JP2776833B2 - Information recording device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an information recording method for recording / reproducing information by irradiating an energy beam,
Particularly, the present invention relates to an information recording method suitable for an optical disk.

[Prior art] In recent years, research and development of rewritable optical disks have been progressing,
There is also a possibility of practical use of ones that can be rewritten (overwritten) by overwriting. As an example of such an optical disk, there is a phase change optical disk using a recording film of In-Se-Tl or the like. When performing overwriting on these optical disks, the laser power is modulated according to the information signal between an intermediate power level and a high power level as shown in FIG.

[Problems to be Solved by the Invention] When a rotating disk is irradiated with a laser beam having a long pulse width by using the above-described conventional technology, the temperature becomes higher at a later irradiation position due to heat conduction, The width of the area to be recorded or erased in the disk radial direction increases. That is, the formed recorded or erased portion has a teardrop shape. When a signal is reproduced from such a shaped part, the reproduced signal waveform is distorted, resulting in poor S / N, and in the case of the pit edge detection method, a reproduced signal corresponding to the recorded signal cannot be obtained correctly. There is a problem.

Also, if you try to erase this teardrop-shaped recorded part,
Since there is a portion where the width in the radial direction of the recording point is larger than the erasable width, the unerased portion becomes large. Also,
At the portion immediately before the falling of the pulse, the amount of heat stored in the periphery is large, so that the cooling is delayed, and there is a possibility that a recording point (mark) may be described. Furthermore, since there is a portion where the temperature of the film surface rises more than necessary, the underlying film is deformed,
The noise may increase.

On the other hand, when irradiation is performed with a wide interval between pulses, the temperature gradually decreases between the next pulse and the optimum recording / rewriting temperature cannot be maintained. As one method for solving such a problem, the present inventors overshoot the laser power at the rising edge of the pulse.
Alternatively, a method of undershooting at the falling portion or both of them was invented, and a patent application was filed (Japanese Patent Application Laid-Open No. 62-259229). However, in order to overshoot even a short pulse portion, a sharp rise and fall of the current is required, so that the waveform forming circuit is expensive.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method capable of performing accurate recording / rewriting with a simple circuit.

[Means for Solving the Problems] The object of the present invention is to reduce the pulse width and pulse interval of the original signal to be recorded, except for the narrowest pulse width and pulse interval. This is achieved by setting a predetermined value after shooting. Further, it is preferable that the power level at the time of the overshoot or the undershoot is made substantially equal to the power level of the portion having the narrowest pulse width or pulse interval.

Preferably, the electric circuit for realizing the power change pattern includes a modulation logic unit, a pulse current driver, and a read power output DC current driver. Further, the modulation logic unit has a flip-flop for data shift and a logic array. The output stage of the logic array has an open collector output.

The output currents of the various current drivers described above are added by connection synthesis to drive an energy beam source such as a laser diode.

It is particularly preferable to use a method in which only a single current source is always operated among the various current sources described above.

[Operation] In the method of the present invention, the pulse width and the pulse interval are the narrowest as a whole overshoot or undershoot, so that the pulse shape is simple. In addition, since the width of the overshoot and undershoot portions is always constant even if the pulse width and pulse interval are wide, overshoot is performed only for a fixed time after the rise of power, or undershoot for a fixed time after the fall of power. And the laser drive circuit can be simplified. Even when recording / erasing is performed by two beams or when recording / erasing is performed by overwriting (overwriting) by one beam, good recording / reproducing / erasing can be performed by using the above method. it can.

As a recording film material, similar results can be obtained by using a write-once material such as a hole formation, a rewritable phase change material or a magneto-optical material, and the effect is great. However, the present invention is applicable to other recording materials. It is effective even if used. The invention is most effective for phase change materials.

Hereinafter, the present invention will be described in detail with reference to examples.

1 and 2 are explanatory diagrams of a recording method according to the present invention. FIG. 3 is an explanatory diagram of a conventional recording method shown for comparison. In each case, recording and reproduction are performed by one beam.

First, a conventional recording method will be described with reference to FIG. Here, a case where recording / reproducing / erasing is performed on a Ge-Sb-Te-Tl-based recording film which is a phase change type optical disk recording film will be described. The optical disk on which the recording film was crystallized was rotated, and irradiation was performed while changing the power of the semiconductor laser light in a pattern as shown in FIG. At the portion irradiated with 16 mW, the recording film is melted and then cooled. Due to the heat conduction in the recording film surface, even the part irradiated with the same 16 mW, the part where the irradiation of 16 mW started, and the part that continued,
The portion immediately before the end is different in the maximum temperature, in the direction perpendicular to the track of the portion having the melting point or higher, and in the cooling rate. Therefore, the state after recording is different, and the light reflectance is different depending on the state, so that a reproduced waveform faithful to the recorded original signal cannot be obtained. Next, when a laser beam is irradiated to a place where another signal is already recorded with a power modulation pattern as shown in FIG. 3, the phenomenon that occurs in the part irradiated at 16 mW is almost the same as above, If there is a region near the amorphous state in a portion irradiated with 8 mW, that portion is crystallized. Since the width of the portion to be crystallized and the strength of the crystallization also differ depending on the location, not only a reproduced signal that is faithful to the recorded information cannot be obtained, but also the previously recorded signal is largely unerased.

On the other hand, in the power modulation pattern shown in FIG. 1 in which both overshoot and undershoot are performed in a portion where the power changes, and in FIG. 2 in which one is performed, a good reproduced signal can be obtained. It is more preferable to perform both.

Next, a method of obtaining the power modulation patterns shown in FIGS. 1 and 2 will be described with reference to FIGS. 4, 5, and 6. FIG.

FIG. 4 is a circuit block diagram of a write data modulating section configured to generate overshoot and undershoot, and includes a modulation logic section 10, a pulse current driver 11-.
DC driver 1 to 11-4 and read light output 12
The modulation logic unit 10 further includes flip-flops 101 and 102 for data shift and a logic array 103. The data to be recorded is shifted from the first-stage flip-flop 101 to the second-stage flip-flop 102 in synchronization with the clock (about 11 MHz in this embodiment) input, and the Q-side outputs 104 and 105 of the flip-flops 101 and 102 are connected to the A of the logic array 103. Input, B input, and generate ▲ ▼, ▲ ▼, ▲ ▼, ▲ ▼ logic calculation outputs including the write pulse ("1" when it is a write sector) input (see the logical formula shown in the figure) Are input to the corresponding laser drive pulse current drivers 11-1 to 11-4. That is, the ▲ ▼ output 14 is the # 1 pulse current driver 11
-1 to generate a current I1. Similarly, output ▲ is output from the # 2 driver 11-2, output 15 is output from the # 3 driver 11-3, output 17 is output from the # 4 driver 11-4. Respectively to generate currents I2, I3, and I4. Note that I ₂ and
Preferably, I ₄ is approximately the same size (0.7I ₄ I ₂ 1.3I ₄ ). In addition, even during writing, a read level setting volume 18 is used to obtain the read level power of the laser beam necessary for focusing and tracking the track.
The predetermined current IR is caused to flow by the DC current driver 12 having a feedback loop that holds the set value. It is possible that I ₁ is 0 and I ₁ + I _R = I _R. The output currents of the various current drivers described above are added by connection synthesis to drive the laser diode 13. FIG. 6 shows a current waveform diagram showing the above operation. FIG. 5 shows the fourth
FIG. 2 shows a specific circuit diagram of the pulse current driver 11 in the block configuration diagram of FIG. 1. Each of the pulse current drivers 11-1 to 11-4 includes a current driving transistor 23, a current value setting variable resistor 22, and an input signal load. (The output stage of the logic array must be an open collector output).

In the above embodiment of the present invention, the shortest pulse width and the shortest pulse interval are the same, but they may be different.

The above-described circuit of the embodiment of the present invention is also applicable to a system in which the narrowest pulse width and pulse interval of a signal to be recorded are overshot or undershoot and then set to a predetermined value. Can be used without substantial changes.

In this case, by allowed to vary depending on the duration and I ₁ high track time width is in the level radial and recording film sensitivity or thermal conductivity with a low level of I ₂ in the first embodiment, more stable There is an effect that the formed recording pit can be formed and the erasing ratio can be increased.

Also, in the power modulation patterns of FIGS. 1 and 2,
Differently from the figure, it goes without saying that it is possible to move to another power level, for example, the 0 level or the read (R) level for a short time.

[Effects of the Invention] According to the present invention, no matter what pattern the original signal to be recorded changes, it is possible to prevent occurrence of distortion in the reproduced signal as long as the signal changes between almost two levels. it can. In addition, it is possible to prevent the electric circuit for that purpose from becoming complicated.

The energy beam power modulation method of the present invention is applied not only to recording with a single laser beam (single light spot) but also to irradiation with two or more laser beams using the same power modulation pattern or different power modulation patterns. In the case where recording is performed, the method can also be implemented as a power modulation method of at least one beam (light spot).

[Brief description of the drawings]

1 and 2 are diagrams of power modulation patterns of laser light in an embodiment of the present invention, FIG. 3 is a diagram of power modulation patterns of conventional laser light, and FIGS. 4 to 6 are diagrams of the present invention. FIG. 2 is a diagram illustrating a configuration of an electric circuit for implementing power modulation.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masatoshi Otake 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Inside the Hitachi, Ltd. Central Research Laboratory (72) Inventor Takehiro Okawa 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Hitachi, Ltd. (56) References JP-A-62-259229 (JP, A) JP-A-58-208938 (JP, A) JP-A-55-139693 (JP, A) JP-A 64-23426 (JP, A) A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 7/00

Claims (7)

(57) [Claims] 1. An information recording apparatus for recording or rewriting information on an information recording medium by irradiating an energy beam of a plurality of pulses, comprising: a laser source of the energy beam; a power level of the energy beam; The read level is changed between at least three levels of a second level higher than the level and a third level higher than the second level. When information is not recorded or rewritten, the read level is set. When recording or rewriting information, if the pulse width is longer than a predetermined width, the pulse width is temporarily set to a level higher than the third level and then to the third level, and the interval between pulses is set to a predetermined level. A modulation circuit that once lowers the level to a level lower than the second level and then changes the level to the second level when the interval is longer than the interval. The information recording apparatus, wherein a clock is input to the modulation circuit, and a time at which the clock is higher than the third level and a time at which the clock is lower than the second level are determined by the clock. . 2. The time according to claim 1, wherein the time that is higher than the third level and the time that is lower than the second level are one clock of the clock. Information recording device. 3. A modulation circuit according to claim 1, wherein when recording or rewriting information, the pulse width is set to a level higher than the third level when the pulse width is equal to or smaller than a predetermined width. 2. The method according to claim 1, wherein the level is changed to a level lower than the second level in the following cases.
Or the information recording device according to any one of 2. 4. An information recording apparatus for recording or rewriting information on an information recording medium by irradiating an energy beam of a plurality of pulses, comprising: a laser source for the energy beam; a power level of the energy beam; The level is changed between at least three levels of a second level higher than the level and a third level higher than the second level. When information is not recorded or rewritten, the read level is set. A modulation circuit that, when performing recording or rewriting of the above, temporarily lowers the level between the pulses to a level lower than the second level and then changes to the second level when the interval between the pulses is longer than a predetermined interval. The modulating circuit receives a clock, and the time during which the clock is at a level lower than the second level is determined by the clock. Information recording apparatus characterized Rukoto. 5. The information recording apparatus according to claim 4, wherein the time at which the level is lower than the second level is one clock of the clock. 6. The modulation circuit according to claim 1, wherein when recording or rewriting information, when the interval between the pulses is less than a predetermined interval, the modulation circuit changes the level to a level lower than the second level. The information recording device according to claim 4. 7. The second level is a level for crystallizing a recording film of the information recording medium, and the third level is a level for at least partially amorphizing the recording film of the information recording medium. The information recording apparatus according to any one of claims 1 to 6, wherein