System for optical recording of data on disks and corresponding methods of reading and writing.

摘要

The invention relates to a system for recording data on an optical disk. Present-day optical disks, readable with lasers of visible wavelengths (between 0.5 and 0.8 microns), have a surface-storage density which is at most of the order of 1 data bit per elementary surface region of about 1 square micrometre. Below that, diffraction does not make it possible to distinguish neighbouring regions. The invention proposes a means for considerably increasing storage capacities: into an elementary region (14) of a layer (16) is inscribed an information bit not in the form of an absorption spot of a laser light, but in the form of a diffracting grating having a specified spacing. Several diffracting gratings with mutually differing spacings can be superimposed on the same spot, enabling several information bits to be inscribed in the same region of the disk. The diffracting gratings are produced by a periodic local variation of the optical index of the layer. They are produced by a high-energy laser beam, in a material whose index can vary as a function of this energy. Reading is done by a frequency-tunable laser (22) which makes is possible to detect, for various frequencies, the presence or the absence of diffracting gratings. <IMAGE>