JPS61216126A - Optical recording system - Google Patents

Abstract

PURPOSE:To obtain a reproduced waveform having good symmetrical properties between the rise and the fall by changing a modulated signal pulse into a proper pulse waveform to control the laser output. CONSTITUTION:The pulses 7a and 7b are produced in response to the front and rear edges of an input modulated signal 5, and a pit or domain is formed with the laser output of a pulse train 6 obtained by giving a time interval 8 between both pulses 7a and 7b. In this case, the interval 8 of the train 6 is increased when the pulse width of the signal 5 is increased. Then the indent 11 of a reproduced signal waveform 10 is increased. Thus the laser output 12 which does not give the effect of the heat dispersion so much is applied to the interval 8. Otherwise it is possible to use a laser output waveform 15 where one or several pulses 16 are put into the interval 8.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an optical data recording system, and is particularly suitable for recording a modulated signal whose data is the rise and fall of a pulse on a recording medium such as an optical disk. Regarding recording methods.

[Background of the invention]

Conventionally, when a modulated signal that uses the rising and falling edges of a pulse as data, such as a signal such as an NPZI code, is recorded on a recording medium such as an optical disk, the intensity of a laser beam is modulated by the modulating signal itself. In other words, the laser output was switched according to the logic rise and fall of the input signal code.

However, with this method, especially when recording signals using thermal properties such as on an optical disc, the reproduction signal rises corresponding to the leading and trailing edges of the pips formed by the recording pulse. ] However, the symmetry of the falling edge deteriorates as the recording pulse width increases, causing errors when obtaining the recording pulse width from the reproduction pulse width through the slice level, making it difficult to obtain high reliability. Ta.

[Purpose of the invention]

The purpose of the present invention is to eliminate the above-mentioned conventional drawbacks, change the modulation signal pulse to an appropriate pulse waveform, and control the laser output.
The object of the present invention is to provide a highly reliable optical recording system that can obtain a reproduced waveform with good rise and fall symmetry.

[Summary of the invention]

Optical disks record information using thermal properties, and the points on the recording medium that correspond to the rising and falling edges of the recording pulse, that is, the leading edge and trailing edge of the pit or magnetized domain formed by the recording pulse, are During the formation of the edge portion, the temperature on the trailing edge side is higher than on the leading edge side due to the effect of thermal diffusion. For this reason, the pit or domain exhibits a shape that expands toward the trailing edge side, and the symmetry of the waveform between the rising edge and the falling edge of the reproduced waveform becomes poor. This tendency becomes stronger as the recording pulse width becomes longer. Even if such a reproduced waveform is passed through a level slicer to detect the recording pulse width, there is a high probability that an error will occur, and high reliability cannot be obtained.

Therefore, in the present invention, by converting the waveform of the input pulse width modulation signal into a waveform that takes into account the effect of thermal diffusion and using it as the laser output waveform, a reproduced waveform with good symmetry of the rising edge and falling edge can be obtained. The resulting signal (pit or magnetized domain) is recorded.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to Examples.

:, 3) In the first embodiment of the present invention, the leading edge and the trailing edge of a recording pulse with a long pulse width, which is strongly affected by thermal diffusion during pit or domain formation, are replaced with pulses with a short pulse width. By forming both pulses and providing a time interval between both pulses, the influence of heat diffusion to the trailing edge side is reduced. That is, as shown in FIG. 1(B), pulses 7a are generated corresponding to the leading and trailing edges of the input modulated signal 5.
.

7b, and the pits or domains are formed by the laser output of the pulse train 6 with a time interval 8 between both pulses. In this case, as 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. Therefore, as shown in FIG. 1(C), even during the pulse interval 8, a laser output [2] which does not strongly affect the thermal diffusion is applied. Alternatively, as shown in FIG. 1(D), a laser output waveform 15 in which one or several pulses 16 are inserted between pulse intervals 8 can also be used.

j Also, the reproduced waveform 4 shown in FIG. 1(A)
1 Forms leading and trailing edges with good symmetry, i.e. pits or domains with little influence of thermal diffusion; 3 Input modulation signal 1 with a short pulse width forms □9. vs. -C4,
□. Yoyo. The input modulation signal 51 has a long recording pulse width with waveform 2 and waveform 1.
For this, laser output waveforms 6, 12, or 15 as shown in (B), (C), or (D) are used.

The second method is to attenuate the pulse height 21 with a certain time constant as the laser output waveform, as shown in Fig. By using the above-mentioned laser beam, the laser beam irradiated portion of the recording medium has a uniform temperature distribution.

Next, we will introduce tie 1 to realize the first method above.
An example of the whipyard is shown in Figure 3.
A%″′−8°”°″′″A″!ii″I
Figure 4 shows an example of a circuit block for obtaining an output. The circuit shown in FIG. 4 includes two delay circuits 45, 4, 6, a circuit 44 for setting the delay time, four logic circuits 47, 48,
49, 50, Karen 1 operated by input recording pulse
~ two pulsed current sources 51.5'2 with switches,
DC current source 53 for pre-bias supply, current addition circuit 5
4, and a semi-sensitive laser 55.

The operation will be explained below using FIG. 3.4.

Delay time τ1. τ2 is set by the delay time setting circuit 44,
The input modulation signal 24 is delayed by a delay time τ2.tau specified by the setting circuit 44. A τ2 delay amount 25 and a τ1+τ2 delay signal 26 are obtained by passing through delay circuits 45 and 46 for τ and +τ2, respectively. Next, the input modulation signal 24 and the τ1+τ2 delayed signal 26 are passed through an AND circuit 47 and a NAND circuit 48, respectively, to obtain a logic signal 27 and a logic signal 28, respectively. Furthermore, the τ2 delay amount 25 and the logic signal 28 are A N
l) Pass through circuit 49 to obtain recording logic signal 29;

Furthermore, the recording logic signal 30 is obtained by passing the logic signal 27 and the τ2 delay amount 25 through an AND circuit 50.

By switching the pulse current source 52 using the recording logic signal 29, a laser drive current having a waveform similar to that of the recording logic signal 29 is obtained. Further, the laser output 31 can be obtained by switching the pulse current source 51 using the recording logic signal 30 and inputting it to the current adding circuit 54.

However, it is assumed that the pulse current values of the pulse current sources 51 and 52 can be individually set from the outside. Note that a semiconductor laser requires an optical system that focuses the laser output from the laser onto a recording film on a rotating optical disk, a photodetection system that detects the reflected light from the optical disk, and a mechanism for adjusting the position of the laser beam on the optical disk. It is incorporated into an optical head consisting of focus control and tracking control. The overall structure of an optical disk device including such an optical head, its moving mechanism, etc. is disclosed in Japanese Patent Application Laid-Open No. 58-9.
No. 1536 describes this in detail.

As shown in FIG. 3, in this embodiment, the input modulation signal 24
As, four kinds of pulse widths P1. P,, P,.

A variable tone code signal consisting of P4 (P, <P2<P3<P4) was used. Here, pulses 7a at the leading and trailing edges of the laser output waveform shown in FIG. 1(B).

7b each pulse width τ4. The setting conditions for τ2 are 1, the minimum repetition pulse frequency T of the input variable length code signal,
□In contrast, τ1≦'r++xw/2 and τ2≦Twy*/2.

In the example of FIG. 2, TWIN”2T1, and τ1≦T1
Moreover, it is shown that τ2≦T1.

2. With respect to the set linear velocity (determined by the disk rotation speed and recording radius) and the recording pulse laser output power, the leading edge and trailing edge as shown in Figure 1 (A) are generated with the laser pulse output of the width. A reproduced waveform 4 with good symmetry can be obtained.

Pulse width P of input modulation code signal 24 used in this example
Engineering f Pal pat p4 is, for example, P□=150
(nsec) P2 = 200 (nsec) P, = 250 (nsec) P4 = 300 (nsec), and regarding the setting of τ1 and τ2, here τ3τ
1 = 2, and from setting condition 1, τ≦150 ('n5ec), and from setting condition 2, τ = 100 (nsec).

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

2τ= 200 (nsec) (generally τ1+τ
2) The following pulse width P1 = 150 (nsec),
P, = 200 (nsec) input pulse 33.34
For the recording pulses 37 and 38, which are simply delayed by τ2 and whose waveforms do not change, are obtained as recording logic signals, and the corresponding pulses 41 and 4 are respectively obtained as recording logic signals.
2 is output as a laser.

On the other hand, the pulse width P3 = 250 [n5ec], P4 = 300 (n
For an input pulse 32.35 of sec), not only is there a τ2 delay 9), but also pulses 7a and 7b with a pulse width τ on both the leading edge side and the trailing edge side (generally, the pulse width on the leading edge side is τ1, and the pulse width on the trailing edge side is Waveforms 36 and 39 each consisting of a pulse train whose edges are τ2) and a time interval of 8 are obtained as recording logic signals. As for the laser output, by changing the pulse current level of the pulse current source 51, a pulse shape 40.43 whose output level is variable in the time interval 8 portion is obtained.

The obtained pit shape and reproduced waveform will be described.

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

Regarding the laser output waveforms 4Q and 43, when the current level of the pulse current source 51 is set to zero, the first
A pit shape 9 and a reproduced signal 10 as shown in Figure (B) were obtained. On the other hand, when the current level was set to an appropriate finite value, a pit shape [3] and a reproduced waveform 14 as shown in FIG. 1(C) were obtained.

In this way, if the input variable length code signal was outputted as it was by the laser, only a reproduced waveform with poor symmetry of rising and falling edges could be obtained for pulses 32.35 with a pulse width of 200 [n5ec] or more. For the fourth
By passing the input variable tone code signal through the circuit shown in the figure and outputting it as a laser, it was possible to obtain a reproduced waveform with good rise and fall symmetry as shown in FIG.

Another example of implementing the first method is to store laser output waveforms corresponding to pulses of various pulse widths constituting the input modulation signal in a ROM (Read Only Me).
It is also possible to store them in advance in a memory (Mory) and output them in synchronization with the input modulation signal.

Next, FIG. 5 shows an example of a circuit block for realizing the second method.

The configuration of the circuit block shown in FIG. 5 will be described.

56 is a circuit that sets the time constant of the differentiating circuit 57 to 3; 58
59 is a voltage level setting circuit that outputs a positive voltage pulse set in response to an input pulse; 60 is a voltage adder circuit;
61 is a voltage-current conversion circuit; 63 is a pulse current source that outputs a laser drive current corresponding to the bias input current waveform;
62 is a DC bias current source, 64 is a current addition circuit,
65 is a semiconductor laser.

The operation of the circuit block shown in FIG. 5 will be explained using the output signals of each circuit shown in FIG.

The input modulation signal 24 is differentiated by the differentiating circuit 57 with a set time constant, resulting in a differentiated output waveform 48 and 66.

Only the positive voltage portion of this signal 66 is extracted by a level slice circuit, resulting in a signal with a waveform like 67. A positive voltage pulse signal synchronized with the input signal 24 is added to this signal 67, and further current conversion is performed to obtain a bias current input signal 68. A bias current input signal 68 was manually input to the pulse current source 63, and the variable tone code signal 24 shown in FIG. 3 was used as the current input modulation signal. As a setting condition for a time constant of 3, ], as shown in Fig. 2, the time constant τ3 is set to give a slope 21 of attenuation that compensates for the effect of heat diffusion toward the trailing edge during the formation of pitch 1- or domains. do.

In this example, for the set linear velocity and the maximum irradiation laser power at the recording medium 2, τ = 300 [n5ec]
By setting, the signal pulses 32, 33, 34, and 4 types of pulse widths constituting the input variable length code signal 24 are set as
For each of 35, the rise as shown in Figure 2,
A reproduced waveform 23 with good fall symmetry was obtained.

〔Effect of the invention〕

1 *□1oyoゎ17.88□%)<)L/Yu. .

-One.

The rise and rise of the reproduced waveform corresponding to
Since it is possible to improve the symmetry of the fall of the pulse,
□Oh, □O8□1st o2□□, 8.3,)
Reducing errors and achieving high reliability is 1.
't-aa.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the first embodiment of the present invention, FIG. 2 is a diagram for explaining the second embodiment of the present invention, and FIG. 3 is a diagram for explaining the first embodiment of the present invention.
FIG. 4 is a block diagram showing the circuit configuration for implementing the first embodiment of the present invention, and FIG. 5 is a time chart for explaining the operation of the circuit for implementing the first embodiment of the present invention. FIG. 6 is a block diagram showing the circuit configuration for implementing the second embodiment, and is a time chart 1 showing the input/output signals thereof.

Claims (1)

[Claims] In an optical recording method that records information on a recording medium by modulating the intensity of a laser beam using an input modulation signal, the intensity of the laser beam is modulated by changing the pulse waveform of the input modulation signal according to its pulse width. An optical recording method characterized by: