GB1218331A - Optical data recording - Google Patents

Abstract

1,218,331. Holography. INTERNATIONAL BUSINESS MACHINES CORP. March 14, 1969 [April 9, 1968], No.13456/69. Heading G2J. A method of holographically recording data comprises bringing together at a recording medium 12 a reference beam 13 and a data beam 10, wherein the transmitted part of the reference beam 15 is redirected through the medium 12 at a location continuing to receive the data beam. The redirected reference beam may be caused to retrace its original path through the medium, or it may return along its original path in the reverse direction. In reconstruction the reference beam follows the same paths as the original reference beam 13 and consequently forms two coincident vertical images at the location of the original object or data source. The transmitted part of the beam 15 may be redirected by a plane mirror 16. If the mirror and reference beam source, laser 14, are interchanged real images are set up. The data record can be used to align optical apparatus by comparing the coincidence of the real or vertical image and the original object. In an alternative embodiment the recording medium is located between a pair of concave mirrors, one of which has an aperture for passage of the reference beam. This beam is caused to re-pass through the medium several times, always from the same side, the number of passes being determined by the resolution of the medium. A further embodiment replaces each concave mirror by two orthogonal reflecting surfaces, the transmitted part of the reference beam repassing the recording medium alternately through opposite sides.