JPH0612670A - Initialization method for recording medium - Google Patents

Abstract

PURPOSE:To eliminate the fluctuation in the level of a reproduced signal of a phase shift optical disk of an overwriting type by suppressing the fluctuation in the width of the uncrystallized regions generated in the course of recording. CONSTITUTION:The reference clock signal formed from the prepit information embedded in the disk is frequency-divided by two to form two patterns 14, 14' for initialization which are synchronized with the reference clock signal and are inverted in phase. The progression of the crystallization of the uncrystallized regions 13' generated in the peripheral parts of the recorded amorphous pits 15, 15' is satd. by alternately overwriting of these patterns plural times, by that, the spread of the width of the crystallized tracks 12 at the time of recording is made invisible. The appearance of the fluctuation in the width of the crystallized tracks is obviated even after the formation of the recording pits and the uncrystallized regions are no longer caught in a laser beam for reproduction and, therefore, the fluctuation in the level of the reproduced signal is eliminated. Consequently, the detection error arising from the fluctuation in the level of the reproduced signal is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device for optically recording / reproducing digital information, and more particularly to a recording portion of a recording medium used in a rewritable optical disk device for recording / reproducing information using a phase change phenomenon. Initialization method and apparatus therefor.

[0002]

2. Description of the Related Art A phase change type optical disk device is an example of a rewritable optical disk device for optically recording and reproducing digital information. To record information with this device, the emitted beam of the semiconductor laser is narrowed down to a minute light spot on the recording medium, and the irradiated portion of the light spot is rapidly heated or rapidly cooled to cause a phase change from a crystalline state to an amorphous state. To form a recording pit. The phase of the recording pit thus formed is in an amorphous state. At the time of reproduction, the fact that the recorded portion in the amorphous state and the unrecorded portion have different refractive indexes is used. When the refractive index is different, the amount of reflected light returning from the recording medium to the photodetector is different, and therefore the presence or absence of a recording pit is detected by the detected amount of reflected light to reproduce the information.

In order to erase the recorded information, first, the recording pits in the amorphous state are irradiated with a laser beam having an intensity approximately between the reproduction level and the recording level. This is performed by advancing the crystallization process by keeping the temperature under the crystallization temperature of the recording film for a certain period of time. This erase time is
It depends on the crystallization rate specific to the recording film material used. Japanese Applied Physics 64 (4), 15 March August (1988) (J.Appl.Phys.64 (4), 15 M
As described in pages 1715 to 1719 of Arch August (1988)), 50 ns is realized in the In ₃ SbTe ₂ film. With digital information in which bits are inverted at time intervals longer than the erasing time, the overwrite operation can be realized by directly modulating the beam intensity between the intermediate level and the recording level. As a conventional technique of this kind, Japanese Patent Laid-Open No. Sho 61-61 is known.
There is -101130.

Chalcogenides containing elements such as Te, Se and S are often used for recording film materials used in phase change recording media. This is vapor-deposited on the disk carrier by a process such as vapor deposition to form a film. The recording film immediately after vapor deposition is in an amorphous state, which is called as-depo state. This is because it is a recording film after vapor deposition (as-depo). The amorphous state generated in the process of recording and erasing is also a form of the amorphous state, but has different physical constants such as molecular arrangement and refractive index from the as-depo state. This is an amorphous phase,
It is caused by being amorphized from a crystalline state, that is, a solid phase (that is, a crystalline state). Therefore, as-d
It is called the epo state and is distinguished from the amorphous phase. In this way, the amorphous state that constitutes the recording pits is as-d
It is not formed even if the recording film in the epo state is irradiated with a light beam to undergo a phase change. The amorphous state cannot be obtained without changing the phase from the crystalline state. Therefore, the recording medium used in the phase-change type optical disk device requires an initialization operation for changing the as-depo state to the crystalline state before using the disk.

In the conventional initialization method, a recording level laser beam is irradiated onto the recording film in the as-depo state to temporarily form an amorphous region. Next, a laser beam having an erase level lower than the recording level is irradiated to form a crystalline state from an amorphous state. The crystallization region formed by this initialization operation is a concentric circle or spiral band region, and recording or reproduction is performed using this as a recording track.

[0006]

The beam intensity distribution of the laser spot generally exhibits a two-dimensional spread that is approximated by a Gaussian distribution. For actual recording / erasing, a distribution near the peak level is used. There is. Therefore, when the beam intensity is raised to the recording level, an amorphous pit is formed on the recording track, and at the same time, the temperature of the uninitialized area outside the recording track (that is, the part in the as-depo state) reaches the erasing temperature. Therefore, the width of the crystallized portion around the recording pit is increased. This crystallization randomly occurs spatially and temporally every time recording and erasing are repeated. In a phase-change optical disc, the reflectance distribution within the range irradiated by the light spot greatly contributes to the amplitude level of the reproduction signal, so the fluctuation of the width of the crystallized portion in the initialization track is the level of the reproduction signal. This will affect the fluctuations and will cause erroneous detection of recording pits.

An object of the present invention is to provide a phase change type optical disk device in which the width of a crystal part in a track does not fluctuate and erroneous detection does not occur when reproducing recorded information.

[0008]

The above object is to adopt a sample servo format for extracting a clock signal serving as a reference for recording / reproducing from pre-pit information provided in advance on a disc, and to realize a densest recording bit pattern and a reverse recording bit pattern. This is achieved by alternating the pattern of phases.

[0009]

By overwriting alternately, the peripheral portion of the recording pit is forcibly recrystallized under the condition of recording power irradiation. As a result, the width of the crystal track is widened to the maximum, and the fluctuation of the width of the crystal track is eliminated during the recording / erasing process.

[0010]

Embodiments of the present invention will be described with reference to the drawings.

In this embodiment, the case where an optical disk of sample servo format is used will be described as an example. In the sample servo format optical disc 21, a track is divided into an integer number of sectors, and one sector is further divided into an integer number of segments. FIG. 2A shows an optical disc, and FIG. 2B shows one segment. As shown in FIG. 2B, one segment includes the servo area 22 and the data area 2.
Divided into three. A wobble pit 24 for obtaining a tracking error signal and a clock pit 25 for obtaining a clock signal are provided in the servo area 22 with a mirror portion 26 therebetween. When the reflected light from the disk 21 is photoelectrically converted by a photodetector (not shown), the prepit portion is detected as a change in the amount of light incident on the photodetector due to a diffraction phenomenon, and is shown in FIG. 2 (c). Such a pre-pit reproduction signal can be obtained. Slice level 27
By binarizing with, at the position of clock pit 25
A clock pit signal 28 signal which becomes High is obtained (FIG. 2 (d)). Based on this clock pit signal 28, a reference clock signal 29 synchronized with the clock pit signal 28 by a PLL (Phase Locked Loop) circuit (not shown).
Is obtained (FIG. 2 (e)). This reference clock signal 29 is used to generate a bit sequence to be recorded on the optical disc. Here, for simplification, the case where an NRZ code sequence is adopted as a bit sequence will be taken as an example. NRZ code is information bit '1'
The recording bit "1" corresponds to the information bit "0", and the recording bit "0" corresponds to the information bit "0".

Next, the initialization procedure of the optical disk in this embodiment will be described with reference to FIG. As shown in FIG. 1 (a), the region 11 on the optical disc before initialization is in the as-depo state, and a laser beam having an intensity corresponding to the crystallization temperature is irradiated onto the region 11 to crystallize the irradiated portion. Progress the conversion. As a result, as shown in FIG. 1B, a band-shaped crystallization track 12 having a width 13 corresponding to the spot diameter of the laser beam is formed. By the way, the track interval is determined to be wider than the reproduction beam spot diameter in order to prevent the reproduction signal from leaking from the adjacent track. For example, when a laser light source with a wavelength of 0.83 μm and a focusing lens with a numerical aperture of 0.5 are used, the beam spot diameter is about 1.6 μm.
The track spacing is usually 1.6 μm. The effective beam spot diameter during crystallization is
Since the intensity level becomes smaller as the intensity level becomes larger than that at the time of reproduction, not all the tracks having a width of 1.6 μm are crystallized, but uncrystallized regions 11 are formed on both sides of the crystal track 12.

Next, the reference clock signal is divided by two to generate a fine repetitive pattern 14 of the NRZ code sequence, and the laser beam intensity is modulated between the recording level and the erasing level in accordance therewith to crystallize. An amorphous pit row 15 is formed on the track 12. As shown in FIG. 6C, crystallization progresses in the uncrystallized region 13 ′ around the formed amorphous pit array 15, and the boundary between the crystallization track 12 and the non-crystallized region 13 ′. The part is modulated in synchronization with the pit train. Next, a laser beam between the recording level and the erasing level is overwritten on the amorphous pit train 15 by a pattern 14 'having a phase opposite to that of the fine repeating pattern 14. When the pattern 14 'is irradiated with the laser beam, crystallization progresses in the uncrystallized region 13' around the formed amorphous pit 15 'as shown in FIG. The width is modulated in synchronization with the pit train. At this time, the region where crystallization has progressed is the region where crystallization has not progressed in FIG. When the operations shown in FIGS. 1 (c) and 1 (d) are alternately repeated a plurality of times, as shown in FIG. 1 (e), the progress of crystallization in the peripheral portion of the amorphous pit is saturated and the crystallization track 12 ' The modulation of is not visible. In this embodiment, an overwrite type phase change optical disk is assumed for explanation, so it can be considered that the initialization operation is completed even in the state of FIG. 7E, but it is left in the process of the initialization operation. The amorphous pit train (15, 15 ') may be erased to form a crystal track 12' having a wide width as shown in FIG.

In the present embodiment, the description has been given assuming that only one laser light source is used for initialization. However, this embodiment is not limited to the case where a plurality of laser light sources are used for reasons such as shortening the time required for initialization. It is applicable without losing its essence. Further, it goes without saying that the present embodiment does not limit the role of each laser light source at that time and the arrangement in the optical disk device. Furthermore, in the present embodiment, the explanation has been made assuming that the initialized state of the track is the crystalline state, but there is a rationale that the initialized state is not necessarily the crystalline state in the phase change optical disk utilizing the reversible change between the crystal and the amorphous. Absent. Therefore, even in the case of forming an amorphous initialization track, the present embodiment can be applied without losing its essence.

[0015]

The effect of the present invention will be described with reference to FIG. When the present invention is not applied, as shown in FIG. 3A, the boundary portion of the crystallization track 36 is modulated according to the recording pattern after the formation of the recording pit. Since the reproducing laser spot light 37 also irradiates the uncrystallized region 38,
This modulation component appears in the reproduced signal 39, and as shown in FIG. 3 (b), the signal level fluctuation portion 31d not present in the recording pattern.
Occurs. On the other hand, when the present invention is applied, as shown in FIG. 3C, the crystallization track 36 'is formed even after the recording pits are formed.
Does not appear and the reproducing laser spot light 37 does not irradiate the uncrystallized region 38 ', so that the level fluctuation of the reproduction signal 39' disappears as shown in FIG. 3 (d). As a result, the detection error due to the level fluctuation of the reproduction signal is suppressed.

[Brief description of drawings]

FIG. 1 is a diagram showing a procedure for initializing a recording track.

FIG. 2 is a diagram showing a procedure of generating a reference clock of a disk format.

FIG. 3 is a schematic diagram showing an effect of the present invention.

[Explanation of symbols]

11 ... Track before initialization, 12, 12 '... Crystallized track, 13', 13 "... Uncrystallized area, 14, 14 '... Recording pattern for initialization, 15, 15' ... Amorphous pit row,
36, 36 '... Crystallized track, 37 ... Reproducing light spot, 38, 38' ... Uncrystallized region, 39, 39 '... Reproduced signal waveform.

Claims (4)

[Claims] 1. A method for initializing an optical recording medium, wherein an optically identifiable information pit string is formed by controlling a temperature by irradiating a laser beam and causing a phase change process between an amorphous state and a crystalline state. In addition, pit information that can be optically detected is provided in advance on a recording track of the optical recording medium, a reference clock signal is extracted from the pit information, synchronized with the reference clock signal, and at least 2 The recording is performed by intermittently irradiating the optical recording medium with the laser beam alternately according to the divided first digital signal for initialization and the second digital signal for initialization having the opposite polarity. A method for initializing an optical recording medium, which comprises initializing a track. 2. The first and second initialization digital signals are respectively supplied to a plurality of different laser light sources, and the light from the laser light sources is irradiated on the same recording track with a time difference. The method of initializing an optical recording medium according to claim 1. 3. The method for initializing an optical recording medium according to claim 1, wherein the recording track is continuously irradiated with the laser beam to bring the recording track into an amorphous or crystalline state. 4. A third laser light source for continuously irradiating a laser beam onto the recording track is provided, and after the initialization operation of the same recording track by the first and second initialization digital signals, 3. The method for initializing an optical recording medium according to claim 2, wherein the recording track is made amorphous or crystalline.