Design and fabrication of a diffractive bar code scanner

A novel bar code scanner that uses plane diffraction gratings on a flat rotating disk as the means of flying-spot laser scanning is designed and implemented. The design incorporates diffraction gratings that provide large angles of diffraction so that the lines generated in the bar code target region have sufficiently large radii for scanning most bar codes. The rotational symmetry exhibited by diffraction from plane gratings with incidence perpendicular to the grating surface is advantageous for the scanner system. The feasibility of the design is demonstrated by a prototype scanner consisting of commercially available diffraction gratings, an off-the-shelf focusing lens, and supporting optomechanical structures and electrooptics. The design concept is further developed towards fabrication and implementation of a custom-designed diffractive disk that can be readily injection molded with state-of-the-art Compact Disk (CD) replication technology. A stigmatic single-element focusing lens is also designed for the scanner system. Recent developments in diffractive optics mastering and replication technologies provide the impetus for this thesis; the possibilities of high efficiency mastering and inexpensive mass-replication of diffractive elements are driven by the semiconductor industry and continue to blossom. The diffractive disk designed in this thesis, however, does push the limits of the new technologies. A significant effort in creating a diffractive master for subsequent replication using a gray-scale mask microlithographic technology is presented. The thesis work falls short of an adequate master for replication. However, alternative mastering techniques for continuation of the project are suggested