Optical storage disc based on the frequency up-conversion effect from rare earth ions

The application of infrared-to-visible upconversion in rare earth (Ho/sup 3+//Yb/sup 3+/) co-doped TeO/sub x/ sol-gel thin film for optical storage has been investigated. Optical discs with the storage layer made from rare-earth co-doped TeO/sub x/ sol-gel thin films have been studied in terms of minimum bit-size and up-conversion efficiency. The possibility of a multi-layered architecture has also been investigated. The choice of using TeO/sub x/ thin films is based on the higher up-conversion efficiency in the rare earth doped chalcogenide glasses. The nonlinear properties of the up-conversion effect lead to the possibility of reducing the 'effective' spot size of the signal region, smaller than that limited by diffraction, hence leading to super-resolution in the storage layer and increased storage density.