An optical-pickup hologram element has six regions on an x-y plane, divided as follows: the first region with a first line (an x-axis) and a second line that connects points (−xa, 0) and (−xb, yb); the second region with the first and second lines and a third line connecting points (xa, 0) and (xb, yb); the third region with the first and third lines; the fourth region with the first line and a fourth line connecting the point (xa, 0) and a point (xb, −yb); the fifth region with the first and fourth lines and a fifth line connecting the point (−xa, 0) and a point (−xb, −yb); and the sixth region with the first and fifth lines (xa<xb and −xb<−xa). The second and fifth, and the other regions are given astigmatism at different angles to the second line.
1. An optical pickup comprising:
a laser source for emitting a laser beam to an optical disc;
a hologram element provided on an optical axis of the laser beam and having a hologram section provided on a specific area of the hologram element, the hologram section diffracting a return beam reflected by the optical disc; and
a photo receptor for receiving the return beam diffracted by the hologram element,
wherein the specific area of the hologram element has an x-y plane having a center coordinate point (0, 0), an x-axis that is a first line passing the center coordinate point (0, 0), and a y-axis that is a second line passing the center coordinate point (0, 0) and crossing the first line, and
the specific area has a first hologram region, a second hologram region, a third hologram region, a fourth hologram region, a fifth hologram region, and a sixth hologram region on the x-y plane,
in which the first hologram region is divided from the second to sixth hologram regions by a first split line that is the first line and a second split line that connects coordinate points (−xa, 0) and (−xb, yb) on the x-y plane,
the second hologram region is divided from the first, third, fourth, fifth, and sixth hologram regions by the first and second split lines and a third split line that connects coordinate points (xa, 0) and (xb, yb) on the x-y plane,
the third hologram region is divided from the first, second, fourth, fifth, and sixth hologram regions by the first and third split lines on the x-y plane,
the fourth hologram region is divided from the first, second, third, fifth, and sixth hologram regions by the first split line and a fourth split line that connects the coordinate point (xa, 0) and a coordinate point (xb, yb) on the x-y plane,
the fifth hologram region is divided from the first, second, third, fourth, and sixth hologram regions by the first and fourth split lines and a fifth split line that connects the coordinate point (−xa, 0) and a coordinate point (−xb, −yb) on the x-y plane, and
the sixth hologram region is divided from the first, second, third, fourth, and fifth hologram regions by the first and fifth split lines on the x-y plane,
in which xa and xb, and −xa and −xb satisfy relations xa<xb and −xb<−xa, respectively, and
the second and fifth hologram regions are applied with astigmatism at a first specific angle to the second line and the first, third, fourth, and sixth hologram regions are applied with astigmatism at a second specific angle different from the first specific angle to the second line.
2. The optical pickup according to claim 1 , wherein the second split line connects the coordinate points (−xa, 0) and (−xb, yb) via a coordinate point (−xa, ya) on the x-y plane in which ya and yb satisfies a relation ya<yb.
3. The optical pickup according to claim 1 , wherein the third split line connects the coordinate points (xa, 0) and (xb, yb) via a coordinate point (xa, ya) on the x-y plane in which ya and yb satisfies a relation ya<yb.
4. The optical pickup according to claim 1 , wherein the fourth split line connects the coordinate points (xa, 0) and (xb, −yb) via a coordinate point (xa, −ya) on the x-y plane in which −ya and −yb satisfies a relation −yb<−ya.
5. The optical pickup according to claim 1 , wherein the fifth split line connects the coordinate points (−xa, 0) and (−xb, −yb) via a coordinate point (−xa, −ya) on the x-y plane in which −ya and −yb satisfies a relation −yb<−ya.
6. The optical pickup according to claim 1 , each of the second to sixth split lines is a straight or a curved line.