Note: Descriptions are shown in the official language in which they were submitted.
PHN. 7340.
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"Record carrier on which informQ-tion is stored in an
optically readable structure"O
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The invention relates -to a record carrier on
which infoxmation, for example video and/or audio i~-
formation, is stored in an optically readable st~ucture
of trackwise arranged areas alternating with intermediate
areas, which areas have a dif~erent influence on a read
beam of radiation than the intermediate areas and the
lands be~ween the tracks the information being con-
tained in at least the spatial frequency of the areas.
The invention also relates to an apparatus for reading
such a record carrier.
In this specification "tracks" is to be under-
stood to m3an track portions which, viewed in the lateral
direction of the track portions, are adjacent to each
other. For a round disk-shaped record carrier a tra~c
is track portion which extends along one revol~ltion
on the record carrier. A "spiral trac]c" is the total
of quasi-concentric tracks which merge inbo each other
on a round disk-shaped record carrier.
It has been proposed, _ alia in "Philips'
Technical Review" 33, No. 7, pages 177 - 193 to record
a colour television programme in the record carrier
described above. The repetition frequency of the areas,
.. ..
which consist of pits pressed into the record carrier
surfaoe, contains information about the lumLnance
.
signal, whilst chrominance and/or audio signals can
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PHN. 7340
be derived from the m~dulation of the lensths of the
areas. For a oorrect reading the tracks must be spaced ~ :
sufficiently far apart, in order that these tracks may
be readily discriminated from each other and can be
followed easily and that no cross-talk occurs between ~-
adjacent tracks during reading. As a result, only a
par;t of the record carrier can be used for the storage
of useful infor~ation.
Instead of providing the complete areas on i
the record carrier it is also possible, to merely
mark the transitions between the areas and intermediate
areas on the record carrier with the aid of so-called .
standard areas of, in principle, equal length. The
information is then contained in the distances between -.
the centres of said standard areas. The average
spatial frequency of said standard areas is twice that
of the areas. For a round reaord carrier in which the : -
same a~.ount of information is stored in an inner track
a~ in a track at the outer circumference of the record
carrier, the standard areas may beccme so densely
packed ~hat they can no longer be detected with satis-
factory resolution.
It is an object of the invention to provide :~
a solution for the tw3 abcve-mentioned problems. A re- .. -
cord carrier according to the invention is there~ore
characterized in that the trackwise arranged areas camr
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PHN. 7340-
7~
prise at least two types of gratings, which types of
gratings differ in that the directions of their grating
lines are different.
In this respect the gratLngs of bw~ adjacent
tracks may be of different types. When reading a track
the adjacent tracks disposed at ei~her side of said
track function as intermediate lands. This enables
to store approximately a twice as high Information
densit~r on the reoord OE rier.
Furthermore, consecutive grating-like areas
of one track may be of different types, allawin~ said
areas to be detected with satisfactory resolution
specially higher spatial frequencies.
.
m e use of gratings yields the additional
advantage that the direction in which the radiation-
of the read beam is diffracted is defined, so that
the detected signal is substantially unaffected by
scratches, dust ~articles and the l~ce on the record
cc~rrier.
If the gratings function as standard areas
the number of grating lines per grating may be lim~t-
ed and for example be only tWD or even one.
It is to be noted that on page 1351 of
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PHN. 73~0-
"Journal of the Optical Society of America" 53 (1963)
in the article "Theta Mbdulation in Optica, the use
of gratings with differently oriented grating lines ;~
for information storage purposes is described. Here
the direction of the grating lines is determined by
the amplitude of the information signal, whereas in
the record carrier according to the invention the
information is recorded in the spatial frequency of
the areas anl the lengths of the areas.
The invention will now be described in more
detail with reference to the drc~wing, in which
Fig. l shows a part of a known optical in-
formation structure of a record carrier,
Figs. 2 and 3 shaw parts of embodlments of
an optical in~ormation structure according to the inr
vention,
Figs. 4, 5 and 6 illustrate the principle
of reading such an information structure, clnd
Fig. 7, partly in perspective, shows an emr
bodiment of an apparatus ~or reading a record carrier
accordiny to the inwention.
Fig. l shows a part of an optical informa-
:::: ~
- tion structure of a reoord carrier 1 to be read, in
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p~. 73~0. `
this case a round record carrier. On the record car-
rier a nu~ber of areas g are arranged in tracks 2. ~;
The areas have a different influence on a beam of
radiation which is incident on the record carrier
than the intermediate areas t and the structureless
intermediate lands 3. The tracks may be concentric
with the centre of the record carrier. The record
carrier may alterna~ively be provided with one con-
tinuous spiral track.
For reading the record carrier a read beam
is directed to a radiation-sensitive detector vla the
record carrier and the record carrier is rot~ted, so
that the read beam is modulated in accordance with
the sequence of areas and intermediate areas in a
track to be read.
m e optical structure may be a transmission
or a reflaction structura, i.e. a read beam is mDdulat-
ed upon passage through the record carrier or upon re-
flection at tha record carrier.
The areas m~y be such that they influance
a read beam in diffarent manners. The areas in a
track ~al be of one type, whilst
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PHN 7340.
~134~
the areas of adjacent tracks are of another -type, as
shown in Fig. 2. When reading a first track (2) the
areas (g') of a second track (2') are not observed,
so that the latter track functions as an intermdiate
strip just like the land 3 in Fig. 1. However, the
track 2' does c~ntain useful information. When read-
ing said track 2' the adjacent tracks 2 function as
lands. It will be obvious that~a record carri~r
according to Fig. 2 can contain twice as much informar
tion as a reoord carrier in acoordance with Fig. 1.
In the record carrier according to Figs. 1 and
2 the information is stored in the transitions between
t~e areas and the intermediate areas. In order to pre-
vent that variations of parameters during the manufac-
ture of the r~cord carrier'affect the signal which is '
read from ~hat reoord carrier at later stage, the tranr
sitions between the areas and intermediate areas in a i''''`"''
track may for example be defined by so-called standard
areas, for example in the'form of standard light dif-
fracting elements. During reading the distances' ~'
between the'centres of the standard areas are then deter- '
mined, which distances are substantially independent of
possible variations of parameters during the manufacture
of a record carrier. The'spatial fre3uency of the -
standard areas is twice as high as that of the areas g
` an~ g~ of Pigs. 1 and 2.
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p~. 73~0. '~
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In a round disk-shaped record carrier in which each track
contains the same amDunt of information the average
spatial frequency of'the areas in an inner track of
the rec~rd carrier is higher (for example a factor 3)
than that of the areas in an outer track. For a suffi-
cient amount of information per revolution the standarcl
areas in an inner track m~st be spaced close to each
other. In order to allow the standard areas to be cle-
tected with sufficient resolution, the consecutive
standard areas according to the invention may take
differen~ forms, as is shown in Fig. 3. This Figure
shows only one outer track and one inner track. It '
is bo be noted that the lenc~chs of the areas, espe~
cially the lengths of the standard areas in the inner
track of Fig. 3, are shc ~ exaggerated relative to ~
the radius of the tracks. As the oonsecutive stan- '
dard areas are observed by diffe~ent detectors, '
said areas may be arranged very close to each other
and even against each other. ~'
According to the~invention the areas g and g' "'
(in Fig. 2) and the'standard areas s and s' (Fig. 3~
.~ .
consist of gratings. The directions of the'gratLng
lines of the areas g and the'standard areas s differ
from those of the'grating lines of the areas g' and
the standard areas s' respectively. Preferably, the said
directions are pexpendicular to each other so as to ensure
an opt~mum discrumination be~een the radiation ori- '
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PHN. 7340.
7~
ginating from the various types of gratings. In order to
reducs the effect of the diffraction of radiation at the
edges of the track, the grating lines are preferabl~ dis-
posed at an angle of approximately 45 relative to -the
longitudinal direction of the tracks. If the inormati~n
is contained in the lengths of the gratings, ~he number
of grating lines per grating must be sufficiently high
to allow the beginning and the end position of the grat-
ings to be detected with sufficient accuracy. However,
if the information is contained in the distances be-
tween the centres of the gratings, the lenqth of a
qrating being no longer very significant, a small numr
ber of lines per grating, preferably tWD, or even one,
may suffice. ~ -
Figs. 4 and 5 illustrate how a reflecting in-
formation structure consistinq of qratinqs can be read.
~ig. 4 shows a part o~ a record carrier in cross-section,
whilst Fig. S shcws a part of an information track in
top plan view.
With the aid of a lens 6 the radiation from
a radiation source 5 is concentrated to a radiation
spot V on a track. When the radiation is incident on
an intermediate area t, said radiation will be rer
flected. Ecwrner, if th~ radiation sp~-t is projected -
onto a grating-shaped area s, the radiation will be -
dif~racted upon reflection, for example b~wards the
detectors Dl and D2, as is shown in Fig. 4. The dire~-
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PHN. 73~0.
76~
tion in which the radiation is diffracbed is determined
by the direction of the grating lines. Fig. 5 shows the
mutual orientations of the gratings s and s' and of the
radiation sensitive surfaces ~f ~our detectors. The
gratings s are associated wi~h tw~ detect~rs, for exam~
ple the detecbors Dl and D2 of Fig. 4, whose radiation-
sensitive surfaces are oriented in accordance with a
and b, whilst the detectors whose ~adiationrsensitive
surfaces are orientel in accordance with c and d are
associated with the gratings s'. The radiation inter-
cepted by the debectors with surfaces oriented in ac-
cordance with a and b are not influenced by the presence
; of the gratings s'. The gratLnss s and s' may be dis-
posed very close to each other.
When reading a reo~rd carrier according to
the invention it is merely required to establish
whether a grating with a certain line orientation is
presenk. It is not necessary to image any gratings.
The optical system of the read apparatus may there-
fore be fairly simple and inexpensive. The lens 6 is
for exa~ple a lens with a numerical ap~rture of 0.3
; and said lens images a diffraction-limited radiation
spot on the~record carrier.
It is obvious ~hat the invention may also be
used in ~onjunction wi~h a radiation-transmitting re-
cord cærier. m e detectors, ~or example debec*ors D
and D2 in Fig. ~, must then be disposed at a side of
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PHN. 7340.
L7~
the recoxd carrier other than the side T~here the radia-
tion source which supplies the read beam is disposed.
m e detectors are arranged so that they can
only observe structures at the location of the read
spot which extend in a specific direction. Possible
scratches, dust particles etc. on the record c æ rier
will only be observed if their orientation is the same
as the orientation of the grating linesO me proposed
method of reading is therefore substantially insensi-
tive to scratches, dust particles etc. on the record
carrier.
As is described in "Philips' Technical Revie~'
33, No. 7, pages 177 - 193, a colour television signal `
can be recorded in a pit structure, which structure is
intended to be read by means of a read beam whose dia-
meter, at the location of the structure, is greater
than the track width. The read beam emerging frcm the
reco~d carrier is concentrated onto a detector with
the aid of a lens of such a numerical aPerture that
it cannot image a pit. me pits function as diffrac-
tion sbructures. Compared with such a pit structure
a grating structure has the advantage that the siqnal
/noise ratio is better, because only ~he radiation
which is diffracted in a certain direction is detec~ed.
For optimwm rea~ing of the pit structure, if a read
spot is projected on~o a pit, the radiation beams comr ;~
ing from the botbom of a pit and from ~he adjacen-t
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P~N. 7340.
~L~4~
record carrier surface must have a phase difference of
180 and must be of equal intensity. As a result, -the
de~th of the pits is defined within fairly narrow li-
mlts. The dimensions of the radiation spot and of the
pits will have to be adapted to each other. A read
spot with which an outer track of a round disk-shaFed
record carrier can be read in an optimum manner will
not readily be suited for correctly reading in an inner
track, whose PitS on -the average are shorter than those
of an outer track. For correctly reading all tracks an ;
inner track would for example have to be made broader
~an an outer track. Because of the different method
of reading, the problems associated with a pit struc-
ture no longer play a part in the case of an informa-
tion structure consisting of gratings with grating
lines of a specific orientation.
As is shcwn in Figs. 4 and 5, two radiation-
sensitive detectors may be used ~or each orientation
of the grating lines, in order to obtain an as large
as possible electrical signal. In order to prevent
that the detectors, in addition to the radiation o~
the read spot which is diffractéd by the grating, inr
tercep~ o~her radiation reflected by the reo~d car-
rier, ~he radiation spot may be imaged onto the detec-
tors Dl and D~ by simple lenses 7 and 8. Instead of
three separate lenseg 6, 7 and 8 it is also possible
to use a lens 6' ha~ing a greater angle of aperture
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PE~. 7340.
than the lens 6, which is disposed at the location of the
lens 6, as is shown in Fig. 6. The central part of the
new lens 6' is then used for projecting a re~d spot V
onto the record carrier, whilst the peripheral zone of
said lens images the gratings onto the detectors. The
element 9 is a mirror which reflects a :radiation beam
which is incident at a certain angle to the plane of
drawing towards the lens 6'. The wedge elements 4 and
4' ensure that the ra~iation beams which are diffract-
ed by the record carrier 1 impinge on tw~ detectors D
2-
Instead of two detectors for each grating
orientation it is also possible to use a co~bination
of one detector and suitable lens elements for any
grating orientation, as is shcwn in Fig. 7.
Fig. 7 s~cws an apparabus for reading a re-
cord carrier acoording to the in~ention in schematic
form and partly in perspective. The record carrier is
rotated by a shaft 30, driven by a motor, not shown, ~ ;
which shaft extends thrDugh a central opening 10 in
the record carrier. The radiation beam represented by
the rays 20, co~ing fr~m a source 5 is focussed onto
the record carrier by a lens 6. The radiation which is
diffracted by the areas with a sp~cific grating orien-
tation, of which radiation only the rays 21 are shcwn,
is interceEt~d by annular lens elements 11 and 12 -
which are disposed round the lens 6, and which concen-
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PHN. 7340.
~L7~
trate the radiation onto one detector 15. The detector
supplies an electrical signal which is m~dulated in ac-
cordance with the sequence of those grating-shaped ~ :
areas in the track to be read, which di:Efract radiation
towards the lens elements 11 and 12. Said signal is fed
to an electronic circuit 17 in which, in known nEnner, :
a video and/or audio signal Si can be derived, which ~:
signal in its turn is applied to a conventional (colour~ :
television receiving apparatus 18. The processing of ~he
detector signals into an information signal in the cir-
cuit 17 falls beyond the scope of the present invention
and will not be described any further.
Around the lens 6 two further annular lens
elements 13 and 14 are disp~sed~ Said lens elements
can co~centrate the radiation, represented by the rays
22r which is diffracted by those gratings whose grat mg
lines have an orientation which differs from that of
the gratings which are imaged onto the detector 15 with
the aid of the lens elements 11 and 12, on~o a second .
detector 16. m e detector 16 is also connected to the
electr~nic circuit 17. m e reference numerals 11 and
12 represent parts of a lens who æ centre is offset
relative to the optical axis 00'. The reference nu~
merals 13 and 14 are parts of another lens wh~se centre
is disposed~either on the optical axis 00' or offset ~-
relative to said axis, but in another direction than ;~
the centre of the lens cons~ituted by 11 and 12. ~ -
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P~. 7340.
76~
An apparatus as sho~n in Fig. 7 enables a re-
cord carrier which is provided with grating-shaped
areas with grating lines of ~w~ diEfer~!nt orientations
to be read. For reading a track with standard areas,
of which the consecutive gratings are oriented differen-t- -
ly, the tw~ detectors 15 and 16 m~st be used and the sig-
nals from said detectors must be combined in the circuit
17. If the grating lines of the gratings of one track ;
have one orientation and those of the gratings of ad-
jacent tracks have another orientation, the two detec-
tors 15 and 16 are required for reading the complete
information on the record carrier; for reading one
track, however only one detector is required. ~ ;
In the last case it is possible that the ad-
jacent tracks are to be read time sequentially. Each
time after a track has been read out it is nec~ssary
to switch from the one detector to the o~her. It is ;
~ . - . .
also possible that a first amount of information i9
stored in a first s~iral track o~ which the areas have
: .
a first grating orientation and that between the traclcs
of said sp~ral track a second spiral trac}c is disposed
of which the areas have a second grating orienta~ion.
~hen reading a record carrier in which two
~ adjacent tracks have different t~pes of areas, it is
possible bo detect in a si~ple manner whether the
read sp~t is centred on the tra~c to be read. If a
,
first ~ack is read, only the detecb~r associated wi~l ~ ~
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PHN~ 7340.
the areas of said track should receive modulated radia-
tion; if a second detector which is associated wlth the
areas of the adjacent track also recei~s modulated rad-
iation this is an indication that the read spot is not
exactly centred on the firs~ track. The electronic cir-
cuit 17 may include prDvisions to convert the signal of
said æcond detecbor into a control signal Sc which may
be employed to correct the position of the read spot,
for example with the aid of a rotatable mirror in the
path from the radiation source 5 to the lens 6, as pro,
posed previously.
If during reading it is also required to kn~w
the direction of a possible positional deviation of the ' '
read spot relative to the track to be read, a reoord
carrier according to ~he'invention may be made in
accordance wlth a previous proposal. In acoordance with
said proposal, described'in Canadian Patent Application '
21L,288r filed October 11, 1974 (PHN. 7190), the tracks
of the record carrier'exhlbi~ periodical excursions in ~'
the lateral direction of the'tracks, the period of which
~xcursions is substantlally greater (for example 1000 x), '
th~n the average period of the areas in the tracks,
whilst the'amplitude of ~he excursions is smaller (for ~ '
example 5 x) than the track width. ~hen reading su~h
25~ a record carrier the'high-frequency component of'the'
detector signal p~ovides the'infcrmation, for exa~ple '-
video'and~or audio inform:tion, whilst the'
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PHN. 7340- -
76~
phase of the low~frequency component of the detector
signal enables the direction of a deviation between ~'
the actual and the desired position of said read spot
~; to be derived.
According to another aspect of the invention
it is possible, when reading a record carrier of which
tWD adjacent tracks have different types of areas, to
detect whether the read beam is focussed on the plane '
of the information structure. If there is a deviation
between the actual position of the plane of the track
portion to be read and the desired position of said - -~
.~ . . . .
plane relati~e to the read objective, the radiation
sp~t imaged onto the reoord carrier will be propor~
tionally larger. In addition to the track to be read, '~
adjacent tracks will then'also be illummated. As a
result, apart from a first;detector which detects
gratings with an orientation oorrespcnding to the track "'~ to be read, a second detector which detects gratings
; with an orientation corresponding to the adjacent
' 20 track ~ill also receive radiation. When the read beam
is properl~ ~ocussed on the track to be read, there
is a ~:ximum difference between the output signals of
~ :
~ ~ the first and of the'seoond detector. Said difference
: ~ : . .
will decrease acoDrling as the focussing of the'read ~'
beam o~ the ~rack to be read deteriorates'. The dif-
: : ~ , :
ference betw:een the output signals of the first and ;'~'
the'seoond detec~or can be processed in the electronic '
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PHN. 7340.
~ 7~
circuit 17 to a lcw-frequency control signal Sc' for
focussing correction, for example by means of an axial
displacement of the objective lens 6.
When determining a focussing error, allowance
should be made ~or the effect oE a deviation between the
ce~tres of the read spot and the track to be read. Said
deviation may be determined by for example a reoord
carrier having tracks which exhibit periodical excur-
sions in the lateral direction of the tracks as describ~
ed previously. me periodical signal Sc which provides
an indication of the error in the centring of read
spot relative to the track to be read, has a specific
fixed frequency, and can thus be discriminated from
the signal Sc' which provides an indication of a pos
sible focussing error. If a television programme is
stored in a round disk-shaped record carrier, one Eield
being recorded per revolution, the tracks may for examr
ple have excursions only at the points which correspond
to the line synchronizing pulses in the television sig-
nal. The frequency of the signal Sc then corresFonds
to the line frequency in the information signal. The
focussing may then be corrected so that the difference
. .
between the output signals of said first and said second
detcctor is maximlm at the zero passages of the signal
Sc
Dur~ng the irst phase of reading, when the
objective is not yet ~ocussed on the record carrier, it
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PHN. 7340.
is also possible to make use of the dif1Eerent grating
orientations in adjacent tracks ~or coaxse adjustment
of the objective. As long as the read beam if focussed
in a plane which is at a relatively great distance from
the plane of the track to be read, the control system -
for centring the read spot on a track to be rec~d is
not yet operative. When the record carrier is moved
in the read direction relative to the radiation source,
the read spot al:o travels over the tracks m the la-
teral direction, the centre of the read spot being al-
- : .
ternately located at a track with a first grating
orientation and at a track with a second grating orien~
tation. m e detec~ors corresponding to said grating
orientations then alternately receive radiation. The
amplitudes of the detector signals increase as -the
focussing of the read bean on the track to be read
improves. These signals are in phase opposition. If
the difference between the two signals is maxImum,
:: .
the control system for centring the radiation spot
relative to the track to be read is rendered opera- ~
tiveO Correction of the centring and fine control o~ - -
the focussing is then ~uuthYr effec*ed as describ~d
hereinbefore. ~ '.
Instead of to a round disk-shaped recDrd
~25 carrier the inNention may also be applied to a record
carrier in the form of a tape or a cylindrical record
.. ..
carrier
,
The record carrier may also contain informa-
~ . .
tion other ~h~n a television programme.
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