JP2559362B2 - Optical recording method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical data recording system, and more particularly to recording a modulated signal whose data is a rising edge and a falling edge of a pulse on a recording medium such as an optical disk. It relates to a suitable recording method.

[Prior Art] Conventionally, when a modulated signal having data of rising and falling of a pulse, for example, a signal such as an NRZI code is recorded on a recording medium such as an optical disc, the intensity of laser light is modulated by the modulating signal itself. Was. That is, the laser output is switched at the rising and falling edges of the logic of the input signal code.

However, in this method, particularly when recording a signal by using the thermal property like an optical disk, the rising and falling edges of the reproduction signal corresponding to the leading edge and the trailing edge of the pit formed by the recording pulse are recorded. The symmetry deteriorates as the recording pulse width increases, and when the recording pulse width is obtained from the reproduction pulse width through the slice level, it causes an error and has a drawback that high reliability cannot be obtained.

[Problems to be Solved by the Invention] An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, to change the modulation signal pulse into an appropriate pulse waveform to control the laser output, and to reproduce with good symmetry of rising and falling. An object of the present invention is to provide a highly reliable optical recording method capable of obtaining a waveform.

[Means for Solving the Problem] Information is recorded on an optical disk by utilizing the thermal property, and is formed by points on the recording medium corresponding to rising and falling of the recording pulse, that is, the recording pulse. The temperature at the time of forming the leading edge portion and the trailing edge portion of the pit or the magnetized domain becomes higher on the trailing edge side than on the leading edge side due to the effect of thermal diffusion. Therefore, the pits or domains have a shape that spreads toward the trailing edge side, and the symmetry between the rising and falling waveforms of the reproduced waveform becomes poor. This tendency becomes stronger as the recording pulse width becomes longer. With such a reproduced waveform, even if an attempt is made to detect the recording pulse width through the level slicer, the probability of error occurrence is high, and high reliability cannot be obtained.

Therefore, in the present invention, by modulating the waveform of the input pulse width modulation signal into a waveform in which the effect of heat diffusion is taken into consideration and using it as the laser output waveform, a reproduced waveform with good rising and falling symmetry can be obtained. Record (pit or magnetized domain).

According to the present invention, for a recording pulse having a long pulse width, which is strongly influenced by thermal diffusion when forming pits or domains, the leading edge and the trailing edge of the recording pulse are each formed with a pulse having a short pulse width, and the time between the two pulses By providing the interval, the effect of heat diffusion to the trailing edge side is reduced.

That is, if the pulse width is short as shown in FIG.
Since the influence of thermal interference can be ignored, the symmetry of the reproduced waveform is maintained. However, when the pulse width of the input signal becomes so long that the asymmetry of the recording mark due to thermal interference cannot be ignored, some measures must be taken.

For example, as shown in FIG. 1 (B), a pulse train 6 in which pulses 7a and 7b are formed corresponding to the leading edge and the trailing edge of the input modulated signal 5 and a time interval 8 is provided between both pulses It is possible to form pits or domains with the laser output of. In this case, if the pulse width of the input modulation signal becomes longer, the pulse interval 8 of the pulse train 6 becomes longer and the recess 11 of the reproduced signal waveform 10 becomes larger, which is not preferable.

Therefore, as shown in FIG. 1 (C), even during the pulse interval 8, the laser output 12 that does not strongly affect the thermal diffusion is obtained.
To give. However, this structure complicates the circuit configuration because two types of levels of pulses are formed.

Therefore, as shown in FIG. 1 (D), by using the laser output waveform 15 in which one or several pulses 16 having the same level are inserted during the pulse interval 8, a desired circuit configuration can be obtained. The mark shape can be obtained.

In the present invention, a short pulse width that forms a symmetry of the leading edge and the trailing edge, such as the reproduced waveform 4 shown in FIG. 1 (A), that is, forms a pit or domain 3 that is less affected by thermal diffusion. For input modulated signal 1 with
The waveform as it is is used as the laser output waveform, and for the input modulation signal 5 having a long recording pulse width, the laser output waveform 6, 12 or 15 composed of the pulse train as shown in (D).
To use. At this time, the leading optical pulse of the pulse train needs the largest power for proper recording because there is no preheating effect due to the preceding optical pulse, and therefore the widest pulse is preferable. .

FIG. 2 shows a comparative example. The laser output waveform 20 is attenuated as indicated by 21 with respect to the input modulation signal waveform 19. The pit shape 22 is controlled to a desired shape, and a desired reproduced signal waveform 23 is obtained. However, there is a problem that a circuit configuration such as a differentiating circuit is required to attenuate the light output. In the present invention shown in FIG. 1 (D), the circuit level is simple because the pulse level does not change and only the pulse width and timing can be controlled.

[Embodiment] Next, an example of a timing chart for implementing the method of the present invention is shown in FIG. 3, and an example of a circuit block for obtaining a laser output from an input modulation signal is shown in a fourth example according to this time chart. Shown in the figure.

The circuit shown in FIG. 4 includes two delay circuits 45, 46, a circuit 44 for setting the delay time, and four logic circuits 47, 48, 4
9,50, Two pulse current sources 51,52 having a current switch operated by an input recording pulse, a DC current source 53 for pre-bias supply, a current adding circuit 54, and a semiconductor laser
It is composed of 55.

The operation will be described below with reference to FIGS. 3 and 4. Set the delay times τ ₁ and τ ₂ with the delay time setting circuit 44,
The input modulation signal 24 is delayed by the delay time τ specified by the setting circuit 44.
₂ and τ ₁ + τ ₂ delay circuits 45 and 46,
₂ delay signal 25 and τ ₁ + τ ₂ delay signal 26 are obtained.

Next, the input modulation signal 24 and the τ ₁ + τ ₂ delay signal 26 are passed through the AND circuit 47 and the NAND circuit 48, respectively, to obtain the logic signal 27 and the logic signal 28, respectively.

Further, the τ ₂ delayed signal 25 and the logic signal 28 are combined with the AND circuit 4
Go through 9 to get recording logic signal 29.

In addition, the logic signal 27 and the τ ₂ delay signal 25 are connected to the AND circuit 50.
To obtain the recording logic signal 30.

By switching the pulse current source 52 with the recording logic signal 29, it is possible to obtain a laser drive current having a waveform similar to that of the recording logic signal 29. The input modulation signal can be divided into a plurality of pulses by adjusting the timing and delay time of the logic signal as described above.
It is possible to obtain the waveform shown in FIG.

Further, by switching the pulse current source 51 by the recording logic signal 30 and inputting it to the current adding circuit 54, the laser output 31 as shown in FIG. 1 (C) can be obtained. However, in this case, the pulse current values of the pulse current sources 51 and 52 must be individually set from the outside.

The semiconductor laser is an optical system that narrows the laser output from the laser to a recording film on a rotating optical disk, a photodetection system that detects reflected light from the optical disk, a position adjustment mechanism for the laser light on the optical disk (focus control). , Tracking control). The overall structure of the optical disk device including such an optical head and its moving mechanism is described in detail in JP-A-58-91536.

As shown in FIG. 3, in this embodiment, the input modulation signal 24
4 pulse widths P ₁ , P ₂ , P ₃ , P ₄ (where P ₁ <P ₂
A modulatable code signal composed of <P ₃ <P ₄ ) was used.

Here, the pulse widths τ ₁ and τ ₂ of the pulses 7a and 7b at the leading and trailing edges of the laser output waveform shown in FIGS. 1B and 1D, respectively.
The setting conditions for are: 1. Minimum repeat pulse frequency of input variable length code signal.
For T _MIN , τ ₁ T _MIN / 2 and τ ₂ T _MIN / 2. The example of FIG. 2 shows that T _MIN = 2T ₁ , τ ₁ T ₁ and τ ₂ T ₁ .

2. The laser pulse output with a pulse width in the range of τ ₂ τ ₁ T ₁ τ ₁ + τ ₂ with respect to the set linear velocity (determined by the disk rotation speed and recording radius) and the recording pulse laser output power, Leading edge as shown in Fig. 1 (A),
A reproduced waveform 4 having good trailing edge symmetry should be obtained.

Pulse width of input modulation code signal 24 used in this embodiment
P ₁ , P ₂ , P ₃ , P ₄ are, for example, P ₁ = 150 [nsec] P ₂ = 200 [nsec] P ₃ = 250 [nsec] P ₄ = 300 [nsec], and τ ₁ and τ _For the setting of ₂ , here τ = τ
₁ = τ _2, and from setting condition 1 τ 150 [nsec] and from setting condition 2 τ = 100 [nsec].

The laser output 31 obtained by the above settings will be described.

Input pulse 3 with pulse width P ₁ = 150 [nsec] and P ₂ = 200 [nsec] less than 2τ = 200 [nsec] (generally τ ₁ + τ ₂ ).
With respect to 3, 34, recording pulses 37, 38 whose waveforms do not change only by being delayed by τ ₂ are obtained as recording logic signals, and the corresponding pulses 41, 42 are laser-outputted.

On the other hand, an input pulse 32,35 having a pulse width P ₃ = 250 [nsec], P ₄ = 300 [nsec] longer than 2τ (generally τ ₁ + τ ₂ ).
In addition to being delayed by τ ₂ , pulses 7a and 7b having a pulse width τ along with the leading edge side and the trailing edge side (generally a pulse train with a leading edge side pulse width of τ ₁ and a trailing edge side of τ ₂ ) Waveforms 36, 39 constructed at time intervals 8 are obtained as recording logic signals. As the laser output, the pulse current source 51
By changing the pulse current level of
The pulse shapes 40 and 43 whose output levels are variable are obtained.

The widths of the pulses 7a and 7b do not necessarily have to be equal. In general, the temperature of the rear side is higher because the heat of the front side pulse is propagated. Therefore, in such a case, it is desirable to shorten the width of the rear side pulse. However, in the case where the influence of thermal interference can be almost completely removed by the present invention, a mark that is symmetrical in the front-rear direction can be formed by making the widths of 7a and 7b equal.

 The pit shape and the reproduced waveform obtained will be described.

With respect to the laser output waveforms 41 and 42, a pit shape 3 and a reproduction waveform 4 as shown in FIG. 1 (A) were obtained.

Regarding the laser output waveforms 40 and 43, when the current level of the pulse current source 51 is set to zero, the pit shape 9 and the reproduction signal 10 as shown in FIG. 1B are obtained. On the other hand, when the current level was set to an appropriate finite value, the pit shape 13 and the reproduced waveform 14 as shown in FIG. 1 (C) were obtained.

In this way, when the level of the input variable length code signal was output as it was, with the pulses 32 and 35 having a pulse width of 200 [nsec] or more, only the reproduced waveform with poor symmetry of rising and falling was obtained. On the other hand, by performing laser output through the input variable length code signal to the circuit shown in FIG. 4, a reproduced waveform with good symmetry of rising and falling as shown in FIG. 1 could be obtained.

As another example of realization, laser output waveforms corresponding to various pulse widths constituting the input modulation signal are stored in ROM (Read only Memory) in advance, and they are synchronized with the input modulation signal. You may make it output.

EFFECTS OF THE INVENTION According to the present invention, the symmetry of the rising and falling edges of the reproduced waveform corresponding to the leading edge and the trailing edge of the recording signal pulse can be improved. When recording and reproducing a modulated recording signal as data on a recording medium, it is possible to reduce errors and obtain high reliability.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention. FIG. 2 is a diagram illustrating a comparative example. FIG. 3 is a time chart for explaining the operation of the circuit for carrying out the first embodiment. FIG. 4 is a block diagram showing a circuit configuration for carrying out an embodiment of the present invention. [Explanation of symbols] 1 ... Input modulation signal, 2,15 ... Laser output waveform, 3,17 ...
… Pit shape, 4,18 …… Playback waveform

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Atsushi Saito 1-280 Higashi Koigakubo, Kokubunji City, Central Research Laboratory, Hitachi, Ltd. (72) Inventor Kazuo Takasugi 1-280 Higashi Koigakubo, Kokubunji City, Central Research Laboratory, Hitachi Ltd. ( 56) References JP-A-57-36439 (JP, A) JP-A-61-216126 (JP, A)

Claims (3)

(57) [Claims] 1. In an optical recording method of irradiating a laser beam whose intensity is modulated by an input signal and recording information on a recording medium by a thermal action of the light, asymmetry of a recording mark due to thermal interference cannot be ignored. When the pulse width of the input signal becomes long, the pulse waveform of the input signal is converted into a pulse train having a head pulse having a predetermined width and a subsequent pulse following the head pulse, and having a time interval between each pulse. An optical recording method in which the intensity of the laser light is modified and the width of at least the pulse adjacent to the head pulse of the subsequent pulses is shorter than the width of the head pulse. 2. The falling level of the first pulse is set to the first level.
Claim 1 wherein the following pulse is a pulse that rises from the first level to the second level and falls from the second level to the first level. The optical recording method according to the item. 3. The optical recording method according to claim 2, wherein both the first pulse and the subsequent pulse are pulses having the same level having the second level as the maximum value.