-hole suspended-core tellurite MOFs. When exposed to atmospheric conditions, such fibers show an alteration of their transmission between 3 and 4 µm. This aging phenomenon leads to the growth of strong additional losses in this wavelengths range over time. Impact of the transmission degradation on spectral broadening is studied through numerical simulations of SC generation.

In June 1876, June 1910 and August 2005, northern Switzerland was severely impacted by heavy precipitation and extreme floods. Although occurring in three different centuries, all three events featured very similar precipitation patterns and an extra-tropical storm following a cyclonic, so called Vb trajectory around the Alps. Going back in time from the recent to the historical cases, we explore the potential of dynamical downscaling a global reanalysis product from a grid size of 220 km to 3 km. We use the full, 56-member ensemble provided in the reanalysis and a regional weather model to investigate sensitivities of the simulated precipitation amounts to a set of differing model configurations. These setups are evaluated by combining spatial verification metrics, inter-subjective visual inspection and an objective similarity measure. The best-performing model setup, featuring a 1-day initialization period and moderate spectral nudging, is then applied to assess the sensitivity of simulated precipitation totals to cyclonic moisture flux along the downscaling steps. The analyses show that cyclone fields and tracks are well defined in the reanalysis ensemble for the 2005 and 1910 cases, while deviations increase for the 1876 case. In the downscaled ensemble, the accuracy of simulated precipitation totals is closely linked to the exact trajectory of the cyclone, with slight shifts producing erroneous precipitation, e.g., due to a break-up of the vortex if simulated too close to the Alpine topography. To reproduce the extreme events, continuous moisture fluxes of > 200 kg m−1s−1 from accurate directions are required. Misplacements of the vortex, in particular for the 1876 case, point to limitations of downscaling from coarse input for such complex weather situations and for the more distant past. On the upside, a well-reasoned selection of reanalysis members for downscaling may be adequate in cases where the driving large-scale features in the atmosphere are well known.

Heavy precipitation on the south side of the central Alps produced a catastrophic flood in October 1868. We assess the damage and societal impacts, as well as the atmospheric and hydrological drivers using documentary evidence, observations and novel numerical weather and runoff simulations. The greatest damage was concentrated close to the Alpine divide and Lago Maggiore. An atmospheric reanalysis emphasizes the repeated occurrence of streamers of high potential vorticity as precursors of heavy precipitation. Dynamical downscaling indicates high freezing levels (4000 m a.s.l.), extreme precipitation rates (max. 270 mm 24 h−1) and weather dynamics that agree well with observed precipitation and damage, and with existing concepts of forced low-level convergence, mid-level uplift and iterative northeastward propagation of convective cells. Simulated and observed peak levels of Lago Maggiore differ by 2 m, possibly because the exact cross section of the lake outflow is unknown. The extreme response of Lago Maggiore cannot be attributed to low forest cover. Nevertheless, such a paradigm was adopted by policy makers following the 1868 flood, and used to implement nationwide afforestation policies and hydraulic structures. These findings illustrate the potential of high-resolution, hydrometeorological models – strongly supported by historical methods – to shed new light on weather events and their socio-economic implications in the 19th century.

Mid-infrared supercontinuum generation from 1.5 to 4.5 &micro, m 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 Schr&ouml, dinger equation are used to determine optimized fiber parameters before experimental demonstrations. We also analyse the coherence properties of the resulting supercontinuum sources.

Development of broadband supercontinuum sources has been studied since decades for its high application potential in various fields like spectroscopy, medical science and others. First experiments were made with silica but the results shown the need to find new materials for supercontinuum generation in the IR wavelength range. Two types of materials have been found interesting for supercontinuum generation: chalcogenide and tellurite glasses. These materials have a high non-linear refractive index and a good transmission in infrared which provides a high potential for applications. Bulks tellurite glasses transmit until 5µm while bulks chalcogenide glasses transmit until 12-20µm depending on their composition. We report here the synthesis of low-OH step-index tellurite fibers and their linear and non-linear characterization. The synthesis is firstly realized by build-in-casting in a glovebox which allows to get a large-core preform(∅clad/∅core  2) and a large core corresponding fiber(∅core  60µm). Then, the rod-in-tube technique allows, from the jacketing of the stretched initial preform, to get a small-core preform and subsequently a small core fiber (∅core  3.5µm). The minimum of losses of the large-core fiber is below 1dB/m, the IR transmission wavelength exceeds 4 µm on several meters of fibers and reaches more than 5 µm on small samples (several centimeters long). We have developed core-clad composition with a large refractive index difference (∆n=0.132) which provides a high confinement in our step-index fibers. We discuss the supercontinuum generation in these fibers exploiting numerical simulations based on the generalized nonlinear Schrodinger equation and then we present the supercontinuum experimental results obtained between 1 and 5µm. Most of pollutant and greenhouse gases emitted by human activity, including methane, carbon dioxide and nitrous oxide, absorbs in the mid-IR. The spectroscopic experiments realized on the gases through supercontinuum generation between 1 and 5 µm are presented.

We present the experimental development of dispersion-engineered tellurite fibers based on a simple step-index profile for mid-infrared supercontinuum generation. A supercontinuum spanning from 1.5 to 4.5 μm is obtained in a 12-cm-long fiber.

We present an overview of the fabrication process and characterization of germanate, germanate-tellurite and tellurite microstructured fibers or step-index fibers with different index contrasts. For microstructured fibers, we exploit the generated SC for methane spectroscopy measurements in the mid-infrared by means of the supercontinuum absorption spectroscopy technique. We demonstrate also an ageing process of microstructured fibers in ambient atmosphere. For stepindex fibers, several compatible core/cladding glasses were explored for fiber manufacturing with a dehydration process, allowing the drawing of low-OH tellurite fibers. We report both numerical and experimental demonstrations supercontinuum (SC) generation in these fibers. Finally we report our latest results in the generation of SC until 5.3 μm in a step-index tellurite fiber.

International audience; We demonstrate the fabrication of arsenic-and antimony-free chalcogenide glasses compatible with glass fiber processing. Optical fibers with distinct index profiles are presented and characterized, namely, single-material fibers with or without a suspended core and standard step-index fibers with varying core diameter. In addition, we evidence their potential for nonlinear photonic devices in the mid-infrared spectral region by means of super-continuum generation experiments in the femtosecond regime. Spectral broadenings extend on several octaves in the mid-infrared from 2 to 14 μm.

We demonstrate broadband supercontinuum generation over two infrared octaves, spanning from 1.3 to 5.3 μm, with an output power of 150 mW in robust step-index tellurite fibers with core diameters between 3.5 and 4.3 μm. As a pump source, we use femtosecond mid-IR pulses from a home-built post-amplified optical parametric oscillator tunable between 1.5 and 4.0 μm at a 43 MHz repetition rate. We study the influence of core size, pump wavelength, and fiber length to optimize the spectral bandwidth. A key requirement for efficient spectral broadening is a low and rather flat average anomalous dispersion over a wide spectral range that can be tailored accordingly by changing the fiber core diameter. Numerical simulations based on the generalized nonlinear Schrodinger equation are in good agreement with experimental results.

We report numerical and experimental demonstrations of flexible group-velocity dispersion regimes in step-index tellurite fibers by fine control of the fiber core diameter. Our simple fiber design allowed us to explore various nonlinear propagation regimes beyond 2 μm, which involved careful control of four-wave mixing processes. Combined with the recent development of 2 μm fiber lasers, we present an easy way to tailor supercontinuum generation and related coherence features in the high-demand 1.5-3.5 μm spectral region.

We present an overview of the fabrication process and characterization of tellurite, germanate, and germanate–tellurite step-index fibers with different index contrasts. Several compatible core/cladding glass pairs were first explored for fiber manufacturing under ambient atmosphere. The potential of the resulting waveguides for nonlinear optics is revealed by means of supercontinuum generation experiments using a near-infrared femtosecond fiber laser. Fabrication of the glass preforms was also adapted to dehydration procedures, allowing the drawing of low-OH step-index tellurite fibers. The beneficial impact of glass purification on supercontinuum generation toward the mid-infrared region is confirmed.