Double-slit apodizer for extending the depth-of-field of imaging linear barcode readers

Pupil apodization is often used in imaging linear barcode readers as a simple way to extend the depth-of-fleld (DOF) by reducing the numerical aperture of the optical system. As a matter of fact the invariance of linear barcodes in the bars direction can be exploited to engineer an apodizing mask which produces a point-spread-function (PSF) which is more invariant to defocus with respect to standard slit apertures. In this paper we will introduce a double-slit apodizer, more effective than standard single slit diaphragm in the DOF extension. The mathematical background of the invention will be discussed as long as the advantages of its industrial application. Finally the comparison between standard single-slit aperture and the proposed apodizer will be presented and discussed in terms of the achievable DOF for several resolutions.