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Optical pickup apparatus and optical disc apparatus using same

a pickup apparatus and optical disc technology, applied in the field of optical disc pickup apparatus and optical disc apparatus using same, can solve the problems of reducing the light use efficiency of the main light flux, prone to direct current fluctuation (referred to as a dc offset hereinafter), and disadvantageous to use the diffraction grating for an outward optical system

Inactive Publication Date: 2008-04-24
KAMISADA TOSHIMASA +4
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0010]In the optical pickup apparatus, generally, in order to correctly irradiate a spot on a given record track in the optical disc, an objective lens is displaced in the focusing direction through the detection of a focus error signal, thus the objective lens being adjusted in the focus direction. Furthermore, the objective lens is displaced in the radial direction of a disc shape recording medium through the detection of a tracking error signal, thus the tracking adjustment is performed. These signals allow the objective lens to be position-controlled.

Problems solved by technology

While a push pull method is known as a tracking error signal detection method of the above error signal detections, it has a problem that a direct current fluctuation (referred to as a DC offset hereinafter) is prone to occur.
However, since the differential push pull method forms a plurality of spots on the optical disc, light use efficiency of the main light flux decreases.
Therefore, it is disadvantageous to use the diffraction grating for an outward optical system from a viewpoint of writing speed.

Method used

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  • Optical pickup apparatus and optical disc apparatus using same
  • Optical pickup apparatus and optical disc apparatus using same
  • Optical pickup apparatus and optical disc apparatus using same

Examples

Experimental program
Comparison scheme
Effect test

embodiment 1

[0056]FIG. 1 is a diagram showing the structure of the optical pickup apparatus according to the present invention.

[0057]A laser light 2 emitted from a semiconductor laser 1 is reflected by a polarizing beam splitter 3 and converted into a parallel light flux by a collimate lens 4. The parallel light flux passes through a polarizing diffraction grating 5 and a one-quarter wave plate 6, and is focused by a objective lens 7 on an optical disc 8. The optical disc 8 is provided with a recording and reproducing layer (information recording layer) comprising two layers of a first layer 9 and a second layer 10, with each layer being formed with a track (not shown) in the direction of arrow 11.

[0058]When any of the two recording and reproducing layers of the optical disc is in focus, the laser light is reflected by the optical disc 8 and passes through the objective lens 7 and one-quarter wave plate 6. Then, the laser flux is divided by the polarizing diffraction grating 5 to enter a plural...

embodiment 2

[0095]FIGS. 7 and 8 show the shapes of divided regions of the polarizing diffraction grating 5 in an embodiment 2 and the shapes of light patterns irradiated onto the light detector 12 at that time. The light pattern 28 of the reflected light from the first layer 9 is focused on the light detector 12, and the light pattern 29 (stray light) of the reflected light from the second layer 10 at that time is shown by oblique lines. A difference from the embodiment 1 is that the width Wc of the regions C1 to C4 in the X-axis direction is narrower. The regions B1 to B4 are larger by just that much. The shapes of the regions A1 to A4 are the same as those of the embodiment 1. Since the regions B1 to B4 are larger, the stray light is more likely to enter the light receiving parts E to F and Q to T when the light detector 12 is displaced. However, an effect is expected that increases the output of the tracking error signal.

embodiment 3

[0096]FIGS. 9 and 10 show the shapes of divided regions of the polarizing diffraction grating 5 in an embodiment 3 and the shapes of light patterns irradiated onto the light detector 12 at that time. The light pattern 28 of the reflected light from the first layer 9 is focused on the light detector 12, and the light pattern 29 (stray light) of the reflected light from the second layer 10 at that time is shown by oblique lines.

[0097]A difference from the embodiment 1 is that there are not the four dividing lines 18 in the X-axis direction that do not pass through the light flux center 14, and the four dividing lines 19 that form an angle of 30 degrees with respect to the Y-axis direction extend longer around the light flux center 14. Therefore, the areas of the region B1 to B4 are reduced, and thereby the outputs of the light receiving parts Q to T are reduced. Accordingly, it is necessary to increase the value of K in the following computing equation for the tracking error signal ac...

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Abstract

A method of detecting a servo signal of an optical disc having a plurality of recording layers includes focusing and irradiating a laser light onto the optical disc, dividing a laser light reflected from the optical disc into a plurality of reflected laser lights by a division element, wherein each of said reflected laser lights having a different outgoing direction, and irradiating the reflected laser lights onto a plurality of light receiving parts of a light detector. A focus error signal is detected under a knife edge method and a tracking error signal is detected.

Description

CROSS REFERENCE TO RELATED APPLICATION[0001]This application is a divisional of U.S. application Ser. No. 11 / 680,705, filed Mar. 1, 2007, the contents of which are incorporated herein by reference. This application relates to U.S. application Ser. Nos. ______, ______, and ______, filed Oct. 30, 2007, which are divisional applications of U.S. Ser. No. 11 / 680,705, filed Mar. 1, 2007.INCORPORATION BY REFERENCE[0002]The present application claims priorities from Japanese applications JP2006-283248 filed on Oct. 18, 2006, JP2006-283245 filed on Oct. 18, 2006, the contents of which are hereby incorporated by reference into this application.BACKGROUND OF THE INVENTION[0003]The present invention relates to an optical disc apparatus for recording information on or reproducing information from an optical disc, and to an optical pickup apparatus used for the same. More particularly, the present invention relates to an optical disc apparatus for recording information on or reproducing informati...

Claims

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Application Information

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IPC IPC(8): G11B5/58G11B7/13G11B7/135
CPCG11B7/0901G11B7/0906G11B7/094G11B7/0943G11B2007/0013G11B7/133G11B7/1353G11B7/1381G11B7/131
Inventor KAMISADA, TOSHIMASAKITADA, YASUOYAMAZAKI, KAZUYOSHIKAWAMURA, TOMOTOKONISHI, YOSHIRO
Owner KAMISADA TOSHIMASA