Step-index high-absorption Yb-doped large-mode-area fiber with Ge-doped raised cladding

• Main Authors: Sidharthan, Raghuraman, Ji, Junhua, Lim, Kang Jie, Lim, Serene Huiting, Li, Huizi, Lua, Jian Wei, Zhou, Yanyan, Tse, Chun Ho, Ho, Daryl, Seng, Yue Men, Chua, Song Liang, Yoo, Seongwoo
• Other Authors: School of Electrical and Electronic Engineering
• Format: Article
• Language: English
• Published: 2020
• Subjects: Engineering::Electrical and electronic engineering; Fiber Design and Fabrication; Fiber Measurements
• Online Access: https://hdl.handle.net/10356/137089
• Institution: Nanyang Technological University

We report an all-solid large-mode-area (LMA) step-index fiber offering high absorption and low core numerical aperture (NA) by introducing a highly ytterbium-doped P:Al core and germanium-doped cladding. The fiber provides core absorption of ∼1200 dB/m at 976 nm with a low 0.07 core NA, due to the raised Ge cladding. Furthermore, matched profiles of P and Al across the core are successfully obtained with high concentration of Yb2O3 around 0.4 mol%. The fiber characteristics are routinely achievable by conventional modified chemical vapor deposition with a solution doping technique. A highly efficient laser with >100 W output power, 86% slope efficiency with respect to launched pump power, and a mean M2 of 1.34 has been demonstrated using the fabricated LMA step-index fiber. We also report 80% laser slope efficiency with 58 W output power (pump power limited) within only 0.5 m of the fiber when pumped by a wavelength-stabilized laser diode.