Optical disk device

Details Optical disk device Optical disk device

1998-08-27

2001-12-04

Psitos, Aristotelis M. (Department: 2651)

Dynamic information storage or retrieval

Specific detail of information handling portion of system

Radiation beam modification of or by storage medium

C369S112280

Reexamination Certificate

active

06327238

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an optical disk device used for recording or reproducing signals on or from an optical disk.
BACKGROUND OF THE INVENTION
A conventional art will be explained based on FIG.
8
.
FIG. 8
shows a cross-sectional configuration of an optical disk device in a conventional example. A laser beam emitted from a radiation source
1
such as a semiconductor laser is converted to parallel light
3
along the z-axis by a collimator lens
2
. This parallel light
3
is incident on a reflecting surface
10
A of a mirror
10
guiding light upward as reflected light
6
. The reflected light
6
is converted to convergent light
8
by an objective lens
7
. The convergent light
8
is transmitted through a surface
9
B of an optical disk substrate
9
, thus being focused on a signal surface
9
A. This convergent light
8
enables signals to be recorded on the signal surface
9
A or signals on a signal surface to be reproduced.
In this optical disk device, its thickness t (the distance from the lower surface
9
B of the optical disk substrate to the bottom face of the mirror
10
) is determined by the sum of t
1
+t
2
. The value of t
1
is determined by adding the vertically movable width of the objective lens
7
to its thickness. The value of t
2
is obtained by adding a margin (that is a thickness of a region that does not contribute to the reflection of the laser beam
3
at a lower part of the mirror
10
because the accuracy of the machined surface cannot be secured) to a beam diameter d before being guided upward. Considering a margin for an error in positioning the objective lens
7
(in the case where the z-axis is in the radial direction of an optical disk, also considering the maximum movable width of the objective lens
7
during tracking), the beam diameter d before being guided upward is larger than the aperture diameter of the objective lens
7
. The aperture diameter is given by 2×NA×f, wherein NA and f represent a numerical aperture of the objective lens and a focal length, respectively. In DVD, the applied NA is 0.6. Since the resolution of the optical disk device is proportional to the square NA, the applied NA can not be further decreased. In order to prevent the objective lens
7
from hitting the substrate surface
9
B, at least 1.3 mm of a working distance (the shortest distance between the substrate surface
9
B and the objective lens surface) is required. Therefore, f is generally at least 2.4 mm in DVD. Consequently, an aperture of at least 2×NA×f=2.88 mm is required in DVD. The beam diameter d is about 3.3 mm including an adjustment margin of 0.4 mm, and the margin of the mirror
10
of 0.3 mm is added thereto, resulting in t
2
=3.6 mm. Furthermore, in the case of f=2.4 mm, t
1
is 4.0 mm in view of its design. Thus, the thickness t of the optical disk device obtained is 7.6 mm.
In such a conventional optical disk device, there has been a problem that it is physically impossible to make the thickness t of the optical disk device less than 7.6 mm unless the working distance and the numerical aperture are changed.
SUMMARY OF THE INVENTION
Considering such a problem, an object of the present invention is to provide optical disk devices that are thin beyond the physical limitations without changing the working distance and the numerical aperture.
In order to attain the object mentioned above, the following means are used.
An optical disk device of the present invention comprises a radiation source, a collimator lens, a prism having at least three polished surfaces of A, B, and C, and an objective lens. A beam emitted from the radiation source is gathered by the collimator lens and enters the surface A of the prism to be refracted (an incidence angle &phgr;, a refraction angle &psgr;). The refracted light is incident on the surface B to be reflected and then on the surface C to be reflected. Then, the light enters the surface B again to be transmitted and is converged on an optical disk signal surface via the objective lens.
Another optical disk device of the present invention comprises a radiation source, a collimator lens, a prism having at least three polished surfaces of A, B, and C, and an objective lens. A beam emitted from the radiation source is gathered by the collimator lens and enters the surface A of the prism to be refracted (an incidence angle &phgr;, a refraction angle &psgr;). The refracted light is incident on the surface B to be reflected and then on the surface C to be reflected. Then, the light enters the surface B again to be refracted (an incidence angle &phgr;′, a refraction angle &psgr;′) and is converged on an optical disk signal surface via the objective lens.
A further optical disk device of the present invention comprises a radiation source, a collimator lens, a first prism having at least three polished surfaces of &agr;, &bgr;, and &ggr;, a second prism having at least three polished surfaces of A, B, and C, and an objective lens. The first prism has the same refractive index as that of the second prism. The first prism and the second prism are joined at the surface &ggr; and the surface A. A beam emitted from the radiation source is gathered by the collimator lens and enters the surface &agr; of the first prism to be refracted (an incidence angle &phgr;, a refraction angle &psgr;). The refracted light is incident on the surface &bgr; to be reflected and then enters the surface &ggr;, i.e. the surface A of the second prism to be transmitted. The transmitted light is incident on the surface B to be reflected and then on the surface C to be reflected. The light enters the surface B again to be refracted (an incidence angle &phgr;″, a refraction angle &psgr;″) and is converged on an optical disk signal surface via the objective lens.
A yet further optical disk device of the present invention comprises a radiation source, a collimator lens, a first prism having at least three polished surfaces of &agr;, &bgr;, and &ggr;, a second prism having at least three polished surfaces of A, B, and C, and an objective lens. The refractive index of the first prism is different from that of the second prism. The first prism and the second prism are joined at the surface &ggr; and the surface A. A beam emitted from the radiation source is gathered by the collimator lens and enters the surface &agr; of the first prism to be refracted (an incidence angle &phgr;, a refraction angle &psgr;). The refracted light is incident on the surface &bgr; to be reflected and then enters the surface &ggr;, i.e. the surface A of the second prism to be refracted (an incidence angle &phgr;′, a refraction angle &psgr;′). The light is incident on the surface B to be reflected and then on the surface C to be reflected. The light enters the surface B again to be refracted (an incidence angle &phgr;″, a refraction angle &psgr;″) and is converged on an optical disk signal surface via the objective lens.
A still further optical disk device of the present invention comprises a radiation source, a collimator lens, a first prism having at least two polished surfaces of &agr; and &bgr;, a second prism having at least three polished surfaces of A, B, and C, and an objective lens. The refractive index of the first prism is different from that of the second prism. The first prism and the second prism are joined at the surface &bgr; and the surface A. A beam emitted from the radiation source is gathered by the collimator lens and enters the surface &agr; of the first prism to be refracted (an incidence angle &phgr;, a refraction angle &psgr;). The refracted light is incident on the surface &bgr;, i.e. the surface A of the second prism to be refracted (an incidence angle &phgr;′, a refraction angle &psgr;′). The light is incident on the surface B to be reflected and then on the surface C to be reflected. The light enters the surface B again to be refracted (an incidence angle &phgr;″, a refraction angle &psgr;″) and is c

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