Browse Prior Art Database

Objective Lens Astigmatism Direction Control

IP.com Disclosure Number: IPCOM000110392D
Original Publication Date: 1992-Nov-01
Included in the Prior Art Database: 2005-Mar-25
Document File: 3 page(s) / 100K

Publishing Venue

IBM

Related People

Dimura, M: AUTHOR [+4]

Abstract

Disclosed is a technique to improve focus servo performance by controlling the inherent direction of astigmatic aberration of the objective lens in an optical disk drive which uses the astigmatic focus error sensing method.

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Objective Lens Astigmatism Direction Control

       Disclosed is a technique to improve focus servo
performance by controlling the inherent direction of astigmatic
aberration of the objective lens in an optical disk drive which uses
the astigmatic focus error sensing method.

      The astigmatic aberration influences onto S-curve linearity
(focus error signal slope) in the astigmatic focus error system,
especially with the astigmatic lens.  This results in much more cross
talk noise between the focus error signal.  This problem is solved by
the disclosed technique.

      The disclosed technique will be best understood with reference
to Figs. 1 and 2.  Fig. 1 shows a typical optical path configuration
of an optical disk drive and Fig. 2 shows an example wherein the
inherent direction of astigmatic aberration of the objective lens is
controlled by the disclosed technique.

      The concept of the disclosed technique is to control the
orientation of the astigmatic axis of the objective lens with respect
to grooves of the optical disk when the objective lens is mounted
into the focusing actuator (fine actuator).  Since these grooves are
at a fixed orientation with respect to the cylindrical axis of the
astigmatic lens, the orientation of the astigmatic axis of the
objective lens with respect to the cylindrical axis of the astigmatic
lens is controlled as shown in Fig. 2.  First, the inherent
astigmatism of the objective lens is determined and then its
o...