JP2000251277A - Device and method for detecting focus error of optical pickup - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use a three-beam system with a DPD system, to increase the sensitivity of non-focusing detection, and to miniaturize an optical pickup by dividing returning light from an optical disk into two light paths, and applying specific astigmatism to the light of each divided light path. SOLUTION: A hologram element 8 has first and second hologram parts. The first hologram divides returning light into first and second light paths. The second hologram applies first astigmatism to the light of the first light path as first processing light, and applies second astigmatism at 90 degrees to the first astigmatism to the light of the second light path as second processing light. The first processing light enters a first detector 11 with four light reception parts, and the second processing light enters a second detector 12 with four light reception parts. A tracking error signal is obtained by an operation circuit being connected to the output side of a light detection part 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup for writing information on an optical disk by using light emitted from a light source or reading information from an optical disk by using return light from the optical disk. The present invention relates to an apparatus and a focus error detection method for an optical pickup.

[0002]

2. Description of the Related Art CD (Compact Disk), CD-ROM,
The information recording surface on the surface of an optical disk such as a DVD (Digital Versatile Disk) is irradiated with the emitted light emitted from the light source to write information on the optical disk such as music and data, or reflected back from the information recording surface of the optical disk. An optical pickup including a light source, an optical system, and a light detection system is used to read information recorded on an optical disk from the returned light.

In this optical pickup, in order to reliably write information on an optical disk or read information from the optical disk, control is performed such that emitted light is always applied to a recording location (for example, a track) on an information recording surface of the optical disk (for example, a track). Hereinafter, it is referred to as “tracking servo control”.)
In addition, it is necessary to perform control so that the emitted light becomes a spot-like point and converges on the recording location (hereinafter, referred to as “focusing servo control”).

[0004] As a focusing servo control system, for example, an "astigmatism method" and a "spot size method" are known.

[0005] The astigmatism method is a method in which a cylindrical lens, a parallel plate, or the like is arranged in an optical system, and return light is received and detected by a 4-split detector.

With this configuration, when the outgoing light is focused on the information recording surface of the optical disk (hereinafter, referred to as "focused"), the return light is circularly formed at the center of the four-divided detector. And the light receiving intensity of each light receiving surface of the quadrant detector is balanced. However, when the outgoing light is not in focus on the optical disc, the return light becomes an oblong shape inclined on the quadrant detector, and the light receiving intensity of each light receiving surface of the detector becomes unbalanced. From this, a signal (hereinafter, referred to as a “focus error signal”) obtained by performing a predetermined operation on the photodetection electric signal photoelectrically converted on each light receiving surface is used to focus the outgoing light on the optical disc or Focusing servo control can be performed by detecting an out-of-focus state and controlling an objective lens or the like of the light exchange optical system so as to feed back a focus error signal.

The astigmatism method has a high out-of-focus detection sensitivity.
Also, since a four-segment detector is used for light detection, the DPD
(Differential Phase Detection) It is easy to calculate the tracking error signal for the tracking servo control in the method. Further, since the entire optical pickup can be miniaturized, there is an advantage that it can be easily applied to an optical pickup of a three-beam system using three light spots.

In the spot size method, a return light is divided into two optical paths by a light detection system, and a focal point (hereinafter, referred to as "front focal point") connected to a front detector and a focal point (hereinafter, referred to as "front focal point") connected to a rear detector. This is a method for generating a “back focus”.

With this configuration, when the emitted light is in focus on the optical disk, the size of the return light spot of the front detector and that of the rear detector are equal. However, when the outgoing light is not in focus on the optical disc, the size of the return light spot of the front detector and that of the rear detector are different, and the light receiving intensity of each detector becomes unbalanced. From this, by the focus error signal obtained by performing a predetermined operation on the photodetection electric signal photoelectrically converted by each detector, it is possible to detect the focus or out of focus of the emitted light on the optical disc, Focusing servo control can be performed by controlling the objective lens and the like of the light exchange optical system so as to feed back the focus error signal.

In the spot size method, a focus error signal is calculated from a difference between a light detection electric signal from a front detector and a light detection electric signal from a rear detector. Therefore, noise (hereinafter, referred to as “track crossing noise”) given to the focus error signal when the emitted light spot crosses the track of the optical disk is canceled by taking the difference between the two detectors. There is an advantage of not receiving.

[0011]

However, the above-described conventional focus error detection method for an optical pickup has the following problems.

1) In the astigmatism method, when an optical pickup has an aberration (eg, astigmatism), it is affected by track crossing noise. Also, in the astigmatism method, when the thickness of the optical disc is not constant and there is a thickness error depending on the location, the shape of the return light spot on the detector is distorted, and light that should not be received originally is reflected on another light receiving surface. It may leak or wrap around, causing an error in the DPD tracking error signal.

2) In the spot size method, the return light is separated into a plurality of optical paths, so that the optical pickup becomes large.
In addition, the combined use with the three-beam method is complicated and difficult.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object to be solved by the present invention is to reduce the influence of a track crossing noise and an optical disk thickness error on a three-beam system and a DPD system. An object of the present invention is to provide a focus error detection device for an optical pickup and a focus error detection method for an optical pickup that can be used together.

[0015]

According to a first aspect of the present invention, there is provided an optical pickup focus error detecting apparatus for writing optical disc recording information on an information recording surface of an optical disc using light emitted from a light source. Or a focus error detection device for an optical pickup that detects a focus error of the emitted light in an optical pickup that reads the optical disc record information from return light that is emitted from the light source and reflected on the information recording surface of the optical disc and returned, The light existing in the first quadrant region and the third quadrant region on the plane perpendicular to the optical axis of the return light is separated into the first optical path, and the light is separated into the second quadrant region and the fourth quadrant region on the optical axis perpendicular plane. An optical path separating unit that separates existing light into a second optical path, a first optical processing unit that imparts a first astigmatism to the light in the first optical path to generate first processing light, A focus error detecting optical element having second optical processing means for imparting a second astigmatism in the direction of 90 degrees with respect to the first astigmatism to the light of the two optical paths to produce a second processing light; A first photodetector having a first light receiving unit divided into four and receiving and detecting the first processing light;
A second photodetector having a second light receiving portion divided into four and receiving and detecting the second processing light; an intensity of each light received by four portions of the first light receiving portion; A focus error discriminating value calculating means for performing a predetermined calculation on the intensity of each light received by the four parts of the unit and outputting a focus error discriminating value is provided.

According to a second aspect of the present invention, in the focus error detecting apparatus for an optical pickup according to the first aspect, the optical path separating means is a first hologram unit having a prism function. The first optical processing means is a second hologram section having a cylindrical lens function having a first direction as a long axis, and the second optical processing means has a long axis at a direction 90 degrees with respect to the first direction. It is a second hologram unit having a cylindrical lens function.

According to a third aspect of the present invention, there is provided a focus error detecting device for an optical pickup according to the first aspect, wherein the focus error detecting optical element is provided on a plane perpendicular to the optical axis. An eccentric cylindrical lens disposed in each of the first quadrant region and the third quadrant region and having a long axis in the first direction;
The eccentric cylindrical lens is disposed in each of the quadrant region and the fourth quadrant region, and has a decentered cylindrical lens whose major axis is a direction at 90 degrees to the first direction.

According to a fourth aspect of the present invention, there is provided a focus error detecting device for an optical pickup according to the first aspect, wherein the first and second photodetectors are laterally disposed. A third photodetector for a + 1st-order sub-beam and a fourth photodetector for a -1st-order subbeam are provided, and control is performed by a three-beam method.

According to a fifth aspect of the present invention, there is provided a focus error detecting device for an optical pickup according to the first aspect, wherein control is performed by a DPD method.

According to a sixth aspect of the present invention, there is provided a method for detecting a focus error of an optical pickup, wherein information recorded on an optical disk is written on an information recording surface of an optical disk by light emitted from a light source, or information recorded on the optical disk is emitted from the light source. A focus error detection method for an optical pickup for detecting a focus error of the outgoing light in an optical pickup that reads the optical disc recording information from return light reflected back from a surface, wherein the focus error is detected on a plane perpendicular to an optical axis of the return light. An optical path that separates light existing in the first and third quadrants into a first optical path and separates light existing in the second and fourth quadrants on the plane perpendicular to the optical axis into a second optical path. Separating means for imparting a first astigmatism to the light on the first optical path,
A first optical processing means for processing light, and a second processing light obtained by adding second astigmatism to the light on the second optical path in a direction of 90 degrees with respect to the first astigmatism to obtain second processing light. A focus error detecting optical element having two optical processing means, a first photodetector having a four-divided first light receiving unit for receiving and detecting the first processing light, and a four-divided second light receiving unit And a second photodetector for receiving and detecting the second processing light is provided. The intensity of each light received by four portions of the first light receiving portion and the four portions of the second light receiving portion are It is characterized in that a predetermined calculation is performed on the intensity of each received light and a focus error discrimination value is output.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a focus error detecting device for an optical pickup according to the present invention will be described below with reference to the drawings.

(1) First Embodiment FIG. 1 is a diagram showing a configuration of an optical pickup according to a first embodiment of the present invention. As shown in FIG. 1A, the optical pickup 100 includes a semiconductor laser 1 as a light source,
It comprises a grating 2, a beam splitter 3, a collimator lens 4, a mirror 5, a quarter-wave plate 6, an objective lens 7, a hologram element 8, and a light detector 9. The objective lens 7 includes an objective lens 7.
There is provided an objective lens driving mechanism (not shown) that can move the lens back and forth in the optical axis direction.

As shown in FIG. 1B, the light detecting section 9 includes a first detector 11, a second detector 12,
It has a third detector 13 and a fourth detector 14. The first detector 11 and the second detector 12 are connected to an arithmetic circuit (not shown) including an adder and a subtracter for performing a predetermined operation based on the output photodetection electric signal.

Laser light L emitted from semiconductor laser 1
Enters the beam splitter 3 via the grating 2. The beam splitter 3 is a half mirror (semi-transparent mirror)
The incident laser light L passes through the beam splitter 3, passes through the collimator lens 4, the optical path is changed to a right angle by the mirror 5, passes through the 波長 wavelength plate 6, and passes through the objective lens 7. Is irradiated on the information recording surface of an optical disk (not shown) located above the optical disk. By this irradiation light, the optical disk recording information can be written on the information recording surface of the optical disk.

The laser light L is reflected on the information recording surface of the optical disk, returns on the same optical path, and enters the beam splitter 3 again through the objective lens 7, the quarter-wave plate 6, the mirror 5, and the collimator lens 4. In this case, the return light has its optical path changed in a direction different from the direction toward the semiconductor laser 1 by the beam splitter 3, passes through the hologram element 8, and enters the light detection unit 9. The light detection unit 9 photoelectrically converts the received light and outputs a light detection electric signal. Optical disc recording information can be read from the light detection electric signal.

Next, a method of detecting a focus error in the optical pickup 100 will be described. As shown in FIG. 1B, the optical pickup 100 divides the return light split by the beam splitter 7 into a first optical path P1 and a second optical path P2 by a hologram element 8, and returns the first optical path P1. The light is received by the first detector 11, the return light of the second optical path P2 is received by the second detector 12, and a predetermined operation is performed on the photodetection electric signal output by the photoelectric conversion to generate a focus error signal.

FIG. 2 is a view for explaining the configuration of the hologram element 8 in the optical pickup 100 described above. The hologram element 8 has a first hologram section 15 and a second hologram section 16.

As shown in FIG. 2A, the first hologram unit 15 converts the light existing in the first quadrant region 15Q1 and the third quadrant region 15Q3 on a plane perpendicular to the optical axis of the return light into the first optical path. It has a function equivalent to a prism that separates the light (shown in the upward direction in FIG. 2A). At the same time, the first hologram unit 15 transmits the light existing in the second quadrant region 15Q2 and the fourth quadrant region 15Q4 on a plane perpendicular to the optical axis of the return light to the second optical path (downward in FIG. 2A). (Shown in FIG. 2). In this case, the first hologram unit 15 corresponds to an optical path separating unit.

In the second hologram section 16, the first quadrant region 16Q1 and the third quadrant region 16Q3 add the first astigmatism to the light on the first optical path to be the first processed light.
This function is performed, for example, by changing the cylindrical lens 17 shown in FIG. 2C to the first quadrant region 16Q1 and the third quadrant region 16Q1.
This is equivalent to the optical element arranged in Q3. The first quadrant region 16Q1 and the third quadrant region 16 of the second hologram unit 16
Q3 corresponds to a first optical processing unit.

The second hologram section 16 has the second
The quadrant region 16Q2 and the fourth quadrant region 16Q4 impart second astigmatism to the light in the above-mentioned second optical path to be second processed light. The second astigmatism has a direction of 90 degrees with respect to the first astigmatism. This function is, for example, shown in FIG.
The cylindrical lens 18 shown in FIG.
This is equivalent to the optical elements arranged in the second and fourth quadrant regions 16Q4. That is, the major axis of the cylindrical lens 18 (the horizontal axis in FIG. 2D) is inclined by 90 degrees with respect to the major axis of the cylindrical lens 17 (the vertical axis in FIG. 2C). I have. The second quadrant region 16Q2 and the fourth quadrant region 16Q of the second hologram unit 16
Reference numeral 4 corresponds to a second optical processing unit. The hologram element 8 corresponds to a focus error detecting optical element.

Next, referring to FIG.
0, the first detector 11 and the second detector 12
Will be described.

As shown in FIG. 3A, the first detector 11 includes four first light receiving units 11A, 11B, 11C, 1
1D. These four first light receiving units 11A to 11A
The boundary line of the light receiving section that partitions 11D is the above-described first to fourth quadrant regions 15Q1 to 15Q4 or 16Q1 to 1Q1.
The detector is inclined at an angle of 45 degrees with respect to the quadrant division line of 6Q4, and is a detector divided into four in an X shape.

The first detector 11 has the configuration shown in FIG.
As shown in (B), the light of the first optical path P1 emitted from the hologram element 8 (the first astigmatism given by the first quadrant region 16Q1 and the third quadrant region 16Q3 of the second hologram unit 16). 1 processing light) is incident. Of the first processing light, the light provided with the first astigmatism in the first quadrant region 16Q1 of the second hologram unit 16 is the first light receiving unit 11A and the first light receiving unit 11A.
Light is incident so as to straddle 1C. Also, of the first processing light, the light provided with the first astigmatism in the third quadrant region 16Q3 of the second hologram unit 16 is the first light receiving unit 11B and the first light receiving unit 11B.
The light enters so as to straddle 1D.

In FIG. 3A, A1 is the first light receiving section 1
C1 denotes the value of a photodetection electric signal output by photoelectrically converting the light received by the first light receiving unit 11B, and B1 denotes the value of the photodetection electric signal output by photoelectrically converting the light received by the first light receiving unit 11B.
Represents the value of a photodetection electric signal output by photoelectrically converting the light received by the first light receiving unit 11C, and D1 represents the value of the first light receiving unit 11D.
Indicates the value of the photodetection electric signal output by photoelectrically converting the received light. Here, the first detector 11 corresponds to a first photodetector.

As shown in FIG. 3B, the second detector 12 includes four second light receiving sections 12A, 12B, 12B.
C and 12D. These four second light receiving units 1
The light receiving unit boundary line that partitions 2A to 12D is the first line described above.
Quadrant region to fourth quadrant region 15Q1 to 15Q4 or 16Q
The detector is inclined at an angle of 45 degrees with respect to the quadrant division lines 1 to 16Q4, and is a detector divided into four in an X shape.

FIG. 2 shows the second detector 12.
As shown in (B), the light of the second optical path P2 emitted from the hologram element 8 (the second astigmatism given by the second quadrant region 16Q2 and the fourth quadrant region 16Q4 of the second hologram section 16). 2 processing light) is incident. Of the second processing light, the light provided with the second astigmatism in the second quadrant region 16Q2 of the second hologram unit 16 is the second light receiving unit 12B and the second light receiving unit 12B.
It is incident so as to straddle 2C. Also, of the second processing light, the light provided with the second astigmatism in the fourth quadrant region 16Q4 of the second hologram unit 16 is the second light receiving unit 12D
It is incident so as to straddle 2A.

In FIG. 3B, A2 denotes the second light receiving unit 1.
C2 denotes the value of the light detection electric signal output by photoelectrically converting the light received by the second light receiving unit 12B, and C2 denotes the value of the light detection electric signal output by photoelectrically converting the light received by the second light receiving unit 12B.
Represents the value of a photodetection electric signal obtained by photoelectrically converting the light received by the second light receiving unit 12C, and D2 represents the value of the second light receiving unit 12D.
Indicates the value of the photodetection electric signal output by photoelectrically converting the received light. Here, the second detector 12 corresponds to a second photodetector.

Next, the operation of the optical pickup 100 when the focal position changes will be described with reference to FIG.
FIG. 4B shows a state of the return light spot in the first detector 11 and the second detector 12 when the light emitted from the optical pickup 100 is in focus on the information recording surface of the optical disk. FIG.

As shown in the upper part of FIG. 4B, at the time of focusing, the light provided with the second astigmatism in the first quadrant region 16Q1 of the second hologram unit 16 of the hologram element 8 is converted to the first light.
The light beam enters as a quarter-circle light spot centered on the boundary between the light receiving portions of the first light receiving portions 11A and 11C of the detector 11, and the second light spot is formed in the third quadrant region 16Q3 of the second hologram portion 16 of the hologram element 8. Of the first astigmatism is
The light is incident as a quarter-circle light spot centered on the boundary between the light receiving portions of the first light receiving portions 11B and 11D of the detector 11.

In this case, 1/4 on the first detector 11
The two circular light spots have the same shape and the same size (area). Therefore, at the time of focusing, in the first detector 11, the light detection electric signal A1 output from the first light receiving unit 11A and the light detection electric signal C1 output from the first light receiving unit 11C are equal. Also, the first light receiving unit 11B
Is equal to the light detection electric signal B1 output from the first light receiving unit 11D. The sum (A1 + C1) of the light detection electric signals A1 and C1 is equal to the sum (B1 + D1) of the light detection electric signals B1 and D1.

As shown in the lower part of FIG. 4B, at the time of focusing, the light to which the second astigmatism has been imparted in the second quadrant region 16Q2 of the second hologram section 16 of the hologram element 8 is focused. The light enters as a quarter-circle light spot centering on the boundary between the second light receiving sections 12A and 12D of the two detectors 12A and 12D. The light to which the astigmatism of 2 is given enters as a 1/4 circular light spot centered on the boundary between the light receiving sections 12B and 12C of the second detector 12.

In this case, 1/4 on the second detector 12
The two circular light spots have the same shape and size (area) respectively, and have the same shape and size (area) as the two quarter-circle light spots in the first detector 11. have. Therefore, at the time of focusing, the second
In the detector 12, the light detection electric signal A2 output from the second light receiving portion 12A is equal to the light detection electric signal D2 output from the second light receiving portion 12D. The light detection electric signal B2 output from the second light receiving unit 12B is equal to the light detection electric signal C2 output from the second light receiving unit 12C. Further, the sum (A2 + D2) of the light detection electric signals A2 and D2 and the light detection electric signal B
The sum of B2 and C2 (B2 + C2) is equal.

The following equation (1) holds: A1 = B1 = C1 = D1 = A2 = B2 = C2 = D2 (1)

From this, the value FE expressed by the following equation (2) FE = (A2 + B2 + C1 + D1)-(A1 + B1 + C2 + D2) (2) is calculated by an arithmetic circuit (shown in FIG. ), The value of FE becomes zero at the time of focusing.

FIG. 4A shows this optical pickup 100.
Is out of focus on the information recording surface of the optical disc and the optical disc is closer than when it is in focus,
FIG. 3 is a diagram illustrating a state of a return light spot in a first detector 11 and a second detector 12.

As shown in the upper part of FIG. 4A, when the optical disk is closer than the in-focus state, the second astigmatism is reduced in the first quadrant region 16Q1 of the second hologram section 16 of the hologram element 8. The applied light is incident as a linear light spot extending on the center line of the first light receiving portion 11C of the first detector 11, and is incident on the second hologram portion 16 of the hologram element 8.
The light provided with the second astigmatism in the third quadrant region 16Q3 is incident as a linear light spot extending on the center line of the first light receiving portion 11D of the first detector 11.

In this case, the two linear light spots on the first detector 11 have the same shape and the same size (area). Therefore, when the optical disk is closer than when the optical disk is in focus, in the first detector 11, the light detection electric signal C1 output from the first light receiving unit 11C is equal to the light detection electric signal D1 output from the first light receiving unit 11D. . In addition, the light detection electric signal A1 output from the first light receiving unit 11A and the light detection electric signal B1 output from the first light receiving unit 11B.
Can be considered almost equal to zero.

As shown in the lower part of FIG. 4A, when the optical disk is closer than when the optical disk is in focus, the second astigmatism is set in the second quadrant region 16Q2 of the second hologram section 16 of the hologram element 8. The aberration-imparted light enters as a linear light spot extending on the center line of the second light receiving portion 12A of the second detector 12, and enters the fourth quadrant region 16Q4 of the second hologram portion 16 of the hologram element 8. The light to which the second astigmatism is given enters as a linear light spot extending on the center line of the second light receiving portion 12B of the second detector 12.

In this case, the two rod-shaped light spots on the second detector 12 have the same shape and size (area), respectively, and are the same as the two rod-shaped light spots on the first detector 11. It has a shape and size (area). Therefore, when the optical disk is closer than when the optical disk is in focus, the second detector 12 uses the second light receiving unit 1
2A output light detection electric signal A2 and second light receiving portion 12B
Output light detection electric signals B2 are equal. In addition, the light detection electric signal C2 output from the second light receiving unit 12C and the light detection electric signal D2 output from the second light receiving unit 12D can be regarded as substantially equal to zero.

The following equation (3) C1 = D1 = A2 = B2 (3) and the following equation (4) A1 = B1 = C2 = D2 = 0 (4) hold.

From the above, when the above conditional expressions (3) and (4) are substituted into the above expression (2), the FE value which is the FE value in this case is given by the following expression (5): FE1 = (A2 + B2 + C1 + D1)-(A1 + B1 + C2 + D2) ) = A2 + B2 + C1 + D1 = 4 × A2 (5), and when the optical disk is closer than when focused, FE
Is a positive value.

FIG. 4C shows that the outgoing light from the optical pickup 100 is out of focus on the information recording surface of the optical disk, and the first light is output when the optical disk is farther than when the optical disk is in focus. FIG. 3 is a diagram illustrating a state of a return light spot in a detector 11 and a second detector 12.

As shown in the upper part of FIG. 4C, when the optical disk is farther from the focused state, the second astigmatism is reduced in the first quadrant region 16Q1 of the second hologram section 16 of the hologram element 8. The applied light is incident as a linear light spot extending on the center line of the first light receiving portion 11A of the first detector 11, and is incident on the second hologram portion 16 of the hologram element 8.
The light provided with the second astigmatism in the third quadrant region 16Q3 is incident as a rod-shaped light spot extending on the center line of the first light receiving portion 11B of the first detector 11.

In this case, the two rod-shaped light spots on the first detector 11 have the same shape and the same size (area). Therefore, when the optical disk is farther than the focused state, in the first detector 11, the light detection electric signal A1 output from the first light receiving unit 11A and the light detection electric signal B1 output from the first light receiving unit 11B are equal. . In addition, the light detection electric signal C1 output from the first light receiving unit 11C and the light detection electric signal D1 output from the first light receiving unit 11D can be regarded as substantially equal to zero.

As shown in the lower part of FIG. 4C, when the optical disk is farther from the in-focus state, the second astigmatism in the second quadrant area 16Q2 of the second hologram section 16 of the hologram element 8 is obtained. The aberration-imparted light enters as a linear light spot extending on the center line of the second light receiving portion 12C of the second detector 12, and enters the fourth quadrant region 16Q4 of the second hologram portion 16 of the hologram element 8. The light to which the second astigmatism has been given enters as a rod-shaped light spot extending on the center line of the second light receiving portion 12D of the second detector 12.

In this case, the two rod-shaped light spots on the second detector 12 have the same shape and size (area), respectively, and are the same as the two rod-shaped light spots on the first detector 11. It has a shape and size (area). Therefore, when the optical disk is farther than at the time of focusing, the second detector 12 uses the second light receiving unit 1
2C output light detection electric signal C2 and second light receiving portion 12D
Output light detection electric signals D2 are equal. Further, the light detection electric signal A2 output from the second light receiving portion 12A and the light detection electric signal B2 output from the second light receiving portion 12B can be regarded as substantially equal to zero.

The following equation (6) A1 = B1 = C2 = D2 (6) and the following equation (7) C1 = D1 = A2 = B2 = 0 (7) are established.

From the above, when the above conditional expressions (6) and (7) are substituted into the above expression (2), the FE value which is the FE value in this case is given by the following expression (8): FE2 = (A2 + B2 + C1 + D1)-(A1 + B1 + C2 + D2) ) = − (A1 + B1 + C2 + D2) = − 4 × A1 (8), and when the optical disk is closer than the in-focus state, FE
Is a negative value.

Therefore, the value FE represented by the above equation (2)
Is used as a focus error signal, focusing is performed when the FE value is zero. When the FE value is positive, the optical disk is closer than when focused, and when the FE value is negative, the optical disk is focused. It can be determined that it is farther than when it is in focus. Therefore, an electric signal obtained by inverting the sign of the focus error signal FE is fed back, and an objective lens driving mechanism (not shown) provided on the objective lens 7 of the optical pickup 100 so that the FE value becomes zero. By controlling, reliable focusing servo control can be performed. In this case, an arithmetic circuit (not shown) connected to the output side of the light detection unit 9 corresponds to a focus error discriminating value calculating means, and the focus error signal value FE corresponds to a focus error discriminating value.

By using the outputs of the first detector 11 and the second detector 12 to calculate a value RF expressed by the following equation (9): RF = A1 + B1 + C1 + D1 + A2 + B2 + C2 + D2 (9) Thus, the optical disc recording information recorded on the optical disc can be read.

The following equations (10), (11), and (1)
2), (13) DPD1 = A1 + C1 (10) DPD2 = B1 + D1 (11) DPD3 = A2 + D2 (12) DPD4 = C2 + B2 (13) Values DPD1, DPD2 represented by (13) , DPD3, DPD4
Is calculated, DPD tracking servo control can be performed by these signals.

Further, if the value PP expressed by the following equation (14) PP = (A1 + C1 + C2 + B2)-(A2 + D2 + B1 + D1) is calculated, the push-pull (Push-
Pull) tracking servo control can be performed.

As shown in FIG. 1B, by disposing a third detector 13 and a fourth detector 14 on both sides of the first detector 11 and the second detector 12, one of them can be used for the + 1st order sub-beam. By using the other for the -1st order sub-beam, it is possible to cope with the three-beam system. In this case, the third detector 13 corresponds to a third light detector, and the fourth detector 14 corresponds to a fourth light detector.

In the above-described method of detecting a focus error in the optical pickup 100, there is no influence of track crossing noise. This will be described with reference to FIG. FIG. 5A shows a pupil plane (a plane perpendicular to the optical axis at the return light convergence position) when crossing the track of the optical disc.
5 shows the light intensity distribution of the track diffracted light image projected on the first and fourth quadrants, and is imbalanced (offset) in the first and fourth quadrants and the second and third quadrants.

In the case of such return light, the first detector 11 and the second detector 12 of the optical pickup 100 have a seemingly unbalanced light intensity distribution as shown in FIG. 5B. However, in the optical pickup 100, since the focus error signal value FE is calculated by the above equation (2), A1 and B2 are subtracted, and A2 and B2 are subtracted.
By subtracting 1, the effect of track crossing noise is cancelled.

In focusing servo control using the astigmatism method, when the optical pickup has an aberration such as astigmatism, as shown in FIG. , 52, 53, and 54, for example, the light intensity of the light receiving units 52 and 54 increases. Since the focus error signal in the astigmatism method is obtained by adding or subtracting the light detection electric signals of the light receiving units in the diagonal direction, when the light intensity distribution becomes unbalanced due to such aberration, the track crossing noise is reduced. As a result, focusing servo control cannot be performed accurately.

However, the optical pickup 10 of the present embodiment
In the case of 0, the light intensity distribution on the detector as shown in FIG. However, in the process of calculating the focus error signal FE by the equation (2), the influence of the imbalance of the light intensity distribution due to the aberration is canceled.

Further, according to the conventional astigmatism method, when the thickness of the optical disk is not constant and there is a thickness error depending on the position, the shape of the return light spot on the detector is distorted, and light that should not be received originally is distorted. The light may leak or wrap around to another light receiving surface, causing an error in the DPD tracking error signal. In the optical pickup 100 of the present embodiment, when there is a disc thickness error, the light spot shapes on the first detector 11 and the second detector 12 are deformed. However, there is no leakage or sneak of light between the quadrant regions, and DPD tracking servo control that does not hinder practical use can be performed.

The optical pickup 1 of the first embodiment described above
At 00, the hologram element 8 and the first detector 1
1, a second detector 12, and an arithmetic circuit (not shown)
Constitutes a focus error detection device.

(2) Second Embodiment

Next, a second embodiment of the present invention will be described. FIG. 7 is a diagram illustrating a configuration of a focus error detection system in the optical pickup according to the second embodiment of the present invention. FIG. 8 is a diagram illustrating the configuration and operation of a lens element in an optical pickup according to a second embodiment of the present invention.

The optical pickup 200 of the second embodiment is
In the optical pickup 100 of the first embodiment, a lens element 28 is provided instead of the hologram element 8 and the light detection section 9 is provided.
However, the difference is that a photodetector 29 is provided instead, and the other components of the optical pickup are the same as those of the optical pickup 100. In addition, the light detector 29 includes the first detector 4
1 and a second detector 42.

As shown in FIGS. 7 and 8, the lens element 28 has a first lens unit 3 in the form of a cylindrical lens decentered in a first quadrant, a second quadrant, a third quadrant, and a fourth quadrant, respectively.
1, the second lens unit 32, the third lens unit 33, and the fourth
The lens unit 34 is provided. FIG. 8 illustrates a side surface shape of each of the lens units 31 to 34. As can be seen from this figure, the major axis direction of the eccentric cylindrical lens including the first lens unit 31 and the third lens unit 33 is
The direction is an angle of 90 degrees with respect to the major axis direction of the eccentric cylindrical lens including the second lens section 32 and the fourth lens section 34.

The lens portions 31 to 34 have both the function of separating the optical path of the incident light and the function of imparting astigmatism to the passing light, and are the same as the hologram element 8 of the first embodiment. Has a function.

With this configuration, as shown in FIGS. 7 and 8, the light emitted from the lens element 28 is split into a first optical path P11 and a second optical path P12, as in the first embodiment. Astigmatism is imparted. In the second embodiment, the lens element 28 corresponds to a focus error detecting optical element.

In the case of the second embodiment, as shown in FIG. 8, the original optical axis 4 before entering the lens element 28 is used.
In contrast to 5, the central axis of the light image irradiated on each of the detectors 41 and 42 moves.

The first detector 41 and the second detector 42 are detectors divided into four crosses. The detectors 41 and 42 are arranged in a state where the detectors 41 and 42 are inclined at an angle of 45 degrees with respect to a “+”-shaped line that is a boundary line of the light receiving unit. The first detector 41 corresponds to a first light detector, and the second detector 42 corresponds to a first light detector.

Next, the operation of the optical pickup 200 according to the second embodiment when the focal position changes will be described with reference to FIG. FIG. 9B shows the state of the return light spot in the first detector 41 and the second detector 42 when the light emitted from the optical pickup 200 is in focus on the information recording surface of the optical disk. FIG. FIG. 9A shows that the light emitted from the optical pickup 200 is out of focus on the information recording surface of the optical disc, and when the optical disc is closer than when it is in focus, the first detector 41 and the FIG. 6 is a diagram illustrating a state of a return light spot in a second detector 42. FIG. 9 (C)
In the case where the light emitted from the optical pickup 200 is out of focus on the information recording surface of the optical disc and the optical disc is farther than when the optical disc is in focus, return light from the first detector 41 and the second detector 42 FIG. 4 is a diagram showing a state of a spot.

As shown in FIG. 9, also in the case of the optical pickup 200 of the second embodiment, if the value fe obtained by a predetermined calculation is used as a focus error signal, focusing is performed when the fe value is zero. When the fe value is non-zero (eg, a positive value), the optical disk is closer to the in-focus state, and when the fe value is another non-zero value (eg, a negative value), the optical disk is farther than the in-focus state. Can be determined. Therefore, an electric signal obtained by inverting the sign of the focus error signal fe is fed back, and an objective lens driving mechanism (not shown) provided on an objective lens (not shown) of the optical pickup 200 so that the fe value becomes zero. (Not shown), reliable focusing servo control can be performed. In this case, an arithmetic circuit (not shown) connected to the output side of the light detection unit 29 corresponds to a focus error discriminating value calculating means, and the focus error signal value fe corresponds to a focus error discriminating value.

As shown in FIG. 10, the third detector 4 is provided on both sides of the first detector 41 and the second detector 42.
By arranging the third and fourth detectors 44, one of them can be used for the + 1st-order sub-beam and the other can be used for the -1st-order sub-beam, so that it is possible to cope with the 3-beam method. In this case, the third detector 43 corresponds to a third light detector, and the fourth detector 44 corresponds to a fourth light detector.

The optical pickup 2 of the second embodiment described above
At 00, the lens element 28 and the first detector 41
, A second detector 42, and an arithmetic circuit (not shown)
This constitutes a focus error detection device.

The present invention is not limited to the above embodiments. Each of the above embodiments is merely an example, and has substantially the same configuration as the technical idea described in the claims of the present invention, and those having the same functions and effects are:
Anything is included in the technical scope of the present invention.

For example, in the above embodiment, the hologram element 8 and the lens element 28 have been described as examples of the optical element for detecting a focus error. However, the present invention is not limited to this example, and the present invention is not limited thereto. An optical element for detecting a focus error, for example, the first hologram unit 15 is combined with another optical element, and the other optical elements are arranged such that the cylindrical lenses are different from each other by 90 degrees in the first to fourth quadrants. It may be. Alternatively, a prism element in which a prism is disposed in the first to fourth quadrants may be used as a first optical element, and the second hologram unit 16 may be used as a second optical element. In short, the first on the plane perpendicular to the optical axis of the return light
Optical path separating means for separating light existing in the quadrant area and the third quadrant area into a first optical path and separating light existing in the second and fourth quadrant areas on a plane perpendicular to the optical axis into a second optical path; A first optical processing unit that imparts a first astigmatism to the light in the first optical path to make the first processing light, and a second optical path in which the light in the second optical path is oriented at 90 degrees to the first astigmatism. Any configuration may be used as long as it is a focus error detecting optical element having a second optical processing unit that imparts the second astigmatism to generate the second processing light.

In the first embodiment, as shown in FIG.
The hologram element 8 is arranged in front of the light detection unit 9, but the polarization hologram element having the same function as the hologram element 8 and having a polarization action is provided by the mirror 5 and the quarter-wave plate 6.
May be provided between them.

[0085]

As described above, according to the present invention, the return light from the optical disk is divided into two optical paths, and a predetermined astigmatism is given to the light in each divided optical path. It is less susceptible to track crossing noise and optical disk thickness error, and can be used in combination with the three-beam method or DPD method. It has the advantages of high out-of-focus detection sensitivity and the ability to reduce the size of the optical pickup. are doing.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a configuration of a hologram element in the optical pickup according to the first embodiment of the present invention.

FIG. 3 is a diagram illustrating configurations and operations of a first detector and a second detector in the optical pickup according to the first embodiment of the present invention.

FIG. 4 is a diagram illustrating an operation of the optical pickup according to the first embodiment of the present invention when the focal position changes.

FIG. 5 is a diagram (1) illustrating advantages of the focus error detection method in the optical pickup according to the first embodiment of the present invention.

FIG. 6 is a diagram (2) illustrating an advantage of the focus error detection method in the optical pickup according to the first embodiment of the present invention.

FIG. 7 is a diagram illustrating a configuration of a focus error detection system in an optical pickup according to a second embodiment of the present invention.

FIG. 8 is a diagram illustrating the configuration and operation of a lens element in an optical pickup according to a second embodiment of the present invention.

FIG. 9 is a diagram illustrating an operation of the optical pickup according to the second embodiment of the present invention when the focal position changes.

FIG. 10 is a diagram illustrating a configuration of a photodetector in an optical pickup according to a second embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 semiconductor laser 2 grating 3 beam splitter 4 collimator lens 5 mirror 6 wavelength plate 7 objective lens 8 hologram element 9 photodetector 11 first detector 11A to 11D first light receiver 12 second detector 12A to 12D second light reception Unit 13 Third detector 14 Fourth detector 15 First hologram unit 15Q1 First quadrant region 15Q2 Second quadrant region 15Q3 Third quadrant region 15Q4 Fourth quadrant region 16 Second hologram unit 16Q1 First quadrant region 16Q2 Second quadrant region 16Q3 Third quadrant region 16Q4 Fourth quadrant region 17, 18 Cylindrical lens 50 Detector 28 Lens element 29 Photodetection unit 31 First lens unit 32 Second lens unit 33 Third lens unit 34 Fourth lens unit 41 First detector 42 Second Detector 43 Third detector 44 Fourth detector 45 Original optical axis 50 Quadrant detector 51 to 54 Light receiving unit 100, 200 Optical pickup L Laser light P1, P11 First optical path P2, P12 Second optical path

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5D118 AA03 AA26 BA01 BB02 BF02 BF03 CC12 CD02 CD03 CD08 CF02 CF06 CF16 DA02 DA17 DA20 DB12 DC03

Claims (6)

[Claims] 1. An optical disk recording information is written on an information recording surface of an optical disk by an emitted light emitted from a light source, or the optical disk recording information is returned from a return light emitted from the light source, reflected by the information recording surface of the optical disk, and returned. A focus error detection device of an optical pickup for detecting a focus error of the emitted light in an optical pickup for reading the light, the light being present in a first quadrant region and a third quadrant region on a plane perpendicular to an optical axis of the return light. Optical path separating means for separating the light existing in the second quadrant area and the fourth quadrant area on the optical axis vertical plane into a second optical path, and separating the light in the first optical path into a first optical path. A first optical processing means for providing astigmatism to make first processing light, and a second astigmatism which gives a direction of 90 degrees to the first astigmatism to the light on the second optical path. And the second processing A focus error detecting optical element having second optical processing means; a first photodetector having a four-divided first light receiving portion and receiving and detecting the first processing light; A second photodetector having a second light receiving unit and receiving and detecting the second processing light; and an intensity of each light received by four parts of the first light receiving unit and four light intensity of the second light receiving unit. A focus error detection device for an optical pickup, comprising: focus error determination value calculation means for performing a predetermined calculation on the intensity of each light received by a portion and outputting a focus error determination value. 2. The focus error detecting device for an optical pickup according to claim 1, wherein the optical path separating unit is a first hologram unit having a prism function, and the first optical processing unit is configured so that the first direction is a long axis. A second hologram unit having a cylindrical lens function, wherein the second optical processing means is a second hologram unit having a cylindrical lens function whose major axis is a direction at 90 degrees to the first direction. Focus error detecting device for an optical pickup. 3. The focus error detecting device for an optical pickup according to claim 1, wherein the focus error detecting optical element is disposed in a first quadrant area and a third quadrant area on the optical axis vertical plane, respectively. An eccentric cylindrical lens whose major axis is in the first direction; and an eccentric cylindrical lens disposed in the second quadrant region and the fourth quadrant region on the plane perpendicular to the optical axis, respectively.
A focus error detecting device for an optical pickup, comprising: an eccentric cylindrical lens having a long axis in a direction of 0 degrees. 4. The focus error detection device for an optical pickup according to claim 1, wherein a third photodetector for a + 1st order sub-beam is provided beside the first photodetector and the second photodetector; A focus error detecting device for an optical pickup, comprising a fourth photodetector for a next sub-beam, and performing control by a three-beam method. 5. The focus error detecting device for an optical pickup according to claim 1, wherein control is performed by a DPD method. 6. An optical disk recording information is written on an information recording surface of an optical disk by an emitted light emitted from a light source, or the optical disk recording information is reflected from a return light emitted from the light source, reflected by the information recording surface of the optical disk, and returned. A focus error detection method for an optical pickup that detects a focus error of the emitted light in an optical pickup that reads the light, the light existing in a first quadrant area and a third quadrant area on a plane perpendicular to an optical axis of the return light. Optical path separating means for separating the light existing in the second quadrant area and the fourth quadrant area on the optical axis vertical plane into a second optical path, and separating the light in the first optical path into a first optical path. A first optical processing means for providing astigmatism to make first processing light, and a second astigmatism which gives a direction of 90 degrees to the first astigmatism to the light on the second optical path. And the second processing A focus error detecting optical element having second optical processing means; a first photodetector having a four-divided first light receiving portion and receiving and detecting the first processing light; A second photodetector having a second light receiving portion and receiving and detecting the second processed light; and an intensity of each light received by four portions of the first light receiving portion and a value of four lights of the second light receiving portion. A focus error detection method for an optical pickup, wherein a predetermined calculation is performed on the intensity of each light received by two portions and a focus error discrimination value is output.