High efficiency and polarization insensitive two-dimensional grating coupler on silicon

We design and demonstrate a two-dimensional grating coupler with high efficiency and low polarization dependent loss. An efficiency of -1.76dB at O-band is realized with the enhancement of a bottom metal mirror. Using two crossing ellipses as the grating cell, the PDL can be reduced to 0.2dB in a wavelength range of 67nm.