POLARIZATION OF BARCODE READERS

In high-quality barcode readers, specular reflection from shiny barcod es is blocked by using a polarized scan laser and a crossed polarizer in front of the detector. When complex scanning geometries are require d, the polarization properties of the mirrors in the system can become a limiting factor in system performance. Polarization raytracing allo ws systems such as barcode readers, LIDAR systems, and other polarizat ion-critical systems to be accurately characterized, Polarization rayt racing often requires the use of a local, ray-based coordinate system for expressing rays' polarization states. yet the choice of coordinate system can have important implications on system analysis. An example is presented in which specular reflection is controlled in a barcode reader by using reflection-enhanced coatings on only one of the four s ets of the mirrors in the system. The coordinate system used to expres s rays' polarization states in the example system provides useful less ons for other systems. The other analytical methods used in this examp le can be applied to a variety of scanning systems. (C) 1998 society o f Photo-Optical Instrumentation Engineers.