JP2002092905A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup device which is hardly influenced by a truck crossing noise or an optical disk thickness error, in which both a 3-beam mode and a DPD mode can be used and which is unaffected by an optical axis deviation. SOLUTION: The optical pickup device is provided with: an optical element for detecting a focal error which has four divided regions of the first quadrant to the fourth quadrant divided by two parting lines which extend in the extension direction of a truck and in the direction perpendicular to the extension direction on the plane perpendicular to the optical path of a return light beam and which splits the return light beam into at least four light beams while imparting astigmatism in the direction rotated mutually by 90 degrees around the optical path to the return light beam which passes through the adjacent regions of the same side divided by the parting line; a photodetector which has a contour corresponding to the parting line in the image surface where the light beam becomes circular, and which has a light receiving element consisting of two light-receiving regions divided by a by-parting line extended approximately parallel to one of the contours; and sub-light receiving elements disposed adjacently, to respective light-receiving regions along the contour corresponding to the parting line of the light receiving element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device in an optical information recording / reproducing apparatus for writing an information signal or reading an information signal on an optical information recording medium such as an optical disk using a light beam.

[0002]

2. Description of the Related Art An optical pickup is a CD (Compac).
t Disk), CD-ROM, DVD (Digita)
1 Versatile Disk) converges a light beam emitted from a light source to a pit row or a track formed spirally or concentrically on an information recording surface on the surface of an optical disc such as a Versatile Disk to form a spot, thereby forming information on the optical disc. In order to read recorded information such as music and data from the returned light reflected back from the recording surface, or to write recorded information to a track or the like, an irradiation optical system including an objective lens and a light detection system are provided. I have.

In this optical pickup, a focus servo and a tracking servo of a so-called objective lens are indispensable for reliably writing information on the optical disk or reading information from the optical disk. Tracking servo control is position control in a radial position of an optical disc with respect to a track of an objective lens so that a light beam is always irradiated onto a recording location (for example, a track) on an information recording surface of the optical disc. The focusing servo control is performed so that the error of the position of the objective lens in the optical axis direction (focusing direction) with respect to the in-focus position, that is, the focus error, is small so that the light beam becomes a spot-like point and converges on the recording position. This is the position control of the objective lens in the optical axis direction.

As a focusing servo control method, for example, light is split into two optical paths in an optical system of return light, and a focus is formed so as to generate a focus connected to a front detector and a focus connected to a rear detector. A spot size method for comparing the size of the light spot on the front and rear detectors, a cylindrical lens or a parallel flat plate arranged in the optical system of the return light, and the return light is received by the four-divided detector and the light on the detector is received. An astigmatism method for detecting a spot shape is known.

[0005] In the spot size method, the return light is divided, so that the entire optical pickup becomes large. However, in the astigmatism method, since the out-of-focus detection sensitivity is high and a four-division detector is used for light detection, a DPD (Differential) is used.
It is easy to calculate a tracking error signal for tracking servo control in a phase detection (Phase Detection) 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.

FIG. 1 shows an example of a conventional optical pickup device using the astigmatism method. The light beam from the semiconductor laser 1 passes through the polarization beam splitter 3, the collimator lens 4, and the quarter-wave plate 6, and is condensed by the objective lens 7 on the optical disk 5 placed near the focal point. Is a light spot SP on the pit row (track) on the information recording surface.

The light reflected back from the optical disk 5 is collected by the objective lens 7, passes through the ４ wavelength plate 6 and the collimator lens 4, is redirected by the polarizing beam splitter 3, and passes through the cylindrical lens 8. A light spot SP near the center of a four-divided photodetector 9 having a light receiving surface divided into four by two lines perpendicular to the track extending direction and the disk radial direction.
To form

As shown in FIG. 2, the cylindrical lens 8 is arranged on the optical path of the return light so that the central axis extends at an angle of 45 degrees with respect to the track extending direction of the optical disk 5, so that the objective lens The return light converged at 7 is given astigmatism, and a linear image M and an image plane B where the light beam is circular (minimum scattering circle) in the optical system provided with astigmatism (hereinafter referred to as a minimum scattering circular image plane) ) And a line image S are formed. Therefore, when the light beam condensed on the recording surface of the optical disk 5 is focused, the cylindrical lens 8 converts the circular light spot SP on the minimum scattering circular image plane B as shown in FIG. When the light is irradiated and out of focus (when the objective lens 7 is far (b) or close (c) from the optical disc 5 shown in FIG. 1), the light is divided into four parts as shown in FIG. 3 (b) or (c). An elliptical light spot SP is irradiated on the four-divided photodetector 9 in the diagonal direction of the surface.

The four-segment photodetector 9 photoelectrically converts the light spots illuminated on the four light receiving surfaces into electric signals in accordance with the light intensities, and supplies the electric signals to the focus error detecting circuit 12. The focus error detection circuit 12
A signal (hereinafter also referred to as a focus error signal or FES) obtained by performing a predetermined operation based on the electric signal supplied from the four-division photodetector 9 is generated and supplied to the actuator drive circuit 13. The actuator drive circuit 13 outputs the focusing drive signal to the actuator 1
5 The actuator 15 moves the objective lens 7 in the focusing direction according to the focusing drive signal. Thus, the position of the objective lens is controlled by feeding back the focus error signal.

As shown in FIG. 4, the four-divided photodetector 9 includes four light-receiving portions DET1 in the first to fourth quadrants which are arranged close to each other with two orthogonal dividing lines L1 and L2 as boundaries, and are mutually independent. To DET4, to which the focus error detection circuit 12 is connected. The four-division photodetector 9 is arranged such that one division line L1 is parallel to the mapping in the recording track extension direction of the optical disk 5, ie, the tangential direction, and the other division line L2 is parallel to the radial mapping. I have. The light receiving unit DE is symmetrical with respect to the center O of the light receiving surface of the quadrant photodetector 9.
Each photoelectric conversion output from T1 and DET3 is added by an adder 22, and each photoelectric conversion output from light receiving units DET2 and DET4 is added by an adder 21, and each output of these adders 21 and 22 is added to a differential amplifier 23. Supplied to Differential amplifier 23
Calculates the difference between the supply signals and outputs the difference signal as a focus error signal (FES).

As described above, in the conventional focus error detection circuit 12, the outputs of the four-divided photodetector 9 are added by the adders 21 and 22, respectively, and the differential amplifier 23 is added.
To generate a focus error component. That is, when the sign of the light receiving portion of the four-segment photodetector 9 is indicated as its output, the focus error signal FES is expressed by the following equation (1).

FES = (DET1 + DET3)-(DET2 + DET4) (1)

FIG. 5 shows a so-called S-shaped characteristic of the focus error signal (FES). At the time of focusing, the light spot intensity distribution is symmetrical with respect to the center O of the light receiving surface of the four-segment photodetector 9, that is, a light spot having a perfect circle as shown in FIG. Are formed in the four-divided photodetector 9, the values obtained by adding the photoelectric conversion outputs of the light receiving units on the diagonal lines are equal to each other, and the focus error component is "0". In addition, when the image is out of focus, an elliptical light spot is formed on the four-division photodetector 9 in the diagonal direction of the light receiving unit as shown in FIG. 3B or 3C, so that the photoelectric conversion of the light receiving unit on the diagonal line is performed. The values obtained by adding the outputs have different polarities.
Therefore, the focus error component output from the differential amplifier 23 has a value corresponding to the focus error.

[0013]

However, according to the astigmatism method, when an optical pickup has an aberration such as astigmatism, noise (hereinafter referred to as a focus error signal) applied to a focus error signal when a light beam spot crosses a track of an optical disk. ,
This is called "track crossing noise." ).
That is, even in the case of focusing shown in FIG.
It may not be 0.

Unnecessary astigmatism in the optical pickup device may be caused by poor alignment accuracy when the light beam transmission surface of optical components such as a diffraction grating and a half mirror is not perpendicular to the optical axis of the emitted light beam. If low, also
This occurs when the emitted light beam of the semiconductor laser itself has astigmatism. In addition, astigmatism also occurs due to birefringence of the disk substrate involved in the irradiation and reflection of the light beam.

Although this unnecessary astigmatism can be canceled out somewhat by optical components such as a shaping prism, for example, 45 ° with respect to the direction corresponding to the tangential (track) direction of the astigmatism direction or the radial direction. The so-called oblique astigmatism component extending in the ° direction remains as the entire optical system. For example, when a focused light beam is irradiated on a polycarbonate (PC) disk substrate, a tangent (track) is generated.
Astigmatism appears at an angle of 45 ° with respect to the direction or the radial direction.

In an irradiation optical system and a light detection optical system of an optical pickup device using an astigmatism method, optical elements (including a semiconductor laser as a light source, an LED, and the like) are designed so as not to generate unnecessary astigmatism. However, it is actually difficult to completely remove unnecessary astigmatism. When there is unnecessary astigmatism not used for the focus servo, track crossing noise occurs when an attempt is made to obtain a focus error signal from an optical disc having lands and grooves on the information recording surface. This is because the distribution of the light intensity is biased in the circular light beam spot on the four-segment photodetector 9.

In the conventional optical pickup for CD, since the numerical aperture NA of the objective lens is small and the depth of focus is large, there is no problem even if the noise rides on the focus error signal to some extent. However, when reading information from an optical disk such as a DVD-RAM having lands and grooves, the numerical aperture of the objective lens is large and the depth of focus is small.
The influence of the FES noise included in the focus error signal on the focus servo of the objective lens increases.
Further, the influence is also increased when the groove depth is set so that a push-pull error occurs.

Further, as shown in FIG. 5, in the conventional astigmatism method, the range in which the astigmatic difference between the line images M and S including the minimum scattering circular image plane B occurs, that is, the focus error signal Sharp response characteristics are obtained within the effective range (capture range), but the response characteristics are not steep outside the capture range. It is desirable that the focus error signal outside the capture range which is not originally effective becomes steep zero. However, in the conventional focus error detection, steep characteristics cannot be achieved because the output gradually begins to increase from the time when the elliptical spot protrudes from the detector, gradually increasing due to defocusing, and the diagonal component output leaks. . If the numerical aperture of the objective lens increases in response to recent high-density optical discs, the range of the operating distance of the objective lens will be further limited. Therefore, accurate detection of the capture range by the conventional astigmatism method is desired. .

In an attempt to accurately know the capture range of the focus servo, see, for example, Japanese Patent Application Laid-Open No. 8-185635.
There is an astigmatism method disclosed in Japanese Unexamined Patent Publication (Kokai) Publication. In this technique, a capture range when reproducing a multilayer disc is detected by an output of an auxiliary detector provided outside a four-segment photodetector. However, in such an astigmatism method, an elliptical spot, which continuously increases due to defocus, starts to output gradually from the point of protruding from the quadrant detector, so that a steep capture range detection signal characteristic cannot be achieved. Furthermore, the optical axis of the light beam spot on the four-segment photodetector is also weak. In the case of conventional focus error detection, the defocused light beam does not protrude significantly from the photodetector because it spreads around the optical axis. Therefore, when reproducing a multi-layer disc with a narrow layer interval such as a DVD in which a plurality of information recording surfaces are stacked in the film thickness direction, the influence of interlayer crosstalk cannot be suppressed unless the area of the photodetector is set extremely small. . Decreasing the area of the light receiving element decreases the capture range, thereby deteriorating the pre-ability of the system.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and the problems to be solved by the present invention are to reduce the effects of track crossing noise, optical disk thickness error, and deviation of the optical axis of a light beam. Hard to receive 3 beam system and D
An object of the present invention is to provide an optical pickup device that can be used together with the PD method.

[0021]

According to the present invention, there is provided an optical pickup device comprising: an irradiation optical system for forming a spot by condensing a light beam on a track on an information recording surface of an optical recording medium; An optical pickup device for detecting a focus error of the light beam, the optical pickup device having a light detection optical system for guiding the returned light to the photodetector, wherein the track extends on a plane perpendicular to the optical path of the returned light. The first and fourth quadrants are divided into four regions from the center of the optical path by two dividing lines extending in the direction and the direction perpendicular to the extending direction, and are the same with the dividing lines as boundaries. Focus error detecting optics that imparts astigmatism in directions rotated by 90 degrees around the optical path to the return light passing through the adjacent region on the side and separates the return light into at least four light beams for each of the regions. Separated from the element In the optical system to which the return light is received, each of which has a contour line corresponding to the dividing line on the image plane where the light beam is circular in an optical system to which astigmatism is imparted, and extends substantially parallel to one of the contour lines. A photodetector having a plurality of spaced light-receiving elements formed by two light-receiving areas divided by two dividing lines; and adjoining each light-receiving area along the contour line corresponding to the division line of the light-receiving element. And sub-light-receiving elements arranged respectively.

In the optical pickup device of the present invention,
The two dividing lines of the light receiving element extend in a direction perpendicular to the track extending direction.
In the optical pickup device of the present invention, the dividing line of the light receiving element is a spot of the received return light on the light receiving element on an image plane where a light beam is circular in an optical system to which astigmatism is given. The signal output from the two light receiving areas of the light receiving element generated by the light receiving element extends to a position where the signals are substantially equal.

In the optical pickup device of the present invention,
Connected to the light receiving element and the sub light receiving element, and to the sum of the differences of the signals output from the two light receiving regions of the light receiving element, the sum of the difference of the signals output from the sub light receiving element, A focus error signal correction arithmetic circuit for generating a focus error signal is provided. In the optical pickup device of the present invention, the focus error detecting optical element may be a cylindrical having a central axis extending in a direction in which the dividing lines are arranged at one diagonal position in the first to fourth quadrants. A lens and a cylindrical lens having a central axis at a direction 90 degrees to the extension direction of the dividing line disposed at each of the other diagonal positions. The central axis of the cylindrical lens is decentered parallel to the dividing line.

In the optical pickup device of the present invention,
The central axes of the cylindrical lenses respectively arranged in the at least one diagonal region are decentered parallel to the dividing line and opposite to each other. In the optical pickup device according to the present invention, the light receiving elements are arranged in parallel with one of the division lines of the focus error detecting optical element.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. (Optical Pickup Device and Optical Path) FIG. 6 is a diagram showing a configuration of an optical pickup according to an embodiment of the present invention. As shown in FIG. 6, the optical pickup 100 includes a semiconductor laser 1, which is a light source, a grating 2, a polarization beam splitter 3, a collimator lens 4, and a mirror 25.
, A quarter-wave plate 6, an objective lens 7, a focus error detecting optical element 18 made of a translucent material, and a photodetector 19. The optical disc 5 is loaded on the objective lens 7 at a distance. As shown in FIG. 7, the focus error detecting optical element 18 includes a first lens unit 31, a second lens unit 32, a third lens unit 33, and a fourth lens unit of a cylindrical lens.
The photodetector 19 includes a first light receiving element 31PD and a second light receiving element 32P corresponding to these lens parts.
D, the third light receiving element 33PD and the fourth light receiving element 34PD are arranged and arranged as a column 19L along one division line. These will be described later in detail. The objective lens 7 is provided with an objective lens driving mechanism (not shown) similar to the related art, which can move the objective lens 7 back and forth in the optical axis direction.

The light beam emitted from the semiconductor laser 1 enters the polarization beam splitter 3 via the grating 2. The polarizing beam splitter 3 has a polarizing mirror, and the incident light beam passes through the polarizing beam splitter 3, passes through the collimator lens 4, changes the optical path to a right angle by the mirror 25, and passes through the quarter-wave plate 6. Then, the light is emitted from the objective lens 7 to the information recording surface of the optical disk 5. The objective lens 7 focuses a light beam on a pit row or track formed in a spiral or concentric shape on the optical disk 5 to form a spot. With this irradiation light beam spot, it is possible to write or read out recorded information on the information recording surface of the optical disk.

The return light reflected by the light beam spot on the information recording surface of the optical disk returns along the same optical path, passes through the objective lens 7, the quarter-wave plate 6, the mirror 25, and the collimator lens 4, and is again polarized. The light enters the beam splitter 3. In this case, the return light has its optical path changed by the polarization beam splitter 3 in a direction different from the direction toward the semiconductor laser 1, and is guided to the focus error detecting optical element 18. The return light that has passed through the focus error detecting optical element 18 is given astigmatism, and as shown in FIG. 7, the first lens unit 31, the second lens unit 32, and the third lens unit 3
The third and fourth lens portions 34 respectively cause the first optical path P
The first light receiving element 31PD and the second light receiving element 32P which are divided into four parts including a first optical path P2, a third optical path P3, and a fourth optical path P4, and are respectively separated from the photodetector 19.
D, and enters the third light receiving element 33PD and the fourth light receiving element 34PD. Each light receiving element of the photodetector 19 photoelectrically converts the received light, performs a predetermined operation on the photodetection electric signal output by the photoelectric conversion, and generates a focus error signal. (Focus Error Detection Optical Element) As shown in FIG. 7, the focus error detection optical element 18 is formed of, for example, glass, and the track extending direction (tangential direction) of the optical disk 5 on a plane perpendicular to the optical path of the return light. And two dividing lines L1 extending in a direction (radial direction) perpendicular to the extending direction,
It has first to fourth quadrant regions divided into four from the center of the optical path by L2 as boundaries, and each region has a cylindrical lens-shaped first lens unit 31, second lens unit 32, third lens unit 33, and The fourth lens unit 34 is provided.

FIG. 8 shows a front view, a right and left side view, a top view and a bottom view of the optical element 18 for detecting a focus error. FIG.
FIG. 4 is a diagram viewed from the photodetector 19 side in the optical axis. As shown in the drawing, the first to fourth lens units 31 to 34 are formed by dividing lines L
Astigmatism (arrows) in directions rotated by 90 degrees with respect to return light passing through adjacent quadrant regions on the same side with 1 or L2 as a boundary, and returning the light by 4
Separate into two. For example, the first and third lens units 31 and 33 respectively arranged in the diagonal quadrants are separated by a dividing line L2.
It consists of a lens surface of a cylindrical lens whose center axis is an axis extending in the (radial) extension direction. Here, the central axis is a set of straight lines at the center of the center radius of curvature of the cylindrical lens. Second and fourth lens units 3 at other diagonal positions
Reference numerals 2 and 34 denote lens surfaces of the cylindrical lens having an axis extending in the direction in which the dividing line L1 (tangential direction) extends as a central axis. The central axis of the lens portion at one diagonal position is rotated by 90 degrees around the optical axis with respect to that at the other diagonal position. With this configuration, astigmatism in directions rotated by 90 degrees is imparted to the return light portion passing through the diagonal position quadrant.

Further, as shown in FIG.
The central axes of the lens portions 31 and 33 coincide with each other in a plane including the optical axis of the return light and the dividing line L2 in parallel with the dividing line L2. On the other hand, the central axes of the second and fourth lens portions 32 and 34 are symmetrical with respect to the plane including the optical axis of the return light and the division line L1, that is, a plane displaced in parallel in the opposite direction from the plane by the same distance SH. Exists parallel to the dividing line L1. Thus, the second and fourth lens units 32,
By making the central axes of the cylindrical lenses 34 decentered in parallel from the dividing line, the first and third lens portions 31 and 33 can receive the second astigmatism from the return light given the astigmatism.
In addition, it is possible to spatially separate return light provided with astigmatism that is rotated by 90 degrees of the fourth lens units 32 and 34. The distance between the second light receiving element 32PD and the fourth light receiving element 34PD in the photodetector 19 can be set by the distance SH between the central axes of the second and fourth lens portions 32 and 34.

In the above description, the first quadrant area is defined as an orthogonal XY coordinate obtained by dividing a plane into four areas by a horizontal X axis and a vertical Y axis perpendicular to the X axis. A region in which both Y coordinates have positive values. 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.
An area in which both the X coordinate and the Y coordinate 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 is an area where the X coordinate is a positive value and the Y coordinate is a negative value. .

Referring to FIGS. 9 to 11, the division of the return light by the astigmatism of the lens unit in the diagonal position quadrant will be described in detail. In FIG. 9, the first of the focus error detecting optical elements 18 is shown.
And only the third lens portions 31 and 33 are shown. First light passing through the first lens unit 31 of the return light from the objective lens
The light component in the quadrant area passes through the first quadrant area up to the line image M, moves to the second quadrant area after passing the line image M, and the line image S
After that, it moves to the third quadrant area. Therefore, in the capture range, the line image spot along the division line L2 changes from the line image spot along the division line L2 to the line image spot along the division line L1 inclined at 90 degrees through the fan-shaped spot in the second quadrant region. No spot is formed in the second quadrant outside the capture range.

On the other hand, the light component in the third quadrant area passing through the third lens portion 33 at the diagonal position passes through the third quadrant area up to the line image M, and moves to the fourth quadrant area after passing the line image M. , After passing through the line image S, it moves to the first quadrant area. Therefore, within the capture range, the line image spot along the division line L2 changes from the line image spot along the division line L2 to the line image spot along the division line L1 inclined at 90 degrees through the fan-shaped spot in the fourth quadrant region. No spot is formed in the fourth quadrant outside the capture range.

FIG. 10 shows only the second and fourth lens portions 32 and 34 of the optical element 18 for detecting a focus error. The light component of the return light from the objective lens in the second quadrant area passing through the second lens unit 32 is the second light component up to the line image M.
After passing through the quadrant area and passing through the line image M, the processing moves to the third quadrant area, and after passing through the line image S, moving to the fourth quadrant area. Therefore, in the capture range, the line image spot along the division line L1 changes to a line image spot along the division line L2 inclined by 90 degrees through the fan-shaped spot in the third quadrant region. No spot is formed in the third quadrant outside the capture range.

On the other hand, the light component in the fourth quadrant region passing through the fourth lens portion 34 at the diagonal position passes through the fourth quadrant region up to the line image M, and moves to the first quadrant region after passing the line image M. , After passing the line image S, it moves to the second quadrant area. Therefore, in the capture range, the line image spot along the division line L1 changes from the line image spot along the division line L1 to the line image spot along the division line L2 inclined at 90 degrees through the fan-shaped spot in the first quadrant region. No spot is formed in the first quadrant outside the capture range.

It should be noted in FIG. 10 that the center axes of the second and fourth lens portions 32 and 34 are respectively set to the dividing line L
Since they are decentered in parallel from 1, the spot of the return light in each quadrant region is displaced away from the dividing line L1 in the opposite direction, and is further spatially separated. FIG. 11 is a diagram obtained by combining FIGS. 9 and 10. As shown in FIG.
Due to the astigmatism given by the fourth lens units 31 to 34, the return light component passing therethrough is spatially divided for each quadrant region. (Light Detector) As shown in FIG.
A first light receiving element 31PD spaced apart from a minimum scattering circular image plane B due to astigmatism so as to receive each return light component separated by the fourth lens units 31 to 34;
The second light receiving element 32PD, the third light receiving element 33PD, and the fourth
It has a light receiving element 34PD. Each light receiving element performs photoelectric conversion into an electric signal according to the intensity of the light received in the light receiving area and outputs the electric signal. Further, the first to fourth light receiving elements 31PD to 3PD
The 4PDs are arranged as columns 19L along the division line L2.

As shown in FIG. 7, each of the first to fourth light receiving elements 31PD to 34PD of the focus error detecting optical element 18 has contour lines PL1 and PL corresponding to the dividing lines L1 and L2.
Two. As shown in FIG. 12, the first light receiving element 3
1PD is composed of two light receiving areas B1 and B2 divided by two dividing lines 60 extending substantially parallel to one of the contour lines PL2. The second light receiving element 32PD includes two light receiving areas C1 and C2 divided by the two dividing lines 60. The third light receiving element 33PD includes two light receiving areas D1 and D2 divided by the two dividing lines 60. The third light receiving element 33PD and the fourth light receiving element 34PD
It consists of two light receiving areas A1 and A2. That is, the dividing line 60 is located at a position where signals output from a pair of light receiving regions generated by a spot of the received return light on each light receiving element on the minimum scattering circular image plane due to astigmatism are substantially equal.
Extend. The first to fourth light receiving elements 31 shown in FIG.
PD to 34PD are views seen through the back surface of the focus error detecting optical element 18 on the optical axis of the return light.

The optical pickup 100 has an arithmetic circuit (not shown) connected to the light receiving area of the light receiving element of the light detector 19.
And outputs a focus error signal and the like. The focus error signal is supplied to the objective lens driving mechanism.
The arithmetic circuit includes light receiving areas (B1, B2), (C1, C2), (D1, D) of the first to fourth light receiving elements 31PD to 34PD.
2), when the signs of (A1, A2) are shown as their outputs,
The focus error signal FES performs an operation represented by the following equation (2).

FES = (A1 + B2 + C1 + D2)-(A2 + B1 + C2 + D1) (2)

Next, the operation of the photodetector 19 when the focal position of the objective lens in the optical pickup 100 changes will be described with reference to FIG. FIG.
(E) corresponds to spots (a) to (e) in FIG.

FIG. 13A shows the optical pickup 10.
The first to fourth light receiving elements 31PD to 34 when the light beam from 0 is in focus on the information recording surface of the optical disk.
FIG. 3 is a diagram illustrating a state of a return light spot in a PD.
At the time of focusing, astigmatism is imparted to each of the quadrant regions of the focus error detecting optical element 18 so that the divided light sandwiches each of the dividing lines 60 and has the same shape and １ ／ of the size (area). The light enters as a circular or fan-shaped light spot. Therefore, at the time of focusing, the light receiving area (B
1, B2), (C1, C2), (D1, D2), (A
Since the photodetection electric signals output from the first and A2) are equal to each other, the FES becomes zero according to the above equation (2).

FIG. 13B shows the optical pickup 10.
The first to fourth light receiving elements 31PD to 34PD when the light beam from 0 is out of focus on the information recording surface of the optical disc and the objective lens is farther than when the optical disc is in focus.
FIG. 5 is a diagram showing a state of a return light spot in FIG. When the optical disk is far, the first and third lens units 31 and 3 in the first and third quadrant regions of the focus error detecting optical element 18 are provided.
The light to which the astigmatism is given in 3 is incident on the light receiving areas B1 and D1 extending in the L2 direction as linear light spots extending in the L2 direction. Also, the light to which astigmatism has been imparted by the second and fourth lens units 32 and 34 in the second and fourth quadrant regions of the focus error detecting optical element 18 is received by the light receiving regions (A1, A2), (C1, On C2), the light spot becomes a linear light spot extending in the L1 direction and enters so as to straddle the light receiving area. Therefore, when the optical disk is farther than the in-focus state, these linear light spots have the same shape and size (area), respectively. The outputs of the areas B1 and D1 are negative values.

FIG. 13 (c) shows the state of the return light spot near the first to fourth light receiving elements 31PD to 34PD when the objective lens is farther than when the optical disc is in focus in the out-of-focus state of the light beam. FIG. If the optical disk is farther beyond the capture range, the first to fourth lens units 31 to 3 of the focus error detecting optical element 18
The light components to which the astigmatism is given in 4 respectively enter the quadrant regions on the opposite side of the diagonal line as light spots enlarged from the line shape beyond the division line. Therefore, when the optical disk is farther than the focused state, the area of these light spots is limited by the contour lines corresponding to the dividing lines L1 and L2 corresponding to the first to fourth light receiving elements 31PD to 34PD. Therefore, FES does not reach any of the light receiving elements and FES becomes zero according to the above equation (2).

FIG. 13D shows this optical pickup 10.
The first to fourth light receiving elements 31PD to 34PD when the light beam from 0 is out of focus on the information recording surface of the optical disc and the objective lens is closer than when the optical disc is in focus.
FIG. 5 is a diagram showing a state of a return light spot in FIG. When the optical disk is close, the first and third lens units 31 and 3 in the first and third quadrant regions of the focus error detecting optical element 18 are used.
The light to which the astigmatism has been imparted in the light receiving areas (B1, B2)
2), (D1, D2) is a linear segment-shaped light spot extending in the L1 direction and is incident so as to straddle the light receiving region. Further, the light provided with astigmatism by the second and fourth lens units 32 and 34 in the second and fourth quadrant regions of the focus error detecting optical element 18 is on the light receiving regions A1 and C1 extending in the L2 direction. , And are incident as linear light spots extending in the L2 direction. Therefore, when the optical disk is closer than when the optical disk is in focus, these linear light spots have the same shape and the same size (area).
Therefore, the FES becomes a positive value of the outputs of the light receiving areas A1 and C1.

FIG. 13E shows the state of the return light spot near the first to fourth light receiving elements 31PD to 34PD when the objective lens is closer to the optical disk in the out-of-focus state than when the optical disk is in focus. FIG. If the optical disk is farther beyond the capture range, the first to fourth lens units 31 to 31 of the focus error detecting optical element 18 will be described.
The light components to which the astigmatism is given in 4 respectively enter the quadrant regions on the opposite side of the diagonal line as light spots enlarged from the line shape beyond the division line. Therefore, when the optical disk is even closer to the focused state, these light spots are limited in area by contour lines corresponding to the division lines L1 and L2 corresponding to the first to fourth light receiving elements 31PD to 34PD. Therefore, FES does not reach any of the light receiving elements and FES becomes zero according to the above equation (2).

Therefore, the value FE expressed by the above equation (2)
If S is used as a focus error signal, the optical disk is in focus when the FES is zero, the optical disk is farther from the optical disk when the FES value is positive, and the optical disk is focused when the FES value is negative. It can be determined that it is closer 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 the focus error signal FE is fed back.
By controlling an objective lens driving mechanism (not shown) provided on the objective lens 7 of the optical pickup 100 so that the S value becomes zero, it is possible to perform reliable focusing servo control.

By using the output of the light receiving element described above,
The following formula (3),

[0046]

[Mathematical formula-see original document] RF = A1 + A2 + B1 + B2 + C1 + C2 + D1 + D2 By calculating the value RF, it is possible to read record information recorded on the optical disc from this RF signal.

Further, the following equations (4), (5), (6),
(7),

[0048]

DPD1 = A1 + A2 (4), DPD2 = B1 + B2 (5), DPD3 = C1 + C2 (6), DPD4 = D1 + D2 (6) ... (7), values DPD1, DPD2, DPD3, DPD4 expressed by
If the calculation is performed by a comparison detector that compares the phases from each other, DPD tracking servo control can be performed by using these signals. In this case, the arithmetic circuit has a comparison detector.

In the focus error detection method in the optical pickup 100 described above, the light in the first to fourth quadrants of the return light is divided into quadrants at diagonal positions. There is no interference. 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 light leakage between the quadrants and the like.
No error occurs in the DPD tracking error signal. Since the degree of light separation for each quadrant on each light receiving element is increased, it is possible to prevent the DPD tracking error signal from being deteriorated to some extent due to an optical axis shift of the light receiving element.
Further, the combination with the three-beam method can be performed without any trouble.

Further, since the two dividing lines of the light receiving element are set to be extended in the radial direction, even if the optical axis shift or adjustment shift of the light detector 19 in the radial direction occurs, as shown in FIG. The upper light beam spot image is divided into two split lines 60.
There is no effect because it moves along. On the other hand, as described above, in the conventional focus error detection such as the spot size method and the four-segment detector astigmatism method, the defocused light does not largely protrude from the light receiving element because it spreads around the optical axis. When reproducing a multi-layer disc with focus error detection, unless the area of the light receiving element is set extremely small, the effect of interlayer crosstalk cannot be suppressed, and the capture range is reduced by reducing the area of the light receiving element. Was. In this regard,
In the focus error detection method according to the present invention, since the light beam on the light receiving element forms a line image at both ends of the capture range, the light beam outside the capture range spreads in a direction largely protruding from the light receiving element. In principle, the focus error detection method according to the present invention can reduce interlayer crosstalk even when a multi-layer disc with a narrow layer interval is reproduced, because the amount of defocused light rays mixed in principle decreases at an early stage.

However, also in the focus error detection method according to the present invention, the area of the light receiving element is set to be large in consideration of the optical axis shift and the like. Therefore, the defocused light beam remains in the light receiving element, and the advantage of the focus error detecting method according to the present invention is lost. Therefore, in order to prevent the defocused light from leaking into other light receiving elements, the distance between the light receiving elements is considered in addition to the multilayer disc.

In each of the light receiving elements which receive astigmatism-returned four-divided return light, the spot size within the capture range is almost the same as that shown in FIG.
(B) The light receiving element is set to a size that is close to the contour of the line image spot shown in (d) in the longitudinal direction. That is, the contour lines PL1, PL of each light receiving element corresponding to the division lines L1, L2 on the minimum scattering circular image plane due to astigmatism.
The light receiving element is set so that the position of No. 2 does not overlap with a spot outside the capture range. As a result, the defocused light beam completely protrudes out of the light receiving element,
No interlayer crosstalk occurs.

Further, the distance d between the contour lines PL1 of the light receiving elements in the column 19L shown in FIG.

[0054]

(Equation 5)

By setting so as to satisfy the condition, interlayer crosstalk can be eliminated within a specific layer interval (t) of the multilayer disc. (Reduction of track crossing noise) In an optical pickup device for reproducing a signal from an optical disk having grooves and lands on an information recording surface by using an astigmatism method, when a focus error signal is obtained from a four-divided photodetector, a light spot is generated. 45 ° occurs when the traverses the land and groove
A noise component caused by astigmatism in the direction was examined.

First, as shown in FIG.
Lands 1 formed spirally or concentrically on the information recording surface of
A light beam is irradiated onto the groove 31 and the groove 132 by an irradiation optical system to form a light spot SP.
Is moved in the radial direction from (a) to (d) as indicated by the dashed arrow, and the noise on the focus error signal when the light spot crosses the track is examined. However, in the case where a so-called oblique astigmatism component in the 45 ° direction remains in the irradiation optical system of the pickup, a DVD-RAM optical disk made of a polycarbonate (PC) disk substrate is used. The groove width and the land width of the optical disk 5 are equal.

FIGS. 16A to 16D show the light receiving surface of the four-segment photodetector 9 when the perfect circular light spot SP at the time of focusing is located at the positions (a) to (d) shown in FIG. 2 shows the light spot intensity distributions mapped onto the respective sections. In the vicinity of the center of the groove 132, the light spot intensity distribution becomes as shown in FIG. 16A, and dark portions occur at B2 and D2.
The light spot intensity distribution as shown in (b) is obtained, and dark portions are generated at A2 and B2, and further, the light spot intensity distribution as shown in FIG. A dark portion is generated and further moved to a point near the taper at the land-groove boundary as shown in FIG.
The light spot intensity distribution as shown in (d) occurs, and dark portions occur at C2 and D2. However, as is clear from the above-mentioned expression of the focus error signal, the output is canceled. Therefore, the influence of the track crossing noise on the focus error signal can be almost canceled.

When the conventional four-segment detector is used, the focus state FES should be 0, but since there is astigmatism in the 45 ° direction with respect to the track (tangent) direction, FIG. In the states shown in (a) and (c), a track cross signal where a local maximum and a local minimum occur occurs, and the FES does not become zero, and the track cross signal which repeats the maximum and the minimum in the groove and the land becomes noise to the FES. The invention has eliminated such noise. (Modification of the focus error detecting optical element) An optical pickup can be constructed by employing the focus error detecting optical element 18a shown in FIGS. 17 and 18 instead of the focus error detecting optical element 18 shown in FIG. it can. Focusing error detecting optical element 18a
Are the first and third lens units 31 and 3 in the first and third quadrants,
7 is the same as the focus error detecting optical element 18 shown in FIG. 7 except that a deflecting prism surface 181 inclined at a different angle with respect to a plane perpendicular to the optical path of the return light is provided on the input side of No. 3. In this case, the distance between the first light receiving element 31PD and the third light receiving element 33PD in the photodetector 19 is adjusted by adjusting the angle of the deflecting prism surface 181 inclined symmetrically from the plane including the division line L1 and the optical axis. GAP can be set.

FIGS. 19 and 20 show a focus error detecting optical element 18b according to another modification. The focus error detecting optical element 18b includes the second and fourth lens units 3 in the second and fourth quadrants.
2 and 34, on the input side, a deflecting prism surface 1 inclined at a different second angle with respect to a plane perpendicular to the optical path of the return light.
82 and the second light receiving element 32PD in the photodetector 19
This is the same as the focus error detecting optical element 18a shown in FIGS. 17 and 18 except that the distance between the second light receiving element 34PD and the fourth light receiving element 34PD is defined. By providing the deflecting prism surface 182, it is possible to use a cylindrical lens in which the central axes of the second and fourth lens units 32 and 34 are decentered, without using a cylindrical lens.
Spatial separation of the returned light in each quadrant is possible. Also,
The distance between the first to fourth light receiving elements 31PD to 34PD in the photodetector 19 is adjusted by adjusting the angles of the deflecting prism surfaces 181 and 182 inclined symmetrically or asymmetrically from the plane including the division line and the optical axis. And the position can be arbitrarily set.

The above-mentioned focus error detecting optical element can be combined with a deflecting prism surface and an eccentric cylindrical lens. Instead of this, all of the first to fourth lens units 31 to 34 shown in FIG. A focus error detecting optical element 18c using an eccentric cylindrical lens may be employed. The focus error detecting optical element 18c has first and third lens portions 31c and 33c whose center axes are both deviated from the division line L2 to the first and fourth quadrants, and whose center axis is both the first and third parts from the division line L1. The second and fourth lens portions 32c and 34c are biased to two quadrants.

As shown in FIG. 21, the center of each light spot image irradiated on the minimum scattering circle image plane moves with respect to the original optical axis before entering the focus error detecting optical element 18c. , The first to fourth light receiving elements 31PD of the photodetector 19
The column 19L of .about.34PD is arranged to be inclined with respect to the dividing line. FIG. 22 shows a change in the spot shape on the inclined light receiving element array 19L when the focal position of the objective lens of the optical pickup 100 changes. As shown in FIG. 22A, when the light beam is focused on the information recording surface of the optical disc, FIG. 22B is when the objective lens is out of focus than when the optical disc is focused, and FIG. Is out of focus beyond the capture range, FIG. 22 (c) is out of focus when the objective lens is closer than when the optical disc is in focus, and FIG. 22 (c) is out of focus further beyond the capture range. This shows the spot shape when in focus. FIGS. 22A to 22E substantially correspond to the spots (a) to (e) in FIG. As is clear from FIG. 22, each of the first to fourth light receiving elements 31PD to 34PD has a substantially triangular shape including a right-angled contour line corresponding to the dividing line according to the spot shape at the time of focusing. Therefore, even in the case of a spot spread outside the capture range (FIGS. 22 (c) and (e)), the margin of the separated element is secured, and unnecessary light does not leak to the adjacent light receiving element. (Focus Error Signal Correction) In the present invention, in addition to the above-described focus error detecting optical element, a sub-light receiving element for correcting a focus error signal is provided. Specifically, in the photodetector 19, FIG.
As shown in the figure, the sub-light receiving elements (a1, a
2), (b1, b2), (c1, c2), (d1, d
The pair 2) is arranged along the contour lines PL1 and PL2 (corresponding to the division lines L1 and L2) of the first to fourth light receiving elements 31PD to 34PD. The sub-light receiving elements are arranged adjacent to each other for each light receiving area, and as shown in FIG.
1, A2), (B1, B2), (C1, C2), (D
1, D2), the sub-light receiving elements (a1, a2),
A pair of (b1, b2), (c1, c2), and (d1, d2) is associated.

As shown in FIG. 24, when the light spot is displaced in the tangential direction even when focusing, that is, when the optical axis is shifted, the sub-light-receiving element is displaced from the light-receiving element. Since the light spot portion is received, the focus error signal FES is properly obtained. In addition, since the signal of the sub-light receiving element is not used for generating the RF signal, leakage to the RF signal in the case of a defocus spot is suppressed.
That is, interlayer crosstalk can be suppressed in a multilayer disc. The same effect can be obtained even when the light spot at the time of focusing shifts in the radial direction and the optical axis is shifted.

The light receiving areas (B1, B2), (C1, C2), (D1, D) of the first to fourth light receiving elements 31PD to 34PD.
2), (A1, A2) and auxiliary light receiving elements (b1, b2),
When the signs of (c1, c2), (d1, d2), and (a1, a2) are indicated as their outputs, the arithmetic circuit causes the correction focus error signal FE expressed by the following equation (9) to be:
It can be configured to perform the operation of S.

FES = (A1 + B2 + C1 + D2 + a1 + b2 + c1 + d2)-(A2 + B1 + C2 + D1 + a2 + b1 + c2 + d1) (9)

This is because the focus error signal corrected by adding the sum of the differences between the signals output from the two light receiving areas of the light receiving elements to the sum of the differences between the signals output from the corresponding pair of sub-light receiving elements. This is achieved by having a focus error signal correction arithmetic circuit that generates That is, the sub light receiving elements (a1,
a2), (b1, b2), (c1, c2), (d1, d
By subtracting the difference signal generated from the signal detected in 2) from the focus error signal, the offset of the focus error signal in a multilayer disc or the like can be prevented.

FIG. 25 shows an embodiment in which the shape of the light receiving element in the above embodiment is modified. As shown in FIG. 25 (a), the outlines facing the outlines PL1 and PL2 corresponding to the division lines of the light receiving element having a substantially right triangle shape are defined as outlines P.
The concave portion facing L1 and PL2 has a minimum area necessary for obtaining a focus error signal. As shown in FIG. 25 (b), the contour lines PL1 and PL2 corresponding to the division line of the light receiving element having a substantially right-angled triangular shape are formed as convex portions toward the normal direction of the contour line, and the high frequency components of the RF reproduction signal are obtained. The outer peripheral portion of the included light beam spot is shaped so as not to leak from the light receiving element. As shown in FIG. 25 (c), the shape of the light receiving element in which the structures shown in FIGS. 25 (a) and 25 (b) are combined is limited to increase the area. As shown in FIG. 25 (d), a sub-light-receiving element is arranged along a protruding contour line on the light-receiving element having the structure shown in FIG. Is prevented from leaking from the light receiving element.

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-described embodiment, a lens element combined with a cylindrical lens has been described as an example of an optical element for focus error detection. However, the present invention is not limited to this example. For example, a blazed quadrant hologram element having a similar function may be used. In the embodiment, as shown in FIG. 6, the focus error detecting optical element 18 is arranged in the order of the photodetector 19, but has the same function as the focus error detecting optical element 18 and has a polarization function. The polarizing lens element may be provided between the mirror 25 and the 波長 wavelength 6.

[0067]

As described above, according to the present invention, it is hardly affected by track crossing noise and optical disk thickness error, and can be used in combination with the three-beam system or the DPD system. An optical pickup with high sensitivity and strong optical axis shift can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an optical pickup device.

FIG. 2 is a perspective view illustrating an operation of a cylindrical lens using an astigmatism method in the optical pickup device.

FIG. 3 is a perspective view for explaining the operation of a four-divided detector when the focal position changes in the optical pickup shown in FIG. 2;

FIG. 4 is a configuration diagram of a focus error detection circuit in the optical pickup shown in FIG. 2;

FIG. 5 is a graph showing focus error signal characteristics obtained by the optical pickup shown in FIG. 2;

FIG. 6 is a perspective view showing a configuration of an optical pickup according to an embodiment of the present invention.

FIG. 7 is a perspective view illustrating a focus error detecting optical element and a photodetector in the optical pickup according to the embodiment of the present invention.

FIG. 8 is a view for explaining a focus error detecting optical element in the optical pickup according to the embodiment of the present invention.

FIG. 9 is a perspective view illustrating the operation of a focus error detecting optical element in the optical pickup according to the embodiment of the present invention.

FIG. 10 is a perspective view illustrating the operation of an optical element for focus error detection in the optical pickup according to the embodiment of the present invention.

FIG. 11 is a perspective view illustrating the operation of a focus error detecting optical element in the optical pickup according to the embodiment of the present invention.

FIG. 12 is a plan view illustrating the operation of the photodetector in the optical pickup according to the embodiment of the present invention.

FIG. 13 is a plan view illustrating the operation of the photodetector when the focal position changes in the optical pickup according to the embodiment of the present invention.

FIG. 14 is a plan view illustrating the operation of the photodetector in the optical pickup according to the embodiment of the present invention.

FIG. 15 is a view for explaining generation of track crossing noise in the optical pickup according to the embodiment of the present invention.

FIG. 16 is a plan view illustrating the action of a photodetector on a change in light intensity during focusing in the optical pickup according to the embodiment of the present invention.

FIG. 17 is a perspective view illustrating a focus error detecting optical element in the optical pickup according to the embodiment of the invention.

FIG. 18 is a perspective view illustrating a focus error detecting optical element in the optical pickup according to the embodiment of the invention.

FIG. 19 is a perspective view illustrating a focus error detecting optical element in the optical pickup according to the embodiment of the invention.

FIG. 20 is a perspective view illustrating a focus error detecting optical element in the optical pickup according to the embodiment of the invention.

FIG. 21 is a perspective view illustrating an optical element for detecting a focus error and a photodetector in the optical pickup according to the embodiment of the present invention.

FIG. 22 is a plan view illustrating the operation of the photodetector when the focal position changes in the optical pickup shown in FIG. 21.

FIG. 23 is a plan view illustrating the operation of the photodetector in the optical pickup according to the embodiment of the present invention.

FIG. 24 is a plan view illustrating the operation of a photodetector for optical axis shift during focusing in the optical pickup according to the embodiment of the present invention.

FIG. 25 is a plan view illustrating a light receiving element of a photo detector in the optical pickup according to the embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Grating 3 Polarization beam splitter 4 Collimator lens 5 Optical disk 6 1/4 wavelength plate 7 Objective lens 18 Focus error detection optical element 19 Photodetector 25 Mirror 31 1st lens part 31PD 1st light receiving element 32 2nd lens Part 32PD second light receiving element 33 third lens part 33PD third light receiving element 34 fourth lens part 34PD fourth light receiving element 60 split line 100 optical pickup A1, A2, B1, B2, C1, C2, D1, D2 light receiving area a1, a2, b1, b2, c1, c2, d1, d2 Sub-light receiving element L1, L2 Dividing line PL1, PL2 Contour line

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5D118 AA18 BA01 BB02 BF02 BF03 CD02 CD03 CD08 CF03 CF05 DA02 DA03 5D119 AA29 BA01 DA01 EA02 EA03 EC07 JA06 JA08 KA02 KA17

Claims (7)

[Claims] An irradiation optical system for converging a light beam on a track on an information recording surface of an optical recording medium to form a spot, and guiding return light reflected back from the spot to a photodetector. An optical pickup device having a light detection optical system and detecting a focus error of the light beam, wherein the optical pickup device corresponds to an extending direction of the track and a direction perpendicular to the extending direction on a plane perpendicular to an optical path of return light. The first to fourth divided from the center of the optical path by two dividing lines extending
A fourth quadrant region, wherein the return light passing through the adjacent region on the same side of the dividing line is provided with astigmatism in directions rotated by 90 degrees around the optical path to the return light, and the return light A focus error detecting optical element that separates the light into at least four light beams for each of the regions, and an optical system that receives the separated return light and has a circular light beam in an optical system to which astigmatism is added. A photodetector having a contour corresponding to the dividing line and having a plurality of spaced light receiving elements consisting of two light receiving regions divided by two dividing lines extending substantially parallel to one of the contours; An optical pickup device, comprising: a plurality of sub-light-receiving elements arranged adjacent to each of the light-receiving areas along the contour line corresponding to the division line of the light-receiving element. 2. The optical pickup device according to claim 1, wherein the two division lines of the light receiving element extend in a direction perpendicular to a direction in which the track extends. 3. The light receiving element formed by the received return light spot on the light receiving element on an image plane where a light beam is circular in an optical system provided with astigmatism. The optical pickup device according to claim 1, wherein the optical pickup device extends at a position where signals output from two light receiving regions of the element are substantially equal. 4. A sum of a difference between signals output from two light receiving regions of the light receiving element, which is connected to the light receiving element and the sub light receiving element, and a sum of a difference between signals output from the sub light receiving elements. The optical pickup device according to any one of claims 1 to 3, further comprising a focus error signal correction operation circuit for adding a focus error signal to generate a focus error signal. 5. A focusing lens detecting optical element comprising: a cylindrical lens having a central axis extending in a direction in which the dividing line is disposed at one diagonal position in each of the first to fourth quadrants; And a cylindrical lens having a central axis at a direction 90 degrees to the direction of extension of the parting line disposed at each of the diagonal positions of the cylindrical lenses. The optical pickup device according to any one of claims 1 to 4, wherein the center axis of (1) is decentered parallel to the dividing line. 6. The apparatus according to claim 5, wherein said central axes of said cylindrical lenses respectively disposed in said at least one diagonal position area are decentered parallel to said dividing line and opposite to each other. Optical pickup device. 7. The optical pickup device according to claim 5, wherein the light receiving elements are arranged in parallel with one of the dividing lines of the focus error detecting optical element. .