Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse...
Reexamination Certificate
1999-12-29
2001-06-05
Dinh, Tan (Department: 2651)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Reexamination Certificate
active
06243327
ABSTRACT:
RELATED APPLICATION DATA
The present application claims priority to Japanese Application No. P11-003208 filed Jan. 8, 1999, which application is incorporated herein by reference to the extent permitted by law.
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention particularly relates to a magneto-optical recording medium for which at least one of recording and reproduction is conducted by irradiating a light onto the magneto-optical recording medium, an optical head for conducting at least one of recording and reproduction by irradiating a light and a recording and reproducing apparatus comprising the optical head.
2. Description of the Related Art
FIG. 16
is a schematic cross-sectional view of an example of a conventional magneto-optical recording medium for which recording or reproduction is conducted by irradiating a light onto the medium and a manner of light irradiation.
In this conventional magneto-optical recording medium
100
, the first dielectric layer
102
made of, for example, SiN and the like, an information recording layer
103
consisting of a magnetic film made of, for example, TbFeCo and the like, the first dielectric layer
104
made of, for example, SiN and the like and a reflection layer
105
made of, for example, Al and the like are sequentially provided on a substrate
101
. A protective layer
107
made of, for example, ultraviolet hardened resin and the like is formed on the reflection layer
105
.
An information signal is written in the magneto-optical recording medium
100
shown in
FIG. 16
in the magnetization direction of the magnetic film
103
. When an information signal is recorded and reproduced, an incidence of a laser light L is carried out from the substrate
101
side as shown in FIG.
16
.
In case of reading the signal recorded on the magneto-optical recording medium
100
shown in
FIG. 16
, a laser light L is incident on an objective lens
124
from a laser light source
121
through a collimator lens
122
and a beam splitter
123
in a recording and reproducing apparatus
120
as shown in FIG.
17
.
Here, it is assumed that the laser light incident on the objective lens
124
is a linear polarized light, whose polarization direction is shown in FIG.
18
.
The laser light L incident on the objective lens
124
is converged onto the information recording layer
103
of the magneto-optical recording medium
100
by the objective lens
124
.
The convergent light is reflected and the polarization state of the reflected light is changed by the Kerr effect from the information recording layer
103
.
The polarization direction of the reflected light is shown in FIG.
19
.
As shown in
FIGS. 18 and 19
, the polarization direction of a return light reflected by the recording medium and returned from the objective lens
124
varies depending on a magnetization direction according to the information recorded on the information recording layer
103
.
As shown in
FIG. 17
, the return light is passed through the objective lens
124
again, incident on the beam splitter
123
, reflected by the beam splitter
123
and fetched.
The return light reflected by the beam splitter
123
and fetched is first incident on a half-wave plate
125
and the polarization direction of the return light is rotated.
Next, the return light is incident on and split by a polarization beam splitter
126
into two polarization components having polarization directions perpendicular to each other. Among them, the polarization component transmitted by the polarization beam splitter
126
is detected by the first photo-detector
127
and that reflected by the polarization beam splitter
126
is detected by the second photo-detector
128
.
In such a system for recording and reproducing the information on a magneto-optical recording medium, it is effective to increase the numerical aperture N. A. of the objective lens for converging a laser light L used for recording and reproduction, to thereby reduce the spot diameter of the light converged by the objective lens and to enhance resolution for the purpose of increasing recording density.
Here, it is assumed that the spot diameter of the light converged by the objective lens is generally expressed as &lgr;/N. A. where &lgr; is the wavelength of a laser light used for recording and reproduction and N. A. is the numerical aperture of the objective lens.
The numerical aperture N. A. of the objective lens is expressed as n
0
·sin&thgr; where n
0
is the refractive index of a medium and &thgr; is the angle of the peripheral light beam of the objective lens. Obviously, therefore, if air is the medium (i.e., n
0
=1), the numerical aperture of the objective lens N. A. does not exceed 1.
As a technique for exceeding the limit, there is proposed a recording and reproducing apparatus using a solid immersion light. The solid immersion lens is supported by and opposite to the magneto-optical recording medium at a distance of less than the wavelength of a light used for recording and reproduction. In the recording and reproducing apparatus using the solid immersion lens, a convergent light is incident on the solid immersion lens and most parts of the incident beams are totally reflected on the end face of the solid immersion lens. Utilizing a so-called evanescent light effused from the end face of the solid immersion lens, the information is recorded on and reproduced from the magneto-optical recording medium. At this time, if a medium having a refractive index n
0
of greater than 1 is used for the solid immersion lens, the numerical aperture N. A. can be made not less than 1.
However, as stated above, if information is recorded on and reproduced from the magneto-optical recording medium using an evanescent light, the light propagated into the magneto-optical recording medium is different in property from a light conventionally applied to information recording or reproduction by the magneto-optical recording medium. Due to this, for example, enhancement conditions of a multilayer structure combined with a transparent dielectric cannot be applied or the information on the phase of the light differs from the incidence direction when a linear polarized light is incident on the medium. As a result, the quality of the reproduced signal disadvantageously deteriorates.
SUMMARY OF THE INVENTION
Under the circumstances, the present invention has been made. It is, therefore, an object of the present invention to provide a magneto-optical recording medium, an optical head and a recording and reproducing apparatus which allows detection of a high quality signal from a return light reflected by and returned from the magneto-optical recording medium while utilizing a solid immersion lens.
A magneto-optical recording medium according to the present invention is characterized in that at least one of recording and reproduction is conducted with respect to the magneto-optical recording medium by irradiating a light onto the magneto-optical recording medium through a convergent lens having a numerical aperture (N. A.) of not less than 1, the magneto-optical recording medium has at least a metallic reflection layer, a back dielectric layer, a magneto-optical recording layer and a light transmitting dielectric layer sequentially provided on a substrate, and is irradiated with the light from a side of the light transmitting dielectric layer; and the light transmitting dielectric layer has a thickness of 50 to 80 nm.
Also, a magneto-optical recording medium according to the present invention is characterized in that at least one of recording and reproduction is conducted with respect to the magneto-optical recording medium by irradiating a light onto the magneto-optical recording medium through a convergent lens having a numerical aperture (N. A.) of not less than 1, the magneto-optical recording medium has at least a metallic reflection layer, a back dielectric layer, a magneto-optical recording layer and a light transmitting dielectric layer sequentially provided on a substrate; and a refraction index n of the light transmitting dielectr
Nakaoki Ariyoshi
Saito Kimihiro
Dinh Tan
Sonnenschein Nath & Rosenthal
Sony Corporation
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