Abstract
The need for Large Mode Area (LMA) fibers for high power laser applications is largely documented in the recent literature and also expressed by the end-users working in the field. More than giving access to Mode Field Diameters (MFD) much larger than 30 μm, it is generally admitted that such fibers should be i) single-mode, ii) flexible so as to support bending radius equal or smaller than 25 cm, iii) polarization-maintaining because most of the high-power applications are based on linearly polarized beams and iv) easy-to-splice, i.e. preferably all-solid. In the quest of LMA fibers geometries, several groups demonstrated that Solid-Core Photonic BandGap Fibers (SC-PBGF) either based on Bragg or ARROW (Anti-Resonant Reflecting Optical Waveguide) geometries possess all the qualities required to reach a high level of performances [1-5]. Among these works, our group demonstrated that 2D SC-PBGF with hetero-structured cladding permit to reach MFD larger than 30 μm in both passive and active geometries [3, 4]. In the present work, this concept is extended to realize a birefringent-core SC-PBGF. Moreover, this fiber proves to exhibit a polarizing effect over a spectral window larger than 30 nm and is single-mode in practice. The geometry considered for this study is a hetero-structured 2D SC-PBGF in the cladding of which some Boron-doped stress rods have been inserted. These rods have been combined with pure silica and Germanium-doped silica elements by the Stack-and-Draw manufacturing process. The hetero-structuration is designed to reject Higher Order Modes (HOM) by resonant coupling of these undesired core modes with the fundamental mode of secondary waveguides of tailored size. A Scanning Electron Microscope (SEM) image of the fiber, together with some details on its structure, is presented on Fig. 1(a). This geometry has been drawn so as to reach a core diameter of about 42 μm. The opto-geometrical properties of the high-index inclusions (Ge-doped) permit to ensure light guidance in the 3rd PBG of the cladding centred around 1025 nm.
© 2015 IEEE
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