Patent ID: 6714351
Filing Date: 2004-03-30
Classification: G02B,G06K,Y10S

Abstract:
A scanner for reading indicia having light and dark areas comprising:(1) illumination apparatus for forming an output beam, the illumination apparatus including: (a) a light source adapted to emit a source beam of linearly-polarized light in a downstream direction along an optical axis, said source beam having a polarization direction transverse to said axis; (b) a fixed birefringent plate that intercepts only a portion of the source beam, said birefringent plate having a fast axis transverse to said optical axis so that the polarization of said source beam is altered only in that portion of the source beam which is intercepted by said birefringent plate so as to form an altered beam having a first portion with a first polarization direction and a second portion with a second polarization direction transverse to said first polarization direction, said first portion having a first intensity distribution relative to said axis, said second portion having a second intensity distribution relative to said axis; (c) at least one polarization-selective element mounted downstream from said birefringent plate, at least one of said polarization-selective element being operative to allow transmission of light having one polarization direction and to prevent transmission of light having another polarization direction, (2) means for sweeping the output beam across the indicia so that the output beam impinges on the light and dark areas of the indicia at different times during such sweeping and so that light reflected from the indicia will have amplitude which varies depending on whether the beam is impinging on a light area or a dark area; and (3) a photodetector for receiving the light reflected from the indicia and producing a signal representing the amplitude of said reflected light, whereby said signal will vary in accordance with said light and dark areas of said indicia.