Progress in the fabrication of optical fibers by the sol-gel-based granulated silica method

Abstract

Novel special optical fibers nowadays can take advantage of several new preform production techniques. During the last years we have devoted our attention to the granulated silica method. It is one of the variants of the powder-in-tube technique and potentially offers a high degree of freedom regarding the usable dopants, the maximum possible dopant concentration, the homogeneity of the dopants, the geometry and minimal refractive index contrast. We developed and refined an approach for the production of doped granulated silica material based on the sol-gel process.Here, we present material analysis results of an ytterbium (Yb) doped, aluminum (Al) and phosphorous (P) co-doped glass on the basis of our sol-gel glass based granulated silica method as well as first measurements of two LMA fibers obtained from this material. For the material analysis we used advanced analysis techniques, such as HAADF-STEM and STEM-EDX spectroscopy to determine the composition of the material and the distribution of the dopants and the codopants. The chemical mapping of the STEM-EDX shows an extremely homogeneous distribution of the dopants and co-dopants in nano-scale. Based on self-made LMA fibers, we measured the refractive index contrast of the sol-gelbased granulated silica derived core compared to the pure silica cladding. In addition we quantified optical characteristics such as the emission and absorption spectrum. The measured upper state lifetime of the optical active dopant ytterbium was 0.99ms, which in turn confirms the homogeneous distribution of the Yb atoms. The propagation losses were determined to be 0.2dB/m at 633nm and 0.02414dB/m at1550nm.

Fabrication and Characteristics of Yb-Doped Silica Fibers Produced by the Sol-Gel Based Granulated Silica Method

“…Our approach is to combine the sol-gel method with the granulated silica method into the so called sol-gel granulated silica approach [38][39][40]. This combination offers a high degree of freedom concerning the composition and concentration of dopants and co-dopants, while also giving more control over the fiber geometry and microstructure [30,34,40].…”

“…The basic principle and development of the sol-gel based granulated silica method for active fiber production has been previously described in detail in [27,38,41]. It starts with mixing silica, dopant, and co-dopant material in the liquid phase.…”

Granulated Silica Method for the Fiber Preform Production

“…Another advantage of the sol-gel method is that it features a high degree of freedom concerning the compositional flexibility [6,7]. This includes not only a higher degree of freedom concerning optically active dopants (e.g., rare earth), optically passive dopants (e.g., phosphorous and aluminum) and its simplicity to incorporate them, but also high dopant concentrations (up to several at.…”

“…These new concepts have radically changed the potential applications that we associate with a fiber [1][2][3][4][5]. During the last 13 years, we have studied two interesting ways of fiber production starting with the preform [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].…”

“…The goal of our studies was on the one hand to gain some compositional flexibility in doping the cores of fibers and on the other hand to have some more control over the microstructure of the fiber [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. To reach these two goals, we have been working on the sol-gel method for fiber material production and on the granulated silica method for preform assembly [6][7][8][9][10][11][12].…”