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Astigmatic Length Reduction for Diode Lasers in Optical Data

IP.com Disclosure Number: IPCOM000111705D
Original Publication Date: 1994-Mar-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 61K

Publishing Venue

IBM

Related People

Bates, KA: AUTHOR [+4]

Abstract

In an optical storage drive, means for maintaining a focused spot of high optical quality at the media is required. Any aberration in the wavefront of the focused spot on the media can result in sub-optimal drive performance. Astigmatism is a particularly troublesome aberration. With astigmatism, the minimum extent of the focused spots along the two orthogonal directions occur at two different focal planes. In terms of drive performance, the impact is that at one focal plane best seeking occurs, while at the other focal plane best on-track reading occurs. It is desired that the separation between these two focal planes be as small as possible. The laser diode itself is a well-known source of astigmatism.

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Astigmatic Length Reduction for Diode Lasers in Optical Data

      In an optical storage drive, means for maintaining a focused
spot of high optical quality at the media is required.  Any
aberration in the wavefront of the focused spot on the media can
result in sub-optimal drive performance.  Astigmatism is a
particularly troublesome aberration.  With astigmatism, the minimum
extent of the focused spots along the two orthogonal directions occur
at two different focal planes.  In terms of drive performance, the
impact is that at one focal plane best seeking occurs, while at the
other focal plane best on-track reading occurs.  It is desired that
the separation between these two focal planes be as small as
possible.  The laser diode itself is a well-known source of
astigmatism.  During time of manufacture, it is possible to
compensate for the astigmatism introduced by the laser diode by
changing the separation between the collimator lens and the laser
diode and subsequently passing this beam through the wedge of a
circularizer.  See Fig. 1.  However, the laser diode astigmatism can
vary after time of manufacture due to changes in optical power,
changes in temperature, and aging of the diode.  This change in
astigmatism affects the drive in the negative ways mentioned above.

      Disclosed is a method for actively compensating for these
changes in laser astigmatism.  Fig. 2 shows the essence of the
disclosure.  By introducing a pair of opposing parallel p...