Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
2001-09-17
2003-07-15
To, Doris H. (Department: 2653)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S044230, C369S044370, C369S044420, C369S112210, C369S112280, C369S112120
Reexamination Certificate
active
06594221
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical pickup device for emitting a beam of light to read information from a storage medium.
2. Description of the Related Art
An optical pickup device is adapted to operate under the focusing servo control and the tracking servo control to accurately read information stored on the tracks of an optical storage medium such as an optical disk. The focusing servo control is adapted to move an objective lens back and forth relative to the storage surface of the storage medium such that a beam of light for illuminating the storage medium is focused on the storage surface. On the other hand, the tracking servo control is adapted to translate the objective lens in a direction perpendicular to the tangential direction of the track such that the beam of light is positioned on the track of the storage surface.
The focusing servo control generates a focus error signal indicative of the degree of focus error in accordance with the level of received light reflected from the storage medium and allows a focusing actuator to drive the objective lens back and forth in order to reduce the focus error signal.
The tracking servo control generates a tracking error signal indicative of the degree of tracking error in accordance with the level of received light reflected from the storage medium and allows a tracking actuator to drive the objective lens in the radial direction of the optical disk in order to reduce the focus error signal.
For example, the methods for generating the focus error signal in the focusing servo control include the so-called spot size method or astigmatism method, while the methods for generating the tracking error signal in the tracking servo control include a so-called three-beam method.
In the spot size method and the three-beam method, a diffraction grating, a hologram or the like is employed to split a single beam of light into one diffracted beam of 0th order and two diffracted beams of +/− first order. Of these beams of light, the beam of 0th order is called the main beam, while the beams of +1st and −1st order are called the side beams.
It has been generally practiced to obtain the focus error signal by the main beam in an optical pickup device that employs a plurality of beams of light as well as in an optical pickup device employing the three-beam method. That is, the side beams other than the main beam are subjected substantially in vain to optical action or would rather have a harmful effect such as crosstalk between optical beam signals on a light-receiving element of an optical detector (hereinafter referred to as the detector). For example, in a generally organized differential size spot method, a hologram element is placed at a portion where the three beams are not separately available, thereby making two light beams having different focal lengths available. The three-beam method provides for a total of 6 light beams (=3×2). This causes the number of optical beam spots to increase on the detector, whereby an additional number of subdivisions (light-receiving elements) are required of the detector corresponding to the increase.
For example, such an optical pickup device has been suggested which employs the three-beam method as disclosed in Japanese Patent Laid-Open Publication No. Hei 8-55363.
As shown in
FIG. 1
, the optical pickup device disclosed therein includes a module which is integrated with a laser detector and has a hologram element formed of parallel flat plates. A divergent beam
63
b
emitted from a semiconductor laser
1
b
is reflected upon a mirror
82
and incident on the hologram element. The hologram element is provided with a hologram
17
and an annular grating
83
. The light beam incident on the hologram element passes through the annular grating
83
and is then split into three beams of 0th and +/− 1st orders, whereby the main and side beams for tracking are generated.
The three beams pass through the hologram
17
and then an objective lens (not shown) to converge each as an optical spot on an optical disk (not shown).
Each optical spot reflected and diffracted on the optical disk passes again through the objective lens to be then incident on the hologram element as a return light beam. Each of the return light beams incident on the hologram element passes through the hologram
17
to be then split into three beams. This yields six beams in total, or diffracted beams of +/− 1st orders are received by an optical detector
13
b
and converted into electrical signals. Then, the electrical signals delivered by the optical detector
13
b
is operated as desired, thereby making it possible to provide a focus error signal, a tracking error signal, and a written information signal.
In the prior art disclosed in Japanese Patent Laid-Open Publication No. Hei 8-55363, the hologram
17
is placed before where the main and side beams of the return light are split physically and spatially. Accordingly, the optical pickup device is optically designed such that, of the nine beams obtained by splitting the main and side beams of the return light, specific diffracted beams are made available. In this prior art, the three-beam method also provides six optical beam spots in total, resulting in an increase in number of the subdivisions of the detector. The optical design of the hologram
17
is also made complicated.
The optical pickup device cannot be made large for use with a storage medium read device such as an optical disk player. It is therefore desired to make compact the portions related to the focusing servo control and the tracking servo control.
OBJECT AND SUMMARY OF THE INVENTION
In view of the aforementioned problems, an object of the present invention is to provide a compact optical pickup device which can accomplish the focusing servo control and the tracking servo control with stability.
The optical pickup device according to the present invention includes an illuminating optical system for focusing a light beam, split in a main beam and at least one side beam, onto a track on an information storage surface of an optical storage medium to form optical spots thereon. The device also includes a light detecting optical system for introducing return light reflected back from the information storage surface, and a polarizing optical element. The polarizing optical element has regions split at the center of an optical path by a parting line extending at least either in a direction of extension of the track or in a direction perpendicular to the direction of extension. The polarizing optical element also splits the main beam return light at least in two for each of the regions on a plane perpendicular to the optical path of the return light of the reflected main beam in the light detecting optical system. The polarizing optical element is disposed where the return light of the main and side beams is spatially separated. The optical pickup device further includes an optical detector disposed in contact with the polarizing optical element. The optical detector has a plurality of main-beam light-receiving elements for receiving the separated main beam return light and a plurality of side-beam light-receiving elements for receiving the separated side beam return light.
In one aspect of the optical pickup device according to the present invention, said polarizing optical element comprises a parallel plate portion formed of an optically transparent material, and a split reflecting surface, formed on a side of light emission of said parallel plate portion, for reflecting return light in said split regions, and
said main and side beam light-receiving elements are formed on the side of light emission of said parallel plate portion, and two or more main-beam light-receiving elements are disposed to allow said separated main beam return light to be reflected at a boundary surface on a side of light incidence of said parallel plate portion to reach said main-beam light-receiving element.
In another aspect of t
Morgan & Lewis & Bockius, LLP
Patel Gautam R.
Pioneer Corporation
To Doris H.
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