Fabrication of 4×4 tapered MMI coupler with large crosssection

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