Microstructured cladding elements to enhance performance and flexibility of large mode area leakage channel fibers

Large mode area fibers are imperative for scaling up the average power of fiber lasers. Single-mode behavior and low FM loss are the crucial functionalities for these fibers. However, for key applications such as picosecond pulsed lasers, the device length needs to at least a few meters. This makes a certain degree of bend tolerance a prerequisite in the fiber design. While rod-type PCFs have been very successful in offering large mode areas, their rigid configuration limits their application domain. Alternatively, leakage channel fibers (LCFs) have shown a great potential for offering substantial bend tolerance along with large mode areas. However, the proposed use of Fluorine-doped rods in the all-solid version limits their practical design space. Here, we propose a novel design concept to attain single-material, large mode area fibers (mode area >~ 1000µm2) with effectively single mode operation coupled with bending characteristics comparable to all-solid LCFs and greater design flexibility and easier splicing that is comparable to rod-type PCFs

First demonstration of single trench fiber for delocalization of higher order modes

We demonstrate an ytterbium-doped single-trench fiber ensuring a high losses ratio (~1000) and low power fraction (~0.7) between the higher-order-modes and fundamental-mode with excellent bend robustness and 85% laser efficiency at a wavelength of 1040nm

Large mode area pixelated trench fiber

We propose a novel fiber that offers excellent suppression of higher-order-modes with loss higher than 10dB/m and low loss for fundamental mode (<0.1dB/m) at 1.06µm, with effective area as large as 1100µm2 and excellent bend-robustness

Novel optical fibers for telecommunications and high-power laser applications

This paper reviews our recent work on multi-element-fiber (MEF) technology for space-division-multiplexed transmission systems and progress towards the mode area scaling using multi-trench-fiber (MTF) design for high power applications

LMA effectively single-mode thulium doped fibre with normal dispersion at wavelengths around 2 µm

During the last few years, an increasing interest in Large Mode Area fibre operating around a wavelength of 2µm for high-power fibre laser applications has been observed. For most pulsed laser applications, it is desirable to operate the fibre in the normal dispersion regime to avoid the limiting effects of modulational instability (MI)/soliton formation. However, it is very difficult to achieve normal dispersion in conventional step-index large mode area fibres operating around a wavelength of 2µm due to the fact that the dispersion of their fundamental mode is mainly dominated by the material dispersion of silica, which is anomalous and very high around this wavelength (e.g.: ~44ps/(nm.km) at 1930nm)

Large mode area hybrid multi-trench fiber for anomalous dispersion

We propose a novel fiber design that shows excellent filtering for higher-order-modes (>6dB/m) and low losses for fundamental mode (<0.05dB/m) at 1064nm, with an anomalous-dispersion>72ps/nm-km and effective area >390µm2 with good bend robustness

Multi Trench Fiber: an ultra large mode area solution for industrial manufacturing

High power fiber lasers with good beam quality have shown their potential for numerous applications in material processing, defense, medicine, and space communications etc. Fiber lasers up to 10kW with single mode output have been demonstrated [1]. However, further scaling of power level requires proper management of non-linear effects (like Stimulated Raman Scattering, Stimulated Brillouin Scattering etc). One approach to mitigate non-linear effects is to increase the effective area (Aeff) of the fundamental mode. However, increasing the Aeff of the fundamental mode by increasing the core size, leads to propagation of higher order modes in a conventional fiber, which in, turn deteriorates the beam quality. In the recent years, several fiber designs having large mode area while ensuring single mode operation have been proposed, like Photonic Crystal Fibers (PCFs) [2] and 2-D all solid Photonic Band Gap Fibers (2D-ASPBGFs) [3]. These fibers have shown potential for high power fiber lasers but their fabrication involve stack and draw process, which is quite time consuming and expensive, making them unsuitable for large scale industrial manufacturability. Recently, we proposed the Multi Trench Fibers (MTFs) for high power fiber laser applications [4]. These are cylindrical symmetrical structures, which can be easily manufactured by a conventional fiber fabrication technique, like Modified Chemical Vapor Deposition (MCVD). Fig. 1 (a) shows the schematic of the proposed MTF. Fig. 1(b) shows the cross sectional image of the MTF fabricated using the MCVD process. MTF offers single-mode operation by offering higher losses to the higher order modes, through resonant coupling to the ring modes. Numerical simulation shows the potential of achieving ultra large Aeff 12,000m2 for a 140 m core with good beam quality (M2<1.2), for MTF in rod type configuration, which cannot be bent. Moreover, MTF can offer Aeff larger than 700m2 at a bend radius of 20cm

Comparaison de methodes d'identification dans leur application au diagnostic de l'etat des systemes

Cette communication pose le problème classique du choix d'une méthode d'identification pour les systèmes linéaires discrets, mais dans le cas moins commun où les paramètres identifiés servent non pas à simuler ou à commander le processus étudié, mais à porter un diagnostic sur son état interne. C'est dans le cadre d'une étude sur la maintenance des turboréacteurs et plus particulièrement sur l'aide au diagnostic par observation du comportement dynamique, que ce problème s'est posé. Les divers aspects de cette méthodologie sont exposés dans un premier paragraphe. Les suivants sont consacrés aux méthodes d'identification testées ainsi qu'à un critère comparatif de l'efficacité des divers algorithmes utilisés

SiN-assisted flip-chip adiabatic coupler between SiPh and Glass OPCBs

We demonstrate, for the first time to our knowledge, a SiN-assisted in-plane adiabatic coupler between SiPh and onboard glass waveguides. Our numerical study is founded on an actual graded index glass waveguide developed by Fraunhofer-IZM. The Silicon taper profile and the optimal length are extracted employing the supermode theory and the adiabatic theorem. Fabrication and assembly issues are investigated, resulting to an optimized coupler design that exhibits a theoretical Si-to-glass loss below 0.1dB over the entire C-band. The proposed solution can be realized utilizing standard passive flip-chip assembly equipment and is, therefore, cost-effective, easy to be fabricated, and well-suited for compact packaging