Optical pickup and optical information recording apparatus using the same
View Patent ↗An optical pickup includes a diffraction grating partitioned into three areas, in which the phase of periodic grating groove structure in an area is successively shifted from that in the adjacent area by 90°. In the generation of a differential push-pull signal, an amplification factor K for sub push-pull signals is varied depending on the type of the optical disk. By such composition of the optical pickup, amplitude deterioration of the tracking error signal accompanying displacement of the object lens is reduced.
1. An optical information recording/reproducing apparatus comprising:
an optical pickup; and
a tracking error signal generation unit which generates a tracking error signal according to a differential push-pull method by executing predetermined operation to signals obtained from the optical pickup;
wherein said optical pickup includes:
a laser light source which emits a laser light beam;
a diffraction grating which diffracts the laser light beam emitted by the laser light source into at least three laser light beams;
a beam splitter which transmits the at least three laser light beams; and
a detector which detects a reflected light beam from an optical disk, wherein:
the diffraction grating includes first, second and third areas, the first area is placed between the second and third areas and the second area has a periodic structure that is shifted from that of the third area by 180° in the phase of the periodic structure,
the second and third areas have periodic structures that are phase shifted from that of the first area,
the detector includes first, second and third photoreceptor surfaces, and
signals from the first, second and third photoreceptor surfaces are combined by addition and/or subtraction.
2. The optical information recording/reproducing apparatus according to claim 1 , wherein the width of said first area is narrower than the width of said second area and said third area.
3. The optical information recording/reproducing apparatus according to claim 1 , further comprising an objective lens which converges the at least three laser light beams diffracted by said diffraction grating on the optical disk,
wherein a range of the width of said first area is found to be 10% to 40% of the aperture of the object lens.
4. The optical information recording/reproducing apparatus according to claim 1 , wherein the signals associated with the second and third photoreceptor surfaces are added together and the result thereof is subtracted from the signal associated with the first photoreceptor surface.
5. The optical information recording/reproducing apparatus according to claim 1 , wherein the periodic structure of the second or third area is phase shifted by approximately 90° from the periodic structure of the first area.
6. An optical information recording/reproducing apparatus comprising:
an optical pickup; and
a tracking error signal generation unit which generates a tracking error signal according to a differential push-pull method by executing predetermined operation to signals obtained from the optical pickup;
wherein said optical pickup includes:
a laser light source which emits a laser light beam;
a diffraction grating which diffracts the laser light beam emitted by the laser light source into at least three laser light beams;
a beam splitter which transmits the at least three laser light beams; and
a detector which detects a reflected light beam from an optical disk, wherein:
the diffraction grating includes first, second and third areas, the first area is placed between the second and third areas and the second area has a periodic structure that is shifted from that of the third area by 180° in the phase of the periodic structure,
the detector includes first, second and third photoreceptor surfaces,
signals from the first, second and third photoreceptor surfaces are combined by addition and/or subtraction, and
the width of said first area is narrower than the width of said second area and said third area.
7. The optical information recording/reproducing apparatus according to claim 6 , further comprising an objective lens which converges the at least three laser light beams diffracted by said diffraction grating on the optical disk,
wherein a range of the width of said first area is found to be 10% to 40% of the aperture of the object lens.
8. The optical information recording/reproducing apparatus according to claim 6 , wherein the signals associated with the second and third photoreceptor surfaces are added together and the result thereof is subtracted from the signal associated with the first photoreceptor surface.
9. The optical information recording/reproducing apparatus according to claim 6 , wherein the periodic structure of the second or third area is phase shifted by approximately 90° from the periodic structure of the first area.