JPH07296446A - Disk drive device - Google Patents

Abstract

PURPOSE:To obtain an accurate focusing error signal without enlarging and complicating constitution by reading an information signal with a difference of transition quantity between the direction of polarization of an incident light and that of a reflected light. CONSTITUTION:A linear polarization luminous flux of a light source 1 makes a focusing point 9 on a recording groove 12 through a beam splitter 2 and an object lens 3. The direction of polarization of an incident luminous flux is parallel to or orthogonal to the groove 12, and it prevents degradation of a reproduced signal caused by double refraction of a disk substrate. A reflected luminous flux at the focusing point 9 is slightly rotated with the direction of polarization of the incident luminous flux as a reference, reflected by the beam splitter 2, enters a cylindrical lens 4, and causes astigmatism in the direction in accordance with the generatrix direction. A light beam is received by detectors 6, 7 in accordance with variation quantity in the direction of poralization by the beam splitter 5, an operation circuit 18 obtains information reading and focusing error signals from outputted light of four light receiving sections, and a driving circuit 19 supplies a current to an actuator coil 20. By using this constitution, offset is not caused in a focusing error signal even if double refraction is caused in a perpendicular direction in the substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information disc such as a so-called magneto-optical disc, which is configured to read an information signal by a difference in the amount of transition of the polarization direction of reflected light with respect to the polarization direction of incident light. The present invention relates to a disk drive device that reads signals.

[0002]

2. Description of the Related Art Conventionally, so-called magneto-optical disks have been proposed, and disk drive devices for reading information signals from the magneto-optical disks have been proposed. The magneto-optical disk is a disk configured to read an information signal based on the difference in the amount of transition of the polarization direction of reflected light with respect to the polarization direction of incident light.

In such a disk drive device, as shown in FIG. 3, an incident light beam, which is a linearly polarized light beam emitted from a light source 1 such as a semiconductor laser, passes through a beam splitter 2 and an objective lens 3, The light is condensed and irradiated on the recording groove 12 formed in a spiral shape on the magneto-optical disk. The recording groove 12 is moved in the direction of the recording groove 12 as shown by an arrow E in FIG. 3 when the magneto-optical disk is rotated.

The incident light beam forms a beam spot 9 on the recording groove 12. The polarization direction of the incident light flux prevents the reproduction signal from deteriorating due to the birefringence of the disk substrate of the magneto-optical disk.
The direction is parallel to or orthogonal to. In addition,
The polarization direction of the incident light beam is determined by the relationship between the beam shape of the light beam emitted from the semiconductor laser and the polarization direction, and the relationship between the birefringence of the disk substrate and the reproduction signal.

A light beam reflected by the disk surface of the magneto-optical disk of the beam spot 9 returns to the beam splitter 2 through the objective lens 3. The reflected light flux undergoes a transition in the polarization direction due to the so-called Kerr effect in accordance with the information signal recorded on the recording groove 12. The transition of the polarization direction occurs as a rotation of a minute angle in any direction with reference to the center direction corresponding to the polarization direction of the incident light flux.

The reflected light beam is reflected by the beam splitter 2
It is reflected by and is incident on the cylindrical lens 4. The direction of the generatrix of this cylindrical lens 4 is as shown in FIG.
As indicated by the middle arrow H, an angle of 45 ° is formed with respect to the direction of the recording groove 12 with respect to the direction around the optical axis of the reflected light flux indicated by the arrow F in FIG. The cylindrical lens 4 produces astigmatism in the direction corresponding to the direction of the generatrix with respect to the reflected light flux.

The reflected light beam passing through the cylindrical lens 4 is split by the polarization beam splitter 5 into two light beams according to the amount of change in the polarization direction with respect to the central direction. That is, the polarization beam splitter 5 makes the amount of light reflected and the amount of light transmitted to be equal for the reflected light flux whose polarization direction is the central direction.

The reflected light beam transmitted through the polarization beam splitter 5 is received by the first photodetector 6. on the other hand,
The reflected light flux reflected by the polarization beam splitter 5 is received by the second photodetector 7.

Each of the photodetectors 6 and 7 is radially divided into four light receiving portions A, B, C and D. The light receiving portions A, B, C and D of the photodetectors 6 and 7 are arranged in the direction corresponding to the direction of the astigmatism generated by the cylindrical lens 4. That is, the above-mentioned astigmatism is generated in the direction from A to C which is the light receiving portion facing each other through the central portions of the photodetectors 6 and 7, or in the direction from B to D. In addition, each of these photodetectors 6, 7
The arrangement direction of the respective light receiving portions A, B, C, D also corresponds to the direction of the recording groove 12. That is, the light receiving portions A and B adjacent to each other correspond to one side of the recording groove 12, and the light receiving portions C and D adjacent to each other correspond to the other side of the recording groove 12.

The difference between the amount of light received by the first photodetector 6 and the amount of light received by the second photodetector 7 corresponds to the information signal read from the magneto-optical disk. That is, 6A, 6B, 6C, 6D, 7A, 7B, 7 are the light detection outputs from the respective light receiving parts A, B, C, D of the respective photodetectors 6, 7.
If C and 7D, the information read signal MO is MO = (6A + 6B + 6C + 6D) − (7A + 7B + 7
C + 7D). This calculation is performed by the calculation circuit 18. Further, the focus error signal FE indicating the amount of deviation between the disc surface of the magneto-optical disc and the beam spot 9 (focus point) in the optical axis direction, that is, the focus error amount is FE = (6A + 6C)-(6B + 6D) or , FE = (7A + 7C) − (7B + 7D). Further, the recording groove 12 of the magneto-optical disk and the recording groove 1 of the beam spot 9 are formed.
The deviation amount in the direction orthogonal to 2 is the tracking error signal TE indicating the tracking error amount,
It is obtained by the so-called push-pull method. That is,
The tracking error signal TE is obtained by TE = (6A + 6B)-(6C + 6D) or TE = (7A + 7B)-(7C + 7D).

The focus error signal FE and the tracking error signal TE are sent to the drive circuit 19. The drive circuit 19 supplies a drive current to the actuator coil 20 according to the error signals FE and TE.
The actuator coil 20 moves the objective lens 3 in the optical axis direction and in a direction orthogonal to the optical axis and the recording groove 12 according to the drive current, and the beam spot 9 is always recorded. It is formed on the land or groove 12.

[0012]

In the disk drive device as described above, particularly when the disk substrate of the magneto-optical disk is made of a synthetic resin material, the vertical direction in the disk substrate is improved. Due to the influence of birefringence, the focus error signal FE may not be accurately obtained.

That is, when the birefringence occurs, a spatially non-uniform intensity distribution is generated in the reflected light beam polarization-detected through the polarization beam splitter 5. Considering the direction around the optical axis of the reflected light flux, this intensity distribution occurs in a symmetrical state about the 45 ° direction with respect to the direction of the recording groove 12. Therefore, the intensity of the reflected light flux from the areas 1 and 3 in the beam spot 9 in FIG. 3 is higher and the intensity of the reflected light flux from the areas 2 and 4 in the beam spot 9 is weaker, Alternatively,
On the contrary, the intensity of the reflected light flux is weaker than the areas 1 and 3 in the beam spot 9, and
The intensity of the reflected light flux becomes stronger than the area indicated by. When such an intensity distribution is generated, when the beam spot 9 is accurately formed on the disk surface, the focus error signal FE does not become 0, that is, the focus error signal FE is offset. It becomes a state having.

In order to prevent such an offset of the focus error signal FE from occurring, the reflected light beam before entering the polarization beam splitter 5 is a photodetector different from the photodetectors 6 and 7. To generate the focus error signal or to return the signal to a signal corresponding to the intensity distribution before polarization detection by the polarization beam splitter 5 by arithmetic processing. This calculation process is as follows: FE = be (6A + 6C)-(6B + 6D) bo + be (7A + 7
C)-(7B + 7D) is used to obtain the focus error signal FE.

If the focus error signal FE is prevented from being offset in this way, the number of photodetectors increases or the arithmetic circuit 18 is complicated, so that the entire disk drive device is not affected. The size and complexity are increased.

Therefore, the present invention is proposed in view of the above situation, and an information signal is read by the difference in the transition amount of the polarization direction of the reflected light with respect to the polarization direction of the incident light such as in a magneto-optical disk. A disc drive device for reading an information signal from a disc configured to perform, and a disc adapted to obtain an accurate focus error signal without offset without causing an increase in size and complexity of the configuration. An object is to provide a drive device.

[0017]

In order to solve the above-mentioned problems and achieve the above-mentioned object, a disk drive device according to the present invention uses an information signal based on the difference in the amount of transition of the polarization direction of reflected light with respect to the polarization direction of incident light. A light source that collects and irradiates an incident light flux that is a linearly polarized light flux onto a disc that is configured to read the data, and a polarization detection that detects the amount of change of the polarization direction of the reflected light flux from the disc from the center direction. Means and astigmatism having a specific directionality with respect to the reflected light beam, and focusing the reflected light beam, and deviating the in-focus point of the incident light beam with respect to the disk surface based on the light intensity distribution at the in-focus point. A focus error signal generating means for generating a focus error signal indicating the amount, and the above-mentioned input to the recording groove formed spirally on the disk surface. A tracking error signal generating means for generating a tracking error signal indicating a deviation amount in the direction orthogonal to the recording grooves of focus of the light beam,
According to the focus error signal and the tracking error signal, the position of the focal point of the incident light beam is set to a focus direction which is a direction perpendicular to the disc surface and a tracking direction which is a direction orthogonal to the recording groove in the disc surface. And a biaxial servo means for controlling movement in the directions, and the direction of the astigmatism generated in the focus error signal generating means is along the central direction of the polarization direction of the reflected light beam, or orthogonal to the central direction. It is the direction in which it is done.

According to the present invention, in the above-mentioned disc drive device, the polarization direction of incident light is parallel to or orthogonal to the direction of the recording groove spirally formed on the disc surface, and the tracking error signal generation is performed. The means detects the tracking servo pits formed on one side and the other side of the recording groove based on the reflected light flux to generate a tracking error signal, which is generated by the focus error signal generating means. The direction of the astigmatism is set to be a direction along the direction of the recording groove or a direction orthogonal to the direction of the recording groove with respect to the direction around the optical axis of the reflected light flux.

Further, according to the present invention, in the above-mentioned disc drive device, the polarization direction of incident light is parallel or orthogonal to the direction of the recording groove spirally formed on the disc surface, and the tracking error generating means is provided. Irradiates a pair of tracking servo light beams on one side and the other side of the recording groove, and generates a tracking error signal based on the difference in the amount of light reflected by the disk surface of these tracking servo light beams. The direction of astigmatism generated in the focus error signal generating means is a direction along the direction of the recording groove or a direction orthogonal to the direction of the recording groove with respect to the direction about the optical axis of the reflected light flux. I decided to stay.

[0020]

In the disk drive device according to the present invention, the combination of the incident light flux with respect to the disk surface of the disk configured to read the information signal by the difference in the transition amount of the polarization direction of the reflected light with respect to the polarization direction of the incident light. The direction of astigmatism generated in the focus error signal generating means for generating the focus error signal indicating the amount of defocus is the direction along the center direction of the polarization direction of the reflected light beam, or the direction orthogonal to the center direction. Therefore, in the polarization detection means for detecting the amount of change of the polarization direction of the reflected light flux from the central direction, the intensity distribution caused by the effect of birefringence in the disc does not occur in the direction of the astigmatism, and the focus error The occurrence of signal offset is prevented.

Further, in the above-mentioned disk drive device, the polarization direction of the incident light is parallel to or orthogonal to the direction of the recording groove spirally formed on the disk surface, and the tracking error signal generating means is The tracking servo pits formed on one side and the other side of the recording groove are detected based on the reflected light flux to generate a tracking error signal, and astigmatism of astigmatism generated in the focus error signal generating means is detected. When the direction is the direction along the direction of the recording groove with respect to the direction around the optical axis of the reflected light beam or the direction orthogonal to the direction of the recording groove, the polarization direction of the incident light beam. Recording an information signal in the direction of the recording groove with the direction perpendicular to the direction of the recording groove. Also in the case of improving the density, the direction of the astigmatism becomes the direction along the center direction of the polarization direction of the reflected light flux or the direction orthogonal to the center direction, and the occurrence of the offset of the focus error signal is prevented. , A tracking error signal can be obtained.

Further, according to the present invention, in the above-mentioned disc drive device, the polarization direction of incident light is parallel or orthogonal to the direction of the recording groove spirally formed on the disc surface, and the tracking error generating means is provided. Irradiates a pair of tracking servo light beams on one side and the other side of the recording groove, and generates a tracking error signal based on the difference in the amount of light reflected by the disk surface of these tracking servo light beams. The direction of astigmatism generated in the focus error signal generating means is a direction along the direction of the recording groove or a direction orthogonal to the direction of the recording groove with respect to the direction about the optical axis of the reflected light flux. In this case, the direction of polarization of the incident light beam is orthogonal to the direction of the recording groove. When raising the recording linear density of the information signals in the direction of the recording groove forms a well,
The direction of the astigmatism is the direction along the center direction of the polarization direction of the reflected light beam or the direction orthogonal to the center direction, and the occurrence of the offset of the focus error signal can be prevented and the tracking error signal can be obtained. it can.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below with reference to the drawings. In this example, the disk drive device according to the present invention is configured as a device for reading an information signal from a so-called magneto-optical disk. The magneto-optical disk is a disk configured to read an information signal based on the difference in the amount of transition of the polarization direction of reflected light with respect to the polarization direction of incident light.

The disk drive device according to the present invention has a light source 1 such as a semiconductor laser as shown in FIG. An incident light flux, which is a linearly polarized light flux emitted from the light source 1, passes through the beam splitter 2 and the objective lens 3 and is condensed on the recording groove 12 formed in a spiral shape on the magneto-optical disk. Is irradiated. The recording groove 12 is moved in the direction of the recording groove 12 as indicated by an arrow E in FIG. 1 by rotating the magneto-optical disk.

The incident light beam forms a beam spot 9 on the recording groove 12. The polarization direction of the incident light flux prevents the reproduction signal from deteriorating due to the birefringence of the disk substrate of the magneto-optical disk.
The direction is parallel to or orthogonal to. In addition,
The polarization direction of the incident light beam is determined by the relationship between the beam shape of the light beam emitted from the semiconductor laser and the polarization direction, and the relationship between the birefringence of the disk substrate and the reproduction signal.

The light beam reflected by the disk surface of the magneto-optical disk of the beam spot 9 returns to the beam splitter 2 via the objective lens 3. The reflected light flux undergoes a transition in the polarization direction due to the so-called Kerr effect in accordance with the information signal recorded on the recording groove 12. The transition of the polarization direction occurs as a rotation of a minute angle in any direction with reference to the center direction corresponding to the polarization direction of the incident light flux.

The reflected light beam is reflected by the beam splitter 2
And is incident on the cylindrical lens 4 constituting the focus error signal generating means. The direction of the generatrix of the cylindrical lens 4 is, as shown by arrow G in FIG. 1, a direction along the direction of the recording groove 12 with respect to the direction around the optical axis of the reflected light flux shown by arrow F in FIG. Has been made. The cylindrical lens 4 produces astigmatism in the direction corresponding to the direction of the generatrix with respect to the reflected light flux. That is, the direction of astigmatism produced by the cylindrical lens 4 is the direction along the central direction of the polarization direction of the reflected light beam or the direction orthogonal to the central direction.

The reflected light beam that has passed through the cylindrical lens 4 is a polarization beam splitter 5 that constitutes polarization detection means.
According to the change amount of the polarization direction with respect to the center direction,
It is split into two light beams. That is, the polarization beam splitter 5 has a polarization dependence having a directional property of 45 ° with respect to the direction of the recording groove 12 with respect to the direction about the optical axis of the reflected light beam. Regarding the reflected light flux in the central direction, the amount of light reflected and the amount of light transmitted are equal.

A part of the reflected light flux transmitted through the polarization beam splitter 5 is received by the first photodetector 6.
On the other hand, a part of the reflected light flux reflected by the polarization beam splitter 5 is received by the second photodetector 7.

Each of the photodetectors 6 and 7 is radially divided into four light receiving portions A, B, C and D. The light receiving portions A, B, C and D of the photodetectors 6 and 7 are arranged in the direction corresponding to the direction of the astigmatism generated by the cylindrical lens 4. That is, the above-mentioned astigmatism is generated in the direction from A to C which is the light receiving portion facing each other through the central portions of the photodetectors 6 and 7, or in the direction from B to D.

The difference between the amount of light received by the first photodetector 6 and the amount of light received by the second optical wiper 7 corresponds to the information signal read from the magneto-optical disk. That is, 6A, 6B, 6C, 6D, 7A, 7B, 7 are the light detection outputs from the respective light receiving parts A, B, C, D of the respective photodetectors 6, 7.
If C and 7D, the information read signal MO is MO = (6A + 6B + 6C + 6D) − (7A + 7B + 7
C + 7D). This calculation is performed by the calculation circuit 18 to which the photodetection outputs of the photodetectors 6 and 7 are supplied.
Further, the focus error signal FE indicating the amount of deviation between the disc surface of the magneto-optical disc and the beam spot 9 (focus point) in the optical axis direction, that is, the focus error amount is FE = (6A + 6C)-(6B + 6D) or , FE = (7A + 7C) − (7B + 7D). These focus error signals FE are
Any one of the photodetectors 6 and 7 may be used, and a photodetector that does not calculate the focus error signal FE does not need to be divided into four light receiving portions.

In this disk drive device, in the servo areas 13 formed intermittently on the magneto-optical disk, there are spaces on both sides of the recording groove 12 and in the direction of the recording groove 12. The tracking error signal TE is detected by detecting the change in the amount of reflected light due to the first and second tracking servo pits 14 and 15 formed in this way, that is, by the so-called sample servo method. The tracking error signal TE indicates the amount of deviation between the recording groove 12 of the magneto-optical disk and the beam spot 9 in the direction orthogonal to the recording groove 12. The first and second tracking servo pits 1
The change in the amount of reflected light due to Nos.
7, the photodetectors 6 and 7 constitute a tracking error signal generating means.

The focus error signal FE and the tracking error signal TE are sent to the drive circuit 19 which constitutes the biaxial servo means. The drive circuit 19 supplies a drive current to the actuator coil 20 forming a part of the biaxial servo means in response to the error signals FE and TE. The actuator coil 20 moves the objective lens 3 in the optical axis direction and in a direction orthogonal to the optical axis and the recording groove 12 according to the drive current, and the beam spot 9 is always recorded. It is formed on the groove 12.

In this disc drive device, for example, when the disc substrate of the magneto-optical disc is made of a synthetic resin material or the like, even if the birefringence in the vertical direction occurs in the disc substrate, the focus error occurs. No offset occurs in the signal FE.

That is, in the reflected light beam polarized and detected through the polarization beam splitter 5, a spatially non-uniform intensity distribution is generated due to the influence of the birefringence. This intensity distribution is the optical axis of the reflected light beam. Considering in the direction with respect to the center of the recording groove 12, it occurs in a symmetrical state about the direction of 45 ° with respect to the direction of the recording groove 12. Therefore, in FIG. 1, the intensity of the reflected light flux is stronger than the areas 1 and 3 in the beam spot 9 and the intensity of the reflected light flux is weaker than the areas 2 and 4 in the beam spot 9. Alternatively, conversely, the intensity of the reflected light flux is weaker than the areas 1 and 3 in the beam spot 9, and the intensity of the reflected light flux is stronger than the areas 2 and 4 in the beam spot 9. Even if such an intensity distribution occurs, the area where the light intensity becomes strong,
Further, since the reflected light fluxes from the region where the light intensity becomes weak are received over the light receiving portions where the photodetection outputs are subtracted from each other in the calculation for obtaining the focus error signal FE, the intensity is calculated in this calculation. The effects of distribution are offset.

Therefore, in this disc drive apparatus, when the beam spot 9 is accurately formed on the disc surface, the focus error signal FE always becomes 0, that is, the focus error signal FE becomes No offset occurs.

In this disc drive device, the direction of the generatrix of the cylindrical lens 4 may be orthogonal to the direction of the recording groove 12 with respect to the direction around the optical axis of the reflected light beam. Also in this case, the offset of the focus error signal FE due to the influence of the birefringence does not occur.

In the disk drive device according to the present invention, the tracking error signal generating means converts the incident light beam from the light source 1 into the incident light beam and the two tracking servo light beams 10 as shown in FIG. , 1
And a pair of tracking servo photodetectors 1 for detecting the reflected light of the tracking servo light beams 10 and 11 reflected by the magneto-optical disk.
The tracking error signal TE may be generated by a so-called three-beam method.

Luminous flux for tracking servo 10, 10
Reference numeral 1 denotes the recording groove 12 by the objective lens 3.
On both sides of the recording groove 12 and at positions spaced apart in the direction of the recording groove 12. The reflected light of the tracking servo light fluxes 10 and 11 from the magneto-optical disk passes through the beam splitter 2, the cylindrical lens 4 and the polarization beam splitter 5, and then the pair of tracking servo photodetectors 16 and
The light is independently received by 17. The tracking error signal TE is obtained by subtracting the photodetection outputs of the tracking servo photodetectors 16 and 17 from each other.

Also in this disc drive device, the recording groove 1 is formed with respect to the direction of the generatrix of the cylindrical lens 4 with the optical axis of the reflected light beam as the center.
The direction may be orthogonal to the direction of 2. Also in this case, the offset of the focus error signal FE due to the influence of the birefringence does not occur.

In the disk drive device according to the present invention, the incident light beam may be polarized in any direction, which is neither parallel nor orthogonal to the direction of the recording groove 12. . In this case, the polarization beam splitter 5 is also rotated in the direction around the optical axis with respect to the above example, corresponding to the polarization direction of the incident light beam. Further, the cylindrical lens 4 is also rotated in the direction around the optical axis with respect to the above-described example corresponding to the direction of the polarization beam splitter 5, so that the direction of astigmatism to be generated is reflected. The direction is along the central direction of the polarization direction of the light flux, or the direction orthogonal to the central direction.

[0042]

As described above, in the disk drive device according to the present invention, the information signal is read by the difference in the transition amount of the polarization direction of the reflected light with respect to the polarization direction of the incident light. The direction of astigmatism generated in the focus error signal generating means for generating the focus error signal indicating the amount of deviation of the focal point of the incident light beam with respect to the disk surface is the direction along the center direction of the polarization direction of the reflected light beam, or The direction is orthogonal to the central direction.

Therefore, in this disc drive device, the intensity distribution produced by the effect of birefringence in the disc in the polarization detecting means for detecting the amount of change of the polarization direction of the reflected light beam from the central direction is the direction of the astigmatism. It is possible to prevent the occurrence of the focus error signal offset.

Further, in the above-mentioned disk drive device, the polarization direction of the incident light is parallel to or orthogonal to the direction of the recording groove spirally formed on the disk surface, and the tracking error signal generating means is The tracking servo pits formed on one side and the other side of the recording groove are detected based on the reflected light flux to generate a tracking error signal, and astigmatism of astigmatism generated in the focus error signal generating means is detected. When the direction is the direction along the direction of the recording groove with respect to the direction around the optical axis of the reflected light beam or the direction orthogonal to the direction of the recording groove, the polarization direction of the incident light beam. Recording an information signal in the direction of the recording groove with the direction perpendicular to the direction of the recording groove. Also in the case of improving the density, the direction of the astigmatism is the direction along the central direction of the polarization direction of the reflected light flux, or the direction orthogonal to the central direction, and it is possible to prevent the occurrence of the offset of the focus error signal, A tracking error signal can be obtained.

Further, according to the present invention, in the above-mentioned disc drive device, the polarization direction of the incident light is parallel to or orthogonal to the direction of the recording groove spirally formed on the disc surface, and the tracking error generating means is provided. Irradiates a pair of tracking servo light beams on one side and the other side of the recording groove, and generates a tracking error signal based on the difference in the amount of light reflected by the disk surface of these tracking servo light beams. The direction of astigmatism generated in the focus error signal generating means is a direction along the direction of the recording groove or a direction orthogonal to the direction of the recording groove with respect to the direction about the optical axis of the reflected light flux. In this case, the direction of polarization of the incident light beam is orthogonal to the direction of the recording groove. When raising the recording linear density of the information signals in the direction of the recording groove forms a well,
The direction of the astigmatism is the direction along the center direction of the polarization direction of the reflected light beam or the direction orthogonal to the center direction, and it is possible to prevent the occurrence of the focus error signal offset and obtain the tracking error signal. .

That is, according to the present invention, an information signal is read from a disk, such as a magneto-optical disk, which is configured to read an information signal by a difference in the amount of transition of the polarization direction of reflected light with respect to the polarization direction of incident light. (EN) It is possible to provide a disk drive device which is capable of obtaining an accurate focus error signal without offset without causing an increase in size and complexity of the structure.

[Brief description of drawings]

FIG. 1 is a perspective view schematically showing a configuration of a disk drive device according to the present invention.

FIG. 2 is a perspective view schematically showing another example of the configuration of the disk drive device.

FIG. 3 is a perspective view schematically showing a configuration of a conventional disk drive device.

[Explanation of symbols]

 1 Light Source 2 Beam Splitter 3 Objective Lens 4 Cylindrical Lens 5 Polarizing Beam Splitter 6 First Photo Detector 7 Second Photo Detector 8 Diffraction Grating 9 Beam Spot 10 First Tracking Servo Light Flux 11 Second Tracking Servo Luminous flux 12 Recording groove 14 First tracking servo pit 15 Second tracking servo pit

Claims (3)

[Claims] 1. An incident light flux, which is a linearly polarized light flux, is converged and applied to a disk configured to read an information signal by a difference in the amount of transition of the polarization direction of the reflected light with respect to the polarization direction of the incident light. Light source, a polarization detection means for detecting the amount of change in the polarization direction of the reflected light beam from the disc, and astigmatism having a specific directionality with respect to the reflected light beam. Focus error signal generating means for generating a focus error signal indicating the amount of deviation of the focal point of the incident light flux with respect to the disc surface based on the light intensity distribution at the focal point, and on the disc surface. Tracking error indicating the amount of deviation of the focal point of the incident light beam with respect to the spirally formed recording groove in the direction orthogonal to the recording groove. Tracking error signal generating means for generating a signal, and the position of the focal point of the incident light beam in the focus direction which is the direction perpendicular to the disk surface and in the disk surface according to the focus error signal and the tracking error signal. And a biaxial servo means for controlling movement in two directions of a tracking direction, which is a direction orthogonal to the recording groove, and a direction of astigmatism generated in the focus error signal generating means is a polarization direction of the reflected light flux. A disk drive device formed in a direction along the center direction of the disk or in a direction orthogonal to the center direction. 2. The incident light is polarized in a direction parallel to or perpendicular to the direction of the recording groove spirally formed on the disk surface, and the tracking error signal generating means is one of the recording grooves. The tracking servo pits formed on the side and the other side are detected based on the reflected light beam to generate a tracking error signal, and the direction of the astigmatism generated in the focus error signal generating means is the reflected light beam. 2. The disk drive device according to claim 1, wherein a direction centered on the optical axis of is the direction along the direction of the recording groove or the direction orthogonal to the direction of the recording groove. 3. The incident light is polarized in a direction parallel to or orthogonal to the direction of the recording groove spirally formed on the disk surface, and the tracking error generating means includes one side of the groove. And a pair of tracking servo light fluxes are radiated to the other side, and a tracking error signal is generated based on the difference in the amount of light reflected by the disk surface of these tracking servo light fluxes, which is generated in the focus error signal generating means. The direction of the astigmatism is the direction along the direction of the recording groove, with respect to the direction around the optical axis of the reflected light beam, or
2. The disc drive device according to claim 1, wherein the disc drive device is formed in a direction orthogonal to the direction of the recording groove.