Optical pickup having a plurality of photodetectors divided into four regions used to obtain both focus and tracking error signals
View Patent ↗An optical pickup comprises: first and second semiconductor lasers ( 11, 14 ); a hologram element ( 17 ) for diffracting light reflected by an optical information recording medium ( 9 or 12 ); and a plurality of photodetectors ( 18 - 23 ). The hologram element ( 17 ) has two or more different diffraction regions. The plurality of photodetectors ( 18 - 23 ) are provided away from the first and second semiconductor lasers ( 11, 14 ) at both sides thereof along an extended line of a line between light emission positions of the first and second semiconductor lasers ( 11, 14 ). The diffracted light generated from the light beam of the first wavelength ( 10 ) by the hologram element ( 17 ) and the diffracted light generated from the light beam of the second wavelength ( 13 ) by the hologram element ( 17 ) are collected at substantially the same position at one side, and part ( 18, 19 ) of the plurality of photodetectors ( 18 - 23 ) are provided at the position. Signals obtained from the photodetectors ( 18 - 23 ) at the both sides are used to obtain a focus error signal and a tracking error signal.
1. An optical pickup, comprising:
a first semiconductor laser for emitting a light beam of a first wavelength;
a second semiconductor laser for emitting a light beam of a second wavelength, the second wavelength being different from the first wavelength;
a hologram element for diffracting reflected light generated by reflecting any one of the light beam of the first wavelength and the light beam of the second wavelength by an optical information recording medium; and
a plurality of photodetectors for receiving the diffracted light from the hologram element,
wherein the hologram element is divided into two or more different diffraction regions by one or more dividing lines passing through a center of the hologram element,
the plurality of photodetectors are provided away from the first semiconductor laser and the second semiconductor laser at both sides of a laser region including the first semiconductor laser and the second semiconductor laser, at least two or more of the plurality of the photodetectors being provided respectively at one side of the both sides and at the other side of the both sides opposite to the one side along an extended line of a line between a light emission position of the first semiconductor laser and a light emission position of the second semiconductor laser,
each of the plurality of the photodetectors provided at the one side of the both sides and at the other side of the both sides is divided into at least four regions in a direction substantially parallel to the extended line,
the diffracted light generated from the light beam of the first wavelength by the hologram element and the diffracted light generated from the light beam of the second wavelength by the hologram element are collected at substantially the same position in an area at the one side of the both sides, part of the plurality of photodetectors being provided at the position,
signals obtained both from the four regions of the plurality of the photodetectors provided at the one side of the both sides and from the four regions of the plurality of the photodetectors provided at the other side of the both sides are used to obtain both a focus error signal and a tracking error signal,
the second wavelength of the light beam of the second semiconductor laser is longer than the first wavelength of the light beam of the first semiconductor laser,
the number of the photodetectors provided at the other side is greater than that of the photodetectors provided at the one side,
the photodetectors provided at the one side are nearer to the first semiconductor laser than the second semiconductor laser, and
the photodetectors provided at the one side are provided away from each other.
2. The optical pickup according to claim 1 , wherein at least one of the photodetectors provided at the other side has a longer dimension in the direction of the extended line than those of the photodetectors provided at the one side.
3. The optical pickup according to claim 1 , wherein each of the plurality of photodetectors is separated with an interval.
4. An optical pickup, comprising:
a first semiconductor laser for emitting a light beam of a first wavelength;
a second semiconductor laser for emitting a light beam of a second wavelength, the second wavelength being different from the first wavelength;
a diffraction grating for dividing any one of the light beam emitted by the first semiconductor laser and the light beam emitted by the second semiconductor laser into a 0th order main beam and 1 st order sub-beams;
a hologram element for diffracting reflected light generated by reflecting the 0th order main beam and the 1st order sub-beams by an optical information recording medium; and
a plurality of photodetectors for receiving the diffracted light from the hologram element,
wherein the hologram element is divided into two or more different diffraction regions by one or more dividing lines passing through a center of the hologram element,
photodetectors for receiving the diffracted light generated from the 0th order main beam by the hologram element are provided away from the first semiconductor laser and the second semiconductor laser at both sides of the first and second semiconductor lasers, at least two or more of the plurality of the photodetectors being provided respectively at one side of the both sides and at the other side of the both sides opposite to the one side along an extended line of a line between a light emission position of the first semiconductor laser and a light emission position of the second semiconductor laser,
each of the plurality of the photodetectors provided at the one side of the both sides and at the other side of the both sides is divided into at least four regions in a direction substantially parallel to the extended line,
the diffracted light generated from the 0th order main beam of the first wavelength by the hologram element and the diffracted light generated from the 0th order main beam of the second wavelength by the hologram element are collected at substantially the same position in an area at the one side of the both sides, the photodetectors being provided at the position,
signals obtained both from the four regions of the plurality of the photodetectors provided at the one side of the both sides and from the four regions of the plurality of the photodetectors provided at the other side of the both sides are used to obtain both a focus error signal and a tracking error signal,
the second wavelength of the light beam of the second semiconductor laser is longer than the first wavelength of the light beam of the first semiconductor laser,
the number of the photodetectors provided at the other side for receiving the diffracted light derived from the 0th order main beam is greater than that of the photodetectors provided at the one side for receiving the diffracted light derived from the 0th order main beam,
the photodetectors provided at the one side are nearer to the first semiconductor laser than the second semiconductor laser, and
the photodetectors provided at the one side are provided away from each other.
5. The optical pickup according to claim 4 , wherein at least one of the photodetectors provided at the other side for receiving the diffracted light derived from the 0th order main beam has a longer dimension in the direction of the extended line than those of the photodetectors provided at the one side for receiving the diffracted light derived from the 0th order main beam.
6. The optical pickup according to claim 4 , wherein each of the plurality of photodetectors is separated with an interval.
7. The optical pickup according to any one of claims 1 and 4 , wherein at least at a side behind the first semiconductor laser when viewed from the position of the second semiconductor laser, when diffracted light generated by the hologram element from the light beam of the first wavelength reflected by an information recording medium and diffracted light generated by the hologram element from the light beam of the second wavelength reflected by an information recording medium have the same diffraction order, these diffracted light impinge on the same photodetector.