JPH0636247B2 - Optical disc media - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical disc medium for optically recording and reproducing information, and particularly has a groove for guiding a light beam spot, and a groove for guiding the light beam spot is used. The present invention relates to an optical disc medium for recording / reproducing information while guiding a light beam spot on the optical disc medium.

[Conventional technology]

Conventionally, for example, in an optical disc for recording digital information in a form that can be optically recorded / reproduced, a groove for guiding a light beam spot is previously provided in the optical disc, and a light beam is used to guide the light beam when recording the information. There has been proposed an optical disc device capable of additionally recording information while guiding the spot (for example, a press).
Information Phillips (Press informatio
n Philips) Nov. 7th 1978, or JP-A-54
-130102).

[Problems to be Solved by the Invention]

The guidance of the light beam spot is possible by monitoring the far-field pattern of the light, which is diffracted by the groove formed in the optical disc. For example, the diffracted light from the optical disc is received by two photodetectors located in parallel with the track across the track, and the respective outputs are differentiated to show the deviation between the light beam spot and the groove. Some get signals. However, since the photodetector is located in the far-field region of the diffracted light, there is a drawback that the tracking signal is not properly performed when the light beam is shaken or the disc is tilted, which causes an offset in the tracking signal.

FIG. 1 is a diagram for explaining the principle of causing an offset in a tracking signal due to spot movement on the photodetector surface in a tracking signal detection device using diffracted light. FIG. 1A shows a photodetector (having light receiving surfaces 1 and 2).
It is a plan view of the spot position above, FIG. 1 (b) is A
FIG. 6 is a cross-sectional view taken along the center line A ′, showing the intensity distribution of a light spot. FIG. 1 (c) is a cross-sectional view showing the positional relationship between the intensity distribution of the light spot condensed by the objective lens on the disk surface and the groove corresponding to the spot on the photodetector. In the case of (a) in FIG. 1 (c), the center 7 of the light spot is located on the surface of the disk where there is no groove.
In the case of (b) of Fig. (C), it coincides with the center 8 of the groove,
In the case of (c) of FIG. 1 (c), the light spot is at the left end of the groove (or inside the rotation of the disc), and in the case of (d) of FIG. 3 (c), the right end of the groove (or rotation of the disc). Outside). In FIG. 1, the spot 4 on the photodetector indicated by the dotted line is generated by moving the optical axis of the objective lens in order to follow the tilt of the disc with respect to the optical axis of the objective lens or decentering. .

In FIG. 1, the photodetector has two light receiving surfaces 1 and 2.
The distance between them is very narrow. When the spot on the disk surface is at the center of the groove 6, the spot on the photodetector surface is as shown in (b) of FIG. 1 (b) and is equal to the two light receiving surfaces 1 and 2 and is as shown by the solid line 3. The amount of diffracted light is incident. However, in this state, when the spot position on the photodetector surface moves due to the tilt of the disk or the movement of the objective lens, it becomes as shown by the dotted line 4.

Since the tracking signal by the diffracted light normally detects the imbalance of the diffracted light, the differential signal of the outputs of the light receiving units 1 and 2 is used as the tracking signal. Then, as described above, when the spot position on the photodetector surface moves, even though the spot center 7 on the disk surface coincides with the center 8 of the groove 6, the differential between the light receiving portions 1 and 2. The signal is not zero,
As a tracking signal, an offset is generated.

Further, when the center 7 of the spot on the disk surface is at the left end of the groove 6 in FIG. 1 (c) (c), the intensity distribution of the spot on the photodetector surface is (c) in FIG. 1 (b). ), The amount of light incident on the light receiving unit 1 increases, and the light receiving unit 1,
An imbalance occurs in the differential output of No. 2 and the shift amount and direction between the spot center and the track center on the disk surface can be known. When the center of the spot on the disk surface is at the right end of the groove as shown in (d) of FIG. 1 (c), the intensity distribution of the spot on the photodetector surface is (d) of FIG. 1 (b). ), The differential output of the light receiving portions 1 and 2 is the reverse of the case of (c) of FIG. 1 (c).

The present invention has been made to solve the above problems, and when recording and reproducing information while tracking control is performed by detecting the imbalance of the diffracted light by the guide groove, the tilt of the disk and the light of the objective lens It is an object of the present invention to provide an optical disk medium that can correct an offset of a tracking signal due to axial movement and can obtain an accurate tracking control signal.

[Means for Solving the Problems]

In order to achieve the above object, the present invention has a groove for guiding a light spot for optically recording and reproducing information, a plurality of sectors provided along the groove, and information in an optically readable form. In an optical disc medium having a recording film for recording, each sector has a sector mark for indicating the start point of the sector, a reflecting surface having a length equal to or larger than the diameter of a spot provided after the mark, and a recording provided after the reflecting surface. It is characterized in that it has a region and the reflecting surface is formed by cutting a part of the groove.

Usually, after the mark, the address information indicating the address of the sector,
It has a control signal area in which a synchronization signal for detecting address information is formed, and has a reflecting surface after the control signal area. The mark, address information, and sync signal are preferably formed in advance. Further, it is preferable to have a buffer area which is not recorded after the recording area.

[Action]

According to the present invention, a part of the groove for guiding the irradiated light beam spot along the rotation direction is cut at predetermined intervals to form a total reflection surface, that is, a mirror surface region that reflects the light beam spot almost as it is. . The offset can be corrected by using the signal obtained from this total reflection surface. That is, since only the offset component of the track signal appears on the total reflection surface and functions as an offset detection area, the offset component is detected and held from this total reflection surface, and the tracking signal due to the diffracted light from the guide groove is corrected and corrected. It is possible to obtain tracking signals and perform tracking control.

The length of the reflecting surface needs to be such that the light spot is not influenced by the surrounding grooves, and specifically, it is equal to or larger than the diameter of the light spot. Further, the reflecting surface needs to be located at a position where the timing at which the light spot passes the position can be reliably detected. Furthermore, in order for the reflecting surface to act as a reflecting surface, it is necessary that the portion is not additionally recorded in this portion.

From the above requirements, the reflection surface is suitable between the sector mark indicating the beginning of the sector and the additional recording area, and more preferably between the control signal area and the additional recording area after the sector mark. That is, the sector mark can be used as a reference of the reflection area, and the reflection area can be detected reliably.
Furthermore, since a time margin is required to start recording in the additional recording area after detecting the sector mark or control signal, it is necessary to prepare a gap area between the control signal area and the additional recording area. However, since this area is not effectively recorded, it is suitable as the area where the reflection area is provided.

The principle of the present invention will be described with reference to FIG. FIG. 2 shows the light receiving parts 1 and 2 in the case where the spot center 7 on the disk surface passes through the groove 6 from the left end to the right end, and the spot position on the photodetector surface is displaced by the shift amount Δ. Differential output 1
5 represents the change in the number 5 and the point 10 represents the case where the spot center 7 on the disk surface is at the left end of the groove 6, and the point 1
1 indicates a case where the center 7 is at the right end of the groove 6, and a black dot 12
Shows the case where the spot center 7 is at the center of the groove 6. The solid line 14 connects the black dots 12, which is the differential output 1
When 4 is regarded as a tracking signal, it represents the relationship between the spot movement on the photodetector surface and the offset.

On the other hand, the dotted line 13 is the case of (a) in FIGS. 1A to 1C, that is, the spot on the disk surface is on the total reflection surface without grooves, and the spot on the photodetector surface is Δ. The differential output of the light receiving parts 1 and 2 when moving is shown.

As is clear from FIG. 2, when the movement amount Δ of the spot on the photodetector surface is small, the ratio of the deviation amount between the dotted line 13 and the solid line 14 with respect to the amplitude of the differential output 15 is small, and is almost the dotted line 13. The solid line 14 may be substituted by the value of. Since the output of the dotted line 13 is the differential output of the light receiving units 1 and 2 on the total reflection surface, the total reflection surface is provided in a part of the groove, and the differential output 13 when the light spot passes through the total reflection surface 13 By extracting the value of, the offset is detected, and the differential output is corrected using this value, an accurate tracking signal without offset can be obtained without being affected by the tilt of the disk or the optical axis movement of the objective lens. You can

As described above, the present invention is an optical disk medium having a conventional tracking guide groove, in which the groove is cut at a predetermined position to form a total reflection surface. In addition to the above-mentioned applications, this total reflection surface can also be used as an inspection area at the time of shipping the medium. That is, the optical head measures the reflectance of the medium and the signal level in the unrecorded state to check whether or not the specified value is satisfied. If a groove is present during such inspection, the reliability of the inspection is lowered because the information of the groove structure is mixed in the detection signal, so the total reflection surface of the present invention is suitable. Also, by recording a test signal on this total reflection surface and observing it directly with a microscope or the like, the optical disc medium can be evaluated. Also in this case, if a groove is formed in the entire medium as in the conventional case, it becomes difficult to observe due to the reflection and diffracted light from the groove.

When reproducing the optical disk medium of the present invention, a detection signal having a constant maximum intensity is obtained from the total reflection surface at a predetermined timing. Therefore, the signal from this total reflection surface is
In addition to the offset detection, it can be used as a reference value of the signal level of the reproduction signal and also as a timing signal.

〔Example〕

FIG. 3 is a diagram schematically showing a main part of an embodiment of the optical disc medium of the present invention provided with a total reflection surface functioning as an offset detection area.

In FIG. 3, a part of the groove 6 is cut and the cut portion is used as a total reflection surface. FIG. 3 (a) is a plan view, and a cross section cut along the line BB 'is shown in FIG. 3 (b).
Is. The cut portion is flat without the groove 6, and its length is preferably such that the spot 20 is not affected by the surrounding groove 6 when the spot 20 is in the cut portion. For example, it is not less than the used spot size (the diameter at which the spot intensity becomes 1 / e ² ).

The depth h of the groove 6 is preferably .lamda. / 8 (.lamda. Is the wavelength used by the laser beam) as an optical optical path length, but may be deviated from this depending on other conditions, and the shape of the groove is also in accordance with the present invention. Of course, it is not limited.

FIG. 4 is a plan view showing an example of the track form of the additionally recordable optical disc according to the present invention. For example, the used area of the disk is 280φ at the outermost circumference and 180φ at the innermost circumference.
In this region, 32,000 tracks, that is, grooves for guiding the light spot along the rotation direction are provided in advance in a concentric or spiral shape at intervals of 1.6 μm in a radial direction of 50 mm. One track is divided into 64 in the circumferential direction, and each sector is a division of information given the name of sector.

In FIG. 4, one track has sectors 30, 31, 32, 3
3, 34, 35, 36, 37, ..., For example, a more detailed structure of the sector 34 is shown in FIG.
It looks like the figure. That is, each sector has a mark (referred to as a sector mark) 40 for detecting that it is the head of the sector, and a circuit for generating a clock for detecting address information (track number and sector number) ( Normally, there is a signal 41 for operating a PLL (Phase Locked Loop), and then address information 42. The above three signals are recorded in advance. Next, a gap 43 is prepared in front of the additional recording area 44.
This is to allow a time margin before the information signal is detected and the recording is started, and the recording is not effectively performed. A region 45 indicated by a dotted line is a buffer region and has a role of absorbing an increase in the recording region due to causes such as rotation fluctuation and clock jitter.

In the above-described optical disk capable of additional recording, the area where additional recording is not performed is preferable, and the area of the gap 43 or the area of the buffer 45 is suitable as a place for inserting the above-mentioned total reflection surface. That is, a part of the guide groove 6 provided along the track in a concentric circle shape or a spiral shape is replaced with the gap 43.
By cutting in the area of the buffer 45, total reflection surfaces functioning as offset detection areas are provided at predetermined intervals. As described above, the length is a length that is not affected by the surrounding grooves when the light spot is at the cut portion, and is set to be equal to or larger than the light spot size. Note that according to the present invention, it is needless to say that any area may be used without being restricted by the above-mentioned sector structure as long as no special problem occurs in data processing.

Next, a method of detecting the total reflection surface functioning as the above-described offset detection area will be described.

First, there is a method of detecting the offset in real time. First, it is necessary to know that there is a light spot at the position of the total reflection surface. In the case of an additionally recordable optical disc, the time interval from the sector mark to the area where the total reflection surface is inserted is known in advance, so first detect the sector mark and then measure the time to determine the area of the total reflection surface. It is sufficient to detect that a light spot has arrived.

According to the method described above, the offset amount can be detected and held by sample-holding the differential output of the photodetector at the timing detected by the method described above.

When a method that causes a time delay to detect that the light spot is on the total reflection surface is used, the differential output of the photodetector may be delayed by the above-mentioned time delay. The analog delay method is CCD (Co
rge Cogpled Device) or a delay line.

FIG. 6 is a diagram showing a configuration of an example of an apparatus for performing recording / reproducing while performing tracking using the medium of the present invention.

In the figure, the light beam from the laser 71 is a lens 72.
Parallel light by the prism 73, λ / 4 plate 74
(Λ: laser wavelength), passes through the focusing lens 75, and converges to a spot of about 1 μmφ on the disk 76 having the guide track. A reflective film or a recording film is vapor-deposited on the disk 76, and the light beam incident on the guide track 77 is reflected and again guided to the information detection system through the focusing lens 75, the λ / 4 plate 74 and the prism 73. Get burned. The information detection system (the auto focus detection system is not shown) is a focusing lens 7.
8 and a photodetector 79 whose light receiving surface for detecting a tracking signal and an information signal is divided into two.

As shown in FIG. 7, the disk 76 comprises a guide track 762 for guiding a light spot for recording / reproducing information, and a sector mark portion 64 for generating a timing for detecting the total reflection area 63. Guide track 62 is λ
Since there is a groove having a depth of about / 8, and the distribution of diffracted light reflected changes depending on the positional relationship of the incident spot with respect to the guide track 62 as described with reference to FIG. Then, the tracking signal is obtained by receiving the light at, and differentiating each signal by the differential amplifier 80.

FIG. 8 shows the output waveform from each circuit. FIG. 8 (a) shows a normal track signal when the disc is not tilted. The portion showing a flat level in the signal shows when the spot passes through the total reflection area. Next, FIG. 8 (b) shows a track signal when the disc is tilted. At this time, the optical axis of the reflected light moves due to the tilt of the disk, which causes an offset of Δ. For this reason, the track servo system tracks the electric zero as the center of the track, resulting in track deviation. The tracking signal at this time has a waveform as shown in FIG. 8C, and has a Δ offset when passing through the total reflection area.
An information signal is obtained by summing the output of the two-divided photodetector 79 with the summing amplifier 81. In the information signal, FIG. 9 (d) focuses on the sector mark portion 64. This output is passed through the sync signal detector 82 to generate a gate signal for extracting the total reflection area 63 (shown in FIG. 8 (e)). The gate signal is guided to the gate circuit 83, and all the tracking signals are extracted. The signal in the reflection area is extracted. The output is guided to the hold circuit 84, which holds the extracted signal and detects the offset signal (shown in FIG. 8 (f)).
This signal is differentiated from the tracking signal by the differential amplifier 85, and a tracking signal in which the offset due to the disc tilt is corrected is obtained at the output of the differential amplifier 85. Drive the device 87. As a result, accurate track tracking can be performed. Here, the case where the track is tracked by the lens has been described, but the same is true when the track is tracked by swinging the beam with a mirror.

〔The invention's effect〕

According to the optical disc medium of the present invention, the offset in the tracking signal generated by the disc tilt can be corrected, so that the information can be recorded / reproduced while the tracking control is performed accurately without being influenced by the disc tilt.

[Brief description of drawings]

FIG. 1 is an explanatory diagram for explaining the principle of offset generation,
FIG. 2 is a waveform diagram for explaining changes in the differential output from the photodetector, FIGS. 3 to 5 are diagrams for explaining the configuration of the optical disc according to the present invention, and FIG. FIG. 7 is a block diagram showing an example of an apparatus using the medium of the present invention, FIG. 7 is a schematic plan view of an optical disk of the present invention, and FIG. 8 is a waveform diagram for explaining the operation of the apparatus of FIG. 71 ... laser, 72 ... lens, 73 ... prism,
74 ... λ / 4 plate, 75 ... Focusing lens, 76 ...
Disc, 77 ... Guide groove, 78 ... Converging lens, 79
...... Two-divided photodetector, 80 ...... Differential amplifier, 81 …… Wading amplifier, 82 …… Synchronous signal detection circuit, 83 …… Gate circuit, 84 …… Hold circuit, 85 …… Differential amplifier, 8
6 ... Track servo circuit, 87 ... Lens drive device.

Front Page Continuation (72) Inventor Shigeru Nakamura 1-280 Higashi Koigokubo, Kokubunji, Tokyo Inside Central Research Laboratory, Hitachi, Ltd. (56) Reference JP-A-59-3728 (JP, A)

Claims (4)

[Claims] 1. Information is recorded in an optically readable form having a groove for guiding a light spot for optically recording and reproducing information and a plurality of sectors provided along the groove. In the optical disc medium, each sector has a mark for indicating the start point of the sector, a reflective surface having a length equal to or larger than the diameter of the spot provided after the mark, and a recording area provided after the reflective surface. An optical disk medium, wherein the reflecting surface is formed by cutting a part of the groove. 2. A control signal area in which address information indicating an address of the sector and a synchronization signal for detecting the address information are formed after the mark, and the reflecting surface is provided after the control signal area. The optical disc medium according to claim 1, further comprising: 3. The mark, the address information, and the sync signal are formed in advance.
The optical disk medium according to item 2 or item 3. 4. The optical disk medium according to claim 1, further comprising a buffer area that is not recorded after the recording area.