JP3314565B2 - Recording / reproducing method of optical information recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recording and reproducing information on an optical disk using a laser beam.

[0002]

2. Description of the Related Art As an optical disk capable of recording / reproducing and erasing a signal, a phase change type optical disk using a chalcogenide as a recording thin film material is known. In general, a signal is recorded by setting the recording thin film material in a crystalline state to an unrecorded state, irradiating a laser beam, melting and rapidly cooling the recording thin film material to an amorphous state. on the other hand,
When erasing a signal, the recording thin film is heated to be in a crystalline state by irradiating a laser beam having a lower power than during recording. In the crystalline state and the amorphous state, the complex refractive index comprising the refractive index n and the extinction coefficient k is different, and a signal is reproduced using the resulting difference in reflectance or transmittance.

As recording thin film materials, for example, Te, In,
It is common to use a material which is mainly composed of Sb, Se and the like and which changes phase between an amorphous and a crystal, or a substance which reversibly changes phase between two different types of crystal structures.

One of the advantages of the phase change recording is that an information signal can be overwritten by using only a single laser beam as recording means. That is, when the laser output is modulated according to the information signal between the recording level and the erasing level according to the information signal and irradiated onto the recorded information track, a new signal can be recorded while erasing the existing information signal. (JP-A-56-145530). Taking advantage of this feature, phase change optical disks are used as document files, image files, and data files.

In an optical disk system generally used for information processing, information is exchanged with the outside at regular intervals called sectors. Although various structures of the sector format have been proposed, they are basically composed of an address section, a data section and a buffer section as shown in FIG. The address portion indicates the physical address of the sector, and is preformatted when the disk is manufactured. The data portion is an area where the user records information, and the VFO is recorded at the head of the data portion. This is a continuous repetitive data pattern provided to enable accurate reproduction of information even when there is a fluctuation in disk rotation. If there is a rotation fluctuation in the disk, the VFO code pattern also fluctuates at the same time. Therefore, if a PLL is locked to this pattern and a clock for reading data is generated, the data can be reliably reproduced.

[0006] Recording methods can be broadly classified into an inter-mark modulation method and a mark length modulation method. In the inter-mark modulation, a signal is detected by detecting the position of the mark during reproduction, whereas in the mark length modulation, both ends of the mark are detected and the signal is detected.
The mark length modulation can increase the recording density as compared with the inter-mark modulation.

[0007]

When information is repeatedly and repeatedly recorded in a specific sector on a phase change optical disk, a recording thin film is formed at the beginning (recording start) and end (recording end) of a series of recording areas. Is changed, and the reproduced signal is disturbed. In particular, when a relatively short series of data is recorded by dividing a track into sectors, the influence of the deterioration of the start and end portions increases. Degradation at the beginning and end in repeated recording is caused by laser irradiation.
This is considered to be due to the fact that the constituent elements of the recording thin film slightly diffuse mainly in the circumferential direction of the disk, and the amount of diffusion movement of the constituent elements of the recording thin film is integrated by repeated laser irradiation. It is considered that the movement of the constituent elements of the recording thin film is caused by several factors (for example, Proceedings of the 2nd Symposium on Phase Change Recording, page 8-20, Proceedings of the 3rd Symposium on Phase Change Recording, 7-32). Page), but the exact details are not yet clear. Since the VFO is arranged at the start end as described above, if the number of repetitions increases, VFO
FO cannot be reproduced. In this case, since the clock cannot be generated, the following data cannot be reproduced. In particular, when the mark length modulation recording is adopted, the start / end deterioration is more remarkable than when the inter-mark modulation recording is adopted.

According to the present invention, in order to solve the above-mentioned problems of the prior art, signal recording for suppressing repetitive recording deterioration at a start end and an end of a data portion when adopting mark length modulation recording on a rewritable phase change optical disk. The aim is to provide a method.

[0009]

In order to achieve the above object, a first configuration of a recording / reproducing method for an optical information recording medium according to the present invention is to record at least a front of a mark to be recorded in a VFO area. The recording is performed by setting the irradiation energy of the laser beam for forming the mark to be smaller than the irradiation energy of the laser beam for forming the shortest mark of the data recording mark.

[0010]

[0011]

According to the first aspect of the optical information recording / reproducing method of the present invention, the irradiation energy of the laser beam for forming at least the mark to be recorded ahead of the marks to be recorded in the VFO area is changed. By performing recording with a smaller energy than the irradiation energy of the laser beam for forming the shortest mark of the recording mark, the VFO can be reliably reproduced even when recording is repeated many times.

[0012]

[0013]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples.

FIG. 1 is a schematic diagram showing the irradiation energy of a laser beam when writing a VFO and a mark array of data in the data section of the same sector for explaining the present invention.
FIG. 1A shows that data following VFO is recorded / reproduced by mark length modulation, and the irradiation energy of laser light for forming a mark to be recorded in the VFO area is formed by forming the shortest mark of the data recording mark. A state in which recording is performed with an irradiation energy smaller than the irradiation energy of laser light for performing the recording is shown. When such recording is performed, if the recording is repeated, the VFO
Since the temperature rise history due to recording in the area is smaller than the temperature rise history in the data portion, deterioration of the start end in repeated recording, in this case, deterioration of the reproduction signal in the VFO is suppressed.

FIG. 1B shows the VFO and the data following the VFO recorded / reproduced by mark length modulation, and at least the mark sequence to be recorded at least in front of the marks recorded in the VFO area. A state in which recording is performed so that the ratio of recording mark lengths is greater than 1 is shown. Even in the case of such recording, when the recording is repeated, the temperature rise history due to the recording in the VFO area is smaller than the temperature rise history when the VFO mark is recorded with the mark interval shortened. At the beginning is suppressed.

In order to eliminate the influence of the deterioration of the terminal part, after the data recording is completed, dummy data is continuously recorded,
The dummy data portion may not be reproduced. The length of the dummy data differs depending on the assumed disk usage mode. In other words, when a large number of repetitions are assumed, dummy data of a sufficient length is required accordingly. When almost no repetitive recording is performed, there is no need to provide dummy data. .

FIG. 3 is a schematic diagram showing a recording format in the data section of the same sector for explaining the present invention. That is, the dermy data is recorded after the VFO, that is, at the beginning of the data, in order to eliminate the influence of the deterioration of the reproduced waveform due to the repetitive recording caused by the non-uniformity of the thermal history of the temperature rise at the boundary between the VFO and the data area. Is shown.
The mark may be recorded in the dummy data in the same modulation method as the true data. Even if dummy data cannot be reproduced by repeated recording, there is no problem as long as true data can be reproduced. At the head of the true data, the head information of the data is recorded. The length of the dummy data differs depending on the assumed disk usage mode.

FIG. 1C is a diagram showing another recording method for removing the influence of the deterioration of the reproduced waveform due to the repetitive recording caused by the thermal history non-uniformity at the boundary between the VFO and the data area. That is, VFO is recorded / reproduced by inter-mark modulation, data following VFO is recorded / reproduced by mark length modulation, and VFO is recorded.
FIG. 9 is a diagram showing a state in which the irradiation energy of a laser beam for forming a mark to be recorded in the front of the O region is smaller than the irradiation energy of a laser beam for forming a mark to be recorded in the rear of the VFO region; is there. When recording is performed in this manner, a sharp thermal history near the boundary between the VFO and the data area does not occur, and the deterioration of the reproduced waveform due to repeated recording is greatly suppressed. Therefore, dummy data is recorded between the VFO and the data. Alternatively, the area of the dummy data can be made very short. In this case, V
Even if the length of the mark forming the FO changes, it is necessary to devise recording and reproduction so that a clock of a constant frequency can be generated when the VFO is reproduced. The first record
The reproduction method is a method in which recording is performed such that the centers of VFO marks are arranged at a constant cycle, and only the mark center is detected during reproduction. The second method is a method in which recording is performed such that the front ends of VFO marks are arranged at a constant period, and only the front ends of the marks are detected during reproduction. The third method is a method in which recording is performed such that the trailing ends of VFO marks are arranged at a constant period, and only the trailing end of the mark is detected during reproduction.

Furthermore, in order to prevent the reproduction waveform from deteriorating due to repeated recording, as disclosed in Japanese Patent Application Laid-Open No. 2-94113, the relative positional relationship between the VFO and data recording start points and the optical information recording medium is determined. When a method of changing the recording for each repetitive recording is used together, better repetitive recording characteristics can be obtained.

FIG. 4 is a block diagram showing an example of an optical disk recording apparatus using this method. The apparatus comprises a rotating optical disc A, an optical system B for condensing laser light on the optical disc A, an information recording section C for modulating the laser light,
It comprises a reproduction control unit D for reproducing information from the optical disk A and controlling the light spot.

The optical disk A is composed of a substrate 1 and a recording thin film 2 on the substrate 1. PMM as the substrate 1
A. A resin having a smooth surface such as a resin such as polycarbonate or glass is used. In the case of an optical disc, usually the substrate plane 3
Are covered with spiral or concentric tracks to guide the laser light. A recording thin film material that records a signal by generating a phase change by irradiation with a laser beam is mainly composed of a substance that reversibly changes its structure between a crystalline state and an amorphous state, for example, Te or In, Se, or the like. Made of a phase-change material. The main component of the well-known phase change material is Te-S
b-Ge, Te-Ge, Te-Ge-Sn, Te-Ge-Sn-Au, Sb-
Te, Sb-Se-Te, In-Te, In-Se, In-Se-Tl,
In-Sb, In-Sb-Se, In-Se-Te and the like.

In the data portion following the address portion, first, V
The VFO pattern train stored in the FO generator 4 is read out in synchronization with the gate signal output from the recording gate generator 5, and the drive circuit 6 generates a pulse having a waveform corresponding to the VFO pattern train. . Subsequently, the data signal temporarily stored in the buffer memory 7 is read out in synchronization with the gate signal output from the recording gate generator 5, and is subjected to, for example, 2-7 modulation by the modulation circuit 8, and the 2 -7 Generates a pulse having a waveform corresponding to the modulation data. When arranging dummy data between the VFO pattern string and the data or after the data, the dummy data
This can be dealt with by storing the respective dummy data in the data generator 9. VFO pattern is one V
When changing within the FO area, the information is
What is necessary is just to store it in the generator 4.

In the optical system B, the light of the semiconductor laser 10 is converted into parallel light by the collimator lens 11, passes through the polarizing beam splitter 12 and the quarter-wave plate 13, and is transferred onto the recording thin film 2 of the optical disk A by the objective lens 14. It is collected. The collected light is reflected by the recording thin film 2,
The light is again reflected by the polarizing beam splitter 12 through the objective lens 14 and the quarter-wave plate 13, and
Is received at. The signal photoelectrically converted by the photodetector 15 is amplified by the preamplifier 16 of the reproduction control unit D.

The reproduction controller D converts the signal from the preamplifier 16 into a control signal using the low-frequency component of the signal from the
Is driven to perform focusing and tracking of the light spot on the optical disk. On the other hand, the demodulation circuit 19 demodulates the signal from the mark train formed on the optical disc A using the high frequency component of the signal from the preamplifier 16. Thus, the reproduced data demodulated is temporarily stored in the buffer memory 20.
By reading the data stored in the buffer memory 20, the data recorded on the optical disk is reproduced.

Hereinafter, the effects of the present invention will be described with reference to specific examples. An optical disk A was prepared, and signals were recorded by rotating the disk at a speed such that the linear velocity in the recording unit was 10 m / s. The optical disc A is provided with a polycarbonate resin having an address area and a guide groove for tracking provided on the surface of the substrate, a Ge ₂ Te ₂ Sb ₅ recording thin film, and a protective layer made of ZnS and an aluminum reflective layer on both sides of the recording thin film. Configuration. The data used for recording was 2-7 RLL
The shortest mark length and the shortest mark interval were set to 0.8 μm using mark length modulation recording of code and EFM. The Reed-Solomon code was used as the signal error correction method. Also, VF
The O region was 50 μm in length. Recording on an optical disk is performed by modulating the power of a semiconductor laser having a wavelength of 780 nm between a recording power and an erasing power according to a data signal. Here, the data recording power is 13 mW, the erasing power is 6 mW, and the reproducing power is 1 mW.
And The recording power and the erasing power are powers at which a reproduction signal error does not occur at the center of the data portion after 50,000 repetitive recordings. The recording power of the VFO was changed as needed. The laser beam irradiation conditions for forming the VFO mark can be freely set by rewriting the data stored in the VFO generation.

The recording section is set under exactly the same laser beam irradiation conditions,
If the mark period is the same in the VFO portion, VF
As the irradiation energy of the laser beam for forming the O mark was lowered, the repetitive deterioration at the head of the VFO was reduced. As a method of lowering the energy, the recording power was reduced, the irradiation time of the recording power was shortened, or an experiment was conducted in which the two were combined. Table 1 shows that, as one of the experimental results, the VF of a periodic mark row having a mark period of 1.6 μm and a mark of 50% duty (corresponding to the shortest mark length in data).
When O is recorded, the recording power for forming the VFO mark and the length of the reproduced waveform degraded area at the head of the VFO after 50,000 recordings are shown. The modulation method is mark length modulation recording of a 2-7 RLL code. The length of the waveform degraded area was defined as the length of the area where the signal was erroneously reproduced. In this case, the recording power holding time for forming a mark in the VFO was equal to the recording power holding time for forming the shortest mark in data. As shown in Table 1, when the recording power for forming a mark in the VFO is reduced, the length of the waveform-deteriorated region at the head of the VFO is shortened, and the VFO is accurately determined.
It can be seen that the FO can be reproduced. However, if the recording power is lowered too much, the amplitude of the reproduced waveform becomes too small to reproduce correctly.

[0027]

[Table 1]

Here, when focusing on the boundary portion where the VFO area ends and the data mark row starts, a waveform distortion of about 10 μm was observed. This is presumably because the average light irradiation power in the VFO region is smaller than the average light irradiation power in the following data part, and a non-uniform boundary occurs in the heat history of the temperature rise. Considering this point, VF
Distortion of a reproduced waveform between VFO and data can be suppressed by gradually increasing the irradiation energy of laser light for forming a mark in O within the VFO region and approaching the average irradiation energy of laser light in data. It was confirmed.

Next, when both the VFO and the data mark have the same modulation method, the same recording power, and the same recording power irradiation duty, the ratio of the mark interval / mark length of the VFO is set within the range permitted by each modulation method. investigated. As a result, it was found that when the ratio of mark interval / mark length was larger than 1, when VFO was recorded with periodic data, the length of waveform deterioration due to repeated recording at the beginning of the VFO was short. Further examination revealed that the effect was remarkable when the ratio of mark interval / mark length was larger than 1.5. That is, it was confirmed that the deterioration length of the VFO head portion was 60% or less as compared with the case where the ratio was 1. Further, in order to reduce the distortion of the reproduced waveform seen at the boundary where the data mark row starts after the end of the above-mentioned VFO area, the ratio of the mark interval / mark length in the VFO area is set to the rear. , That is, it was confirmed that it is effective to make the ratio smaller at the rear.

[0030]

As described above, according to the present invention,
The laser beam irradiation energy for forming at least the mark to be recorded ahead of the marks to be recorded in the VFO area is smaller than the laser beam irradiation energy for forming the shortest mark of the data recording mark. By doing so, the VFO can be reliably reproduced even when recording is repeated many times.

The VFO and the data following the VFO are recorded / reproduced by mark length modulation, and at least the mark sequence to be recorded ahead of the marks recorded in the VFO area is determined by the recording mark interval and the recording mark length. By recording the ratio so as to be larger than 1, the VFO can be reliably reproduced even when recording is repeated many times.

[Brief description of the drawings]

1A is a diagram showing an example of a recording method according to an embodiment of the present invention. FIG. 1B is a diagram showing another recording method. FIG. 1C is a diagram showing another recording method.

FIG. 2 is a diagram showing a configuration of a sector format on an optical disc;

FIG. 3 is a diagram showing a recording format in a data portion of the same sector in one embodiment of the present invention.

FIG. 4 is a diagram showing an embodiment of an optical information recording / reproducing apparatus according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Recording thin film 3 Substrate surface 10 Semiconductor laser 11 Collimator lens 12 Polarization beam splitter 13 Quarter-wave plate 14 Objective lens 15 Photodetector 18 Voice coil

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuo Akadaira 1006 Kazuma Kadoma, Kazuma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-6-319109 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G11B 7/005

Claims (6)

(57) [Claims] 1. An optical information recording medium having a recording thin film on a substrate which undergoes a phase change by laser light irradiation and reversibly shifts to a state having different optical constants, is irradiated with laser light of a predetermined wavelength. A method for recording and reproducing information continuously in the data portion of a sector obtained by dividing a track,
A VFO is recorded at the head of the data portion, data is subsequently recorded, and data following the VFO is recorded / reproduced by mark length modulation, and is recorded at least in front of marks recorded in a VFO area. Recording / reproduction of an optical information recording medium, wherein recording is performed with the irradiation energy of laser light for forming a mark smaller than the irradiation energy of laser light for forming the shortest mark of a data recording mark. Method. 2. Recording is performed with the irradiation energy of laser light for forming a mark to be recorded in front of the VFO area smaller than the irradiation energy of laser light for forming a mark to be recorded in the rear of the VFO area. 2. The recording / reproducing method for an optical information recording medium according to claim 1, wherein: 3. After the data recording is completed, a dummy
2. The recording / reproducing method for an optical information recording medium according to claim 1, wherein data is recorded. 4. The recording / reproducing method for an optical information recording medium according to claim 1, wherein dummy data is recorded between the VFO and the data. 5. The VFO is recorded so that the front end interval of the mark is equal, the reproduction of the VFO is performed by detecting the front end of the mark, and the data following the VFO is recorded and recorded by mark length modulation.
3. The method for recording / reproducing an optical information recording medium according to claim 2, wherein the recording / reproducing is performed. 6. The VFO is recorded such that the trailing edge of the mark is at equal intervals, the VFO is reproduced by detecting the trailing edge of the mark, and the data following the VFO is recorded by mark length modulation.
3. The method for recording / reproducing an optical information recording medium according to claim 2, wherein the recording / reproducing is performed.