Sébastien Février

White-light supercontinuum generation in normally dispersive optical fiber using original multi-wavelength pumping system

We report on the experimental demonstration of a white-light supercontinuum generation in normally dispersive singlemode air-silica microstructured fiber. We demonstrate that the simultaneous excitation of the microstuctured fiber in its normal and anomalous dispersion regimes using the fundamental and second harmonic signals of a passively Q-switched microchip laser leads to a homogeneous supercontinuum in the visible range. This pumping scheme allows the suppression of the cascaded Raman effect predominance in favor of an efficient spectrum broadening induced by parametric phenomena. A flat supercontinuum extended from 400 to 700 nm is achieved.

Stimulated Raman scattering in an ethanol core microstructured optical fiber

We show that high efficiency stimulated Raman scattering can be obtained using hollow core photonic crystal fiber with the core filled with a low refractive index nonlinear liquid. This new architecture opens new perspectives in the development of nonlinear functions as any kind of nonlinear liquid media can now be used to implement them, with original properties not accessible with silica core fibers.

Low-loss singlemode large mode area all-silica photonic bandgap fiber.

We describe the design and characterization of solid core large mode area bandgap fibers exhibiting low propagation loss and low bend loss. The fibers have been prepared by modified chemical vapor deposition process. The bandgap guidance obtained thanks to a 3-bilayer periodic cladding is assisted by a very slight index step (5.10-4) in the solid core. The propagation loss reaches a few dB/km and is found to be close to material loss.

High-power photonic-bandgap fiber laser

An original architecture of an active fiber allowing a nearly diffraction-limited beam to be produced is demonstrated. The active medium is a double-clad large-mode-area photonic-bandgap fiber consisting of a 10,000 ppm by weight Yb(3+)-doped core surrounded by an alternation of high- and low-index layers constituting a cylindrical photonic crystal. The periodic cladding allows the robust propagation of a approximately 200 microm(2) fundamental mode and efficiently discriminates against the high-order modes. The M(2) parameter was measured to be 1.17. A high-power cw laser was built exhibiting 80% slope efficiency above threshold. The robust propagation allows the fiber to be tightly bent. Weak incidence on the slope efficiency was observed with wounding radii as small as 6 cm.

Solid-Core Photonic Bandgap Fibers for High-Power Fiber Lasers

An overview of various designs of large-mode-area photonic bandgap fibers (PBGFs) is presented in this paper. Bending properties of these structures are discussed and compared with those of step-index and air-silica microstructured fibers. Peculiarities of active PBGF fabrication are considered, and novel high-power laser architecture based on such fibers is described.

Characterizations at high temperatures of long-period gratings written in germanium-free air-silica microstructure fiber.

We report what is to our knowledge the first characterization at high temperatures of long-period fiber gratings written in Ge-free air-silica microstructure fiber. The gratings written with the electric-arc technique suffer a low shift of the resonance wavelengths when the temperature is increased from 20 degrees C to 1200 degrees C. This shift is studied and compared with that of a long-period fiber grating written in a standard single-mode fiber by the same technique. Good thermal stability of the grating and of the fiber after annealing at 1200 degrees C for 1 h is demonstrated.

Chalcogenide As

A chalcogenide optical fiber of special design is proposed to convert a short-wavelength infrared radiation (around 2 mum) up to a second transparency window of atmospheric air (around 4.5 mu m) by degenerate four-wave mixing. The fiber supports a small core surrounded by three large air holes. The zero-dispersion wavelength is shifted down to 2 mum in this fiber by properly tailoring the fiber core. We demonstrate by solving the nonlinear Schrodinger equation that efficient wavelength-conversion can be obtained by pumping the fiber with a Tm:SiO2 pulsed fiber laser.

_{2}

We propose a new design of microstructured fiber combining large doped area (500 μm2), high rare earth concentration and single mode propagation despite the high core refractive index (nSi + 0.01). Actually, original guiding properties, based on a total internal reflection guidance regime modified by coupling between core and resonant cladding modes (close to the ARROW model) ensure single mode propagation. Moreover spectral properties which are largely governed by characteristics of high index cladding rods can be adjusted by properly choosing diameter and refractive index of the rods.

S

Very large-mode-area Yb(3+)-doped single-mode photonic bandgap (PBG) Bragg fiber oscillators are considered. The transverse hole-burning effect is numerically modeled, which helps properly design the PBG cladding and the Yb(3+)-doped region for the high-order mode content to be carefully controlled. A ratio of the Yb(3+)-doped region diameter to the overall core diameter of 40% allows for single-mode emission, even for small spool diameters of 15 cm. Such a fiber was manufactured and subsequently used as the core element of a cw oscillator. Very good beam quality parameter M(2)=1.12 and slope efficiency of 80% were measured. Insensitivity to bending, exemplified by the absence of temporal drift of the beam, was demonstrated for curvature diameter as small as 15 cm.

_{3}

Three numerical approaches for the analysis of photonic crystal fibres are presented and compared. A full-vector finite element method based on the resolution of the Maxwell equations is found to be a very efficient and reliable tool for accurately modelling these optical guiding structures. The localized function method in the scalar form applies as long as the air-filling fraction is not too large. We present a very simplified novel model based on an equivalent averaged refractive index profile that is in good accordance with the finite element method as long as the optical wavelength is not too enlarged. Finally, comparisons between numerical results and measurements are taken into account in order to discuss the reliability of the three models.