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Optical Recording/Erasure with Overlapping Focal Spots from Multiple Beams

IP.com Disclosure Number: IPCOM000113751D
Original Publication Date: 1994-Sep-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 6 page(s) / 186K

Publishing Venue

IBM

Related People

Asthana, P: AUTHOR [+3]

Abstract

It is often difficult to obtain sufficiently reliable performance at high powers (as needed for MO optical drive recording or erasure) and at a low cost from laser diodes, particularly those of shorter visible wavelengths. Such unavailability is a major barrier towards the implementation of higher density recording that would require blue wavelength lasers. By combining a longer wavelength, near IR, laser, with the lower power short wavelength laser, the power demand on the short wavelength laser is reduced and its reliability increased.

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Optical Recording/Erasure with Overlapping Focal Spots from Multiple
Beams

      It is often difficult to obtain sufficiently reliable
performance at high powers (as needed for MO optical drive recording
or erasure) and at a low cost from laser diodes, particularly those
of shorter visible wavelengths.  Such unavailability is a major
barrier towards the implementation of higher density recording that
would require blue wavelength lasers.  By combining a longer
wavelength, near IR, laser, with the lower power short wavelength
laser, the power demand on the short wavelength laser is reduced and
its reliability increased.

      The most damaging use of the laser in an MO optical disk drive
is during erasure where the laser is run CW for extended periods of
time.  By combining the beams of the short wavelength laser with a
higher reliability, longer wavelength laser the functions between
erase and write can be separated.  The longer wavelength laser with
its larger spot is used for erasure, and the shorter wavelength laser
with its smaller spot is used for forming data marks.  The shorter
wavelength laser is also used for read-back of the data.

      One embodiment, which is illustrated in Fig. 1., involves the
use of two lasers with overlapping focal spots for mark formation.
One of the lasers, designated the primary laser as it will also be
used for readout, is placed in an optical subassembly which contains
servo and data detectors.  This laser may be a short wavelength
(e.g., 670 nm) laser for example.  The other laser, used for
assistance in media heating for mark formation or erasure is referred
to herein as the secondary or additional laser.  This laser may be of
identical or longer wavelength (e.g., 780 nm) to the primary laser.
Note that during mark formation, it is best if both lasers are
simultaneously pulsed.  Having different pulse lengths for each laser
may be of benefit in mark size control.

      The beam path of the primary laser may be laid out in a similar
fashion to the beam path of any laser in a conventional single laser
optical drive.  This beam is collimated, circularized, and directed,
via a beam bender, to an objective lens which focuses it on the disk.
The beam from the secondary laser is also collimated (and
circularized if necessary) and is combined with the primary beam by
the use of a beam splitter as shown.  The two beams are now
essentially colinear and will form superimposed focal spots.  Note
that the coatings in the optics in the common beam path may be
optimized for the primary laser beam.  Also note that it may be
beneficial to use achromatic optics for collimation and
circularization to prevent asymmetric shifts induced by wavelength
shifts.  An advantage of this invention is that multiple actuators
and focus and tracking servos for each of the laser beams are NOT
needed.  The servo and actuator system of the primary beam is
sufficient.

      There is an inherent loss...