Image-forming apparatus

Abstract

Apparatus for forming at or closer than infinity an image of a primary image source is disclosed. The apparatus employs a reflection-type holographic analog of a spherical mirror and a birefringent array of optical elements. The primary image source is linearly polarized and made incident upon the holographic mirror analog. The light from the primary image passing through the analog is given a circular polarization by a first quarter-wave plate, and a fraction of this light is reflected by a plane beam-splitting mirror back to the analog where it is collimated and transmitted again through the first quarter-wave plate, beam-splitting mirror, a second quarter wave plate and a second polarizer for viewing by an observer. The remaining fraction of circularly polarized light from the primary image passing through the first quarter-wave plate which is not reflected by the beam-splitting mirror passes through the second quarter-wave plate, which gives that light a linear polarization at a 90.degree. angle to the polarization direction of the second polarizer so that it is blocked from viewing by the observer. Although the holographic analog is produced with monochromatic light, there is no dispersion of the broad band polychromatic image source because the analog acts as a narrow band filter in the apparatus. The use of the holographic analog reduces the bulk of prior art image-forming apparatus and eliminates undesired optical aberrations encountered with the use of curved glass mirrors in prior art apparatus.