Nonchemical-vapor-deposition process for fabrication of highly efficient Yb-doped large core fibers.
A new fabrication process of active optical silica glass based on direct sand vitrification is proposed. This method, an alternative to chemical vapor deposition (CVD), allows the fabrication of homogeneous and highly Yb(3+)-doped rods that are ten times larger in diameter than those produced by CVD. For large-mode-area fibers fabricated by the stack-and-draw method, this is a tremendous technical breakthrough that could offer great flexibility in fiber design. As a proof of concept, we focused here on the fabrication and characterization of active core material surrounded by pure silica. Consequently, we draw a simple multimode step-index fiber. The index ripple in the core that matches our objectives is approximately 2.2x10(-4). For this first demonstration, the core material is codoped with Yb(2)O(3) (3600 parts in 10(6)(ppm) by weight) and Al(2)O(3), yielding a 180 dB m(-1) absorption at a wavelength of 975 nm, whereas the background loss is around 0.8 dB m(-1). The continuous-wave laser obtained with this fiber exhibits 74% slope efficiency.