Browse Prior Art Database

Athermalization of an Optical System Through Proper Lens Design

IP.com Disclosure Number: IPCOM000120876D
Original Publication Date: 1991-Jun-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 84K

Publishing Venue

IBM

Related People

Gardner, TS: AUTHOR [+2]

Abstract

In an optical storage drive, means for maintaining proper focus of the high numerical aperture objective lens is required. An error signal created through optical means is exploited, along with the proper electronics, to move the objective lens in such a way as to keep it in focus on the surface of the storage media. The Astigmatic Focus Servo technique is a common example of an optically generated focus error signal (1),(2). Fig. 1 displays the essence of the Astigmatic Focus Servo Systems. Note that the 4-segment (quadrant) detector must be placed at the circle focus position for proper usage. The separation between the astigmatic lens and this quadrant must be held to typically better then +/- 10 microns over the wide temperature ranges that optical drives will experience.

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Athermalization of an Optical System Through Proper Lens Design

      In an optical storage drive, means for maintaining proper
focus of the high numerical aperture objective lens is required.  An
error signal created through optical means is exploited, along with
the proper electronics, to move the objective lens in such a way as
to keep it in focus on the surface of the storage media.  The
Astigmatic Focus Servo technique is a common example of an optically
generated focus error signal (1),(2).  Fig. 1 displays the essence of
the Astigmatic Focus Servo Systems.  Note that the 4-segment
(quadrant) detector must be placed at the circle focus position for
proper usage.  The separation between the astigmatic lens and this
quadrant must be held to typically better then  10 microns over
the wide temperature ranges that optical drives will experience.  In
general, this problem has been solved by properly choosing the
materials of the detector holder, the lens mount, and the overall
housing, in a way that exactly compensates for the thermally induced
changes in the optical properties of the lens (2). More recently, it
has been proposed (3), in a general sense, to do the opposite.  In
other words, to properly choose the optical properties of the lens in
such a way as to exactly compensate for a fixed set of materials.

      Disclosed is a method, similar to the latter technique, for
maintaining the proper separation between the astigmatic lens system
and the quadr...