DISK HOLOGRAPHIC SCANNER WITH SCAN LINE CORRECTION
Original Publication Date: 1980-Jun-30
Included in the Prior Art Database: 2004-Apr-02
Xerox Disclosure Journal
Figure 1 illustrates a holographic scanning system wherein a number of holographic gratings 2 are formed on the surface of a reflective-type spinner 4. As the spinner is rotated about the rotor axis 6, a reconstruction light beam is incident on the spinner surface and is diffracted at some angle towards an image plane 10. Positioned between spinner 4 and image plane 10 is cylindrical lens 12. The purpose of lens 12 is to perform a transform between curved and linear space; e.g., in the absence of lens 12 the focus of the scan trace on image plane 10 would be a curved line. Lens 12 alters the nature of the scan beam in a number of important ways. If the scan angle/ approaches 90'O and the facet aperture is not increased to compensate for the decrease in the f# of the system in the sagittal direction, the holographic facet begins to act more like a cylindrical focusing element instead of a spherical focusing element. In the case where,& = 90°, the holographic facet functions as a cylindrical lens having focusing power and f# in the tangential plane determined by the grating properties of the hologram, while in the sagittal plane, the light would spread out from the small, effective aperture due to diffraction. It is apparent that the scanner, under these conditions,/=90° can be made to have the same f # in both the tangential and sagittal planes if a cylindrical lens is utilized to focus the sagittal rays to the image plane. The inclusion of lens 12 aliows a system designer to achieve a given f # in the sagittal plane independent of scan angle and facet aperture. This added flexibility permits larger scan angles to be utilized, which result in a straightening out of the scan line.