JP2000276742A - Device and method for detecting optical pickup focusing error - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the adverse effect caused by a track crossing noise and a thickness error of an optical disk and to allow a three beam system and a differential phase detection(DPD) system to be combinedly used. SOLUTION: In an optical pickup 100, returned light beams from an optical disk are divided into a first optical path P1 and a second optical path P2 by a hologram element 8. Then, a prescribed astigmatism and focus are given to the beams of each path and photodetection is conducted by a first detector 11 and a second detector 12. By conducting prescribed computations, focus error signals are obtained.

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. In order to read information recorded on an optical disk from the returned light, an optical pickup including a light source, a light transmitting / receiving optical system, and a light detecting system is used.

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.

The astigmatism method is a method in which a cylindrical lens, a parallel plate, and the like are arranged in a light transmitting and receiving optical system, and return light is received and detected by a quadrant 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 the other light receiving surface. Leakage or wraparound may occur, causing an error in the focus 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 means for separating existing light into a second optical path, and applying a first astigmatism to the light in the first optical path to obtain a first processing light and a light in the second optical path. A first optical processing means for applying a second astigmatism in a direction of 90 degrees to the first astigmatism to produce a second processing light, and a first focus on the first processing light A third processing light, and a second error processing means for giving a second focus to the second processing light to obtain a fourth processing light. A first light-receiving unit that has four rectangular first light-receiving units formed by being divided into four and receives and detects the third processing light;
A photodetector, and four rectangular second light receiving portions formed by dividing a light receiving region into four by parallel lines;
A second photodetector that receives and detects the processed light; and a second photodetector configured to determine the intensity of each light received by the four portions of the first light receiving portion and the intensity of each light received by the four portions of the second light receiving portion. And a focus error discriminating value calculating means for outputting the focus error discriminating value.

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 has a cylindrical lens function having a first direction as a long axis with respect to the light of the first optical path, and a direction of 90 degrees with respect to the light of the second optical path with respect to the first direction. Is a second hologram unit having a cylindrical lens function having a long axis as a major axis, wherein the second optical processing means has a convex lens function with respect to the first processing light and has a convex lens function with respect to the second processing light. A third hologram unit, wherein a convex lens for the first processing light and a convex lens for the second processing light have different focal lengths.

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

According to a fifth aspect of the present invention, there is provided a method of 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 for reading 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 unit that, as processing light, imparts a second astigmatism to the light on the second optical path in a direction of 90 degrees with respect to the first astigmatism to form second processing light; A focus error having a second optical processing means for giving a first focus to the first processing light to make it a third processing light and for giving a second focus to the second processing light to make it a fourth processing light A detection optical element, a first photodetector having four rectangular first light receiving portions formed by dividing a light receiving region into four by parallel lines, and receiving and detecting the third processed light; A second photodetector for receiving and detecting the fourth processing light is provided, the second photodetector having four rectangular second light receiving portions formed by dividing the region into four by parallel lines, and The intensity of each light received by the three portions and the intensity of each light received by the four portions of the second light receiving portion are determined by a predetermined function. And outputs a focus error discrimination value after.

[0020]

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.

FIG. 1 is a diagram showing a configuration of an optical pickup according to an embodiment of the present invention. As shown in FIG. 1A, this optical pickup 100 includes a semiconductor laser 1 as a light source, a grating 2, and a beam splitter 3
, A collimator lens 4, a mirror 5, a 波長 wavelength plate 6, an objective lens 7, a hologram element 8, and a light detection unit 9. Also, the objective lens 7 includes
An objective lens driving mechanism (not shown) capable of moving the objective lens 7 back and forth in the optical axis direction is provided.

The light detector 9 includes a first detector 11
And a second detector 12 (see FIG. 4).
This will be described later. The light detection unit 9 is connected to an arithmetic circuit (not shown) including an adder and a subtractor for performing a predetermined operation based on the light detection electric signals output from the first detector and the second detector.

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 beam 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 via 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. 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 return light of the first optical path P1 to a first detector 11 (see FIG. 4), and return light of the second optical path P2 is received by a second detector 12 (FIG. 4) described later.
A predetermined operation is performed on the photodetection electric signal output by the photoelectric conversion to generate a focus error signal.

Next, the configuration of the hologram element 8 will be described. The hologram element 8 includes a first hologram unit 15
, A second hologram section 16 and a third hologram section 19. FIG. 2 shows the first hologram section 15 of the hologram element 8 in the optical pickup 100 described above.
FIG. 3 is a diagram illustrating a configuration of a second hologram unit 16.
FIG. 3 is a diagram illustrating the configuration of the third hologram unit 19 of the hologram element 8 in the optical pickup 100.

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 impart 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 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 hologram unit 16 corresponds to a first optical processing unit.

In the third hologram section 19, the first quadrant region 19Q1 and the third quadrant region 19Q3 give a first focus to the above-mentioned first processing light to make it a third processing light. Also,
In the third hologram unit 19, the second quadrant region 19Q2 and the fourth quadrant region 19Q4 impart the second focus to the above-described second processing light to be the fourth processing light. The third hologram unit 19 corresponds to a second optical processing unit. The hologram element 8 corresponds to a focus error detecting optical element.

In the above description, the first quadrant region is defined as a case where the plane is divided into four regions by a horizontal X-axis and a vertical Y-axis perpendicular to the X-axis. It refers to a positive value area. The second quadrant area is an area adjacent to the first quadrant area among the four areas described above, and is an area where the X coordinate is a negative value and the Y coordinate is a positive value. The third quadrant area is an area adjacent to the second quadrant area among the four areas described above, and has an X coordinate and a Y coordinate.
This is an area where both coordinates have negative values. The fourth quadrant area is an area adjacent to the first quadrant area and the third quadrant area among the four areas described above, and the X coordinate is a positive value and Y
It is an area where the coordinates have negative values.

Next, based on FIG.
The configuration and operation of the first detector and the second detector at 0 will be described.

As shown in FIG. 4A, the first detector 11 has a rectangular light receiving area and has four first light receiving portions A1, A2, B1, and B2. These four
Light receiving unit boundary lines 61, 6 that partition the two first light receiving units A1, etc.
2 and 63 are the above-described first to fourth quadrant regions 15 to 15, respectively.
Q1 to 15Q4 or 16Q1 to 16Q4 or 19Q1
Line in the Y-axis direction (vertical line) among quadrant division lines in 19Q4
Is a straight line parallel to. For this reason, the first light receiving units A1, A
2, B1, and B2 have the entire light receiving area divided into four by parallel lines, and each has a rectangular shape.

Further, the first detector 11 applies the light of the first optical path P1 emitted from the hologram element 8 (the first quadrant region 19Q1 and the third quadrant region 19Q of the third hologram unit 19).
The third processing light (first focused light) at 3 is incident.
Of the third processing light, the light emitted from the first quadrant region 19Q1 of the third hologram unit 19 enters so as to straddle the first light receiving units B1 and B2. Further, of the third processing light, the light emitted from the third quadrant region 19Q3 of the third hologram unit 19 enters so as to straddle the first light receiving units A1 and A2. Here, the first detector 11 corresponds to a first photodetector.

As shown in FIG. 4B, the second detector 12 has a rectangular light receiving area, and has four second light receiving sections C1, C2, D1, and D2. These four
Light receiving unit boundary lines 64 and 6 that partition the two second light receiving units C1 and the like.
5 and 66 are the above-described first to fourth quadrant regions 15 to 15, respectively.
Q1 to 15Q4 or 16Q1 to 16Q4 or 19Q1
Line in the Y-axis direction (vertical line) among quadrant division lines in 19Q4
Is a straight line parallel to. Therefore, the second light receiving units C1, C
2, D1, and D2 have the entire light receiving area divided into four by parallel lines, and each has a rectangular shape.

Further, the second detector 12 supplies the light of the second optical path P2 emitted from the hologram element 8 (the second quadrant region 19Q2 and the fourth quadrant region 19Q of the third hologram unit 19).
In step 4, the fourth processing light (second focused light) is incident.
Of the fourth processing light, the light emitted from the second quadrant region 19Q2 of the third hologram unit 19 enters so as to straddle the second light receiving units C1 and C2. Further, of the fourth processing light, the light emitted from the fourth quadrant region 19Q4 of the third hologram unit 19 enters so as to straddle the second light receiving units D1 and D2. 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. 5B shows the state of the return light spot on 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. 5B, at the time of focusing, the third processed light from the first quadrant region of the lens element 8 is linearly applied to the first light receiving portions B1 and B2 of the first detector 11. The light is incident as a light spot, and the third processed light from the third quadrant region of the lens element 8 is incident on the first light receiving portions A1 and A2 of the first detector 11 as a linear light spot.

As shown in the lower part of FIG. 5B, at the time of focusing, the fourth processing light from the second quadrant region of the lens element 8 is directed to the second light receiving portions C1 and C2 of the first detector 12. Incident as a light spot in the shape of
The fourth processing light from the quadrant region enters the second light receiving units D1 and D2 of the second detector 12 as a linear light spot.

In this case, at the time of focusing, the light detection electric signal A1 output from the first light receiving section A1, the light detection electric signal B1 output from the first light receiving section B1, and the light detection electric signal output from the second light receiving section C1. The signal C1 and the light detection electric signal D1 output from the second light receiving unit D1 are equal to each other. When focusing, the first
The light detection electric signal A2 output from the light receiving portion A2, the light detection electric signal B2 output from the first light receiving portion B2, the second light receiving portion C2
And the light detection electric signal D2 output from the second light receiving portion D2 are equal to each other.

Therefore, the following equation (1) A1 = B1 = C1 = D1 (1) and the following equation (2) A2 = B2 = C2 = D2 (2) hold.

From this, the value FE expressed by the following equation (3) FE = (A2 + B2 + C1 + D1)-(A1 + B1 + C2 + D2) is calculated by an arithmetic circuit (not shown) connected to the output side of the light detection unit 9. ), The value of FE becomes zero at the time of focusing.

FIG. 5A 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. 5A, when the optical disk is closer than when the optical disk is in focus, the third processing light from the first quadrant region of the lens element 8 is transmitted to the first detector 11 of the first detector 11. A light spot having a shape of a quarter of an ellipse is incident on the light receiving sections B1 and B2, and the third processed light from the third quadrant region of the lens element 8 is transmitted to the first light receiving section A of the first detector 11.
1. A light spot having a shape of a quarter of an ellipse is incident on A2.

In this case, 1/4 on the first detector 11
The two elliptical light spots have the same shape and the same size (area). The ratio B1: B2 of the light detection electric signal B1 output from the first light receiving portion B1 to the light detection electric signal B2 output from the first light receiving portion B2 is, for example, 6:
It is 4. The same applies to A1 and A2. Therefore, when the optical disk is closer than the one at the time of focusing, in the first detector 11, the following expressions (4) and (5) A1 = B1 = 6k (4) A2 = B2 = 4k (4) 5) holds. Here, k is an arbitrary positive value.

As shown in the lower part of FIG. 5A, when the optical disk is closer than when the optical disk is in focus, the fourth processing light from the second quadrant area of the lens element 8 is applied to the second detector 1
The second light receiving portion C2 of the second detector 12 is incident on the second light receiving portion C2 of the second detector 12 as a light spot having a shape of a quarter of an ellipse.
No light is incident on 1. Further, the fourth processing light from the fourth quadrant region of the lens element 8 is incident on the second light receiving portion D2 of the second detector 12 as a light spot having a shape of a quarter of an ellipse. Does not enter the second light receiving section D1.

In this case, the light detection electric signal C1 output from the second light receiving portion C1 and the light detection electric signal D1 output from the second light receiving portion D1 can be regarded as equal to zero. Therefore, when the optical disk is farther than the in-focus state, in the second detector 12, the following expressions (6) and (7) C2 = D2 = 10k (6) C1 = D1 = 0 (6) 7) holds.

From this, when the above conditional expressions (4), (5), (6), and (7) are substituted into the above expression (3), the FE value FE1 in this case is calculated by the following expression (8) FE1 = (A2 + B2 + C1 + D1)-(A1 + B1 + C2 + D2) = (4k + 4k)-(6k + 6k + 10k + 10k) =-24k (8) If the optical disk is closer than the in-focus state, FE
Is a negative value.

FIG. 5C shows this optical pickup 100.
Is out of focus on the information recording surface of the optical disc and the optical disc is farther than when focused,
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. 5C, when the optical disk is farther from the in-focus state, the third processing light from the first quadrant region of the lens element 8 is applied to the first detector 11 of the first detector 11. The light is incident on the light receiving portion B2 as a light spot having a shape of a quarter of an ellipse, and is not incident on the first light receiving portion B1 of the first detector 11. Further, the third processing light from the third quadrant region of the lens element 8 is supplied to the first light receiving unit A of the first detector 11.
The light is incident on the light detector 2 as a light spot having a shape of a quarter of an ellipse, and is not incident on the first light receiving portion B1 of the first detector 11.

In this case, the light detection electric signal B1 output from the first light receiving portion B1 and the light detection electric signal A1 output from the first light receiving portion A1 can be regarded as being equal to zero. Therefore, when the optical disk is farther than the in-focus state, in the second detector 12, the following expressions (9) and (10) A2 = B2 = 10k (9) A1 = B1 = 0 (9) 10) holds.

As shown in the lower part of FIG. 5C, when the optical disk is farther from the in-focus state, the fourth processing light from the second quadrant area of the lens element 8 is supplied to the second detector 1.
The second processing light from the fourth quadrant region of the lens element 8 is incident on the second light receiving portions C1 and C2 of the second detector 12 as a light spot having a shape of a quarter of an ellipse. A light spot having a shape of a quarter of an ellipse is incident on the light receiving portions D1 and D2.

In this case, 1/4 on the second detector 12
The two elliptical light spots have the same shape and the same size (area). The ratio C1: C2 between the light detection electric signal C1 output from the second light receiving portion C1 and the light detection electric signal C2 output from the second light receiving portion C2 is, for example, 6:
It is 4. The same applies to D1 and D2. Therefore, when the optical disk is farther than the focused state, the second detector 12 uses the following formulas (11) and (12) C1 = D1 = 6k (11) C2 = D2 = 4k (.) 12) holds.

From the above, when the above conditional expressions (9) to (12) are substituted into the above expression (3), the FE value, which is the FE value in this case, is given by the following expression (13). ) = (10k + 10k + 6k + 6k) − (4k + 4k) = 24k (13), and when the optical disk is farther than the in-focus state, FE
Is a positive value.

Therefore, the value FE expressed by the above equation (3)
Is used as a focus error signal, focusing is performed when the FE value is zero, when the FE value is a negative value, the optical disk is closer to the focus state, and when the FE value is a positive value, 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 the value RF expressed by the following equation (12): RF = A1 + A2 + A3 + A4 + B1 + B2 + B3 + B4 (14) Thus, the optical disc recording information recorded on the optical disc can be read.

The following equations (15), (16), and (1)
7), (18) DPD1 = A1 + A2 (15) DPD2 = B1 + B2 (16) DPD3 = C1 + C2 (17) DPD4 = D1 + D2 (18) Values DPD1, DPD2 represented by (18) , DPD3, DPD4
Is calculated, DPD tracking servo control can be performed by these signals.

By calculating the value PP expressed by the following equation (19): PP = (A1 + A2 + C1 + C2)-(B1 + B2 + D1 + D2) (19)
Pull) tracking servo control can be performed.

Although not shown, a third detector and a fourth detector are arranged on both sides of the first detector 11 and the second detector 12, and one of them is used for the + 1st-order sub-beam, and the other is used for the -1st-order subbeam. By using for the sub beam, it is possible to correspond to the three beam system. In this case, the third
The detector corresponds to a third light detector, and the fourth detector corresponds to a fourth light detector.

The focus error detecting method in the optical pickup 100 has the following advantages.

(1) There is no interference between the quadrants of the return light on the detector. For this reason, even when the thickness of the optical disc is not constant and there is a thickness error depending on the location, there is no leakage of light between quadrants.

(2) The leakage of the track crossing signal is small.

(3) The detection system is compact, and can be used in combination with the three-beam system without any problem.

(4) DPD tracking error can be detected.

In the optical pickup 100 described above,
The lens element 8, the first detector 11, the second detector 12, and an arithmetic circuit (not shown) constitute a focus error detection device.

The present invention is not limited to the above embodiment. The above embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the scope of the claims of the present invention. It is included in the technical scope of the invention.

For example, in the above embodiment, the hologram element 8 has been described as an example of the focus error detecting optical element. However, the present invention is not limited to this example. An optical element, for example, an optical element configured by combining a prism, a convex lens, or the like may be used. In short, the light existing in the first and third quadrants on a plane perpendicular to the optical axis of the return light is separated into the first optical path, and the second and fourth quadrants on the plane perpendicular to the optical axis. An optical path separating means for separating light existing in the first optical path into a second optical path;
The first astigmatism is given to the light on the optical path to be a first processing light, and the second astigmatism is applied to the light on the second optical path in a direction of 90 degrees with respect to the first astigmatism. A first optical processing means for converting the first processing light into a second processing light, and a first processing light to a third processing light, and a second processing light to a second focus. Any configuration may be used as long as it is a focus error detecting optical element having the second optical processing means for converting light.

In the above embodiment, as shown in FIG.
Although the lens element 8 is arranged before the light detection unit 9,
A polarizing lens element having the same function as the lens element 8 and having a polarizing action may be provided between the mirror 5 and the quarter-wave plate 6.

[0069]

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 on each of the divided optical paths, so that a predetermined focal point is obtained. Because it is added, it is less susceptible to track crossing noise and optical disc thickness error, and it can be used in combination with the 3-beam method or DPD method, has high out-of-focus detection sensitivity, and can be downsized. This is an advantage.

[Brief description of the drawings]

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

FIG. 2 is a diagram (1) illustrating a configuration of a hologram element in the optical pickup according to one embodiment of the present invention.

FIG. 3 is a diagram (2) illustrating a configuration of a hologram element in the optical pickup according to the embodiment of the present invention.

FIG. 4 is a diagram illustrating configurations and operations of a first detector and a second detector in the optical pickup according to the embodiment of the present invention.

FIG. 5 is a diagram illustrating an operation when the focal position changes in the optical pickup according to the 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 波長 wavelength plate 7 objective lens 8 hologram element 9 photodetector 11 first detector 12 second 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 19 Third hologram unit 19Q1 First Quadrant area 19Q2 Second quadrant area 19Q3 Third quadrant area 19Q4 Fourth quadrant area 61-66 Light receiving unit boundary line 100 Optical pickup L Laser light P1 First optical path P2 Second optical path

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5D118 AA13 AA26 BA01 CA22 CD02 CF05 DA02 5D119 AA28 AA41 EA03 EC07 EC41 JA09 JA24 JB01 KA04

Claims (5)

[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. The first processing light is provided with astigmatism, and the second processing light is provided with second astigmatism in the direction of 90 degrees with respect to the first astigmatism on the light in the second optical path. The first And Manabu processing means, first to the first processing light
A focus error detecting optical element having second optical processing means for imparting a third focal point to the third processing light and for imparting a second focal point to the second processing light to produce a fourth processing light; Is a rectangular 4 formed by being divided into four by parallel lines.
A first photodetector having two first light receiving portions and receiving and detecting the third processing light; and a rectangular photodetector formed by dividing a light receiving region into four parallel lines.
A second photodetector having two second light receiving portions and receiving and detecting the fourth processing light; and an intensity of each light received by four portions of the first light receiving portion and a fourth light receiving portion of the second light receiving portion. 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 two portions and outputting a focus error determination value. 2. The focus error detecting device for an optical pickup according to claim 1, wherein said optical path separating means is a first hologram section having a prism function, and said first optical processing means is adapted to detect light in said first optical path. A second hologram unit having a cylindrical lens function having a first direction as a long axis and a cylindrical lens function having a long axis at 90 degrees to the first direction with respect to light in the second optical path. Wherein the second optical processing means has a convex lens function with respect to the first processing light and a third hologram unit having a convex lens function with respect to the second processing light. A focal length of the convex lens for the second processing light is different from a focal length of the convex lens for the second processing light. 3. The focus error detecting 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. 4. The focus error detecting device for an optical pickup according to claim 1, wherein control is performed by a DPD method. 5. 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. The first processing light is provided with astigmatism, and the second processing light is provided with second astigmatism in the direction of 90 degrees with respect to the first astigmatism on the light in the second optical path. The first And Manabu processing means, first to the first processing light
A focus error detecting optical element having second optical processing means for imparting a third focal point to the third processing light and for imparting a second focal point to the second processing light to produce a fourth processing light; Is a rectangular 4 formed by being divided into four by parallel lines.
A first photodetector having two first light receiving portions and receiving and detecting the third processing light; and a rectangular photodetector formed by dividing a light receiving area into four parallel lines.
A second photodetector for receiving and detecting the fourth processing light; and an intensity of each light received by four portions of the first light receiving section and a second light receiving section for receiving the fourth processing light. A focus error detection method for an optical pickup, wherein a predetermined calculation is performed on the intensities of respective lights received by four parts and a focus error determination value is output.