The optical storage medium, in particular a read-only optical disc, comprises a substrate layer, a read only data layer comprising a pit structure and being arranged on the substrate layer, a mask layer comprising nanoparticles for providing a super resolution near field effect, and a dielectric layer arranged between the data layer and the mask layer. The dielectric layer has a thickness, which changes in dependency of the pit structure and is for example a plastic layer having a completely flat surface for providing a uniform arrangement of the nanoparticles. For the manufacturing of a respective optical storage medium, the dielectric layer is arranged on the data layer advantageously by means of spin coating.