Illumination apparatus with polarizing elements for beam shaping

A scanner for reading indicia having light and dark areas comprising:

• (1) illumination apparatus for forming an output beam including:
• (a) a support structure;
• (b) a light source including a laser diode and a lens mounted to said support structure for directing a source beam light in a downstream direction along an optical axis and focusing the source beam at a focal location on said optical axis, the light of the source beam having a polarization direction transverse to the axis;
• (c) a birefringent plate having a hole therein mounted to said support structure so that said hole is aligned with said axis and the fast axis of the birefringent plate is transverse to the optical axis, said hole being sized so that a peripheral portion of said source beam impinges on said birefringent plate around said hole whereas a central portion of said source beam passes through said hole;
• and
• (d) a polarizer mounted to said support structure downstream from said birefringent plate, said polarizer having a transmission axis transverse to said axis;
• (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.

A method of scanning information-bearing elements comprising:

• (1) providing an output light beam by:
• (a) directing a source beam of linearly-polarized light in a downstream direction along an optical axis;
• (b) nonuniformly altering the polarization direction of said source beam by intercepting only a portion of said source beam with a birefringent plate to provide 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;
• and
• (c) passing the altered beam through a fixed polarization-selective element having a transmission axis so as to allow light having a polarization direction matching the transmission axis of said fixed polarization-selective element to pass downstream into an output beam and substantially exclude components with polarization directions perpendicular to the transmission axis of said fixed polarization-selective element from said output beam;
• (2) moving said output beam relative to the information-bearing elements so that the output beam passes over light and dark regions of the information-bearing elements at different times, and
• (3) detecting light reflected by the information-bearing elements so as to produce a signal representing the light and dark regions.

Illumination apparatus for forming an output beam, the apparatus comprising:

• (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;
• wherein said source includes a laser diode;
• wherein said source further includes a lens downstream of said laser diode, said lens focusing light from said laser diode at a focal location on said axis;
• and wherein said birefringent plate abuts said lens.