A fully etched high efficiency silicon nitride waveguide grating coupler

The rapid development in the field of optoelectronic integration requires highly efficient coupling between optical fibers and on-chip waveguides. Here, we report an efficient vertical grating coupler which is compatible with COMS process and suitable for silicon nitride photonic integration. The optimized design, fabrication and optical characterizations are presented in details for a silicon nitride waveguide grating coupler. The preliminary results show that the output power of the optimal device structure is 0.25dBm, in good agreement with the simulation result. The fully etched waveguide design needs only one-step etching, which greatly simplifies the fabrication process. Meanwhile, spin coating of Ma2400 series photoresist is innovatively used instead of evaporating SiO2 as the cladding layer of the device, which offers an efficient and economic way to obtain a flat top surface for integration of other devices. Our study provides an alternative method for the heterogeneous integration of functional devices on the COMS compatible silicon nitride platform.