Holographic Line Beam Scanner with Liquid Crystal on Silicon Modulator

Abstract

A laser scanning device can be used for contour or pattern reconstruction with associated image processing or recognition algorithm. For a better accuracy or accommodating to a high efficiency algorithm, the laser beam often needs reshaping to a specific pattern, such as a line beam, or homogenization so as to reduce the spatial variation of the device performance. In addition, a scanning mechanics is normally inevitable. Both beam shaping and scanning module take quite a volume in the whole system, which could be an issue for the applications in which miniature device is highly desired. In this paper, a holographic scanner has been proposed to perform both laser beam shaping and scanning function. A pure phase modulation liquid crystal on silicon (LCoS) device is used for implementing the dynamic hologram. The LCoS has a pixel size of 3.74 mu m, and provides 16 phase level with a full phase depth of 2 pi. A line beam with 20mm and uniformity up to 70% is generated and it is scanned back and forth in the orthogonal direction of the line with a stroke of 20mm. The scanning line pattern is generated based on iterative Fourier transform algorithm (IFTA) and the first diffraction order pattern is exploited with the zero order being blocked and absorbed so that the noise in the scanning line pattern is minimized. The proposed scheme is a compact and versatile solutions for patterned laser beam scanning devices.