CA1047644A - Record carrier on which information is stored in an optically readable structure - Google Patents
Record carrier on which information is stored in an optically readable structureInfo
- Publication number
- CA1047644A CA1047644A CA219,532A CA219532A CA1047644A CA 1047644 A CA1047644 A CA 1047644A CA 219532 A CA219532 A CA 219532A CA 1047644 A CA1047644 A CA 1047644A
- Authority
- CA
- Canada
- Prior art keywords
- record carrier
- areas
- track
- tracks
- gratings
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
- G11B7/005—Reproducing
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
- G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
- G11B7/0938—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following servo format, e.g. guide tracks, pilot signals
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
- G11B7/2407—Tracks or pits; Shape, structure or physical properties thereof
- G11B7/24085—Pits
Landscapes
- Optical Recording Or Reproduction (AREA)
- Optical Record Carriers And Manufacture Thereof (AREA)
Abstract
ABSTRACT
A record carrier is described which is provided with an optically readable structure of trackwise arranged areas alternating with intermediate areas.
Areas of at least two different types are provided As a result, a high information density can be achieved.
The different types of areas may also be used for center-ing a read beam relative to a track and for focussing the beam onto the track.
A record carrier is described which is provided with an optically readable structure of trackwise arranged areas alternating with intermediate areas.
Areas of at least two different types are provided As a result, a high information density can be achieved.
The different types of areas may also be used for center-ing a read beam relative to a track and for focussing the beam onto the track.
Description
PHN. 7340.
: .
"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 ,~ .
: .
"Record carrier on which informQ-tion is stored in an optically readable structure"O
______ __ :
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 .: .
, .
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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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.
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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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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- ' . .
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~-':, _ g _ :
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 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.
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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
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-" ' , . ., ~ :.
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. ~ -- 14 ~ .
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' '. ', '..~
;,-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.
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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.
., . ,:
_ 19 _ . . .
~ . .. . : . , i .
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 ~ , , ~' ' "
'': '.
, .
~ , . ~: :;: : . .,. . , , . ,:
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 .: .
, .
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 .; ", , .
'.': ', '' ' ~' ~' .~' ' ' .
... . . .
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 ;
, . "
-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.
:
' . ' .
~:, :. ;
p~. 73~0. '~
. , .
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- ' . .
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~-':, _ g _ :
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 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 ~'- .
..: '~' ~ , :
.':, 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 :
..................................................................................... .: .
~ ` ~
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
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-" ' , . ., ~ :.
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. ~ -- 14 ~ .
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 ~ ~
':::
. ~.
- 15 ~
' ' ~ . , , . ., `, ' '. ' . ' ', ! . . . '. . , . ', , . .~ , .
,' .
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' '. ', '..~
;,-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 ' . .
~' ~ - 17 ~ ::
' ... .
, ' .: ., .
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 ' .
` , ~ .
,~ . .
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.
., . ,:
_ 19 _ . . .
Claims (12)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A record carrier on which information, for example video and/or audio information, is stored in an optically readable structure of trackwise arranged areas alternating with intermediate areas, which areas have a different influence on a read beam of radiation than the intermediate areas and the lands between the tracks, the information being contained in at least the spatial frequence of the areas, and wherein adjacent areas of the trackwise arrangement consist of gratings of different types, which types of gratings differ in that the directions of their grating lines are different.
2. A record carrier as claimed in Claim 1, char-acterized in that the gratings of two adjacent tracks are of different types.
3. A record carrier as claimed in Claim 2, char-acterized in that the tracks, viewed in the lateral direction of the tracks, exhibit periodical excursions, the period of said excursions being substantially greater than the aver y period of the areas in the tracks, whilst the amplitude of the excursions is smaller than the width of the tracks.
4. A record carrier as claimed in Claim 2 or 3 of the round disk-shaped type, characterized in that two coplanar spiral tracks are provided, the tracks of one spiral information track serving as lands for the tracks of the second spiral information track.
5. A record carrier as claimed in Claim 1, char-acterized in that a track contains gratings with dif-ferently oriented grating lines.
6. A record carrier as claimed in Claim 5, char-acterized in that two consecutive gratings comprise differently oriented grating lines and that the dimen-sions of the gratings in the longitudinal direction of a track is independent of the information, whilst the spatial frequency of the gratings is determined by the information.
7. A record carrier as claimed in Claim 1, char-acterized in that the orientations of the grating lines of the two types of gratings are perpendicular to each other and that said orientations enclose an angle of 45°
with the longitudinal direction of the tracks.
with the longitudinal direction of the tracks.
8. A record carrier as claimed in Claim 6, char-acterized in that the record carrier comprises tracks in which per grating maximum two grating lines are provided.
9. An apparatus for reading a record carrier as claimed in Claim 1, including a radiation source which supplies a read beam, a radiation-sensitive signal detection system for converting the read beam which is modulated by the record carrier into an elec-trical signal which is modulated in accordance with the sequence of areas and intermediate areas in a track, and an electronic circuit in which the electrical sig-nal is processed to an information signal, characterized in that the signal detection system consists of at least two radiation-sensitive detectors which detectors are disposed so that they receive radiation only when the read beam impinges on a grating whose grating lines have a specific orientation.
10. An apparatus as claimed in Claim 9, charac-terized in that a number of lens elements are associated with each detector, which lens elements con-centrate the radiation which is diffracted in a certain direction by a grating on the record carrier onto the relevant detector.
11. An apparatus as claimed in Claim 9 or 10, characterized in that in the electronic circuit a low frequency control signal for correcting the position of the read beam relative to the track to be read is derived from the detector signals.
12. An apparatus as claimed in Claim 9 or 10, characterized in that in the electronic circuit a low frequency control signal for correcting the focus-sing of the read beam on the track to be read is derived from the detector signals.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL7401858A NL7401858A (en) | 1974-02-12 | 1974-02-12 | REGISTRATION CARRIER ON WHICH INFORMATION IS INDICATED IN AN OPTICALLY READABLE STRUCTURE. |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1047644A true CA1047644A (en) | 1979-01-30 |
Family
ID=19820729
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA219,532A Expired CA1047644A (en) | 1974-02-12 | 1975-02-06 | Record carrier on which information is stored in an optically readable structure |
Country Status (16)
| Country | Link |
|---|---|
| JP (1) | JPS50119517A (en) |
| AT (1) | AT338889B (en) |
| AU (1) | AU497709B2 (en) |
| BE (1) | BE825379A (en) |
| CA (1) | CA1047644A (en) |
| CH (1) | CH592350A5 (en) |
| DE (1) | DE2503975A1 (en) |
| DK (1) | DK138567B (en) |
| ES (2) | ES434588A1 (en) |
| FR (1) | FR2260911B1 (en) |
| GB (1) | GB1501141A (en) |
| IT (1) | IT1031581B (en) |
| NL (1) | NL7401858A (en) |
| NO (1) | NO750416L (en) |
| SE (1) | SE410808B (en) |
| ZA (1) | ZA75131B (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL7510035A (en) * | 1975-08-26 | 1977-03-01 | Philips Nv | REGISTRATION CARRIER WITH AN OPTICALLY READABLE, TRACK-SIZED, INFORMATION STRUCTURE AND DEVICE FOR READING THIS. |
| JPS5363002A (en) * | 1976-11-18 | 1978-06-06 | Sony Corp | Signal recording system and disk type medium for recording signal |
| US4161752A (en) * | 1977-06-28 | 1979-07-17 | International Business Machines Corporation | High density video disk having two pit depths |
| NL7803517A (en) * | 1978-04-03 | 1979-10-05 | Philips Nv | RECORD CARRIER WITH AN OPTICALLY READABLE PHASE STRUCTURE AND DEVICE FOR READING. |
| JPS57103132A (en) * | 1980-12-16 | 1982-06-26 | Matsushita Electric Ind Co Ltd | Recording information carrier and its recorder and reproducer |
| NL8100098A (en) * | 1981-01-12 | 1982-08-02 | Philips Nv | RECORD CARRIER WITH OPTICALLY READABLE INFORMATION STRUCTURE. |
| GB8309447D0 (en) * | 1983-04-07 | 1983-05-11 | Combined Tech Corp Plc | Optical data storage |
| US4623784A (en) * | 1984-12-20 | 1986-11-18 | Drexler Technology Corporation | Laser recording apparatus with off-center lens and error detection |
| DE68923833T2 (en) * | 1988-06-20 | 1996-06-13 | Mitsubishi Electric Corp | Optical head with tilt correction servomechanism. |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3314052A (en) * | 1963-04-12 | 1967-04-11 | Ibm | Light modulation system |
| FR2014594B1 (en) * | 1968-07-15 | 1974-02-22 | Ibm | |
| JPS5117405B2 (en) * | 1972-05-15 | 1976-06-02 |
-
1974
- 1974-02-12 NL NL7401858A patent/NL7401858A/en not_active Application Discontinuation
-
1975
- 1975-01-07 ZA ZA00750131A patent/ZA75131B/en unknown
- 1975-01-31 DE DE19752503975 patent/DE2503975A1/en not_active Withdrawn
- 1975-02-06 CA CA219,532A patent/CA1047644A/en not_active Expired
- 1975-02-07 GB GB5302/75A patent/GB1501141A/en not_active Expired
- 1975-02-07 DK DK45475AA patent/DK138567B/en unknown
- 1975-02-10 AT AT98275A patent/AT338889B/en not_active IP Right Cessation
- 1975-02-10 SE SE7501407A patent/SE410808B/en unknown
- 1975-02-10 BE BE153229A patent/BE825379A/en unknown
- 1975-02-10 NO NO750416A patent/NO750416L/no unknown
- 1975-02-10 IT IT20089/75A patent/IT1031581B/en active
- 1975-02-10 ES ES434588A patent/ES434588A1/en not_active Expired
- 1975-02-10 AU AU78025/75A patent/AU497709B2/en not_active Expired
- 1975-02-10 CH CH156575A patent/CH592350A5/xx not_active IP Right Cessation
- 1975-02-12 JP JP50017757A patent/JPS50119517A/ja active Pending
- 1975-02-12 FR FR7504326A patent/FR2260911B1/fr not_active Expired
-
1976
- 1976-10-27 ES ES452770A patent/ES452770A1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DK138567C (en) | 1979-03-05 |
| ZA75131B (en) | 1976-08-25 |
| NL7401858A (en) | 1975-08-14 |
| GB1501141A (en) | 1978-02-15 |
| NO750416L (en) | 1975-08-13 |
| IT1031581B (en) | 1979-05-10 |
| DE2503975A1 (en) | 1975-08-14 |
| AU497709B2 (en) | 1979-01-04 |
| DK138567B (en) | 1978-09-25 |
| FR2260911A1 (en) | 1975-09-05 |
| CH592350A5 (en) | 1977-10-31 |
| JPS50119517A (en) | 1975-09-19 |
| ATA98275A (en) | 1977-01-15 |
| SE7501407L (en) | 1975-08-13 |
| BE825379A (en) | 1975-08-11 |
| AU7802575A (en) | 1976-08-12 |
| DK45475A (en) | 1975-10-06 |
| AT338889B (en) | 1977-09-26 |
| ES434588A1 (en) | 1977-03-16 |
| ES452770A1 (en) | 1977-10-01 |
| FR2260911B1 (en) | 1982-03-05 |
| SE410808B (en) | 1979-11-05 |
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