JPH01119921A - Recording method for optical disk - Google Patents

Abstract

PURPOSE:To prevent generation of a reading error by shift of a reproduction signal pulse by executing recording or erasing and initializing by the pulse trains of the frequency higher than a recording frequency. CONSTITUTION:The recording (including 1 beam overwriting) as well as erasing and initializing are executed by the pulse trains of the frequency higher than the writing (recording) frequency. Namely, a high-output laser is used in intermittent driving and, therefore, the medium is not deformed and the temp. rise thereof is sharp. The delay in the timing of an amorphous mark is lessened. Since the laser is used in the intermittent driving, the effect of heat accumulation in the medium is small. The amorphous mark is thereby prevented from having a tear drop shape and the signal having less signal jitters can be recorded; in addition, the 1-beam overwriting is possible.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for recording on or erasing an optical disk that efficiently achieves high-density recording, and in particular, a method for recording on or erasing an optical disk that enables one-beam override. Concerning erasure and initialization methods.

C. Prior Art] Optical disk media that have been put into practical use or researched in the past include:
They are broadly divided into: ■ write-once type that creates holes (pits), ■ rewrite type that uses a rare earth-transition metal amorphous magnetic film, and ■ phase change rewrite type that uses crystal-amorphous phase transition. The principles of recording on these media are well known, but the basic principle is to irradiate the medium with light from a light source such as a semiconductor laser, and use the heat to cause changes such as pits, reversed magnetic domains, and phase transitions. . However, (2) raises the temperature of the medium portion to which the laser is applied above the Curie temperature or compensation temperature, and causes magnetization reversal during cooling in the direction of the bias magnetic field, which is normally of opposite polarity to that during heating. That is, in either case, recording or erasing is performed by first increasing the temperature of the medium.

The conventional technology will be explained below using a phase change type rewritable medium as an example.

Figure 6 shows a conventional method in which the amorphous mark/crystal boundary (edge of the amorphous mark) contains information regarding the reflectance difference between the medium determined by the amorphous mark and the crystalline state. (A) laser drive and (B) in case of edge recording method
It shows an amorphous mark string, (C) an analog playback signal, and (D) the timing of a playback signal pulsed based on the analog playback signal. Here, "amorphization"
Recording is done by doing this, and erasing is done by "crystallization". Also, the medium is erased (crystallized) in advance.
It is assumed that

Near the rise of the first recording pulse 110 in FIG. 6(A), the temperature of the disk does not exceed the melting point of the medium, so the amorphous mark 111 on the medium shifts backward on the medium and recording begins. Furthermore, since the medium has a high melting point and the first amorphous mark 111 is a short pulse, an amorphous mark smaller than the normal writing laser pulse width is recorded (
FIG. 6<B)) Therefore, the reproduced signal pulse shown in FIG. 6(D) has a time delay τ1 and a time advance τ2. Next, when recording long amorphous marks, as shown in Fig. 6 (A)
As in the second and third pulses 120 and 130 of
Due to the heat storage effect of the protective film and the underlayer, the number of large amorphous regions increases, and a wider amorphous mark is recorded toward the trailing edge of the pulse. That is, an amorphous mark generally has a teardrop shape as shown in amorphous marks 121 and 131. As a result, the amorphous mark 121 causes a shift of 111% delay τ3 in the reproduced signal pulse of FIG. 6(D). Furthermore, in the third pulse that follows, due to the diffusion of heat in the medium due to the recording of the pre-amorphous mark 121, the reproduction signal pulse advances by τIt, contrary to the aforementioned short pulse. As a result, when a long pulse is recorded, the two amorphous marks approach each other, causing so-called interference between the recorded amorphous marks.

In other words, in conventional recording methods, the formation of amorphous marks mainly occurs due to the increase in heat capacity (when the temperature rises) of the protective film and underlayer provided to prevent deformation of the medium, and conversely due to the heat storage effect during cooling. A shift occurs, and a read error occurs due to the shift of the reproduced signal pulse.

The thermal interference of amorphous marks as described above is even more obvious in the one-beam override example, which will be explained in FIG. FIG. 7A shows an example of driving the recording laser, where L8 is the high level of the amorphous mark recording beam, and L is the level of the crystallization (erasing) beam. Other symbols are the same as in FIG. FIG. 7 shows a state in which an amorphous mark is written in Lt while erasing (crystallization) is performed in L. Amorphous mark 140 recorded as shown in FIG. 7(B)
．． Part of 141.142 150.151.152 includes:
Recrystallization occurs under the influence of the heat of the subsequent crystallization erasing beam, resulting in incomplete amorphous marks being recorded. 2 of FIG. 7(B). The amorphous mark corresponding to the third pulse is also incomplete for the same reason (140, 14
1,142 (shaded area). As a result, jitters 161 to 166 as shown in FIG. 7(D) occur.

On the other hand, initialization and erasing to make the medium state either crystalline or amorphous are normally driven with a lower laser power than for recording, since this is a crystallization process. Therefore, since the range covered by the laser beam is smaller than that during recording, when erasing or initializing, the outer ring of the recorded amorphous mark generally remains unerased. This situation will be explained below.

Recording films for rewritable optical discs that utilize crystal-amorphous phase transition are usually produced by various sputtering or vapor deposition methods. The state of the film after deposition is generally a mixed crystal-amorphous state (referred to as an as-dopo state). In order to make digital information "1" and "0" correspond, this film is transferred to one of the states. This is called initialization. Normal initialization often results in an amorphous state, so
The following explanation will be based on this case.

FIG. 8 explains the normal initialization process.

210 represents the width of a groove provided in an optical disc (not shown). Currently, the distance between this groove and the adjacent groove is often 1.6 μm. Initialization is usually recorded in the as-dopo state using a relatively low laser power (8th
Figure (a)). At this time, the region of 220 crystallizes, but the region of 220
Since the laser power at this time is small, the area indicated by 30 cannot be initialized and remains in the as-dopo state. In such an initialized state, when actual signals are recorded and erased, unerased portions remain. For example, after initialization using this method, an amorphous mark 241 is recorded as shown in FIG. 8(b). A crystallized region indicated by 221 is formed around the amorphous mark. This is because the amorphous mark is recorded with high power while the laser beam profile remains unchanged. Thereafter, erasing is performed using the same laser power as in FIG. 8(a). In this state, as shown in FIG. 8(c), a crystallized ring 222 remains around the groove due to the effect of recording the amorphous mark. Therefore, it can be observed that the crystallization signal remains after erasing.

In other words, in terms of signal processing, it is considered as a residual of reverse polarity,
Either way, it will cause an error.

FIG. 9 is another conventional example proposed to improve the drawbacks of FIG. 8. In Fig. 9(a), the width of the groove of the optical disc is 21.
Amorphous mark recording is performed with direct current at a power level that turns a considerable portion of zero into amorphous. An amorphous region indicated by 240 and a crystallized region indicated by 223 remain in the groove. After that, the track is again moved to the crystallized region 220 with weak power.
The initialization is completed as shown in FIG. 9(a). In this method, (1) the process is increased twice, (2) the crystallization state is slightly different between 220 and 223, and the difference in reflectance causes noise, and (3) the first step of initialization is Since recording is performed at high power, problems such as damage to the medium and large deformation occur.

[Problem that the invention seeks to solve]

As described above, in the conventional recording or one-beam override method, the protective film is mainly provided to prevent deformation of the medium, the increase in heat capacity of the underlayer (when the temperature rises),
On the other hand, during cooling, the amorphous mark shifts due to the heat accumulation effect, causing a problem in that reading errors occur due to the shift of the reproduced signal pulse. Furthermore, during erasing and initialization, the laser beam is driven with a smaller laser power than during recording, so the range covered by the laser beam is smaller than during recording. Therefore, when erasing and initializing, there is a problem that the outer ring of the recorded amorphous mark remains unerased, or that two processes are required to eliminate it.

[Means for solving problems]

In an optical disc recording method for a writable optical disc recording and reproducing apparatus that is equipped with a light source such as a semiconductor laser, its driving circuit, an optical system for condensing the light source, and a focus/track servo system, a pulse train with a frequency higher than the recording frequency is used. Records are erased and initialized. Here, the envelope of the peak value of the pulse train has a temporal rising part of the light irradiation for recording, and the subsequent irradiation time is preferably shorter than the rising part. It is preferable that the rise or fall time of the envelope of the pulse train is advanced with respect to the timing of light irradiation for the purpose.

Furthermore, in erasing for crystallization, it is preferable that the envelope of the peak value of the pulse train be DC-driven with medium power.

[For production]

Then, the present invention uses the above-mentioned means to perform writing (recording).
Recording (including 1-beam override), erasing, and initialization can be performed using a pulse train with a higher frequency than the 1-beam override, so there is no need to worry about timing shifts in amorphous marks or shifts in playback signal pulses based on teardrop-shaped amorphous marks (pulse jitter). ), and a simple and effective erasing method that leaves less data to be erased can be provided.

〔Example〕

1 to 4 show first to fourth embodiments of the present invention. In each drawing, (A) is a schematic diagram showing a recording pulse for laser driving, and (B) to (D) are a schematic diagram showing an amorphous mark and an analog reproduction, respectively, as explained in FIGS. 6 and 7. The signal is a reproduction signal pulse. however,
In FIGS. 2 to 4, the diagrams (B) to (D) are omitted, and only the recording pulses for laser driving similar to those in FIG. 1 (A) are shown. Prior to recording, the media described below was heated to 60 Orpm.
, the track was crystallized (initialized) with 12 mW (600 MHz high frequency superimposition). The medium was placed on a polycarbonate substrate with grooves formed at a pitch of 1.6 μm,
The base layer of □ is 1100n, Sbo, 5sTeo,
It consisted of a 4s recording film of 1100n and a 5iOz protective film of 100nra on top.

(Example 1) FIG. 1 shows Example 1 in which a high-output laser was used and pulse-driven. The experimental conditions were: laser; 50 mW (20 mW irradiation on the medium) pulse; 600 MHz (D
Driven by uty 50χ).

The same amorphous mark was recorded at a signal frequency of 2MH2 (peripheral speed 5 m/s, recording pulse envelope width 250 n5ec, period 500 n5ec, which corresponds to a pitch of 2.5 μm on the medium).

Corresponding to the recording pulse train 1 shown in FIG. 1(A), the first
An amorphous mark 11 as shown in Figure (B) is recorded. Further, FIGS. 1(C) and 1(D) respectively represent an analog playback signal and a playback signal pulse formed into a pulse based on the analog playback signal.

(Example 2) FIG. 2 shows Example 2 in which the envelope of the recording laser drive pulse train is made into two stages. The high level was driven at 25 mW and the low level was driven at 18 mW. High level duration 2 is 5
Q n5ec. The recording pulse envelope width was 250 n5ec and the period was 500 n5ec at a circumferential speed of 5 m/s.

The conditions were the same as in Example 1 except that the same amorphous marks were recorded at a pitch of 2.5 μm on the medium.

(Example 3) Figure 3 shows the rise time 3 of the recording laser drive pulse.
60 n5ec, fall time 4 30 n5ec
advanced (shifted) the recording timing by
Example 3 is shown. The peak value of the laser was set at 201- constant.

Other conditions were the same as in Example 2.

(Comparative Example 1) Comparative Example 1 is an image recorded by the conventional laser drive shown in FIG. The peak value of the laser is 12 mW.

(Example 4) Figure 4 shows erasing (laser pulse peak value = 9 mW) and recording (laser pulse peak value = 25 mW) by pulse train driving.
1. Example 4 in which high level duration 5 = 50 nsec, high level laser pulse wave height value Lz* = 15 mW) is shown.

l MHz (Dut
The signal of y50χ) was recorded. The recording frequency during override is 2 MHz and Duty=50χ.

(Comparative Example 2) One-beam override recording was performed using the conventional method shown in FIG. IM Hz prior to override recording
(Duty 50χ) signal was recorded. The recording frequency during override is 211Hz, Duty = 502, L
+□8mW.

Lm・121.

(Example 5) The amorphous mark recorded in Example 1 was erased using the pulse train shown in FIG. 6 is the peak value of the pulse train for laser driving,
7 indicates the reproduction level of laser power during reproduction. Here, the peak value of the laser pulse train was set to 1211IW.

(Comparative Example 3) The amorphous mark recorded in the example was erased at a power level of 8Il+W for normal crystallization recording (erasing).

The above results are shown in Table 1.

Table 1 Comparison of jitter amount and unerased amount *1; Ratio of jitter to signal period 500 n5ec.

*2; Frequency 2 MHz (peripheral speed 5 m/s, recording pulse envelope width 250 n5ec, period 500 n5ec
) is recorded and then erased using 10 mW DC.

*3: IMHz signal amount for 2M) lz signal when recording with 1 beam override.

From Table 1, the following can be seen.

(1) In Comparative Example 1, pulse jitter of 10 to 15% of the recording period was observed, whereas in Examples 1 to 3, it was within 5%.

(2) In the comparison of 1-beam override recording, -25 dB of unerased noise was observed in the case of Example 4, and 1-beam override without any problems could be realized in practice.

On the other hand, in the conventional comparative example 2, there was a lot of jitter and the erasing characteristics were also incomplete.

(3) Regarding the erasing characteristics, the erasing method of the present invention has -25
A characteristic of ~-30 dB was obtained.

Next, an example in which the method of the present invention is applied to initialization of a medium will be described below.

(Embodiment 6) Initialization can be performed in the same manner as in Embodiment 5 shown in FIG. FIG. 5 is a schematic diagram showing recording pulses for laser driving. The horizontal axis represents time, and the vertical axis represents laser power. 6 is the peak value of the pulse train for driving the laser, and 7 is the reproduction level of the laser power for reproduction. Such a pulse train irradiates an area sufficient to crystallize the entire track width to be initialized.

The optical disk medium used in the experiment was a polycarbonate substrate with grooves formed at a pitch of 1.6 μm, Sbo, 5
sTeo, as recording film l00nn+, and Z on top of it.
A protective film of 80 nm was constructed of nS. The disk rotation speed was 600 rpm.

The area of the disk in the as-dopo state after film formation was initialized using the following procedure. First, a high-power laser was pulse-driven (600 MHz (Duty 50χ)), and the peak value of the laser was set to 12 mW on the medium. The medium reflectance after initialization observed from the servo sum signal increased compared to the as-dopo state, and it was presumed that crystallization had occurred. Thereafter, for confirmation, recording and erasure were performed under the conditions shown below.

Frequency i 1” MHz (recording pulse envelope width 500
n5ec, period 1000nsec) signal at 15 mW
It was recorded in At this time, the reflectance of the medium decreased, and an amorphous mark as shown in FIG. 6(B) was written in the recorded area. After that, it was erased again under the same conditions as the initialization.

(Comparative Example 4) - A medium similar to that in Example 6 was initialized using the conventional laser driving method shown in FIG. 8, and then recorded and erased for confirmation. Initialization is 8mW (DC), recording is 12mW.

Frequency: IMHz (recording pulse envelope width 500n5e
c.

Erasing was performed at a period of 1000 nsec) under the same conditions as initialization.

(Comparative Example 5) The two-process conventional method explained in Fig. 9, that is, the first process uses 11 mW (DC) and the second process uses 6 mW.
(DC) initialized. Recording and erasure were performed thereon under the same conditions as in Comparative Example 4.

The above results are shown in Table 2, focusing on the servo sum signal level (shown as a relative value with the as-dopo level as O and the Example 6 level as 1) and the amount of remaining eraser. In Comparative Example 4, the servo sum signal is small, and only the central portion of the groove is initialized. In Comparative Example 5, almost the entire groove width is initialized, but the large amount of unerased material indicates that the medium is deformed. In this example, the level of the servo sum signal and the amount of unerased signal of -30 dB are values that pose no practical problems, and initialization is almost completely achieved.

Table 2: Comparison of unerased amounts [Effects of the invention] As explained above, compared to the conventional example, the present invention uses a high-power laser with intermittent drive, so the medium does not deform and its temperature rises rapidly and is amorphous. There is little delay in the timing of quality marks. Furthermore, since the laser is used intermittently, the heat storage effect of the medium is small. As a result, the amorphous mark does not have a teardrop shape, and a signal with less signal jitter can be recorded, and one beam override is possible. In addition, the medium deformation mode often observed when conventionally recording with a high laser beam does not occur in the present invention.

In erasing, we obtained a value of -25 dB or less, which poses no problem in practice. In addition, initialization can be implemented in a single process, making it possible to implement a simple method with a wide margin.

Furthermore, since the laser is pulse-driven, the output is stable and
It can extend the lifespan.

[Brief explanation of the drawing]

1 to 5 are diagrams for explaining each embodiment of the optical disc recording method to which the present invention is applied, FIG. 6 is a diagram for explaining the recording process when driving with a conventional laser, and FIG. 7 is a diagram for explaining the recording process in the case of conventional laser driving. Figures 8 and 9 are diagrams explaining the recording process in the case of beam override.
FIG. 3 is a diagram illustrating recording and erasing operations. 1-...Pulse train, 11.121.131.140.1
41.142.240 - Amorphous mark, 2.5 - Duration, 3 - Rise time, 4 - Fall time, 6 - Peak value, 7 - Playback level, 110.12
0.130---Pulse, 161,162.163
．． 164.165.166- Jitter, 210- Groove width, 220, 221.223-... Crystal region, 222-...
Crystallized ring, 240--amorphous region.

Claims (4)

[Claims] (1) In an optical disc recording method of a writable optical disc recording/reproducing device equipped with a light source such as a semiconductor laser, its driving circuit, an optical system for condensing the light source, and a focus/track servo system, the frequency is higher than the recording frequency. An optical disc recording method characterized by recording, erasing, and initializing using a frequency pulse train. (2) The envelope of the peak value of the pulse train is such that the temporal rise of light irradiation for recording is made high, and the subsequent irradiation time is made shorter than the rise. The optical disc recording method according to item 1. (3) The optical disc recording method according to claim 1, wherein the rise or fall time of the envelope of the pulse train is advanced with respect to the timing of light irradiation for recording. (4) The optical disk recording method according to claim 1, characterized in that the envelope of the peak value of the pulse train is driven in a direct current manner with medium power for erasing for crystallization.