JPH0438633A - Optical disk - Google Patents

Abstract

PURPOSE:To allow tracking control by using an optical system of the same space cut-off frequency as heretofore while having the recording tracks of the density equivalently twice larger than the conventional density by forming the tracks by shifting the beginning end of the prepattern which follows the terminal of the preceding prepattern by 1/2 the track pitch. CONSTITUTION:Spiral guide grooves G are parted at every one round on the same radius of the disk, by which plural pieces of the guide grooves Gi, Gj are formed. These grooves are formed by shifting the beginning end Gjs of the guide groove by 1/2 the track pitch p from the terminal Gif of the preceding guide groove. The groove parts and 'partition' parts or the 'partition' parts and the groove parts are, therefore, respectively continued in the track direction in the parted regions. The recording tracks of the density equivalently twice larger than heretofore are formed in this way. The tracking control by using the optical system of the same space cut-off frequency as heretofore is thus possible.

Description

[Detailed description of the invention] The invention will be explained in the following order.

A. Industrial field of application B0 Summary of the invention C9 Prior art 0 Problems to be solved by the invention E0 Means for solving the problems F8 Effects G. Embodiments G1 Structure of an embodiment (Fig. 1) G2 Operation of one embodiment (Figures 1 to 4) G3 Other operations of one embodiment (Figures 1, 4 to 6) C4 Configuration of another embodiment (Figure 7) C5 Other operations Operation of the Embodiment (FIGS. 7 to 9) H, Effects of the Invention A, Industrial Application Field The present invention relates to an optical disk suitable for high-density recording.

B0 Summary of the Invention This invention provides an optical disk in which a pre-pattern for tracking is formed in advance, in which the starting end of a subsequent pre-pattern is formed at a distance of 1/2 of the track pitch from the end of the preceding pre-pattern. By doing so, it is possible to perform trunking control using an optical system having the same spatial cutoff frequency as the conventional optical system, while having recording tracks that are equivalently twice as dense as the conventional optical system.

C1 Prior Art In a conventional optical disc, as shown in FIG. 10, a continuous spiral guide groove G is formed in advance, and along this guide groove,
In some cases, recording tracks are formed. In the normal case, information is written in the tracks of each groove portion G i - L Gi, G t+t, and the "threshold" portion between the grooves is used as a margin for reading the information without error.

Further, some conventional optical discs have guide marks formed in advance for each track in order to determine the positions where recording tracks are to be formed. Usually, in this type of optical disc, recording tracks are formed concentrically.

When recording or reproducing an optical disc, tracking control of the optical pickup is performed so that the light beam automatically follows the recording track of the optical disc.

First, in order to understand the present invention, various tracking control methods for optical discs will be explained.

When recording or reproducing a continuous groove type optical disc, the first
As shown in Figure 1, the reflected light beam from the optical disc D passes through the objective lens (2) of the optical pickup (1) and the beam splitter (3), and is guided to the photodetector (4) where it receives a tracking control signal. is formed.

This control signal is supplied to the two-axis actuator (5), and the optical pickup (1) is driven in the radial direction of the optical disc D.

In the example shown in FIG. 11, a two-split photodetector arranged symmetrically with respect to the center of the track is used as the photodetector (4), and the difference between the detection outputs of the two light receiving elements (formerly L (4r)) is expressed as: A so-called push-pull method is used to detect tracking errors.

In the push-pull method, as shown in FIG. 12, the diameter of the beam spot SPo is set approximately equal to the track pitch p of, for example, 1.6 μm.

When the position of the beam bond in the radial direction of the disk is X with the center of any track Ti as a reference, the light receiving element (old) (4r) corresponding to the beam spot SPo
The detection outputs Sl and Sr are shown in FIG. 13A.

As shown in B, the spatial period is equal to the track pitch P, and the spatial phase is shifted by 1/2 of the track pitch P, resulting in mutually opposite phase sine waves, and the following (la),
It is expressed as formula (Ib).

Sl = sin (2rc x/p) ...1l
a) Sr - 8 in (2π The difference signal Sso becomes a sine wave as shown in the following equation (2), and this difference signal Sso is used as a tracking control signal.

5so= 2sin (2πX/P) ・−・・(2)
In addition, for tracking error detection of optical discs, the first
A three-spot method as shown in FIG. 4 may also be used.

In the 3-spot method, in addition to a recording or reproducing light beam (main beam), two sub-beams using first-order diffraction light are irradiated onto the optical disc, and a point is determined with respect to the main beam bond SPo formed by the main beam. Two sub-beam spots SPa and SP are created by the sub-beams so that they are symmetrical.
b is formed on the optical disk.

The diameter of each beam spot is approximately equal to the track pitch P, which is, for example, 1.6 μm, and the distance between the both side beam spots SPa, SPb and the main beam spot SPo is equal to the track pitch P in the radial direction of the disk. It is considered to be 1/4.

The two sub-beams reflected from the optical disk are each detected by a separate photodetector element of the optical pickup.

When the position of each beam spot in the radial direction of the disk is X with the center of an arbitrary track Ti as a reference, the detection outputs Sa and Sb corresponding to the sub beam spots SPa and SPb are as shown in FIG. Similarly to the case shown in B, the sine waves have opposite phases to each other as expressed by the following equations (3a) and (3b).

Sa = sin (2πX/P) ...13a)
Sb --sin (2πX/P) = (3b) The difference signal Sab between the detection outputs Sa and Sb crosses zero in the positive direction at the center of any track Ti, as shown in FIG. 13C above. This becomes a sine wave, which is expressed as the following equation (4).

5ab=2sin (2πX/P) . . . (4) In the three-spot method, this difference signal Sab is used as a tracking control signal.

Further, in the guide mark type optical disc, tracking control is performed by a so-called sample servo method.

As shown in Figure 15, a pair of control pits (so-called servo bits) are located in a specific area (so-called servo area).
PTa and PTb are provided at a predetermined distance along the track and at an interval of, for example, 1/4 of the track pitch p from the center line of the track. Furthermore, on the center line of the track at a predetermined distance from the servo bits PTa and PTb,
A third control pit PTo is provided as a reference.

During recording or playback, servo bits PTa, PTb
is scanned by a light beam with a diameter approximately equal to the track pitch p, and the detection outputs Sa and Sb obtained at timings corresponding to the servo bits are as follows (5a)
, as expressed by equation (5b), become sine waves with mutually opposite phases.

5a=-sin(2πX/P)...(5a)Sb
= sin (2rt x/p) ...-(5b)
The difference signal Sba between the detection outputs Sa and Sb becomes a sine wave that zero-crosses in the positive direction at the center of an arbitrary track Ti, as shown in FIG. expressed.

5ba=2sin(2πx/p) (6) This difference signal Sba is used as a tracking control signal even in a servo bit type disk.

D0 Problem to be Solved by the Invention However, in conventional optical discs, as the track pitch p becomes smaller, the reciprocal of this pitch exceeds the spatial cantoff frequency of the optical pickup, making it impossible for the optical pickup to read the disc. First, since an optical image cannot be obtained, there is a problem that a tracking signal cannot be obtained.

For example, when the wavelength λ of the light and the numerical aperture NA of the objective lens are λ - 0.78 pm and NA = 0.5, respectively, the spatial cutoff frequency fc is f c = 2 NA/
λ-1/λ 1280 lines/mm, p≦λ-0,7
When the track pitch p is 8 μm or less than the wavelength λ of light, tracking servo cannot be performed.

In view of this point, the object of the present invention is to equivalently solve the conventional two problems.
The object of the present invention is to provide an optical disk that can perform tracking control using an optical system with the same spatial cutoff frequency as the conventional optical disk, although it has recording tracks with twice the density.

80 Means for Solving the Problems This invention provides an optical disc in which a pre-pattern G for obtaining a tracking control signal is formed in advance in a signal recording area, in which the following pre-pattern is Starting point Gjs to track pitch P
This is an optical disc that is formed so as to be shifted by 1/2.

F0 Effect According to this configuration, a recording track with equivalently twice the density of the conventional one is formed, and tracking control becomes possible using an optical system with the same spatial cutoff frequency as the conventional one.

G. Embodiment Hereinafter, an embodiment of the optical disc according to the present invention will be described with reference to FIGS. 1 to 6.

Configuration of G1 embodiment FIG. 1 shows the configuration of an embodiment of this invention.

In FIG. 1, a spiral guide groove G is divided every round on the same radius of the disk, and a plurality of guide grooves Gi, G
j is formed, and the start end Gjs of the following guide groove is at a track pitch p with respect to the end Gif of the preceding guide groove.
It is formed with a shift of 1/2.

As a result, in the divided region, the groove portion and the “threshold” portion, or the “threshold” portion and the groove portion, are continuous along the track direction.

G2 Operation of Embodiment Next, with reference to FIGS. 2 to 4, a tracking control operation when the push-pull method is applied to an embodiment of the present invention will be described.

In this case, as shown in Figure 2, the main beam
In addition to SPo, a sub beam spot SPa is used, which uses, for example, first-order diffracted light. This sub-beam sub-bolt
-3Pa is formed radially outward of the disk at an interval (offset) from the main beam spot SPo by 1/4 of the track pitch p. The rest of the configuration is the same as that shown in FIG. 12 above.

As shown in FIG. 3, the photodetector (10) includes two pairs of photodetecting elements (111), (llr), (121), and
(12r). Control signal formation circuit (20)
In one differential amplifier (21), the outputs of the pair of detection elements (111) and (llr) are subtracted, and in the other differential amplifier (22), the outputs of the other pair of detection elements (111) and (llr) are subtracted. 121) and the outputs of (12r) are subtracted. Both differential amplifiers (21) in the multiplier (23)
, (22) is multiplied, and the output of the multiplier (23) is passed through the terminal OUT as a tracking control signal.
Optical pink-up 2-axis actuator (see Figure 11)
supplied to

In this example, when the push-pull method is applied, the detection element (111) corresponding to the main beam SPo
, (llr) are sine waves with mutually opposite phases, as described above, and are expressed as in equations (la) and (lb), respectively. Then, by the differential amplifier (21), the rain detection output Sol,
The difference signal Sso formed from Sor is expressed as the above equation (2), and as shown in FIG.
It becomes a sine wave that crosses zero in the positive direction at the center of .

In addition, a photodetection element (
121), (12r) detection output Sal, Sa
r, whose spatial phase is the above-mentioned detection element (111),
With respect to the detection outputs Sol and Sor of (llr), they become cosine waves with mutually opposite phases that advance by π/2 (1/4 of the track pitch P), and the following (7a), (
7b) It is expressed as in the formula.

5al= −cos (2rt x/p) −(7a)
Sar-cos(2πx/P)...(7b) From these detection outputs Sal and Sar, the difference signal Ssa formed by the differential amplifier (22) is expressed as the following equation (8). , as shown in FIG. 4B, becomes a cosine wave whose spatial period is equal to the track pitch p and which takes its maximum value at the center of any track Ti.

5sa=2cos (2πX/P) (8) In the multiplier (23), the above-mentioned difference signal S so
, Ssa, and a tracking control signal ST2 as expressed by the following equation (9) is output from the multiplier (23).

ST2= Sso −5sa −2sin(2・2πx/p) ・・・(9)
As shown in FIG. 4C, this tracking control signal ST
2 has a spatial period of 1/2 of the track pitch p, and zero crosses in the positive direction at the center of any track Ti and at every midpoint between two adjacent tracks, for example, Ti and Ti+1. It becomes a sine wave.

As a result, in this embodiment, when the push-pull method is applied, tracks with a density of 1/2 of the conventional track pitch P, that is, twice the conventional one, are created while using the same light source and lens system as the conventional one. You can follow it well.

Note that since the response of the tracking servo loop is slow, the distance from the end Gif of the running track to the start end Cr1 of the end track is
Transients when moving to s are not a problem.

Therefore, on continuous groove type optical discs, it is possible to write and read information even to the "threshold" between the grooves, which is normally considered as margins, and information can be written to and read from optical discs at double the density of conventional optical discs. Can be recorded and played back.

Other operations of the G3 embodiment Next, with reference to FIGS. 5 and 6, a tracking control operation when the three-spot method is applied to an embodiment of the present invention will be described.

In this case, as shown in FIG.
In addition to Po and the two sub-beam spots SPa and SPb, a third sub-beam spot SPc that uses, for example, second-order diffracted light is used. This sub beam spot SPc
is formed at an interval (offset) from the main beam spot SPo by 1/2 of the track pitch p on the outside in the radial direction of the disk, and with respect to the second sub-beam spot SPb, the main beam spot SPo is Become symmetrical. The rest of the configuration is the same as that shown in FIG. 14 above.

The four beam spots mentioned above SPo, SPa, SP
b. Corresponding to SPc, the photodetector (IOA) is the sixth
As shown in the figure, four photodetecting elements (11), (12
), (13), and (14). In one differential amplifier (21) of the control signal forming circuit (20), the output of the detection element (13L (12)) is subtracted, and in the other differential amplifier (22), the detection element (14), (11) is subtracted.In the multiplier (23), both differential amplifiers (21) and (22
) is multiplied by the output of the multiplier (23), and the output of the multiplier (23) is output to the terminal O.
Via the UT, it is supplied as a tracking control signal to the two-axis actuator of the optical pickup (see FIG. 11).

When the three-spot method is applied in this example,
In principle, the detection outputs Sa and Sb of the detection elements (12) and (13) corresponding to the beam spots SPa and SPb are sine waves with opposite phases to each other, as described above, and are expressed by the equations (3a) and (3b), respectively. It is expressed as follows. and,
The difference signal Sab formed from the rain detection outputs Sa and Sb by the differential amplifier (21) is expressed as the above equation (4), and as shown in FIG. 4A above, the spatial period is is equal to the track pitch p, and becomes a sine wave that zero-crosses in the positive direction at the center of any track Ti.

Furthermore, the detection outputs So and Sc of the photodetecting elements (11) and (14) corresponding to the main beam spot SPo and the third sub-beam spot SPc have spatial phases that are similar to those of the above-mentioned detection elements (12) and (13). ) are cosine waves that advance by π/2 (1/4 of the track pitch P) with respect to the detection outputs Sa and Sb, respectively, and have mutually opposite phases.

The difference signal Sco formed from the detection outputs So and Sc by the differential amplifier (22) is expressed as the following equation (10), and as shown in FIG. 4B, the spatial period is is equal to the track pitch p, and becomes a cosine wave that takes its maximum value at the center of any track Ti.

5co-2cos(2πx/p) (10) In the multiplier (23), the difference signals Sba, S as described above are
A tracking control signal ST2 expressed by the following equation (11) is output from the multiplier (23).

5T2=5ba-3c.

-28 inches (2·2πx/p) (11) As shown in FIG. 4C above, this tracking control signal ST2
has a spatial period of 1/2 of the track pitch p, and the center of any track Ti and two adjacent tracks,
For example, the waveform becomes a sine wave that zero-crosses in the positive direction at every midpoint between T i and T i+1.

As a result, in this embodiment, even when the three-spot method is applied, the density is 1/2 of the conventional track pitch p, that is, twice the conventional one, while using the same light source and lens system as the conventional one. Tracks can be followed well.

Therefore, on continuous groove type optical discs, it is possible to write and read information even to the "threshold" between the grooves, which is normally considered as margins, and information can be written to and read from optical discs at double the density of conventional optical discs. Can be recorded and played back.

G4 Structure of Other Embodiments Next, other embodiments of the optical disc according to the present invention will be described with reference to FIGS. 7 to 9.

FIG. 7 shows the overall structure of another embodiment of the present invention, and FIG. 8 shows the structure of its main parts.

In FIG. 7, for example, on the same diameter of the disk, a plurality of concentric tracks are divided, for example, every half circumference, to form a plurality of semicircular arc-shaped tracks T i , T jTk, TI
is formed. The radius of each track Ti to T1 is set to increase sequentially by 1/2 of the track pitch p, so that
The starting ends Tjs and Tls of the respective succeeding tracks are formed to be shifted by 1/2 of the track pitch p.

As shown in FIG. 8, in this embodiment, each track Ti
- For each Tl, the conventional servo bit pair Psi (PTa, P
In addition to servo bit pair Ps2 (PTc)
, PTd) are provided. The new servo bit pair Ps2 is located at a predetermined distance from the original servo bit pair Psi in the track direction, and the new servo pit PTc,
PTd is on the center line of track Ti and on the preceding track T.
The new servo pit PT is placed on the midline with i-1.
c and PTd are spaced from the original servo pits PTa and PTb by 1/4 of the track pitch p in the radial direction of the disk.

Although the illustration of the control pit PTo on the intermediate line is omitted, the rest of the configuration is the same as that shown in FIG. 15 above.

G5 Operation of Other Embodiments Next, referring also to FIG. 9, a tracking control operation when the sample servo method is applied to another embodiment of the present invention will be described.

Four servo pits PTa, PTb PT as described above
c.

As shown in FIG. 9, the control signal forming circuit (30) has four sample and hold circuits (
31), (32), (33), and (34). Each sample and hold circuit (31) to (34) is supplied with the detection output of the photodetector (IOB), and the timing signal generation circuit (36) is controlled by this detection output via the PLL circuit (35). ) provides an appropriate timing signal.

In one differential amplifier (37), the first. The outputs of the second sample and hold circuits (31) and -(32) are subtracted, and in the other differential amplifier (38), the outputs of the third sample and hold circuits (31) and -(32) are subtracted. Fourth sample and hold circuit (33).

The outputs of (34) are subtracted, the outputs of both differential amplifiers (37) and (38) are multiplied in a multiplier (39), and the output of the multiplier (39) is sent to the terminal OUT for tracking control. The signal is supplied to the two-axis actuator of the optical pickup (see FIG. 11).

In this embodiment, when the sample servo method is applied, the first servo pin (PTa, PTb) corresponds to the original servo pin (PTa, PTb).
As described above, the detection outputs Sa and Sb obtained from the second sample and hold circuits (31) and (32) are sinusoidal waves having opposite phases to each other, as described in (5a) above.

It is expressed as equation (5b). Then, the differential amplifier (3
7), the difference signal Sba formed from the rain detection outputs Sa and Sb is expressed as the above-mentioned equation (6), and the difference signal Sba formed from the rain detection outputs Sa and Sb is
As shown in FIG. A, it becomes a sine wave whose spatial period is equal to the track pitch P and zero-crosses in the positive direction at the center of any track Ti.

In addition, in response to the new servo pits PTc and PTd, the third
, fourth sample and hold circuit (33), (34)
The detection outputs Sc and Sd obtained from
The detection outputs Sa and Sb from the sample-and-hold circuits (31) and (32) described above are cosine waves that advance by π/2 (1/4 of the track pitch p) and have mutually opposite phases.

The difference signal Sdc formed from the detection outputs Sc and Sd by the differential amplifier (38) is expressed as the following equation (12), and as shown in FIG. 4B, the spatial period is is equal to the track pitch p, and becomes a cosine wave that takes the maximum value at the center of any track Ti.

5dc-2cos(2πX/p) (12) In the multiplier (39), the difference signal S ba as described above,
S dc is multiplied, and a tracking control signal ST2 expressed by the following equation (13) is output from the multiplier (39).

5T2=5ba-3dc=2sin (2・2πx/p) ・=・(13) As shown in FIG. 4C above, this tracking control signal ST
2 has a spatial period of 1/2 of the track pitch p, and zero-crosses in the positive direction at every midpoint between the center of any track Ti and two adjacent trunks, for example, Tj-1°Ti. It becomes a sine wave like this.

As a result, even when the sample servo method is applied in this embodiment, the same light source and lens system as the conventional one are used, but the conventional track pinch p is reduced to 1/2, that is, the conventional one. It is possible to sufficiently track tracks with a density twice that of the conventional optical disk.

H0 Effects of the Invention As detailed above, according to the present invention, in the pre-pattern formed in advance for tracking, the starting end of the subsequent pre-pattern is shifted by 1/2 of the track pitch with respect to the ending end of the preceding pre-pattern. With this structure, an optical disc can be obtained which has recording tracks equivalently twice the density of the conventional disc, but which can perform tracking control using an optical system with the same spatial cutoff frequency as the conventional disc.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing the configuration of an embodiment of an optical disc according to the present invention, FIG. 2 is a plan view illustrating a tracking control technique applied to an embodiment of the invention, and FIG. FIG. 4 is a waveform diagram for explaining the tracking control operation of an embodiment of the present invention, and FIG. 5 is a block diagram showing an example of the configuration of a control circuit system according to the technique. FIG. 6 is a block diagram showing an example of the configuration of a control circuit system using this technique; FIG. 7 is a plan view showing the configuration of another embodiment of the optical disc according to the present invention. , FIG. 8 is a route plan view for explaining a tracking control technique applied to another embodiment of the present invention, FIG. 9 is a block diagram showing an example of the configuration of a control circuit system according to this technique, and FIG. 10 is a conventional one. FIG. 11 is a perspective view for explaining the present invention; FIG. 12 is a plan view for explaining the tracking control technique applied to the conventional example;
FIG. 3 is a waveform diagram for explaining the tracking control operation of the conventional example, FIG. 14 is a route plan diagram for explaining another tracking control technique applied to the conventional example, and FIG. 15 is the main points of the other conventional example. It is a route plan view showing the configuration of the section. (10), (108), (10B) are photodetectors, (
20), (30) is a control signal forming circuit, (21)
, (22), (37), and (38) are differential amplifiers, (23), and (39) are multipliers, and (31) to (3
4) is a sample hold circuit, (35) is a timing signal generation circuit, Gi, Gj are guide grooves, Ti, TI are tracks, p is a conventional track pitch, 5Pa='SPo
is the beam spot, PTa=PTd is the servo bit, S
T2 is a tracking control signal.

Claims (1)

[Claims] In an optical disc in which a pre-pattern for obtaining a tracking control signal is pre-formed in a signal recording area, the starting end of the following pre-pattern is set at 1 track pitch with respect to the end of the preceding pre-pattern. An optical disc characterized in that it is formed to be shifted by /2.