Optical pick up apparatus with a single beam system and having a diffraction grating
An optical pickup apparatus includes a semiconductor laser for emitting a laser light, an objective lens for irradiating the light flux emitted from the semiconductor laser onto an optical disc, and a light detector for receiving the light flux reflected from the optical disc. The light detector has a light receiving part that comprises five regions of a region 1 , a region 2 , a region 3 , a region 4 and a region 5.
1. An optical pickup apparatus with a single beam system, comprising:
a semiconductor laser for emitting a laser light;
an objective lens for irradiating the laser light emitted from the semiconductor laser as a single beam onto an optical disc;
a diffraction grating for dividing the laser light reflected from the optical disc; and
a light detector for receiving the laser light divided by the diffraction grating, wherein
the diffraction grating has five regions of a region 1 , a region 2 , a region 3 , a region 4 and a region 5 ;
the region 1 and the region 3 are line-symmetrical to the region 2 and the region 4 of the diffraction grating with respect to a center line of the diffraction grating;
the region 5 of the diffraction grating is formed line-symmetrically with respect to the center line and is formed on the center line;
the regions 1 and 2 of the diffraction grating include portions which become narrower in width with the distance away from the center line, wherein the portions also become narrower in width in a light irradiated area of the diffraction grating with distance away from the center line;
the portion of the region 1 defines boundaries between the regions 1 and 3 , and the portion of the region 2 defines boundaries between the regions 2 and 4 ;
the portions of the regions 1 and 2 extend beyond the light irradiated area of the diffraction grating, so that when the portions of regions 1 and 2 are at a point of crossing an end of the light irradiated area of the diffraction grating, opposite straight edges of the portion of the region 1 are non-parallel to each other and opposite straight edges of the portion of the region 2 are non-parallel to each other;
signals detected by the light detector from diffracted lights in the region 1 , the region 2 , the region 3 and the region 4 of the diffraction grating are outputted by the light detector; and
the center line extends in parallel to a track direction of the optical disc.
2. The optical pickup apparatus with the single beam system of claim 1 , wherein each of the regions 1 and 2 has a non-rectangular substantially trapezoidal configuration from a position of a beginning of narrowing of the width of the portions of the regions 1 and 2 .
3. The optical pickup apparatus with the single beam system of claim 1 , wherein the width of the portions of the regions 1 and 2 is at least partially delimited by the opposite non-parallel straight edges which become closer to one another as the distance from the center line increases.
4. The optical pickup apparatus with the single beam system of claim 1 , wherein the portions of the regions 1 and 2 are arranged line-symmetric with respect to another line that extends in a direction perpendicular to the center line, wherein the another line cuts the regions 1 and 2 in a half.
5. The optical pickup apparatus with the single beam system of claim 4 , wherein the width of the portions of the regions 1 and 2 is measured in a direction perpendicular to the another line.
6. An optical disc apparatus, comprising:
an optical pickup apparatus with a single beam system comprising:
a semiconductor laser for emitting a laser light;
an objective lens for irradiating the laser light emitted from the semiconductor laser as a single beam onto an optical disc;
a diffraction grating for dividing the laser light reflected from the optical disc; and
a light detector for receiving the laser light divided by the diffraction grating, wherein
said diffraction grating has five regions of a region 1 , a region 2 , a region 3 , a region 4 and a region 5 ;
the region 1 and the region 3 are line-symmetrical to the region 2 and the region 4 of the diffraction grating with respect to a center line of the diffraction grating;
the region 5 of the diffraction grating is formed line-symmetrically with respect to the center line and is formed on the center line;
the regions 1 and 2 of the diffraction grating include portions which become narrower in width with the distance away from the center line, wherein the portions also become narrower in width in a light irradiated area of the diffraction grating with distance away from the center line;
the portion of the region 1 defines boundaries between the regions 1 and 3 , and the portion of the region 2 defines boundaries between the regions 2 and 4 ;
the portions of the regions 1 and 2 extend beyond the light irradiated area of the diffraction grating, so that when the portions of the regions 1 and 2 are at a point of crossing an end of the light irradiated area of the diffraction grating, opposite straight edges of the portion of the region 1 are non-parallel to each other and opposite straight edges of the portion of the region 2 are non-parallel to each other;
signals detected by the light detector from diffracted lights in the region 1 , the region 2 , the region 3 and the region 4 of the diffraction grating are outputted by the light detector;
the center line extends in parallel to a track direction of the optical disc; and
a servo signal generating circuit for generating a tracking error signal using a signal outputted from said optical pickup apparatus, wherein the servo signal generating circuit generates the tracking error signal according to
(A1−A2)−k×(A3−A4)
wherein, A 1 is a signal corresponding to a light incident in the region 1 and detected by the light detector, A 2 is a signal corresponding to a light incident in the region 2 and detected by the light detector, A 3 is a signal corresponding to a light incident in the region 3 and detected by the light detector, A 4 is a signal corresponding to a light incident in the region 4 and detected by the light detector, and k is a coefficient for correcting amounts of light.
7. The optical pickup apparatus with the single beam system of claim 6 , wherein each of the regions 1 and 2 has a non-rectangular substantially trapezoidal configuration from a position of a beginning of narrowing of the width of the portions of the regions 1 and 2 .
8. The optical pickup apparatus with the single beam system of claim 6 , wherein the width of the portions of the regions 1 and 2 is at least partially delimited by the opposite non-parallel straight edges which become closer to one another as the distance from the center line increases.
9. The optical pickup apparatus with the single beam system of claim 6 , wherein the portions of the regions 1 and 2 are arranged line-symmetric with respect to another line that extends in a direction perpendicular to the center line, wherein the another line cuts the regions 1 and 2 in a half.
10. The optical pickup apparatus with the single beam system of claim 9 , wherein the width of the portions of the regions 1 and 2 is measured in a direction transverse to the another line.