Laser scanning system employing light collection surfaces having optical axes disposed off the bragg angle of the holographic optical elements of the holographic scanning disc thereof

摘要

A holographic laser scanning system for scanning bar code symbols. The system comprises a holographic scanning disc having a plurality of holographic optical elements disposed thereon for scanning the plurality of laser beams directed at the same incident angle. Each holographic optical element as substantially the same Bragg angle. The parabolic light reflective surfaces are disposed beneath the holographic scanning discs. Each parabolic light reflective surface has an optical axis disposed off the Bragg angle of the holographic optical elements, for focusing towards a focal point above the holographic scanning disc, the reflected light rays collected by each holographic optical element. A photodetector is disposed at the focal point of the corresponding parabolic light reflective surface above the holographic scanning disc, and is radially aligned with the optical axis of one parabolic light reflective surface. The light diffraction efficiency of each holographic optical element at the angle of incidence of each laser beam during scanning is substantially greater than the light diffraction efficiency of the focused laser light transmitted from each parabolic light reflective surface through the holographic optical elements towards corresponding photodetector during light detection. This enables the collected light rays, focused by the parabolic light reflective surface, to be efficiently transmitted through the holographic optical elements, to the photodetector for detection and generation of a scan data signal for subsequent processing. By virtue of this novel arrangement, the present invention enables the construction of a holographic laser scanner having substantially reduced height characteristics.