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Optical head device and optical information reproducing device

a head device and optical information technology, applied in the direction of data recording, disposition/mounting of heads, instruments, etc., can solve the problems of deterioration of recording/reproducing characteristics, avoid adverse effects of recording/reproducing characteristics, and improve the signal to noise ratio of rf signals.

Inactive Publication Date: 2009-07-30
NEC CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The present invention provides a method for detecting radial tilt of an optical recording medium in an optical head device with an improved signal to noise ratio of the RF signal. The method involves dividing emitted light from a light source into a main beam and a sub-beam, focusing the main beam and the sub-beam onto the optical recording medium, and receiving the reflected light by four light receiving sections. The position of the peaks of the focused spots in the radial direction of the optical recording medium is shifted due to coma aberration caused by the substrate of the medium, resulting in a phase shift between the track error signals by the main beam and the sub-beam. By detecting this phase shift, the radial tilt of the optical recording medium can be determined. The optical head device and optical information recording / reproducing device of the present invention comprise the light source, diffractive optical element, objective lens, and photodetector for achieving this detection method.

Problems solved by technology

On the other hand, when the optical recording medium tilts against the objective lens in the radial direction, the shape of the focused spot becomes disturbed due to coma aberration caused by a substrate of the optical recording medium so that the recording / reproducing characteristics become deteriorated.

Method used

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  • Optical head device and optical information reproducing device
  • Optical head device and optical information reproducing device
  • Optical head device and optical information reproducing device

Examples

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first embodiment

[0031]FIG. 1(A) shows an optical head device according to the present invention. Light emitted from a semiconductor laser 1 is collimated by a collimator lens 2. The collimated light is then divided into three light beams by a diffractive optical element 3a which are 0th-order light as a main beam and ±1st-order diffracted lights as sub-beams. The light beams enter a polarizing beam splitter 4 as P polarized light and substantially 100% transmit therethrough. Then, they transmit through quarter-wave plate 5 to be converted from linearly polarized light to circularly polarized light thereby to be focused onto a disk 7 by an objective lens 6.

[0032]Three light beams reflected from the disk 7 transmit inversely through the objective lens 6 and then transmit the quarter-wave plate 5 to be converted from the circularly polarized light to linearly polarized light whose polarization direction is orthogonal to that in the outward path. The light beams then enter the polarizing beam splitter ...

fourth embodiment

[0062]In the first to fourth embodiment, when there is residual error, caused by eccentricity of the disk 7 and the like, in the track error signal used for applying track servo, offset due to the residual error is also generated in the track error signal by the sub-beams as the radial tilt signal.

[0063]However, if the signal obtained by subtracting the track error signal used for applying the track servo from the track error signal by the sub-beams is used as the radial tilt signal, it is possible to detect radial tilt without generating offset in the radial tilt signal due to the residual error.

[0064]In a fifth embodiment of an optical head device according to the present invention, the diffractive optical element 3a in the first embodiment is replaced with a diffractive optical element 3e. FIG. 5(A) is a plan view showing the diffractive optical element 3e. The diffractive optical element 3e has the following structure. Diffraction gratings, which are divided into two regions 11e...

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Abstract

The light emitted from a semiconductor laser is divided by a diffractive optical element into three light beams which are 0th-order light as the main beam and ±1st-order diffracted lights as the sub-beams, and the track error signals by the main beam and the sub-beams are detected, respectively, by a differential phase detection method. By the effect of the diffractive optical element, the light intensity distributions of the main beam and the sub-beams become different when making incidence on an objective lens. Therefore, when there is radial tilt in a disk, the phases of the track error signals by the main beam and the sub-beams are shifted with each other. Based on the shift in the phases of the track error signals, radial tilt of the disk is detected.

Description

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS[0001]This application is a division of application Ser. No. 10 / 437,915, filed May 15, 2003, now pending, and based on Japanese Patent Application No. 2002-149074, filed May 23, 2002, by Ryuichi Katayama, which are incorporated herein by reference in their entirety. This application claims only subject matter disclosed in the parent application and therefore presents no new matter.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates to a method for detecting radial tilt of an optical recording medium in an optical head device for performing recording / reproducing on an optical recording medium, an optical head device, and an optical information recording / reproducing device. More specifically, it relates to a method for detecting radial tilt of an optical recording medium in an optical head device, which is capable of detecting radial tilt of a read-only type optical recording medium, an optical hea...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): G11B7/135G11B7/09G11B7/095
CPCG11B7/0956G11B7/0906
Inventor KATAYAMA, RYUICHI
Owner NEC CORP
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