| 摘要 |
A system for the reading of information elements stored in optical form makes use of the fact that the light of the illumination source of the optical disk is a coherent source to constitute a hologram on an array of photodetectors. This hologram is the composition of the unmodulated incident beam of the source with the beam reflected by the disk, modulated by the information elements to be read. An operation comprising signal processing by Fourier transform, shifting in the spatial frequencies plane and reverse Fourier transform is used to reach the information elements recorded on the disk. The detection of the information elements can be far more complete than in the case of the conventional reading of optical disks for it brings into play not only the total modulation of light energy of the laser beam but also the phase modulation. This makes it possible to increase the information storage density, reduce the precision needed for the optical and mechanical systems of the reader and carry out electronic signal processing operations to correct optical system defects and focusing defects.
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