Multi-layer optical storage disc based on the frequency up-conversion effect from rare-earth ions

The application of frequency up-conversion in rare earth (Ho³⁺ and Yb³⁺) co-doped glasses for optical storage has been investigated. Optical discs with the storage layer made from rare-earth doped tellurite glasses have been studied in terms of minimum bit-size and up-conversion efficiency. The possibility of multi-layered architecture has also been investigated. The choice of using tellurite glasses is based on previous experimental results indicating this type of materials gives extremely high up-conversion efficiency. Since the up-conversion effect is dependent on the square of the intensity of the pump beam, it is possible that the 'effective' spot size of the signal region can be a significantly smaller than that limited by diffraction, hence leading to super-resolution in the storage layer and increased storage density.