Browse Prior Art Database

Active Collimation for Substrate Astigmatism Compensation

IP.com Disclosure Number: IPCOM000106266D
Original Publication Date: 1993-Oct-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 2 page(s) / 81K

Publishing Venue

IBM

Related People

Finkelstein, BI: AUTHOR [+6]

Abstract

Optical data storage media substrate's vertical birefringence introduces astigmatism in the optical path, which can be compensated by detuning the laser collimation, i.e., by adjusting the spacing between the laser diode and the collimation lens. Since this vertical birefringence is different amongst material and stamping process, by making the collimation system active, the drive then can adjust to the astigmatic correction that works best for any given disk, improving both data integrity and seek reliability.

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Active Collimation for Substrate Astigmatism Compensation

      Optical data storage media substrate's vertical birefringence
introduces astigmatism in the optical path, which can be compensated
by detuning the laser collimation, i.e., by adjusting the spacing
between the laser diode and the collimation lens.  Since this
vertical birefringence is different amongst material and stamping
process, by making the collimation system active, the drive then can
adjust to the astigmatic correction that works best for any given
disk, improving both data integrity and seek reliability.

      The Figure shows the experimental data of wavefront rms (dotted
line) and normalized astigmatism (solid line) as a function of the
collimation lens position.  This suggests that the range of motion
required between the collimation lens and the laser diode is on the
order of microns.  This motion can be achieved using micromechanism
on the laser diode or piezo-electric transducer on the collimation
lens.

      The mechanism should be designed so that its default or rest
position is for an astigmatic correction that is a "best guess,"
normally in the middle of the adjustment range.  The mechanism can
then move in for more or less astigmatic correction, depending on the
need.

      The lens to diode optimum distance should be determined during
spin-up as part of the drive's calibration procedures.  After the
normal servo calibration is complete, there are several ways to
determine the best lens to diode position f...