Browse Prior Art Database

AC FOCUSING SYSTEM FOR AN OPTICAL DISC

IP.com Disclosure Number: IPCOM000024870D
Original Publication Date: 1982-Feb-28
Included in the Prior Art Database: 2004-Apr-04
Document File: 2 page(s) / 73K

Publishing Venue

Xerox Disclosure Journal

Abstract

Although marking materials for optical disc applications should exhibit very low reflectivity to maximize light absorbed thereby providing an optimum marking sensitivity, some reflectivity is required if optical focusing with marking radiation is implemented in a writing engine. For many materials such as dyes, existing focusing schemes do not perform adequately because the reflectivity is low.

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XEROX DISCLOSURE JOURNAL

AC FOCUSING SYSTEM FOR AN OPTICAL DISC US. C1. 350/255
Vlad Novotny
Michael A. Hopper
George Horner

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Proposed Classification

Int. Cl. G02b 7/02

-----

- - - - - -- SINGLE CR DIFFERENTIAL

1 PHOTCOETECTOR

----La IN

-. - AMPLI FlER

- - -LOUDSPEAKER 8

OWECTIM: LENS

----- OPTICAL DISC SUBSTRATE

Although marking materials for optical disc applications should exhibit very low reflectivity to maximize light absorbed thereby providing an optimum marking sensitivity, some reflectivity is required if optical focusing with marking radiation is implemented in a writing engine. For many materials such as dyes, existing focusing schemes do not perform adequately because the reflectivity is low.

This disclosure describes a very sensitive focusing scheme for low reflectivity systems. As in other systems, an objective lens is attached to the voice coil of the modified loud speaker which provides the translational motion needed to keep the light focused on the marking surface. A small AC signal is superimposed on the translational motion and this results in small AC changes in the intensity of the reflected light falling on the photodetector. The signal from the detector is coupled into a lock-in amplifier which provides a phase sensitive DC signal capable of being used in a feedback system to control the magnitude and direction of the translational motion of the lens. Use of AC detection provides a considerable increase in focusing sensitivity when compare...