Tailoring freeform lenses for barcode lighting

In this paper we will describe a high efficiency lighting system for imaging barcode readers equipped with a freeform element which shapes the incoherent beam emitted by LEDs, in order to form a sharply defined, high uniformity, illumination pattern. The freeform optical element has been designed assuming the polynomial expansion of the surface equation; the coefficients have been calculated running a least-mean-square optimization, targeting both the uniformity of the pattern and its irradiance value. Computer ray tracing has been carried out for both the generation of the surface and the simulation of the lighting pattern. The injection-molded prototypes we realized showed a good agreement with the predicted performances. A collection efficiency as high as 65% has been achieved along with an outstanding sharpness of the illuminated area within the whole depth-of-field of the reader.