JP2616722B2 - Optical head device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device and, more particularly, to an optical head device for recording and reproducing information using super-resolution for the purpose of increasing the density of an optical disk.

[0002]

2. Description of the Related Art In recent years, for the purpose of increasing the density of an optical information recording medium, there has been proposed an optical head device in which the focused spot diameter is reduced by using super-resolution (Japanese Patent Laid-Open No. 4-74320). FIG. 13 shows a configuration diagram of an example of a conventional optical head device using this super-resolution. In the figure, a semiconductor laser 1
Is collimated by the collimator lens 2, enters the diffraction grating 54, and is divided into a main beam as transmitted light and two sub-beams as ± 1st-order diffracted light.

[0003] These beams are split by a beam splitter 55.
, And is condensed on the optical disk 8 by the objective lens 7. The reflected light from the optical disk 8 travels backward through the incident optical path, passes through the objective lens in the opposite direction, and passes through the beam splitter 55.
After the light is reflected by the lens 12 and passes through the lens 12 and the cylindrical lens 13, the light is received by the photodetector 56.

FIG. 14 is a diagram showing an example of the configuration of a diffraction grating 54. As shown in the drawing, the diffraction grating 54 has a grating formed only in the central region 57 in the light beam cross section of the incident light. Of the incident light, the light at the center incident on the region 57 is almost completely diffracted, and becomes two sub-beams of ± 1st-order diffracted light. Further, the light of the peripheral portion incident on the outside of the region 57 is almost completely transmitted and becomes a main beam.

FIG. 15 shows the intensity distribution of the main beam and two sub-beams at the condensing position on the optical disk 8. Since the intensity of the main beam becomes almost zero at the center part by the diffraction grating 54, the optical disk 8
As shown in FIG. 15, the diameter of the main lobe 58a at the upper condensing position is reduced as compared with the case where the diffraction grating 54 is not provided, while the side lobe 58a is reduced.
The height of b increases.

The sub-beams 59 and 60 have almost zero light intensity in the periphery due to the diffraction grating 54.
Due to the apodization effect, the condensed spot has a large main lobe diameter and almost no side lobes occur.

FIG. 16 shows an arrangement of a main beam and two sub beams with respect to a track on the optical disk 8. The center of the main beam 58 is located substantially at the center of the track 19, and one of the sub-beams 59 and 60 is located at a position preceding the spot of the main beam 58, and
9, the other of the two sub-beams is a position following the spot of the main beam 58,
And it is controlled by the track servo so as to be located on the left or right edge of the track 19.

FIG. 17 shows the pattern of the light receiving portion of the photodetector 56 of FIG. 13 and the arrangement of the spots on the light receiving portion. The photodetector 56 has four divided light receiving units 61 to 64 and independent light receiving units 65 and 66. The main beam 58 reflected by the optical disk 8 forms a spot 67 at substantially the center of the four divided light receiving units 61 to 64. The sub-beams 59 and 60 reflected by the optical disk 8 separately form spots 68 and 69 on the independent light receiving units 65 and 66, respectively.

Output values of electric signals obtained by photoelectric conversion by the light receiving units 61 to 66 are respectively represented by V (61) to V (6).
Assuming that the focus error signal is expressed by 6), the focus error signal is obtained by a known astigmatism method by {V (61) + V (64)} − ΔV
(62) + V (63)}. Further, the track error signal is obtained by a known three-beam method by ΔV (6
5) -V (66)}, the information signal is {V
(61) + V (62) + V (63) + V (64)}.

As described above, by reducing the condensing spot diameter of the main beam by using the super-resolution in the optical head device, not only the optical disk having the normal track pitch but also the track pitch for high density can be reduced. The reproduced optical disk can be reproduced.

[0011]

However, in the above-described conventional optical head device, the sub-beams 59 and 60 are not provided.
In order to make the center of the spot on the optical disk coincide with the edge of the track 19, in the case of an optical disk having a normal track pitch and the case of an optical disk having a reduced track pitch, a straight line connecting the center of each spot of the sub-beams 59 and 60 is It is necessary to change the angle made. Since this requires rotation of the diffraction grating 54 or the entire optical head device, there is a problem that the mechanism becomes complicated.

In the conventional optical head device, the diameter of the converging spot of the sub-beams 59 and 60 is enlarged by the apodization effect. Therefore, there is a problem that accurate tracking operation cannot be performed.

The present invention has been made in view of the above points,
In both cases of an optical information recording medium having a normal track pitch and an optical information recording medium having a reduced track pitch, a track error signal can be obtained without providing a complicated mechanism. An object of the present invention is to provide an optical head device capable of obtaining a sufficient amplitude of a track error signal even for a recording medium.

[0014]

In order to achieve the above object, the present invention provides a light source for emitting laser light, and diffracts a central portion of a light beam cross section of the laser light from the light source as first and second sub-beams. A diffraction grating for transmitting a peripheral portion as a main beam, and a main beam and first and second sub-beams from the diffraction grating condensed on a track of the optical information recording medium. A spot formed by the second sub-beam is disposed at a position different from each other in the longitudinal direction of the track and in the track width direction, and an objective lens that transmits reflected light from the optical information recording medium, and an optical path between the diffraction grating and the objective lens. First and second light separating means provided therein for separating the laser light from the light source and the reflected light from the optical information recording medium, respectively.
An optical system that condenses the reflected light separated by the first light separating means, restricts light transmission near the light condensing point, and transmits a main lobe of a main beam, and receives light transmitted through the optical system. A configuration including a first photodetector and a second photodetector that receives the reflected light separated by the second light separation unit and obtains a track error signal and a focus error signal;
The second photodetector 4 receives the main beam of the reflected light.
It is composed of a divided first light receiving unit, and second and third light receiving units that separately receive reflected light of the first and second sub-beams, and the difference between the outputs of the second and third light receiving units or In this configuration, a track error signal is obtained based on a difference between outputs of the first light receiving unit.

Further, according to the present invention, the above-mentioned diffraction grating diffracts the central portion of the cross section of the light beam of the laser beam from the light source as first and second sub-beams, and makes the portion between the central portion and the peripheral portion the third and second sub-beams. The second photodetector is configured to diffract as a fourth sub-beam and transmit a peripheral portion as a main beam, and the second photodetector is configured to include a first divided light receiving unit that receives a main beam of reflected light; A second and a third light receiving unit for separately receiving reflected light of the second and third sub-beams;
And a fourth and a fifth light receiving unit for separately receiving reflected light of the fourth sub-beam, and a difference between outputs of the second and third light receiving units or a difference between outputs of the fourth and fifth light receiving units. And a track error signal is obtained based on the

[0016]

According to the first aspect of the present invention, in the case of an optical information recording medium having a normal track pitch, the track error signal is converted into the second and second track beams by a three-beam method using a main beam and first and second sub-beams. 3 for an optical information recording medium with a reduced track pitch, based on the output difference of the first light receiving unit by a push-pull method using a main beam. When the angle formed by the straight line connecting the centers of the first and second sub-beams with the track is an optical information recording medium having a normal track pitch, the first and second sub-beams can be obtained.
By setting the center of the sub-beam to coincide with the edge of the track, the diffraction grating and the optical head device can be used for both the optical information recording medium having a normal track pitch and the optical information recording medium having a reduced track pitch. Recording and reproduction can be performed without rotation.

In addition, for an optical information recording medium having a reduced track pitch, a track error signal can be obtained using a main beam having a reduced focused spot diameter due to the super-resolution effect.

According to the second aspect of the present invention, two sets of two sub-beams are generated by the diffraction grating, and in the case of an optical information recording medium having a normal normal track pitch, the first and second sub-beams are formed together with the main beam. 3 using sub-beam
By the beam method, a track error signal can be obtained based on the output difference between the second and third light receiving units. In the case of an optical information recording medium with a reduced track pitch, the third and fourth light beams are output together with the main beam. 3 using the sub-beam of
By the beam method, a track error signal can be obtained based on the output difference between the fourth and fifth light receiving units.

Therefore, when the angle formed by a straight line connecting the centers of the first and second sub-beams of the first set with the track is for an optical information recording medium having a normal track pitch, the center of the first and second sub-beams is The angle formed by the straight line connecting the centers of the third and fourth sub-beams of the second set with the track is set so as to coincide with the edge of the track. By setting the center of the fourth sub-beam so as to coincide with the edge of the track, a diffraction grating or an optical head can be used for both an optical information recording medium having a normal track pitch and an optical information recording medium having a reduced track pitch. Recording and reproduction can be performed without rotating the device.

In addition, the first set of first and second sub-beams has a condensed spot diameter enlarged due to the apodization effect, while the second set of third and fourth sub-beams has super-resolution and Due to both of the effects of the defocusing, the focused spot diameter becomes smaller than the first and second sub-beams. Therefore, for an optical information recording medium having a reduced track pitch, the third and the third focused beam diameters are small. A track error signal can be obtained using the fourth sub-beam.

[0021]

Next, an embodiment of the present invention will be described. FIG. 1 shows a configuration diagram of a first embodiment of the optical head device according to the present invention. 13, the same components as those in FIG. 13 are denoted by the same reference numerals. In FIG. 1, a semiconductor laser 1 as a light source, a collimator lens 2, a diffraction grating 3, polarizing beam splitters 4 and 5, a quarter-wave plate 6, an objective lens 7, lenses 9 and 12, a pinhole 10, Photodetector 11
And 14, and a cylindrical lens 13. The configurations of the diffraction grating 3 and the photodetector 14 will be described later.

Next, the operation of this embodiment will be described.
Light emitted from the semiconductor laser 1 is collimated by the collimator lens 2 and then enters the diffraction grating 3. Diffraction grating 3
Divides an incident laser beam into a main beam that is transmitted light and two sub beams that are ± first-order diffracted light. These beams almost completely pass through the polarizing beam splitter 4 and the polarizing beam splitter 5, respectively, are converted from P-polarized light to circularly polarized light by the quarter-wave plate 6, and then condensed on the optical disk 8 by the objective lens 7. Is reflected.

The reflected light from the optical disk 8 is transmitted through the objective lens 7 in the opposite direction, and then is converted from circularly polarized light into
The light is converted into polarized light and is incident on the polarizing beam splitter 5,
Here, the light is separated into transmitted light and reflected light. The reflected light of the polarization beam splitter 5 is condensed by a lens 9 and is incident on a pinhole 10 provided at a condensing point.

The pinhole 10 blocks the side lobe component in the main beam of the incident reflected light and the two sub-beams, transmits only the main lobe component in the main beam, and makes the photodetector 11 receive the light. Photodetector 11
, An information signal is detected based on an electric signal obtained by photoelectrically converting incident light.

On the other hand, the transmitted light of the polarizing beam splitter 5 is almost completely reflected by the polarizing beam splitter 4, passes through the lens 12 and the cylindrical lens 13, and is received by the photodetector 14. The electric signal obtained by photoelectric conversion by the photodetector 14 is used for detecting a focus error signal and a track error signal.

FIG. 2 shows a configuration diagram of an example of the diffraction grating 3 of FIG. As shown in the figure, the diffraction grating 3 has a grating formed only in the central region 15 in the light beam cross section of the incident light. Of the incident light, the light at the center incident on the region 15 is almost completely diffracted, and becomes two sub-beams of ± 1st-order diffracted light. Further, the light of the peripheral portion incident on the outside of the region 15 is almost completely transmitted and becomes a main beam.

FIG. 3 shows the intensity distribution of the main beam and the two sub-beams at the converging position on the optical disk 8.
Since the intensity of the main beam in the central portion of the main beam 16 becomes almost zero due to the diffraction grating 3, the main beam 16 at the condensing position on the optical disk 8 due to the super-resolution effect as shown in FIG.
While the diameter of the main lobe 16a is reduced as compared with the case where the diffraction grating 3 is not provided, the height of the side lobe 16b is higher than when the diffraction grating 3 is not provided.

Since the sub-beams 17 and 18 have almost zero light intensity in the peripheral portion due to the diffraction grating 3, the condensed spot has a large main lobe diameter due to the apodization effect, and almost no side lobes are generated.

FIG. 4 shows an arrangement of a main beam and two sub-beams for a track on an optical disk in which the track pitch is reduced to about 1/2 of a normal track. Main beam 16
Is located substantially at the center of the track 19. The sub beams 17 and 18 are the main beam 16
Are arranged at positions different from each other in the longitudinal direction and the track width direction of the track 19 with respect to the spots. That is, the center of one of the sub-beams 17 and 18 is located at a position preceding the spot of the main beam 16 and
The center of the other spot of the two sub-beams is located at a position following the spot of the main beam 16 and is located between the track 19 and the adjacent track on the right or left side thereof. It is controlled by the track servo so as to be located at the middle.

FIG. 5 shows an arrangement of a main beam and two sub beams with respect to a track on an optical disk having a normal track pitch. The center of the spot of the main beam 16 is located substantially at the center of the track 20. The sub beams 17 and 18 are arranged at positions different from each other in the longitudinal direction of the track 20 and the track width direction with respect to the spot by the main beam 16. That is, the center of one spot of the sub beams 17 and 18 is located at a position preceding the spot of the main beam 16 and at the right or left edge of the track 20, and the center of the other spot of the two sub beams is It is controlled by the track servo so as to be located at a position following the 16 spots and on the left side or edge of the track 20.

FIG. 6 shows the pattern of the light receiving portion of the photodetector 14 and the arrangement of spots on the light receiving portion. The photodetector 14 has four divided light receiving units 21 to 24 and two divided light receiving units 25, 26, 27, and 28. The main beam 16 reflected by the optical disk 8 forms a spot 29 at substantially the center of the four divided light receiving units 21 to 24. The sub beams 17 and 18 reflected by the optical disk 8
Separately form spots 30 and 31 at substantially the center of the light receiving units 25 and 26, respectively, and substantially at the center of the light receiving units 27 and 28, respectively.

The output values of the electric signals obtained by the photoelectric conversion by the light receiving units 21 to 28 are respectively represented by V (21) to V (2).
8), the focus error signal is calculated by the known astigmatism method as {V (21) + V (24)} − ΔV
(22) + V (23)}.

On the other hand, in the case of an optical disk having a normal track pitch, the track error signal is obtained by a known three-beam method.
{V (25) + V (26)} − {V (27) + V (2
8) Obtained from the operation of｝. In the case of an optical disk in which the track pitch is smaller than a normal value, the track error signal is calculated by a known push-pull method by using ΔV (21) + V
(22) It is obtained from the calculation of {− {V (23) + V (24)}. Alternatively, by a known differential push-pull method,
{V (21) + V (22)} − {V (23) + V (2
4)｝ -K [｛V (25) + V (27)｝-｛V (2
6) + V (28)}] (K is a constant). In the simple push-pull method, the light receiving sections 25 and 2
6. The light receiving units 27 and 28 may be integrated.

In the simple push-pull method, when the objective lens 7 moves in a direction perpendicular to the longitudinal direction of the track, an offset occurs in the track error signal. On the other hand, in the differential push-pull method in which a track error signal is obtained not only from the main beam but also from two sub beams, even if the objective lens 7 moves in a direction orthogonal to the longitudinal direction of the track, the track of the main beam Since the offset amount of the track error signal of the two sub-beams is subtracted from the offset amount of the error signal, no offset occurs in the entire track error signal. Since the diameter of the focused spot of the two sub-beams is enlarged by the apodization effect, the track error signal of the sub-beam does not have a sufficient amplitude, but only the offset amount can be obtained correctly.

As described above, according to the present embodiment, not only an optical disk having a normal track pitch but also an optical disk having a reduced track pitch for higher density can be used without providing a complicated mechanism. A signal can be obtained and any reproduction can be performed.

Next, a second embodiment of the present invention will be described. FIG. 7 shows a configuration diagram of a second embodiment of the optical head device according to the present invention. In the figure, the same components as those of FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 7, in the present embodiment, a semiconductor laser 1 as a light source, a collimator lens 2, a diffraction grating 32, polarization beam splitters 4 and 5, a 波長 wavelength plate 6, an objective lens 7, lenses 9 and 12, a pinhole 10, It comprises photodetectors 11 and 33 and a cylindrical lens 13. This embodiment is characterized in that a diffraction grating 32 and a photodetector 33 are provided in place of the diffraction grating 3 and the photodetector 14 of the first embodiment.

Next, the operation of this embodiment will be described.
The light emitted from the semiconductor laser 1 is collimated by the collimator lens 2 and then enters the diffraction grating 32. The diffraction grating 32 divides the incident laser light into a main beam as transmitted light and four sub-beams as ± 1st-order diffracted lights.

The pinhole 10 blocks the side lobe component and the four sub-beams in the main beam of the incident reflected light, transmits only the main lobe component in the main beam, and enters the photodetector 11 to receive the light. Photodetector 11
, An information signal is detected based on an electric signal obtained by photoelectrically converting incident light.

On the other hand, the light transmitted through the polarizing beam splitter 5 is almost completely reflected by the polarizing beam splitter 4, passes through the lens 12 and the cylindrical lens 13, and is received by the photodetector 33. The electric signal obtained by photoelectric conversion by the photodetector 33 is used for detecting a focus error signal and a track error signal.

FIG. 8 shows an example of the configuration of the diffraction grating 32 shown in FIG. As shown in the drawing, the diffraction grating 32 has a grating formed in a central region 35 in the light beam cross section of the incident light and a region 34 in a portion between the central portion and the peripheral portion. However, the grating formed in the region 35 and the grating formed in the region 34 have different pitches or directions.

Of the incident light, the light at the central portion incident on the region 35 is almost completely diffracted, and becomes a first set of two sub-beams of ± 1st-order diffracted light. The light in between is diffracted almost completely, and becomes a second set of two sub-beams that are ± 1st-order diffracted light. Also,
The light in the peripheral portion incident on the outside of the region 34 is almost completely transmitted and becomes a main beam.

FIG. 9 shows the intensity distribution of the main beam and the four sub-beams at the condensing position on the optical disk 8.
Since the intensity of the main beam at the center portion of the main beam becomes substantially zero due to the diffraction grating 32, the main beam 36 at the condensing position on the optical disk 8 has a diameter of the main lobe 36a as shown in FIG. While the size is reduced as compared with the case where the diffraction grating 32 is not provided, the height of the side lobe 36b is higher than the case where the diffraction grating 32 is not provided.

The first set of sub-beams 39 and 40
Since the light intensity of the peripheral portion becomes almost zero due to the diffraction grating 32, the diameter of the main lobe is large in the condensed spot due to the apodization effect, and the side lobe hardly occurs. In the second set of sub-beams 37 and 38, since the light intensity in the central part and the peripheral part becomes almost zero due to the diffraction grating 32, the condensed spot is shown in FIG. 9 by the effects of both super-resolution and apodization. As shown, both the diameter of the main lobe and the height of the side lobe indicate intermediate values between the main beam 36 and the sub beams 39 and 40.

FIG. 10 shows that the track pitch is reduced to about 1/2 of the normal pitch.
2 shows the arrangement of the main beam and the four sub beams with respect to the track on the reduced optical disk. Main beam 3
The center of the spot No. 6 is located substantially at the center of the track 19. The center of one spot of the first pair of two sub-beams 39 and 40 is located at a position preceding the spot of the main beam 36, and is located between the track 19 and the adjacent track on the right or left side of the track 19. The center of the other spot of the one sub-beam is controlled by the track servo so as to be located at a position following the spot of the main beam 36 and between the track 19 and the left or right track.

The center of one spot of the two sub beams 37 and 38 of the second set is located at a position preceding the spot of the main beam 36 and at the right or left edge of the track 19, and The center of the other spot is controlled by the track servo so as to be located at a position following the spot of the main beam 36 and on the left side or edge of the track 19.

FIG. 11 shows an arrangement of a main beam and four sub beams with respect to a track on an optical disk having a normal track pitch. The center of the spot of the main beam 36 is located substantially at the center of the track 20. Also, the center of one spot of the two sub beams 39 and 40 of the first set is located at a position preceding the spot of the main beam 36 and at the right or left edge of the track 20, and
The center of the other spot of one sub-beam is located at a position following the spot of the main beam 36, and
Is controlled by the track servo so as to be located on the left side or the edge of the.

The center of the spot of the sub beam 37 of the second set of two sub beams 37 and 38 is located between the center of the spot of the main beam 36 and the center of the spot of the sub beam 39 and the center of the track 20. The center of the spot of the sub-beam 38 is located at a position between the center of the spot of the main beam 36 and the center of the spot of the sub-beam 40, and is located between the center of the track 20 and the edge. Controlled by servo.

FIG. 12 shows the pattern of the light receiving section of the photodetector 33 of FIG. 7 and the arrangement of the spots on the light receiving section. The light detector 33 has four divided light receiving sections 41 to 44 and four independent light receiving sections 45 to 48. The main beam 36 reflected by the optical disk 8 is divided into four divided light receiving sections 41 to 44
A spot 49 is formed substantially at the center. The first set of two sub-beams 39 and 4 reflected by the optical disc 8
0 forms spots 52 and 53 substantially at the center of the light receiving sections 47 and 48, respectively, and the second set of two sub-beams 37 and 38 separates the spots 50 and 51 almost at the center of the light receiving sections 45 and 46, respectively. Formed.

The output values of the electric signals obtained by photoelectric conversion by the light receiving sections 41 to 48 are respectively represented by V (41) to V (4
8), the focus error signal is calculated by the known astigmatism method by {V (41) + V (44)} − ΔV
(42) + V (43)}.

On the other hand, in the case of an optical disk having a normal track pitch, the track error signal is obtained by a known three-beam method.
It is obtained from the operation of {V (47) -V (48)}. In the case of an optical disk in which the track pitch is smaller than a normal value, the track error signal is obtained from the calculation of {V (45) -V (46)} by a known three-beam method.

As described above, according to the present embodiment, not only an optical disk having a normal track pitch but also an optical disk having a reduced track pitch for higher density can be used without providing a complicated mechanism. A signal can be obtained and any reproduction can be performed.

The present invention is not limited to the above-described embodiment. For example, the optical information recording medium may be a recording medium of another shape such as a card.

[0053]

As described above, according to the present invention,
Since recording and reproduction can be performed on both the optical information recording medium having a normal track pitch and the optical information recording medium having a reduced track pitch without rotating the diffraction grating or the optical head device, the diffraction grating or the optical head device can be used. A track error signal can be obtained for both an optical information recording medium having a normal track pitch and an optical information recording medium having a reduced track pitch without providing a complicated mechanism for rotating.

Further, according to the present invention, for an optical information recording medium having a reduced track pitch, a main beam having a reduced focused spot diameter due to the super-resolution effect, or both super-resolution and apodization. With the effect of (1), a track error signal can be obtained by using the third and fourth sub-beams having a small focused spot diameter, so that a sufficient track error signal can be obtained even for an optical information recording medium having a reduced track pitch. The amplitude can be obtained, and the reliability of recording and reproduction can be improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a first embodiment of an optical head device according to the present invention.

FIG. 2 is a configuration diagram of the diffraction grating of FIG.

FIG. 3 is a diagram illustrating an example of a beam intensity distribution at a focus position on an optical disc.

FIG. 4 is a diagram showing an example of a beam arrangement with respect to a track on an optical disk having a track pitch of about 1/2 of a normal track pitch.

FIG. 5 is a diagram showing an example of a beam arrangement with respect to a track on an optical disc having a normal track pitch.

FIG. 6 is a diagram showing a pattern of a light receiving unit and a spot arrangement on the light receiving unit of the photodetector of FIG.

FIG. 7 is a configuration diagram of a second embodiment of the optical head device of the present invention.

8 is a configuration diagram of the diffraction grating of FIG.

FIG. 9 is a diagram illustrating an example of a beam intensity distribution at a focus position of an optical disc.

FIG. 10 is a diagram showing an example of a beam arrangement with respect to a track on an optical disc having a track pitch of about 1/2 of a normal track pitch.

FIG. 11 is a diagram illustrating an example of a beam arrangement with respect to tracks on an optical disc having a normal track pitch.

12 is a diagram showing a pattern of a light receiving section of the photodetector of FIG. 7 and a spot arrangement on the light receiving section.

FIG. 13 is a configuration diagram of an example of a conventional optical head device.

14 is a configuration diagram of an example of the diffraction grating of FIG.

FIG. 15 is a diagram illustrating an example of a beam intensity distribution at a focus position on an optical disc.

FIG. 16 is a diagram showing an example of a beam arrangement with respect to tracks on an optical disc.

17 is a diagram showing a pattern of a light receiving unit of the photodetector of FIG. 13 and a spot arrangement on the light receiving unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Collimator lens 3, 32 Diffraction grating 4, 5 Polarization beam splitter 6 1/4 wavelength plate 7 Objective lens 8 Optical disk 9, 12 Lens 10 Pinhole 11, 14, 33 Photodetector 13 Cylindrical lens 16, 36 Main Beams 17, 39 First sub-beam 18, 40 Second sub-beam 21 to 24, 41 to 44 Quadrant divided light receiving section 25 to 28, 45 to 48 Light receiving section 37 Third sub-beam 38 Fourth sub-beam

Claims (2)

(57) [Claims] A light source that emits laser light; a diffraction grating that diffracts a central portion of a light beam cross section of the laser light from the light source as first and second sub-beams and transmits a peripheral portion as a main beam; The main beam and the first and second sub-beams from the diffraction grating are converged on a track of the optical information recording medium, and the spot by the first and second sub-beams is positioned on the track by the length of the track with respect to the spot by the main beam. And an objective lens that transmits reflected light from the optical information recording medium, and is provided in an optical path between the diffraction grating and the objective lens.
First and second light separating means for respectively separating laser light from the light source and reflected light from the optical information recording medium; and condensing the reflected light separated by the first light separating means. An optical system that restricts light transmission near the focal point and transmits a main lobe of a main beam; a first photodetector that receives light transmitted through the optical system; and a second light separating unit. And a second photodetector for receiving the reflected light separated by the above and obtaining a track error signal and a focus error signal. The second photodetector receives a main beam of the reflected light. A split first light receiving unit, and second and third light receiving units for separately receiving the reflected light of the first and second sub-beams, wherein the output of the second and third light receiving units is A track error signal based on the difference or the difference between the outputs of the first light receiving unit. An optical head and wherein the obtaining. 2. A light source for emitting laser light, and a central portion of a light beam cross section of the laser light from the light source is diffracted as first and second sub-beams, and a portion between the central portion and the peripheral portion is a third and a second portion. A diffraction grating that diffracts as a fourth sub-beam and transmits a peripheral portion as a main beam; and condenses the main beam and the first to fourth sub-beams from the diffraction grating on a track of an optical information recording medium. An objective lens for arranging the spots of the first to fourth sub-beams at positions different from each other in the longitudinal direction and the track width direction of the track with respect to the spot of the main beam, and transmitting reflected light from the optical information recording medium; Provided in the optical path between the diffraction grating and the objective lens,
First and second light separating means for respectively separating laser light from the light source and reflected light from the optical information recording medium; and condensing the reflected light separated by the first light separating means. An optical system that restricts light transmission near the focal point and transmits a main lobe of a main beam; a first photodetector that receives light transmitted through the optical system; and a second light separating unit. And a second photodetector for receiving the reflected light separated by the above and obtaining a track error signal and a focus error signal. The second photodetector receives a main beam of the reflected light. The divided first light receiving unit, the second and third light receiving units that separately receive the reflected light of the first and second sub beams, and the reflected light of the third and fourth sub beam separately And fourth and fifth light receiving sections for receiving light. An optical head and wherein the obtaining a track error signal based on the difference between the output of the difference or the fourth and fifth light receiving portion of the output of the light receiving portion of the.