JPH0223554A - Magneto-optical disk and recording and reproducing system using thereof - Google Patents

Abstract

PURPOSE:To correctly reproduce recorded data with an inexpensive device by providing a buffer area containing no embossed bit between a servo area and recording area. CONSTITUTION:In this recording and reproducing system using a magneto-optical disk, a buffer area having a 5-channel bit length is provided between a servo area containing embossed bits PW1 and PW2 and data area. Since the mark position of 4/15 modulation can be any arbitrary position of the 1st-14th channel bits, the shortest interval among a magneto-optical mark MO, the embossed bit PW1, and a clock bit PC becomes 9-channel bits. Therefore, the mark MO, bit PW1, and bit PC are separated from each other by 9X0.501 (=4.5)mum or more even along the innermost periphery. Accordingly, influences of the embossed bits PW1 and PW2 can be reduced to <=4.5mum and the demodulation of magneto-optical signals is not influenced.

Description

[Detailed description of the invention] Technical field The present invention relates to a magneto-optical disk.

BACKGROUND ART In recent years, read-only and write-once optical discs have been put into practical use, and rewritable optical discs are also about to be put into practical use. In any of these types of optical discs, the track pitch is very narrow, about 1 to 2 μm, so concave or convex bits or grooves are previously formed on the disc to follow the tracks. By diffraction of the light that is irradiated onto the disk and reflected by these bits or grooves, it is possible to detect the relative positional relationship in the disk radial direction between the track and the beam spot for information reading, and thereby the tracking servo that makes the beam spot follow the track. can be done. Bits are also used for information needed to record or reproduce data and to generate locks, information to partition sectors, information to access sectors, information to partition the inside of a sector into blocks, etc. These various types of information are read by diffraction of light by the bits. As described above, the bits which are formed in advance on the disk and whose purpose is to obtain information by diffraction of light are called embossed pits.

Examples of the arrangement (so-called format) of embossed pits on a disk are shown in FIGS. 2 to 5.

In the format shown in FIGS. 2-5, a virtually spiral track formed on the disk is divided into 1376 equiangular segments per revolution. Furthermore, one sector is composed of 43 consecutive segments. Therefore, one track (one track) consists of 32 sectors.

FIG. 2 is a diagram showing a segment configuration within one sector. Every segment consists of a 2-byte servo area and a 16-byte header area or data area, a total of 18 bytes. The first segment has a 16-byte header area, and the second to 43rd segments have a 16-byte data area. Note that one byte of all bytes in the servo area, header area, and data area is divided into 15 channel bits.

FIG. 3 is a diagram showing the configuration of the servo area.

One segment of servo area consists of 2 bytes.

The bytes constituting the servo area are respectively referred to as a first servo byte and a second servo byte. Two embossed pits are formed in the first servo bite. These are formed to be shifted from the virtual track center by about 1/4 track pitch in opposite directions in the radial direction of the disk. The first wobbled bit PWI is
The wobbled pits PW2 are formed at the position of the third or fourth channel bit while being switched every 16 tracks, and the second wobbled pit PW2 is formed at the position of the eighth channel bit. Using these two wobbled pits, a tracking error signal can be generated in a sampling manner once per segment. That is, when the beam spot passes through the virtual track center, it passes between the two wobbled pits, so the degree of diffraction in each wobbled pit is equal, and the reflected light is also equal.

Therefore, the tracking error signal obtained by taking the difference between the signals obtained by photoelectrically converting the amount of reflected light is zero (
(no error). Further, when the beam spot passes through the track with a deviation from the center of the virtual track, a difference occurs in the reflected light from the two wobbled pits, so a tracking error signal corresponding to the direction and amount of deviation is obtained. Since there are 1,378 segments in one rotation, the tracking error signal obtained by sampling at each servo byte is almost equivalent to one obtained continuously, making it possible to perform tracking servo. .

Furthermore, one embossed pit is formed in the second servo bit exactly on the virtual track center at the position of the 12th channel bit. This is the clock bit P
It is called C. The clock bit PC is located at a fixed position in each servo byte, one per segment, so by synchronizing the PLL with a signal generated from this bit at regular intervals, the clock at the frequency of the channel bit rate can be set. can be generated. When recording data,
Modulation is performed using this clock, and demodulation is also performed using this clock during data reproduction.

Note that since there is a mirror surface between PW2 and PC, it is possible to generate a stable focus error in a sampling manner that is not affected by the presence or absence of bits.

Furthermore, since the interval between PW2 and PC is an interval (19 channel bits) that cannot occur in the 4/15 modulation method described later, segment synchronization can be performed by detecting this interval. be.

FIG. 4 is a diagram showing the configuration within the header area. 1st
In the bite, sink marks are formed by embossed pits. Sync marks are No. 2, 7.8. Bits are formed in 9 channel bits, and 4/1 as described later.
In the 5 modulation method modulation upgrade table, this is a special pattern that does not correspond to any NRZ data. Therefore, by detecting this, sector synchronization can be performed. The second byte is a sector address within one track, and the third to seventh bytes are track addresses within a disk, which are formed by embossed pits. These are modulated using a 4/15 modulation method, which will be described later, for each byte.

The 8th to 13th bites are reserved areas whose uses have not been determined, and have mirror surfaces without embossed pits.

The 14th to 16th bites are laser power control areas, and are initially mirror surfaces without embossed pits. When recording or erasing on a disc, it is desirable to use appropriate optical power, but in this area it is permissible to emit recording or erasing power on a trial basis from the optical pickup and correct the output power based on that. has been done.

FIG. 5 is a diagram showing the data area. The data area is 1
It is 6 bytes long, and in the unrecorded state, it has a mirror surface with no embossed pits. NRZ data is modulated one byte at a time using the 4/15 modulation method described later and recorded in this area. In the case of the write-once type, recording involves physical changes such as holes in the recording film. In the case of a rewritable disk that utilizes the magneto-optical effect (hereinafter referred to as a magneto-optical disk), such a physical change does not occur, but there is a change in which the direction of the magnetic field of the recording film is reversed.

The data area in one sector is 16x42-672.
There are bytes, which consist of user data, error correction codes, etc., but the details will not be described here.

Next, the 4/15 modulation method will be explained with reference to FIG. 4/15 modulation method 1 byte is converted into 15 channel bits, and from these 15 places, the original 256
For the NRZ data on the street, there are 4 locations (2 odd and even 2 locations each) that correspond one-to-one using the conversion table.
One place at a time. However, the 15th channel bit is excluded. ). That is, in the case of a write-once type, an operation such as making a hole in the recording film is performed, and in the case of a magneto-optical disc, the direction of magnetization of the recording film is reversed. Note that, as in the example shown in Figure 6, the marks are adjacent to each other (see 12.13.1).
4 channel bits), but there is always a space of at least 2 channel bits (10.11th channel bits) between marks that are not adjacent to each other (9th and 12th channel bits). However, as an exception, there are cases where the 14th channel bit of one byte and the 1st channel bit of the next byte become a mark, leaving only one channel bit (15th channel bit) between them, but the 15th channel bit was originally a mark. Since this will never occur, there will be no harmful effect during demodulation.

Next, demodulation of data using 4/15 modulation method will be explained. FIG. 6 shows reproduced waveforms corresponding to the marks.

In addition, in the case of drilling records, the reflected light at the mark position is darker than the reflected light at the unmarked position (mirror surface).
Also, some media that are not perforated undergo the opposite change.

However, the level of the mark position on the 4/15 modulation method and 1
! Demodulation is possible if there is a difference between the level at the top of the demodulation circuit.Therefore, the reproduced waveform in Figure 6 does not mean that the upper part of the diagram is brighter, but simply shows the voltage level at a certain point in the demodulation circuit. shall be.

In addition, in the case of magneto-optical disks, it is not a mirror level, but
This is the erasure level. For demodulation, it is sufficient to specify the mark positions of 2t1 of odd-numbered bits and 2 of even-numbered bits of the 1st to 14th channel bits of a certain byte. Therefore, for example, by performing A/D conversion at the bit center of the first to fourteenth channel bits and comparing the magnitudes of the obtained digital data, the position of the mark can be specified.

For example, in the example of FIG. 3. 5. 7.
9. Among the 11.13 channel bits, the 13th channel bit has the highest level, and the 9th channel bit has the second highest level. (In this example, there is a mark on the 14th channel bit and the 1st channel bit of the next byte, so the level of the 15th channel bit may be higher than the level of the 9th channel bit, but the 15th channel bit may not become a mark.) (Since there are no marks, they are not compared in size, and therefore do not cause a problem in demodulation.) In other words, it can be seen that among the odd-numbered bits, there are marks on the 9th and 13th channel bits. Similarly, the second degree 4.6,
Among the even-numbered channel bits of 8.10.12.14, the 12th. It can be seen that there is a mark on the 14th channel bit. The original NRZ data can be demodulated from these four marks using the conversion table.

In short, demodulation of the 4/15 modulation method is based on comparing the reproduction levels at the center of each channel bit.

Next, an outline of the magneto-optical disk will be explained.

First, as with write-once optical discs, portions that will become embossed pits are created on a glass master disc by mastering, and a stand bar is created by electroforming.

Next, a substrate 1/-t on which the embossed pits have been transferred is produced by injection molding a polycarbonate resin or the like using this stubber as a mold.

Next, a thin film of TbFeCo alloy or the like is formed as a recording film on this substrate by a method such as sputtering to obtain a magneto-optical disk as shown in FIG.

The recording film 1 of the magneto-optical disk as shown in FIG. 7 produced in this way usually has a uniform reflectance of about several tens of percent. Therefore, light of uniform intensity is reflected in the mirror surface portion 2 without embossed pits.

Further, in the embossed pit portion 3, the amount of reflected light is approximately equal to the number of mirror portions 2+96 due to a diffraction phenomenon.

Note that 4 is a substrate.

Next, an outline of the recording principle of a magneto-optical disk will be explained. In the initial state where a recording film is formed by a method such as sputtering as described above, the magnetic domains of the recording film are randomly arranged upward and downward in a direction perpendicular to the film surface. Generally, a magnetic field Hm stronger than the coercive force Hc of the film is applied to the disk in this initial state to align the direction of magnetization in one direction (erasing direction). This creates a disc with no signal (completely erased). This disk has a magneto-optical disk device (hereinafter referred to as a drive).
When recording information with , it is weaker than HC and the direction is Hm.
While applying a magnetic field Hr opposite to the above, a strong recording beam is irradiated only when a mark is to be recorded on a channel bit.

Then, the temperature of that part rises and the coercive force becomes smaller than Hr, so the magnetization direction is reversed, and after the beam spot passes, the magnetization direction of that part becomes Hr, and a mark cannot be recorded. That means that.

When erasing recorded data using a drive, a strong erasing beam is applied while applying a magnetic field He that is weaker than Hc and in the same direction as Hm. As a result, in the portion irradiated with the erasing beam, the direction of the magnetic field becomes a no-signal state (erased state) regardless of the presence or absence of a mark. In other words, the mark has been erased.

During reproduction, a linearly polarized reproduction beam, which is weaker than the recording beam or erasing beam, is irradiated. The plane of polarization of the reflected light is slightly rotated by the Kerr effect, but the direction of rotation depends on the direction of magnetization. By detecting this with an analyzer, converting it into a change in intensity, and photoelectrically converting it, it is possible to obtain the potential difference between the mark location and the non-mark location.

Note that a differential optical system is generally used as a reproduction signal detection optical system of a magneto-optical pickup.

Although not particularly shown, this method divides the reflected light from the disk into two systems using a polarizing beam splitter, and by taking the difference between the respective photoelectrically converted signals, it obtains a magneto-optical reproduction signal and eliminates semiconductor laser noise and disk noise. It is well known that the in-phase noise such as minute reflection unevenness from the optical system is suppressed, and that it is indispensable as an optical system for reproducing magneto-optical signals. Note that the reproduced signal of the embossed pit is obtained by summing the two systems of signals.

When demodulating data recorded on a magneto-optical disk in the format described above, segment synchronization is first performed by detecting the interval between the embossed pits of PW2 and PC shown in Figure 3, and then Sector synchronization is performed by detecting the sync mark shown in FIG. As shown in FIG. 6, by A/D converting the magneto-optical signal reproduction waveform of each byte and comparing the sizes, it is possible to determine whether the recorded mark (i.e. direction of magnetization is changed from the erased state). (inverted channel bits)
Since the position of the data can be known, it is possible to demodulate the recorded data.

However, in the case of the above format, the first byte of the data area is close to the embossed pit (clock bit) in the servo area, and the 16th byte of the data area is also close to the embossed pit (clock bit) in the servo area. Since the embossed pits are close to the embossed pits, the magneto-optical reproduction signal is adversely affected by the embossed pits, which is a disadvantage in demodulating the embossed pits. This drawback will be explained below with reference to FIGS. 8 to 13.

Figures 8 to 13 show that magneto-optical signals are recorded on tracks near the innermost circumference (radius 30 am) of a disk having the format shown in Figures 2 to 5, and when the signals are reproduced, the servo area is 1st and 2nd servo byte SBI, SB2
and the first in the data area immediately before and after the servo area.
It is a photograph showing the oscilloscope waveform of the signal obtained from the 6th data byte DB+6 and the 1st data byte DB.

The disc rotation speed during recording and reproduction was 301 PS. Therefore, the channel bit rate is 30 (RPS) x 3
2 (sector/track) x 43 (segment/sector') x 18 (byte/segment) x 15 (channel bit/byte) - 11,1456 (Mb i
t/S). Therefore, the time for one channel bit is approximately 90 (ns), and the time for one byte is approximately 1635 (μ
S).

Furthermore, the linear velocity at a radius of 30 mm is 30 (mm
) X2πX30 (RPS) ”-+1355(am
/S), so the length of one channel bit is approximately 0. 51
(μm).

Figures 8 to 13 (all horizontal axes are 500ns/D
IV, the vertical axis is arbitrary), Figures 8, 10, and 12 show the photoelectric conversion outputs CHI and CH2 of the two systems of the differential optical system (the upper part of the figure shows the reflected light from the disk). The waveform is shown below.

Figures 9, 11 and 13 show the above CHI and CH2
The magneto-optical reproduction signal a generated by taking the difference (CHI-CH2) (the level of the mark is above the figure) and CHI
The waveform of the embossed pit reproduction signal generated by summing (CH1+CH2) is shown.

Moreover, FIGS. 8 and 9 show waveforms in a state fi in which a recording film is formed by sputtering (a state in which a magnetic field Hm stronger than Hc is not applied), and FIGS. While applying a weaker magnetic field He, a strong erase beam is irradiated only in the data area,
The waveform is shown when only the data area is erased (signalless). In addition, FIGS. 12 and 13 show that after only the data area is erased (signal-free) by a drive, a magnetic field Hr, which is weaker than Hc and in the opposite direction to He, is applied to the first to third areas of the data area. For all 16 bytes, a strong recording beam is irradiated on the 1st, 4th, 7th, 10th and 13th channel bits, and the waveforms are shown in a state where marks are recorded.

Note that the mark patterns recorded in FIGS. 12 and 13 conform to the 4/15 modulation method modulation layer rule in that there is always a 2-channel bit non-mark between marks. , they do not match in that there are five marks in one byte. However, this waveform was intentionally recorded for the purpose of explanation, and does not deviate from the spirit of the present invention.

Now, in FIG. 13, looking at the magneto-optical signal, the level of the marks in the first and fourth channel bits of the first data byte is lower than the level of the marks after the seventh channel bit. Similarly, the level of the mark in the 13th channel bit of the 16th data byte is higher than the level of the mark in the 110th channel bit and earlier. As explained in Fig. 6, 4/15 modulation can be demodulated by comparing the levels at the center of the bits of the 1st to 14th channel bits. It is clear that this is harmful.

Next, looking at the magneto-optical signal in FIG. 11, it can be seen that the erasure (no signal) level in the first half of the first data byte and the second half of the 16th data byte is not flat. That is, the reason why the recorded waveform shown in FIG. 13 is not normal is that the mark was recorded on an uneven erase level.

Next, looking at FIG. 9, it can be seen that the magneto-optical signal is already not flat in the initial state where only the recording film is formed.

Next, looking at Figures 8, 10, and 12, the reason why the magneto-optical signal is not flat is that the two signals CHI□CH2 of the differential optical system have slightly different movements near the embossed pit. It can be seen that this is due to the fact that As is well known, magneto-optical signals are detected using the phenomenon (Kerr phenomenon) in which the plane of polarization of reflected light slightly rotates depending on the direction of magnetization of the recording film, and the rotation angle is 0. Very small, around 5'.

Therefore, as is clear from the waveforms in FIG. 12, the amplitude of the magneto-optical recording signal actually obtained in each channel of the differential optical system is much smaller than the amplitude due to the diffraction of the embossed pits. Therefore, even if CHI and CH2 have slightly different waveforms in the vicinity of the embossed pits, this will have a significant adverse effect on the reproduction of the optical/magnetic signal.

Therefore, in order to prevent this phenomenon from occurring, the differential balance of the optical system should be improved as much as possible, and
It is also necessary to strictly control local optical behavior abnormalities in the vicinity of the embossed pits of the disk, but this may complicate adjustment and increase costs.

Summary of the Invention The present invention has been made in view of the above points, and includes:
It is an object of the present invention to provide a magneto-optical disk and a recording/reproducing method using the magneto-optical disk, which can reproduce recorded data without error using an inexpensive device.

In order to achieve the above object, in the magneto-optical disk according to the present invention, a buffer area in which no embossed pits are present is arranged between the servo area and the recording area.

It is preferable that the buffer area has a mirror surface.

In addition, in the recording and reproducing method using the magneto-optical disk according to the present invention, when information is recorded in the area following the servo area including embossed pits and used as a recording area, a non-recording area is created as a buffer area before and after the servo area. I am trying to set it up.

It is preferable to generate a focus error signal in the buffer area.

EXAMPLE Hereinafter, an example of the present invention will be described in detail with reference to FIG.

In FIG. 1, first and second wobbled bits PWI and PW2 and a clock bit P in the servo area are shown.
C is formed similarly to the format shown in FIGS. 2 to 5. However, in this example, a buffer area with a length of 5 channel bits is arranged between the servo area and the data area.

In the above configuration, the mark position in 4/15 modulation can be any position of the 1st to 14th channel bits, so the shortest distance between the magneto-optical mark MO and the embossed pits PW1 and PC is as shown in FIG. , resulting in 9 channel bits. Therefore, the magneto-optical mark MO and the embossed pit PWI, PC are 9XO, 501μ even on the innermost circumference.
They are separated from each other by more than m (approximately 4.5 μm). Therefore, as is clear from the oscilloscope waveform in Figure 11, the influence of the embossed pits is within about 9 channel bits (about 8QQns), or about 4.5 μm, so there is no effect on the demodulation of the magneto-optical signal. .

Also, the distance between the first wobbled pit PWI and the 'W&2 wobbled bit PW2 and the second wobbled bit PW
2 and the clock pit 20 are the same as those in the format shown in FIGS. 2 to 5, so tracking servo and focus servo can be performed in the same way as with conventional disks in the format shown in FIGS. 2 to 5. can.

Note that the number of channel bits in one segment was 15×18-270 in the formats shown in FIGS. 2 to 5, but in this example, it is increased by 10 bits, so it becomes 280. Therefore, the size of one channel bit is approximately 3.6%
becomes smaller. However, with this degree of change, the increase in code amount interference between adjacent marks is very small, and the effect of reducing the negative effects of embossed pits is far greater.

It is also conceivable to further increase the shortest distance between the embossed pit and the magneto-optical mark by shortening the distance between the first wobbled pit PWI and the second wobbled bit PW2 or the distance between the second wobbled pit PW2 and the clock pit 20.

At this time, the buffer area has a mirror surface, so
A focus error signal can be generated in the buffer area, and thereby stable focus servo can be performed.

The effects of the magneto-optical disks having the formats shown in FIGS. 2 to 5 have been explained above as a conventional example. It can be applied even if

Furthermore, in the above embodiment, the shortest distance between the embossed pit and the magneto-optical mark was set to 9 channel bits, but the shortest distance between the embossed pit and the magneto-optical mark may be determined depending on the modulation method, shortest channel bit length, etc. It goes without saying that it can be set to any value, and is not limited to the above values.

Effects of the Invention As detailed above, in the magneto-optical disk and the recording/reproducing method using the magneto-optical disk according to the present invention, since the buffer area is arranged between the servo area and the recording area, the local area near the embossed pits is It is possible to eliminate the adverse effects on recorded data due to abnormalities in optical behavior.

Therefore, according to the present invention, it is easy to manufacture a disk,
It becomes possible to supply inexpensive disks. In addition, the tolerance range for structural unbalance of the differential optical system is expanded,
Furthermore, since the tolerance range for adjustment of the differential optical system is widened and the tolerance range for variations in optical components is also widened, recorded information can be reproduced with an inexpensive device.

Further, by making the buffer area mirror-like, it is possible to generate a focus error signal, which is preferable.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the present invention, and FIGS.
Figure 6 shows the recording format of a conventional magneto-optical disk, Figure 6 shows the correspondence between the recording state of the data area and the waveform of the read signal, and Figure 7 is a cross-section showing the structure of the magneto-optical disk. 388 to 13 are photographs showing oscilloscope waveforms of signals obtained from a magneto-optical disk by a pickup. Explanation of codes of main parts PWI, PW2, old... Wobbled Bit PC...
...Clockbit Applicant Pioneer Corporation

Claims (4)

[Claims] (1) A magneto-optical disk in which servo areas including embossed pits for generating servo error signals and recording areas in which information signals are recorded are arranged alternately in the circumferential direction, and the servo areas and recording areas are arranged alternately in the circumferential direction. A magneto-optical disk characterized in that a buffer area having no embossed pits is arranged between the buffer area and the buffer area. (2) The magneto-optical disk according to claim 1, wherein the buffer area has a mirror surface. (3) A recording/reproducing method using a magneto-optical disk having embossed pits for generating error signals for servo, in which information is recorded in the area following the servo area including the embossed pits and used as a recording area. A recording/reproducing method characterized by providing a non-recording area as a buffer area before and after the area. (4) The recording/reproducing method according to claim 3, wherein a focus error signal is generated in the buffer area.