Browse Prior Art Database

Off-Axis Scanning Holographic Double-Disk

IP.com Disclosure Number: IPCOM000035148D
Original Publication Date: 1989-Jun-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 3 page(s) / 54K

Publishing Venue

IBM

Related People

Dickson, LD: AUTHOR

Abstract

This article describes a holographic disk construction that provides reduced chromatic aberration, increased scan-angle range, increased scan-angle multiplication, more easily obtained aberration-free scanning, lower Fresnel-reflection losses, and greater light-collection efficiency. All of this is accomplished by using a "Double-Disk" sandwich construction for the holographic disk.

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Off-Axis Scanning Holographic Double-Disk

This article describes a holographic disk construction that provides reduced chromatic aberration, increased scan-angle range, increased scan-angle multiplication, more easily obtained aberration-free scanning, lower Fresnel- reflection losses, and greater light-collection efficiency. All of this is accomplished by using a "Double-Disk" sandwich construction for the holographic disk.

U. S. patent 4,245,882 describes a technique for making an on-axis holographic optical element by sandwiching together (emulsion to emulsion) two off-axis holographic optical elements. The major motivation behind Chang's patent was to provide a method for producing an on-axis holographic optical element (HOE), since conventional HOE's are generally used in an off-axis geometry.

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Generally, one would not envision using a sandwich design for off-axis HOE's since off-axis HOE's are easily generated with a single element design. However, the off-axis sandwich design has some unique properties that are particularly attractive in scanning disk applications.

The construction of a double-disk sandwich is shown in Fig. 1. A master/copy process is assumed along with use of Dichromated Gelatin (DCG).

H2 is constructed with the DCG emulsion on the lower side of Disk 2 so that incoming beam R2 produces the desired output beam, 0. H1 is constructed with the DCG emulsion on the upper side of Disk 1 so that the input beam R1 produces the desired output beam, R2.

When the two disks are sandwiched together, bottom of H2 to top of H1, with an index matching adhesive, the sandwich double-disk is formed. Illuminating the double-disk with a reconstruction beam equivalent to R1 produces the output beam 0.

Several double disk geometries will now be described along with the resultant advantages. All geometries will exhibit less chromatic aberration than a single disk. The geometries are shown in Figs. 2 and 3.

Geometry (A) will give an increased scan-angle multiplication with less aberration at the ends of the scan line than would be present for a single-disk scanner. This double-disk geometry will have lower Fresnel-reflection losses than a single-d...