Materials for multilayer recording

An attractive feature of optical discs is their capacity. Recent research has indicated that the capacity of optical discs can be increased by using multiple layers of bitwise data. Layers are spaced along the depth dimension of the discs. Individual layers are recorded and information is retrieved in a manner that is very similar to conventional optical disc systems using a single layer. The data capacity of each layer is nearly equal to the capacity of a single layer, thus increasing the capacity of a disc by a factor equal to the number of layers. In fact, dual-layer optical discs are already commercially available. With some storage materials, it is possible to record hundreds of data layers. However, system engineering trade-offs, like readout speed, are of concern. More conventional materials can also be used for multilayer recording, but the number of layers is limited by the transmission properties of each layer. This article reviews the materials systems for multilayer recording, the interplay between materials properties and performance, and the optical systems used for multilayer recording.