JPH0689480A - Magneto-optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To enable the recording and reproducing of a high density and high capacity by a short-wavelength light source by using a laser beam consisting of two beams; a beam for recording and erasing and a beam for reproducing. CONSTITUTION:The two-beam system of the beam for recording and erasing and the beam for reproducing is used. A longwavelength semiconductor laser 2 which is the light source of a high output and long wavelength is used as the laser beam for recording and erasing. For example, the max. laser power on the medium surface at 830nm wavelength is 15mW. On the other hand, the short-wavelength semiconductor laser 3 which is the light source of a short output and short wavelength is used as the laser beam for reproducing. For example, the the max. laser power on the medium surface at 430nm wavelength is 1mW.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a magneto-optical recording / reproducing apparatus, and more particularly to a large-capacity magneto-optical recording / reproducing apparatus for realizing recording / reproducing by a short wavelength light source.

[0002]

2. Description of the Related Art Magneto-optical disks have been extensively studied as rewritable optical disks, and some have already been commercialized. The two main subjects of current research are high speed and high density, but various methods have been proposed for high density. As one of them, the recording pit can be made smaller by shortening the wavelength of the light source,
As a result, there is recording / reproduction by a short wavelength light source that realizes high density and high capacity. However, this method has the following two
There are two problems. (1) With the conventionally used magneto-optical magnetic material, the Kerr effect, which governs the reproducing performance, is rapidly reduced when the wavelength of light is shortened, so that a sufficient C / N ratio cannot be obtained. (2) The wavelength of the semiconductor laser used in the magneto-optical recording / reproducing apparatus currently on the market is 830 nm, but assuming that the size of the recording pit simply depends on the wavelength, the size of the recording pit is 1 / 2 or less, that is, the wavelength of the laser needs to be 600 nm or less in order to double the recording density. In the case of magneto-optical recording,
In the process of erasing, it is necessary to generate heat by irradiating light, so that a certain level of laser power is required.

Regarding the above (1), as a new magneto-optical recording layer, a noble metal / transition metal artificial lattice film, a light rare earth metal-transition metal film, a garnet oxide, etc. have been studied. It has been evaluated several times as a disk, and is considered to be the most practical material. On the other hand, regarding (2) above, as a semiconductor laser with an oscillation wavelength of 600 nm or less, SHG (Seco
nd Harmonic Generation: There is a semiconductor laser that uses a wavelength conversion element typified by a second wavelength modulation element) to shorten the wavelength and a wide bandgap material typified by the II-VI group. However, in either case, the laser power is small for use in magneto-optical recording. At present, the shortest wavelength of a semiconductor laser having a laser power that can be used as a magneto-optical recording / reproducing light wave is only about 680 nm, which cannot be expected to achieve sufficient high density and high capacity.

[0004]

An object of the present invention is to provide a magneto-optical recording / reproducing apparatus that realizes recording / reproducing by a short wavelength light source and realizes magneto-optical recording of higher density and higher capacity than conventional ones. It was made for the purpose of providing.

[0005]

In order to achieve the above object, the present invention provides (1)
A magneto-optical recording / reproducing apparatus for recording / erasing / reading information by irradiating a magnetic recording layer with a laser beam modulated according to a certain intensity or recording information while applying a magnetic field modulated according to the recording information. The laser light is composed of a recording / erasing beam and a reproducing beam, and a high-power and long-wavelength light source is used as the recording / erasing laser beam and a low output is used as the reproducing laser beam. Use a light source with a short wavelength for output, and (2) use a wavelength conversion element as a light source used in the process of recording / erasing,
By using a light source with a shorter wavelength in the reproduction process,
Further, (3) in (1) or (2) above, the diameter of the recording pit is about the wavelength of the short wavelength light source used in the reproducing process, and (4) above ( In 1) or 2), the characteristic of the recording layer of the magneto-optical recording medium is that it exhibits a sufficient magneto-optical effect even at the wavelength of the light source used in the reproducing process. Hereinafter, description will be given based on examples of the present invention.

FIG. 1 is a block diagram for explaining one embodiment of a magneto-optical recording / reproducing apparatus according to the present invention. In the figure, 1 is a magneto-optical medium, 2 is a long wavelength semiconductor laser, and 3 is a short wavelength semiconductor laser. Is. Here, a two-beam system for recording / erasing and reproducing is used. As a semiconductor laser for recording and erasing,
Maximum laser power of 15 mW on the medium surface at a wavelength of 830 nm
It was used. As the light source for reproduction, a light source converted to a wavelength of 430 nm using an SHG element was used. The maximum laser power on the medium surface at that time was about 1 mW. As the recording medium, a disk having a diameter of 90 mm was used, which used a TbFeCo film conventionally used as a magnetic layer material and a Pt / Co artificial lattice film corresponding to a short wavelength. As the recording conditions, the laser power, the recording frequency, and the disc rotation speed were adjusted so that the minimum pit diameter was about 0.4 μm. The size of the recording pit was directly observed by the colloidal SEM method. The reproduction C / N of the magneto-optical disk recorded in this way is shown in Table 1 below.
Shown in.

[0007]

[Table 1]

The values shown in Table 1 are the C / N values obtained respectively.
The values are standardized with the maximum value being 1.
For comparison, the results obtained using a conventional magneto-optical recording / reproducing device are also shown. As you can see from Table 1,
Good results have been obtained with the device according to the invention. Also,
It can be seen that better results are obtained with a recording medium compatible with short wavelengths. Although Pt / Co was used as the magneto-optical medium compatible with short wavelengths in the examples of the present invention, the effect of the present invention is not limited to this material, and magneto-optical properties compatible with other short wavelengths are used. The same effect can be obtained in the medium.

The principle of magneto-optical recording is that the temperature of the magnetic layer is raised to the Curie temperature or higher by irradiating laser light and the external magnetic field is switched to perform digital recording. Therefore, in the process of recording / erasing data, the size of the recording pit is determined by the temperature distribution of the magnetic layer rather than the wavelength of light. From this, it is understood that small recording pits can be formed by adjusting the temperature distribution by the method described above. However, it is necessary that the diameter of the recording pit is about the wavelength of the short wavelength light source used in the reproducing process.

FIG. 2 is a diagram showing another embodiment of the magneto-optical recording / reproducing apparatus according to the present invention, in which 4 is a mirror and 5 is an SH.
In the G (Second Harmonic Generation) element (wavelength conversion element), other parts having the same functions as those in FIG. 1 are denoted by the same reference numerals. Here, a light source including a high-power semiconductor laser 2 and an SHG element 5 which is one of wavelength conversion elements is used. The laser power of the high-power semiconductor laser is about 100 mW at the emission surface and the wavelength is about 860 n.
m was used. By using this laser light with the SHG element, the laser power is about 3 mW on the medium surface and the wavelength is about 4 mW.
It was possible to convert into a 30 nm laser beam. At the time of recording / erasing, by moving the mirror 4 shown in the figure, the laser beam of the semiconductor laser is directly irradiated onto the medium.
The recording condition is that the recording pit is about the size of the wavelength of the laser used during reproduction, that is, the pit diameter is 0.4.
The laser power, the disk rotation speed, the recording frequency, etc. are adjusted so as to be about μm. The size of the recording pit was confirmed by using the same method as in Example 1 shown in FIG. At the time of reproduction, the mirror shown in the figure is provided in front of the semiconductor laser to irradiate the SHG element with laser light,
The recording pit was read with a laser beam having a shorter wavelength. The same recording medium as in Example 1 was used. The reproduction C / N of the magneto-optical disk thus recorded is shown in Table 2 below.

[0011]

[Table 2]

The values shown in Table 2 are standardized in the same manner as in Example 1. For comparison, the results obtained using a conventional magneto-optical recording / reproducing device are also shown.
As can be seen from Table 2, as in Example 1, the device according to the present invention gave better results. In the embodiment shown in FIG. 2, the mirror is used as a method of changing the optical path of the laser beam, but the effect of the present invention is not limited to this, and the effect of the present invention can be obtained even if another method is used. To be Also, regarding the arrangement of the wavelength conversion element and the semiconductor laser,
The embodiments of the present invention are merely examples and do not limit the effects of the present invention.

[0013]

As is apparent from the above description, the present invention has the following effects. (1) Effect corresponding to claim 1: It is possible to realize high density and high capacity by a short wavelength light source, which could not be realized conventionally. That is, when recording data on a medium, the recording pits are made smaller by using a semiconductor laser having a sufficient laser power, which is conventionally used in a magneto-optical reproducing recording apparatus,
At the time of reproduction, reproduction is performed with light having a wavelength corresponding to the small recording pit. When erasing, the same semiconductor laser as that used for recording is used. The formation of small pits using a conventional semiconductor laser can be performed by adjusting the rotational speed of the disc, the laser irradiation time, and the thermal design of the disc. (2) Effect corresponding to claim 2: It can be simplified as compared with the device of claim 1. That is, the number of semiconductor lasers can be one. However, various wavelength conversion elements can be used, and the effect of the present invention is not particularly limited. (3) Effect corresponding to Configuration 3: Recording and reproduction with a good short wavelength light source can be realized. (4) Effect corresponding to configuration 4: Since the Kerr effect in the wavelength region of 600 nm or less is small in the conventionally used magnetic layer material typified by TbFeCo, a recording layer having the characteristics as shown in configuration 4 is formed. By using the provided magneto-optical recording medium, it is possible to realize recording / reproduction with a good short wavelength light source.

[Brief description of drawings]

FIG. 1 is a configuration diagram for explaining an embodiment of a magneto-optical recording / reproducing apparatus according to the present invention.

FIG. 2 is a diagram showing another embodiment of the magneto-optical recording / reproducing apparatus according to the present invention.

[Explanation of symbols]

1 ... Magneto-optical medium, 2 ... Long wavelength semiconductor laser, 3 ... Short wavelength semiconductor laser, 4 ... Mirror, 5 ... SHG (Second Harmo)
nic Generation: Second harmonic generation element (wavelength conversion element).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Saeaki Tokita 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inquirer Yoshiko Kurosawa 1-3-6 Nakamagome, Ota-ku, Tokyo In Ricoh Co., Ltd. (72) Inventor Masaetsu Takahashi 1-3-6 Nakamagome, Ota-ku, Tokyo In Ricoh Co., Ltd.

Claims (2)

[Claims] 1. Light for recording / erasing / reading information by irradiating a magnetic recording layer with a laser beam modulated according to a certain intensity or recording information while applying a magnetic field modulated according to the recording information. In a magnetic recording / reproducing apparatus, the laser beam is composed of a recording / erasing beam and a reproducing beam, and a high-power and long-wavelength light source is used as the recording / erasing laser beam. A magneto-optical recording / reproducing apparatus characterized by using a light source of low output and short wavelength as laser light. 2. The light according to claim 1, wherein a wavelength conversion element is used as a light source used in the process of recording / erasing, and a single light source is used by using a light source having a shorter wavelength in the process of reproduction. Magnetic recording / reproducing device.