Large-scale computer-generated absorption holograms of 3D objects: I. Theoretical background and visual concepts

Over many years, the subject of computer generation of holograms has been visited in various guises. Historically, the obvious restrictions imposed by computational power and computer generated hologram (CGH) fabrication techniques have placed limits on what can be taken seriously in terms of image complexity. Modern advances in computational hardware and electro-optic systems now permit both the calculation and the manufacture of CGH's of complex 3D objects which fill a significant volume of space. New methods permit the recording to be made within a reasonable timescale. In addition to advancing fixed CGH generation techniques, the motivation for the work reported here includes assessment of design algorithms, modulation strategies and image quality metrics. These results are of relevance for a novel electroholography system, currently under development at DERA Malvern. This paper describes a complete process of data generation, computation, data manipulation and recording leading to practical techniques for the creation of large area CGH's. As a support to the advances in theoretical understanding and computational methods, we describe (in Part II) a new laser plotter technique that enables, in principle, an unlimited size of pixel array to be plotted efficiently with a rigorous estimate of duration of the plot run time. The results reported here are limited to 2048 X 2048 pixels. In this example, the novel switching techniques employed on the laser plotter permit the pixel array to be printed in approximately 1 hour. However, paths towards easily raising the pixel count and its associated printing rate are presented for both the computational engine and laser plotting processes.