DD201625A5 - RECORDING DEVICE WITH AN OPTICALLY READABLE INFORMATION STRUCTURE AND DEVICE FOR READING IT - Google Patents

Abstract

What is described is a recording medium with an optically readable information structure, in which information areas of juxtaposed information samples of different phase depths have, and a device for reading out the same. By suitable choice of the phase depths and by electronic phase rotation of the signals supplied by the read detectors, the crosstalk between adjacent tracks can be almost completely eliminated.

Description

Berlin, the 3.3.1982 59 900/13

Record carrier with an optically readable information structure and device for reading the same

Field of application of the invention

The invention relates to a recording medium with an inf ormationsst structure, which is arranged in Inf urinationsspuren, optically readable Inforrnationsgebieten is constructed in which juxtaposed information track portions differ from each other in that they bzv from information areas with a first phase depth; ₄ sine constructed of information areas a second phase depth, The invention further relates to an apparatus for reading such a record carrier,

characteristics the known technical solutions

Such a. On drawing rägsr and a device for reading the same are described in DE-OS 29 12 215. Preferably, the first phase depth is about 180 and the second phase depth is about 120.

When scanning the information structure with a readlet bundle, this bundle is split into a subset zerosr order and a number of higher order subbeams. 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 subbands, if the center of the readout generated on the information structure.

3.3.1982 2 ~. 59 900/13

stain with the middle of an xnf ο rrna tungsgsbie t it coincides. In the mentioned DE-OS 29 12 215 it is demonstrated that, if the information areas in each case two, side by side. lying inf ormatior.sspurteile different phase parts, these track parts can be arranged closer together than if the information structure is constructed of information areas, which all have the same phase depth. The information content of a record carrier can then be increased by z, for example a factor of 2, without the crosstalk between adjacent track parts substantially increasing.

Then, however, the information track portions having different phase depths must be read out in various manners by reading out the change in the total intensity of the radiation originating from the record carrier and passing through the pupil of the readout optical element. This is the so-called integral or "Central Aperture" read-out method. The information track portions with the smaller phase depth are read out by determining the difference in intensities in two tangentially different halves of the pupil of the readout objective. This is the so-called differential readout method *

It has been found that in the read-out of an information track having the larger phase depth taking place by the integral method, there still occurs a little crosstalk from an adjacent information track having the smaller phase depth.

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Object of the invention

The aim of the invention is to avoid the aforementioned disadvantages of the prior art.

Explanation of the essence of the invention

The invention has the task of eliminating the residual crosstalk.

According to a first aspect of the invention the record carrier is characterized in this _t that the difference between the first and second phase depth nearly f? '/ 2 wheel.

In this ^! In addition to the difference in phase depths, upon introducing an additional electronic phase shift of a detector signal or both detector signals, the desired crosstalk reduction can be obtained.

It is possible to adjust only the larger Phasentisfe, z. B, to bring to 7 ^ / 5 Rad., And to keep the smaller phase depth on the value given in DE-OS 29 12 215 of 2it / 3 Rad, = 4 ^ / 6 Rad. Then, the information track parts having the larger phase depth must be read out by the integral method and the information track parts having the smaller phase depth by the differential method. Since the two readout methods have different modulation transfer functions ("MT" F, "), the alternate use of the two readout methods in the signal finally output by the readout device may

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In addition, when using the differential method, the information areas with lower spatial frequencies can no longer be optimally read out.

Preferably, therefore, the information areas are sized so that they can all be read out by the integral method. A preferred embodiment of the recording medium is characterized in that the first phase depth is about 51Γ / 4 rad., And the second phase depth is about 3 ^ / 4 Rad.

The two phase depths can be obtained in different ways, z_ B * through areas with different refractive indices. Preferably, the information areas are based on pits or humps, slides has the advantage that the record carriers in large series with the aid of. Pressing techniques can be produced. In the case of pits or mounds infor - mation areas, the Phasentiafa is given a geometric depth or height. In the case of pits or mounds with steep walls, the phase depth is determined essentially by the geometric depth or height. If the pits or humps have less steep walls, the phase depth is determined by the angles of inclination of these walls,

In another feature of the record carrier, successive track parts within an information track are distinguished from one another by being constructed from information areas having the first phase depth and information areas having the second phase depth, respectively. This will allow the visibility of transitions between the two types of information

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device permanently reduced signal «

In order to timely can select the desired electronic phase rotation when reading the record carrier, a pilot signal may be for a "Eiteren feature on the recording medium 'out of an information signal may be stored _7, the transitions between Inf orrnationsgebieten with the first phase depth and Inforrnationsgeoieten with the second phase depth ,, and vice versa, indicating »

According to a second aspect of the invention, there is provided a device for reading out a record carrier having information areas with two different phase depths, said device comprising a readout beam, a bending beam focusing the readout beam to a blank on the radiation source The information includes and includes a number of optional detectors located in the far field of the information structure on either side of a line that is effectively transverse to the track direction, the outputs of the two detectors being connected to an adder circuit characterized in _t that is connected to at least one of the detectors via a phase rotating element to the adder circuit, which element causes a phase rotation of constant magnitude of the detector signal "

If the two phase depths of the information areas are chosen such that the entire information structure can be read out by the integral method, the phase-rotating element must introduce a phase shift equal to the difference between the two phase depths.

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d. " h β is a phase shift of about 1/2 " *.

The two phase depths may also be chosen such that one type of information area is suitable for being read out by the integral method, while the other type of information area is suitable for being read out by the differential method. A read-out device _T which is suitable for reading such a recording medium ,, characterized ,,, that the outputs of the two detectors is also connected to a subtracting circuit, are such that the outputs of the adder circuit and the subtracter circuit are connected via a switching element with a signal processing circuit, and that a control input of the switching elements is connected to an electronic circuit, in which a switching signal is derived from the signal read from the record carrier. This device is not only suitable for reading out a Informationsst.ruktur in the Phasentief s of 717 "/ 5 Rad, and 2 ^ / 3 Rad» are present, but can also be used to read the recording medium according to DE-OS 29 12 216, Thus, a record carrier with phase depths of * 5j "'Rad., and of 2 ^ / 3 Rad. ,, be used» Then, only in one of the connections between the detectors and the adder a phase-rotating element is arranged, while the detectors directly with In a device for reading out a record carrier having a phase depth of 7 π / 6 radians, and 2.1 c / 3 radians, at least one detector is connected to both the adder circuit and the subtractor circuit via a phase-rotating element ., In the two latter devices, the phase-rotating element introduces a phase shift of about * h * / 3 rad. »

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ts is preferable from symmetry considerations, both in a device in which only uses the integral read method \ rd _(as well as in a device ν the integral read method and the differential read-out methods are used in, each of the detectors via a phase rotating element with only the D: Ese elements must then introduce phase rotations that are equal but "opposite in sign." In a device that uses only the integral readout method, the phase-shifting elements must also be adjustable such that the signs of the two Phasendrshungen can be changed.

Thus, even at low spatial frequencies of Information.sgebiets the suppression of the upper speech according to the invention is still effective, preferably the detectors ie are set against an edge of the effective pupil of the objective system. The effective pupil is the image of the pupil in the plane of the two detectors.

Exemplary Example

Ein-Sige embodiments of the invention are illustrated in the drawings and will be described in more detail below * It show: -

Fig. 1 is a plan view of a part of a first embodiment of a recording medium;

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2 shows a tangential section through this recording medium;

Fig. 3: a radial section through this record carrier;

Fig. 4 is a plan view of a part of a second embodiment of a recording medium;

Fig. 5j shows a tangential section through this record carrier;

Fig. 6: a radial section through this record carrier;

7 shows an embodiment of a read-out device;

Fig. 3: the arrangement of the detectors with respect to the different diffraction orders;

9 shows a first embodiment of the electronic circuit for processing the detector signals,

Fig. 10: a second embodiment of this electronic circuit;

Fig.11: a third embodiment of this electronic circuit ,, and

Fig *. FIG. 12 shows the form of a radial error signal in an output of a servo system for the radial location of the readout spot. FIG.

3 * 3.1932

3 Λ 1 6 2 4 " ⁹ ~ ^{59 9} °° / ¹³

In these figures, the same elements are always designated by the same reference numerals.

In Figures l * _t. 2 and 3 is a first embodiment of a. Record carrier according to the invention shown. Fig. 1 is a plan view, Fig. 2 shows a tangential section along the line II-II ^f of Fig ... I through and Fig * 3 shows a radial section along the line III-III ¹ of FIG. 1 through the record carrier 1. The information is in a variety of information areas A ₁ z. B * Pits in the substrate 6 _f . set «These areas are arranged according to the tracks 2. ,. Intermediate areas 5 are located between the information areas 4. The tracks 2 are separated from one another by narrow strips 3. The spatial frequency and possibly the lengths of the areas are determined by the information.

The areas of the adjacent information tracks have different phase depths. As can be seen from Fig. 3, _1; are the pits of a first track * of a third track, etc .. deeper than the pits 4 ^{1 of} the second track * of the fourth track, etc ». The geometric depths of the pits 4 and 4, 'are denoted by d ₁ and dp. Due to the different depths, the first track, the third track, etc. can be visually distinguished from the second track * of the fourth track, and so on. These tracks can then be close to each other.

In a practical embodiment of a record carrier according to the invention, the radial period of the information tracks was 0 ^ 85 ym, the width of these tracks was 0 _t 5 ^ m and the width of the strip 3 was 0.35 ym ».

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, - 10 · * "

The information-bearing surface of the recording medium may be rendered reflective rf B ¹ I ,, that thereon a layer 7 of metal; · z B ¹¹ J aluminum vapor deposited * ISFF

It should be noted "that in Figs. 1, 2 and 3 the areas are shown exaggeratedly large for the sake of clarity *

In Fig. 4, a part of a second embodiment of a recording medium according to the invention is shown in plan view. This Fig. * Shows a larger part of the recording medium than Fig ^. ^ 1+ because the individual Inform mationsgebiete can no longer be distinguished · The information tracks are now in parts a and b divided, the parts a of information areas with greater phase depth (deeper pits) and the parts sindv b composed of information areas with a smaller phase depth

In Fig. 5, which shows an enlarged tangential section along the line VV * of Fig. 4 through a track, the pits are designated with a depth d ^ again with 4 * and the pits with a depth d- with 4. ¹

Fig. 6 shows a radial section along the line VI-VI * of Fig. 4 through the second embodiment of the recording medium j

In FIGS. 1 to 6, the information areas have vertical walls and the phase depth is determined by the geometric depths of the information areas. In practice, the information areas are sloping walls aufweiseni Then, the phase depth is determined by the angle of inclination of these walls influenced ¹ ^

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In Fig, 7 is a .Ausführungsform a device for reading the record carrier is shown a- "0s round disc-shaped record carrier is shown in radial section" The information tracks are thus perpendicular to the plane of the drawing * It is assumed _t. that the information structure is located on top of the record carrier and is reflective. "so that it is read through the substrate. The information structure may still be coated with a protective layer 8. By means of a shaft IS ₁ driven by a motor 15, the record carrier can be rotated.

A radiation source ₁ 1O z '8, a helium-neon Laser.oder a semiconductor diode laser ·, supplies a read beam 11. This beam is reflected by mirror 12 to einem- a schematically represented by a single lens Objektivsystern. 13 By way of the readout beam 14 is arranged an auxiliary lens · ,, which ensures that the pupil of Objekt.ivsystems is possible well filled. Then, a read spot V of minimum dimensions is generated on the information structure,

The readout bundle is reflected by the information structure and modulated upon rotation of the record carrier in accordance with the order of the information areas in the information track to be read. By moving the readout spot and the record carrier in the radial direction with respect to each other, the entire information surface can be scanned *

The modulated readout bundle goes through the lens system again and is again reflected by the mirror 12 · Im

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Radiation path are arranged means for mutual separation of the modulated and the Unmödulierten Auslesebünde'ls .. These means can z ... B * consist of a polarization-sensitive subprism and a j 71 plate (\ = wavelength of the readout beam) .. In Fig .. 7, for the sake of simplicity, it is assumed that the said means are formed by a semitransparent mirror 17. This mirror reflects the modulated readout beam to a radiation-sensitive detection system 20.

This detection system comprises two radiation-sensitive detectors 22 and 23 'are arranged in the information structure in the so-called "far field" ,, d, h * in a plane in which the focal points of Teilbündsl generated by the information structure, especially the zero-order sub-beam and the subset of the first orders _{} are} separated ». The detection system may be arranged in the plane 21 in which an image of the exit pupil of the objective system 13 is generated by the auxiliary lens 18. In FIG. 7, the image C of the point C of the exit pupil is indicated by dashed lines.

The information structure *, which consists of adjacent information tracks consisting of information areas and intermediate areas, behaves like a two-dimensional array of diffraction. The cluster of objects becomes a zero-order subset, a number of first-order sub-sets, and a number Partial bundles of higher orders split * Some of the radiation re-enters the object system after reflection at the information structure *. In the plane of Aus ·

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when an image of this exit pupil is generated, the centroids of the partial bundles are separated.

In Fig. 5, the situation is shown in the plane 21 of Fig. 7. "

The circle 40 with the center 45 represents the cross section of the zero-order sub-beam in this plane. The circles 41 and 42 with midpoints 46 and 47, respectively, steep the cross-sections of the sub-beams deflected in the tangential direction, the orders (+ I ₁ O) and ( The X-axis and the Y-axis in Fig. 3 correspond to the tangential direction or the track direction, the radial direction or the direction transverse to the track direction on the recording medium. The distance f of the centers 45 and from the Y-axis is determined by: T [Zp ₁ where ρ represents the local spatial periods of the information areas in the information part to be read and 7 \ the length of the read-out beam.

To read the information, the. Phase changes of the sub-beams of the orders (+1,0) and (-1,0) with respect to the zero-order sub-beam used * In the areas hatched in Fig. 8, these first-order sub-beams overlap the zeroth order sub-beams, and there are interferences ». The phases of the first-order sub-beams change at high frequencies as a result of the movement of the read-out link in the tangential direction with respect to the information peak. As a result, intensity changes in the exit pupil or in its image _{t occur,} whereby these changes are detected by the detectors 22 and 23 can be detected »

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When the center of the readout spot coincides with the center of an information area, there is a certain phase difference - between the first-order sub-beams and the zero-order sub-beam. This phase difference is referred to as the phase depth of the information area ♦ As the readout spot transitions from a first information area to a second information area, the phase of the subset of order increases (^ I ₁ O by 2 TT ") in the tangential direction, the phase of this sub-beam varies with respect to the sub-beam nuliter order with LJX. in this case ,, Uj is a time frequency. which is determined by the spatial frequency of the information areas and by the speed with which the read spot moves across the track, becomes.

The phases O (+1,0) and O (-1,0) of the first-order sub-beams with respect to the zero-order sub-beam can be represented by:

9 C ⁺ I / ⁰ ) = ^ + ^ω t θ & -l, 0) = "f - Wt *

The intensity changes brought about by the interferences of the first-order sub-beams with the zero-order sub-beam are converted by the detectors 22 and 23 into electrical signals. The time-dependent output signals S ₂ -, and S _{22 of} the detectors 23 and 22 can be represented by:

S ₂₃ = 8 (Y) COsC * + ta> t). = B (S-OcO-

Here, 3 (4 ") is a factor * that is proportional to the geometric depth of the pits, and for * f * = % , B (. F) can be set equal to zero.

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In a first embodiment of a record carrier according to the invention, the phase depth ^ f ₁ of the information areas 4 is the same 7f "/ 6 wheel. And the phase depth ¹ Y ₉ of the information areas 4 * equal to 2 tu / 3 wheel. Are in the device for reading this record carrier As indicated in FIG. 9, the outputs of the detectors 22 and 23 are connected to the phase-rotating elements 24 and 25. The element 24 shifts the phase of the detector signal S ₂₂ over + 2 radians, while the element 25 "shifts" the phase of the detector signal S ₂ - over -0 radians. The signals S ₂₂ and S _? _, then go over to:

SZ ₂₃ = 3 (y), cos (ψ '+ (a / t-0)} = B ( ψ ) .cos (* - - + (jJ t-0) S' ₂₂ = B ( ψ ) .cos I V - (Wt + ^) f = B (Ψ) .cos (^ - ω tP) .-

If the information areas of an instantaneously read information track have the greater phase depth ψ _Λ - 7 ^ / 6 rad., The signals S _'22 and. 3 * _ο _ are added to each other while, when the information areas of the currently read Informaticnsspurteiles the smaller phase depth ψ "~ 2 β- / 3 Rad», the signals S. ' ₂₂ and S.'p- subtracted must v '/ ground from each other by * · can. ,, as indicated in Fig. 9, the signals S * _{t 22} and p ¹ ρ3 one hand the adding circuit and the other part of the subtracter circuit 27 are supplied to the outputs of the circuits 26 and 27 are connected to the two input terminals e ,, e ₂ and a IVechselschalters 28. *; which has a main terminal e »This switch * depending on the designed at its control input control signal S * either the sum signal of the detectors 22 and 23 or the D.ifferenzsignal these detectors to a demodulation circuit 29 by * in which the read signal is demodulated and for reproduction

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with a television set 30 suitable,

To control the switch 28, a control signal must be generated. A pilot signal may be recorded in the record carrier in addition to the actual information signal, indicating the positions on the record carrier in which a transition from the information areas having a first phase depth to the information areas having a second phase depth occurs where a television picture is recorded per information track rotation, the vertical synchronization pulses or frame synchronization pulses present in the television signal can be used to generate the control signal S ^ and no special pilot signal is required, but the pilot signal may be required if an audio signal is recorded *

As shown in Fig. 9, when the information of the lines of a television picture is set in track parts a and b of Fig. 4, in the horizontal sync pulse separator 31, the horizontal sync pulses can be separated from the signal of the demodulation circuit 29 * in the circuit 33, .the z * B »is a bistable multivibrator, the pulses 32 in a control signal S. for the switch 28 is converted, whereby this is switched in each case after reading a television line *

If each information track of the information structure contains only one kind of areas, the element 31 is a vertical sync pulse separator and the switch 28 is switched after reading out one information track or two television fields.

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If the point e _o in the switch is connected to the point e * the so-called integral read-out method is used »The signal supplied to the demodulator 29 then has the form:

S- = Sl ₂₃ + S ^f ₂₂ = 2.8 (ψ) .cos ( ¹ P- ^) cos ( U / t ). If the point e with the point e ,. is connected, reading takes place by the so-called, differential method. The signal supplied to the demodulator then has the form: *

.S ₀ = S ^l ₂₃ - S _'22 = -2.B ( ψ ). Sin (ir-P). Sin (Wt). The integral method is used when reading the information areas with a phase depth Ψ. = 7 ^ / 6 wheel used. The signal S _T is maximal when COs (^. -Β) = i, that is, when β = if / Q Rad. f: for the information areas with a phase difference f _o = 2 1Γ / 3 rad., then cos ( γ _o -β) = O ₄ Thus, when read by the integral method, the information areas with the smaller phase depth are not "seen". Conversely, if the differential readout method is used, the information areas 4 "with a phase depth Ψ _η = 2 Ii" / 3 radians *

2ΊΓ ^

optimally read ,,, because sin {! -β) is then equal to 1 ,.

while the information areas 4 with a phase depth

Rad "are then not" seen "* because -j3) is then equal to O. It is also possible to use * instead OCE two phase-shifting elements 24 and 25, the phase-shifting element 25th If the phase rotation β of the element ^ T / Z Rad ,, is selected, the same result is achieved *. ·

With a device in which a detector signal or the two detector signals are subjected to an additional phase rotation, "the

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Drawing support according to the Dt-OS 29 12 215, so the Auf-drawing support with the phase depths ^ ₁ = «» Rad. and f " ₂ = 2 U / 3 Rad .. The device adapted for reading this recording medium is shown in FIG.

The signals of the detectors 22 and 23 are supplied directly to the subtracting circuit 27 ... In the connections between these detectors and the inputs of the adding circuit phase-rotating elements 24 and 25 are arranged, which has a constant phase rotation of +0 Rad »or - "During the readout of the information areas with the phase depth Y ₂ = 2 Ή ~ / 3 Rad., which takes place by the differential method, the information fields with dsr phase depth ^ f = T" Rad, have no crosstalk The crosstalk of the information areas with Ύ ₉ = 2 u / 3 wheel, during the read-out by the integral method of the information areas with V ₁ = w Rad., Can be almost completely suppressed if φ = ^ / 'S Rad, The amplitude of the signal S _T decreases through this phase shift somewhat, but is still sufficiently large 'It is also possible ^. to use only the phase rotator 24 ^ of but then must perform a phase shift of ^ / S wheel ,,.

At the above values for the phase depth ^% ϋ _λ and 4 "p and the phase shift 0 , the integral readout method and the differential readout method must alternately be used ... However, these two methods have different optical transfer functions * When a video signal is recorded on the record carrier z * B «is a transfer function, other shades of gray or some other color saturation in the end

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valid TV picture as the other transfer function. In the case of an audio signal in the form of a frequency-modulated signal, the switching between the transmission functions can be heard as an undesired frequency.

More often, for reading out lower spatial frequencies of the information areas, the transfer function of the differential method is worse than that of the integral method.

Preferably, therefore, the phase depths Y ₁ and Y * _{2 are} chosen such that they are symmetrical to 1Ϊ "Rad." The phase depth f, is then equal to 5 1Γ / 4 radians, and the phase slopes * f _o equal to 3 1? "/ 4 wheel ,. The magnitudes of the phase shift β is then

FIG. 11 shows a signal processing circuit of a device for reading out this recording medium . Detectors 22 and 23 are each connected to a phase-shifting element 24 or _# 25. Element 2ί introduces a phase shift Δβ and element 24 produces a phase shift β . , where the size of β is equal to 1Γ / 4 rad. * The sign of β must now be changed to information areas with the smaller phase depth and vice versa on the transition from information areas with the greater phase depth * When reading the information areas with the larger phase depth, β = + TF / 4 Rad, and when reading the information areas with the smaller phase depth, β = - 1Γ / 4 Rad * To change the sign of the phase shift β , the signal S can be used again.

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The information signal S ^ is always passed through

When reading out the information areas 4 with the phase depth V ₁ = 5 T / 4 Rad *, ψ = + "^ / 4 Rad. Then cos ('f, .-" S * / 4) equals 1. For the information areas 4. ' with the phase depth * r * ₂ = 3 "^ / 4 Rad. COs (T ₂ - It / A-) equals 0 _# so that these information sources have no crosstalk. * During the reading of the information areas 4 ', 0 = - 9 "/ 4 Rad" ,,, and 'then cos (^ f ₀ + r ~ / 4) is equal to I ₁ while cos ( "γ. + F / 4) is equal to O, so that the information areas 4 with the larger phase depth not "seen", and thus have no crosstalk.

The above values for the phases are not critical values, deviations of the order of a few degrees are allowed *

It is possible that the difference between the phase depths V ₁ and Vp deviates ^from "^" / 2 rad. By adapting the electronic phase rotation JZ! Nevertheless, care can be taken to ensure that the cross-talk between neighboring information samples remains minimal *

Until now, only the first-order sub-bundles deflected in the tangential direction had been discussed. "From the information structure, the read-out radiation is also deflected in higher tangential orders and in different radial and diagonal orders. The information areas that show a difference between the phase depths f for the tangential first orders. and V ₂ of ff ~ / 2 Rad, but also for the higher tangential orders and for the radial and diagonal ones

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The partial bundles _c, which are deflected in other than the tangential first orders, will not significantly affect the effect of reducing the upper-crosstalk and need not be further discussed.

It has been assumed above that the signals supplied by the detectors have a fixed phase difference, which is determined by the phase depth of the information areas., In that this phase difference is influenced by means of an electronic phase rotation, when reading out information areas with a first phase Phase depth, the signal of these information areas is made maximum and the signal of the information areas with a second phase depth is minimized. It is assumed that the detector 22 is hit only by the bundle 42 and the detector 23 only by the bundle 41 * Be lower spatial frequencies of the information areas, ie at coarser periods ρ these areas, Oer distance f in Fig. 3 is smaller, and the beam will overlap 41 and 42 first orders * Then, the detector would or 22 or ·· 23 not only radiation of the beam 42 · 41, but also receive radiation from the bundle 41 or »42. Then the phases of the bundles of first orders could no longer be influenced individually and no reduction of the crosstalk according to the invention could be obtained, in order to be able to obtain a sufficient reduction of the crosstalk even at lower spatial frequencies, the radiation-sensitive surfaces of the detectors take place, as shown in FIG. 8 is indicated by the solid lines: close to each other and in the center of the pupil * as far as possible from each other and arranged at the edge of the pupil. In Fig. 8

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the latter locations of the detectors are indicated by dashed lines 22, '; and 23. ' indicated * The limit for the spatial frequencies at which the detector 22 is hit only by the bundle 42 and the detector 23 only by the bundle 41; is thereby shifted down considerably.

During readout, the readout spot must remain positioned exactly on the center of the track to be read. For this, the read-out device contains a fine control for the radial position of the readout spot * · As indicated in Fig. 7, the mirror 12 may be arranged rotatably * The axis of rotation 38 of the mirror is perpendicular to the drawing plane, so that by rotation of the mirror 12 of the readout spot is moved in the radial direction, the rotation of the mirror is obtained by means of the drive element 39. This element can take many forms; it is z -B * 'an electromagnetic element of the type shown in Fig. 7 or a piezoelectric element. The drive element is "controlled by a control circuit 50, the input of which is a radial error signal S, ie a signal which is an indication of a deviation of the position of the readout spot with respect to the center of the track is _t .

The signal S can be generated by means of two detectors * arranged in dsr plane 21 on both sides of a line * which is effectively parallel to the track direction ·. », As z *, B * described in DE-OS 2,342,906 is "because" that the output signals of these detectors are subtracted from each other, "; a radial error signal S is obtained, *. In this case, an asymmetry in the radial direction, the radiation distribution in the pupil, is then determined. This is the so-called differential sequential method,

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The servo system may be arranged to track the information track portions having the longer phase depth * z * B, * f * = 5 ^ / 4 rad *,:,. In FIG. 11, the full line shows the signal S as a function of the radial position r of the readout spot in the event that only those information track portions would be present. If the readout spot is exactly above a deep depth of orbiting, ie, in , 2r etc », the signal S is zero». The servo system for tracking is set up in such a way that with a negative value of S the tilting mirror 12 in Fig. 7 in the. is rotated in the opposite direction of the ear-pointer direction, so that the center of the read-out spot is positioned exactly on the center of the animal information track 2. At a positive value of S, the mirror 12 is rotated in the clockwise direction. The dots D in Fig. 12 are the stable pines for the servo system.

In a record carrier according to the invention are still shallow information track parts 2 ¹ between the deep information samples 2 * The middle of the information track 2. *: corresponding point E on the curve for S is an unstable point * Weηα the read spot is slightly to the right of the center of the information track 2. ' would be, so if S were positive, the mirror 12 would be rotated in the clockwise direction and would become the readout spot. move it further to the right. * In a similar way, if there is a deviation to the left of the location of the readout spot, this spot would be moved further to the left. "Without further action, the readout spot could not be located on a shallow infonnation 'remain positioned, but the readout spot would always lead to a deep information **

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Mach the invention is for reading a shallow information track or a shallow Informationssspurteiles the signal S ^. before it is supplied to the control circuit 50 ·, inverted · The inverted signal S is shown in Figure "12 by the dashed curve * The center of the information track member 2 * corresponding to point E on the curve S is a stable point, -. and the points D on this curve are unstable points »

In the apparatus of Fig. 7, a combination of an inverter stage 51 and a circuit 52 is mounted. As a result, the signal S can optionally be supplied to the controller 50 after inversion. The switch 52 is controlled by the signal S in synchronism with the switch 28 of Fig. 9. In reading a shallow information track, the signal S is not inverted , and when reading a shallow information track, this is probably a case. When reading an information track 2, the part of the curve drawn in bold is used for 3, while; Au-slesen an information track 2. ' the bold-drawn part of the dashed curve is used for S *

It should be noted · ;, that the radial error signal contains S posts ,, the-from the information track portions 2 and from the information track portions 2., * Derive "result ¹ of different phase depths γ f =" 5-7i "/ 4 wheel * and _ = 3 fr / 4 Rad., These contributions would be out of phase with each other. However, since the information track parts 2, 'are shifted with respect to the information track parts 2 by a distance equal to half the radial period, only of the information track parts 2, the said contributions in the signal S will enhance each other mutually. "

nO / 1 C 0 t ~>'' 3.3..1982.

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The detectors for reading the information (22 and 23 in FIG. 10) and the detectors for generating the radial error signal may be combined in the form of four detectors * located in the four different quadrants of an XY coordinate system Reading the information, first the signals of the detectors in the first and the fourth quadrant are added to each other, same as the signals of the detectors in the second and third quadrant, the sum signals thus obtained are either added to each other or subtracted from each other , as described above Generating the radial error signal, first the signals in the first and in the second quadrant are added to each other _t equal to "the signals of the detectors in the third and in the fourth quadrant." The sum signals thus obtained are subtracted from each other, whereby the signal S_ is obtained »

The differential tracking method can except for reading a recording medium with phase depths ^ f ₁ = 5 ^/ u '/ 4 Rad ,, and Y ₂ = 3T / 4 Rad. Also when reading a recording medium with ψ. = 7 ίϊ ~ / 6 Rad, and Y ₂ = 2ΪΓ / 3 Rad. Uses verden. In the latter recording media, the tracking .can 3 "in other ways _t z 'are obtained in the manner described in DE-PS 23 20 477 way * In addition to the read-out spot two Servoflecka can be projected on the information structure * These spots are such positioned relative to each other _{that., when the. In the middle of the readout spot, exactly at the center of the information track to be read, _{e is} the center of the "Seisoflecke", which are two edges of this information track. "Dedem servo spot is assigned a special detector * The difference between the signals

162 4 ³ ' ³¹⁹⁸²

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These detectors are determined by the size and direction of the radial location of the readout spot.

When reading a recording medium with phase depths Y ₁ = 71Γ / 6 Rad. And ^ ₂ = 2 1Γ / 3 Rad., A radial error signal can also be generated by the fact that when reading the read-out spot and the information track to be read in the radial direction periodically with respect to each other with a small amplitude ^., ζ .. Β, equal to one tenth of the track width, and at a relatively low frequency, z ~ B *. 30 kHz, moved: * The signal supplied by the information detectors then contains an additional component whose frequency and phase are determined by the radial position of the readout spot. The relative movement of the readout spot and the information track can be obtained by periodically shifting the readout bundle in the radial direction. Also, as described in the Dc-OS 24 48 032, the. Information tracks are to be executed as meandering tracks. Also, a position error signal generated in this way must be a shallow depth when reading out. Track are inverted *.

The invention has been described with reference to a reflective record carrier. It is also possible to apply the invention to a record carrier having a phase structure which is read out transparently. If the phase structure consists of pits, these must be deeper or .. Higher than the pits or, hump of a reflective record carrier »

Furthermore, the invention can also be used when reading a tape-shaped recording medium. In this case, the phrase "radial direction" used above must be read as the direction perpendicular to the track direction.

Claims (1)

1 »record carrier having an information structure which is constituted of are arranged in information tracks optically readable information master, in which adjacent information track portions differ from each other in _t that they respectively of information areas with a first phase depth" of the Information. are constructed with a second phase depth, characterized in that _f the difference between the first and the second phase depth is almost # "/ 2 rad. 2 _e record carrier according to item 1, 'characterized in that the first phase depth about 5 T / 4 Rad, and the second phase depth © about 3 1Γ / 4 Rad. 3 * record carrier according to item 1 or Z _7, characterized in that successive track parts within an information track are distinguished from one another in that they are composed of information areas with the first Phasentisfe or information areas with the second phase depth. 4 "record carrier according to item 1, 2 or 3, characterized in that in addition to an information signal, a pilot signal is stored indicating the transitions between information areas with the first phase depth and information areas with the second phase depth and vice versa, 5 * Device for reading out a recording medium, in which information areas with two different phases / 1 CO I 3.3.1982 J 4 I ο Z 4 ^2S " ^{59 90} ° / ¹³ depths, this apparatus comprising a radiation source providing a read beam, an objective system for focusing the read beam into a readout spot on the information structure and two radiation sensitive detectors located in the "far field", the information structure on either side of a line. which is effectively transverse to 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 adder circuit via a phase-rotating element, this element inducing a phase rotation of constant magnitude of the detector signal. 5 * Device according to item 5, characterized in that the two detectors are also connected to a subtracting circuit, that the outputs of the adding circuit and the subtracting circuit are connected via a switching element to the input of a signal processing circuit, and that a control input of the switching element with an output of a electronic circuit is connected, in which a switching signal is derived from the signal read from the record carrier. 7, device according to item 6, characterized in that each of the detectors is connected to the adding circuit via a phase-rotating element, the two phase-rotating elements introducing phase rotations which are equal but of opposite sign, Q / ICO / ³ · ³ · ¹⁹⁸² JH ID Z- H ~ 29 - 59 900/13 8 * device according to point 6 *, characterized in that each of the detectors has a phase-rotating element with. the adder circuit and connected to the subtracting circuit, wherein the two phase-rotating elements introduce phase rotations which are equal in magnitude but opposite in sign, 9 *. Device according to item 5, characterized in that connected via a phase rotating element with der'Äddierschaltung each of the detectors is _t with the two phase rotating elements introduce a phase shift whose magnitude * constant, but whose sign is adjustable, wherein the phase rotations eggs two elements always are of the same size but of opposite sign, and the control inputs of the phase-driving elements are connected to an electronic circuit in which a control signal is derived from the signal emitted by the record carrier. " 10 _Λ Apparatus according to one of the items 5 to 9 _f characterized in that the radiation-sensitive surfaces of the two detectors are each set against an edge of the effective pupil of the objective system. ...: - Is 11. Vorrichtung- any one of items 5 to 10, which is provided with a servo system, with the aid of Auslee efleck ^r dauernd- on the center of an information track positioned and 'comprising a radiation-sensitive detection system for generating a Lagenfehler-, signal and a .e control circuit for converting this 23U6 2.4 30 - 59 900/13 Signal in a control signal for an actuator _t contains the radial position of the readout: can be changed, characterized in that between the detector system and the control circuit, a switchable inverter stage is arranged _r of which a. Control input is connected to the output of an electronic circuit ', in which a switching signal, from the up. derived signal carrier is derived » For this 5 pages drawings