LASER THULIUM EFFICACE BASE SUR UNE FIBRE A GRANDE AIRE MODALE A TRIPLE GAINE FABRIQUEE PAR LA METHODE REPUSIL

National audienceNous rapportons ici une fibre à large aire modale de 18 µm de diamètre de coeur dopée thulium fabriquée par un procédé alternatif nommé Repusil et présentant un profil à triple gaine. Cette fibre, caractérisée en configuration laser, nous a permis d'obtenir un faisceau monomode transverse proche de la limite de diffraction (M x,y 2 < 1,1) avec une efficacité laser de 50,4%

High-power fiber laser based on a non filamented-core fully-aperiodic large pitch fiber

International audienceSince the double-clad fiber architectures development, fiber-based laser have witnessed an impressive power scaling [1]. The extracted power rising has been accompanied by the development of Very Large Mode Area (VLMA) fiber designs allowing overcome some key hurdles like the non-linear process or photo-darkening [2]. However, due to the very large core size of fiber architectures, a new phenomenon, referring to modal instabilities, has been evidenced recently like the current limitation which hampers any further power increase in the field of fiber laser sources without a dramatic degradation of the emitted beam quality [3]. In order to push away the appearance power threshold of this limitation, new aperiodic cladding microstructurations have been proposed to improve the higher-order modes (HOM) rejection out of the gain region and then to optimize the amplification of the sole fundamental mode [4]. These aperiodic microstructures have proved recently their potential to enhance an efficient HOM delocalization enabling singlemode confinement in the core region with passive VLMA fibers [5].In this communication we report on the first high power emission demonstration obtained using a solid non-filamented core fully-aperiodic large pitch fiber manufactured by the REPUSIL method based on the sintering and vitrification of micrometric doped silica powders. Using a simple laser cavity, an average output power of 233 W was achieved with an available pump power of 400 W for the first time in such a fiber. The preliminary M2 measurements have shown an excellent beam quality with values less than 1.4

All-solid aperiodic Large Pitch Fibers for operation in high power regime

International audienceThis communication intends to summarize the recent strides carried out by the study of original Very Large Mode Area fibers (VLMA) that offer remarkable beam qualities. This work also aims in pushing farther the threshold of appearance for non-linear processes as well as thermal induced beam degradation hindering the power scaling in optical fibers. So as to fulfil this objective, thorough investigations of fibers modal content has been performed, leading to the evidencing of primordial statements for exacerbation of the beam quality and its robustness. Theoretical principles driven toward the conception of aperiodic Large Pitch Fibers (LPFs) will be reported together with experimental validation into passive fiber designs. The relevance of these original structures will then been discussed in regard to the power scaling

High-power passively mode-locked dissipative soliton fiber laser featuring cladding-pumped non-CVD thulium-doped fiber

International audienceWe are reporting on the characterization of a thulium-doped fiber laser applying new powder technology in the mode-locking regime. A high average output power of 185 mW at a repetition rate of 9 MHz was achieved directly from the oscillator, which resulted in 21 nJ of pulse energy. The single-pulse operation regime was confirmed by careful numerical modeling of the laser cavity

New solid fully-aperiodic large pitch fibers with non-filamented core for high-power singlemode emission

International audienceWe report on the first high power laser emission of a solid triple-clad fully-aperiodic large mode area fiber with non-filamented core based on Repusil process. The average power is 184 W with a singlemode fashion

Ultra large mode area fibers with aperiodic cladding structure for high power single mode lasers

International audienceThis communication presents the latest designs, fabrication steps and first results of large mode area fibres with aperiodic cladding structure for high power singlemode emission. Pre-compensation of thermal loading and first laser emission are detailed

Nouvelles architectures de fibres optiques a tres large aire modale pour la montee en puissance des lasers fibres

National audienceNous rapportons ici la première démonstration expérimentale d'une nouvelle architecture de fibres optiques à très grande surface de mode destinée à renforcer la propagation d'un mode transverse unique. L'originalité de ce travail repose sur une rupture contrôlée de la périodicité de la gaine optique microstructurée afin de favoriser la délocalisation des modes d'ordre supérieur au bénéfice du confinement du seul mode fondamental. Le caractère monomode des structures fabriquées a été conforté en utilisant un interféromètre à faible cohérence. Comme prédit lors d'une approche numérique préliminaire, un tel comportement est mis en évidence sur une large bande spectrale allant de 1 à 2 µm et ce pour des diamètres de coeur allant de 30 à 140 µm

Inner cladding influence on large mode area photonic crystal fiber properties under severe heat load

International audienceThe influence of the size and the air-filling fraction of the inner microstructure on the first HOM confinement in Yb-doped LMA PCFs under different heat load values has been investigated with a full-vector modal solver based on the finite element method, used also to solve the steady-state heat equation. In particular, the air-cladding inner dimension and the air-hole diameter in Symmetry-Free PCFs and Large Pitch Fibers have been modified in order to study which conditions facilitate the coupling between HOM and cladding modes, thus improving the delocalization of the former and making the fiber single-mode behavior more robust

Analysis of the modal content into large-mode-area photonic crystal fibers under heat load

International audienceThanks to their capability to provide very large mode area together with effective suppression of high-order modes, while allowing strong pump absorption and efficient conversion, Yb-doped double-cladding photonic crystal fibers are one of the key enabling factors for the development of high power fiber lasers. Thermal effects are currently appointed as the main bottleneck for future power scaling since, beyond a certain average power, they allow guidance of high order modes and energy transfer to them, causing a sudden degradation of the beam quality. In this paper the effects of heat load on the modes of double cladding fibers are thoroughly analyzed with a full-vector modal solver based on the finite-element method with integrated steady-state heat equation solver. Fibers with different inner cladding designs are compared to provide a deeper understanding of the mechanisms beyond the mode reconfinement and coupling. The influence of the fiber design on the robustness of the single-mode regime with respect to fiber heating has been demonstrated, providing a clear picture of the complex interaction between modes. On the basis of simulation results it has been possible to group fiber modes into three families characterized by peculiar reaction to heating. Index Terms—Photonic crystal fibers, thermo-optic effect, fiber lasers and amplifiers

Large mode area aperiodic fiber designs for robust singlemode emission under high thermal load

International audienceIn this paper, we investigate the potential of various large mode area bers under thermal load, that is the state-of-the-art air-silica large pitch bers, as well as the recently devised symmetry-reduced photonic crystal ber and aperiodic all-solid by carefully considering the degrees of freedom oered all along the ber fabrication. This work aims to discuss the mode ltering ability of these structures in regard to the power scaling and to conrm their potential for robust singlemode operation at high power level. Structural principles contributing to improve their performances such as the impact of air holes / solid inclusions size will be presented. We also intend to establish that the range of average absorbed/output power for which a robust singlemode operation is available can be shifted to full user requests in term of power range