Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
1999-12-03
2002-10-29
Korzuch, William (Department: 2653)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S044140, C369S013330
Reexamination Certificate
active
06473385
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical head and an optical recording and/or reproducing apparatus, and more particularly, to an optical head adapted use an evanescent light from the end face of a solid immersion lens disposed opposite to a recording medium to write and/or read a signal to and/from the recording medium, and an optical recording and/or reproducing apparatus using the optical head.
2. Description of the Related Art
Referring now to
FIG. 1
, there is schematically illustrated the construction of a magneto-optical disc (will be referred to as “MO disc” hereinafter) as a recording medium to and/or from which data is magneto-optically written and/or read. The MO disc is generally indicated with a reference
100
. As shown, the MO disc
100
comprises a substrate
101
, a first dielectric layer
102
formed on the substrate
101
from SiN or the like, a magnetic layer
103
formed on the first dielectric layer
102
from TbFeCo or the like, a second dielectric layer
104
formed on the magnetic layer
103
from SiN or the like, and a light-reflective layer
105
formed on the second dielectric layer
104
from Al or the like. The first dielectric layer
102
, magnetic layer
103
, second dielectric layer
104
and light-reflective layer
105
form together, a magneto-optical recording multilayer
106
(will be referred to as “MO multilayer” hereinafter). The MO multi-layer thin film
106
has formed thereon a protective layer
107
of an ultraviolet-curable resin or the like.
The MO disc
100
has written thereto a signal as a magnetized direction of the magnetic layer
103
. For write and/or read of the signal to and/or from the MO disc
100
, a laser light is irradiated from the substrate
101
towards the MO multilayer
106
as shown in FIG.
1
.
Referring now to
FIG. 2
, there is schematically illustrated an example of the conventional optical head used to write and/read a signal to and/or from the above-mentioned MO disc
100
. Note that the optical system for focusing servo and tracking servo is not shown in
FIG. 2
for the simplicity of illustration and explanation of the optical head. The optical head is generally indicated with a reference
120
.
For reading a signal recorded in the MO disc
100
with the aid of the optical head
120
shown in
FIG. 2
, a laser light is emitted from a laser source
121
. It is guided through a collimator lens
122
and beam splitter
123
to be incident upon an objective
124
. The laser light incident upon the objective
124
has been linearly polarized as shown in FIG.
3
. The laser light incident upon the objective
124
is focused on the MO multilayer
106
of the MO disc
100
through the objective
124
.
The light focused on the MO multilayer
106
of the MO disc
100
is reflected by the MO multilayer
106
. At this time, the reflected light is changed in polarization state under the polar Kerr effect of the magnetic layer
103
, as will be seen from
FIGS. 4 and 5
.
Note that the magnetized direction of the magnetic layer
103
is represented by a non-diagonal component ∈
xy
of dielectric tensor.
FIG. 4A
shows a dielectric tensor
6
f the magnetic layer
103
, given by a following expression (1-1).
FIG. 4B
shows the polarized direction of the reflected light.
(
ϵ
xx
ϵ
xy
0
-
ϵ
xy
ϵ
xx
0
0
0
ϵ
xx
)
(1-1)
FIG. 5A
shows a dielectric tensor of the magnetic layer
103
whose magnetized direction is opposite to that shown in
FIG. 4A
, given by a following expression (1-2).
FIG. 5B
shows the polarized direction of the reflected light.
(
ϵ
xx
-
ϵ
xy
0
ϵ
xy
ϵ
xx
0
0
0
ϵ
xx
)
(1-2)
As seen from
FIGS. 4 and 5
, the polarized direction of a return light from the MO multilayer
106
back to the objective
124
is changed depending upon the magnetized direction of the magnetic layer
103
. As shown in
FIG. 2
, the return light passes through the objective
124
gain and is incident upon the beam splitter
123
which reflects the return light which will thus be taken out.
The return light reflected by the beam splitter
123
and taken out is first incident upon a half-wave plate
125
by which the polarized direction of the return light is rotated 45 deg. as shown in FIG.
6
. Note that
FIG. 6
shows the polarized direction having been rotated clockwise under the effect of polar Kerr effect of the magnetic layer
103
as shown in FIG.
5
.
Next, the return light is incident upon a polarizing beam splitter
126
which will split t into two polarized components whose polarized directions are orthogonal to each other. The polarized component having been transmitted through the polarizing beam splitter
126
will be detected by a first photodetector
127
, while the polarized component having been reflected by the polarizing beam splitter
126
will be detected by a second photodetector
128
.
Referring now to
FIG. 7
, there is illustrated how the polarized light is split by the polarizing beam splitter
126
. The polarization state of the light incident upon the polarizing beam splitter
126
is in two kinds. One is a case A that the polarized light returns after having the polarized direction thereof rotated through an angle &thgr;
k
as shown in
FIG. 7
counterclockwise depending upon the magnetized direction of the magnetic layer
103
, and the other is a case B that the polarized light returns after having the polarized direction thereof rotated through an angle &thgr;
k
clockwise depending upon the magnetized direction of the magnetic layer
103
. Note that in
FIG. 7
, the I-axis corresponds to the polarized component transmitted through the polarizing beam splitter
126
and the J-axis corresponds to the polarized component reflected by the polarizing beam splitter
126
.
More particularly, the light transmitted through the polarizing beam splitter
126
(namely, the light detected by the first photodetector
127
) is a projection of the polarized light beams indicated with references A and B, respectively, onto the I-axis as in
FIG. 7
, and the light reflected by the polarizing beam splitter
126
(namely, the light detected by the second photodetector
128
) is a projection of the polarized light beams indicated with references A and B, respectively, onto the J-axis as in FIG.
7
. Thus, in the case of the polarized light beam A, J>I, and in the case of the polarized light beam B, J<I. A magneto-optical signal (will be referred to as “MO signal” hereinafter) indicative of a magnetized direction of the magnetic layer
103
is detected as a difference (|I|
2
−|J|
2
) between an intensity of the polarized light detected by the first photodetector
127
and an intensity of the polarized light detected by the second photodetector
128
.
In the magneto-optical disc system, the recording density can effectively be increased by focusing a laser light used for write and/or read of a signal through an objective having a larger numerical aperture (NA) which will lead to a smaller diameter of a light spot focused by the objective and thus to a higher resolution.
The diameter of the light spot focused by the objective is generally expressed by &lgr;/NA where &lgr; is a wavelength of a laser light used for write and/or read and NA is a numerical aperture of the objective. Also, the numeral aperture (NA) of the objective is expressed by n·sin &thgr; where n is a refractive index of a medium and &thgr; is an angle of marginal light incident upon the objective. Therefore, when the medium is air (that is, n=1), the NA of the objective cannot exceed 1.
For an NA larger than 1, an optical head has been proposed in which a solid immersion lens (will be referred to as “SIL” hereinafter) is used as an objective. The SIL is supported opposite to an MO disc with a space between them, the space being smaller than the wavelength of a light used for write and/or read of a signal to and/or from the MO disc. The opt
Chu Kim-Kwok
Korzuch William
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Sony Corporation
LandOfFree
Optical head, and optical recording and/or reproducing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical head, and optical recording and/or reproducing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical head, and optical recording and/or reproducing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2961359