Note: Descriptions are shown in the official language in which they were submitted.
1C~957l~Z
The present invention relates to carriers upon
w~ich high-density information can be recorded, these data
carrier~ being capable of optical read-out by mean~ of concen-
trated radiation.
Optically readable data carriers comprise,
generally speaXing, a layer in which a characteristic element,
capable of modulating the read-out radiation, can v~ry between
two values. This element may be the refractive index, the
thickness, the transmission factor or the reflexion factor for
example.
Recording of information leads to the formation of
an impression constituted by domains of variable size-~ in
which the characteristic element passes qucce~sively from one
value to the other.
In particular, photosensitive resin layers and thin
layers of diazo compound~, have been used.
The action of a recording beam on the~e layers
- makes it possible either to locally diYsolve the resin (in
which case thickne~s variation~ are produced) or to block the
formation of a pigment in the case of diazo compound~ (in
which case variations in the transmission coefficient are
obtained). A data carrier covered with a layer of metal
having a low melting point ha~ al~o been use : under the action
of the recording beam, the metal melts or volatilises. If the
metal layer has been completely pierced by the action of the
recording beam, the tran~mi~ion factor i~ equal to 1 or to
O in accordance with whether the success~ve domain~ have or
have not been Rubjected to the beam. If, by contra~t, the
layer is not~
578~
completely pierced~ then a reflective layer is produced which
contains crests and troughs~
Chemical processes, local dissolving of a resin layer or
the creation of a pigment, have the drawback that they require
a developin~ phase and this makes it impossible to effect
read-out im~ediately after recording.
The thermal method consists in volatilising a low melting
point metal layer and produces a data carrier whose resolution
is low. In other words, melting of the metal is accompanied
by a phenomena of capillarity and later heat diffusion beyond
the heated zone~ which affect the sharpness of ~he recorded
domain. The information density which is capable of being
recorded is thus low.
~oreover, all data carriers obtained by the aforementioned
methods have the drawback of being fragile and consequently
difficult to store unless they are subjected to a supplementary
process consisting for example of covering them with a protec-
tive transparent layer. Finally, the layer obtained in this
way (photosensitive, diazo or metallic) lacks chemical stability
and may kherefore change in the course of time, making it
extremely difficult to store these data carriers for long
periods of time, whether recorded or not.
The object of the present invention is a data carrier not
subject to these drawbacks. In particular, the layer on which
the domains are recorded and whose characteristic element may
be the refractive index, the transmission coefficient etc., is
stable before and after recording and the data carriers which
5782
have these layers can therefore be readily stored. Moreover,
the recording process, which is matched to the recording of
layers of this kind, does not involve the necessity of any
developing operation.
According to the invention, there is provided a method
of manufacturing a data carrier which can be optically read
comprising a phase during which a material made up of at least
one oxide, chosen from amongst the following : titanium oxide,
iron oxide, chromium oxide, manganese oxide, tin oxide and
zirconium oxide? is deposited by vaporisation under vacuum,
upon one face of a substrate, said vaporisation being performed
with a loss of oxygen atoms, the deposited layer thus being
formed of a sub-oxide.
For a better understanding of the invention and to show
how the same may be carried into effect, reference will be
made to the following description and the attached drawings
among which :
Fig. 1 illustrates explanatory graphs ;
Fig. 2 illustrates the first phase of the process of
manufacturing the data carrier ;
Fig. 3 illustrates the phase of recording the data carrier ;
Fig. 4 illustrates a device for reading out thls kind of
data carrier.
The invention is based llpon the optical properties of the
oxides and the sub-oxides obtained from the latter.
The explanatory graphs of Fig. 1 illustrate one of these
properties, which is the variation in the transmission of the
radiation by more or less oxidized mixtures as a function of
1095782
the wavelength of the radiation passing through them.
The mixture used is a mixture of titanium oxide Ti 2
and iron oxide Fe2 3 comprising 30 ~ of titanium oxide and
70 % of iron oxide.
The graph (a) illustrates the variations in the coeffi-
cient of transmission of a layer around 500 angstrom units
thick, of a decomposed mixture of this kind, that is to say
a layer which has lost oxygen atoms as a consequence of a
process which may for example be vaporisation under vacuum
The graph (b) illustrates the variations in the coeffi-
cient of transmission of the same layer, this mixture having
been reoxidized by the capture of oxygen atoms from the ambient
air at a temperature of around 300C.
The decomposed mixture is brown and particularly absorbent
for wavelengths in the neighbourhood of and less than 4 500
angstrom units (blue and violet) and its transmission coeffi-
cient increases slowly for longer wavelengths. ~he reoxidized
mixture has a transmiss;on coefficient slightly greater than
that of the decomposed mixture, for wavelengths around and
2~ less than ~ 500 angstrom units, but increases quite rapidly
with wavelength to reach o.8 at 6 300 angstrom units. The
mixture then has an orange colour. There is at this point an
increase o around 30 % in the light intensity transmitted by
the reoxidized layer, in relation to that transmitted by the
decomposed la~er.
To this variation in the transmission coe~ficient (and
absorption) of the oxide mixture~ there is added a property of
1~9578Z
variation in the refractive index of the mixture depending
upon whether or not i~ is decomposed or reoxidized. Thus, in
the case of the aforesa1d mixture a the refracti~e index of the
decomposed mixture is equal to 2 whilst that of the reoxidized
mixture is equal to 2.4. One or the other or again both of
these ~ptical properti~es can be used for the optical read-out
of a data carrier comprising domains which are alternately
formed by decomposed oxides or sub-oxides, and oxides.
To obtain this kind of data carrier, the manufacturing
method described below can be used. In a first phase, illus-
trated in F'ig. 2, an appropriate substrate 1 constituted for
example b~ a perfectly flat polished glass disc~ is arranged
in an evacuated enc:lose 2 containing a high vacuum, for
example 10 6 mm of mercur~. If it is required tc produce a
data carrier which can be read by a reflexion, then a reflec-
tive substrate must be used~ for example a previously metalli-
sed substrate. A vaporisation source 3 containing the mixture
of oxides to be deposited upon one face of the substrate, emits
a stream of particles towards the latter. This vaporisation
gives rise to a loss of ox~gen akoms and the mi~ture deposited
on the substrate is oxygen deficient. If the source comprises
a rnixture of rl`i 2 and Fe203, the mixture deposited contains
molecules of Ti O and molecules of Fe304, and more oxidized
molecules are ]ef~. The composition of the mixture is non-
stoichio-metric. The thickness of the deposited layer 4 should
be appropriately selected if the thickness is too large the
radiation will be totally absorbed even at the reoxidized zones
1~5782
whilst if it is too smallg the variation in the luminous inten-
sity transmitted, from the sub-oxidized zones to the reoxidized
zones, will be too weak to be detected at the time of read-out-
The thickness is therefore chosen so that t~e absolute varia-
tion is maximal at the time of read-out.
At completion of this first phase, the substrate upon
which the layer of decomposed oxides (or sub-oxidesj has been
deposited, can be stored for a very long time under normal
temperature conditions.
The recording of this kind of data carrier is performed
by means o a device of the kind shown schematically in Fig. 3
It comprises a radiation source of LASER type, 5, emitting
the radiation beam 6. The source should have a sufficient
power for the radiation which it emits to locally raise the
layer of sub-oxides to an adequate temperature and bring about
the oxidation of the layer. The temperature will typically be
of the order of 200-300C. The LASER source used for recording
thus has a power of some tens of milliwatts. Its wavelength
is a matter of arbitrary choice. The radiation is modulated
by means of an optical modulator 7 which is additionally
supplied with the electrical signal S which is to be optically
recorded on the data carrier. This recording radiation, modu-
lated in on/off fashion, is reflected by a mirror 8 and concen-
trated by an ob,jective lens ~ on the sub-oxide layer 4 carried
by a substrate 1 rotating about its axis at angular speed ~
The domains which receive the radiation heat up and the oxygen
atoms present in the ambient air are captured by the molecules
l~9S782
of the layer. The layer locally changes colour and, as descri-
bed before3 its opkical properties are modified.
The thus recorded data carrier is highly stable at
ordinary temperatures since the chemical reaction can only
take place within a fairly high temperature range. ~iloreover,
the oxide layer is extremely hard both in the highly oxidized
zones and in the sub-oxidized ~ones. Consequently, it is
highly resistant to abrasion by dust and can readily be
cleaned. The optical power required for this recording, some
tens of milllwatts, is substantially smaller than that required
in ablation techniques. Finally, ~s indicated earlier, the
wavelength of the L~SER source used for recording, is not
critical.
This kind of data carrier is particularly suitable for
professional equipment since the recorded information can be
read out immediately after recording.
Fig. 4 illustrates a device for reading out a recorded
disc, the disc being assumed to be readable by reflexion. It
comprises a read~out LASER source 10 of low power, typically 0.7
milliwatts, operating at a wavelength of around 6 300 angstrom
units, emitting radiation which is reflected by a mirror 11
on to the recorded face 4 of the data carrier. The radiation
passes through a partially reflective plate 12, a read-out
objective lens 13 and is ~ocused at point 0. The data carrier
rotates about its axis at the angular speed ~. The radiation
passes through or is partially absorbed by the thin layer and
is reflected , it passes through the objective lens 13 again,
lt~7~32
is reflected by the partially reflective plate 12 on to a
read-out cell 15 and the latter furnishes an amplitude-modula-
ted signal L which translates the impression recorded on the
disc in the situation where the disc is read out by variation
in amplitude of the radiation emerging from the oxide layer.
In fact, the variation in refractive index of the oxide means
that the emergent beam is modulated in amplitude and phase.
The read-out of data carriers of this kind can therefore
be performed either by reflexion or by transmission depending
upon the type of substrate (reflectïve or otherwise) upon
which the oxide layer has been deposited~ and in each case
read-out can be performed in amplitude or in phase. The
sub-oxide layer which has been locally reoxidized cannot be
returned to its initial state. Consequently~ discs of this
kind can only be used as dead stores.
Data carriers of this kind are perfectly suitable for
the production of special recordings in small numbers of
copies, that is to say particularly suitable for the profes-
sional field but are not very well suited to the reproduction
of a large number of copies. In other words, a disc comprising
an oxide layer carrying information, cannot be reproduced by
a conventional photographic technique since the known oxides
are too absorptive at the actinic wave]engths located in the
violet range of the spectrum.
This kind of duplication is possible, however, but requires
the use of layers formed of diazo compounds sensitive to higher
wavelengths (red~ which do not belong to the current techniques.
~95782
The invention is not limited to the embodiment and manu-
facturing process described. In particular~ a glass substrate
has been described but the substrate used could be of any
kind, rigid or flexible. ~loreover, the indicated mixture of
oxides is not the only one which can be used. Other oxides
possess the property o having a transmission coefficient
which varies in accordance with the oxygen content, this
content being capable of increase by heating~ as well as the
property of having a refractive index likewise variable as
a function of the oxygen content. By way of example, it is
possible to quote chromium oxide, manganese oxide, tin oxide
and zirconium oxide or mixtures of these oxides if capable
of mixing. It is possible to add to these oxides an element
which promotes the oxidation reaction.
It should be noted that at the time of recording, if the
air in the neighbourhood of the layer contains insufficient
oxygen, it is possible to carry out recording in an oxygen -
enriched atmosphere.
