JP2510131B2 - Magneto-optical storage device - Google Patents

Description

Detailed Description of the Invention

According to the present invention, a magnetic recording medium having an easy axis of magnetization in the direction perpendicular to the film surface is irradiated with a light beam such as a laser beam to partially raise the temperature of the recording medium, and the coercive force at the irradiated portion is increased. The present invention relates to a magneto-optical storage device in which magnetic domains are arrayed in accordance with the direction of a magnetic field acting on the region to record and erase information, while reproducing information by the magneto-optical effect.

In recent years, optical storage devices have become higher in density and capacity,
Also, it has been widely studied as a memory device capable of high-speed access. Among them, a device for forming a fine pit row on a storage disk and reproducing by utilizing a diffraction phenomenon of a light beam in the pit portion, and a reflection of a storage medium. A device for reproducing by utilizing the rate change has reached the range of practical application. However, the above-mentioned device has only the function of being read-only or capable of additionally recording information, and the optical storage device having the information erasing function, which is one of the major features of the memory device, is still in the research and development stage. .

The present invention relates to a magneto-optical storage device capable of recording / reproducing / erasing information. Next, problems of this magneto-optical storage device will be described.

The basic structure of the magneto-optical storage device is shown in FIG.
Reference numeral 1 is a laser light source capable of emitting predetermined light energy required for recording and reproduction, 2 is a polarizer for transmitting a predetermined polarized beam, and 3 is a prism having two prisms for guiding reflected light to a detector side. The combined beam splitter 4 stores the laser beam emitted from the laser light source 1 in the storage medium 5.
A diaphragm lens for collecting light on the upper side, 6 a substrate, 7 an analyzer for detecting reflected information light on a polarization plane to obtain an information signal, 8
Is a photodetector.

Recording and reproduction of information using the magneto-optical storage device having the above-described basic structure can be easily achieved by a known method, but the laser light source 1 is required for downsizing the device.
Has no choice but to use a low-power laser device such as a semiconductor laser. Therefore, the recording medium 5 has a low recording sensitivity of MnB.
TbDyFe, GdTbFe, GdDyF produced by combining rare earth metals such as Gd, Tb, Dy, Sm and transition metals such as Fe, Co, Ni having a higher recording sensitivity than crystalline magnetic materials such as i, MnBiAl, MnBiCu.
Therefore, amorphous magnetic materials such as e and TbFe are used. However, the magneto-optical effect of the amorphous magnetic material is weaker than that of the crystalline magnetic material, the so-called Kerr rotation angle is limited to 0.1 ° to 0.2 °, and the S / N of the reproduced signal is low. It was difficult to set the azimuth angle of the analyzer 7. Therefore, efforts have been made to increase the Kerr rotation angle by a method of optically increasing the Kerr rotation angle of reflected light by improving the memory element structure as shown in FIG. FIG.
9 is a substrate made of glass or acrylic resin, 10 is a reflective film made of a metal thin film of Al, Au, Cu or the like, 11 is an amorphous magnetic material of rare earth / transition metal, 12 is SiO ₂ , SiO Is a thin film made of a transparent dielectric material such as, and is sequentially laminated by a vapor deposition method, a sputtering method, or the like. The thickness of each thin film is appropriately set so that the Kerr rotation angle increases due to the interference effect of the thin films.
The present applicant previously filed a patent application entitled “Magnetic Optical Storage Element” on July 2, 1981 (Japanese Patent Application No. 56-1040).
72). In the above-mentioned specification, the amorphous thin film of rare earth / transition metal has a thickness of 250 or less, and
When a reflective film is formed on the back surface of the amorphous thin film, the incident light is reflected on the surface of the amorphous thin film, passes through the amorphous thin film, and is reflected by the reflective film, so that two types of reflected light are combined. It is described that the apparent Kerr rotation angle is increased by adding the Kerr effect and the Faraday effect.

In view of the above situation, the present invention utilizes the polarization characteristics of a beam splitter, which is indispensable for a magneto-optical storage device, and further enhances the magneto-optical effect to improve the S / N of a reproduced signal and set the azimuth of a detector for detection. It was made to facilitate.

The configuration of the magneto-optical storage device according to the present invention will be described below.

FIG. 1 is an explanatory diagram showing the basic structure of a magneto-optical storage device according to the present invention. The same elements as those of the optical element shown in FIG. 2 are designated by the same reference numerals. Further, the effect of the present invention is particularly effective in the case of reproduction, so that a reproduction method will be described.

The laser beam emitted from the semiconductor laser 13 is collimated by the condenser lens 14 and passes through the polarizer 2 set in a predetermined azimuth direction, as shown by the arrow in the figure, in the direction of the arrow in the drawing. It becomes a linearly polarized beam (P wave) that oscillates. The linearly polarized beam has R _S > R
_{In order} to effectively have the polarization characteristics of _P ( _RS : S-wave energy reflectance, R _P : P-wave energy reflectance), two prisms are combined on a slope and a dielectric thin film is multi-layer coated on the prism slope. Beam splitter 15. Dielectric thin film has low light absorption, and ZnS, Ce
O ₂ and TiO ₂ can be used (Hiroshi Kubota, et al. 2
Masterpiece "Optical Technology Handbook Supplement Edition", August 10, 1980, Asakura Shoten Co., Ltd., Supplement Edition 5th Issue, 666
page). As described above, since the incident polarized light is the P wave, the polarization state is preserved and only the transmitted energy becomes T _P times (T _P :
P-wave energy transmittance of the beam splitter 15). Next, the polarized laser beam is applied by a diaphragm lens 4 in a spot shape onto the storage medium 5 which has already been magnetically recorded. And
The polarized laser beam hitting the irradiation point is reflected as a polarized laser beam rotated by the Kerr rotation angle α under the magneto-optical effect known as the so-called Kerr effect according to the magnetization state of the irradiation point. That is, as shown in FIG. 4, in the area recorded on the incident polarized light P and subjected to the magnetization reversal, −
In α and other regions where the initial magnetic domains remain, reflected laser beams Q ₁ and Q ₂ whose polarization planes are rotated by + α can be obtained. The reflected laser beam enters the beam splitter 15 again, but the laser beams reflected to the photodetector side are R ₁ and R ₂ due to the effect of the above-mentioned polarization characteristic, and the polarization plane rotation angle β is increased from α. It will be. In this case, the P-wave amplitude reflectance √ R _P of the beam splitter 15 is almost half (0.5), and the S-wave reflectance √ R _S is close to 1, which is the fourth factor. Also shown in the figure. Therefore, when the analyzer 7 is set so that its transmission axis is T in FIG. 4, when the detector 8 scans a portion where the recording areas are arranged in a pulse shape through the condenser lens 16, A pulse-shaped information signal is obtained as shown in FIG. However, in reality, the reflected laser beams Q ₁ and Q ₂ are depolarized by the magneto-optical characteristics of the recording medium 5 and a phase difference is generally generated between the S wave and the P wave reflected by the beam splitter 15. The arriving polarized light is a little elliptically polarized light, and the signal output is as shown in FIG.

As described above, when the reflection polarization characteristic of the beam splitter 15 in which the prism slant surface is coated with a plurality of dielectric thin films is set as described above, the Kerr rotation angle can be effectively increased. Setting 7 becomes easy. Furthermore, in magneto-optical reproduction

[0011]

[Equation 1]

(P: optical energy reaching the analyzer, θ
_K : Kerr rotation angle), the P-wave energy reflectance R _P and the S-wave energy reflectance R _S of the beam splitter are set so that √P · θ _K is increased.
/ N was also improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration of a magneto-optical storage device according to the present invention.

FIG. 2 is a diagram showing a basic configuration of a conventional magneto-optical storage device.

FIG. 3 is a side view showing a configuration of a memory element.

FIG. 4 is an explanatory diagram showing a reproducing principle in the magneto-optical storage device according to the present invention.

FIG. 5 is a waveform diagram showing an example of a reproduction signal of information by a magneto-optical effect.

FIG. 6 is a waveform diagram showing another example of a reproduction signal of information by the magneto-optical effect.

[Explanation of symbols]

 1 Laser Light Source 2 Polarizer 3 Beam Splitter 4 Aperture Lens 5 Storage Medium 6, 9 Substrate 7 Analyzer 8 Photodetector 10 Reflective Film 11 Amorphous Magnetic Material of Rare Earth / Transition Metal 12 Dielectric Thin Film 13 Semiconductor Laser 14 Focusing Lens 15 Beam splitter 16 Condenser lens

Claims (1)

(57) [Claims] 1. A storage medium comprising an amorphous magnetic thin film of a rare earth / transition metal having perpendicular magnetic anisotropy, a semiconductor laser light source, and a dielectric on a prism slope for passing a laser beam from the semiconductor laser light source. A beam splitter having a multi-layered thin film coating, a diaphragm lens that irradiates the storage medium with P waves that have passed through the beam splitter in a spot shape, and a Kerr rotation angle according to the magnetization state of the magnetic thin film at the irradiation point. An analyzer for receiving a laser beam whose polarization plane is rotated by ± α and which is reflected by the diaphragm lens, enters the beam splitter, and is reflected by the prism slope and emitted. The polarization characteristics of the photodetector that receives the light detected by the photon and the beam splitter in which the multilayer coating of the dielectric thin film is applied to the prism slope are A layer coated, incident on the beam splitter from the storage medium, is reflected by the multilayer coating of the dielectric thin film of the prism inclined surfaces, S wave amplitude reflectance of the laser beam emitted toward on the detected photons 1
And the rotation angle of the polarization plane of the laser beam is increased to ± β, where β> α. / N
An improved magneto-optical storage device.