JPH05197956A - Pit position recording system and recordable optical disk used for it - Google Patents

Abstract

PURPOSE:To lower BER and to enhance C/N by delaying or starting to advance recording in the track recording from then by a half clock to an adjacent track recorded previously and deviating a clock synchronizing pit by a distance corresponding to a half clock in the longitudinal direction of a track between adjacent tracks themselves. CONSTITUTION:The disk is provided with a great number of tracks formed into a concentric circular shape or a spiral shape, and the clock synchronizing pits are formed on respective tracks 11, 12 along the upper part of a straight line prolonging in the radial direction from the center of the disk. At this time, when a clock signal is generated regarding the clock synchronizing pit as a reference and a recording pit is formed in accordance with the signal, recording in the track recording from then is delayed or started to advance by a half clock to the adjacent track recorded previously. Further, the clock synchronizing pit is deviated by a distance corresponding to a half clock in the longitudinal direction of the track between the adjacent tracks 11, 12 themselves. Thus, the BER is reduced and the LC/N is enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a pit position recording system which is a kind of a method for recording on an optical disk and an improvement of a recordable type optical disk used for the method.

[0002]

2. Description of the Related Art Recently, an optical recording / reproducing system having characteristics such as high density, large capacity, high access speed, and high recording / reproducing speed has been put into practical use, and further research and development for further improvement have been made. ing. The optical information recording medium used for this has a disc shape and is called an optical disc. This is roughly classified into a read-only type and a recordable type.

In the read-only type, projections or depressions called pits are formed in the recording layer during the manufacture of the disc, and the presence or absence or the length thereof represents information. The recordable type is roughly classified into a write-once type (also referred to as write-once or DRAW) that can be recorded only once and a rewritable type that can repeatedly record and erase. The former has a recording layer made of Te-C, Te-Se-Pb, a resin containing a dye, or the like, and when a laser beam is irradiated on this, a hole (pit) is opened. Information is represented by the presence or absence of this pit or its length.

As the latter, a phase change type (crystalline ← → amorphous) and a magneto-optical type are currently in practical use. Phase change type is Te
It has a crystalline phase recording layer made of O ₂ -Tb-Ge or InSe, which is irradiated with a strong laser beam to heat the crystalline phase above its melting point and then rapidly cooled to form amorphous pits (recently marked (Also called). Information is represented by the presence or absence of this pit or its length.

The erasing laser beam heats the pits in the amorphous state to a temperature higher than the crystallization temperature and then removes them to crystallize (erasing). Immediately after this erasing laser beam, a recording laser beam is irradiated to perform recording according to information. With this, recording and erasing are repeated. The magneto-optical type has a recording layer made of a magnetic thin film that can be perpendicularly magnetized. Once the direction of magnetization is aligned upward or downward (referred to as initialization), a laser beam is applied to this and recording is performed simultaneously. By applying a magnetic field, a minute region (pit) whose magnetization direction is reversed is formed. Information is represented by the presence or absence of this pit or its length. When the pit is irradiated with linearly polarized light (weak laser beam), the plane of polarization of reflected light or transmitted light rotates by + θ _k . This is called the Kerr effect or the Faraday effect. On the other hand, "ground" other than the pit
Part rotates -θ _k . Therefore, when the reflected light or the transmitted light is passed through a polarizer (detector), the pits can be captured as a change in the light amount. The change in the amount of light can be captured by the photoelectric conversion element as a change in the strength of the electric signal.

Typical magneto-optical recording layers include rare earth-transition metal amorphous alloys such as TbFe, GdFe and Gd.
Single layer films such as Co, DyFe, GdTbFe, GdFeCo, GdFe / TbFe,
There are two-layer films such as GdFeCo / TbFeCo. By the way, if the binary information (original information) desired to be recorded is recorded as it is, an error is likely to occur when reproduced. So, for example, 2
The original information is converted into a code composed of 0 and 1 by a method such as -7 modulation. On the other hand, the recording method is roughly classified into a pit length (or mark length) recording method and a pit position recording method (also referred to as a mark interval recording method). The former expresses information by the pit length, and the latter expresses information by the pit position. Therefore, in the latter case, the pits have the same length. In the latter case, the position of the pit is important, so when forming the pit, it is formed at a predetermined position according to the clock signal. Then, reproduction is performed according to the clock signal.
Therefore, it is necessary that the clock signals be synchronized during recording and reproduction.

In order to achieve synchronization, the clock signal is generated at the start point of the clock synchronization pit formed in advance on the disc during recording and reproduction. The clock synchronization pits are formed by protrusions, depressions, or minute areas (pits) having different optical properties. One or more clock synchronization pits are formed in each track along a straight line extending in the radial direction from the center of the disc. In a sample servo system medium, generally, one track or more is provided with 1000 or more data areas at predetermined intervals, and a clock synchronization pit, a tracking signal and a mirror section for focusing are provided in front of each data area. (No pit) is provided.

[0008]

Currently, the track pitch of a recordable optical disc is about 1.6 μm,
The value of this pitch is ISO (International Organization)
For Standerization (International Organization for Standardization). However, there is a demand for higher recording capacity and higher recording density, and future track pitches will be smaller (narrower tracks).
There is a need to. When the track is narrowed, the track-to-track spacing (groove width) will be narrowed from the current 0.4 μm to 0.2 μm, and the depth will be from the current 950 Å.
It becomes as shallow as 600 Å.

Therefore, the present inventor made a prototype of an optical disc having such a narrow track, and attempted recording and reproduction.
As a result, bit error rate (BER, read error rate)
It was found that there was a problem that An object of the present invention is to solve this problem.

[0010]

Information is recorded by irradiating an optical disk with a laser beam and forming pits by the heat of the light. The light intensity of the cut surface cut perpendicularly to the direction of travel of the beam has a Gaussian distribution and is highest at the center. Therefore, the temperature at the irradiation position also has a distribution state close to a Gaussian distribution. Therefore, the relationship between the temperature distribution and the pit size is shown in FIG. Pits are formed when a predetermined temperature (position indicated by reference numeral 22 in FIG. 2) is exceeded. Therefore, the size of the pit is indicated by the line segment 23.

As can be seen from FIG. 2, the peripheral portion outside the pit formation region is widely spread in the track width direction. According to the research conducted by the present researcher, when the track is narrowed, the heat of the peripheral portion is transmitted to the adjacent track, which adversely affects the pits of the adjacent track such as deformation and destruction, and thus the BER is increased. .. As a result of earnest research, the present inventor has found that such an adverse effect disappears if the pits are formed by shifting the positions of adjacent pits by half a clock, and thus the present invention has been accomplished.

Therefore, according to the present invention, firstly, "" there is a large number of tracks formed concentrically or spirally, and a clock synchronization pit is provided on each track along a straight line extending in the radial direction from the center of the disk. In the pit position recording method in which a clock signal is generated with respect to a clock-synchronous pit as a reference, and a recording pit is formed along this clock signal, the track to be recorded from now on. The recording is started at a step delayed or advanced by a half clock with respect to the adjacent track which has already been recorded (claim 1).

Secondly, "there is a large number of tracks formed concentrically or spirally, and clock synchronization pits are formed in each track along a straight line extending in the radial direction from the center of the disk. In a recordable type optical disc, the clock synchronization pits of adjacent tracks are offset from each other by a distance corresponding to a half clock in the longitudinal direction of the tracks (claim 2).

[0014]

As shown in FIG. 1, the position of the pit is shifted by half a clock with respect to the adjacent track. Therefore, even if the heat of the peripheral portion outside the pit formation area reaches the adjacent tracks, the pits of the adjacent tracks are not in the immediate vicinity (conventional example) and are slightly apart, so that the pits are not adversely affected.

According to the first aspect of the invention, the reproducing apparatus side delays by half a clock, while the second aspect of the invention delays the disk side by half a clock.

[0016]

Reference Example 1 FIG. 3 is a conceptual diagram showing a main circuit configuration of a general magneto-optical recording apparatus. The original information you want to record is the input section
In (33), this is encrypted in the next 2-7 modulator circuit (34). The cipher also consists of 0 and 1. The laser drive current supplied from the power source (38) to the optical head (32) is pulse-modulated by the pulse modulation circuit (36) of the pit position recording system. The pulse modulation is performed according to the code input from the 2-7 modulation circuit (34). Also, pulse modulation is
This is performed at predetermined time intervals based on the clock signal from the clock signal generation circuit (35). A clock signal (here, 11 MHz) is read by the optical head (32) at a clock synchronization pit on a predetermined track of the optical disc (31) and is output with this synchronization pit as a starting point.

The present invention is divided into two inventions. First
Is to shift the recording device by half a clock. Secondly, the clock synchronization pits on the disk are shifted by a half clock in advance (claim 2). To implement the former, it is necessary to read the track number in advance. Generally, the recording device is provided with a track number reading device and knows which track is to be recorded. Therefore, for example, the first invention can be implemented by delaying the tracks of even-numbered tracks by half a clock. To delay by half a clock, a half clock adding circuit is provided, after reading the clock synchronization pit, a half clock is added and then a clock signal is output.

Therefore, a device provided with a "half clock addition circuit" for delaying a half clock by an even numbered track based on the output from the track number reading device is referred to as a first recording device, and this "half clock addition circuit" is provided. The device that does not include the device is referred to as a second recording device.

[0019]

Reference Example 2 A typical magneto-optical recording medium having a diameter of 130 mm was prepared as an optical disc. The basic structure of the medium comprises a glass substrate, a resin molded body layer formed thereon, and a recording layer formed thereon. A large number of grooves for tracking are formed concentrically on the surface of the resin molded body layer. In general, the integrated body of the glass substrate and the molded body layer is 2P.
Called the substrate. An ultraviolet curable resin liquid is dropped on a mold called a stamper, a glass substrate is pressed against the liquid, and the resin is cured by irradiating with ultraviolet rays in that state, whereby a resin molded body layer is formed. Since the resin molded body layer is in close contact with the glass substrate, peeling it off from the mold results in 2
A P substrate is obtained. A recording layer is formed on the entire surface of the 2P substrate. Then, the recording layer also has a groove. This groove serves as a tracking guide. This groove is a separation zone that separates the tracks.

This medium has a track pitch of 1.4 μm and a track interval of 0.3 μm. Each track is divided into 31 sectors by a straight line extending in the radial direction from the center of the disk, and each sector is further divided into 43 segments. And
A clock synchronization pit is provided at the beginning of each segment. The clock synchronization pit is on a straight line extending in the radial direction from the center of the disc. The clock synchronization pit is a “dent”, and this “dent” is formed in the resin molded body layer of the 2P substrate. Therefore, the recording layer also has a depression. The depth of the depression is about 1/4 wavelength and can be read by the optical head (32) according to the same principle as the pit of CD or LD. Pits are formed in this medium when the pulse-modulated laser drive current is at a high level (here, 7 mW). The recording magnetic field Hb from the bias magnetic field applying means (37) shown in FIG. 3 is necessary for forming the pits.

[0021]

Reference Example 3 A magneto-optical recording medium (optical disk) having a diameter of 130 mm was prepared. This medium is the same as Reference Example 2 except for the following points. That is, the clock synchronization pit is formed behind the even-numbered track by a distance corresponding to a half clock.

[0022]

Example 1 Recording was performed on the disk of Reference Example 2 using the first device of Reference Example 1. Then, when it was regenerated with a commercially available regenerator, the BER was 1 × 10 ⁻⁴ or less.

[0023]

Comparative Example Recording was performed on the disk of Reference Example 1 using the first device of Reference Example 1. Then, when it was regenerated with a commercially available regenerator, the BER was 5 × 10 ⁻³ .

[0024]

Example 2 Recording was performed on the disk of Reference Example 3 using the second device of Reference Example 1. Then, when it was regenerated with a commercially available regenerator, the BER was 1 × 10 ⁻⁴ or less.

[0025]

As described above, according to the present invention, even if the track pitch is narrowed, the BER is 10 ⁻³ to 10 of the conventional one.
^-4 or less and C / N is also improved.

[Brief description of drawings]

FIG. 1 is a conceptual view of a pit formed on a track according to the present invention as viewed from above.

FIG. 2 is a graph showing a distribution state of medium temperature at a laser beam irradiation position.

FIG. 3 is a conceptual diagram showing a main circuit configuration of a general magneto-optical recording device.

[Explanation of symbols]

11 ... Track 1 12 ... Track 2 13 ... Groove (separation zone) 14 ... Track 1 pit 15 ... Track 2 Pit 21 ... Temperature distribution curve 22 ... Predetermined temperature level 33 ... Information input section 34 ... 2-7 Modulation circuit 35 ... Clock signal generation circuit 36-Pulse modulation pulse modulation circuit 37-Bias magnetic field applying means 38-Power supply

Claims (2)

[Claims] 1. A recordable disc having a large number of concentric or spiral tracks, and clock synchronization pits formed on each track along a straight line extending in the radial direction from the center of the disk. In the pit position recording method in which a clock signal is generated with reference to a clock synchronization pit, and a recording pit is formed along this clock signal, the recording on the track to be recorded has already been recorded. A method characterized by starting or advancing by a half clock with respect to an adjacent track. 2. A recordable mold having a large number of concentric or spiral tracks, and clock synchronization pits formed on each track along a straight line extending in the radial direction from the center of the disk. In the optical disc, the optical disc is characterized in that the clock synchronization pits of adjacent tracks are shifted in the track longitudinal direction by a distance corresponding to a half clock.