Data Storage in Optical Discs with Nano-Structured Gratings
Hans Joachim Eichler
Microholographic data storage combines the potentially high capacity of holographic storage systems with the mature compact disc and DVD technology. Amicroholographicwrite-systemuses twocounterpropagating strongly focussed laser beams generating a microscopic reflection grating in a photopolymer disc. The grating planes with submicron diameter are perpendicular to the beam directions diameter and have a period of about 130 nm for a write wavelength of about 400nm. The axial extension of the grating may be in the order of 5mm. These nanostructured, reflective microgratings are read out by a single laser beam so that the pickup may be similar as in a DVD-drive and downward compatible.The microgratings can be written along a spiral path into a photopolymer disc with an aerial density close to the pit density on a compact disc. Several layers of microgratings have been written parallel to the photopolymer surface to increase the storage capacity beyond the DVD-limit. Further increase of the storage capacity is possible by writing overlapping gratings with different periods using several different wavelengths. The construction of microholographic write and read devices as well as investigations of storage materials is overviewed.