JPH02201733A - Method and device for optical disk recording - Google Patents

Abstract

PURPOSE:To form an approximately circular amorphous mark with high quality and with less or no jitters by modulating light beams, and recording the beams in a state of the relative speed between the light beams and a recording film is approximately zero. CONSTITUTION:According to a certain clock signal 6, the light beam is applied with high-frequency modulation in the medium running direction. Signals 3 corresponding to an information string is recorded at certain timing synchronizing with the clock signal 6. At such a time, the recording timing is selected so that the relative speed between the recording film and the optical beams is sufficiently small or zero. Thus the circular amorphous mark can be recorded with less jitters, and when it is reproduced, the reproduced signal with high quality can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention mainly relates to a method and apparatus for efficiently and high-quality recording of information on a recording film of a rewritable optical disc.

[Conventional technology]

Conventionally, optical disks include write-once optical disks that generate physical deformation (bits) in a recording film, magneto-optical disks that record signals with perpendicular magnetization (N pole or S pole) using a magnetic material as a recording film, and crystalline disks. There are phase-change optical disks and the like that record information on a recording film by utilizing an amorphous phase change phenomenon.

When recording information, all recording methods use a common mechanism in which a laser beam is irradiated onto the recording film and recording is completed by causing a change in the state of the medium in that area.

Here, explanation will be given below using a phase change optical disc as an example.

When recording information on a phase change optical disk, an amorphous mark is usually formed by irradiating the recording film with a laser beam to heat the recording film material above its melting point and then rapidly cooling it. Furthermore, when erasing information, a laser beam is irradiated with a power lower than that used during the recording, usually with a power such that the temperature of the recording film is below its melting point, to convert the amorphous mark on the recording film into a crystalline state. This is done by changing.

FIG. 4 is a diagram explaining the conventional recording process, (a) is a diagram showing the recording timing waveform, (bl is a diagram showing the spread shape of the laser beam, (C1 is a diagram showing the temperature profile of the recording film) , (dl is the spread and wide shape of an amorphous mark formed on a recording film), and tel is a diagram showing a signal obtained by reproducing the amorphous mark.

Here, the horizontal axis X of +a) to (dl in the same figure) is the position coordinate of the recording film in the traveling direction of the light beam when the optical disk is stationary (stopped rotating), and the vertical axis is (a) and (e ) is the voltage, (b) and (dl are the widths in the direction crossing the track,
(C) is the temperature.

First, the optical head moves relatively in the direction shown by arrow 51,
During a section 52 in the middle, the gate is opened and the recording laser beam is irradiated onto the recording film (FIG. 4(a)). The length l of this section 52 is #=vbXt.

It is expressed as (2) is the moving speed of the laser beam, and tg is the time the gate is open.

Next, in FIG. 4(b), 53 and 54 indicate the spread of a laser beam with a normal Gaussian distribution, and correspond to the positions x1 and x2a of the above (al).X in FIG. 4(b) The axis is the center of the track.The temperature profile 56 of the recording film at this time has the shape shown in the figure (C1).

Here, 57 in the same figure (C) is a temperature corresponding to the melting point of the recording film, and a phase change occurs in a region above the melting point, for example,
Phase change to amorphous state. At this time, the temperature on the recording film does not rise easily in the initial passage region of the laser beam, reaches its maximum before and after the laser beam finishes passing, and then rapidly decreases.

[Problem to be solved by the invention]

Therefore, the shape of the amorphous mark formed generally has a waveform as shown at 58 in +dl in the figure.

The waveform of the reproduction voltage of the amorphous mark having such a shape is approximately as shown by 59 in the same figure (e),
It is greatly different from the reproduced voltage waveform 60 in the case of the ideal amorphous mark 58a shown in the same figure (dl. In this case, 6
If this voltage 59 is modulated at the slice level indicated by 1,
A jitter shown at 62 will occur.

The reason why the amorphous mark produced by the spot of the laser beam projected onto the recording film with a circular diameter becomes an ellipse and also has a waveform is considered to be based on the following factors.

(2) Since the recording film and the optical head have a relative speed, the laser beam moves relative to the recording film by ΔX during the recording start timing.

(2) At this time, a symmetrical temperature distribution cannot be obtained because the recording film generally has a delay in temperature rise due to diffusion, a delay in temperature decrease due to heat accumulation, etc.

Therefore, in order to avoid such a phenomenon, the rising edge of the recording timing should be made higher than the peak value of the laser beam irradiation that follows.In other words, the laser beam power at the start of recording should be high, and then the laser beam power should be kept at normal power. One possible method is to end the recording. However, this method also requires delicate adjustment because the relative speed between the recording film and the optical head changes every moment as the optical head seeks in the track direction.

Further, from the viewpoint of high-density recording, it is desirable that the amorphous mark be as close to a circle as possible. However, due to the relative movement between the recording film and the light beam (ΔX), it had to be an ellipse.

The present invention has been made in view of the above circumstances, and its purpose is to solve the conventional problems such as deformation of amorphous marks, enable high-density recording, and obtain high-quality reproduction signals. The goal is to make it possible.

[Means to solve the problem]

For this purpose, the optical disk recording method of the present invention is an optical recording/reproducing system comprising an optical disk having a recordable or rewritable recording film and an optical head capable of recording/reproducing data on/from the recording film. The optical beam is modulated in the traveling direction of the recording film, and a recording signal is applied to the recording film at an arbitrary timing synchronized with the modulation frequency.

Further, the optical disc recording device of the present invention is an optical recording/reproducing system comprising an optical disc having a recordable film that can be written once or rewritable, and an optical head capable of recording/reproducing information on/from the recording film. The device includes an optical component that modulates a light beam emitted from the optical component, and a control section that controls the optical component.

〔Example〕

FIG. 1 is a diagram for explaining the optical disc recording method of the present invention. First, waveform 1 in (a) represents the displacement y of the light beam in the recording film traveling direction, waveform 2 in (b) represents the displacement speed of the light beam, (c-1), (c-2 ) The waveform 3.4 represents an impulse-like gate signal for recording timing, and the symbol 5 represents a delay time.

The horizontal axis of each figure is time t. In addition, (d) to (fl
is a diagram when the scale of time t on the horizontal axis is set large; e) shows a clock signal 6, according to which the displacement waveform 1 is modulated.

Now, assume that the light beam is modulated (displaced) in the traveling direction of the recording film by 3' = As1nωot. At this time, the displacement speed Vb of the light beam becomes V b = A ωocO3ωo1. Therefore, when vl,=vl11 (where vl,l is the traveling speed of the recording film), the recording gate signal 3 is generated. At this time, it is also possible to use the gate signal 4 shown in FIG. 4(c-2), which is generally delayed from the clock signal 6 by a delay time 5 in consideration of the rise time of the laser beam and the like. The same figure with a larger time scale (
Looking at dl, (fl), (fl, the optical beam is modulated by the clock signal 6, and at the same time this clock signal 6
A recording gate 3 is created based on. As a result, jitter-free recording becomes possible.

The condition of the recording film at this time is shown in FIG. This figure corresponds to FIG. 4, which shows the conventional recording method.

In the recording method of the present invention, since recording is performed at a timing when the relative velocity between the recording film and the light beam becomes zero (vb = Vm), it is assumed that recording is performed while the optical recording medium is stationary. It's fine. At the recording timing 7 shown in fa) of the same figure, the laser beam is spread with a normal Gaussian distribution as shown by 8 in part (b) of the same figure. Note that 9 is the center of the track. At this time, the temperature profile of the recording film takes the shape shown at 10 in FIG. Then, a phase change occurs in the region of temperature 58 or above, which corresponds to the melting point, and for example, the phase change occurs in the shaded area 11 in the figure (dl) to an amorphous state.The reproduced signal obtained by reproducing this is 12. The result is a symmetrical waveform with no jitter as shown.

As is clear from the above examples, in this example, recording is performed at a timing such that the relative velocity between the recording film and the light beam becomes zero, resulting in ideal recording. Therefore, recording of amorphous marks with high density and high quality can be achieved.

FIG. 3 is a diagram showing an example of the configuration of an optical head for implementing the recording method of the present invention. 21 is a light source that emits a light beam such as a laser beam; 22 is a collimator lens; 23
24 is a beam shaping prism, 24 is an optical component, 25 is a polarizing beam splinter, 26 is a quarter wavelength plate, 27 is an objective lens, and 28 is an optical disk (recording medium). As the optical component 24, an acousto-optic element or the like can be used. 29 is a servo circuit system, and 30 is a reproduction signal detection system. Also, 3
1 is a carrier frequency signal fc generator, 32 is a modulation frequency signal fm generator, 33 is a frequency signal Δfi generator, 34
is a modulator, 35 is an amplifier, and these are optical components 24
Configures the control unit.

Now, the light emitted from the light source 21 is transmitted to the collimator lens 2
2. The beam passes through the beam shaping prism 23 and enters the optical component 24 at an angle θ. Here, a certain frequency is given to the optical component 24. The first-order diffracted light 36 (diffraction angle 2θ) of the light beam from this optical component 24 is guided to the objective lens 27 and focused onto a point 37 on the recording film on the optical disk 28 (solid line in FIG. 3). Note that the 0th order diffracted light is indicated by the symbol 38.

The reflected light from the condensing point 37 on the optical disk 28 passes through the quarter-wave plate 26 provided on the optical path, is reflected by the polarizing beam splitter 25, and is guided to the servo circuit system 29 and the reproduced signal detection system 28. . Note that a configuration may be adopted in which a beam shaping lens (not shown) is provided between the beam shaping prism 23 and the optical component 24 in order to make the optical component 24 work effectively.

Here, in order to operate the optical component 24, reference numerals 31 to 31 to
A constant frequency signal fc is applied to the optical component 24 from a control section consisting of a section 35. When the frequency applied to the optical component 24 is changed in the range from fc to fc-fm, the first-order diffracted light is displaced in the range of the first-order diffracted light 36 shown by a solid line in FIG. 3 and the first-order diffracted light 36a shown by a broken line in FIG. Above, the light collection is displaced between a light collection point 37 and a light collection point 39 .

Therefore, the optical component 24 is moved at a frequency (velocity) of Δfi.
By modulating (changing) the frequency range from c to fc-fm, the light beam is focused at a focal point 37 on the optical disk 28.
The angular frequency ω is between 39 and 39 focal points. (=2πΔfi)
Now, the optical component 24 is a Te0z (tellurium dioxide) acousto-optic element (f c = 80 MHz, fm = 2 MHz).
), a laser with a wavelength of λ-830 nm is used as the light source 21, and the incident beam diameter d is 500 μm, then Δfi=0.54Xv/d #4.5 MHz. Here, V is the sound velocity (#4.2×103 m/s) of light transmitted through the TeO□ acousto-optic element.

Also, regarding the amplitude A of the first-order diffracted light, Δ(2θ)=f
From mXλ/V -8,5X 10-2 (rad, ), assuming that the light beam enters the objective lens 27 with an optical path length of 10 mm, A = 8.5 μm.

Therefore, the displacement speed vb of the light beam is Vb = kXAXω0 = k X 240 (m/s) (0<k<
1), and can follow up to a sufficiently high relative speed between the recording film and the light beam.

As described above, the optical disc recording method of the present invention can be summarized as follows.

(2) High-frequency modulation of the light beam in the medium running direction according to a certain clock signal.

(2) A signal corresponding to an information string is recorded at a certain timing synchronized with this clock signal.

At this time, the recording timing is selected so that the relative velocity between the recording film and the light beam is sufficiently small or zero. As a result, circular amorphous marks can be recorded without jitter, and high-density recording can be achieved.

Moreover, when it is reproduced, a high quality reproduction signal can be obtained.

Note that the optical component 24 that modulates the beam is not limited to an acousto-optic element, and of course, for example, a polygon mirror, a galvanometer, and others can be used. It goes without saying that the present invention can also be applied to write-once optical discs and rewritable magneto-optical discs.

〔Effect of the invention〕

As described above, according to the present invention, a light beam is modulated.
In other words, since the light beam is swung in the traveling direction of the recording film, recording can be performed in a state where the relative velocity between the light beam and the recording film is approximately zero. Therefore, it is possible to form a high-quality amorphous mark with little or no jitter and a nearly circular shape. Therefore, high-density recording can be achieved, and high-quality reproduction signals can also be obtained during reproduction.

[Brief explanation of the drawing]

1 and 2 are explanatory diagrams showing an optical disc recording method according to an embodiment of the present invention, FIG. 3 is a schematic diagram of an optical disc recording apparatus according to an embodiment of the present invention, and FIG. 4 is a conventional optical disc recording method. FIG. 1... Displacement waveform of the light beam in the recording film traveling direction, 2...
- Speed waveform of light beam, 3.4... Recording gate signal, 5... Delay time, 6... Clock signal, 7...
Recording timing, 8... spread shape of laser beam,
10... Recording film temperature profile, 11... Amorphous mark, 12... Reproduction signal waveform.

Claims (2)

[Claims] (1) In an optical recording/reproducing system comprising an optical disc having a recordable or rewritable recording film and an optical head capable of recording/reproducing information on/from the recording film, a light beam emitted from the optical head is directed to the recording film. modulates in the direction of travel,
An optical disc recording method characterized in that a recording signal is applied to the recording film at an arbitrary timing synchronized with the modulation frequency. (2) In an optical recording/reproducing system comprising an optical disc having a recordable or rewritable recording film and an optical head capable of recording/reproducing information on/from the recording film, a light beam emitted from a light source is modulated on the optical head. What is claimed is: 1. An optical disc recording device comprising: an optical component that controls the optical component; and a control section that controls the optical component.