Browse Prior Art Database

Magneto-Optic and Phase Change Optical Head Design for Optical Storage

IP.com Disclosure Number: IPCOM000115548D
Original Publication Date: 1995-May-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 171K

Publishing Venue

IBM

Related People

Gardner, TS: AUTHOR [+6]

Abstract

Various types of optical storage methods are used to store and retrieve customer data. Read-Only drives read pre-embossed data patterns by measuring the variation in reflected light off the media. Examples include CD-ROM and O-ROM media. Write-Once drives have the capability of writing to a particular area of the disc only one time by physically melting away the top higher reflectivity layer. Written data is again read by measuring the variation in the reflected light off the media. An example of a Write-Once media is the so-called WORM media. Erasable drives have the capability to read, write, and erase data. One approach is to magneto-optically write and erase the data, while optically reading using a differential detection technique taking advantage of the Kerr Effect. MO media is used in these drives.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 45% of the total text.

Magneto-Optic and Phase Change Optical Head Design for Optical Storage

      Various types of optical storage methods are used to store and
retrieve customer data.  Read-Only drives read pre-embossed data
patterns by measuring the variation in reflected light off the media.
Examples include CD-ROM and O-ROM media.  Write-Once drives have the
capability of writing to a particular area of the disc only one time
by physically melting away the top higher reflectivity layer.
Written data is again read by measuring the variation in the
reflected light off the media.  An example of a Write-Once media is
the so-called WORM media.  Erasable drives have the capability to
read, write, and erase data.  One approach is to magneto-optically
write and erase the data, while optically reading using a
differential detection technique taking advantage of the Kerr Effect.
MO media is used in these drives.  Another approach for erasable
drives is the Phase change approach.  High power is used to write and
erase which changes the reflectivity of the media.  Lower power is
used to read by measuring the variations in the reflected light.
This media is called Phase Change media.  Usually specialized drives
are used for each type of media.

      Recently some multi-function drives have become commercially
available.  For example, IBM* has a combination MO and WORM drive.
Other companies combine Read-Only and WORM as well as MO and
Read-Only.  For several reasons it would be attractive to offer an MO
and Phase-Change multi-function optical drive:
  o   Capacities are increasing rapidly through a decrease in laser
       wavelength.  The blue laser will be commercially available
soon.
       It offers just such an increase in capacity.  Phase-Change
media
       seems better suited for required performance at this
wavelength.
       However, MO has been generally more widely accepted than
       phase-change and dowmward compatability with existing MO media
       would be desirable.
  o  By definition, if a drive is capable of reading both MO and
phase
      change media, then it is also capable of reading (and writing)
      WORM and Read-Only media as well
  o  Phase Change Media is cheaper than MO media.

      Currently no company offers such a product.  What is disclosed
here is an optical head configuration that would enable such a
product to be constructed.

      Fig. 1 shows a typical Read-Only, WORM, or Phase Change style
head.  As described above, reading is accomplished by measuring the
change in light level reflected from the media.  The key attribute of
this optical path relevent to the disclosure is the presence of the
quarter-waveplate and polarizing beamsplitter.  This is a so-called
"light-diode," and enables all the light from the laser to go toward
the disc and all the light from the disc to go toward the detection
path.  This means that feedback of light from t...