JPH0421254B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention includes an information structure comprising an optically readable information area disposed on an information track;
The present invention relates to a record carrier in which adjacent information track portions are made to differ from one another in that the adjacent information track portions each comprise an information area of a first phase depth and an information area of a second phase depth.

This type of record carrier and its reading device are disclosed in Japanese Patent Application No. 54-39418 (Japanese Unexamined Patent Publication No. 54-39418) filed by the applicant.
No. 136303) as stated in the specification. The record carrier described therein preferably has a first phase depth of about π radians and a second phase depth of about 2π/radians.
It is set at 3 radians.

When an information structure is scanned by a reading beam, the reading beam is divided into a zero-order sub-beam and a plurality of higher-order sub-beams. The phase depth is the difference between the phase of the zero-order sub-beam and the phase of one primary sub-beam when the center of the reading spot formed in the information structure coincides with the center of the information area. As established in the above-mentioned Japanese Patent Application No. 54-39418, if each information section of two adjacent information track portions exhibits a different phase depth, then
These track sections can be placed closer together than if the information structures were all comprised of information areas of the same phase depth. In this way, the information content of the record carrier can be doubled, for example, without any increase in crosstalk between adjacent track sections.

However, in such a case, it is necessary to read the information track portions having different phase depths using different methods. The information track portion with a large phase depth is read by determining the change in the total intensity of the light received from the record carrier and passing through the pupil of the reading objective. This reading method is a so-called integral reading method, that is, a center hole reading method. The information track portion with a small phase depth is read by determining the intensity difference of the light passing respectively through two pupil halves of different reading objectives in the tangential direction of the track.
This reading method is a so-called differential reading method.

Even when reading using the method described above, when reading an information track portion with a large phase depth, for example, about π radians, by the integral method, strokes from adjacent information track portions with a small phase depth, e.g., about 2π/3 radians, are read using the integral method. I confirmed that there is a certain amount.

The object of the invention is to eliminate such residual crosstalk and to provide a record carrier in which the information areas can be read out entirely by integral methods.

The invention is characterized in that, in a record carrier of the type mentioned at the outset, the first phase depth is approximately 5π/4 radians and the second phase depth is approximately 3π/4 radians.

Choosing the phase depth difference to be approximately π/2 radians as described above allows for the desired reduction of crosstalk by additional electronic phase shifting of one or both detector signals. be able to.

For example, the larger phase depth is set to about 7π/6 radians, and the smaller phase depth is set to
As specified in No. 39418, it can be maintained at 2π/3 radians, but in this case, the information track portion with a large phase depth should be read based on the integral method, and the information track portion with a small phase depth should be read based on the integral method. must be read based on the differential method. Since these two reading methods have different response functions (modulation response functions; "MTF,"), the alternating use of the two reading methods will be perceptible in the signal ultimately provided by the reading device. . Furthermore, when using differential methods, information areas with low spatial frequencies can no longer be read optimally.

For this reason, all information areas are preferably sized so that they can be read by integral methods. Therefore, in the recording carrier according to the present invention, the first phase depth is defined as approximately 5π/4 radians, and the second phase depth is defined as approximately 3π/4 radians.

The two phase depths can be realized in various ways, for example by different reflection coefficients of the information areas. Preferably, the information area consists of pits or hills. In this way, the record carrier can be mass-produced using a pressing method. When information areas are thus shaped like pits or hills, the phase depth is related to their geometric depth or height. If the pit or hill has steep walls, the phase depth is determined primarily by the geometric depth or height. If the walls of the pit or hill are not so steep, the phase depth is determined by the angle of inclination of these walls.

According to a further preferred embodiment of the record carrier according to the invention, successive track portions of an information track each consist of an information area of a first phase depth and an information area of a second phase depth. make the difference so that it is done. In this way it is possible to reduce the visible influence of the transition between the two types of information areas appearing in the signal finally supplied by the reading device.

In order to properly time the electronic phase shift during reading of the record carrier, a preferred practice of the invention includes providing the record carrier with an information area of a first phase depth and an information area of a second phase depth in addition to the information signal. Pilot signals may also be included to indicate transitions to and from the information area and vice versa.

Like the record carrier according to the invention described above,
A device for reading a record carrier containing information areas of two different phase depths includes a light source for generating a read beam, an objective lens system for focusing the read beam into a read spot on the information structure, and a transverse beam across the lens system from the record carrier. placed in the optical path of the incoming light,
two light-sensitive detectors, each capturing light from a different half of the exit pupil of the lens system, the outputs of both detectors being connected to a summing circuit, and at least one of the detectors being phase shifted. Preferably, the detector signal is connected to the adder circuit through an element, and the phase shift element is configured to shift the phase of the detector signal by a certain amount.

If the two phase depths of the information area are chosen in such a way that the entire information structure can be read out by integral methods, the phase-shifting element adjusts the phase amount corresponding to the difference between the two phase depths, for example about π/ It is made to exhibit a phase shift of 2 radians.

The phase depth of the information area can also be chosen to be two phase depths, such that one type of information area is read integrally and the other type information area is read differentially. In a preferred embodiment of a reading device used for reading such record carriers, the two detectors are also connected to a subtraction circuit, and the output terminals of the addition and subtraction circuits are connected via switching elements to the signal processing circuit. A control input terminal of the switching element is connected to an output terminal of an electronic circuit such that a switching signal of the electronic circuit is derived from a signal read from the record carrier. This device is not only suitable for reading information structures with a phase depth of 7π/6 radians and 2π/3 radians, but also suitable for reading information structures having a phase depth of π radians, as described in the above-mentioned Japanese Patent Application No. 54-39418. It can also be used to read record carriers of 2π/3 radians. In this case, the phase shift element is provided only on one connection line between the detector and the addition circuit, and both detectors are directly connected to the subtraction circuit. The phase depth is 7π/6 radians.
In a device for reading a 2π/3 radian record carrier, at least one detector is connected via a phase shift element to both an adder circuit and a subtracter circuit. In the last two devices mentioned above, the phase shift element provides a phase shift of approximately π/3 radians.

Because of symmetry, in both devices using integral reading only and devices using integral and differential reading, each detector can be connected via a phase-shifting element to either only a summing circuit, or a summing circuit and a subtracting circuit. It is preferable to connect to both. In this case, the signal from the detector is equalized by the phase shift element, but
Shift the phase to the opposite sign. In devices using only integral reading methods, it is necessary to be able to adjust the phase shift elements so that the sign of the two phase shifts of both elements can be changed.

In order to also reduce crosstalk in the information area at low spatial frequencies, it is advantageous to arrange each detector opposite the edge of the effective pupil of the objective lens system. What is the effective pupil referred to here?2
This means the pupil image on the plane where the detectors are arranged.

The invention will be explained with reference to the drawings.

1, 2 and 3 show a first example of a record carrier 1 according to the present invention, FIG. 1 is a plan view showing a part of this record carrier 1, and FIG. 3 is a radial sectional view taken along the line -' of FIG. 1. The information is contained in a number of information areas 4, such as pits, on the substrate 6. These areas are arranged based on track 2. An intermediate area 5 is inserted between the information areas 4. Each track 2
They are separated by a narrow land section 3. The spatial frequency of the information zones and possibly the length of each zone is determined by the information.

The phase depth of each section of adjacent information tracks is made different. Therefore, as shown in FIG. 3, the pits 4 in the first track, third track, etc. are made deeper than the pits 4' in the second track, fourth track, etc. In FIG. 3, the geometric depths of the pits 4, 4' are indicated by d ₁ and d ₂ . By making the depths of the pits different between adjacent tracks in this way, each track such as the first track, the third track, etc. can be optically distinguished from each track such as the second track, the fourth track, etc. . This allows the information tracks 2 to be placed closer together.

In an embodiment of the record carrier according to the invention, the radial period of the information tracks is 0.85 μm, the width of these tracks is 0.5 μm, and the width of the land portion 3 is
It was set to 0.35 μm.

The information-bearing surface of the record carrier can be made reflective by depositing a metal layer 7, such as aluminum, on that surface.

Note that the dimensions of each area in FIGS. 1, 2, and 3 are shown enlarged for convenience.

FIG. 4 is a plan view of a portion of a second example of a record carrier according to the invention. This FIG. 4 shows a larger part of the record carrier than in FIG. 1, so that in this case it is no longer possible to identify the individual information areas. The information track is divided into parts a and b, where part a consists of information areas with a large phase depth (deep pits), and part b consists of information areas with a small phase depth.

In FIG. 5, which shows an enlarged cross-sectional view of the track in the tangential direction along the line _{- '} in FIG. It is shown.

FIG. 6 is an enlarged radial cross-sectional view taken along the line -' of FIG. 4, showing a second example of the recording carrier.

The information areas in Figures 1-6 have vertical walls;
The phase depth is determined by the geometric depth of the information area. In practice the information area has sloping walls. In this case as well, the phase depth is determined by the angle of inclination of the inclined wall.

FIG. 7 is a diagram showing an example of a device for reading record carriers, in which a round disc-shaped record carrier 1 is shown in radial section. The information tracks therefore extend perpendicular to the plane of the drawing. It is assumed that the information structure is located above the record carrier and is reflective so that the reading operation takes place via the substrate 6. The information structure can also be coated with a protective layer 8. The record carrier is a spindle 1 driven by a motor 15.
It can be rotated through 6.

A reading beam 11 is generated by a radiation source 10, such as a helium-neon laser or a semiconductor diode laser. Mirror 12 reflects this beam to objective lens system 13 . In addition, in this figure, the objective lens system 13 is only diagrammatically shown as a single lens. An auxiliary lens 14 is provided in the optical path of the reading beam, which ensures optimal filling of the pupil of the objective system with the beam. In this way, a reading spot V of minimum size is formed in the information structure.

The reading beam is reflected by the information structure and, as the recording carrier rotates, such beam is modulated based on successive information areas in the information track to be read. By moving the reading spot and the recording carrier radially relative to each other, the entire information surface can be scanned.

The modulated reading beam traverses the objective lens system again and is reflected again by mirror 12. The beam path is also provided with means for separating the modulated and unmodulated read beams. This means can consist, for example, of a polarization-sensitive splitter prism and a λ/4 plate (λ being the wavelength of the reading beam). For convenience, the above means is shown in FIG. 7 as being constituted by a semi-transparent mirror 17. This semi-transparent mirror 17
reflects the modulated beam to a photosensitive detection system 20.

This detection system consists of two photosensitive detectors 22 and 2.
3 (Figure 8). These detectors are arranged in the so-called "far field of the information structure", ie in the plane where the center trajectories of the sub-beams formed by the information structure, in particular the zero-order sub-beam and the first-order sub-beam, diverge. The detection system 20 is the objective lens system 1.
Three exit pupil images can be provided in the plane 21 formed by the auxiliary lens 18. 7th
In the figure, the imaging optical path of the image C' at the point C of the exit pupil is shown by a broken line.

An information structure comprising a number of adjacent tracks of information areas and intermediate areas acts as a two-dimensional diffraction grating. The diffraction grating splits the read beam into a zero-order subbeam, a plurality of first-order subbeams, and a plurality of higher-order subbeams. Some of the light enters the objective lens system again after being reflected by the information structure. In the plane of the exit pupil of this objective system, or in the plane in which the image of this exit pupil is formed, the intermediate trajectories of the various sub-beams are separated from each other. FIG. 8 shows the state on the plane 21 of FIG. 7.

A circle 40 whose center is represented by 45 is in the plane 2
1 shows a cross section of the zero-order sub-beam at 1. Circles 41 and 42 with centers 46 and 47 respectively are tangentially diffracted (+1,0) and (-
1, 0) respectively show the cross-sections of the following sub-beams.
The X-axis and Y-axis in FIG. 8 correspond to the tangential, ie, track, direction and the radial direction, ie, the direction perpendicular to the track direction on the record carrier.
The distance f from the centers 46 and 47 to the Y axis is λ/
is determined by P, where P is the local spatial period of the information area in the information track section to be read and λ is the wavelength of the reading beam.

When reading information, phase shifts of the (+1, 0)-order and (-1, 0)-order sub-beams with respect to the 0-order sub-beam are used. In the shaded area in FIG. 8, the first-order sub-beam and the zero-order sub-beam overlap, causing interference. The phase of the primary sub-beam changes at high frequency as the reading spot moves tangentially to the information track. As a result, the light intensity of the images of the exit pupil and the immediate exit pupil changes, and this change is reflected by the detectors 22 and 2.
3.

When the center of the reading spot coincides with the center of a certain information area, a certain phase difference ψ will occur between the first order sub-beam and the zero order sub-beam. This phase difference is called the phase depth of the information area.
At the transition from the first information area to the second information area of the reading spot, the phase of the (+1,0) sub-beam is incremented by 2π. Therefore, when the reading spot moves in the tangential direction, the phase of the sub-beam with respect to the zero-order beam changes by ωT. where .omega. is the temporal frequency determined by the spatial frequency of the information area and the speed at which the reading spot travels on the track.

The phases θ(+1,0) and θ(−1,0) of the first-order sub-beam with respect to the zero-order sub-beam can be expressed as follows.

θ(+1,0)=ψ+ωt θ(−1,0)=ψ−ωt Intensity changes due to interference between the primary sub-beam and the 0th-order sub-beam are converted into electrical signals by the detectors 22 and 23. The time-dependent output signals S ₂₂ and S ₂₃ of the detectors 23 and 22 can be expressed as:

S ₂₃ =B(ψ)cos(ψ+ωt) _S22 =B(ψ)cos(ψ−ωt) where B(ψ) is a coefficient proportional to the geometric depth of the pit. When ψ=π/2, B(ψ)=0.

In a preferred embodiment of the record carrier according to the invention, the phase depth ψ ₁ of the information area 4 is 7π/6 radians, and the phase depth ψ ₂ of the information area 4' is 2π/3 radians.
No. 9 for reading a record carrier as described above.
In the reading device shown in the figure, the output terminals of the detectors 22 and 23 are connected to a phase shift element 24.
and connect to 25. Element 24 shifts the phase of the output signal S ₂₂ of the detector 22 over +ψ radians, and element 25 shifts the phase of the output signal S 22 of the detector 23 by +ψ radians.
Shift the phase of S ₂₃ by −ψ radians.
Due to such a phase shift, the signals S ₂₂ and S ₂₃ change as follows.

S′ ₂₃ =B(ψ)・cos{ψ+(ωt−φ)} =B(ψ)・cos(ψ+ωt−φ) S′ ₂₂ =B(ψ)・cos{ψ−(ωt+φ)} =B( ψ)・cos(ψ−ωt−φ) When the phase depth of the information area of the information track part to be read is greater than ψ ₁ = 7π/6 radians, the signals S′ ₂₂ and S′ ₂₃ should be added together. , and when the phase depth of the information area of the information track portion to be read is less than ψ ₂ =2π/3 radians, the signal S′ ₂₂
and S′ ₂₃ must be subtracted from each other. For this purpose, the signals S′ ₂₂ and
S' ₂₃ can both be supplied to an adder circuit 26 and a subtracter circuit 27. The output terminals of these two circuits 26 and 27 are connected to two input terminals e ₁ and e ₂ of a switch 28 which has one master terminal e. The switch 28 transfers either the sum signal of the detectors 22 and 23 or the difference signal of these detectors to the demodulation circuit 29, depending on the control signal S _c supplied to its control input terminal. In this demodulation circuit, the read signal is demodulated, and for example, a television receiver 3
This is a signal suitable for playback at 0.

To control switch 28, a control signal must be generated. In addition to the actual information signal, the record carrier can contain a pilot signal indicating the position at which the transition in the record carrier from the information area of the first phase depth to the information area of the second phase depth occurs. When a television signal is recorded, this signal is
In the case where the control signal Sc is recorded at a rate of 2, the control signal S _c can be generated using the image synchronization pulse, ie, the field synchronization pulse, contained in the actual television signal, and no pilot signal is required. A pilot signal is required if an audio signal is recorded on the recording carrier.

The information on the lines (horizontal scanning lines) of the television image is based on the track portion a of the recording carrier shown in Fig. 4.
and b, a line (horizontal) synchronization pulse 32 as shown in FIG. 9 can be extracted from the signal of the demodulation circuit 29 by a line synchronization pulse generator 31. The line synchronization pulse 32 is converted in a circuit 33, such as a bistable multivibrator, into a control signal S _c for the switch 28, so that said switch 28 is toggled each time after a certain television line has been read.

If each information track of the information structure covers only an area of a certain type, the element 31 is an image synchronization pulse generator and after each information track is read, ie two television fields are read. The switch 28 is then turned on every time.

If input terminal e ₂ of switch 28 is connected to master terminal e, a so-called integral reading method is used. In this case, the signal supplied to the demodulator 29 can be expressed as follows.

S ₁ = S' ₂₃ + S' ₂₂ = 2・B(ψ)・cos(ψ−φ)・cos(ωt) When the input terminal _e1 of the switch 28 is connected to the master terminal e, the so-called differential method Reading is performed based on the In this case, the signal supplied to the demodulator 29 can be expressed as follows.

S _D = S′ ₂₃ −S′ ₂₂ = −2・B(ψ)・sin(ψ−φ)・sin(ωt) When reading an information area with a phase depth of ψ ₁ = 7π/6 radians, the integral method is used. Use. In this case, the signal
S ₁ is maximum when cos(ψ ₁ −φ)=1, ie, φ=π/6 radians. When reading an information area with a phase depth of ψ ₂ = 2π/3 radians, the signal S ₁ is cos
(ψ−φ)=0. Therefore, when reading based on the integral method, information areas with small phase depth are "observed"
Not done. On the other hand, when using the differential method, the information zone 4' with a phase depth of ψ ₂ = 2π/3 radians is optimally read, in which case S _D is sin(2π/3
−φ)=1, and the phase depth is ψ ₁ =7π/6
The information area of radians is not “observed” and is sin(7π/
6-φ) becomes 0.

Instead of the two phase shift elements 24 and 25, only one phase shift element 25 can also be used. The same result can be obtained by selecting the phase shift amount of this element to be π/3 radians. Japanese Patent Application No. 54-39418 (Japanese Unexamined Patent Publication No. 54-136303) by a device that additionally shifts the phase of one detector signal or both detector signals.
It is possible to significantly improve the reading method of the record carrier described in , ie, a record carrier whose phase shift depth each has an information area.

The apparatus used to read the record carrier is shown in FIG.

The signals from detectors 22 and 23 are sent to subtraction circuit 2
7 directly. The connecting wires between the detector and the adder circuit 26 include +φ radians and − radians, respectively.
Phase shift elements 24 and 25 are provided which exhibit a constant phase shift amount of φ radians. During the differential reading of the information area with phase depth ψ ₂ =2π/3 radians, the information area with phase depth ψ ₁ =π radians does not generate any crosstalk. During the integral reading of the information area of ψ ₁ = π radians, the crosstalk from the information area of ψ ₂ = 2π/3 radians is φ=
If it is π/6 radian, it can be almost eliminated. As a result of this phase shift, the amplitude of the signal S ₁ is reduced somewhat, but the amplitude value is still sufficiently high. Only one phase shift element 24 may be used as the phase shift element, and in this case, the amount of phase shift of this phase shift element must be π/3 radian.

When the phase depths ψ ₁ , ψ ₂ and the phase shift amount φ are as described above, it is necessary to alternately use the integral reading method and the differential reading method. However, these two methods have different modulation response functions. If a video signal is being recorded on the recording carrier, for example, one response function will produce a different glacier, ie a different color saturation, in the final television image than the other response function. If an audio signal in the form of a frequency modulated signal is recorded on the recording carrier, switching between the two response functions will be audible as undesired frequencies.

Furthermore, the response function of the differential method is inferior to the response function of the integral method when reading information areas with low spatial frequencies.

Therefore, the phase depths ψ ₁ and ψ ₂ are these π
It is preferable to choose it symmetrically with respect to radians. Therefore, in a first embodiment of the recording carrier according to the invention, the phase depth ψ ₁ is set to 5π/4 radians, and the phase depth ψ ₂ is set to 3π/4 radians. At this time, the magnitude of the phase shift amount φ is assumed to be π/4 radian.

FIG. 11 shows a signal processing circuit of an apparatus for reading such a record carrier. Each detector 22
and 23 are connected to phase shift elements 24 and 25, respectively. Element 25 exhibits a phase shift of -φ, and element 2
4 exhibits a phase shift of +φ. Note that the size of φ is π/4 radian. The sign (polarity) of φ needs to be reversed at the transition from an information area with a large phase depth to an information area with a small phase depth, or vice versa. φ = +π/4 radians when reading an information area with a large phase depth, and φ = -π/4 radians when reading an information area with a small phase depth.
It is 4 radians. The signal S _c can also be used to change the sign of the phase amount φ.

The information signal S ₁ is always expressed as follows.

S ₁ = S′ ₂₃ + S′ ₂₂ = 2・B(ψ)・cos(ψ−φ)・cos(ωt) Information zone 4 with phase depth ψ ₁ = 5π/4 radians
When reading, φ=+π/4 radians.
At this time, cos(ψ−π/4)=1. When reading information areas 4' with a phase depth of ψ ₂ =3π/4 radians, no crosstalk occurs in these information areas since −cos(ψ ₂ −π/4)=0. When reading the information area 4', φ = -π/4 radians, and cos (ψ ₂ - π/4) = 1, and
Since cos(ψ ₁ +π/4)=0, the information zone 4 with large phase depth is not "observed" and therefore no crosstalk occurs.

The previously specified phase depth values are not necessarily limited to these values, and a certain degree of deviation can be tolerated.

The difference between phase depths ψ ₁ and ψ ₂ can be displaced from π/2 radians. However, by applying electrical phase shifting, crosstalk between adjacent information track portions can also be minimized.

So far we have talked about tangentially diffracted primary sub-beams, but the information structure also diffracts the reading beam tangentially into higher order beams, as well as radially and diagonally into various order beams. do. However, for the tangential primary beam, the information zone exhibiting a difference between phase depths ψ ₁ and ψ ₂ of π/2 radians is different for the tangential higher order beams, the radial and diagonal various beams. also exhibits a similar phase difference.

Sub-beams that are tangentially diffracted other than the primary sub-beams do not have a significant effect on the crosstalk reduction effect, and these beams do not need to be taken into account as much.

In the foregoing it has been assumed that the signals provided by the detector exhibit a constant phase difference determined by the phase depth of the information area. By varying this phase difference using an electronic phase shifter, the signal generated by the information area can be maximized during the reading of the information area of a first phase depth, and the signal generated by the information area of the first phase depth can be maximized during the reading of the information area of the first phase depth.
The signal from the phase depth information area can be minimized. In this case, it is assumed that the detector 22 receives only the beam 42 and the detector 23 receives only the beam 41. At locations where the spatial frequency of the information area is low, ie, where the period P of the information area is large, the distance f in FIG. 8 becomes small and the primary beams 41 and 42 overlap each other. In such a case, detector 22 or 23 no longer detects beam 42.
Alternatively, not only the light of beam 41 is received, but also the light of beams 41 and 42, respectively. Therefore, the phase of the primary beams is no longer individually influenced and the crosstalk reduction according to the invention is no longer achieved. In order to be able to satisfactorily reduce the crosstalk at low spatial frequencies, instead of arranging the light-sensitive areas of the detectors as close as possible to each other in the center of the pupil, as shown in dashed lines in FIG. Place them at the edge of the pupil, as far apart as possible from each other. 8th
In the figure, the last mentioned positions of these detectors are 22',
It is shown at 23'. In this case, detector 22 receives only beam 42 and detector 23 receives beam 42.
The limit value for spatial frequencies that receive only 1 is significantly reduced.

During reading, it is necessary to position the reading spot precisely in the center of the track to be read. For this purpose, the reading device is provided with a control section for finely adjusting the position of the reading spot. As shown in FIG. 7, the mirror 12 can be rotatably mounted. The axis of rotation 38 of this mirror is perpendicular to the plane of the drawing so that the reading spot can be displaced radially by rotating the mirror 12. The mirror 12 is rotated by a drive element 39. This drive element can be of various forms,
For example, it can be an electromagnetic element as shown in FIG. 7, or a piezoelectric element. The drive element is controlled by a control circuit 50, the input of which is supplied with a radial error signal S _r indicative of the displacement of the reading spot with respect to the center of the track.

The signal S _r is arranged in the plane 21, as described for example in German Patent No. 2 342 906;
It can be generated by two detectors, each located on either side of a line parallel to the track direction. The radial error signal S _r is obtained by subtracting the output signals of these detectors from each other. In this way, the radial asymmetry of the radiation (light) distribution at the pupil location is determined. This is the so-called differential tracking method.

The servo system can be used to track portions of the information track with a large phase depth, for example ψ ₁ =5π/4 radians. The solid line section of FIG. 12 shows the signal S _r as a function of the radial position r of the reading spot in the presence of only the information track section as described above. If the reading spot is located exactly on a deep information track portion, ie, if the spot is located at position r ₀ , 2r ₀ , etc., the signal S _r will be zero. When the value of S _r is a negative value, the tracking servo system rotates the tilting mirror 12 in FIG. Use it to position.
If the value of S _r is positive, the mirror 12 is rotated clockwise. Point D in FIG. 12 is a stable point for the servo system.

In the record carrier according to the invention, shallow information track portions 2' are located between deep information track portions 2. Corresponds to the center of information track section 2'
Point E on the curve of S _r is an unstable point. When the reading spot is located slightly to the right of the center of the information track portion 2', that is, when S _r is positive, the mirror 12 rotates clockwise and the reading spot is further displaced to the right. It becomes like this. Similarly, if the position of the reading spot is shifted to the left, this spot will be displaced further to the left. Therefore, unless some measure is taken, the reading spot will not remain in the shallow information track portion 2', but will always be controlled towards the shallow information track portion.

For this purpose, the _polarity of the signal S _r is inverted before it is supplied to the control circuit 50 when a shallow information track section or a part of the track is to be read. This inverted signal _r is shown by a broken line in FIG. On the curve of the signal _r , a point E corresponding to the center of the shallow information track portion 2' is a stable point, and a point D on this curve is an unstable point.

The device based on FIG. 7 is provided with a combination of an inverter 51 and a switch 52. This causes the signal S _r
can be supplied to the control circuit 50 in inverted or non-inverted form. Switch 52 is controlled by signal S _c in synchronization with switch 28 of FIG. When reading a deep information track portion, the signal S _r is not inverted, and when reading a shallow information track portion, the signal S _r is inverted. During the reading period of deep information track 2, the thick part of the curve for signal S _r is used,
Further, during the reading period of the shallow information track 2', the thick portion of the curve shown by the broken line for the signal _Sr is used.

The radial error signal S _r contains information track part 2.
It is clear that the shared error formed by and 2' is included. Since the phase depths are different as ψ ₁ =5π/4 radians, the phases of the shared errors are opposite to each other. However, since the information track section 2' is displaced with respect to the information track section 2 over a distance corresponding to 1/2 of the radial period of this track section 2, the above-mentioned shared errors in the signal S _r mutually increase. do.

Detector for information reading (22 and 2 in Figure 10)
3) and the detectors for radial error signal generation can be combined into four detector configurations, with each detector located in a different quadrant of the X-Y coordinate system. When reading information, the signals from the detectors in the first and fourth quadrants and the signals obtained from the detectors in the second and third quadrants are added together. The sum signals thus obtained are added or subtracted from each other as described above. When generating a radial error signal,
The signals from the first and second quadrant detectors are added together, and similarly the signals from the third and fourth quadrant detectors are added together. The sum signals thus obtained are subtracted from each other to form the signal S _r .

In the differential tracking method, the phase depth is ψ ₁ = 5π/
In addition to being used to read record carriers with phase depths of 4 radians and ψ ₂ =4π/3 radians, it may also be used to read record carriers with phase depths of ψ ₁ =7π/6 radians and ψ ₂ =2π/3 radians. I can do it. This last-mentioned tracking of the record carrier can be carried out, for example, in the patent application filed in 1973 by the applicant.
This can be carried out by the method described in No. 118302 (Japanese Unexamined Patent Publication No. 50-68413). In addition to the reading spot, two servo spots can be projected onto the information structure. These spots are positioned relative to each other such that when the center of the reading spot coincides exactly with the center of the information track section to be read, the center of each servo spot is located at the two edges of the information track section. A separate detector is provided for each servo spot. The difference in signals from these detectors determines the magnitude and direction of the radial position error of the read spot.

If the phase depth is ψ ₁ = 7π/6 radians and ψ ₂ =
When reading a 2π/3 radian record carrier,
The reading spot and the information track to be read,
A radial error signal can also be generated by periodic relative radial movement with a low amplitude, eg 0.1 times the track width, and at a relatively low frequency, eg 30 KHz. In this case, the signal provided by the information detector contains an additional component whose frequency and phase depend on the radial position of the reading spot. The reading spot and the information track can be moved relative to each other by periodically moving the reading beam in the radial direction. The information track is based on the already published patent application No. 50954 (1983) filed by the applicant.
13123), it can also be a meandering track. The polarity of the position error signal thus generated must also be reversed when a shallow information track is to be read.

Although the invention has been described with respect to a reflective record carrier, the invention can also be applied to record carriers having a transparently readable phase structure.
If the phase structure consists of pits or hills, these must be respectively deeper and higher than the respective pits or hills of the reflective recording carrier.

[Brief explanation of drawings]

FIG. 1 is a plan view showing a part of a first embodiment of the recording carrier according to the present invention, and FIG.
An enlarged cross-sectional view in the track tangent direction on the line,
3 is an enlarged radial sectional view taken along the line -' in FIG. 1, FIG. 4 is a plan view showing a portion of a second embodiment of the recording carrier according to the present invention, and FIG. 5 is a sectional view taken along the line -' in FIG. 6 is an enlarged radial sectional view along the line -' of FIG. 4, FIG. 7 is a line diagram showing an example of a device for reading a record carrier, and FIG. FIG. 9 is a block diagram showing a first example of an electronic circuit for processing a detector signal, and FIG. 10 is a diagram showing an example of an electronic circuit for processing a detector signal. A block diagram showing a second example, FIG. 11 a block diagram showing a third example of the electronic circuit, and FIG. 12 a waveform diagram of a radial error signal in an example of a servo that controls the radial position of the reading spot. It is. 1...Record carrier, 2...Information track, 3
... land area, 4 ... pit (information area), 5 ... intermediate area, 6 ... substrate, 7 ... metal layer, 8 ... protective layer, 10 ... light source, 11 ... reading beam, 12 ...
... Mirror, 13 ... Objective lens system, 14 ... Auxiliary lens, 15 ... Motor, 16 ... Spindle,
17...Semi-transparent mirror, 18...Auxiliary lens, 20...
Photosensitive detection system, 22, 23...Photosensitive detector, 2
4, 25... Phase shift element, 26... Addition circuit, 27
... Subtraction circuit, 28 ... Switch, 29 ... Demodulation circuit, 30 ... Television receiver, 31 ... Line synchronous pulse generator, 33 ... Bistable multivibrator, 39 ... Mirror drive shaft, 50 ... ...control circuit, 51 ...inverter, 52 ...switch, V ...reading spot, S _c ...control signal, S _r ...
...radial error signal.

Claims (1)

Claims: 1. An information structure comprising an optically readable information area disposed in an information track, wherein adjacent information track portions include an information area of a first phase depth and an information area of a second phase depth. In a record carrier having respective information zones so that adjacent information track portions are different from each other, the first phase depth is approximately 5π/4 radians and the second phase depth is approximately 3π/4 radians. A record carrier characterized in that it is configured as follows. 2. A record carrier according to claim 1, in which consecutive track portions of one information track are different from each other, so that these track portions contain information areas of a first phase depth and information areas of a second phase depth. A record carrier comprising: 3. A record carrier according to claim 1 or 2, in which the record carrier includes, in addition to the information signal, a transition section between an information area of a first phase depth and an information area of a second phase depth; A recording carrier characterized in that a pilot signal indicating a reverse switching section is also recorded.