Optical: systems and elements – Lens – With support
Reexamination Certificate
2000-09-20
2002-10-29
Ben, Loha (Department: 2873)
Optical: systems and elements
Lens
With support
C359S823000, C359S813000, C359S814000, C369S219100
Reexamination Certificate
active
06473248
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an optical pickup that is used to read and write information from and onto an optical recording medium, and to a method for manufacturing this optical pickup.
(2) Description of the Related Art
In recent years, optical recording media, such as a compact disc (CD) and a digital versatile-disc (DVD), are increasingly used to store various types of information, and such recording media are rapidly becoming in widespread use. An optical pickup is usually used as an optic device that performs a read from and a write onto such an optical recoding medium.
FIG. 1
shows a construction of a conventional optical pickup
400
in a vertical section view.
As shown in the figure, the optical pickup
400
has a movable member
406
which is movable and which carries an objective lens
401
and coils
405
. A fixed member
407
supports the movable member
406
almost horizontally via four wires
412
which are positioned in parallel to one another. The fixed member
407
is fixed to an optical base
409
.
Since this figure is a section view obtained by vertically cutting the optical pickup
400
, two out of the four wires
421
are not shown in the figure.
In addition to the fixed member
407
, a yoke
410
that supports a magnet
411
, an integrated component
402
, a collimating lens
420
, and a mirror
403
are positioned onto the optical base
409
.
The integrated component
402
contains a semiconductor laser and a photodetector. The semiconductor laser emits a laser beam, which is then collimated by the collimating lens
420
to generate a collimated beam. The mirror
403
has an optical path of the collimated beam changed ninety degrees upward to have the beam enter into the objective lens
401
, which then focuses the beam onto the recording surface of an optical recording medium
412
. The beam is then reflected on the surface of the recording medium
412
, and reverses along the above optical path. The photodetector in the integrated component
402
detects this beam, so that a signal recorded on the recording medium
412
can be read by the optical pickup
400
. Hereafter, the beam reflected on the recording medium
412
is called “a return beam”.
Optical recording media tend to vertically vibrate when rotated. Accordingly, it is necessary to keep positioning the recording surface of the optical recording medium
412
within the depth of field of the laser beam L
1
converged by the objective lens
401
by moving the objective lens
401
in a direction of its optical axis.
Eccentricities in the rotation of the optical recording medium
412
make it also necessary to reposition the laser beam L
1
so that it correctly follows a track on the optical recording medium
412
. Accordingly, an optical pickup is required to have an adjusting function and an error detecting function for having the laser beam correctly focused on a recording medium, and for having the laser beam correctly follow a track.
The conventional optical pickup
400
therefore has the photodetector in the integrated component
402
detect a focusing error and a tracking error by receiving the return light, and suitably controls currents supplied to the coils
405
. Currents passed through the coils
405
interact with a magnetic filed generated by the magnet
411
fixed to the yoke
410
so that Lorentz forces are generated. As a result, the objective lens
401
moves in a focusing direction (i.e., a direction of the laser beam L
1
being projected), and in a tracking direction (i.e., a direction which traverses tacks) that has the laser beam L
1
correctly projected onto a track of the recording medium
412
. By performing these operations, the optical pickup
400
can accurately perform a write onto and a read from the optical recording medium
412
.
With this conventional optical pickup
400
that moves the objective lens
410
in this way, the integrated component
402
, the collimating lens
120
, and the mirror
403
are all fixed to the optical base
409
although only the objective lens
401
is movable to correct the focusing error and the tracking error. As a result, a displacement is generated between the optical axis of the objective lens
401
and a principal ray of the laser beam emitted by the semiconductor laser, so that a lens aberration is generated. This decreases optical properties of the optical pickup
400
, and so precision of the optical pickup
400
for a write onto and a read from the optical recording medium
412
decreases.
One method to solve the above problem is to position the semiconductor laser, the photodetector, and the collimating lens
420
into the movable member
406
that supports the objective lens
401
so as to maintain the constant positional relationship between these optical components all the time and thereby prevent optical displacements from being generated.
FIG. 2
is a simplified diagram showing a construction of an optical pickup
500
achieved according to this method.
As shown in the figure, the optical pickup
500
includes a movable enclosure
505
that carries an objective lens
501
, a semiconductor laser
502
, a photodetector
503
, and a beam splitter
504
. (Hereafter, an optical pickup that has a movable enclosure carrying all the optical components of the optical system is called an “optical-component-integrated optical pickup”.) The movable enclosure
505
is fixed to a fixed member
506
via four wires
507
in a manner that allows the movable enclosure
505
to move in both the focusing direction and the tracking direction. The bottom portions of the movable enclosure
505
is also combined with a flexible printed circuit
508
, which supplies electric power to the semiconductor laser
502
and the photodetector
503
, and transfers a signal to/from them.
When the entire optical system is included in the movable enclosure
505
in this way, displacements, due to movements of the objective lens
501
, no longer occur between the optical axis of the objective lens
501
and the principal ray of the laser beam. However, the flexible printed circuit
508
exerts an unnecessary force to the movable enclosure
505
which is suspended by the four wires
507
. This not only prevents smooth vertical and horizontal movements of the movable enclosure
505
, but also produces unnecessary resonance due to the elasticity of the flexible printed circuit
508
when the enclosure
505
moves. This prevents the optical pickup
500
from correctly following a track, and therefore the construction of the above optical-component-integrated optical pickup becomes meaningless. Hereafter, the capability of an optical pickup correctly following a track is called a “trackability” of the optical pickup.
The conventional optical pickup
500
also has the following problems due to its supporting construction with the four wires
507
.
The four wires
507
have the same length and the same thickness, and are made of the same material. As a result, each wire
507
has the same elastic coefficient in both the focusing direction and the tracking direction, and ends of these wires
507
are burdened with an almost uniform mass (i.e., one-fourth the mass of the movable enclosure
505
). This results in each wire
507
having almost the same resonance frequency in both the tracking direction and the focusing direction. Should an external perturbation occur in either of these two directions, the other direction is also affected by this perturbation. This can result in, at worst, the movable enclosure
505
moving in circles, and make it difficult to have the laser beam correctly follow a track.
SUMMARY OF THE INVENTION
In order to solve the above problems, the present invention aims, as the first object, to provide an optical pickup that contains a movable enclosure carrying the whole optical system, which performs operations from emission of a laser beam to reception of a return light, and that is capable of keeping correctly focusing the laser beam on a track of an optical recording medium.
The p
Ijima Shin'ichi
Nakanishi Hideyuki
Nakanishi Naoki
Onozawa Kazutoshi
Takasuka Shoichi
Ben Loha
Matsushita Electronics Industrial Co. Ltd.
Price and Gess
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