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Proceedings Paper

Diffraction analysis of beams for barcode scanning
Author(s): Jay M. Eastman; Anna Marie Quinn
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Paper Abstract

Laser based bar code scanners utilize large f/# beams to attain a large depth of focus. The intensity cross-section of the laser beam is generally not uniform but is frequently approximated by a Gaussian intensity profile. In the case of laser diodes the beam cross-section is a two dimensional distribution. It is well known that the focusing properties of large f/# Gaussian beams differ from the predictions of ray tracing techniques. Consequently analytic modeling of laser based bar code scanning systems requires techniques based on diffraction rather than on ray tracing in order to obtain agreement between theory and practice. The line spread function of the focused laser beam is generally the parameter of interest due to the one-dimensional nature of the bar code symbol. Some bar code scanners utilize an anamorphic optical system to produce a beam that that maintains an elliptical cross-section over an extended depth of focus. This elliptical beam shape is used to average over voids and other printing defects that occur in real world symbols. Since the scanner must operate over the maximum possible depth of field the beam emergent from the scanner must be analyzed in both its near field and far field regions in order to properly model the performance of the scanner.

Paper Details

Date Published: 1 February 1991
PDF: 10 pages
Proc. SPIE 1384, High-Speed Inspection Architectures, Barcoding, and Character Recognition, (1 February 1991); doi: 10.1117/12.25322
Show Author Affiliations
Jay M. Eastman, Photographic Sciences Corp. (United States)
Anna Marie Quinn, Photographic Sciences Corp. (United States)

Published in SPIE Proceedings Vol. 1384:
High-Speed Inspection Architectures, Barcoding, and Character Recognition
Michael J. W. Chen, Editor(s)

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