Glass Preforms for Next-Generation Fiber Lasers

Project Overview

The compositions and quantities of glass preforms commercially available for fiber lasers are generally limited by processes initially developed to make fibers with a core/cladding structure. While the advent of photonic crystal fibers (PCFs) has opened many possibilities in terms of fiber design and performance, it has also shifted the material needs for modern fiber laser groups. Thus, a new approach is needed to produce large quantities of high-purity SiO2 with a wide selection of dopant ions to effectively explore the design space for modern PCF fiber lasers. Furthermore, suppliers of custom-doped fiber preforms via conventional approaches are dwindling due to the standardization of production for high-volume customers.

In this study, we have produced the large-volume monoliths of silica glass doped with rare earth ions. Our approach was chemically flexible, allowing it to be utilized for a range of conventional and yet-unexplored rare-earth compositions. This method involved dip coating silica tubes with sol-gels, doping the coated surfaces using reactive metal salts, and consolidating stacks of coated tubes mounted on a glass lathe using an oxygen-hydrogen flame. Fully dense Nd-doped and Yb-doped glass preforms have been fabricated here. Those glass preforms were pulled into a fiber laser and lased with an output power of ~500 mW. We demonstrated Yb and Nd amplifiers with 42% (Nd, 1063nm) and 72% (Yb,1063nm) slope efficiencies and very low passive loss.

Mission Impact

This project was aligned with LLNL's directed-energy missions and would strengthen core competencies in laser and optical science and technology and advanced materials and manufacturing. This work established a new capability to prepare high-purity, custom-doped preforms for fiber pulling at LLNL. As a result, critical S&T questions were addressed, which will maintain LLNL's reputation as a leader in glass science and optics. This technology could be immediately integrated into ongoing directed-energy efforts supported by DOD to develop the next generation of fiber lasers with improved power and lifetime performance.

Publications, Presentations, and Patents

Lange, A., et al. "System and Method for Optical Fiber Preform Preparation Via High-Surface-Area Coating." US Patent App. 16/899,069 filed 2020, pending.

Lange, A. P., et al. 2021. "Fabrication of Optical Fiber Preforms Via Sol-Gel Coating." Presentation, Glass and Optical Materials Division Conference (GOMD), Vancouver, BC., Canada. December 2021.

Moore, W. G., et al. "Simulating Dopant Diffusion in a Detailed Porous Structure." Technical Report, Lawrence Livermore National Lab (August 2021); doi: 10.2172/1817990.