Optical element and optical pick-up

Details Optical element and optical pick-up Optical element and optical pick-up

2001-01-16

2004-06-01

To, Doris H. (Department: 2697)

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

06744720

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical element comprising a plurality of prisms which differ in their refractive indices and to an optical pick-up including the optical element.
2. Description of the Related Art
FIG. 1
is a schematic view of an example of an optical pick-up of the related art.
This optical pick-up
56
comprises a semiconductor laser
4
, a collimator lens
5
, a beam shaping prism (anamorphic prism)
9
, a beam splitter
3
, an objective lens
2
, and a not shown photodetector.
The semiconductor laser
4
emits a linearly polarized laser beam to the collimator lens
5
.
The collimator lens
5
collimates the laser beam from the semiconductor laser
4
to make it a parallel beam directing to the beam shaping prism
9
.
The beam shaping prism
9
shapes the laser beam from the collimator lens
5
and emits it to the beam splitter
3
.
The beam splitter
3
passes the laser beam from the beam shaping prism
9
and emits it to the objective lens
2
.
The objective lens
2
converges the laser beam from the beam splitter
3
and emits it to an optical disk
80
to form a beam spot on the recording surface of the optical disk
80
. In addition, the objective lens
2
returns the laser beam reflected from the optical disk
80
(reflected laser beam) to the beam splitter
3
.
The beam splitter
3
is struck by the laser beam from the objective lens
2
, reflects the incident laser beam by an inner reflecting mirror, and emits it to the photodetector.
The photodetector receives the laser beam from the beam splitter
3
at a receiving unit and generates an output signal.
The output laser beam of the semiconductor laser
4
has a spread angle in the vertical direction different from that in the horizontal direction, so the sectional shape of the output laser beam is elliptical or near elliptical.
The beam shaping prism
9
changes the sectional shape of the laser beam from the semiconductor laser
4
from an ellipse to a circle to make the diameter of the beam in the long axis direction and short axis direction equal or substantially equal. In this way, the beam shaping prism
9
outputs the incident light beam spread in one direction.
FIG. 2
is a schmatic view of the configuration of another example of an optical pick-up of the related art.
This optical pick-up
57
comprises a semiconductor laser
4
, a collimator lens
5
, a beam shaping prism
39
, an objective lens
2
, and a not shown photodetector.
The semiconductor laser
4
emits a linearly polarized laser beam to the collimator lens
5
.
The collimator lens
5
collimates the laser beam from the semiconductor laser
4
to make it a parallel beam directing to the beam shaping prism
39
.
The beam shaping prism
39
shapes the laser beam from the collimator lens
5
and emits it to the objective lens
2
.
The objective lens
2
converges the laser beam from the beam shaping prism
39
and directs it to an optical disk
80
to form a beam spot on the recording surface of the optical disk
80
. In addition, the objective lens
2
returns the laser beam reflected at the optical disk
80
(reflected laser beam) to the beam shaping prism
39
.
The beam shaping prism
39
is struck by the laser beam from the objective lens
2
, reflects the incident laser beam, and emits it to the photodetector.
The photodetector receives the laser beam from the beam shaping prism
39
at the receiving unit and generates an output signal.
The output laser beam of the semiconductor laser
4
has a spread angle in the vertical direction different from that in the horizontal direction, so the sectional shape of the output laser beam is elliptical or near elliptical.
The beam shaping prism
39
changes the sectional shape of the laser beam output from the semiconductor laser
4
from an ellipse to a circle to make the diameter of the beam in the long axis direction and short axis direction equal or substantially equal. In this way, the beam shaping prism
39
outputs the incident light beam spread in one direction.
Further, the beam shaping prism
39
also has the function of a beam splitter which reflects the laser beam from the objective lens
2
and directs it to the photodetector.
Note that Japanese Unexamined Patent publication (Kokai) No. 9-80212 discloses an invention of a beam shaping prism and an optical head using the same.
This publication discloses to make the direction of the incident light beam approximately perpendicular to the direction of the emitted light beam by a beam shaping prism having a first prism and a second prism.
In addition, it discloses an optical head which changes the direction of the laser beam from a semiconductor laser (incident laser beam) using the beam shaping prism, sends this laser beam to an optical disk, reflects the laser beam reflected by the optical disk in a direction the same as the incident laser beam by a polarization film, and emits it to a photodetector.
The optical pick-up
56
of
FIG. 1
includes a beam splitter
3
and a beam shaping prism
9
, so the number of parts rises. This is liable to undesirably lead to higher cost, a larger size, and more complicated production process.
In addition, there is the disadvantage that if the beam shaping prism and/or the beam splitter is tilted, this inclination of the beam shaping prism and/or the beam splitter results in a large change of the optical axis of the laser beam emitted to the photodetector.
Compared with the optical pick-up
56
in
FIG. 1
, the optical pick-up
57
in
FIG. 2
has a beam shaping prism
39
comprising an integrally formed beam splitter
3
and beam shaping prism
9
, so it is capable of reducing the number of parts.
There is also the disadvantage that when the beam shaping prism is tilted, the change of the optical axis of the laser beam emitted to the photodetector becomes even larger than the inclination of the beam shaping prism.
SUMMARY OF THE INVENTION
A first object of the present invention is to provide an optical pick-up able to reduce the change of the optical axis of the light beam emitted to a photodetector when the beam shaping prism is tilted. A second object is to provide an optical element able to be used in the above optical pick-up.
The first optical element according to the present invention comprises a first prism having a first refractive index and including a first incidence surface and a first emission surface forming a first angle with the first incidence surface and a first reflection surface facing the first incidence surface and forming a second angle with the first emission surface, a second prism having a second refractive index and including a second incidence surface in contact with the first emission surface and a second emission surface facing the second incidence surface, a third prism having the second refractive index and including a third incidence surface in contact with the second emission surface and a first incidence-emission surface forming a fourth angle with the third incidence surface and a third emission surface forming a fifth angle with the third incidence surface, a film between the second emission surface and the third incidence surface and cooperating with the second emission surface and the third incidence surface to emit the light beam striking the third incidence surface from the second emission surface as a first emitted light beam through the first incidence-emission surface, and to emit a second incident light beam striking the third incidence surface from the first incidence-emission surface as a second emitted light beam through the third emission surface. The first prism shapes the incident light beam with a wavelength striking the first incidence surface at an incident angle, and makes the light beam reflected at the first reflection surface parallel to the optical axis of the second prism and strike the second incidence surface, the first emission surface and the second incidence surface are defined so as to cancel the change of an optical axis caused by the change of the wavelength of the incid

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