JPH0573912A - Recording system for optical disk - Google Patents

Abstract

PURPOSE:To accurately execute overwrite without a magnetic field by using temperature distribution having a steep inclination effective in erasing a recording point. CONSTITUTION:A laser beam having a short wave length (530nm) and a laser beam having a long wave length (780nm) is cast at a same point on an optical disk and the intensity of the laser beam having the long wave length is modulated. High speed recording can be executed while the temperature distribution having the steep inclination obtained by the short wave length beam is maintained, then high density recording is attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc recording system for recording, reproducing and erasing information by using a laser beam.

[0002]

2. Description of the Related Art Conventionally, when recording information on an optical disk, laser light of one kind of wavelength is used. The light source is
A semiconductor laser with a wavelength of around 800 nm is used, but in order to improve the recording density, it is essential to shorten the wavelength of the laser light source. That is, since the diameter of the light spot focused on the optical disk by the lens is proportional to the wavelength, it becomes possible to decompose and read a smaller recording point by shortening the wavelength. In addition, a small light spot is required to continuously and stably record small recording points. As described above, the recording and reproducing of the minute recording point requires the light source having the shorter wavelength than the conventional one, but the current short wavelength laser has a problem that the power required for the recording cannot be obtained. Further, it is difficult to modulate the light intensity at high speed with an SHG (second harmonic generation) laser, which is promising as a short-wavelength light source in the near future. As a method for solving this problem, for example, as described in Japanese Patent Publication No. 62-59375, there is a method of reading a recording point recorded by a laser beam of a long wavelength with a laser beam of a short wavelength. However, it is difficult to continuously and stably record minute recording points.

[0003]

When a short wavelength laser is used in a conventional optical disk recording method using light of one type of wavelength, the power required for recording cannot be obtained, or the intensity of light is increased at a high speed. There was a problem that it could not be modulated to.

It is an object of the present invention to provide a recording system capable of continuously and stably recording minute recording points even with a short wavelength laser which is not capable of low power or high speed modulation.

[0005]

The above-mentioned object can be achieved by irradiating the same spot on the optical disk with light having at least two kinds of wavelengths and modulating the intensity of light having at least one kind of wavelength. Particularly, in the case of a short-wavelength laser capable of high-speed modulation with a low output, it is used in combination with a laser having a longer wavelength and a higher output. At this time, the intensity of the long-wavelength laser may be kept constant to modulate the intensity of the short-wavelength laser, or conversely, the intensity of the short-wavelength laser may be kept constant to modulate the intensity of the long-wavelength laser. Further, in the case of this combination of lasers, the above object can be achieved even if the intensities of both lasers are modulated at the same timing. Further, a magneto-optical disk capable of overwriting with no magnetic field or a constant magnetic field (for example, Japanese Patent Laid-Open No. 59-113506).
In Japanese Patent Laid-Open Publication No. 2003-242242, both lasers are alternately modulated, recording is performed with an optical pulse having a long wavelength, and erasing is performed with an optical pulse having a short wavelength, whereby overwriting can be performed more reliably.

In the case of a short wavelength laser such as an SHG laser, which is difficult to perform high speed intensity modulation, it is used in combination with a long wavelength laser capable of high speed modulation. That is, recording is performed by keeping the intensity of the short wavelength laser constant and modulating the intensity of the long wavelength laser.

As a means for irradiating the same spot on the disk with light of two wavelengths, there is a method of combining two lights into one by using an interference filter. In addition, the SHG laser
YAG or YVO excited by semiconductor laser light
In the case of the type that uses the second harmonic of the laser light, the semiconductor laser light and the SHG laser light can be emitted at the same time by selecting an optical component that constitutes the SHG laser. At this time, if the semiconductor laser is modulated at a frequency (20 kHz or higher) faster than the response speed of the YAG or YVO laser, the semiconductor laser light is modulated light, SHG.
The light has a constant intensity. By focusing the light of these two wavelengths with a lens, it is possible to irradiate the same spot on the disk more easily and accurately. Further, when the SHG laser is of a type that uses the second harmonic of the semiconductor laser light, the semiconductor laser light (fundamental wave) and the SHG light are adjusted by adjusting the shape of the crystal that generates the second harmonic. It can be emitted at the same time.

[0008]

Since the recording on the optical disk utilizes the heat generated by the absorption of the laser beam by the recording film, the recording can be performed if the temperature of the portion irradiated with the light reaches the recording temperature. At this time, if a small light spot of short wavelength light is used, the temperature distribution of the recording film becomes steeper, so that minute recording points can be recorded stably. Fig. 1 shows light with a wavelength of 800 nm, light with a wavelength of 400 nm, and light with a wavelength of 800 nm.
2 shows the temperature distribution of the recording film when light is irradiated with light having a ratio of 1 to 400 nm superimposed on each other. The peak value of each temperature distribution is standardized as 1. The temperature distribution when the two lights are superposed has an intermediate shape between the temperature distributions of the two lights alone. Therefore, by superimposing the high-output long-wavelength light on the low-output short-wavelength light and adjusting the intensities of both, the temperature distribution near the recording temperature can be made a sharp temperature distribution obtained with the short-wavelength light. Recognize. In the case of a short-wavelength laser where high-speed modulation is difficult, by modulating the intensity of the long-wavelength laser at high speed, the temperature of the recording film is modulated near the recording temperature while maintaining the temperature distribution obtained with short-wavelength light. Can be made

In a magneto-optical disk capable of overwriting with no magnetic field or a constant magnetic field, the movement of the domain wall is used to erase the recorded magnetized drain. At this time, the steeper the temperature distribution, the easier the domain wall moves. The light intensity required for erasing may be lower than the light intensity required for recording, but it is difficult to obtain the intensity required for recording with the current short wavelength laser. Therefore, overwrite can be achieved by alternately modulating lasers of two kinds of wavelengths, recording with a long wavelength optical pulse, and erasing with a short wavelength optical pulse.
This overwriting can also be performed by modulating light of either one of the wavelengths.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

Example 1 FIG. 2 shows an SH having a wavelength of 530 nm.
1 shows an optical system of an optical head equipped with a G laser 1 and a 670 nm semiconductor laser 2. The maximum power of both lasers is 20 mW. The two kinds of laser light are shaped into a circular parallel beam by a lens (and a prism), and then are combined into one by an interference filter 3, pass through a beam splitter and a rising mirror, and a diameter of a lens 130 is reduced by a narrowing lens 4.
The same spot on the recording film of the magneto-optical disk 5 of mm is irradiated. The maximum light intensity on the recording film is both 6 mW.
The light reflected from the disc is reflected by the beam splitter.
It is divided into a servo system and a signal detection system. The magneto-optical disk is rotating at a rotation speed of 3600 rpm and is 530 nm.
It is not possible to perform high-speed recording only with the light. Therefore,
The light intensity of 530 nm was kept constant and the light intensity of 670 nm was modulated.

FIG. 3 shows the optical pulse waveforms of the two lasers. In the signal reproducing state, the intensity of 530 nm is 1.5 m
The intensity at W 6,670 nm is 0 mW. In the recorded state, the intensity at 530 nm was fixed at 4 mW, and the intensity at 670 nm was modulated between 0 mW and 4 mW. The modulation frequency is 38 MHz. When recording was carried out at a position where the disk radius was 60 mm under these conditions, circular recording points having a diameter of 0.3 μm could be continuously and stably recorded.

The combination of such lasers may be semiconductor lasers. For example, when a semiconductor laser having a wavelength of 670 nm and a maximum output of 20 mW is to be used for recording on a disk rotating at 3600 rpm or more, it is used in combination with a semiconductor laser having a wavelength of 780 nm. In this case, either one of the lasers may be modulated, or both lasers may be simultaneously modulated. Further, the recording method described above is applicable not only to the magneto-optical disk but also to any type of optical disk such as a write-once optical disk and a phase change optical disk.

Example 2 The same recording as in Example 1 was performed using the SHG laser shown in FIG. The light having a wavelength of 810 nm emitted from the semiconductor laser is narrowed down by the YAG laser 7, but a part of the light passes through the concave mirror 9 without being absorbed by the YAG. The intensity of the transmitted light of 810 nm is YAG
The thickness and the optical characteristics of the concave mirror can be adjusted appropriately. On the other hand, the excited YAG laser emits light having a wavelength of 1060 nm, which is KTP.
By passing through the crystal 8, SHG light with a wavelength of 530 nm is generated. This 810 nm light was modulated at a frequency of 38 MHz and recording was performed at a position where the disk radius was 60 mm. The light intensity on the disc is 5mW for 530nm light, 810nm
In light, it is 0 mW and 2 mW. As a result, the diameter is 0.3μ
The circular recording points of m 2 could be recorded continuously and stably.

Example 3 FIG. 5 shows wavelengths of 780 nm and 67
FIG. 7 shows optical pulse waveforms when performing non-magnetic overwriting on a magneto-optical disk using two types of 0 nm semiconductor lasers. Recording pulse intensity of 780 nm is 1.5
Erase pulse intensity from mW to 10 mW, 670 nm is 0
Modulation was performed by changing the timing from one mW to 5 mW and shifting the timing by one pulse. Here, in order to perform servo, 780n
The minimum intensity of m was set to 1.5 mW. Under this condition, 360
When overwriting was performed at a frequency of 2 MHz and 3 MHz at a position of a radius of 60 mm of a disk rotating at 0 rpm, the erasing ratio (difference between carrier levels before and after overwriting at a certain frequency) was 30 dB or more. Such overwriting is possible by modulating either one of the lasers.

[0016]

By using the optical disk recording system of the present invention, even a short-wavelength laser that cannot be low-output or high-speed modulated can be obtained with short-wavelength light by combining it with a long-wavelength laser that can be high-output or high-speed modulated. Since high-speed recording is possible while maintaining a steep temperature distribution, high-density recording can be achieved. Further, by using this recording method, it is possible to more surely perform the non-magnetic field overwrite in the magneto-optical disk.

[Brief description of drawings]

FIG. 1 is a temperature distribution diagram of a recording film of an optical disc showing an operation of the present invention.

FIG. 2 is an explanatory diagram of an optical system of an optical head used for a recording method of an optical disc according to an embodiment of the present invention.

FIG. 3 is an optical pulse waveform diagram showing a recording system of an optical disc according to an embodiment of the present invention.

FIG. 4 is an explanatory diagram of an SHG laser for generating light of two wavelengths according to another embodiment of the present invention.

FIG. 5 is an optical pulse waveform diagram showing another embodiment of the present invention.

[Explanation of symbols]

1 ... SHG laser, 2 ... Semiconductor laser, 3 ... Interference filter, 4 ... Focusing lens, 5 ... Magneto-optical disk, 6 ... 8
10 nm semiconductor laser, 7 ... YAG laser, 8 ... KTP
Crystal, 9 ... concave mirror.

Claims (7)

[Claims] 1. A recording system of an optical disc, wherein a recording film is provided on a predetermined substrate, and the recording film is irradiated with light to record information, and light of plural kinds of wavelengths is irradiated onto the same part of the optical disc. A recording method for an optical disc, wherein the intensity of light having at least one wavelength of the light is modulated to record information. 2. The optical disc recording method according to claim 1, wherein the optical disc is irradiated with light of two different wavelengths, the intensity of light of one wavelength is made constant, and the intensity of light of the other wavelength is modulated. 3. The optical disc recording method according to claim 2, wherein the intensity of the shorter wavelength light of the two types of wavelengths is constant and the intensity of the longer wavelength light is modulated. 4. The optical disk recording method according to claim 3, wherein a semiconductor laser is used as the light having a long wavelength and a second harmonic generating laser is used as the light having a short wavelength. 5. The optical disk according to claim 1, wherein the optical disc is irradiated with light of two different wavelengths, and the second harmonic of YAG laser or YVO laser light excited by the semiconductor laser light is used for the light of shorter wavelength. , A recording method for an optical disc, in which the semiconductor laser light is used for light having a longer wavelength. 6. The optical disk according to claim 1, wherein the optical disc is irradiated with light of two different wavelengths, the second harmonic of the semiconductor laser light is used for the light of the shorter wavelength, and the semiconductor laser is used for the light of the longer wavelength. Optical disc recording method using light. 7. The optical disk according to claim 1, wherein the optical disc is irradiated with light of two kinds of wavelengths, the intensities of both lights are alternately modulated, information is recorded by a light pulse of a long wavelength, and light of a short wavelength is used. An optical disc recording method that overwrites information by erasing the information.