A high index contrast grating (HICG) structure is disclosed. The HICG structure includes plurality of gratings fabricated from a high refractive index layer. The high refractive index layer is situated over a low refractive index substrate, wherein the high refractive index layer is patterned after determining a period and a duty cycle of each of the plurality of gratings for a desired reflection phase profile based on a lookup table. The low refractive index substrate includes sapphire. The plurality of gratings includes polycrystalline or amorphous silicon. The HICG structure includes subwavelength gratings for incident wavelengths of equal to or greater than 2.5 microns. An exemplary method for forming the HICG structure is also disclosed.