Performance Enhanced Butt Coupling for Effective Interconnection Between Fiber and Silicon Nanowire

Abstract

A performance enhanced butt coupling structure incorporating a vertically and laterally tapered SiON polymer core on silicon (Si) to tunnel and widen propagating optical modes of adiabatic taper is proposed. The proposed structure can effectively overcome the strong back reflections caused at the interface between fiber and Si nanowire to enable higher coupling efficiency. The placement of the SiON polymer core is chosen to restrict the passage of light through the bottom cladding to avoid unnecessary leakage. The performance of the structure is characterized for distinct features, including taping length, coupling efficiency, and coupling bandwidth for both single as well as cacaded configurations, compared with the state-of-the-art grating coupler. It is found that, with the right set of design specifications, butt couplers can outperform grating couplers in both coupling efficiency and bandwidth, although grating couplers are considered friendlier for wafer-level testing.