Recording/reproducing apparatus

Patent metadata

Field	Value
Publication number	US-2016171997-A1
Application number	US-201615050665-A
Country	US
Kind code	A1
Filing date	Feb 23, 2016
Priority date	Sep 10, 2013
Publication date	Jun 16, 2016
Grant date	—

Abstract

According to an embodiment, a recording/reproducing apparatus includes a diffraction grating and a light-receiving element. The diffraction grating divides return light from the guide layer in accordance with areas. The areas include a first area and a second area that does not overlap the first area. The light-receiving element includes (i) a first detecting cell group which receives a zero-order beam to which astigmatism is imparted, (ii) a second detecting cell group which receives at least one of a positive and negative first-order beam, which passes the first area and made astigmatic, and (iii) a third detecting cell group which receives at least one of a positive and negative first-order beam, which passes the second area and made astigmatic.

First claim

What is claimed is:

1 . A recording/reproducing apparatus comprising:
an objective lens which focuses guide light on a guide layer in an information recording medium and which focuses information recording light on an information recording layer in the information recording medium; an area-dividing diffraction grating which divides return light from the guide layer in accordance with a plurality of areas, including a first area and a second area that does not overlap the first area; an astigmatic optical system which imparts astigmatism to a zero-order beam, a positive first-order beam and a negative first-order beam, into which the return light is divided by the area-dividing diffraction grating; a light-receiving element including (i) a first light-detecting cell group which receives a zero-order beam to which astigmatism is imparted by the astigmatic optical system, (ii) a second light-detecting cell group which receives at least one of a positive first-order beam and a negative first-order beam, which passes the first area and made astigmatic by the astigmatic optical system, and (iii) a third light-detecting cell group which receives at least one of a positive first-order beam and a negative first-order beam, which passes the second area and made astigmatic by the astigmatic optical system; and a generation circuit which generates a focus error signal based on an amount of light falling on the first light-detecting cell group, and generates a wobble reproduction signal based on an amount of light falling on the second light-detecting cell group and the third light-detecting cell group.

2 . The apparatus according to claim 1 , wherein the generation circuit generates a tracking error signal based on the amount of light falling on the second light-detecting cell group, generates a sub tracking signal based on the amount of light falling on the third light-detecting cell group, and compensates for a variation of an offset component of the tracking error signal, which is caused when the objective lens is driven, by the sub tracking signal.

3 . The apparatus according to claim 2 , wherein the generation circuit compensates for the variation of the offset component by multiplying the sub tracking signal by a positive constant and subtracting a resultant mathematical product from the tracking error signal.

4 . The apparatus according to claim 1 , wherein the generation circuit generates a tracking error signal based on the amount of light falling on the second light-detecting cell group, generates a sub tracking signal based on the amount of light falling on the third light-detecting cell group, and generates the wobble reproduction signal by multiplying the sub tracking signal by a positive constant, adding a resultant mathematical product to the tracking error signal, and extracting a high-frequency component corresponding to a result of addition.

5 . The apparatus according to claim 1 , wherein the first area includes an interference area caused by the zero-order beam and the positive and negative first-order beams of the return light from the guide layer.

6 . The apparatus according to claim 1 , wherein the area-dividing diffraction grating includes a first diffraction grating element corresponding to the first area and a second diffraction grating element corresponding to the second area, and
the first diffraction grating element and the second diffraction grating element are different in characteristics.

7 . The apparatus according to claim 6 , wherein the generation circuit generates the focus error signal based on an astigmatic method.

8 . The apparatus according to claim 7 , wherein the first diffraction grating has a diffraction efficiency of the zero-order beam lower than that of the second diffraction grating.

9 . The apparatus according to claim 7 , wherein the second area includes a third area which is a center portion close to an optical axis of the return light and a fourth area which is a circumferential portion other than the third area,
the second diffraction grating element includes a third diffraction grating element corresponding to the third area and a fourth diffraction grating corresponding to the fourth area, the third diffraction grating has a diffraction efficiency of the zero-order beam lower than that of the fourth diffraction grating.

10 . The apparatus according to claim 9 , wherein the first diffraction grating element has a diffraction efficiency of the zero-order beam lower than that of the fourth diffraction grating element.

Assignees

• Toshiba Kk

Inventors

• Okano Hideaki
• Watabe Kazuo
• Ogawa Akihito
• Usui Takashi

Classifications

• G11B7/1374

  Objective lenses {(optical objectives per se G02B9/00)} · CPC title

• G11B7/13927 Primary

  during transducing, e.g. to correct for variation of the spherical aberration due to disc tilt or irregularities in the cover layer thickness · CPC title

• G11B7/1353

  Diffractive elements, e.g. holograms or gratings {(diffraction gratings per se G02B5/18; holograms per se G02B5/32; grating systems G02B27/44)} · CPC title

• G11B7/0053

  Reproducing non-user data, e.g. wobbled address, prepits, BCA · CPC title

• G11B7/0903

  Multi-beam tracking systems · CPC title