High coupling efficiency and low signal light loss (2 + 1) × 1 coupler*
Chen Xiaoa), Xiao Qi-Rongb), Jin Guang-Yonga), Yan Pingb), Gong Ma-Lib)†
       
Schematic side view of a side-pumping system consisting of a DC fiber and an MM fiber with a silica-clad doped with fluorine.