Silicon nitride tri-layer 1×3 couplers with arbitrary splitting ratio for 3D photonic integrated circuits

We design tri-layer Si
₃
N
₄
1×3 couplers with arbitrary power splitting ratio and small reflection for 3D photonic integrated circuits. We demonstrate the power splitting ratio from 1:1:4 to 1:22:27 with 0.185 dB excess loss.