  We report a comprehensive study on the performance of uniform and non-uniform
based subwavelength grating couplers in Silicon-on-Insulator. The two
performance metrics, coupling efficiency and bandwidth enhancement and
trade-offs is presented. We also present, design parameters to achieve
high-efficiency and broadband operation based on the detailed study of various
loss mechanisms in the grating. Based on the detailed analysis subwavelength
grating coupler designs with efficiency as high as 84 % with a 1 dB bandwidth
of 50 nm and 98 % with a 44 nm 1 dB bandwidth is presented.
