Browse Prior Art Database

Dual-Sided Disk Structure and Magnetic Head for Direct Overwrite Magneto-Optic Recording

IP.com Disclosure Number: IPCOM000115484D
Original Publication Date: 1995-May-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 97K

Publishing Venue

IBM

Related People

McDaniel, TW: AUTHOR

Abstract

Disclosed is a two-sided Magneto-Optic (MO) disk andassociated optical-magnetic head to support the "fixed head" Magnetic Field Modulated (MFM) Direct OverWrite (DOW) function in rewritable optical data storage. This invention solves the prior problems of this technology: o Poor access time performance; o Excessive power consumption in the magnet coil; o Restriction to low data rate recording; o Restriction to single-sided disks; o Need for improved flexibility in choice and manufacture of disk substrates.

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This is the abbreviated version, containing approximately 52% of the total text.

Dual-Sided Disk Structure and Magnetic Head for Direct Overwrite
Magneto-Optic Recording

      Disclosed is a two-sided Magneto-Optic (MO) disk andassociated
optical-magnetic head to support the "fixed head" Magnetic Field
Modulated (MFM) Direct OverWrite (DOW) function in rewritable optical
data storage.  This invention solves the prior problems of this
technology:
  o  Poor access time performance;
  o  Excessive power consumption in the magnet coil;
  o  Restriction to low data rate recording;
  o  Restriction to single-sided disks;
  o  Need for improved flexibility in choice and manufacture of disk
      substrates.

      Existing "fixed head" MFM DOW head-disk systems typically place
a bias magnetic field source coil on the side of the disk opposite
that of the illumination optics.  The resultant single-sided MO disk
system is plagued with the need for clumsy servoing of a bulky coil
in concert with the optics.  A conventional double-sided MO disk is
impractical for such a configuration because the substrate thickness
then enforces a 1.5 mm separation between the coil and the MO film,
which renders switching of a 200 Oersted field at Recording Rates
(RF) impractical from a power dissipation and electromagnetic
radiation viewpoint.  Even a 0.2 mm separation with single-sided disk
with protective coat leads to hard power and radiation limitations on
data rate.

      The Figure illustrates a design for a head and disk
architecture which enables MFM DOW MO data storage on both surfaces.
The MO storage film(s) lies relatively close to the outer surface of
the disk (typically <50 &mu.m).  This configuration features an
"inverted" multifilm structure, in which the radiation used for
writing and reading enters through a thin (several 10's of &mu.m)
protective coating onto a sequence of dielectric and storage films,
which in turn rests on a separate reflector layer, or on the
substrate itself.

      The central optical issue surrounding the proposed film
structure in the Figure relates to the adequacy of laser irradiation
through a relatively thin "cover sheet" in the presence of sub- and
super-micron particulate debris.  Knowing NA and the indices of
refraction of the films of the medium establishes the geometry of the
irradiating light cone, and allows one to model the light
scattering/absorption effectiveness of particulate contaminants of
various sizes at the cover plate surface.  Analysis of this type
suggests that overcoat thicknesses in the vicinity of 50 &mu.m would
allow satisfactory operation with particulate debris below about 10
&mu.m in diameter.

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