Abstract

Because electron beam lithography is currently tailored to meet the needs of the integrated circuit industry, its use in the production of computer-generated holograms can be difficult. In the case of the Cambridge e-beam machine, exposure patterns are limited to collections of rectangles and a small number of trapezoids. On this machine, fringe patterns are drawn by fitting rectangles together in an effort to approximate the desired fringe. This method introduces an undesirable noise from scattering at the corners of the rectangles. To produce a better hologram one needs the ability to control the exposure of each tiny exposure element or exel. Unfortunately the file size required to completely specify the fringes in this manner is unmanageable. An alternate pattern data format which utilizes a combination of run length encoding and an adaptive compression technique called Lempel-Ziv-Welch compression can be used to achieve significantly smaller pattern data files. This method has been tested on holograms that produce a spherical wavefront at about one fringe line pair per micron. The result is a file size that is 16 times smaller than the equivalent bit-mapped representation and about 103 times smaller than the standard pattern data format.

© 1989 Optical Society of America