An efficient and broadband perfectly vertical grating coupler is reported based on asymmetric grating trances on SOI. The symmetrical nature of the diffraction is broken by implementing steps grating at one end of the primary groove while another end kept unaltered. The vertically incident light on the engineered subwavelength grating surface diffracted and coupling with the nano waveguide efficiently for the broad wavelength range in the C band by reducing backward propagation, reflection at the incident and coupling into the substrate simultaneously.
Our method for vertically incident light coupling between dimension mismatch waveguides provides solution in packaging problem for the high dense photonic integrated circuits (PIC).