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Holographic Disc Test Apparatus

IP.com Disclosure Number: IPCOM000045889D
Original Publication Date: 1983-Apr-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Wolfheimer, AD: AUTHOR

Abstract

This article describes a differential circuit for locating the interface between two adjacent facets on a holographic disc. A timing mark is placed on the disc at a known angular displacement from the interface.

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Holographic Disc Test Apparatus

This article describes a differential circuit for locating the interface between two adjacent facets on a holographic disc. A timing mark is placed on the disc at a known angular displacement from the interface.

A known type of supermarket checkout scanner uses a rotating disc as a beam deflecting element. The disc carries an annular ring of perhaps twenty holographic generated facets. The disc also carries a timing mark which is used in measuring disc rotational speed. The timing mark has to be placed at a precise position relative to the interface between two adjacent facets. Experience has shown that it is extremely difficult to visually detect the exact location of the interface.

Referring to the drawing, the illustrated circuit can be used to locate the interface. When a beam 10, generated by a laser 12, passes through disc 14, a single output beam is normally generated. However, when the beam is at an interface, two output beams 16 and 18 are generated. The locations of beams 16 and 18 depend upon the holographic characteristics of facets 20 and 22, respectively. The beams 16 and 18 are directed at a pair of photovoltaic devices 24, 26, connected in a bucking configuration. A microammeter 28 is connected across the series combination of the devices 24 and 26. Assuming the facets 20 and 22 have the same diffraction efficiency, beams 16 and 18 have the same intensity when the laser beam 10 is on the interface between facets 20...