Browse Prior Art Database

Optical Recording System with Dual Layer Media

IP.com Disclosure Number: IPCOM000115640D
Original Publication Date: 1995-Jun-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 66K

Publishing Venue

IBM

Related People

Belser, K: AUTHOR

Abstract

This invention is an optical disk recording system in which the user recorded data is placed on one media layer and the read only overhead information (servo and header data) is placed on another layer. The motivation is to lower media noise by recording on a flat surface and to maximize the usable capacity by getting the overhead off of the data surface.

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

Optical Recording System with Dual Layer Media

      This invention is an optical disk recording system in which
the user recorded data is placed on one media layer and the read only
overhead information (servo and header data) is placed on another
layer.  The motivation is to lower media noise by recording on  a
flat surface and to maximize the usable capacity by getting the
overhead off of the data surface.

      Laser diodes oscillate at several frequencies simultaneously
because of their short internal resonant cavity.  External cavity
feedback can cause one frequency to be dominant.  External cavity
feedback is maximized when the spot is in focus on the disk.  Since
the index of refraction of the lenses changes with wave length
depending
on the dispersion (chromatic aberration) of the glass, the focus
position
of the spot will change when the wave length changes.  The laser
naturally tends to adjust its wave length so that the spot is in
focus
on the media.

      The  invention is to use two media surfaces, each accessed with
a different laser wave length such that:
  1.  A short wave length laser (data) spot is used to record user
       data.
  2.  A long wave length laser (ROM) spot is used to sense embossed
       information.
  3.  The user data surface is perfectly flat and the focus error
       signal is generated from this surface using the data spot.
  4.  The overhead surface contains the header and radial position
       sensing features which are sensed with the ROM spot.
  5.  The optics are designed to have low dispersion for the data
spot
       and a high dispersion for the ROM spot so that only the ROM
spot
       experiences auto-focusing.
  6.  The data spot focus will be controlled by the focus control
       system.  The ROM spot should be nominally in focus when the
data
       spot is in exact focus.  Auto focusing will correct for any
error
       in the nominal ROM spot focus.
  7.  The formatting and/or encoding of the radial position sensing
       signal, the header data and timing information can u...