JP3266971B2 - How to record optical information - 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 and apparatus for recording signals on an optical information recording member centered on an optical disk for recording and reproducing optical information at high speed and high density using a laser beam or the like. is there.

[0002]

2. Description of the Related Art Techniques for reproducing or recording high-density information using a laser beam are well known, and are mainly put to practical use as optical disks. Optical disks can be broadly classified into a read-only type, a write-once type, and a rewritable type. The reproduction-only type is commercialized as a compact disk on which music information is recorded, a laser video disk on which image information is recorded, and the write-once type is commercialized as a document file, a still image file, or the like. At present, research and development are being conducted mainly on rewritable types, and are being commercialized as data files for personal computers.

The rewritable type uses a recording thin film that reversibly changes between two or more states by changing the irradiation conditions of a laser beam or the like, and the main types are a magneto-optical type and a phase change type. Of these, the phase-change disk records the signal by changing the recording film reversibly between amorphous and crystalline by changing the irradiation conditions of the laser light, and records the signal, and optically detects the difference in the reflectance between the amorphous and crystalline. To play. Therefore, similar to the read-only type or the write-once type, the signal can be reproduced as a change in the reflectance of the laser beam. By modulating the laser power between the erasing level and the recording level, overwriting can be performed with one beam. Therefore, there is an advantage that the device configuration can be simplified.

[0004] In most cases, the method of recording a signal on a rewritable optical disk already commercialized is
The position of each recording mark is a pulse position modulation method (hereinafter referred to as PPM) corresponding to 1 of the digital signal. However, in order to further increase the density, a pulse width modulation method (hereinafter, PWM) in which the edge positions before and after the recording mark correspond to 1 of the digital signal has been studied.

[0005]

In the PWM system, since the width of a recording mark has information, it is necessary to record the recording mark without distortion, that is, symmetrically in the longitudinal direction. However, when recording a signal on an optical disk, the laser irradiator reaches a higher temperature at the end point than at the irradiation start point due to the heat storage effect.
The recording mark has a problem that the width of the end is wider than the front end, and the shape of the recording mark is thin at the front end and thick at the end and is distorted like teardrops. In some cases, this causes distortion of a reproduced waveform, which may cause a recorded signal to be incorrectly read. Therefore, the inventors have proposed an overwrite method in which one recording mark is formed by irradiating a plurality of short pulse trains as a method of reducing the distortion of the recording mark (Japanese Patent Laid-Open No. Hei 3-185628).

However, in this method, when the relative speeds of the laser spots are different from each other such as the inner circumference and the outer circumference when the optical disk is rotated at a constant speed, the laser power becomes insufficient particularly in a region where the relative speed is high, In some cases, a new problem that the design becomes difficult occurs.

[0007]

[Means for Solving the Problems] On an optical information recording medium,
When a pulse width modulated digital signal is recorded using one laser spot, a correction waveform obtained by correcting the pulse waveform of the input signal to be recorded according to the pulse waveform
The waveform is corrected according to the shape, and the waveform is corrected based on the corrected waveform.
To record a signal with a recording pulse modulated by user power
A is, changing the correction waveform in accordance with the relative speed between the laser spot and the optical information recording medium.

In order to facilitate this, the pulse waveform of the input signal to be recorded is corrected by a correction waveform corresponding to the pulse waveform.
Correction waveform means for correcting the waveform in advance, and before irradiation on the optical information recording medium attached to the spindle motor.
And position determining means for determining the position of the serial laser spot,
According to the determination result of the position determination means, and correction waveform selecting means as a correction waveform pulse waveform of one of said input signal by selecting the correction waveform of the plurality of correction waveform means,
Based on the correction waveform selected by the correction waveform selection means,
Recording level and erasing level or lower than the erasing level
Laser power modulated between any of the
Means for recording a signal on a scientific information recording medium
The device or the pulse waveform of the input signal to be recorded is
Multiple corrections to correct the waveform to a correction waveform corresponding to the pulse waveform
Corrugated means, said spindle attached to a spindle motor
Relative speed between the optical information recording medium and the laser spot
Speed determination means for determining the relative speed, and the relative speed determination means
Of the plurality of correction waveform means according to the determination result of
Select one correction waveform and change the pulse waveform of the input signal
Correction waveform selection means for setting a correction waveform, and selecting the correction waveform
Recording level and erasing based on the correction waveform selected by the means
Level or a level lower than the erase level
And means for recording a signal on the optical information recording medium by laser power modulation between them.

[0009]

According to the present invention, a digital signal pulse-width-modulated by a practical device configuration is always recorded on an optical disk in a region having a different linear velocity or on a different kind of disk used at a different rotational speed. Can be recorded with a small distortion, and the reproduced waveform distortion can be reduced, and high-density recording can be performed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings. The cause of a recording mark being distorted like teardrops when a signal is first recorded on an optical disk will be described with reference to FIG. FIG. 8A shows a waveform of an input signal to be recorded.
In the conventional method, the signal is recorded by directly modulating the laser beam output with the input signal between the erasing power level Pb and the recording power level Pp as shown in FIG. In this case, the ultimate temperature of the recording film is higher at the terminal end portion than at the front end portion of the recording mark due to the heat storage effect as shown in FIG. Is wider and distorted like teardrops. The heat storage effect is the relative speed between the optical disk and the laser spot (hereinafter referred to as the linear speed)
, The teardrop-like distortion also increases as the linear velocity decreases. Since this distortion causes distortion of the reproduced waveform, the recorded signal may not be correctly read in some cases.
Therefore, the present inventors have proposed an overwrite method in which one recording mark is formed by irradiating a plurality of short pulse trains as a method for reducing the distortion of the recording mark (Japanese Patent Application Laid-Open No. HEI 3 (1993) -197686).
-185628).

This is achieved by converting an input signal as shown in FIG. 9A into a short pulse train and then modulating the laser output between an erasing power level Pb and a recording power level Pp as shown in FIG. 9B. This is what overwrites. Here, the short pulse train is composed of a wide leading pulse and a narrower succeeding pulse train.The width of the leading pulse is always constant regardless of the length of the recording mark, and the width and interval of each pulse in the succeeding pulse train are respectively The number of pulses in the subsequent pulses when forming an equal and n-th recording mark is n-1. For example, an 8-14 modulated signal (hereinafter referred to as EFM) employed in a compact disc
Signal) from 3T (T is the clock cycle) to 11T
However, when recording this EFM signal, the shortest 3T pulse is only the first pulse, and the next 4T pulse is the first pulse and one succeeding pulse. In addition, the pulse of 5T is the first pulse and 2
To the next 11 pulses, and so on.
The T pulse is converted into a first pulse and eight subsequent pulses. By performing the conversion with such regularity, the signal conversion circuit can have a simple configuration. In this case, as shown in (c), the ultimate temperature of the recording film sharply rises at the leading end due to a wide leading pulse, but thereafter, irradiation is performed by a pulse train, so that the rising end temperature is suppressed, and as a result, As shown in (d), the shape of the recording mark is improved in symmetry between the leading end and the trailing end, and teardrop-shaped distortion is reduced.

The above-described method of recording by shortening the pulse is very effective when the linear velocity is low and the recording frequency is low. However, when the linear velocity is high or the frequency of the recording signal is high, the recording method is short. It has been found that new issues may arise.

When the recording waveform is made shorter, the energy applied to the recording film becomes smaller than that of the conventional method, and therefore a large recording power Pp is required. This is not a problem when the linear velocity is low, but when the linear velocity is increased and a larger recording power is required, a high-output laser light source is required, which increases the cost of the recording apparatus.

In order to shorten the input signal, the pulse period of the input signal (T in the case of the EFM signal) is used.
Requires a clock signal with a period that is 1 / integer of
If the frequency of the recording signal is high, the frequency of the clock signal becomes too high, making circuit design difficult. Further, the more the laser output is modulated at a high frequency, the greater the waveform distortion becomes.

Considering a general method of using an optical disc, when the optical disc is rotated at a constant rotation speed (hereinafter referred to as CAV), the linear velocity is higher at the outer periphery than at the inner periphery. You
In other words, the linear velocity is not affected by one optical disc.
It can be generated by the method of rotating the optical disk,
For example, changes even if the linear velocity is high or low according to the specifications of the optical disk
I do. Furthermore, in order to increase the recording density by making the recording mark length the same at the inner circumference and the outer circumference, a method of increasing the recording frequency toward the outer circumference has been proposed. When the optical disk is rotated at a constant linear velocity in all areas (hereinafter referred to as CL)
V) But when recorded on different types of disks on the same recording apparatus, it is necessary to change the linear velocity and the recording frequency depending on the type of the disc.

In view of the above points, the present inventors have conducted a detailed study, and have found that a pulse width modulated digital signal is recorded on an optical disk using one laser spot .
In particular, in the case of overwriting, it has been found that correcting the recording laser waveform to an optimum shape in accordance with the change in the linear velocity is very effective in solving the above-mentioned problem.

For example, when the input signal is as shown in FIG. 1 (1) (assuming an EFM signal here), and when the linear velocity is lower than a preset value L0, the modulation waveform of the laser is as shown in (2). (Hereinafter, the shortened pulse train is referred to as a recording waveform A). When the pulse train is faster than L0, the modulated waveform of the laser is a pulse whose input pulse width is slightly shortened as shown in (3) (hereinafter, this waveform is referred to as recording waveform A). The waveform is converted into a recording waveform B) and irradiated onto the optical disc.

Next, a specific embodiment will be described. (Example 1) First, recording and reproduction were performed on one phase-change optical disk while changing the linear velocity and the recording waveform variously, and the relationship between the linear velocity and the reproduced waveform distortion was obtained.

FIG. 2 shows the structure of the optical disk used in the experiment. The substrate 1 is a disc having a diameter of 200 mm made of polycarbonate and provided with signal recording tracks. The recording film 2 is GeSb
It was made of ternary Te, and its film thickness was 20 nm. The dielectric films 3 and 4 above and below the recording film are made of ZnS, and the substrate
0 nm and 15 nm on the opposite side. A as the reflection film 5
u was provided to 50 nm. After the entire surface of the recording film of the optical disk was crystallized in advance (the signal was erased), the signal was recorded as an amorphous recording mark by laser irradiation.

The linear velocity of an optical disk can be changed to 1.5 m / s, 3 m / s, 6 m / s, 9
Four speeds of m / s were selected.

An EFM signal was used as an input signal.
And 1) a method of directly modulating the semiconductor laser with an EFM input waveform (hereinafter, this waveform is referred to as a recording waveform C),
A signal was recorded by driving according to 2) a method of correcting and modulating into a short pulse train like a recording waveform A, and 3) a method of modulating and modulating a pulse train slightly shorter like a recording waveform B.

FIG. 3 shows a specific recording waveform shape employed in this embodiment. (1) is an example of an input waveform of the EFM signal, and T is a clock cycle. (2) is a recording waveform C obtained by directly modulating the laser with the input waveform of (1).
(3) is a recording waveform A. In this case, the width of the first pulse in the short pulse train was 1.5 T, and the width and interval of the subsequent pulse were both 0.5 T. That is, the clock cycle of the recording waveform A is 0.5T, so that a clock having a frequency twice as high as that of the EFM signal is required. (4) is a recording waveform B. In this case, the width of all recording pulses is set to EF
It is shorter than the M signal by T.

The clock frequency of the EFM signal was changed so that the recording mark length would be the same even if the linear velocity changed. Specifically, 4.3 MH at 1.5 m / s
8.6 MHz at z, 3 m / s, 1 at 6 m / s
It is 25.8 MHz at 7.2 MHz and 9 m / s.

The recorded signal was reproduced, and the magnitude of the distortion of the reproduced waveform was obtained. For quantitative evaluation of the reproduced waveform distortion, the reproduced waveform was binarized in advance and then input to a time interval analyzer to determine the amount of jitter as a phase margin. The larger the phase margin, the smaller the amount of shift between the edge positions before and after the recording mark, and the smaller the distortion of the recording mark.

FIG. 4 shows the relationship between the maximum phase margin and the linear velocity under each condition, and FIG. 5 shows the relationship between the recording power (on the surface of the optical disk) and the linear velocity at that time. Note that the erasing power was kept constant at each linear velocity regardless of the difference between all recording waveforms.

As is clear from FIG. 4, in the case of the recording waveforms B and C, the phase margin increases as the linear velocity increases. This indicates that, in the method of recording one recording mark with one pulse, the distortion of the recording mark increases as the linear velocity decreases, and the distortion of the reproduced waveform also increases.
Here, the recording waveform B has a larger phase margin than the recording waveform C. This is presumably because in the case of overwriting, the recording mark is longer than the recording pulse width in the track direction because the recording film is irradiated with a power higher than the erasing level and is always preheated. That is, it is shown that in order to obtain a recording mark of a desired length, it is better to irradiate with a recording pulse shorter than the length.

In the case of the recording waveform A, the recording waveform A is almost independent of the linear velocity, and is substantially constant. In particular, a large phase margin is obtained even at a low linear velocity, and it can be seen that the recording waveform A is superior to the recording waveforms B and C. However, as the linear velocity increases, the phase margin in the case of the recording waveforms A and B approaches and becomes almost equal at 6 m / s. In the case of 9 m / s, the clock for the circuit for converting the input waveform to the recording waveform A was too high, and the recording / reproduction with the recording waveform A was not performed.

As shown in FIG. 5, the recording power increases in the order of the recording waveforms C, B, and A. In the recording waveform A, since the energy given to the recording film is given in a short pulse train,
A large recording power is required, and therefore, a semiconductor laser having a large output is required as a light source especially at a high linear velocity.

As described above, according to FIGS. 4 and 5, in the configuration of this embodiment, the recording waveform A is excellent when the linear velocity is lower than about 6 m / s, and the recording waveform A is higher when the linear velocity is higher than about 6 m / s. B is excellent. Therefore, it is understood that it is desirable to detect the linear velocity of the optical disc and change the recording waveform correcting means based on the linear velocity from the viewpoints of phase margin, apparatus configuration, recording sensitivity, and the like.

Also, as in the recording waveform D in FIG. 6, the laser power may be lower than the erase level before and after the recording pulse train of the recording waveform A in FIG. In this way, when the recording is performed with the mark interval narrowed, the heat interference in the area irradiated by the recording power is diffused backward, and the next recording mark is largely written. ,
This is effective for widening the phase margin. If the period during which the laser power is lower than the erasing level is too long, the recording film does not reach the crystallization temperature or higher, and unerased portions are left. However, when the period τ is lower than the erase level, τ ≦ λ /
If it is within the range of V (λ: laser wavelength, V: relative speed of laser spot and optical disk), irradiation is repeated with Pb and Pp before and after the period, and Pb and Pp before and after the period. Since the temperature is also increased by the conduction heat from the region irradiated by the above, the recording film reaches the crystallization temperature and can be erased and the remaining residue can be reduced.

In the recording waveform D, the laser power is lower than the erasing level both before and after the recording pulse train. However, it is sufficient to use only the front or rear laser power.
If the level lower than the erasing level is the reproduction power level or the laser off level, the device configuration can be simplified.

Also, in the recording waveform B of FIG. 3, a level lower than the erasing level may be provided before and / or after the recording power.

Furthermore, as the recording waveform E of Fig. 6 the recording waveform A in FIG. 3, in a period corresponding to the recording pulse train, for example, reproduction power level or laser Ofure of
Power level lower than erase power level like bell
And the recording power. In this method, the recording film is rapidly cooled after melting at all locations in the recording mark, so that a stable recording mark can be formed, and this is effective in widening the phase margin. Note that the erase power level is
Lower power level, recorded in the recording pulse train.
Power level lower than recording power and erasing power level
The number of divisions and the width depend on the input signal to be recorded.
It is appropriately selected and used.

As shown in FIG. 4, a good phase margin can be obtained even with the recording waveform C where the linear velocity is high. That is, when the linear velocity is high, the laser power may be directly modulated by the input signal, and when the linear velocity is low, the laser power may be converted into a pulse train such as a recording waveform A, and then the laser power may be modulated to record the signal. . In this case, when the linear velocity is high, the waveform conversion circuit is unnecessary, and the device configuration is simplified.

(Embodiment 2) Next, an optical disk apparatus according to the present invention will be described with reference to FIG. The optical disk 6 is attached to a spindle motor 7 and rotates at a constant rotation speed. Here, the optical disk 6 used was the same disk as in the first embodiment. The optical head 8 uses a semiconductor laser as a light source, and forms a laser spot on the optical disk by a collimator lens, an objective lens, and the like. The semiconductor laser is driven by a laser drive circuit 9. When recording a signal, the input signal is subjected to waveform correction by either the waveform correction circuit A (10) or the waveform correction circuit B (11). Input to the laser drive circuit. Here, the input signal is an EFM signal, and the waveform correction circuit A
This is a circuit for converting a signal into a short pulse train (for a concrete circuit configuration, see, for example, JP-A-3-185628). When a laser drive circuit is modulated with a short pulse train, the recording waveform shown in FIG. Can be The waveform correction circuit B is a circuit for converting the pulse width to be short. When the laser drive circuit is modulated with the shortened waveform, the recording waveform shown in FIG. 3D is obtained. The waveform correction circuit B can be constituted by a delay element and an AND circuit. That is, after the input signal is passed through the delay element, the logical product of the input signal and the original input signal is obtained to obtain FIG.
Is obtained.

When recording a signal, the present apparatus first irradiates a laser spot onto an optical disk and writes an address signal provided in advance on a signal track to an address reproducing circuit 1.
2 and the system controller 13 calculates the linear velocity of the laser spot irradiation part. If the linear velocity is lower than the preset value, the waveform correction circuit A is selected by the switch 14 as the waveform correction means. Conversely, if the linear velocity is higher than the preset value, the waveform correction circuit A is selected by the switch 14 as the waveform correction means. The correction circuit B is selected.

That is, according to this apparatus, it is possible to easily provide a recording means having a wide phase margin over the entire area of the optical disk by making use of the result of the first embodiment.

In this embodiment, two waveform correction circuits are used as the waveform correction means, but a plurality of different types of correction means may be used. That is, in the above embodiment, the optical disk is divided into two regions having different linear velocities and the optimum recording waveforms are respectively associated with the regions. However, the region having different linear velocities is further divided into three or more regions, and each region is divided into three or more regions. The present invention includes making an optimum recording waveform correspond to an area.

Further, in the first and second embodiments, as a waveform correcting means, a signal is recorded after a recording pulse is waveform-corrected into a pulse train composed of a plurality of short pulses in a region with a low linear velocity, and a signal is recorded in a region with a high linear velocity. The method of recording a signal after correcting the waveform of a short pulse was described. However, the optimum waveform correcting means may vary depending on the structure of the optical disc and the type of recording medium, and the waveforms shown in the first and second embodiments are not always the optimum correcting means.

For example, in some cases, regardless of the linear velocity, a recording pulse is output at a power level lower than the erasing power level.
It adopts a method of waveform correction pulse train consisting of a plurality of short pulses having a Le a recording power level, changing the width of the leading pulse of the short pulse train revise by the linear speed fast area and slow region (e.g. line Widening in a high-speed area) or changing the last pulse width of a short pulse train.
It is also possible to increase the phase margin over the entire area of the optical disc by using the single or appropriate combination .
Such a correction method is also included in the present invention. Again,
Recording power level and erasing power level in short pulse train
Power level and / or erase power
The level value of the lower power level and / or
The width of the power level lower than the erase power level
It is necessary to select and use as appropriate according to the input signal to be
Same as above.

Further, a method of correcting the waveform of the recording pulse into a pulse train composed of a plurality of short pulses regardless of the linear velocity is adopted, and the pulse width of the short pulse train converted in the high linear velocity region and the low linear pulse region is changed. Is also good. For example, in a region where the linear velocity is low, the recording waveform is the recording waveform F in FIG. 10A, and in a region where the linear velocity is high, the pulse width of the short pulse train of the recording waveform F is widened to obtain the recording waveform G in FIG. To Since the heat storage effect during signal recording decreases as the linear velocity increases, the tear-like distortion does not increase even if the pulse width of the short pulse train is increased. When the pulse width of the short pulse train is increased, the energy supplied to the recording film increases, and as a result, the recording power can be reduced as compared with the case where the pulse width is narrow.

In the recording waveforms F and G shown in FIG. 10, the laser power is made lower or lower than the erasing level before and / or after the recording pulse train as shown in the recording waveforms D and E in FIG. It goes without saying that the modulation may be performed between the recording power and the reproduction power level or the off level of the laser during the corresponding period.

[0043]

According to the optical information recording method and recording apparatus of the present invention, it is possible to form a good recording mark having a small distortion over the entire area of an optical disk with a simple apparatus configuration, and to reduce the jitter of the reproduced waveform while keeping it small. Can be recorded. This leads to a reduction in the error rate of the optical disk, and thus the recording capacity of the optical disk can be increased.

[Brief description of the drawings]

FIG. 1 shows a recording waveform provided by the present invention.

FIG. 2 is a cross-sectional view of an optical disk used in an embodiment.

FIG. 3 is a diagram showing a recording waveform employed in the embodiment.

FIG. 4 is a diagram showing a relationship between a linear velocity and a phase margin when a plurality of recording waveforms are employed.

FIG. 5 is a diagram showing a relationship between linear velocity and recording power when a plurality of recording waveforms are employed.

FIG. 6 is a diagram showing another recording waveform provided by the present invention.

FIG. 7 shows a recording device provided by the present invention.

FIG. 8 is a diagram for explaining a conventional recording method.

FIG. 9 is a diagram for explaining a conventional recording method.

FIG. 10 is a diagram showing another recording waveform provided by the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 substrate 2 recording film 3, 4 dielectric film 5 reflection film 6 optical disk 7 spindle motor 8 optical head 9 laser drive circuit 10 waveform correction circuit 11 waveform correction circuit 12 address reproduction circuit 13 system controller

──────────────────────────────────────────────────の Continuing on the front page (72) Noboru Yamada, Inventor No. 1006 Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Nobuo Akahira No. 1006, Kadoma, Kadoma, Kadoma, Osaka Matsushita Electric Industrial Co., Ltd. (56) References JP-A-2-278518 (JP, A) JP-A-3-185628 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B ^7/ 00-7 / 013 G11B 7/125

Claims (4)

(57) [Claims] 1. A pulse width-modulated digital signal is applied to an optical information recording medium having a recording thin film which reversibly changes between optically identifiable states by irradiation of a laser beam by using one laser spot. In the method for recording optical information to be recorded, when recording a signal with a recording pulse that is laser power modulated based on a correction waveform obtained by correcting a pulse waveform of an input signal to be recorded according to the pulse waveform, the optical information recording is performed. When the relative speed between the medium and the laser spot is lower than a predetermined speed,
After correcting the waveform of the recording pulse for forming one recording mark into a pulse train composed of a plurality of short pulses, modulating the laser power and recording a signal, when the relative speed is higher than a predetermined speed, A method for recording optical information, wherein a signal is recorded by directly modulating a laser power with the input signal. 2. A pulse width-modulated digital signal is formed on one optical spot on an optical information recording medium having a recording thin film which reversibly changes between optically identifiable states by irradiation with a laser beam. In the method for recording optical information to be recorded, when recording a signal with a recording pulse that is laser power modulated based on a correction waveform obtained by correcting a pulse waveform of an input signal to be recorded according to the pulse waveform, the optical information recording is performed. When the relative speed between the medium and the laser spot is lower than a predetermined speed,
After correcting the waveform of the recording pulse for forming one recording mark into a pulse train composed of a plurality of short pulses, modulating the laser power and recording a signal, when the relative speed is higher than a predetermined speed, A method for recording optical information, comprising shortening a pulse width of a recording pulse for forming one recording mark, correcting the waveform, and then modulating a laser power to record a signal. 3. A process according to claim 1 or 2 modulation of the laser power is characterized by being made between the one lower than the recording level and erasing level or the erase level Level
Recording method of optical information described in 1. Wherein one recording mark in at least one of before and after the laser light irradiation to form a, according to claim 1 to 3, characterized in that a lower than a predetermined period erase level laser power level The optical information recording method according to any one of the above.