Optical scanner using an axicon and an aperture to aspherically form the scanning beam

摘要

The use of linear axicons or similar optical elements in a bar code scanner produces a scanning spot of a size correlated generally with dimensions of features of the scanned information, wherein the spot size remains substantially constant for varying distances between the scanner and the symbol over a substantial range of distances. Optical elements of this type produce a diffraction pattern comprising a central lobe and a number of rings surrounding the central lobe. An aperture is provided to limit the beam and thus the number of rings in the pattern which actually reach the symbol during scanning. The extent of the limited beam and the phase front tilt angle produced by the optical element are chosen to produce a desired resolution, which relates to the density of symbols the scanner is to read, and to produce a desired working range. The invention also provides a modular light emitting device including a universal light emitting module and an optical assembly, including the axicon and aperture, mounted on the module to adapt the optical characteristics of light from the module to conform to the requirements of a particular scanning application.