Optical: systems and elements – Lens – With support
Reexamination Certificate
2000-04-03
2002-11-19
Ben, Loha (Department: 2873)
Optical: systems and elements
Lens
With support
C369S112040, C369S112120, C369S112170, C369S044120, C369S044230, C369S103000
Reexamination Certificate
active
06483650
ABSTRACT:
TECHNICAL FIELD
This invention relates to an integrated optical element used for an optical pickup for recording and/or reproduction of signals by irradiating with a light beam a signal recording surface of an optical type disc (hereinafter referred to as optical disc) such as a mini disc (MD), a magneto-optical disc (MO), a compact disc (CD) or a CD-ROM, an optical pickup using this integrated optical element, and an optical disc device having this optical pickup.
BACKGROUND ART
Conventionally, an optical pickup constituted, for example, as shown in
FIG. 1
is proposed as an optical pickup for an optical disc. The optical pickup
1
shown in
FIG. 1
has a semiconductor laser element
2
as a light source, an optical member
3
made of a transparent material such as glass or plastics, an objective lens
4
for converging a light, and a photodetector
5
for receiving a light and converting the light to an electric signal.
Of these elements constituting the optical pickup
1
, the light-emitting element
2
, the optical member
3
and the photodetector
5
are integrated as an integrated element, which is provided in the state of being fixed to a base, not shown. The objective lens
4
is provided on the base via a biaxial actuator, not shown. As the biaxial actuator is driven, the objective lens
4
is minutely moved in biaxial directions, that is, in the direction of radius of an optical disc D and in the direction toward and away from the optical disc D.
In this optical pickup, as the base is fed in the direction of radius of the optical disc D by the driving of a thread feed motor, not shown, a desired recording track on the optical disc can be accessed.
In this optical pickup
1
, the optical member
3
has two surfaces in parallel to each other. These two surfaces are arranged to be substantially perpendicular to the optical axis of the light beam from the semiconductor laser element
2
. On a first surface (lower-center side in
FIG. 1
) of the optical member
3
on the side of the semiconductor laser element
2
, a grating
3
a
for diffracting a light beam directed toward the optical disc D into the direction corresponding to the direction along the recording track on the optical disc D and for splitting the light beam into a plurality of beams including at least a main beam and two side beams is formed on the optical axis of the light beam from the semiconductor laser element
2
.
Also, on a second surface (upper-center surface in
FIG. 1
) of the optical member
3
on the side of the optical disc D, a hologram
3
b
for diffracting a return light beam reflected from the signal recording surface of the optical disc D and for guiding the return light beam to the photodetector
5
is formed on the optical axis of the light beam from the semiconductor laser element
2
.
The hologram
3
b
functions as optical path branching means for branching the optical path of the return light beam directed toward the photodetector
5
from the optical path of the light beam directed toward the optical disc D, by diffracting the return light beam from the optical disc D incident on the second surface of the optical member
3
and thus directing the return light beam toward the photodetector
5
.
The hologram
3
b
has two hologram areas
3
b
-
1
and
3
b
-
2
for diffracting the incident return light beam by different diffraction angles, respectively, as shown in FIG.
1
. The boundary between these hologram areas
3
b
-
1
and
3
b
-
2
is formed on the second surface of the optical member
3
so as to be substantially coincident with the direction corresponding to the direction of radius of the optical disc D. The return light beam from the optical disc D becomes incident on the hologram
3
b
with its center located on the boundary between the two hologram areas
3
b
-
1
and
3
b
-
2
, and is bisected along the boundary. The bisected portions are diffracted by different diffraction angles, respectively.
That is, the hologram
3
b
also functions as return light beam splitting means for bisecting the incident return light beam along a splitting line in the direction corresponding to the direction of radius of the optical disc D.
The photodetector
5
has a center light-receiving section
5
a
for receiving a return light of the main beam, from among the plurality of beams generated by the grating
3
a
, and light-receiving sections e and f for receiving return lights of the side beams, provided on both sides of the center light-receiving section
5
a
, specifically, on both sides of the direction corresponding to the direction along the recording track on the optical disc D, as shown in FIG.
1
. The center light-receiving section
5
a
further has four light-receiving sections a, b, c and d which are divided by a division line d
1
in the direction corresponding to the direction of radius of the optical disc D and a division line d
2
in the direction along the recording track on the optical disc D.
The division line d
1
on the center light-receiving section
5
a
extends in the direction corresponding to the direction of radius of the optical disc D along the direction of diffraction of the hologram
3
b
in order to prevent generation of any deviation of the focusing error signal level of a light spot in a focused state due to a change in the oscillation wavelength of the semiconductor laser element
2
or due to a change in the refractive index of the optical member
3
by a temperature change.
In this optical pickup
1
, the light beam emitted from the semiconductor laser element
2
becomes incident on the optical member
3
from its first surface, then is split into a plurality of beams by the grating
3
a
, and then passes through the optical member
3
. The optical beam which has passed through the optical member
3
is converged by the objective lens
4
and is cast as a fine light spot onto the signal recording surface of the optical disc D. In this case, three light spots are formed on the signal recording surface of the optical disc D by the main beam and two side beams generated by the grating
3
a
. In
FIG. 1
, only the main beam is shown.
The light beams cast on the signal recording surface of the optical disc D reflected by the signal recording surface of the optical disc D so as to be return light beams. The return light beams pass again through the objective lens
4
and become incident on the optical member
3
from its second surface. The return light beams incident on the optical member
3
are diffracted by the hologram
3
b
formed on the second surface of the optical member
3
. Specifically, the return light beams become incident on the hologram
3
b
with their centers located on the boundary between the two hologram areas
3
b
-
1
and
3
b
-
2
, and the portions incident on the individual hologram areas
3
b
-
1
and
3
b
-
2
are diffracted by different diffraction angles, respectively. The return light beams diffracted by the hologram areas
3
b
-
1
and
3
b
-
2
of the hologram
3
b
pass through the optical member
3
so as to be directed toward the photodetector.
Of the return light beams directed toward the photodetector
5
, the return light beam which is a return light of the main beam and is diffracted by the one hologram area
3
b
-
1
of the hologram
3
b
becomes incident on the two light receiving sections a and b of the center light-receiving section
5
a
of the photodetector
5
. Of the return light beams directed toward the photodetector
5
, the return light beam which is a return light of the main beam and is diffracted by the other hologram area
3
b
-
2
of the hologram
3
b
becomes incident on the remaining two light receiving sections c and d of the center light-receiving section
5
a
of the photodetector
5
. Of the return light beams directed toward the photodetector
5
, the return light beams of the side beams become incident on the light-receiving sections e and f of the photodetector
5
.
The photodetector
5
converts the lights incident on the light-receiving sections a, b, c, d, e and f to electric signals, and s
Ben Loha
Kananen, Esq. Ronald P.
Rader & Fishman & Grauer, PLLC
Sony Corporation
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