JPH02166639A - optical recording medium - Google Patents

Abstract

PURPOSE:To simplify the production process of a master disk for the recording medium and to reduce bad influence of tracking error signals by partitioning the area of the optical recording medium into servo areas and data areas and providing preformat pits in the servo area in a manner that the pit is positioned at the center of the track width with its longitudinal direction in the track direction. CONSTITUTION:The medium has several blocks 22 consisting of the data area 24 into or from which informations are optically written or read out, and the servo area 23 which separated from this data area 24 and produces tracking error signals. The servo area 23 has at least one pit in the center position of its width with the longitudinal direction of the pit along the track direction. By this method, the master disk can be easily produced and bad influence of a tracking error signal due to a defect comparable to the pit size can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical recording medium on which information is optically written or read.

[Prior Art] In recent years, the types of optical memory devices have become diverse, ranging from playback-only optical video discs and compact discs to write-once optical discs using metal thin films and dye-based recording materials, as well as magneto-optical recording systems and phase transition systems. Rewritable optical discs using this recording method have been developed, and their applications are expanding from consumer products to external memory for computers.

One of the important technologies in these optical memory devices is an error signal detection method. Optical discs generally have a warped surface or a misalignment of the center of rotation, and as the optical disc rotates,
The truck being watched may experience downward movement or sideways vibration. Therefore, in order to read and write information to and from the information track of an optical disk, a focus servo technology (hereinafter referred to as rAFJ) that makes a minute light spot follow the vertical movement of the optical disk, and a focus servo technology (hereinafter referred to as rAFJ) that tracks the horizontal vibration of the track are required. A tracking servo technology (hereinafter referred to as rATJ) is required.

First, AF will be briefly explained.

FIGS. 4(a) and 4(b) are explanatory diagrams of AF using the astigmatism method. In the same figure, the reflected light from the optical disk is condensed by a condenser lens 151 as shown in FIG. 4(a),
Astigmatism is provided by the cylindrical lens 152. When a four-segment photodetector 153 is placed at the position of the circle of least confusion, the shape of the light beam on the detector will be as shown in FIG. Become. Each section element of the 4-part photodetector 153 is arranged as shown in the figure.
, b, c, d, the signal for the amount of light is FE
By setting l = (a + c) (b + d), the focus error signal FEI is 1! Tareko FEl
Control IjJ so that it becomes O.

FIG. 5 is a diagram for explaining AF using the critical angle prism method. In the figure, reflected light from an optical disk 154 passes through an objective lens, is reflected by a critical angle prism 155, and enters a 1/2 photodetector 156. FIG. 5(a) shows that when the optical disk 154 is far away, FIG.
The figure shows the case of in-focus, and Fig. 5(C) shows the case of closeness. As shown in FIGS. 5(a) and 5(C), when the light beam is out of focus, the light beam incident on the critical angle prism converges or diverges.

At this time, the angle of incidence of half of the luminous flux is smaller than the critical angle,
Some of the light passes through the prism.

A focus error signal FE2 is obtained by detecting each of the half luminous fluxes by the two-split detector 156 and setting FE2=(ab), and this FE2 is controlled to become zero.

FIG. 6 is a diagram for explaining AF using the Naifetsu method. In the figure, a two-part photodetector 158 is placed at a position where the reflected light from the optical disk 157 forms an image when focused.

At this time, half of the light beam is blocked by the knife 159, and when the optical disk 157 moves away, the reflected light forms an image in front of the photodetector 158 and enters the dividing element (FIG. 6(a)). Conversely, when the optical disk 157 approaches, the reflected light forms an image after the 7-photodetector 158 and enters the dividing element a (FIG. 6(C)). (Fig. 6(b)).

Hereinafter, a conventional example of AF has been explained.

Next, AT will be briefly explained.

FIG. 7 is a diagram explaining the push-pull method.

In the push-pull method, the far-field optical φ distribution of the reflected light diffracted by the pits and guide grooves of the optical disk is detected using a two-split photodetector with 1:4 lines corresponding to the direction along the track, and each The tracking error signal is obtained by averaging over time to eliminate the influence of pits.

Figure i7 shows the far field pattern on the detector surface due to spot deviation when the pit depth is approximately 15n (n is the refractive index of the cover layer). This causes an asymmetry in the amount of light. That is, a tracking error signal can be obtained by detecting the difference in the amount of light incident on the dividing elements a and b of the two-part photodetector and averaging the difference over one hour. The push-pull method has a simple electrical circuit, but has the disadvantage of being very sensitive to the depth of the pit or guide groove. In general, the t-racking error signal of the push-pull method with a depth of I/8n is maximum, and the depth of I/4n
It is known that it becomes O when . However, if you try to obtain a recording signal as the sum signal of dividing elements a and b of a two-split detector, the maximum value will be reached when input/4 n, and
Since it is known that the depth is 0 or more, which is known to be minimum at 8 n, when AT is performed using an information pit string in the push-pull method, it is said that the pit depth is preferably about λ/5 n. In addition, when performing AT with a continuous guide groove, the depth of the briformant pit that represents the tracking number, sector mark, etc., and the depth of the guide groove used in the push-pull method are two types of depth that are suitable for each. Become.

Furthermore, the push-pull method has the disadvantage that an offset occurs in the error signal if the disk is tilted or the objective lens is moved laterally and the optical axis is shifted.

Figures 8 and 9 illustrate AT using the heterogain method.
1 is a diagram.

In the heterodyne method, a far field pattern of pits is detected using a four-part photodetector. 4 minutes;!
When the A photodetector is placed as shown in FIG. 8, as the spot scans the pit, the far field pattern on the detector moves as explained in FIG. 7. This is detected by the dividing elements a, b, c, and d of the IA detector at 4 minutes', and it is assumed that RF=a+b+c+d HTD=(a+c)−(b+d). Here, RF is a reproduction signal of recorded information, and HTD
is a heterodyne signal. As can be seen in FIGS. 8(a) and 8(c), when the spot shifts, the RF signal and the HTD signal are out of phase by 90° in the positive or negative direction. Utilizing this fact, signal processing is performed as shown in FIG.

That is, from the RF signal S1, the rising pulse S3 and the rising pulse r
Create Riva JL/S S 4 and send HTD mail'-'f S
Sampling and holding the signal S5 with the pulse S3 that raises the signal 2, sampling and holding the signal Sa with the pulse S4, and then taking the difference between these signals S5 and 56 to detect the tracking error S7. obtain. This heterotine method has advantages over the push-pull method in that it does not depend much on the depth of the beam and generates less offset.

However,
It requires a reference signal such as , and can only be used for video discs with continuous pits, and so far it has not been usable for write-once or replaceable discs.

FIG. 10 is a diagram illustrating AT using the three-beam method.

In the same figure, the light from the light source is converted into O-order light AO by the diffraction grating.
and ±1st order light A1. A2 and is imaged at a slight angle with respect to the track. Compatible with these 3 beams17
3-division detector (segmentation elements Bo, Bl, B
2) When detecting, the spot is rightward L/l, when B1
>B2 (Figure 10(a)), B1=82 when on track
(Fig. 10(b)), when it shifts to the left, Bl<82 (first
0(c)). In other words, by setting TE=B, -B2, a tracking error signal can be obtained and TE=0
control so that Although this method can be used for both AT using continuous guide grooves and AT using bit rows, it has the drawbacks of being difficult to adjust in assembly and being unstable against heat.

As mentioned above, the push-pull method has the disadvantage that offset occurs when the objective lens moves or the disk tilts. However, in the high frequency range, the push-pull signal is used as is, and in the low frequency range, the push-pull signal is used as is, and in the low frequency range, the push-pull signal is There is a composite track servo system in which pits are arranged in a special manner and a signal without offset is extracted using the pits to perform AT. Figure 11 shows the pattern of sectors in the track of this composite trunk servo system.
This is a diagram.

FIG. 11C&) shows a correction using a mirror surface, and a mirror surface portion without a guide groove is provided at one location in one sector. The reflected light from this mirror surface section contains only an offset component, and this value is held and corrected. FIG. ti(b) shows offset correction using asymmetric pits, in which focus pairs distributed left and right from the track center are provided in one sector. When the spot scans the pit versus the soil, changes in reflected light ();- are compared, and track deviation is detected and corrected. This signal includes
To L Shijin. Deshi\Kashi%-1-hsl- or 4'-g
Composite track servo such as R cannot suppress offset in a high frequency region, and is equivalent to a push-pull method during track jumps or high-speed access, and has the disadvantage that offset occurs.

:tS12 is a diagram illustrating a sample servo type AT. As shown in this figure, the l block is divided into a servo area and a data area.

Wobbled bits are preformatted in part of the servo area. There are 1,000 blocks within one revolution of the disk.
This is a completely discontinuous servo system in which the traffking error signal is obtained only from this servo area, with approximately 1,400 servo areas.

The advantages are that since the servo area and data area are separated temporally and spatially, there is no interference between the respective signals, there is no offset in the tracking error signal, so the accuracy of the optical system can be relaxed, and the accuracy of the optical system can be relaxed. For example, it is easy to detect abnormalities in servo signals due to defects. However, when making a disk for sample servo, there are difficulties in having to position the wobbled bit pair accurately at a distance of approximately ±1/4 of the track width from the center of the track. If a sample point is destroyed by a defect, it is impossible to detect an abnormality in the servo signal, and there is a drawback that a large defect extends to the adjacent sample point on both images.

[The problem that the invention tries to solve! &i] To summarize the problems of AT in the conventional examples described above, in the push-pull method and the composite track servo method, offset due to movement of the objective lens and inclination of the disk became a problem during high-speed access. The three-beam method had problems with difficulty in adjusting the optical system set and instability with respect to heat. The problem with the heterodyne method is that AT cannot be performed in continuous guide grooves, making it unusable for write-once and rewritable disks.

The problem with the sample servo method was the difficulty of creating a master disk and the influence of the servo signal on pit-sized defects.

Therefore, an object of the present invention is to improve the sample servo system in particular so that it can be used for write-once type and old replacement type IFJ, easy to create master discs, and reduce the negative influence of tracking error signals on pit-sized defects. The objective is to provide optical recording media.

[Means to solve the problem] According to the invention, the above objectives are achieved.

An optical recording medium comprising a plurality of blocks, each block comprising a data area for optically writing or reading information, and a servo area separated from the data area and capable of generating a tracking error signal.

The servo area is achieved by an optical recording medium characterized in that it includes at least one pit that is preformatted at the center position in the width direction of the track and has a longitudinal direction in the track direction.

Preferably, the width of the bit is less than half the track width and the length is longer than the track width.

[Example] Reference is made to FIG. 1, which shows an example of the present invention. In the figure, 21 is a track on the optical disk, 22 is a block, and 2
3 is a servo area, 24 is a data area, 25 is a tracking servo bit, 26 is a focusing servo area, 27 is a clocking bit, the text is the width of the track, P
l indicates the bit length, and FW indicates 10 pits.

On the optical disc, the track width (approximately 1 to 2 pm)
The optical recording medium of the present invention, in which the tracks 21 are provided in a spiral or concentric shape, basically does not require a guide groove, and one track consists of approximately 30 sectors. I know.

Further, the sector is divided into approximately 40 blocks. One block 22 has a configuration as shown in FIG.

As shown in FIG. 1, the block 22 is divided into a servo area 23 and a data area 24.

The servo area 23 includes a servo pit 25 for tracking, a servo area (mirror area) 26 for focusing, a clocking pit 27 for synchronizing the reproduced clock of the data area, and the like. The AF and AT error signals are sent to the focusing servo area 26 of the servo area 23,
It is obtained from the tracking servo pit 25, performs AF and AT, and holds the position until the next adjacent servo area. In this embodiment, the far field pattern of each of the three tracking servo bits is detected by a four-part photodetector as explained in FIGS. 8 and 9, and a tracking error signal is obtained for each pit by the hetero gain method. You can average the values for the three pits and use that value as the error signal, or you can use the error signal of one representative pit.Here, the three pits that are being detected are This is to eliminate the erroneous detection of bit-sized defects, which is a drawback of the conventional sample servo method. All you have to do is hold.

Next, the preferred size of the servo bit will be explained. Now, let the width of the track be D and the diameter of the scanning spot be D.

If 1>D is not the case, it will be affected by the pits of adjacent tracks.In addition, in order to increase the tracking error signal by the above-mentioned heterodyne method, the l112PW of the servo pit is slightly smaller than the size of D/2, It is desirable that the length PM is greater than or equal to D. In other words, it is preferable that the size of the servo pit with respect to the track width pattern of the optical disc is FW<l/2, P pattern>.

According to this embodiment, the servo pits and pre-pits such as addresses can all be made with the same width FW, and all can be placed on the center of the track, so the difficulty of creating a conventional master disk is greatly alleviated. .

In FIG. 2, ■ is a semiconductor laser, 2 is a collimator lens, 4 is an objective lens, 5 is an optical disk, 6 is a condensing lens, 7 is a cylindrical lens, 8 is a beam shaping prism, 9 is a polarizing beam splitter, and 10 is 1 4-wave plate,
11 is a four-part photodetector.

This figure shows a writing and reading optical system when the optical recording medium of the present invention is applied as a write-once optical disc.
The light emitted from the semiconductor laser 1 is linearly polarized light that vibrates within the plane of the paper, and is passed through a collimator lens 2 and a beam shaping prism 8.
After that, it becomes a circular light. Polarizing beam splitter 9
Then, most of the light is transmitted and becomes circularly polarized light by the 174-wave plate 10. A minute spot is focused on the optical disk S using the objective lens 4. This minute spot is used to write information and read desired information. The reflected light from the optical disk 5 passes through the objective lens 4 again, returns to its destination, becomes linearly polarized light with vibration perpendicular to the plane of the paper at the quarter-wave plate IO, and passes through the polarized beam splinterical lens 7.
After being given astigmatism, the optical disc enters a four-segment photodetector 11 at a position where it becomes a circular beam until it is focused. One dividing line of a 4-part photodetector is
It is placed parallel to the image of the truck. Further, the generatrix of the cylindrical lens 7 is arranged at an angle of 45° therewith. AF is performed by the astigmatism method, and AT is performed by the heterogain method for the focused beam.

However, since it is an astigmatism system, it must be noted that the image on the 4-split photodetector is rotated by 90'. Also, polarized beano, splitter 9 and 1/4
The wave plate 10 may be a non-polarizing beam splitter, or a beam splitter 7 may be arranged between the polarizing beam splitter 7 and the condensing lens 6 to split the light beam, and the light beam is split into the newly created optical path. A condenser lens and a 4-split photodetector may be arranged to detect a focus error in the former optical path and a tracking error in the latter optical path.

FIG. 2 is a block diagram illustrating a method of loading and reading.

In the figure, 31 is an optical disk of the present invention, 32 is a center hole, 33 is a spindle motor, 34 is an optical head,
35 is a stepping motor, 36 is a feed screw, 37 is a guide shaft, 38 is a modulation circuit, 39 is a laser drive circuit, 40
41 is an AF-AT servo circuit, and 42 is a binarization circuit.

43 is a spindle motor control, 44 is a stepping motor control, 45 is a four-division photodetector, 48 is a rising pulse generation circuit, 49 is a falling pulse generation circuit, 50.51 is a gate circuit, and 52.53 is a hold circuit.

Explain the operation. The optical disc 31 is fixed to a spindle motor 33 through a center hole 32 and is driven to rotate. The spindle motor 33 is kept at a constant angular velocity or at a constant angular velocity for each area of the optical disc by a spindle motor control 43. Hikari Herad 3
Reference numeral 4 is composed of the optical system, actuator, etc. shown in FIG. For convenience of explanation, the four-part photodetector 45 is shown extracted from the optical head 34 in FIG. The optical disc 34 is driven by a feed screw 36 and a guide shaft 37, and is driven by a stepping motor 35 to move the optical disk 3.
1 radial direction and can advance on any track. Stepping motor 35 is controlled by stepping motor control 44 .

First, writing will be explained. The optical head 34 moves onto a track on which no information is written. The old information signal 54 is modulated by a modulation circuit 38, such as 4-15 modulation. The oscillation of the semiconductor laser is controlled by the laser drive circuit 39 in accordance with this modulation signal, and is written on the optical disk 31 as a pit train.

Next, reading will be explained. The reflected light from the optical disk 31 passes through the optical system described in FIG. 2 and enters the four-part photodetector 45 (11 in FIG. 52). 4
The electric signals from each element a, b, c, d of the divided photodetector 45 are summed by 1g, and the Rf signal 47 and the HDT
The signal becomes signal 46. Here, Rf=(a+b+c+d) HDT=(a+c)-(b+d).

These signals are time-shared. That is, it is divided into tracking time, focusing time, writing or reading time, etc. according to the format on the optical disc. During the reading time, Rf entering the binarization circuit 42
A clock signal and a binary signal are obtained from the signal 47, and a reproduced signal 55 is obtained by the demodulation circuit 40.

Next, AF and AT will be explained. During the focusing time, the HDT signal 46 based on the reflected light from the focusing servo area (mirror surface part) 26 of the optical disk becomes a focus error signal based on the astigmatism method, and the AF-AT servo circuit 41 adjusts the AF so that HDT=0. servo signal to light, vqame7〃sheep-eta to ■JA
Perform F and hold focusing until the next focusing time. Also, in terms of tracking time,
Considering that the image on the 4-split photodetector 45 is rotated by 90 degrees and that it is a focused image, the trunking error signal TE56 is obtained by the heterodyne method as explained in FIG. 9. Tracking error signal TE
The AF-AT servo circuit 41 sends an AT servo signal to the actuator of the optical radar 34 so that the AT becomes O.
and hold tracking until the next tracking time.

:j In the optical disc explained in Figure S1, three pits are shown as tracking servo pits, but this number may be increased or decreased depending on the amount of pit-sized defects. The positions of these may be interchanged, and in this case, the tracking pit and clocking pit may also be used to increase the recording capacity. As explained above, it can also be used as a reproduction disc or a fortune-telling disc.

Furthermore, the invention can also be applied to other optical recording media such as optical cards in which a plurality of linear tracks are arranged in parallel.

Note that for AF, the focus error signal may be used without being held, and the focus error signal is filtered through a low-pass filter to remove the influence of bits.

[Effects of the Invention] As described below, according to the present invention, the area of an optical recording medium is divided into a servo area and a data area, and the napo area is preformatted at the center position in the width direction of the track. By providing at least one bit having a longitudinal direction in the recording medium, it is possible to simplify the creation of a master disk for manufacturing the recording medium, and to reduce the negative influence of a tracking error signal due to a bit-sized defect. Can be done.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the format of the optical disc of Unreleased II, Fig. 2 is a schematic diagram of an optical system for writing or reading information using the optical disc of the present invention, and Fig. 3 is a diagram illustrating the format of the optical disc of the present invention. Figure i4 is an explanatory diagram of the astigmatism method, Figure 5 is an explanatory diagram of the critical field prism method, Figure 6 is an explanatory diagram of the Naifetsu method, Figure 7 is an illustration of the push-pull method, Figures 8 and 9 are illustrations of the heterogain method, Figure 10 is an illustration of the three-beam method, Figure 11 is an illustration of the composite tracking method, and Figure 12 is an illustration of the composite tracking method. FIG. 3 is an explanatory diagram of a sampling servo method. 21 Ni-track, 22 Ni-block, z3: Servo area, 24: Data area 525 Ni-tracking servo pit, 26: Focusing servo area, 27: Clocking bit. Agent Patent Attorney Johei Yamashita (0) Figure (b) (C) Figure (b) (C)

Claims (5)

[Claims] (1) In an optical recording medium that includes a plurality of blocks each consisting of a data area for optically writing or reading information and a servo area that is separated from this data area and can generate a tracking error signal, the above-mentioned An optical recording medium, wherein the servo area includes at least one pit that is preformatted at the center position in the width direction of the track and has a longitudinal direction in the track direction. (2) The optical recording medium according to claim 1, wherein the pit has a width less than half the track width and a length longer than the track width. (3) The optical recording medium according to claim 1 or 2, wherein at least one of the pits is a tracking servo pit. (4) The optical recording medium according to claim 3, wherein at least one tracking servo pit also serves as a clocking pit. (5) The optical recording medium according to any one of claims 1 to 4, wherein the servo area includes a mirror surface portion.