Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to information
storage and processing and, particularly, is concerned
with me-thods of erasing information.
This invention can be used in compu-ters, in
video and sound recording devices, in information
storage and processing systerns, and, in par-ticular, in
external memories of computers.
Known in the art is a method of erasing
information in optical storage devices, which consists
in that portions of an optical information carrier, on
which information had been recorded, are exposed to a
ligh-t beam so that they are reversibly converted into
a state having initial optical properties. Such
exposure of the optical carrier leads to changes in
the degree of crystallization of the recording layer
of the carrier (FR~B, 2 482 756).
This method is deficien-t in that it is too
lengthy since the optical carrier has to be heated
very slowly and the temperature has to be controlled
precisely after heating. The method is not efficient
and the reliability of repeated recordings is too low
because recording and erasing cycles adversely affect
-the structure of the recording layer, its thickness
becomes irregular.
Also known in the art is a method for
erasing information recorded on an optical carrier
having a recording layer (U.S.A. 4,403,318), which
consists in that the optical carrier is subjec-ted to
external exposure erasing recorded information, e.g.
by heating. To this end, two or more light beams are
produced, focused on -the carrier, and scanned along
the recording layer of the information carrier so that
portions of this recording layer are heated
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differently. This is achieved by changing the density
of the beam by changing the radiation intensity or the
size of the spot.
This method is deficient in that it cannot
provide multiple use of the optical information
carrier due to the reasons listed above.
The invention is to provide a method of
erasing information, which permits multiple repeated
recordings of informa-tion on the same optical
information carrier after information has been erased
from this carrier.
This is achieved in that a method of
erasing information recorded on an optical information
carrier having a recording layer, according to the
invention, consists in that the optical information
carrier equipped with an air-tight space and provided
with a recording layer on the internal surface of said
space, is filled with gas inert in relation to the
material of the recording layer and to the material of
the optical information carrier, said gas being under
a pressure selected from a range from 10 kPa to 10
kPa, then the optical information carrier is heated,
and, after the heating is over, the recording layer is
regenerated.
This method of erasing information permits
multiple use of the same optical information carrier
and makes this optical carrier more mechanically
strong.
An additional amount of material for the
recording layer may be placed into the air-tight
closed space of the optical information carrier in
order to maintain a permanent thickness of the
recording layer in the process of rewriting
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information, when the air-tight space is made as a
cylinder and the recording layer is provided on the
lateral surface thereof.
The invention will now be described in more
detail with reference to the accompanying drawing
wherein an optical information carrier is shown as an
embodiment realizing the method for erasing
information, according to the invention.
The method for erasing information recorded
on an optical information carrier can be realized by
the use of a specially designed carrier whose one
embodiment is illustrated in the drawing.
An optical information carrier comprises a
base which in this embodiment is a cylinder 1 made of
a material transparent for laser-emitted light (the
laser is not shown in the accompanying drawing), e.g.
of glass. But, it should be pointed out that the
claimed method can be realized on an optical
information carrier equipped with a base made, for
example, of two coaxial disks, or any other similar
construction.
The cylinder 1 is hollow and a recording
layer 2 is provided on the internal lateral surface
thereof as a thin film of, for example, Te or Bi.
Sealing bushings 3 and 4 are installed in the butt
ends of the cylinder 1 to confine an air-tight space 5
inside the cylinder 1, the recording layer 2 being
inside said air-tight space 5. A tube 6 is fitted
into the bushing 3 for evacuation of air from the
space 5 and for further pumping of gas which is inert
in relation to the material of the recording layer 2
and to the material of the cylinder 1, that is to
tellurium, bismuth, and glass at the same time. This
may be nitrogen or argon.
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The pressure of gas inside the air-tight
space 5 may range from 10 to 103 kPa. If the gas
pressure is brought lower than 10 kPa, the speed of
transfer of the material of the recording layer 2 from
gaseous to liquid phase is too high and the thickness
of the regenerated recording layer 2 becomes
irregular. If the gas pressure is higher than 103
kPa, the speed of regeneration of the recording layer
2 is slowed down and the efficiency of the process is
affected.
Preferably, -the gas pressure inside the
air-tight space 5 should be kept closer to the
atmospheric pressure.
It should be noted that, for the optical
carrier designed as described above, both external and
internal pressure may be excessive. It is for this
reason that the cylindrical shape of the carrier is
advantageous since with minimal wall thickness of the
carrier base it can best withstand the excess pressure
from any direction. Gas pumped into the air-tight
space 5 can bring the excess pressure to an acceptable
level. The optical information carrier having this
design is mechanically very strong.
An electrically conducting layer 7 is also
provided on the external surface of the cylinder 1.
This conducting layer 7 should be transparent for the
laser-emitted light and electrically connected to an
axial support 8. An electrode 9 is installed in the
air-tight space 5 and electrically connected to a
cover 10 made from an electrically conducting
material.
Information is recorded on this optical
carrier by any known method by a focused beam whose
intensity, or shape, or area or any other parameter is .-
modulated by the signal to be recorded. The optical ~
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information carrier is set into rotation by any known
drive (not shown) about its geome-trical axis.
Recording of information consists in that certain
changes in the relief of the surface of the recording
layer 2 are made.
P~ecorded information can, therefore, be
erased by the following method.
The optical information carrier ls exposed
to some external action, e.g. it is heated by any
known method. The material of the recording layer 2
evaporates almost completely. Heating is then
discontinued and the recording layer 2 is regenerated
by cooling the optical carrier. The material of the
recording layer 2 available in a gaseous state within
the air-tight space 5 of the optical carrier is
deposited on the cool walls of the optical carrier as
a liquid at first and as a solid matter finally.
Since the air-tight space 5 of the optical carrier
contains gas inert in relation to the material of the
cylinder and the recording layer 2, the process is
substantially slowed down. The uniformity of the
regenerated recording layer 2 is achieved by this
slowed down process, whereby practically no drops are
formed on the inside surface of the cylinder, even
though the materials of the recording layer 2 are
characterized by a high surface energy. The uniform
regenerated recording layer 2 ensures high quality of
repeated recordings. The number of rewrite cycles in
the proposed method and device realizing this method
is also achieved by using low-power laser emission for
recording information because in this case a high
surface energy material can be used as the recording
layer 2, whlch substantially re_uces its d=structi~n
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To control the regeneration ra-te of the
recording layer 2 af-ter heating is stopped, the
optical information carrier is exposed to an
electrical field. To this end, a potential difference
is applied to the electrode 9 and to the conducting
layer 7. This potential difference reduces the rate
of lon deposition in the regenerated layer 2. The
degree of ionization of vapour of the material of the
recording layer 2 can be intensified by additional
exposure to radiation of the cylinder 1 or some other
method, in case natural factors are insuffi.cient.
This means that only a negligible par-t of the material
of the recording layer 2 is in a liquid phase at any
stage of the process due to the correct selection of
the slow-down potential applied to the optical carrier
and availability of gas within the air-tight space 5,
which cut down the free run of par-ticles of the
material of the recording layer 2 and drastically
reduce the rate of deposition of the recording layer 2
on the internal surface of the cylinder 1.
Some additional amount of the material of
the recording layer 2 may be placed into the
air-tight space 5 of the optical information carrier
in order to maintain the thickness of the recording
layer 2 constant even with frequent and multiple
rewrite cycles, when some material may be deposited on
the butt end walls of the space 5. This can, for
example, be done by applying a layer 11 of the same
material on the butt end walls of the space 5.
The herein disclosed method for erasing
information offers the advantage of a substantial
increase in the number of rewrite cycles and,
simul-taneously, more reliability for the processes of
information recording and readout. This is due to the
fact that the recording layer located inside an
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air-tight spaee of the optieal information earrier
eannot be damased or dirtied. The use of a
eylindrieally shaped optieal information carrier also
eontributes to the reliability of information storage
and processing due to its considerable mechanical
strength.
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