Optical assembly for controlling beam size in bar code scanners

Details Optical assembly for controlling beam size in bar code scanners Optical assembly for controlling beam size in bar code scanners

1996-03-07

1998-02-10

Hajec, Donald T.

Registers

Coded record sensors

Particular sensor structure

235454, 359558, G06K 710

Patent

active

057171947

ABSTRACT:
In order to control the width of the scanning beam in the scanning direction over a significant range in front of the scanner, an optical assembly including a phase mask is utilized through which the beam passes after being configured into curved wavefronts, as by a lens which provides a focus in the vicinity of the far end of the range. The F/ number of the optical assembly is high and the cone of the beam in the scanning direction is small, for example, less than 5.degree.. The mask is preferably transparent and has a region which may be rectangular, elliptical or circular forming a step through which the center of the beam passes which imposes a phase change with respect to the phase of the wavefronts which do not propagate via the region. The phase change may be uniform or in the form of a weak quadratic phase variation in this region of the mask which changes phase and thus slightly refocuses the beam. The transmissivity of the region may also be varied and reduced with respect to the transmissivity of the mask outside of the region. The beam may be scanned via a scanning mirror or by scanning the optical assembly.

REFERENCES:
patent: 4808804 (1989-02-01), Krichever et al.
patent: 5080456 (1992-01-01), Katz et al.
patent: 5332892 (1994-07-01), Li et al.
patent: 5386105 (1995-01-01), Quinn et al.
patent: 5438187 (1995-08-01), Reddersen et al.
Casperson, L.W., How Phase Plates Transform and Control Laser Beams, May, 1994, pp. 223-228.

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