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 tapered length and the different input mode fields. (a) LP01 mode, coupling efficiency 98.72%; (b) LP33 mode, coupling efficiency 40.87%.