Image-forming apparatus

• US 3,940,203 A
• Filed: 04/01/1975
• Issued: 02/24/1976
• Est. Priority Date: 04/01/1975
• Status: Expired due to Term

• Current Assignee: Farrand Optical Company Incorporated
• Original Assignee: Farrand Optical Company Incorporated
• Inventors: La Russa, Joseph Anthony
• Primary Examiner(s): Stern, Ronald J.
• Application Number:
  US05/564,188
• Time in Patent Office: 329 Days
• Field of Search: 350/3.5, 350/147, 350/157, 350/293, 35/12 N
• US Class Current: 359/15
• CPC Class Codes: G02B 5/3083 Birefringent or phase retarding elements G02B5/3008, G02B5/3016 take precedence; systems for polarisation control G02B27/286; manufacturing phase modulating patterns by lithographic processes G03F7/001
• CPC Class Codes: G02B 5/32 Holograms used as optical elements

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° 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.

Claims

1. Image-forming apparatus comprising:

a. a reflection-type holographic analog of a curved mirror;

b. a first quarter-wave plate disposed on a side of of the holographic analog corresponding to the concave side of the mirror;

c. a plane beam-splitting mirror disposed on the side of the first quarter-wave plate remote from said analog;

d. a second quarter-wave plate disposed on the side of the beam-splitting mirror remote from said first quarter-wave plate; and

e. a polarizer on the side of the second quarter-wave plate remote from said beam-splitting mirror;

the first and second quarter-wave plates having their fast axes oriented with respect to each other at a first substantially integral multiple of 90°

, and the polarizer having its direction of polarization oriented substantially at an odd integral multiple of 45°

to the fast axis of the second quarter-wave plate.

2. Image-forming apparatus according to claim 1 further comprising:

another polarizer disposed on the side of the analog remote from the first quarter-wave plate, the direction of polarization of said polarizer and said other polarizer being oriented with respect to each other at a second substantially integral multiple of 90°

, both said first and second multiples of 90°

being even or both being odd.

3. Image-forming apparatus according to claim 1 wherein said holographic analog is an analog of a concave spherical mirror.

4. Image-forming apparatus according to claim 1 wherein said analog, quarter-wave plates, plane beam-splitting mirror and polarizer are constituted of flat sheets assembled together in a package.

5. Apparatus for forming at or closer than infinity a dispersion-free image of a polychromatic primary image comprising:

a reflection-type monochromatic holographic analog of a concave mirror arranged to receive light from said primary image on a side of the analog; and

optical means associated with said analog for reflecting a fraction of the light transmitted from said primary image through said analog back to the other side of the analog of said mirror for reflection thereby;

for transmitting light so reflected to an observer; and

for blocking the direct transmission of light transmitted from said primary image through said analog to said observer.

6. Apparatus according to claim 5, said holographic analog acting as a reflection filter, selecting and collimating a narrow band of illumination from said polychromatic primary image.