Recording/reproducing apparatus

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, 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.

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,
• 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,
• the first diffraction grating element and the second diffraction grating element are different in characteristics,
• the generation circuit generates the focus error signal based on an astigmatic method, and
• the first diffraction grating has a diffraction efficiency of the zero-order beam lower than that of the second diffraction grating.

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,
• 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,
• the first diffraction grating element and the second diffraction grating element are different in characteristics,
• the generation circuit generates the focus error signal based on an astigmatic method,
• 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, and
• the third diffraction grating has a diffraction efficiency of the zero-order beam lower than that of the fourth diffraction grating.