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)†
       
Coupling efficiencies of (2 + 1) × 1 couplers with the same input mode field and the different two pump tapered lengths inside (2 + 1) × 1 coupler. (a) Tapered length 8 cm and 5 cm, coupling efficiency 88.23%; (b) tapered length 8 cm and 15 cm, coupling efficiency 89.94%.