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Browse Prior Art Database

Lens Pair for Fine Focusing of Optical Storage Device

IP.com Disclosure Number: IPCOM000104104D
Original Publication Date: 1993-Mar-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 4 page(s) / 95K

Publishing Venue

IBM

Related People

Stahl, RP: AUTHOR

Abstract

In a typical Optical Storage Device, the optical path begins at a laser diode/collimator package that provides a collimated beam. This beam is focused through an objective onto the surface of a medium. The objective is typically held in an actuator that provides two axis of fine motion; axially for focus control of the spot on the medium, and perpendicular to the medium direction of motion to follow run-out of data tracks. Seeking of the optical drive from track to track is performed by movement of the two axis actuator and objective by a coarse positioning actuator. One of the limits to drive access time is the mass which must be moved by the coarse actuator. Light reflected from the medium is collected and re-collimated by the objective and is sent, via a beam splitter, to data and servo signal generation optics.

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Lens Pair for Fine Focusing of Optical Storage Device

      In a typical Optical Storage Device, the optical path begins at
a laser diode/collimator package that provides a collimated beam.
This beam is focused through an objective onto the surface of a
medium.  The objective is typically held in an actuator that provides
two axis of fine motion; axially for focus control of the spot on the
medium, and perpendicular to the medium direction of motion to follow
run-out of data tracks.  Seeking of the optical drive from track to
track is performed by movement of the two axis actuator and objective
by a coarse positioning actuator.  One of the limits to drive access
time is the mass which must be moved by the coarse actuator.  Light
reflected from the medium is collected and re-collimated by the
objective and is sent, via a beam splitter, to data and servo signal
generation optics.

      Fig. 1 shows the Focus of the laser beam onto the medium
surface is critical for maintaining small spot sizes at the medium.
The objective focus actuator is controlled by a servo that receives
its input from a focus detector.  There are many focus detector
schemes in use on optical drives and common to all of these schemes
is that they are measuring the collimation of the returning beam as
it enters the servo signal generation optics.  When the objective is
not focused onto the medium surface, the beam returning from the
objective will either be converging (for objective positioned too far
from the medium) or diverging (for objective positioned too close to
the medium).

      This disclosure presents a focus actuator which can be placed
off of the coarse actuator, reducing coarse actuator mass.  It is
also compatible with current focus detector schemes.  This actuator
contains an afocal lens pair whose s...