CA1182916A - Record carrier having an optically readable information structure and apparatus for reading said record carrier - Google Patents
Record carrier having an optically readable information structure and apparatus for reading said record carrierInfo
- Publication number
- CA1182916A CA1182916A CA000388128A CA388128A CA1182916A CA 1182916 A CA1182916 A CA 1182916A CA 000388128 A CA000388128 A CA 000388128A CA 388128 A CA388128 A CA 388128A CA 1182916 A CA1182916 A CA 1182916A
- Authority
- CA
- Canada
- Prior art keywords
- phase
- information
- record carrier
- read
- signal
- 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
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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
- G11B7/24—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
-
- 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
- G11B7/007—Arrangement of the information on the record carrier, e.g. form of tracks, actual track shape, e.g. wobbled, or cross-section, e.g. v-shaped; Sequential information structures, e.g. sectoring or header formats within a track
- G11B7/00736—Auxiliary data, e.g. lead-in, lead-out, Power Calibration Area [PCA], Burst Cutting Area [BCA], control information
Landscapes
- Optical Recording Or Reproduction (AREA)
- Optical Record Carriers And Manufacture Thereof (AREA)
Abstract
ABSTRACT:
A record carrier having an optically readable information structure and apparatus for reading said record carrier.
A record carrier is described which has an optically readable information structure in which information areas of adjacent information track portions have different phase depths, and an apparatus for reading said record carrier. By a suitable choice of the phase depths and by an electronic phase shift of the signals supplied by the read detectors, cross-talk between adjacent tracks can substantially be eliminated.
A record carrier having an optically readable information structure and apparatus for reading said record carrier.
A record carrier is described which has an optically readable information structure in which information areas of adjacent information track portions have different phase depths, and an apparatus for reading said record carrier. By a suitable choice of the phase depths and by an electronic phase shift of the signals supplied by the read detectors, cross-talk between adjacent tracks can substantially be eliminated.
Description
PHN. 10.121 The invention relates to a record carrier having an information structure which comprises optically readable information areas arranged in information tracks, adjacent information track portions c~iffering from each o-ther in tha-t they comprise information areas of a first phase depth and information areas oE a second phase depth respectively. The invention also relates to apparatus for reading such a record carrier.
Such a record carrier and apparatus for reading this record carrier are described in the Applicants' Canadian Patent 1,137,628 - issued December 14, 1982 (PHN 9083). In the record carrier described therein the :Eirst phase depth is preferably approximately ~ rad. and the second phase depth approximately 2 ~ rad..
When the inf:orma.tion structure is scanned with a read beam, this beam is split into a zero-order subbeam and a plurality of higher order subbeamsA The phase depth is defined as the difference between the phase of the zero order subbeam and the phase of one of the first order s~bbeams ~hen the centre of the read spot formed on the information struc~
ture coincides with tlle centre of an information area. In said Canadian Patent 1,137,62~ supra (P~IN 90~3) it i.s demonstrated that if the informati.on areas of each time two adjacent informa~ion tra.ck poXtions have different phase depths, these track portions can be arranged more closely to each other tllan in the case that the information structure comprises information. areas which all have the same phase depth. The information content of a record may then for example be doubled, without any significant increase in cro~s-talk between adjacent track portions.
However, the information track portions of dif-ferent phase depths should ~hen be read in different manners~ The infor~ation trac~ portions with the gxeatex phase depths are read by determining the variation of the total intensity of the radiation received from the record ,~
PHN. 10.121 2 carrier and passing through the pupil o~ the read objective.
This is the so-called integral or central aperture read method. The information track portions with the smaller phase depth are read by determining the difference of the intensities in two tangentially different halves of the pupil of the read objective. This is the so-called differential read method.
It has been found that when an information track portion with the greater phase depth is read by the integral method there is ne~ertheless some cross-talk from an adjacent information track portion having the smaller phase depth.
It is the object of the present invention to eli-minate this residual cross-talk. In accordance with a first aspect oE the invention the record carrier is therefore char-acterized in that the diffexence between the first and thesecond phase depth is substantially _~ rad.
When the difference in phase depths is thus chosen, the desired cross-talk reduction can be achieved by applying an additional electronic phase shift of one detector signal or of both detector signals.
It is possible to adapt only the greater phase depth, for example, to ma]ce it 7 7~ rad., and to maintain the smaller phase depth a-t the ~alue oE 2 ~ rad. as speciEied in Canadian Patent l,137,628 (PHN 9083). The information track portions ~ith the greatex phase depth should then be read in accordance with the integral method and the informa-tion track portions With the smaller phase depth in accordance with the differential method As the two read methods have different optical transfer functions ("modulation transEer function"; "M.T~F."), the alternate use of the two read methods could become perceptible in the signal which is ultimately supplied by the read apparatus. Moreover, the information areas with lower spatial frequencies can PHN 10121 3 10.9.1981 no longer be read in an optimum manner when the differential method is used.
Preferably, the lnformation areas are therefore di-mensioned so that they can all be read by means of the inte-- 5 gral method. The preferred embodiment of the record carrier is characterized in that the first phase depth is approximately J ~r rad and the second phase depth approximately 31T rad..
The two phase depths may be realized in different lO manners, for example by areas with different refractive in-dices. Suitably, the information areas comprise pits or hills.
The advantage of this is that the record carriers can be manufactured in large ~uantities using pressing techniques.
In this case of information areas in the form of hills or pits the phase depth is related to a geometrical depth or heigth. In the case of pits or hills with steep walls the phase depth is mainly determined by the geometrical depth or heigth. If the walls of the pits or hills are less steep, the phase depth is also determined by the angles of inclina 20 tion of said walls.
In accordance with a further ~2ac~ristic feature of the record carrier consecutive track portions within one information track differ from each other in that they com-prise information areas oE the first phase depth and informa-25 tion areas of the second phase depth respectively. Thisenables the visual efEect of transitions betw~en the two types of information areas ;n the signal which is ul-timately supplied by the read apparatus to be reduced.
For a correct timing of the desired electronic 30 phase shit during read-out of the record carrier, in accor-dance with a further characteristic feature, the record carrier may contain a pilot signal in addition to an informa-tion signal, which pilot signal identifies the transitions between information areas of the first phase depth and infor~
35 mation areas of the second phase depth and vice versa.
In accordance with a second aspect of the invention an apparatus for reading a record carrier containina informa tion areas of two different phase depths, which apparatus com-PHN. 10.121 4 prises a radiation source producing a read beam, an objec-tive system for focusing the read beam to a read spot on the information structure, and two radiation-sensitive detectors which are disposed in the far field of -the information struc-ture one on each side of a line which is effectively transverse of the track direction, the outputs of the two detec-tors being connected to an adder circuit, is characteri~ed in that at least one of the detectors is connected to the adder circuit via a phase-shifting element, which element sub-jects the detector signal to a phase shift of constant magni-tude.
If the two phase depths of the information areas have been selected so that the entire information structure can be read by means of the integral method, the phase shifting element should i.ntroduce a phase shift which is equal to the difference between the two phase depths, viz. a phase shift of approximately 2 rad.
Alternati~ely, the two phase depths may be selected so that one -type of information areas is adapted to be read with the integral method, whilst the other type of information areas is adapted to be :read with the differential method.
A read apparatus Which is adapted to read such a reco.rd car-rier is characteriz.ed in that the outputs of the two detectors are also connected to a sub-tractor circuit, that the outputs of the adder circuit and the subtractor circuit are connected to a signal processing circuit ~ia a switching element, and that a control input of the switching element is connected to an electronic circuit in. which a switching signal is derived from the signal which is read from the record carrier~ This apparatus is not only suitable for reading an information structure in which phase depths of ~ rad. and ~ rad.
occur, but may also be used for reading the record carrier wllich is described in Canadian Patent 1,137,628 (PHN 9083), i~e. a record carrier with phase depths of ~ rad. and of
Such a record carrier and apparatus for reading this record carrier are described in the Applicants' Canadian Patent 1,137,628 - issued December 14, 1982 (PHN 9083). In the record carrier described therein the :Eirst phase depth is preferably approximately ~ rad. and the second phase depth approximately 2 ~ rad..
When the inf:orma.tion structure is scanned with a read beam, this beam is split into a zero-order subbeam and a plurality of higher order subbeamsA The phase depth is defined as the difference between the phase of the zero order subbeam and the phase of one of the first order s~bbeams ~hen the centre of the read spot formed on the information struc~
ture coincides with tlle centre of an information area. In said Canadian Patent 1,137,62~ supra (P~IN 90~3) it i.s demonstrated that if the informati.on areas of each time two adjacent informa~ion tra.ck poXtions have different phase depths, these track portions can be arranged more closely to each other tllan in the case that the information structure comprises information. areas which all have the same phase depth. The information content of a record may then for example be doubled, without any significant increase in cro~s-talk between adjacent track portions.
However, the information track portions of dif-ferent phase depths should ~hen be read in different manners~ The infor~ation trac~ portions with the gxeatex phase depths are read by determining the variation of the total intensity of the radiation received from the record ,~
PHN. 10.121 2 carrier and passing through the pupil o~ the read objective.
This is the so-called integral or central aperture read method. The information track portions with the smaller phase depth are read by determining the difference of the intensities in two tangentially different halves of the pupil of the read objective. This is the so-called differential read method.
It has been found that when an information track portion with the greater phase depth is read by the integral method there is ne~ertheless some cross-talk from an adjacent information track portion having the smaller phase depth.
It is the object of the present invention to eli-minate this residual cross-talk. In accordance with a first aspect oE the invention the record carrier is therefore char-acterized in that the diffexence between the first and thesecond phase depth is substantially _~ rad.
When the difference in phase depths is thus chosen, the desired cross-talk reduction can be achieved by applying an additional electronic phase shift of one detector signal or of both detector signals.
It is possible to adapt only the greater phase depth, for example, to ma]ce it 7 7~ rad., and to maintain the smaller phase depth a-t the ~alue oE 2 ~ rad. as speciEied in Canadian Patent l,137,628 (PHN 9083). The information track portions ~ith the greatex phase depth should then be read in accordance with the integral method and the informa-tion track portions With the smaller phase depth in accordance with the differential method As the two read methods have different optical transfer functions ("modulation transEer function"; "M.T~F."), the alternate use of the two read methods could become perceptible in the signal which is ultimately supplied by the read apparatus. Moreover, the information areas with lower spatial frequencies can PHN 10121 3 10.9.1981 no longer be read in an optimum manner when the differential method is used.
Preferably, the lnformation areas are therefore di-mensioned so that they can all be read by means of the inte-- 5 gral method. The preferred embodiment of the record carrier is characterized in that the first phase depth is approximately J ~r rad and the second phase depth approximately 31T rad..
The two phase depths may be realized in different lO manners, for example by areas with different refractive in-dices. Suitably, the information areas comprise pits or hills.
The advantage of this is that the record carriers can be manufactured in large ~uantities using pressing techniques.
In this case of information areas in the form of hills or pits the phase depth is related to a geometrical depth or heigth. In the case of pits or hills with steep walls the phase depth is mainly determined by the geometrical depth or heigth. If the walls of the pits or hills are less steep, the phase depth is also determined by the angles of inclina 20 tion of said walls.
In accordance with a further ~2ac~ristic feature of the record carrier consecutive track portions within one information track differ from each other in that they com-prise information areas oE the first phase depth and informa-25 tion areas of the second phase depth respectively. Thisenables the visual efEect of transitions betw~en the two types of information areas ;n the signal which is ul-timately supplied by the read apparatus to be reduced.
For a correct timing of the desired electronic 30 phase shit during read-out of the record carrier, in accor-dance with a further characteristic feature, the record carrier may contain a pilot signal in addition to an informa-tion signal, which pilot signal identifies the transitions between information areas of the first phase depth and infor~
35 mation areas of the second phase depth and vice versa.
In accordance with a second aspect of the invention an apparatus for reading a record carrier containina informa tion areas of two different phase depths, which apparatus com-PHN. 10.121 4 prises a radiation source producing a read beam, an objec-tive system for focusing the read beam to a read spot on the information structure, and two radiation-sensitive detectors which are disposed in the far field of -the information struc-ture one on each side of a line which is effectively transverse of the track direction, the outputs of the two detec-tors being connected to an adder circuit, is characteri~ed in that at least one of the detectors is connected to the adder circuit via a phase-shifting element, which element sub-jects the detector signal to a phase shift of constant magni-tude.
If the two phase depths of the information areas have been selected so that the entire information structure can be read by means of the integral method, the phase shifting element should i.ntroduce a phase shift which is equal to the difference between the two phase depths, viz. a phase shift of approximately 2 rad.
Alternati~ely, the two phase depths may be selected so that one -type of information areas is adapted to be read with the integral method, whilst the other type of information areas is adapted to be :read with the differential method.
A read apparatus Which is adapted to read such a reco.rd car-rier is characteriz.ed in that the outputs of the two detectors are also connected to a sub-tractor circuit, that the outputs of the adder circuit and the subtractor circuit are connected to a signal processing circuit ~ia a switching element, and that a control input of the switching element is connected to an electronic circuit in. which a switching signal is derived from the signal which is read from the record carrier~ This apparatus is not only suitable for reading an information structure in which phase depths of ~ rad. and ~ rad.
occur, but may also be used for reading the record carrier wllich is described in Canadian Patent 1,137,628 (PHN 9083), i~e. a record carrier with phase depths of ~ rad. and of
2 rad. In that case a phase-shifting PHN 10121 5 10.9.1981 element is included only in cne of the connections between the detectors and the adder circuit, whilst the detectors are connected directly to the subtractor circuit. In apparatus for reading a record carrier with phase depths of 7~ rad, and of 27~ rad,at least one detector is connected both to the adder circuit and the subtractor circuit via a phase-shifting - element. In the two last-mentioned apparatus the phase-lO shifting element introduces a phase shift of approximately 7~ rad..
For reasons of symmetry it is preferred, both in an apparatus which solely employs the integral read method and in an apparatus which employs both the integral read method 15 and the differential read method, to connect each of the detectors vi a a p ha s e sh i f t i n g eleme r,t the adder circuit only or to both the adder circuit and the subtractor circuit. Said element should then introduce phase shifts which are equal but of opposite sign. In the 20 apparatus which only employs the integral read method, the phase-shifting elements should moreover be ad~ustable in such a way that the signs of the two phase shifts can be changed.
In order to ensure that the cross-talk reduction in accordance with the invention is still operative at smaller 25 spatial frequencies of the information areas, the detectors are preferably each disposed against an edge oE the effective pupil of the objective system. The efEective pupil is to be understood to mean the image of the pupil in the plane of the two detectors.
30The invention will now be described in more~detail with reference to the drawing. In the drawing :
Figure 1 is a plan view of a part of a first embodi-ment of a record carrier, Figure 2 is a tangential sectional view of said 35 record carrier, Figure 3 is a radial sectional view of said record carrier, PHN 10121 6 10.9.1981 Figure 4 is a plan view of a part of a second embodiment of a record carrier, Figure 5 is a tangential sectional view of said - record carrier, Figure 6 is a radial sectional view of said recorcl carrier, - Figure 7 shows an embodiment of a read apparatus, Figure 8 shows the arrangement of the detectors relative to the various diffraction orders, Figure 9 shows a first version of the electronic circuit for processing the detector signals, Figure 10 shows a second version of said electro-nic circuit, Figure 11 shows a third version of said electronic lS circuit, and Figure 12 represents the waveform of a radial error signal in an embodiment of a servo system for controlling the radial position of the read spot.
In these Figures similar elements always bear the 20 same reference numerals.
Figures 1, 2 and 3 show a first embodiment of a record carrier in accordance with the invention. Figure 1 is a plan view, Figure 2 a tangential sectional view taken on the line II-II' in Figure 1, and Figure 3 a radial sectional 25 view taken on the line III-III' in Figure 1 of the record carrier. The information is contained in a multitude of in-formation areas ~, or example pits in the substrate 6. These areas are arranged in accordance with tracks 2. Between the information areas 4 intermediate areas 5 are interposed. The 3n tracks 2 are spaced by narrow lands 3. The spatial frequency, and as the case may be the lengths, of the areas is determi-ned by the information.
The areas of the adjacent information tracks have different phase depths. As is shown in Figure 3, the pits of 35 a first track, a third track etc. are therefore deeper than the pits 4' of the second track, the fourth track etc. The geometrical depths of the pits 4 and 4' are designated d1 and . d2. Owing to the different depths the first track, the third P~N 10121 7 10.9.1981 track etc. can optically be distinguished from the second track, the fourth track etc. This enables said tracks to be packed more densely.
In a practical embodiment of a record carrier in - 5 accordance with the invention the radial period of the in-formation tracks was 0.85/um, the width of these tracks was 0.5/um and the width of the lands 3 was 0.35/um.
The information carrying surface of the record carrier can be made reflecting, for example by vacuum-depo-10 sition of a metal layer 7 such as aluminium, on said surface.
It is to be noted that the size of the areas inthe Figures 1, 2 and 3 has been exaggerated for the sake of clarity.
Figure 4 is a plan view of a part of a second em-bodiment of a record carrier in accordance with the invention.
This Figure shows a larger part of the record carrier than Figure 1, the individual information areas being no longer discernible. The information trac]cs are now divided into portions a and b, the portions a comprising information areas 20 of greater phase depth (deeper pits) and the portions _ in-formation areas of smaller phase depth.
In Figure 5, which is an enlarged tangential sec-tional view of a track taken on the line V-V' in Figure 4, the pits of the depth d2 are again designated 4' and the 25 pits of the depth d1 are designated 4.
Figure 6 is a radial sectional view, taken on the line VI-VI' in Figure 4, of the second embodiment of the record carrier.
In Figures 1 through 6 the information areas have 30 perpendicular walls and the phase depth is dictated by the geometrical depth of the information areas. In practice the information areas will have oblique walls. The phase depth is then also determined by the angles of inclination of said walls.
Figure 7 shows an embodiment of an apparatus for reading a record carrier. The round disc-shaped record carrier is shown in a radial sectional view. The information tracks thus extend perpendicularly to the plane of the drawing~ It P~IN 10121 8 10.9.1981 is assumed that the information structure is disposed on the upper side of the record carrier and is reflecting, so that reading is effected through the subs-trate 6. The information structure may furthermore be covered wi-th a protective layer 6. The record carrier can be rotated by means of a spindle 16, which is driven by a motor 15.
A radiation source 10, for example a helium-neon - laser or a semiconductor diode laser, produces a read heam 11.
A mirror 12 reflects this beam to an objective system 13, which is schematically represented by a single lens. The path of the read beam includes an auxiliary lens 14, which ensures - that the pupil of the objective system is filled in an opti-mum manner. A read spot V of minimal dimensions is then formed on the information structure.
The read beam is reflected by the information structure and, as the record carrier rotates, is modulated in accordance with the sequence of the information areas in the information track to be read. By moving the read spot and the record carrier relative to each other in a radial direction, 20 the entire information surface can be scanned.
The modulated read beam again traverses the ob-jective system and is again reflected by the mirror 12. The radiation path included means for separating the modulated and the unmodulated read beam. These means may for example 25 comprise a polarization-sensitive splitter prism and al/4 plate (wherein ~ is the wavelen~th of the read beam). For the sal~e of simplicity it is assumed in Figure 7 that the said means are constituted by a semitransparent mirror 17. This mixror reflects the modulated beam to a radiation-sensitive 30 detection system 20.
This detection system comprises two radiation-sensitive detectors 22 and 23, which are disposed in the so-called "far field of the information structure", i.e. in a plane in which the centroids of the subbeams formed hy the information structure, specifically of the zero-order sub-beam and the first-order cubbeams, are ceparated. The de-tection system may ~e disposed in the plane 21 in which an image of the exit pupil of the objective system 13 is formed P~ 10121 9 10 ~.1981 by the auxiliary lens 18. In Figure 7 the image C' of the point C of the exit pupil is represented by dashed lines.
The information structure which comprises adjacent information tracks, which tracks comprise information areas and intermediate areas, behaves as a two-dimensional diffrac-tion grating. This grating splits the read beam into a zero-- order subheam, a plurality of first-order subbeams and a plurality of higher-order subheams. After being reflected by the information structure a part of the radiation re-enters lO the objective systemO In the plane of the exit pupil of the objective system, or in the plane in which an image of this exit pupil is formed, the centoids of the subbeams are sepa -rated from each other. Figure 8 represents the situation in the plane 21 of Figure 7.
The circle 40 with the centre 45 represents the cross-section of the zero order subbeams in this plane. The circles 41 and 42 with the centres 46 and 47 represent the cross-sections of the tangentially diffracted subbeams of the orders (+1, 0) and (-1, 0). The X-axis and the Y-axis in 20 Figure 8 correspond to the tangential direction, or the track direction, and the radial direction, or the direction transverse of the track direction, on the record carrier. The distance f from the centres 46 and 47 to the Y-axis is deter-mined by A/p, where p is the local spatial period cf the 25 information areas in the information trac]c portion to he read and A the wavelength of the read beam.
For reading the informa-tion use is made of the phase shifts of -the subheams of the (+1, 0) and ~-1, o) orders relative to the zero-order subheam. In the hatched 30 areas in Figure 8 said first-order subbeams and zerc-order suh-beam cverlap, so that interference occurs. The phases of the first-order subbeams vary with high frequencies as a result of the tangential movement of the re;~l spot re1ative to the information track. This results in the intensity variations 35 in the exit pupil, or in the image thereof, which variations can be detected by the detectors 22 and 23.
When the centre of the read spot coincides with the centre of an information area a specific phase difference ~
PHN 10121 10 10,9.1981 will occur between the first-order subbeam and the zero-order subbeam. This phase difference is called the phase depth of the information area. At the transition of the read spot from a first information area to a second information area the phase of the subheam of the (+1, 0) order increases by 2 r~ . Therefore, when the read spot moves in a tangential direction the phase of said subbeam relative to the zero~
order subbeam will vary by W t. Here, W is a time frequency which is determined by the spatial frequency of the informa-tion area and by the speed with which the read spot travelsover the track.
The phases ~(+1, 0) and ~(-1, 0) of the first-order subbeams relative to the zero-order subbeam may be re-presented by :
a (+1, o) -~+ ~t ~ (-1, O) = ~- Wt The intensity variations as a result of interference of the first-order subbeam with the zero-order subbeam are converted into electric si~nals by the detectors 22 and 23. The time-20 dependent output signals S23 and S22 of the detectors 23 and22 may be represented by :
S23 = B (~) cos (~ + ~ t) S22 = ~ (~) cos (~ - ~t) Here B ( ~) is a factor which is proportional to the geome-25 trical depth of the pits. For ~ it may be assuemd that B ( ~) is zero.
In a first embodiment o a record carrier in accor-dance with the invention the phase depth ~1 cf the information 30 areas 4 is 7 r~/6 rad.and the phase depth ~2 of the information areas 4' is ~ l~3 rad. In the apparatlls forreading said re -cord carrier, as is shown in Figure 9, the outputs of the detectors 22 and 23 are connected to the phase shifting ele -ments 2~ and 25. The element 24 shifts the phase of the detec-tor S22 through + ~ rad, whilst the element 25 shifts the phaseof the detector signal S23 through - ~ rad. The signals S22 and S23 then change to :
9~l~
PHN 10121 11 10.9.1981 S 23 = B (~).cos~r+ (~ t - ~ = B (~).cos (~y-~ t - ~) S'~2 = B (~).cos~ - (~ t-~0)~ = B (~).cos (~- ~t - ~) When the information areas oE an information track portion being read have the greater phase depth ~P1 = 7~;/6 rad.
- the signals S'22 and S'23 should be added, whilst if the informatior- areas of the information track portion being read have the smaller phase depth, ~2 - 2~~/3rad, the signals S'22 and S'23 should be subtracted from each other. For this purpose, as is shown in Figure 9, the signals S'22 and S'23 may be applied both to the adder circuit 26 and to the subtractor circuit 27. The outputs o the circuits 26 and 27 are connected to the two input terminals e1 and e2 of a switch 28 haviny one master terminal e. Depending on the control signal Sc applied to its control input said switch transfers either the sum signal of the detectors 22 and 23 or the difference signal of said detectors to a demodulation cir-cuit 29. In this circuit -the signal read is demodulated and 20 rendered suitable for reproduction with for example a television set 30.
For controlling the switch 28 a control signal should be generated. In addition to the actual information signal the record carrier may contain a pilot signal, which 25 indicates the positions on -the record carrier where a transi-tion OCCUl-S from the information areas of a first phase depth to the information areas of a second phase depth. If a tele-vlsion signal has been recorded, one television signal being recorded per information track revolution, the picture syn-30 chronizing pulses or field synchronizing pulses contained in the actual television signal may be employed for generating the control signal Sc and no separate pilot signal is needed.
The pilot signal may be needed if an audio signal has been recorded.
If the information of the lines of a television picture is contained in track portions a and b in accordance with Figure 4, the line synchronizing pulses 32, as shown in Figure 9, may be extracted from the signal from the demodula-PHN 10121 12 10.9.1981 tion ircuit 29 in the line synchronizing pulse separator 31.
Inthe circuit, 33, which is for example a bistable multivi-brator, the pulses 32 are converted into a control signal Sc For the switch 28, so that said switchis changed over each time after reading one television line.
If each information track of the information struc-ture contains only one type of areas, the element 31 is a picture synchronizing pulse separator a,nd the switch 28 is changed over after read-out of each information track or two lO television fields.
When point e2 in the switch is connected to point e, the so-called integral read method is employed. The signal applied to the demodulator 29 may then be expressed by :
SI = S'23 t S'22 = 2-B (~)-cos (~ -0)-cos (W t)-If point e is connected to point e1, reading is effected in accordance with the so-called differential method. The signal applied to the demodu]ator may then be expressed by :
D S 23 S 22 = -2.B (~ ).sin (~ - 0).sin ( ~ t).
The integral method is employed when reading information areas 20 having a phase depth ~1 = 7 ~/6 rad. The signal SI is then a maximum if cos (~1 ~ 0) = 1, l.e. if 0 = l~/6 rad. For the information areas of the phase depth ~2 = 2~C/3 rad, cos (~ - 0) = 0. Thus, when reading in accordance with the integral method, the inormation areas of the smaller phase 25 depth are not "observed". Conversely, when the differential read method is used the information areas ~' of a phase depth ~ 2 = 2 r~/3 rad. wlll be read in an optimum manner, for sin ( 2~C- 0 ) is then 1, whilst the information areas 4 of 30 the phase depth ~1 = 7~ rad. are then not "observed", for sin ( 7~- 0) is then 0. 1, Instead of the two phase-shifting elements 24 and 25 35 it is alternatively possible to use the phase shifting ele-ment 25 only. If the phase shift 0 of said element is selected to be ,~/3 rad., the same result is obtained.
By means of an apparatus in which one detector slgnal PHN 10121 13 10.9.1981 or both detector signals are s~kjected to an additional phase shift, it is also possible to obtain a substan-tial improve-ment of the read-out of the record carrier described in Netherlands Patent Application no. 78 03517, l.e. of the record carrier having the phase depths ~ rad and ~ 2 = ~ rad..
The apparatus adapted for reading this record carrier is shown in Figure 10.
The signals from the detectors 22 and 23 are applied lO directly to the subtractor circuit 27. In the connections between said detectors and the inputs of th^e adder circuit 26 phase shifting elements 24 and 25 are included, which intro-duce a constant phase shift of ~ 0 rad. and - 0 rad. respec-- tively. During differential read-out of the information areas 15 of the phase depth ~2 = 2l~ rad., the information areas of the phase depth ~ rad. will produce no cross-talk. The cross-talk from the information areas of ~2 = 2~ rad. during 20 read-out by the integral method of information areas of ~1 =
~I rad. can be substantially eliminated if 0 = 1~ rad..As a result of this phase shift the amplitude of the signal SI de-creases slightly, but is still sufficiently high. It is al-25 ternatively possible to employ the ~hase shifter 24 only,which should then introduce a phase shift of l~ rad, For the values of the phase depths ~ 2 and the phase shift 0 specified in the foregoing, the integral read 30 method and the differential read method m-st be used alter-nately. However, these two methods havedifferent optical modula-tion transfer functions. If a video signal is stored on the record carrier the one transfer function will for example cause different grey shades or a different colour saturation 35 in the ultimate television pictu e than the other transfer func-tion. In the case of an audio signal in the form of a frequen-cy~modulated s~gna', switching between the transfer functions m~y become audible as an undesired frequency.
PHN 10121 14 10.9.1981 Furthermore, for reading lower spatial frequencies of the information areas, the transfer function of the dif-ferential method is worse than that of the integral method, Suitably, the phase depths ~1 and ~2 are therefore selected so that they are symmetrical re]ative to ~ rad..
The phase depth ~1 is then 51~ rad. and the phase depth ~ 2 is then 3~ rad,,The magnitude of the phase shift 0 is then l~ rad..
Figure 11 shows a signal processing circuit of an appa-ratus for reading this record carrier. The detectors 22 and 23 are each connected to a phase shifting element 24 and 25 respectively. The element 25 introduces a phase shiEt -15 and the element 24 a phase shift -~ 0 , the magnitude of 0 being r~4 rad..The sign of ~ should now bech~ed at the transi-tion from information areas of the greater phase depth to information areas of the smaller phase depth and vlce versa.
When reading the information areas of the greater phase depth 20 0 = + ~/4 rad.and when reading information areas of the smaller phase depth ~ = - r~4 rad.,For changing the sign of the phase shift ~ it is again possible to employ the signal Sc.
The information signal SI is always given by :
I S 23 + S 22 = 2.B (~).cos (~- 0 ).cos (W t).
When the information areas 4 of the phase depth ~1 = 5 ~/4 rad.
are read, then ~ = + ~/4 rad..Then, cos (~ /4) is equal to 1. For the information areas 4' of the phase depth ~2 =
30 3 ,~/4 rad., cos ( ~2 ~ ~/4) is equal to 0, so -that these information areas will produce no cross-talk. When the informa -tion areas 4' are read ~ /4 rad.and cos (~ 2 + J~/4) is 1, whilst cos ( ~1 + ~Z/4) is 0, so that the information areas 4 of the greater phase depth are not "observed" and thus pro-35 duce no cross-talk.
The values for the phase depths specified in the fore-going are no strict values. Deviations of the order of some degrees are permissible.
PHN 10121 l5 10.9.1981 It is possible that the difference between the phase depth ~11 and ~2 deviate~ from ~L rad..However, by adapting the electronic phase shift ~ it is still possible to ensure - 5 that the cross-talk between adjacent information track portions is mini~ized So far only the tangentially diffracted first~order subbeams have been discussed. The information structure also diffracts the read radiation in higher tangential orders lO and in various radial and diagonal orders. The information areas, which for the tangential first orders exhibit a difference be-tween the phase depths ~1 and ~2 of l~ rad.~ however, will also exhibit such a phase depth difference for the higher tangential 15 orders and for the radial and diagonal orders. The subbeams which are diffracted otherwise than in the tangential first orders will not significantly influence the effect of cross-talk reduction and need not be further considered.
In the foregoing it has been assumed that the signals 20supplied by the detectors have a fixed phace difference which is determined by the phase depth of the information areas. By influencing this phase difference with the aid of an electronic phase shifter, the signal produced by said information areas can be maximized during read-out of information areas of a 25first phase depth and the signal from information areas with a second phase depth can be minimized. It ls then assumed that the detector 22 only receives the beam 42 and the detec-tor 23 only receives the beam 41. At lower spatial frequencies of the information areas, i.e. at greater periods p of said
For reasons of symmetry it is preferred, both in an apparatus which solely employs the integral read method and in an apparatus which employs both the integral read method 15 and the differential read method, to connect each of the detectors vi a a p ha s e sh i f t i n g eleme r,t the adder circuit only or to both the adder circuit and the subtractor circuit. Said element should then introduce phase shifts which are equal but of opposite sign. In the 20 apparatus which only employs the integral read method, the phase-shifting elements should moreover be ad~ustable in such a way that the signs of the two phase shifts can be changed.
In order to ensure that the cross-talk reduction in accordance with the invention is still operative at smaller 25 spatial frequencies of the information areas, the detectors are preferably each disposed against an edge oE the effective pupil of the objective system. The efEective pupil is to be understood to mean the image of the pupil in the plane of the two detectors.
30The invention will now be described in more~detail with reference to the drawing. In the drawing :
Figure 1 is a plan view of a part of a first embodi-ment of a record carrier, Figure 2 is a tangential sectional view of said 35 record carrier, Figure 3 is a radial sectional view of said record carrier, PHN 10121 6 10.9.1981 Figure 4 is a plan view of a part of a second embodiment of a record carrier, Figure 5 is a tangential sectional view of said - record carrier, Figure 6 is a radial sectional view of said recorcl carrier, - Figure 7 shows an embodiment of a read apparatus, Figure 8 shows the arrangement of the detectors relative to the various diffraction orders, Figure 9 shows a first version of the electronic circuit for processing the detector signals, Figure 10 shows a second version of said electro-nic circuit, Figure 11 shows a third version of said electronic lS circuit, and Figure 12 represents the waveform of a radial error signal in an embodiment of a servo system for controlling the radial position of the read spot.
In these Figures similar elements always bear the 20 same reference numerals.
Figures 1, 2 and 3 show a first embodiment of a record carrier in accordance with the invention. Figure 1 is a plan view, Figure 2 a tangential sectional view taken on the line II-II' in Figure 1, and Figure 3 a radial sectional 25 view taken on the line III-III' in Figure 1 of the record carrier. The information is contained in a multitude of in-formation areas ~, or example pits in the substrate 6. These areas are arranged in accordance with tracks 2. Between the information areas 4 intermediate areas 5 are interposed. The 3n tracks 2 are spaced by narrow lands 3. The spatial frequency, and as the case may be the lengths, of the areas is determi-ned by the information.
The areas of the adjacent information tracks have different phase depths. As is shown in Figure 3, the pits of 35 a first track, a third track etc. are therefore deeper than the pits 4' of the second track, the fourth track etc. The geometrical depths of the pits 4 and 4' are designated d1 and . d2. Owing to the different depths the first track, the third P~N 10121 7 10.9.1981 track etc. can optically be distinguished from the second track, the fourth track etc. This enables said tracks to be packed more densely.
In a practical embodiment of a record carrier in - 5 accordance with the invention the radial period of the in-formation tracks was 0.85/um, the width of these tracks was 0.5/um and the width of the lands 3 was 0.35/um.
The information carrying surface of the record carrier can be made reflecting, for example by vacuum-depo-10 sition of a metal layer 7 such as aluminium, on said surface.
It is to be noted that the size of the areas inthe Figures 1, 2 and 3 has been exaggerated for the sake of clarity.
Figure 4 is a plan view of a part of a second em-bodiment of a record carrier in accordance with the invention.
This Figure shows a larger part of the record carrier than Figure 1, the individual information areas being no longer discernible. The information trac]cs are now divided into portions a and b, the portions a comprising information areas 20 of greater phase depth (deeper pits) and the portions _ in-formation areas of smaller phase depth.
In Figure 5, which is an enlarged tangential sec-tional view of a track taken on the line V-V' in Figure 4, the pits of the depth d2 are again designated 4' and the 25 pits of the depth d1 are designated 4.
Figure 6 is a radial sectional view, taken on the line VI-VI' in Figure 4, of the second embodiment of the record carrier.
In Figures 1 through 6 the information areas have 30 perpendicular walls and the phase depth is dictated by the geometrical depth of the information areas. In practice the information areas will have oblique walls. The phase depth is then also determined by the angles of inclination of said walls.
Figure 7 shows an embodiment of an apparatus for reading a record carrier. The round disc-shaped record carrier is shown in a radial sectional view. The information tracks thus extend perpendicularly to the plane of the drawing~ It P~IN 10121 8 10.9.1981 is assumed that the information structure is disposed on the upper side of the record carrier and is reflecting, so that reading is effected through the subs-trate 6. The information structure may furthermore be covered wi-th a protective layer 6. The record carrier can be rotated by means of a spindle 16, which is driven by a motor 15.
A radiation source 10, for example a helium-neon - laser or a semiconductor diode laser, produces a read heam 11.
A mirror 12 reflects this beam to an objective system 13, which is schematically represented by a single lens. The path of the read beam includes an auxiliary lens 14, which ensures - that the pupil of the objective system is filled in an opti-mum manner. A read spot V of minimal dimensions is then formed on the information structure.
The read beam is reflected by the information structure and, as the record carrier rotates, is modulated in accordance with the sequence of the information areas in the information track to be read. By moving the read spot and the record carrier relative to each other in a radial direction, 20 the entire information surface can be scanned.
The modulated read beam again traverses the ob-jective system and is again reflected by the mirror 12. The radiation path included means for separating the modulated and the unmodulated read beam. These means may for example 25 comprise a polarization-sensitive splitter prism and al/4 plate (wherein ~ is the wavelen~th of the read beam). For the sal~e of simplicity it is assumed in Figure 7 that the said means are constituted by a semitransparent mirror 17. This mixror reflects the modulated beam to a radiation-sensitive 30 detection system 20.
This detection system comprises two radiation-sensitive detectors 22 and 23, which are disposed in the so-called "far field of the information structure", i.e. in a plane in which the centroids of the subbeams formed hy the information structure, specifically of the zero-order sub-beam and the first-order cubbeams, are ceparated. The de-tection system may ~e disposed in the plane 21 in which an image of the exit pupil of the objective system 13 is formed P~ 10121 9 10 ~.1981 by the auxiliary lens 18. In Figure 7 the image C' of the point C of the exit pupil is represented by dashed lines.
The information structure which comprises adjacent information tracks, which tracks comprise information areas and intermediate areas, behaves as a two-dimensional diffrac-tion grating. This grating splits the read beam into a zero-- order subheam, a plurality of first-order subbeams and a plurality of higher-order subheams. After being reflected by the information structure a part of the radiation re-enters lO the objective systemO In the plane of the exit pupil of the objective system, or in the plane in which an image of this exit pupil is formed, the centoids of the subbeams are sepa -rated from each other. Figure 8 represents the situation in the plane 21 of Figure 7.
The circle 40 with the centre 45 represents the cross-section of the zero order subbeams in this plane. The circles 41 and 42 with the centres 46 and 47 represent the cross-sections of the tangentially diffracted subbeams of the orders (+1, 0) and (-1, 0). The X-axis and the Y-axis in 20 Figure 8 correspond to the tangential direction, or the track direction, and the radial direction, or the direction transverse of the track direction, on the record carrier. The distance f from the centres 46 and 47 to the Y-axis is deter-mined by A/p, where p is the local spatial period cf the 25 information areas in the information trac]c portion to he read and A the wavelength of the read beam.
For reading the informa-tion use is made of the phase shifts of -the subheams of the (+1, 0) and ~-1, o) orders relative to the zero-order subheam. In the hatched 30 areas in Figure 8 said first-order subbeams and zerc-order suh-beam cverlap, so that interference occurs. The phases of the first-order subbeams vary with high frequencies as a result of the tangential movement of the re;~l spot re1ative to the information track. This results in the intensity variations 35 in the exit pupil, or in the image thereof, which variations can be detected by the detectors 22 and 23.
When the centre of the read spot coincides with the centre of an information area a specific phase difference ~
PHN 10121 10 10,9.1981 will occur between the first-order subbeam and the zero-order subbeam. This phase difference is called the phase depth of the information area. At the transition of the read spot from a first information area to a second information area the phase of the subheam of the (+1, 0) order increases by 2 r~ . Therefore, when the read spot moves in a tangential direction the phase of said subbeam relative to the zero~
order subbeam will vary by W t. Here, W is a time frequency which is determined by the spatial frequency of the informa-tion area and by the speed with which the read spot travelsover the track.
The phases ~(+1, 0) and ~(-1, 0) of the first-order subbeams relative to the zero-order subbeam may be re-presented by :
a (+1, o) -~+ ~t ~ (-1, O) = ~- Wt The intensity variations as a result of interference of the first-order subbeam with the zero-order subbeam are converted into electric si~nals by the detectors 22 and 23. The time-20 dependent output signals S23 and S22 of the detectors 23 and22 may be represented by :
S23 = B (~) cos (~ + ~ t) S22 = ~ (~) cos (~ - ~t) Here B ( ~) is a factor which is proportional to the geome-25 trical depth of the pits. For ~ it may be assuemd that B ( ~) is zero.
In a first embodiment o a record carrier in accor-dance with the invention the phase depth ~1 cf the information 30 areas 4 is 7 r~/6 rad.and the phase depth ~2 of the information areas 4' is ~ l~3 rad. In the apparatlls forreading said re -cord carrier, as is shown in Figure 9, the outputs of the detectors 22 and 23 are connected to the phase shifting ele -ments 2~ and 25. The element 24 shifts the phase of the detec-tor S22 through + ~ rad, whilst the element 25 shifts the phaseof the detector signal S23 through - ~ rad. The signals S22 and S23 then change to :
9~l~
PHN 10121 11 10.9.1981 S 23 = B (~).cos~r+ (~ t - ~ = B (~).cos (~y-~ t - ~) S'~2 = B (~).cos~ - (~ t-~0)~ = B (~).cos (~- ~t - ~) When the information areas oE an information track portion being read have the greater phase depth ~P1 = 7~;/6 rad.
- the signals S'22 and S'23 should be added, whilst if the informatior- areas of the information track portion being read have the smaller phase depth, ~2 - 2~~/3rad, the signals S'22 and S'23 should be subtracted from each other. For this purpose, as is shown in Figure 9, the signals S'22 and S'23 may be applied both to the adder circuit 26 and to the subtractor circuit 27. The outputs o the circuits 26 and 27 are connected to the two input terminals e1 and e2 of a switch 28 haviny one master terminal e. Depending on the control signal Sc applied to its control input said switch transfers either the sum signal of the detectors 22 and 23 or the difference signal of said detectors to a demodulation cir-cuit 29. In this circuit -the signal read is demodulated and 20 rendered suitable for reproduction with for example a television set 30.
For controlling the switch 28 a control signal should be generated. In addition to the actual information signal the record carrier may contain a pilot signal, which 25 indicates the positions on -the record carrier where a transi-tion OCCUl-S from the information areas of a first phase depth to the information areas of a second phase depth. If a tele-vlsion signal has been recorded, one television signal being recorded per information track revolution, the picture syn-30 chronizing pulses or field synchronizing pulses contained in the actual television signal may be employed for generating the control signal Sc and no separate pilot signal is needed.
The pilot signal may be needed if an audio signal has been recorded.
If the information of the lines of a television picture is contained in track portions a and b in accordance with Figure 4, the line synchronizing pulses 32, as shown in Figure 9, may be extracted from the signal from the demodula-PHN 10121 12 10.9.1981 tion ircuit 29 in the line synchronizing pulse separator 31.
Inthe circuit, 33, which is for example a bistable multivi-brator, the pulses 32 are converted into a control signal Sc For the switch 28, so that said switchis changed over each time after reading one television line.
If each information track of the information struc-ture contains only one type of areas, the element 31 is a picture synchronizing pulse separator a,nd the switch 28 is changed over after read-out of each information track or two lO television fields.
When point e2 in the switch is connected to point e, the so-called integral read method is employed. The signal applied to the demodulator 29 may then be expressed by :
SI = S'23 t S'22 = 2-B (~)-cos (~ -0)-cos (W t)-If point e is connected to point e1, reading is effected in accordance with the so-called differential method. The signal applied to the demodu]ator may then be expressed by :
D S 23 S 22 = -2.B (~ ).sin (~ - 0).sin ( ~ t).
The integral method is employed when reading information areas 20 having a phase depth ~1 = 7 ~/6 rad. The signal SI is then a maximum if cos (~1 ~ 0) = 1, l.e. if 0 = l~/6 rad. For the information areas of the phase depth ~2 = 2~C/3 rad, cos (~ - 0) = 0. Thus, when reading in accordance with the integral method, the inormation areas of the smaller phase 25 depth are not "observed". Conversely, when the differential read method is used the information areas ~' of a phase depth ~ 2 = 2 r~/3 rad. wlll be read in an optimum manner, for sin ( 2~C- 0 ) is then 1, whilst the information areas 4 of 30 the phase depth ~1 = 7~ rad. are then not "observed", for sin ( 7~- 0) is then 0. 1, Instead of the two phase-shifting elements 24 and 25 35 it is alternatively possible to use the phase shifting ele-ment 25 only. If the phase shift 0 of said element is selected to be ,~/3 rad., the same result is obtained.
By means of an apparatus in which one detector slgnal PHN 10121 13 10.9.1981 or both detector signals are s~kjected to an additional phase shift, it is also possible to obtain a substan-tial improve-ment of the read-out of the record carrier described in Netherlands Patent Application no. 78 03517, l.e. of the record carrier having the phase depths ~ rad and ~ 2 = ~ rad..
The apparatus adapted for reading this record carrier is shown in Figure 10.
The signals from the detectors 22 and 23 are applied lO directly to the subtractor circuit 27. In the connections between said detectors and the inputs of th^e adder circuit 26 phase shifting elements 24 and 25 are included, which intro-duce a constant phase shift of ~ 0 rad. and - 0 rad. respec-- tively. During differential read-out of the information areas 15 of the phase depth ~2 = 2l~ rad., the information areas of the phase depth ~ rad. will produce no cross-talk. The cross-talk from the information areas of ~2 = 2~ rad. during 20 read-out by the integral method of information areas of ~1 =
~I rad. can be substantially eliminated if 0 = 1~ rad..As a result of this phase shift the amplitude of the signal SI de-creases slightly, but is still sufficiently high. It is al-25 ternatively possible to employ the ~hase shifter 24 only,which should then introduce a phase shift of l~ rad, For the values of the phase depths ~ 2 and the phase shift 0 specified in the foregoing, the integral read 30 method and the differential read method m-st be used alter-nately. However, these two methods havedifferent optical modula-tion transfer functions. If a video signal is stored on the record carrier the one transfer function will for example cause different grey shades or a different colour saturation 35 in the ultimate television pictu e than the other transfer func-tion. In the case of an audio signal in the form of a frequen-cy~modulated s~gna', switching between the transfer functions m~y become audible as an undesired frequency.
PHN 10121 14 10.9.1981 Furthermore, for reading lower spatial frequencies of the information areas, the transfer function of the dif-ferential method is worse than that of the integral method, Suitably, the phase depths ~1 and ~2 are therefore selected so that they are symmetrical re]ative to ~ rad..
The phase depth ~1 is then 51~ rad. and the phase depth ~ 2 is then 3~ rad,,The magnitude of the phase shift 0 is then l~ rad..
Figure 11 shows a signal processing circuit of an appa-ratus for reading this record carrier. The detectors 22 and 23 are each connected to a phase shifting element 24 and 25 respectively. The element 25 introduces a phase shiEt -15 and the element 24 a phase shift -~ 0 , the magnitude of 0 being r~4 rad..The sign of ~ should now bech~ed at the transi-tion from information areas of the greater phase depth to information areas of the smaller phase depth and vlce versa.
When reading the information areas of the greater phase depth 20 0 = + ~/4 rad.and when reading information areas of the smaller phase depth ~ = - r~4 rad.,For changing the sign of the phase shift ~ it is again possible to employ the signal Sc.
The information signal SI is always given by :
I S 23 + S 22 = 2.B (~).cos (~- 0 ).cos (W t).
When the information areas 4 of the phase depth ~1 = 5 ~/4 rad.
are read, then ~ = + ~/4 rad..Then, cos (~ /4) is equal to 1. For the information areas 4' of the phase depth ~2 =
30 3 ,~/4 rad., cos ( ~2 ~ ~/4) is equal to 0, so -that these information areas will produce no cross-talk. When the informa -tion areas 4' are read ~ /4 rad.and cos (~ 2 + J~/4) is 1, whilst cos ( ~1 + ~Z/4) is 0, so that the information areas 4 of the greater phase depth are not "observed" and thus pro-35 duce no cross-talk.
The values for the phase depths specified in the fore-going are no strict values. Deviations of the order of some degrees are permissible.
PHN 10121 l5 10.9.1981 It is possible that the difference between the phase depth ~11 and ~2 deviate~ from ~L rad..However, by adapting the electronic phase shift ~ it is still possible to ensure - 5 that the cross-talk between adjacent information track portions is mini~ized So far only the tangentially diffracted first~order subbeams have been discussed. The information structure also diffracts the read radiation in higher tangential orders lO and in various radial and diagonal orders. The information areas, which for the tangential first orders exhibit a difference be-tween the phase depths ~1 and ~2 of l~ rad.~ however, will also exhibit such a phase depth difference for the higher tangential 15 orders and for the radial and diagonal orders. The subbeams which are diffracted otherwise than in the tangential first orders will not significantly influence the effect of cross-talk reduction and need not be further considered.
In the foregoing it has been assumed that the signals 20supplied by the detectors have a fixed phace difference which is determined by the phase depth of the information areas. By influencing this phase difference with the aid of an electronic phase shifter, the signal produced by said information areas can be maximized during read-out of information areas of a 25first phase depth and the signal from information areas with a second phase depth can be minimized. It ls then assumed that the detector 22 only receives the beam 42 and the detec-tor 23 only receives the beam 41. At lower spatial frequencies of the information areas, i.e. at greater periods p of said
3~areas, the distance f in Figure 8 becomes smaller and the first-order beams 41 and 42 will overlap each other. The detector 22 or 23 would then no longer receive radiation of the respective beam 42 or 41 only, but also radiation of the beam 41 and 42 respectively. The phases of the first-order 35beams could then no longer be influenced individually, so that no cross-talk reduction in accordance with the inven-tion could be obtained. In order to enable a satisfactory cross-talk reduction to be realized at lower spatial frequen-Pl-~ 10121 16 10.9.1981 cies, the radiation-sensitive areas of the detectors, in-stead of being disposed as closely as possible to each other and in the centre of the pupil, as is shown in Figure 8 by the uninterrupted lines, are arranged as far as possible 5 from each other and at the edge of the pupil. In Figure 8 the last-mentioned positions of the detectors are represented by the dashed lines 22' and 23'. The limit for the spatial frequencies at which the detector 22 only receives the beam 42 and the detector 23 only the beam 41, is then considerably 10 reduced.
During reading the read spot should remain accurately positioned on the centre of the track to be read. For this purpose the read apparatus comprises a fine control for the radial position of the read spot. As is shown in Figure 7, 15 the mirror 12 may be mounted for rotation. The axis of rotation 3~ of the mirror is perpendicular to the plane of drawing, so that by rotating the mirror 12 the read spot is shifted in the radial direction. The rotation of the mirror is obtained by means of the drive element 39. This element may take various 20 fcrms ; it is for example an electromagnetic element as shown in Figure 7, or a piezo~electric element. The drive element is controlled by a control circuit 50, to whose input a radial error signal Sr is applied, i.e. a signal which provides an indica-tion of a deviation of the position of the read spot relative 25 to the centre of the track.
The signal Sr may be generated by means of two detectors which are disposed in the plane 21, one on each side of a line which is effectively parallel to the track direction, as is described in for example German Patent Application No.
30 2,342,906. By subtracting the output signals of these detectors from each other a radial error signal Sr is obtainedO Thus, an asymmetry in a radial direction of the radiation distribu-tion in the pupil is determined. This is the so-called differen-tial tracking method.
The servosystem may be adapted so that the information track portions of the greater phase depth, for example ~1 = 5~ 4 rad., are followed. In Figure 12 the uninterrupted line represents the signal Sr as a function of the radial position r of the PHN 10121 17 10.9.1981 read spot in the case that only these information track por-tions would be present. If the read spot is situated exactly on a deep information track portion, i.e. at the locations r, 2r etc., the signal Sr will be zero. The servo system Eor the trackirg is adapted so that in the case of a negative value of Sr the tilting mirror 12 in Figure 7 is pivoted anti-clockwise, so that the centre of the read spot is positioned exactly on the centre of the deep information track portion 2. For a positive value of Sr the mirror 12 is pivoted clock-wise. The points D in Figure 12 are the stable points for the servosystem.
In a record carrier in accordance with the invention shallow information track portions 2' are located between the deep information track portions 2. The pointE cn the curve for Sr, which point corresponds to the centre of the informa-tion track portion 2', is an unstable point. When the read spot is situated slightly to the right of the~centre of the informa-tion track portion 2', i.e. if Sr were positive, the mirror 12 would be pivoted clockwise and the read spot would be shifted even further to the right. In a similar way in the case of a deviation to the left of the position of the read spot,said spot would be shi~ted further to the left. Without further steps the read spot would not remain positioned on a shallow information track portion 2', but the read spot would constantly be controlled towards a deep information track portion.
In accordance with the invention, for reading a shallow information traclc or track portion, the signal Sr is inverted before being applied to the control circuit 50. The inverted signal Sr is represented by the dashed curve in Figure 12. The poirlt E on the curve for Sr , which point corresponds to -the centre of the information track portion 2', is a stable point and the points D on said curve are unstable points.
In the apparatus in accordance with Figure 7 there is provided a combination of an inverter 51 and a switch 52.
This enables the signal Sr ~o be applied to the control 50 in inverted or non-inverted form. The switch 52 is controlled by the signal S in synchronism with the switch 28 of Figure 9~
PHN. 10.121 18 When a deep information track portion is read the siynal Sr is not inverted and when a shallow information track portion is read it is inverted. During read-out of an information track 2 the heavy portion of the curve for Sr is used and during read-out of an information track 2' the heavy portion of the dashed curve for Sr is employed.
It is to be noted that the radial error signal S
contains contributions produced by the information track por-tions 2 and by the information track portions 2'. As a result of the different phase depths ~ rad. and ~2 =
3~ rad., these contributions would be in phase opposition.
However, as the information track portions 2' are shifted relative to the information track portions 2 over a distance equal to half the radial period of solely the information track portions 2, the said contributions in the signal Sr will augment each other.
The detectors for reading the information (22 and 23 in Figure 10) and those for generating the radial error signal may be combined, in the form of four detectors which are disposed in the four different quadrants of an ~-Y
coordinate system. For reading the information the signals from the detectors in the first and the fourth ~uadrant as well as the signals obtained from the detec-tors in the second and the third quadrants are added to each other. The sum signals thus obtained are either added to each other or sub-tracted from each other as described in the foregoing. For generating the radial error signal the signals from the detectors in the first and the second quadrant are added to each other and so are the signals from the detectors in the third and the fourth quadrant. The sum signals thus obtained are subtracted from each other, yielding the signal Sr.
Apart from being used for reading a record carrier with phase depths ~1 = 5~ rad. and ~2 = 34~ rad., th~
differential tracking method may also be employed for reading a record carrier with ~1 ~ 7r rad. and ~2 = 23f~rad.. For the last-mentioned record carriers tracking may also be realized as for example described in the Applicants' Cana~dian Patent 987,029 - issued April 6, 1976 tpHN 6296~, ~8~
PHN. 10.12] 19 which has been laid open to public inspection. In addition -to the read spot, two servo spots may be projected onto the in-Eormation structure. These spots are positioned so relative to each other that when the centre of the read spot exactly coincides with the centre of the information track portion to be read, the centres of the servo spots are situated at the two edges of this information track portion. For each servo spot there is provided a separate detector. The difference of the signals from said detectors is determined by the mag-nitude and the direction of the radial positional error ofthe read spot.
When reading a record carrier with the phase depths ~ rad. and ~2 = ~ rad., a radial error signal may also be generated by radially moving the read spot and the information track to be read periodically relative to each other with a low amplitude, for example o.l times the track width and with a comparatively low frequency, for example 30 kHz. The signal supplied by the information detectors then contains an additional component whose fre~uency and phase depend on the radial position oE -the read spot. The relative movement of the read spot and the information trac]c can be obtained by periodically moving the read beam ln the radial dire~tion. ~lternatively, as is described in -the Applican-ts' Canadian Patent 1,038,078 - issued September 5, 1978 (PHN 7190), which has been laid open to public inspec-tion, the information tracks may be undulating tracks. A positional error signal thus generated should also be inverted when a shallow track is to be read.
The invention has been described for a reflecting record carrier. It is also possible to employ the invention in conjunction with a record carriex having a phase structure which is read in transmission. If the phase structure com-prises pits or hills, they should be deeper and higher respectively than the respective pits or hills of a reflect-ing record carrier.
Furthermore, the in~ention may also be used forreading a record carrier in thQ form of a tapeO In that case the expression ~Iradial direction" used in the foregoing PHN 10121 20 l0.9.1981 I
should read: the direction perpendicular to the track direction.
ZO
~5
During reading the read spot should remain accurately positioned on the centre of the track to be read. For this purpose the read apparatus comprises a fine control for the radial position of the read spot. As is shown in Figure 7, 15 the mirror 12 may be mounted for rotation. The axis of rotation 3~ of the mirror is perpendicular to the plane of drawing, so that by rotating the mirror 12 the read spot is shifted in the radial direction. The rotation of the mirror is obtained by means of the drive element 39. This element may take various 20 fcrms ; it is for example an electromagnetic element as shown in Figure 7, or a piezo~electric element. The drive element is controlled by a control circuit 50, to whose input a radial error signal Sr is applied, i.e. a signal which provides an indica-tion of a deviation of the position of the read spot relative 25 to the centre of the track.
The signal Sr may be generated by means of two detectors which are disposed in the plane 21, one on each side of a line which is effectively parallel to the track direction, as is described in for example German Patent Application No.
30 2,342,906. By subtracting the output signals of these detectors from each other a radial error signal Sr is obtainedO Thus, an asymmetry in a radial direction of the radiation distribu-tion in the pupil is determined. This is the so-called differen-tial tracking method.
The servosystem may be adapted so that the information track portions of the greater phase depth, for example ~1 = 5~ 4 rad., are followed. In Figure 12 the uninterrupted line represents the signal Sr as a function of the radial position r of the PHN 10121 17 10.9.1981 read spot in the case that only these information track por-tions would be present. If the read spot is situated exactly on a deep information track portion, i.e. at the locations r, 2r etc., the signal Sr will be zero. The servo system Eor the trackirg is adapted so that in the case of a negative value of Sr the tilting mirror 12 in Figure 7 is pivoted anti-clockwise, so that the centre of the read spot is positioned exactly on the centre of the deep information track portion 2. For a positive value of Sr the mirror 12 is pivoted clock-wise. The points D in Figure 12 are the stable points for the servosystem.
In a record carrier in accordance with the invention shallow information track portions 2' are located between the deep information track portions 2. The pointE cn the curve for Sr, which point corresponds to the centre of the informa-tion track portion 2', is an unstable point. When the read spot is situated slightly to the right of the~centre of the informa-tion track portion 2', i.e. if Sr were positive, the mirror 12 would be pivoted clockwise and the read spot would be shifted even further to the right. In a similar way in the case of a deviation to the left of the position of the read spot,said spot would be shi~ted further to the left. Without further steps the read spot would not remain positioned on a shallow information track portion 2', but the read spot would constantly be controlled towards a deep information track portion.
In accordance with the invention, for reading a shallow information traclc or track portion, the signal Sr is inverted before being applied to the control circuit 50. The inverted signal Sr is represented by the dashed curve in Figure 12. The poirlt E on the curve for Sr , which point corresponds to -the centre of the information track portion 2', is a stable point and the points D on said curve are unstable points.
In the apparatus in accordance with Figure 7 there is provided a combination of an inverter 51 and a switch 52.
This enables the signal Sr ~o be applied to the control 50 in inverted or non-inverted form. The switch 52 is controlled by the signal S in synchronism with the switch 28 of Figure 9~
PHN. 10.121 18 When a deep information track portion is read the siynal Sr is not inverted and when a shallow information track portion is read it is inverted. During read-out of an information track 2 the heavy portion of the curve for Sr is used and during read-out of an information track 2' the heavy portion of the dashed curve for Sr is employed.
It is to be noted that the radial error signal S
contains contributions produced by the information track por-tions 2 and by the information track portions 2'. As a result of the different phase depths ~ rad. and ~2 =
3~ rad., these contributions would be in phase opposition.
However, as the information track portions 2' are shifted relative to the information track portions 2 over a distance equal to half the radial period of solely the information track portions 2, the said contributions in the signal Sr will augment each other.
The detectors for reading the information (22 and 23 in Figure 10) and those for generating the radial error signal may be combined, in the form of four detectors which are disposed in the four different quadrants of an ~-Y
coordinate system. For reading the information the signals from the detectors in the first and the fourth ~uadrant as well as the signals obtained from the detec-tors in the second and the third quadrants are added to each other. The sum signals thus obtained are either added to each other or sub-tracted from each other as described in the foregoing. For generating the radial error signal the signals from the detectors in the first and the second quadrant are added to each other and so are the signals from the detectors in the third and the fourth quadrant. The sum signals thus obtained are subtracted from each other, yielding the signal Sr.
Apart from being used for reading a record carrier with phase depths ~1 = 5~ rad. and ~2 = 34~ rad., th~
differential tracking method may also be employed for reading a record carrier with ~1 ~ 7r rad. and ~2 = 23f~rad.. For the last-mentioned record carriers tracking may also be realized as for example described in the Applicants' Cana~dian Patent 987,029 - issued April 6, 1976 tpHN 6296~, ~8~
PHN. 10.12] 19 which has been laid open to public inspection. In addition -to the read spot, two servo spots may be projected onto the in-Eormation structure. These spots are positioned so relative to each other that when the centre of the read spot exactly coincides with the centre of the information track portion to be read, the centres of the servo spots are situated at the two edges of this information track portion. For each servo spot there is provided a separate detector. The difference of the signals from said detectors is determined by the mag-nitude and the direction of the radial positional error ofthe read spot.
When reading a record carrier with the phase depths ~ rad. and ~2 = ~ rad., a radial error signal may also be generated by radially moving the read spot and the information track to be read periodically relative to each other with a low amplitude, for example o.l times the track width and with a comparatively low frequency, for example 30 kHz. The signal supplied by the information detectors then contains an additional component whose fre~uency and phase depend on the radial position oE -the read spot. The relative movement of the read spot and the information trac]c can be obtained by periodically moving the read beam ln the radial dire~tion. ~lternatively, as is described in -the Applican-ts' Canadian Patent 1,038,078 - issued September 5, 1978 (PHN 7190), which has been laid open to public inspec-tion, the information tracks may be undulating tracks. A positional error signal thus generated should also be inverted when a shallow track is to be read.
The invention has been described for a reflecting record carrier. It is also possible to employ the invention in conjunction with a record carriex having a phase structure which is read in transmission. If the phase structure com-prises pits or hills, they should be deeper and higher respectively than the respective pits or hills of a reflect-ing record carrier.
Furthermore, the in~ention may also be used forreading a record carrier in thQ form of a tapeO In that case the expression ~Iradial direction" used in the foregoing PHN 10121 20 l0.9.1981 I
should read: the direction perpendicular to the track direction.
ZO
~5
Claims (11)
1. A record carrier having an information structure which comprises optically readable information areas arranged in information tracks, adjacent information track portions differing from each other in that they comprise information areas of a first phase depth and information areas of a second phase depth respectively, characterized in that the difference between the first phase and the second phase depth is substantially rad.
2. A record carrier as claimed in Claim 1, charac-terized in that the first phase depth is approximately rad. and the second phase depth approximately rad.
3. A record carrier as claimed in Claim 1, charac-terized in that the consecutive track portions within one information track differ from each other in that they com-prise information areas of the first phase depth and informa-tion areas of the second phase depth respectively.
4. A record carrier as claimed in Claim 1, 2 or 3, characterized in that in addition to an information signal a pilot signal is recorded, which pilot signal indicates the transitions between information areas of the first phase depth and information areas of the second phase depth, and vice versa.
5. An apparatus for reading a record carrier, con-taining information areas of two different phase depths, which apparatus comprises a radiation source producing a read beam, an objective system for focusing the read beam to a read spot on the information structure, and two radiation-sensitive detectors which are disposed in the far field of the information structure, one on each side of a line which is effectively transverse of the track direction, the outputs of the two detectors being connected to an adder circuit, characterized in that at least one of the detectors is connected to the adding circuit via a phase shifting element, which element subjects the detector signal to a phase shift of constant magnitude.
6. An apparatus as claimed in Claim 5, characterized in that the two detectors are also connected to a subtractor circuit, that the outputs of the adder circuit and the sub-tractor circuit are connected to the input of a signal pro-cessing circuit via a switching element, and that a control input of the switching element is connected to an output of an electronic circuit, in which a switching signal is derived from the signal being read from the record carrier.
7. An apparatus as claimed in Claim 6, characterized in that each of the detectors is connected to the adder circuit via a phase-shifting element, the two phase-shifting elements introducing phase shifts which are of equal magni-tude but opposite sign.
8. An apparatus as claimed in Claim 6, characterized in that each of the detectors is connected to the adder circuit and to the subtractor circuit via a phase-shifting element, the two phase-shifting elements introducing phase shifts which are equal but of opposite sign.
9. An apparatus as claimed in Claim 5, characterized in that each of the detectors is connected to the adder circuit via a phase-shifting element, the two phase-shifting elements introducing a phase shift of constant magnitude but of variable sign, and the phase shifts of the two elements always being equal but of opposite sign, and that the control inputs of the phase-shifting elements are connected to an electronic circuit in which a control signal is derived from the record carrier.
10. An apparatus as claimed in Claim 5, 6 or 9, char-acterized in that the radiation-sensitive surfaces of the two detectors are each arranged against an edge of the effective pupil of the objective system.
11. An apparatus as claimed in Claim 5, 6 or 9, equipped with a servo-system for keeping the read spot positioned on the centre of an information track, which servo-system comprises a radiation-sensitive detection system for generating a positional error signal, a control circuit for converting said signal into a control signal for an actuator by means of which the radial position of the read spot can be varied, characterized in that a switchable inver-ter is included between the detection system and the control circuit, a control input of said inverter being connected to the output of an electronic circuit in which a switching signal is derived from the signal read from the record carrier.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL8103504 | 1981-07-24 | ||
| NL8103504A NL8103504A (en) | 1981-07-24 | 1981-07-24 | RECORD CARRIER WITH AN OPTICALLY READABLE INFORMATION STRUCTURE AND DEVICE FOR READING IT. |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1182916A true CA1182916A (en) | 1985-02-19 |
Family
ID=19837845
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000388128A Expired CA1182916A (en) | 1981-07-24 | 1981-10-16 | Record carrier having an optically readable information structure and apparatus for reading said record carrier |
Country Status (11)
| Country | Link |
|---|---|
| JP (2) | JPS5819748A (en) |
| AT (1) | AT371621B (en) |
| BE (1) | BE890760A (en) |
| CA (1) | CA1182916A (en) |
| DD (1) | DD201625A5 (en) |
| DE (1) | DE3141103A1 (en) |
| ES (1) | ES506292A0 (en) |
| GB (1) | GB2103409B (en) |
| IT (1) | IT1140225B (en) |
| NL (1) | NL8103504A (en) |
| SE (1) | SE453543B (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4121505A1 (en) * | 1991-06-28 | 1993-01-07 | Sonopress Prod | DISK-SHAPED MEMORY FOR BINARY INFORMATION |
| CA2108457A1 (en) * | 1992-02-14 | 1993-08-15 | Seiji Kobayashi | Information recording medium, information recording apparatus, information reproducing apparatus and information recording and reproducing apparatus |
| EP1950750B1 (en) * | 1999-06-30 | 2009-08-12 | Sharp Kabushiki Kaisha | Optical disc device for reproducing an optical disc having pits of different depth formed therein |
| WO2008012985A1 (en) * | 2006-07-27 | 2008-01-31 | Mitsubishi Electric Corporation | Optical disc medium and optical disc device |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL7803517A (en) * | 1978-04-03 | 1979-10-05 | Philips Nv | RECORD CARRIER WITH AN OPTICALLY READABLE PHASE STRUCTURE AND DEVICE FOR READING. |
| NL7810462A (en) * | 1978-10-19 | 1980-04-22 | Philips Nv | REGISTRATION CONTAINER IN WHICH INFORMATION IS PRESENTED IN AN OPTICALLY READABLE RADIATION-REFLECTING INFORMATION STRUCTURE |
| CA1165871A (en) * | 1978-11-08 | 1984-04-17 | Kornelis Bulthuis | Optically inscribable record carrier |
-
1981
- 1981-07-24 NL NL8103504A patent/NL8103504A/en not_active Application Discontinuation
- 1981-10-16 CA CA000388128A patent/CA1182916A/en not_active Expired
- 1981-10-16 BE BE0/206263A patent/BE890760A/en not_active IP Right Cessation
- 1981-10-16 DE DE19813141103 patent/DE3141103A1/en active Granted
- 1981-10-16 JP JP56164382A patent/JPS5819748A/en active Granted
- 1981-10-16 IT IT24539/81A patent/IT1140225B/en active
- 1981-10-16 DD DD81234162A patent/DD201625A5/en unknown
- 1981-10-16 AT AT0444881A patent/AT371621B/en not_active IP Right Cessation
- 1981-10-16 SE SE8106133A patent/SE453543B/en not_active IP Right Cessation
- 1981-10-16 GB GB08131237A patent/GB2103409B/en not_active Expired
- 1981-10-16 ES ES506292A patent/ES506292A0/en active Granted
-
1990
- 1990-08-20 JP JP2217238A patent/JPH03116456A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| BE890760A (en) | 1982-04-16 |
| JPH0421254B2 (en) | 1992-04-09 |
| DD201625A5 (en) | 1983-07-27 |
| JPH0366735B2 (en) | 1991-10-18 |
| GB2103409B (en) | 1986-04-23 |
| DE3141103C2 (en) | 1991-05-29 |
| JPH03116456A (en) | 1991-05-17 |
| IT1140225B (en) | 1986-09-24 |
| NL8103504A (en) | 1983-02-16 |
| ES8207370A1 (en) | 1982-09-01 |
| DE3141103A1 (en) | 1983-02-10 |
| ES506292A0 (en) | 1982-09-01 |
| SE453543B (en) | 1988-02-08 |
| JPS5819748A (en) | 1983-02-04 |
| IT8124539A0 (en) | 1981-10-16 |
| SE8106133L (en) | 1983-01-25 |
| GB2103409A (en) | 1983-02-16 |
| AT371621B (en) | 1983-07-11 |
| ATA444881A (en) | 1982-11-15 |
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