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In recent years there has been a resurgent of research activities in the area of computer-generated holograms. The results of these activities have been the development of tools and methodologies for making the computer-generated holograms. The tools for making computer-generated holograms have progressed from the CRT displays, computer plotters and computer printers used in the 60's and 70's to more sophisticated systems such as laser scanners and E-beam graphic output devices. Many techniques for encoding the wavefront information into the holograms have been investigated 4. Moreover, the limitations imposed on the performance of the computer-generated holograms by the resolutions of the output systems have also been fully explored. It has also been recognized that computer-generated holograms are more versatile and are more compact than conventional lenses. However, the replacement of lenses by computer-generated holograms has not yet taken place due to difficulties both in material processing and fabrication in achieving high light diffraction efficiency in the holographic optics. It is interesting to note that computer-generated holograms belong to the class of diffractive optical elements. With this point of view, one discovers that computer-generated holograms have already been employed in many practical optical applications. For example, multiple beam gratings generated by computer or other means are used currently in compact disc audio players. More recently, computer-generated holograms are further utilized in compact audio disc players and optical disk drives to replace many of the conventional optical components. In this paper we will discuss a number of different computer-generated holograms which have been used in optical data storage systems. The fabrication process of each of these optical elements are also briefly reviewed.
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