A method including forming a substrate to form a template which includes areas of high relief and areas of low relief; and forming a high refractive index diffraction grating in the template by adding high refractive index material to the template to form a continuous low relief surface. The high refractive index material fills the areas of low relief and covers the areas of high relief of the template to form a high refractive index diffraction grating. The high refractive index diffraction grating includes the high refractive index material configured to have a low relief side corresponding to the continuous low relief surface and configured by the template to have a periodic side including areas of high relief and areas of low relief which periodically alternate in the first direction with the first periodicity and are interconnected by the high refractive index material.