Browse Prior Art Database

Volumetric CD-ROM with Enhanced Read-back Signal

IP.com Disclosure Number: IPCOM000115397D
Original Publication Date: 1995-Apr-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 110K

Publishing Venue

IBM

Related People

Baumann, GW: AUTHOR [+3]

Abstract

Disclosed is a modification to the multi-surface CD-ROM technology. This enhancement improves data reliability and error rates by increasing read-back signals.

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

Volumetric CD-ROM with Enhanced Read-back Signal

      Disclosed is a modification to the multi-surface CD-ROM
technology.  This enhancement improves data reliability and error
rates by increasing read-back signals.

      In the prior art, multiple CD-ROMs are physically attached to
one another, their data surfaces either uncoated or coated with a
partially reflective coating, thus enabling the laser beam to
penetrate through the stack of CD-ROMs and reflect back from the most
distant data surface to the read (or detection) optics.  When the
data surfaces are uncoated, the mis-match of refractive index between
the plastic disk (typically polycarbonate, with a refractive index of
1.58) and the adjacent air gap provides about 5% reflectivity, thus
returning a part of the beam to the read optics.  While reflective
coatings can increase the returned beam strength from the nearest
surface to any arbitrary level between this 5% and nearly total
reflection of 100%, the reflectivity of the nearest surfaces
interferes with the passage of the beam to and from the most distant
surface.  The more data surfaces in a structure, the lower the
optimal reflectivity of the coatings applied to the data surfaces
nearest to the optics.  The prior art teaches the use of different
coatings on each data surface, seeking to optimize read-back signals.

      This invention addresses the interference of non-data surfaces
with the laser beam.  In large stacks of more than 5-10 CD-ROMs,
gains from anti-reflective treatment of non-data surfaces are
substantial.  When used in combination with reflective coatings, the
gains are even more significant.

      This system is understood by considering the natural
limitations resulting when anti-reflective coatings are not used.
For such systems using reflective coatings on data surfaces, the
optimal reflectivity on the data surface furthest from the optics is
1.0, and on all other data surfaces it decreases monatonically, with
least reflectivity on the data surface nearest the optics.  The
optimal reflectivity of all data surfaces except the 7 furthest from
the optics is less than the natural interface reflectivity between
polycarbonate and air.  Hence, reflective coatings are applicable to
only...