JPS59101050A - Reproducing device - Google Patents

Abstract

PURPOSE:To obtain an excellent reproduced output through the change in ellipticity due to magnetooptic Kerr effect, by setting the thickness of a magnetic film to a limited one and making an arrangement that no layer, in which absorption is performed, can be installed to one surface of the magnetic film opposite to the substrate side, and using a polarization beam splitter and lambda/4 plate. CONSTITUTION:A magnetic film 5 is installed on the surface of a substrate, for example glass substrate 10, which does not absorb any lights to be used for reproducing and the thickness d1 of the magnetic film 5 is made extremely thin, for instance, 100-200Angstrom . Moreover, the surface of the magnetic film 5 opposite to the substrate 10 side is, for instance, directly exposed to air or covered with a protective film 11 made of SiO2, etc., to prevent a layer in which absorption of lights is performed from producing on the surface. When the thickness of the magnetic film 5 is set to, for example, 150Angstrom , the Kerr ellipticity epsilonk can be increased substantially and reproduction can be performed with a device utilizing the Kerr ellipticity. The reproduction can be performed from either sides of the substrate 10 side and protective film 11 side. The most suitable thickness of the magnetic film 5 can be changed slightly depending on the material, but an excellent result can be obtained when the thickness is set to 50- 300Angstrom .

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a reproduction device using the magneto-optical Kerr effect.

Background Art and Problems Reproducing devices using the magneto-optical Kerr effect (hereinafter abbreviated as the Kerr effect) can be roughly divided into two types: a method that uses Kerr rotation angle and a method that uses Kerr ellipticity. be.

In other words, FIG. 1 shows the case where the Kerr rotation angle is used,
A light beam from a light source (1) is made into a predetermined plane of polarization by a polarizer (2). This light beam is a half mirror (3),
The magnetic film (5) is irradiated through the condensing lens (4).

When arbitrary perpendicular magnetization is performed in this magnetic film (5), the irradiated light beam is reflected with its plane of polarization rotated according to the state of magnetization of the irradiated part due to the Kerr effect. This reflected light beam travels backward through the condenser lens (4) and is reflected by the half mirror (3).

The light beam from this half mirror (3) is then irradiated onto a photodetector (7) through an analyzer (6), and a reproduced output corresponding to the plane of polarization rotated according to the above-mentioned state of magnetization is extracted. It will be done.

In this device, the amount of light passing through the polarizer (2) is .

, the energy reflectance by the magnetic film (5) is ρ, and the polarizer (
2) and the analyzer (6), the amount of light Ia reaching the photodetector (7) is i=-! -1
oρ[(cosθ±φ1(sinθ)2+εksln2
θ]...(1)4. Here, φ +1gk is a complex Kerr rotation angle, φ is a Kerr rotation angle, and ε is a Kerr ellipticity. Also (1)
(±) in the equation is ←) for the recorded bit and (=) for the magnetization around it.

Therefore, when the Kerr rotation angle φk of the reflected light beam is changed depending on the magnetization state of the magnetic film (5), the scene Ia changes,
A photodetector (7) outputs an output according to the state of magnetization of the magnetic film (5).

However, in this case, since the half mirror (3) is used, the same amount of light that reaches the photodetector (7) returns to the incident light side. For this reason, when a semiconductor laser, for example, is used as the light source (1), there are problems such as destabilization of output due to returned light and increase in noise.

On the other hand, Fig. 2 shows a case where Kerr ellipticity is used, and the light beam that is made p-polarized by the polarizer (2) to the polarization beam slittor (8) is polarized beam slit. The light passes through the ivy (8) and enters the λ/4 wavelength plate (9). The light beam, which is converted from linearly polarized light to circularly polarized light by this λ/4 wavelength plate (9), passes through the condensing lens (4) and passes through the magnetic film (
5) is irradiated. If arbitrary perpendicular magnetization is performed in this magnetic film (5), the irradiated circularly polarized light beam becomes elliptically polarized light, and its ellipticity changes depending on the state of magnetization of the irradiated part due to the Kerr effect. is changed and reflected. When this reflected light beam travels backward through the condenser lens (4) and enters the λ/4 wavelength plate (9), the light beam is converted into two linearly polarized lights according to the ellipticity of the polarized light. When this light beam is incident on a polarization beam snoritter (8), arbitrary linearly polarized light components are separated. The separated light beam is then irradiated onto a photodetector (7), and a reproduced output corresponding to the ellipticity changed according to the above-mentioned state of magnetization is extracted.

In this device, the amount of light Ib reaching the photodetector (7)
Ib = ρ engineering. (1±2εk) (2). Therefore, when the Kerr ellipticity εk of the reflected beam changes depending on the magnetization state of the magnetic film (5), the light intensity changes, and the photodetector (7) detects the The output is not coming out.

In this case, there is almost no returning light to the incident light side, so the laser output may become unstable due to the above-mentioned returning light.
Problems such as increase in noise do not occur.

By the way, in the device using the Kerr rotation angle shown in Fig. 1,
When θ = 45 degrees in equation (1), the signal component ∆ 8 and the DC component are 1 and ρ, respectively.
SA when shot noise is dominant as a noise component
The ratio is proportional to.

On the other hand, the SIN ratio in the device using the Kerr ellipticity shown in FIG. 2 is proportional to ='4216kl --(6) from equation (2).

Here, by comparing equations (5) and (6), we get 1
When φkl>2tfflε is 1 (7), a device that uses Kerr rotation angle is better at -11s/N, and 1φ is 1 < 201ε is 1 (8) In this case, the device that uses Kerr ellipticity has a better S/N ratio.

However, in general, rare earth-transition metal amorphous systems (
In conventionally known perpendicular magnetization films such as amorphous GdCo) and MnB1, the complex Kerr rotation angle is Iφ!
1 for 1ε is extremely small compared to , and for this reason, equation (7) holds true, making it impossible to perform good reproduction with a device that utilizes Kerr ellipticity.

OBJECTS OF THE INVENTION In view of these points, the present invention is intended to increase the substantial Kerr ellipticity so that good reproduction can be performed.

Summary of the Invention The present invention provides a magnetic film that is provided on a substrate that does not absorb light used for reproduction, and that the thickness of the magnetic film is 50 to 30 mm.
0A, and by preventing the absorption layer from being provided on the opposite side of the magnetic film from the substrate, and by using a polarizing beam sinter and a λ/4 plate, the magneto-optical Kerr effect can be achieved. This is a reproducing apparatus which obtains a reproducing output by changing the ellipticity. According to this, the substantial Kerr ellipticity is increased and good reproduction is performed.

Embodiment In FIG. 3, there is no absorption with respect to the source used for regeneration.
For example, a magnetic film (5) is provided on a glass substrate αQ, and the thickness dl of this magnetic film (5) is, for example, 100 to
It is formed extremely thin at 200A. Further, the surface of the magnetic film (5) opposite to the substrate α1 may be exposed directly to an air layer or may be provided with a protective film αη of 5IO2 or the like so that no absorbing layer is provided.

The increase in the Kerr ellipticity ε of the magnetic film (5) thus formed will be demonstrated below.

For example, when Tb-Fe is used as the material of the magnetic film (5), T at the wavelength λ of the light beam = 800 nm
The refractive index of b-Fe was measured to be nt = 2.8-13.6.

Here, if the refractive index of the substrate 0Q is no = 1.5 and the refractive index of air is nz = 1.0, the complex Kerr rotation angle when the thickness dl of the magnetic film (5) is sufficiently thick is φ = - 14,8',
ε = 4.0'. Also, ρ=0.466.1φ and '1r=10.1'. Therefore, when d1=ω, it is acceptable to satisfy the equation (7), but the system US/IV that uses Kerr ellipticity is not good.

On the other hand, Fig. 4 shows that ε is 1 when dl is changed.
This figure shows the change in the value of 7 for ε that determines ρ and SA, and in the figure, when dl is 15OA, ε
The value of 〆7 has the peak value. Therefore, by substituting the value at this time into equation (6), this magnetic film (5)
S/1'J when used in a device using Kerr ellipticity
becomes .

On the other hand, if we substitute ρ and φk when dl=■ into equation (5) to find the SA of the device that uses Kerr rotation angle, we get:
From these equations, it can be seen that the reproducing method using the Kerr ellipticity according to the equation (9) is 10.3 dB better in s//N than the reproducing method using the Kerr rotation angle according to the 01 equation.

In the reproducing method using one rotation angle, in equation (1), the term (+62k) and the polarizer (2) and the analyzer are at a maximum when θ→end. In other words, in the limit of θ→Ryo, equation 99 becomes equation (5), 93
dB higher, and the α0 formula is 7.5 dB higher than the 99 formula. However, even in this case, under the above conditions, the reproduction method that uses Kerr ellipticity still has better eyes than the reproduction method that uses Kerr rotation angle.

In this way, by setting the thickness of the magnetic film (5) to, for example, 150 A, the Kerr ellipticity εk can be substantially increased, and reproduction can be performed in an apparatus that utilizes the Kerr ellipticity. Also, in that case, the koji will be better than the conventional device using the Kerr rotation angle.

Furthermore, since there is no light returning to the incident light side, there is no fear of destabilizing the semiconductor laser output or increasing noise.

Note that reproduction may be performed from either the substrate α@ side or the protective film αη side. In addition, the best thickness of the magnetic film (5) varies somewhat depending on the material of the magnetic film, but is approximately 50 to 300 mm.
Good results were obtained in the range A.

Effects of the Invention According to the present invention, the substantial Kerr ellipticity is increased, making it possible to perform good reproduction.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of a playback device using Kerr rotation angle, Figure 2
The figure is a block diagram of a reproducing apparatus using Kerr ellipticity, FIG. 3 is a block diagram of an example of the present invention, and FIG. 4 is a diagram for explaining the same. (5) is a magnetic film, (8) is a polarizing beam splitter, (9
) is a λ/4 wavelength plate, and αQ is a substrate. Figure 3 Figure 4 Mountain (8) Procedural amendment (February 8, 1982 1 1. Indication of the case 1982 Patent Application No. 211681 2. Title of the invention Reproduction device (3. Representative of the person making the amendment) Director Noriyoshi Ohga 5, date of amendment order: 6, 1939,
Number of inventions increased by amendment 7, subject of amendment Akira iW: Detailed description of invention column 8, content of amendment 1) In the specification, delete the line 4th negative 1st line "It is considered to be elliptically polarized light." do. 2) On the same page, in the second line, "ellipticity" is corrected to "reflectance." Same, the 5th line of Dosei [polarized light...linear polarized light]
"S-polarized light conforming to the polarizing beam splitter (8) whose intensity differs depending on the ellipticity of the magnetic film." 4) Same, same page, line 7, “Optional separation” should be changed to “
"Reflected as S-polarized and C-polarized without reducing intensity."that's all

Claims (1)

[Claims] A magnetic film is provided on a substrate that does not absorb light used for reproduction, and the thickness of the magnetic film is 50 to 300A,
The absorbing layer is not provided on the surface of the magnetic film opposite to the substrate, and the polarizing beam splitter and λ
A playback device that uses a /4 plate to obtain playback output by changing the ellipticity due to the magneto-optical Kerr effect.