Browse Prior Art Database

Multiple Values Per Pit on Optical Storage

IP.com Disclosure Number: IPCOM000105293D
Original Publication Date: 1993-Jul-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Gregg, LE: AUTHOR [+3]

Abstract

Disclosed is a method which increases storage density for optical storage media. This method allows increases in storage density which far outreach the incremental, predictable rates. This improvement is achieved by storing multiple bit values per "spot" on the disk.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Multiple Values Per Pit on Optical Storage

      Disclosed is a method which increases storage density for
optical storage media.  This method allows increases in storage
density which far outreach the incremental, predictable rates.  This
improvement is achieved by storing multiple bit values per "spot" on
the disk.

      For ablative WORM (Write Once Read Many) recording techniques,
an active layer of material is applied over the disk substrate.  To
record data, pits are ablated through the active layer.  The
resulting surface results in varied reflectivity which can be
detected and used to indicate 1s and 0s.  Another technique, phase
change, uses a polycrystalline surface is applied over the disk
substrate.  Heating this polycrystalline substance with the disk
write laser changes the substance from an amorphous to crystalline
state.  This results in a change in reflectivity which can be
detected and used to indicate 1's and 0's.

      To increase the storage density the power of the write laser is
modulated to not just 2 states (off and on), but instead to "N"
states where N is some power of 2, for example 4 or 8.  With the
write laser power modulated in this way the size of the pit, or the
degree of phase change, is varied.

      The detector is of course likewise modified to detect
variations in the amount of reflectivity.  Instead of a simple 0/1
output the detector output is digitized to output multiple levels of
0..00, 0..10, 0..11, etc.  The variations in reflectivity are
controlled so that the lowest reliably detectable change corresponds
to the value 00..01.  The next detectable change corresponds to the
value 00..10, etc.

      These situations are most easily illustrated using the ablative
or pit-forming method.  See Fig. 1 for a simple side view of part of
an ablative WORM disk surface representing the binary values 0, 1,
and 0.  This is utilizing the current technology where each area on
the media represents a single bit.  See Fig. 2 for a simple side view
of an ablative WORM disk surface with 2...