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Defocussed Erasing for Improved Signal to Noise Ratio

IP.com Disclosure Number: IPCOM000109054D
Original Publication Date: 1992-May-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 1 page(s) / 53K

Publishing Venue

IBM

Related People

Fennema, AA: AUTHOR [+5]

Abstract

Proposed is a slightly defocussed erase for rewritable optical media, such as magneto optic (MO) or phase change (PC) media. This defocus causes the path erased by the laser to be slightly wider than the spots written by that same laser, Figure 1. This can provide a more complete erasure of written data on rewritable media. By not leaving portions of bits unerased on the rewritable media, a higher signal-to-noise ratio could be achieved when this erased area is rewritten.

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Defocussed Erasing for Improved Signal to Noise Ratio

      Proposed is a slightly defocussed erase for rewritable optical
media, such as magneto optic (MO) or phase change (PC) media.  This
defocus causes the path erased by the laser to be slightly wider than
the spots written by that same laser, Figure 1.  This can provide a
more complete erasure of written data on rewritable media.  By not
leaving portions of bits unerased on the rewritable media, a higher
signal-to-noise ratio could be achieved when this erased area is
rewritten.

      The idea here is that erasing the media with the same focused
beam that wrote the media may mean that the written areas are not
completely erased.  The laser may not track exactly the same way
during the erase as it did during the writing of the information.
So, having the erase path slightly larger than the size of the
written spot will give a more complete erasure of the rewritable
media.

      The path erased by the laser in its slightly defocussed mode
would not be so wide as to erase adjacent tracks of data.  This idea
would only erase the unwanted data in the groove and the undesired
fringes along the adjacent lands.

      This defocussed erase also slightly reduces the temperature of
the center of the erased stripe.  This lowering of the center
temperature can contribute to a longer media life.

      The slight amount of defocus required is achieved by changing
the focus offset DAC (digital to analog c...