(a) Schematic diagram of a planar HCG structure on a subwavelength scale under incident beam with E-field polarization perpendicular to the grating bars. (b) The reflectivity distributions calculated by FDTD method for the Si-bar width t in a range from 50 nm to 800 nm and wavelength from 1.2 μm to 2.0 μm. (c) The reflectivity distributions for the Si-bar thickness d in a range from 50 nm to 500 nm and wavelength from 1.2 μm to 2.0 μm. (d) Reflection coefficient and phase for a strictly periodic Si grating with T = 1 μm, t = 200 nm, and d = 250 nm.