Fabrication of 4 x 4 tapered MMI coupler with large cross section

MMI coupler with large cross section has low coupling loss between the devi ce and fiber. However, large chip area is required. Recently proposed N x N tapered MMI coupler shows a substantial reduction in device geometry. No s uch kind of devices with N > 2 has yet been realized up to now. The authors have demonstrated a 4 x 4 parabolically tapered MMI coupler with large cro ss section that can match the SM fiber in silicon-on-insulator (SOI) techno logy. The device exhibits a minimum uniformity of 0.36 dB and excess loss o f 3.7 dB, It represents a key component for realization of MMI-based silico n integrated optical circuit technology.