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 (1 + 1) × 1 and (2 + 1) × 1 couplers with the same tapered length and the same input mode field. (a) Tapered length 8 cm, coupling efficiency 90.35%; (b) tapered length 8 cm, coupling efficiency 89.66%. The arbitrary unit is abbreviated to a.u. in the figure.