OPTICAL GRATING

摘要

According to one aspect of the invention, there is provided an optical grating comprising a substrate comprising a plurality of protrusions with a space in between any two adjacent protrusions; and a cap provided on at least one of the plurality of protrusions at an end that is furthest from the substrate, wherein the cap has a higher degree of optical attenuation compared to the substrate material and wherein the combination of each protrusion and the respective cap thereon has a generally symmetric cross-sectional profile.