JPH0668541A - Optical pickup device, photodetection element and focus error signal detection method - Google Patents

Abstract

(57) [Summary] [Structure] The light beam R ₁ emitted from the light source 1 is divided into three by the diffraction grating 2, guided to the composite element 7, and focused on the magneto-optical disk by the objective lens 6. The reflected light fluxes R ₂ , R ₃ , and R ₄ reflected by the magneto-optical disk are divided into two according to the polarization state by the composite element 7,
The light beam becomes six light beams and is received by the light receiving element 9. [Effect] Since the composite element 7 functions as both a beam splitter and an analyzer, simplification of the configuration due to reduction of parts,
Easy manufacturing is possible.

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 for reading an information signal from a magneto-optical recording medium such as a so-called magneto-optical disk, a photo-detecting element suitable for use in such an optical pickup device, and The present invention relates to a focus error signal detection method for detecting a focus error signal in such an optical pickup device.

[0002]

2. Description of the Related Art Conventionally, a magneto-optical recording medium such as a so-called magneto-optical disk has been proposed. This magneto-optical disk is composed of a disk substrate made of a transparent material and a signal recording layer made of a magnetic material adhered to the disk substrate. An external magnetic field is applied to this signal recording layer, and a focused laser beam is applied to a minute area and heated to a temperature higher than the so-called Curie temperature, and the magnetization direction in the minute area is imitated by the external magnetic field. Thus, the information signal is written. The magnetization direction of this signal recording layer is so-called perpendicular magnetization, which is perpendicular to the main surface portion of the disk substrate. That is, the information signal written in this signal recording layer is a binary signal which is indicated by whether the magnetization direction of this signal recording layer is upward or downward.

An optical pickup device is used to read information signals from the magneto-optical recording medium such as the magneto-optical disk. This optical pickup device includes a light source such as a semiconductor laser, a photodetector such as a photodiode, and various optical devices such as an objective lens and a collimator lens.

The optical pickup device collects and irradiates a linearly polarized light beam emitted from the light source as an irradiation light beam on the signal recording layer through the various optical elements. This irradiation light beam is polarized in the polarization direction by the so-called Kerr effect according to the magnetization direction of the signal recording layer,
It is reflected by the signal recording layer. Then, in this optical pickup device, the reflected light flux, which is the light flux reflected by the signal recording layer, is received by the photodetector. In this optical pickup device, the reflected light flux is separated and deflected by an optical element such as a three-beam Wollaston prism into three light fluxes scattered in three directions in one plane according to the polarization direction. In the photodetector, the respective reflected light fluxes thus separated are individually received by the three light receiving portions which are adapted to individually output the photodetection outputs. In this optical pickup device, a difference signal between photodetection outputs from a pair of light receiving portions located on both sides of the photodetector serves as a read signal of the information signal written in the signal recording layer.

Further, the optical pickup device can obtain a focus error signal and a tracking error signal which indicate the amount of positional deviation between the focal point of the irradiation light beam and the recording track formed on the signal recording layer. Is configured. In the magneto-optical disk, the recording track is formed in a spiral shape that is substantially concentric. The information signal is written along this recording track. The focus error signal is a signal indicating a distance between the converging point and the surface of the signal recording layer in the optical axis direction of the irradiation light beam, that is, in a direction substantially perpendicular to the surface of the signal recording layer. . The tracking error signal is a signal indicating a distance between the condensing point and the recording track in a direction perpendicular to the optical axis of the irradiation light beam and the recording track, that is, in the radial direction of the disk substrate. .

The focus error signal and the tracking error signal are obtained based on the photodetection signal from the light receiving portion located at the center of the photodetector. The light receiving portion located in the central portion is divided into four light receiving portions radially arranged at equal angular intervals. And
Each light receiving portion forming this light receiving portion is configured to be able to independently output a light detection signal.

Further, in this optical pickup device, the reflected light flux is made to have astigmatism by an optical element such as a cylindrical lens. The direction and amount of this astigmatism change in accordance with the change in the focus error amount, that is, the direction and distance in the optical axis direction of the irradiation light flux from the surface of the signal recording layer to the converging point of the irradiation light flux. To do. Therefore, in the above photodetector, the four photoreceptive portions forming the photoreceptive portion located in the central portion are summed with respect to the photodetection outputs output from the two photoreceptive portions facing each other through the central portion of the photoreceptive portion. If you generate a signal and a difference signal between these sum signals,
This difference signal becomes the focus error signal.

Further, in this optical pickup device, the reflected light flux has a direction and a distance with respect to a direction perpendicular to the optical axis of the irradiation light flux from the recording track to the converging point and the recording track, that is, tracking. The light intensity distribution changes according to the change in the error amount. Therefore, with respect to the four light receiving portions forming the light receiving portion located in the central portion of the photodetector, the light detection output from the two light receiving portions facing each other through the dividing line in the direction corresponding to the recording track is detected. When a sum signal is generated for each output and a difference signal between these sum signals, that is, a so-called push-pull signal is generated, the push-pull signal becomes the tracking error signal.

[0009]

The optical pickup device as described above includes a beam splitter. The beam splitter guides the emitted light beam emitted from the light source to the objective lens side for condensing the light beam on the magneto-optical recording medium, and the reflected light beam reflected by the magneto-optical recording medium to the light source. It is guided to the photodetector side without being returned to. As this beam splitter, a pair of triangular prisms each having a right-angled isosceles triangular prism shape and used in a rectangular shape by bonding their slant surface portions to each other is used. In this beam splitter,
The bonding surface of each of the triangular prisms serves as a reflecting surface for the emitted light flux and a transmissive surface for the reflected light flux.

That is, this optical pickup device must include both the beam splitter and the optical element that splits the light beam according to the polarization state, such as the three-beam Wollaston prism. Therefore, it is difficult to reduce the size of the optical pickup device and the manufacturing thereof is complicated.

As a structure for detecting the tracking error signal in the optical pickup device, a diffraction grating is arranged between the light source and the beam splitter, and the emitted light beam is made into at least three light beams. There is one that is divided into three beam spots arranged along the direction of the recording track on the magneto-optical disk.

However, this diffraction grating and the above three beams
In an optical pickup device including both a Wollaston prism and a Wollaston prism, on the light receiving surface of the photodetector, at least nine condensing points, that is, three converging points each are formed. Three rows of light spots are formed. Then, four condensing points corresponding to the four corners of these nine condensing points are not used for detecting a focus error signal, a tracking error signal, and the like, so that not only energy efficiency will decrease in the future. However, a so-called crosstalk component with respect to the detection of these signals may occur, which may interfere with accurate signal detection.

Therefore, the present invention has been proposed in view of the above-mentioned circumstances, and when reading an information signal recorded on a magneto-optical recording medium, a focus error signal or the like can be favorably detected, and The present invention provides an optical pickup device in which the number of parts is reduced to simplify the configuration, reduce the size, and facilitate manufacturing, and also provides a photodetection element suitable for use in such an optical pickup device. Furthermore, it is an object of the present invention to provide a focus error signal detection method in such an optical pickup device.

[0014]

In order to solve the above problems and achieve the above objects, an optical pickup device according to the present invention comprises a light source and a light beam emitted from this light source, which is at least 0th order light and ± 1st order light. A diffraction grating that divides the light into three light fluxes, a composite optical element that guides the light fluxes that have passed through the diffraction grating to the magneto-optical recording medium side, and the light fluxes that have passed through the composite optical element are provided on the magneto-optical recording medium. And a light condensing unit for condensing the light fluxes into the two light fluxes which are spread in two directions according to the polarization states of the light fluxes. Then, through astigmatism means that causes astigmatism in these light beams,
The light is guided to the photodetector side that receives each of the light fluxes.

Further, the photodetector according to the present invention is emitted from a light source and is divided by a diffraction grating into at least three rays of 0th order light and ± 1st order light. Detecting means for dividing each of the light fluxes collected and reflected by the magneto-optical recording medium into two light fluxes which are spread in two directions according to the polarization state of the light fluxes, and astigmatism is generated in these light fluxes. A first and a second photodetecting element for receiving light via astigmatism means, wherein the 0th-order light of the light flux that has passed through the diffraction grating correspondingly receives the two light fluxes divided by the composite optical element. A light-receiving unit, a third light-receiving unit that receives at least one of the two light beams split by the composite optical element from the + 1st-order light of the light beam that has passed through the diffraction grating, and the -1 of the light beam that has passed through the diffraction grating. Next light to compound optics And a fourth light receiving portion for receiving at least one of the two light beams divided into two parts, wherein the first and second light receiving portions have a difference signal between their light detection outputs in the recording track. It is used as a read signal of the recorded information signal, and is divided into four light receiving portions that are radially arranged at equal angular intervals, and two sets of two light receiving portions facing each other through the central portion of the light receiving portion are provided. The difference signal between the sum signals of the light detection outputs of the light receiving portions is a focus error signal, and the difference signal between the light detection outputs of the third and fourth light receiving portions is a tracking error signal. is there.

Further, in the photo-detecting element according to the present invention, in the photo-detecting element, at least one of the first and second light receiving portions is on one side of a division line in a direction corresponding to a tangential direction of a recording track. The difference signal between the sum signal of the photodetection outputs of the light receiving portions located on the other side and the sum signal of the photodetection outputs of the light receiving portions located on the other side of the dividing line is a push-pull signal.

Further, the photodetector according to the present invention is emitted from a light source and is divided by a diffraction grating into at least three rays of 0th order light and ± 1st order light. Detecting means for dividing each of the light fluxes collected and reflected by the magneto-optical recording medium into two light fluxes which are spread in two directions according to the polarization state of the light fluxes, and astigmatism is generated in these light fluxes. A first and a second photodetecting element for receiving light via astigmatism means, wherein the 0th-order light of the light flux that has passed through the diffraction grating correspondingly receives the two light fluxes divided by the composite optical element. A light-receiving unit, a third light-receiving unit that receives at least one of the two light beams split by the composite optical element from the + 1st-order light of the light beam that has passed through the diffraction grating, and the -1 of the light beam that has passed through the diffraction grating. Next light to compound optics And a fourth light receiving portion for receiving at least one of the two light beams divided into two parts, wherein the first and second light receiving portions have a difference signal between their light detection outputs in the recording track. The read signal of the recorded information signal is used, and the third and fourth light receiving portions are arranged such that the difference signal between their photodetection outputs is a tracking error signal, and each of them is radially arranged at equal angular intervals. It is divided into four light receiving portions in the light receiving state, and the difference signal between the sum signals of the light detection outputs of the two light receiving portions facing each other through the center of the light receiving portion is used as the focus error signal. is there.

In the photodetector according to the present invention, in the photodetector, at least one of the first and second light receiving portions is divided into two parts by a dividing line in a direction corresponding to the tangential direction of the recording track. The difference signal between the photodetection output of the light receiving portion located on one side of the dividing line and the photodetection output of the light receiving portion located on the other side of the dividing line is a push-pull signal.

In the focus error signal detecting method according to the present invention, at least three light beams of 0th order light and ± 1st order light emitted from the light source are divided by the diffraction grating, and the light is condensed on the recording track of the magneto-optical recording medium. And an astigmatism for analyzing the light beams that are respectively focused on and reflected by the magneto-optical recording medium into two light beams that are spread in two directions according to the polarization states of the light beams. The light detecting element receives the light through an astigmatism means that causes the above-mentioned astigmatism, and the light detecting element corresponds to two light fluxes obtained by dividing the 0th-order light of the light flux passing through the diffraction grating by the composite optical element. The first and second light receiving portions for receiving the light by the first and second light receiving portions, and the third light receiving portion for receiving one of the two light fluxes obtained by dividing the + 1st-order light of the light flux passing through the diffraction grating by the composite optical element, and the diffraction grating. Through A fourth light receiving portion for receiving one of the two light fluxes obtained by splitting the −1st-order light of the light flux by the composite optical element and the + 1st-order light of the light flux passing through the diffraction grating are split by the composite optical element 2 A fifth light receiving portion for receiving the other of the two light beams and a sixth light receiving for receiving the other of the two light beams divided by the composite optical element from the -1st-order light of the light beam that has passed through the diffraction grating. Each of the third and sixth light receiving portions or the fourth and fifth light receiving portions, and each light receiving portion is radially arranged at equal angular intervals. It is assumed that the light receiving portion is divided into four light receiving portions in the separated state, and a difference signal between the sum signals of the light detection outputs of the two light receiving portions facing each other through the central portion of the light receiving portion is obtained, and these difference signals are obtained. It is added to form a focus error signal.

Further, the focus error signal detecting method according to the present invention is such that a diffraction grating emitted from a light source divides the light into at least three light beams of 0th order light and ± 1st order light, and a focusing means is provided on a recording track of the magneto-optical recording medium. And an astigmatism for analyzing the light beams that are respectively focused on and reflected by the magneto-optical recording medium into two light beams that are spread in two directions according to the polarization states of the light beams. The light detecting element receives the light through an astigmatism means that causes the above-mentioned astigmatism, and the light detecting element corresponds to two light fluxes obtained by dividing the 0th-order light of the light flux passing through the diffraction grating by the composite optical element. The first and second light receiving portions for receiving the light by the first and second light receiving portions, and the third light receiving portion for receiving one of the two light fluxes obtained by dividing the + 1st-order light of the light flux passing through the diffraction grating by the composite optical element, and the diffraction grating. Has passed The fourth light-receiving portion that receives one of the two light beams divided by the composite optical element, and the + 1st-order light of the light flux that has passed through the diffraction grating is divided by the composite optical element. A fifth light receiving portion for receiving the other of the two light beams, and a sixth light receiving portion for receiving the other of the two light beams divided by the composite optical element by the -1st-order light of the light beam passing through the diffraction grating. A light receiving portion, wherein the third to sixth light receiving portions are divided into four light receiving portions radially arranged at equal angular intervals, and the center of the light receiving portion in each 2 facing each other
The difference signal between the sum signals of the light detection outputs of the light receiving portions of the set is obtained, and all of these four difference signals are added to form a focus error signal.

[0021]

In the optical pickup device according to the present invention, the composite optical element includes a light flux emitted from a light source and divided by a diffraction grating into at least three light fluxes of 0th order light and ± 1st order light. And the respective luminous fluxes condensed by the condensing means on the magneto-optical recording medium and reflected by the magneto-optical recording medium into two luminous fluxes diverged in two directions according to the polarization states of these luminous fluxes. Since the light beams are split and guided to the photodetector side that receives the respective light beams via the astigmatism means for generating astigmatism in these light beams, both the beam splitter and the analyzer function.

Further, the photodetector according to the present invention is emitted from a light source and divided into at least three rays of 0th order light and ± 1st order light by a diffraction grating, and each of them is focused on a recording track of a magneto-optical recording medium by a converging means. Detecting means for dividing each of the light fluxes collected and reflected by the magneto-optical recording medium into two light fluxes which are spread in two directions according to the polarization state of the light fluxes, and astigmatism is generated in these light fluxes. First and second light receiving elements which are photodetection elements for receiving light via astigmatism means, and which receive correspondingly the two light fluxes of the zero-order light of the light flux that has passed through the diffraction grating. Section, a third light receiving section for receiving at least one of the two light fluxes of the light flux that has passed through the diffraction grating divided by the composite optical element, and the -1st-order light flux that has passed through the diffraction grating. The light is transmitted by the composite optical element. And a fourth light receiving portion for receiving at least one of the divided two light beams, the first
And the second light-receiving portion, in which the difference signal between the photodetection outputs is used as a read signal of the information signal recorded on the recording track, and the second light-receiving portions are arranged radially at equal angular intervals. Is divided into light receiving portions, and the difference signal between the sum signals of the light detection outputs of the two light receiving portions facing each other through the center of the light receiving portion is used as the focus error signal, and the third and fourth light receiving portions are received. Since the difference signal between the photodetection outputs is used as a tracking error signal, the section outputs a good focus error signal which is less affected by birefringence generated in the magneto-optical recording medium.

Further, in the photodetector element, at least one of the first and second light receiving portions has a light detection output of a light receiving portion located on one side of the dividing line in the direction corresponding to the tangential direction of the recording track. When the difference signal between the sum signal of the push-pull signal and the sum signal of the photodetection outputs of the light-receiving portions located on the other side of the dividing line is a push-pull signal, the push-pull signal can be easily changed without changing the configuration. Can be obtained.

Further, the photodetector according to the present invention is emitted from a light source and is divided by a diffraction grating into at least three rays of 0th order light and ± 1st order light. Detecting means for dividing each of the light fluxes collected and reflected by the magneto-optical recording medium into two light fluxes which are spread in two directions according to the polarization state of the light fluxes, and astigmatism is generated in these light fluxes. First and second light receiving elements which are photodetection elements for receiving light via astigmatism means, and which receive correspondingly the two light fluxes of the zero-order light of the light flux that has passed through the diffraction grating. Section, a third light receiving section for receiving at least one of the two light fluxes of the light flux that has passed through the diffraction grating divided by the composite optical element, and the -1st-order light flux that has passed through the diffraction grating. The light is transmitted by the composite optical element. And a fourth light receiving portion for receiving at least one of the divided two light beams, the first
And the second light-receiving unit, the difference signal between the light-detecting outputs of the two is used as a read signal of the information signal recorded on the recording track, and the third and fourth light-receiving units of the third and fourth light-receiving units are connected to each other. Is used as a tracking error signal and divided into four light-receiving portions that are radially arranged at equal angular intervals, and two sets of light-receiving portions facing each other through the central portion of the light-receiving portion are provided. Since the difference signal between the sum signals of the light detection outputs of the portions is used as the focus error signal, a good focus error signal that is less affected by the birefringence generated in the magneto-optical recording medium is output.

In the photodetector, at least one of the first and second light receiving portions is divided into two by a dividing line in a direction corresponding to the tangential direction of the recording track,
If the difference signal between the photodetection output of the light receiving portion located on one side of the dividing line and the photodetection output of the light receiving portion located on the other side of the dividing line is a push-pull signal, it is easy to A push-pull signal can be obtained.

In the focus error signal detecting method according to the present invention, the recording track of the magneto-optical recording medium is divided into at least 0-order light and ± 1st-order light emitted from the light source by the diffraction grating and divided by the converging means. Each of the light fluxes collected on the above and reflected by this magneto-optical recording medium,
According to the polarization state of these light fluxes, light is received by the photodetector through an analyzing means for splitting the light fluxes into two light fluxes that spread in two directions and an astigmatism means for producing astigmatism in these light fluxes. A light beam which has passed through the diffraction grating and the first and second light receiving portions which receive the two light beams corresponding to the 0th-order light of the light beam which has passed through the diffraction grating and which are divided by the composite optical element. Third light-receiving portion for receiving one of the two light beams of which the + 1st-order light is split by the composite optical element and the -1st-order light of the light beam that has passed through the diffraction grating are split by the composite optical element. A fourth light receiving portion for receiving one of the two light fluxes and a fifth light receiving portion for receiving the other of the two light fluxes obtained by dividing the + 1st order light of the light flux passing through the diffraction grating by the composite optical element. Of the light flux passing through the diffraction grating −
A sixth light receiving portion for receiving the other of the two light fluxes divided by the composite optical element, and the third and sixth light receiving portions, or the fourth light receiving portion. And any one of the fifth light receiving portions is divided into four light receiving portions in a state where the respective light receiving portions are radially arranged at equal angular intervals, and the respective light receiving portions are connected via the central portion of the light receiving portion. Since the difference signal between the sum signals of the light detection outputs of the two sets of light receiving portions facing each other is obtained and these difference signals are added to each other to form a focus error signal, there is little influence of birefringence occurring in the magneto-optical recording medium. It is possible to detect various focus error signals.

Further, in the focus error signal detecting method according to the present invention, at least three light beams of 0th order light and ± 1st order light emitted from the light source are divided by the diffraction grating, and the focusing means of the magneto-optical recording medium is used. A light analyzing unit for dividing each light flux focused on the recording track and reflected by the magneto-optical recording medium into two light fluxes which are diverged in two directions in accordance with the polarization state of the light fluxes, and to these light fluxes. The light is detected by the photodetector through the astigmatism means that produces astigmatism, and the photodetector is divided by the composite optical element into the 0th-order light of the light flux passing through the diffraction grating.
A first and a second light receiving portion for receiving the corresponding light beam, and a third light beam for receiving one of the two light beams divided by the composite optical element from the + 1st-order light of the light beam passing through the diffraction grating. The + 1st-order light of the light beam passing through the diffraction grating and the fourth light-receiving part that receives one of the two light beams divided by the composite optical element A fifth light receiving portion that receives the other of the two light beams split by the composite optical element, and a − of the light beams that have passed through the diffraction grating.
And a sixth light receiving portion for receiving the other of the two light fluxes of which the primary light is split by the composite optical element, wherein the third to sixth light receiving portions are equiangularly spaced. Is divided into four light receiving portions arranged in a radial pattern with each other, and a difference signal between the sum signals of the light detection outputs of the two light receiving portions facing each other through the central portion of the light receiving portion is obtained. Since all four difference signals are added to obtain the focus error signal, it is possible to detect a good focus error signal that is less affected by the birefringence generated in the magneto-optical recording medium.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below with reference to the drawings. In this example, the optical pickup device according to the present invention, which is configured to have the photodetector according to the present invention, is configured as an optical pickup device of a reproducing device for reproducing a so-called magneto-optical disk 6 which is a magneto-optical recording medium. It is an example. As shown in FIGS. 1 and 2, this optical pickup device is configured to have an optical block portion 10 made of a synthetic resin material, a metal material, or the like, and faces the magneto-optical disk 6 supported in the reproducing device. As described above.

The magneto-optical disk 6 has a disk substrate made of a transparent material such as polycarbonate and a signal recording layer made of a magnetic material adhered to the disk substrate. An external magnetic field is applied to this signal recording layer, and a focused laser beam is applied to a minute area and heated to a temperature higher than the so-called Curie temperature, and the magnetization direction in the minute area is imitated by the external magnetic field. As a result, the information signal is written. The magnetization direction of the signal recording layer is so-called perpendicular magnetization, which is the direction perpendicular to the main surface portion of the disk substrate. That is,
The information signal written in this signal recording layer is a binary signal which is indicated by whether the magnetization direction of this signal recording layer is upward or downward.

A chucking hole 6a is formed in the center of the magneto-optical disk 6. In the reproducing apparatus, the magneto-optical disk 6 is supported by the chucking mechanism of the reproducing apparatus on the periphery of the chucking hole 6a with the chucking hole 6a as a position reference.
The magneto-optical disk 6 is rotated together with the chucking mechanism.

Recording tracks are formed on the signal recording layer. The recording track is formed on the signal recording layer in a spiral shape that is substantially concentric. The center of curvature of the recording track coincides with the center of the chucking hole 6a. The information signal is written along this recording track.

The optical block portion 10 of the optical pickup device is supported so as to be movable in the radial direction of the magneto-optical disk 6, as indicated by the arrow T in FIG. As shown in FIGS. 1 to 3 and 5, a laser diode 1 serving as a light source, various optical devices for guiding an emission light flux R ₁ emitted from the laser diode 1, and a light are provided in the optical block unit 10. The detector 9 and the like are built in. In addition, an objective lens driving device 11 that movably supports the objective lens 5 that serves as a light converging unit is attached to the optical block unit 10. The objective lens driving device 11 supports the objective lens 5 so as to face the main surface portion of the magneto-optical disk 6, and when a predetermined drive current is supplied, the objective lens 5 is driven by the optical axis of the objective lens 5. The moving operation is performed in the axial direction, that is, in the contact / separation direction with respect to the magneto-optical disk 6, and in the radial direction of the magneto-optical disk 6, which is the direction orthogonal to the optical axis of the objective lens 5.

The laser diode 1 is constructed by housing a laser chip 1a in a can 1b. The front surface of the can 1b is opened as a light beam emission hole, and the cover glass 1d is fitted therein. In addition, a plurality of electrode terminals 1c are provided on the rear surface of the can 1b. The laser chip 1a is supplied with a drive current via the electrode terminal 1c, emits a laser beam, and passes through the cover glass 1d to be emitted to the front side. This laser light flux is in a linearly polarized state, as indicated by the line P in FIG.

In this optical pickup device, the emitted light beam R ₁ emitted from the laser diode ₁ is
The light passes through the diffraction grating 2 and reaches the composite optical element 7. The diffraction grating 2 splits the emitted light flux R ₁ into at least three light fluxes of 0th-order light and ± 1st-order light that are spread in three directions in one plane. The spreading directions of these light fluxes substantially correspond to the tangential direction of the recording track.

The composite optical element 7 has a first prism 7a made of an isotropic medium such as glass and a second prism 7b made of a uniaxial crystal medium. Each of the prisms 7a and 7b is a prism having an isosceles right triangular prism shape, and the inclined surface portions thereof are adhered to each other via a polarizing film 7c to form a cubic optical element. In this composite optical element 7, the polarizing film 7c is formed at an angle of 45 ° with respect to the optical axis of the 0th order light of the emitted light flux R ₁ , and the substantially square first surface of the first prism 7a is formed. It is arranged so as to be perpendicular to the optical axis of the 0th order light of the emitted light beam R ₁ . As shown by an arrow P in FIG. 3, the polarization direction of the emitted light beam R ₁ is the direction of incidence in the P polarization state on the polarization film 7c. The polarizing film 7c has the transmittance Ts of the S-polarized incident light flux higher than the transmittance Tp of the P-polarized incident light flux. Therefore, the emitted light beam R ₁ is emitted from the polarizing film 7c.
And the optical path is changed by 90 °, and the light is vertically emitted from the substantially square second surface of the first prism 7a.

The polarizing film 7c is the same as the polarizing film 7c.
With the configuration in which the phase difference between the P-polarized component and the S-polarized component of the light beam reflected by is suppressed, the emitted light beam R ₁ can be reflected in a good linear polarization state.

The emitted light beam R ₁ is collimated by the collimator lens 3
As a result, each of the three divided light beams is made into a parallel light beam, reflected by the mirror 4, the optical path thereof is changed, and incident on the objective lens 5. This objective lens 5 is shown in FIG.
As shown in, the incident outgoing light beam R ₁ is transmitted through the disk substrate and focused on the signal recording layer of the magneto-optical disk 6.

[0038] The objective lens driving device 11, by moving operating the objective lens 5 based on the focus error signal and the tracking error signal will be described later, as shown in FIG. 4, 0-order light of the light rays emitted R ₁ The converging point of the light flux of is always positioned on the recording track 12. The light condensing points of the light beams of the ± 1st order light of the emitted light beam R ₁ are formed at positions substantially arranged in the direction along the recording track 12 with the light condensing points of the 0th order light being sandwiched therebetween.
It is formed at a position slightly off the recording track 12.
The focus error signal is the optical axis direction of the irradiation light flux R ₁ between the converging point of the 0th-order light and the surface of the signal recording layer, that is, a direction substantially perpendicular to the surface of the signal recording layer. Is a signal indicating the distance to. Further, the tracking error signal is a direction perpendicular to the optical axis of the emitted light beam R ₁ between the condensing point of the 0th-order light and the recording track 12 and the recording track 12, that is, the radial direction of the disk substrate. Is a signal indicating the distance to.

The cross-sectional shape of the emitted light beam R ₁ focused on the recording track 12, that is, the recording track 1
As shown in FIG. 4, the beam spot formed on the beam 2 has an elliptical shape corresponding to the near field pattern of the emitted light beam R ₁ emitted from the laser diode 1. The beam spot is formed such that the major axis direction of the ellipse is orthogonal to the recording track 12. This is to improve the recording density of the information signal on the recording track 12 and the so-called CN ratio. Further, the emitted light beam R ₁ has a polarization direction orthogonal to the recording track 12 as shown by an arrow P in FIG. This is to suppress the influence of birefringence due to the disk substrate.

Then, the emitted light beam R divided into three parts
₁ is reflected by the magneto-optical disk 6 and becomes a 0th order reflected light beam R ₂ , a + 1st order reflected light beam R ₃ and a −1st order reflected light beam R ₄ . Of the reflected light fluxes R ₂ , R ₃ , and R ₄ , the 0th-order light reflected light flux R ₂ has a so-called Kerr effect according to the information signal recorded on the recording track 12.
The polarization direction is rotated by a small angle. Each of the reflected light beams R ₂ , R ₃ , and R ₄ passes through the objective lens 5, the mirror 4, and the collimator lens 3 and returns to the first prism 7 a of the composite optical element 7. Here, each of the reflected light fluxes R ₂ , R ₃ and R ₄ is generated by the first prism 7a.
And the polarizing film 7c.

The direction of the crystal axis of the second prism 7b forming the composite optical element 7 is the line D in FIG.
As shown in _1, perpendicular to the optical axis of the zero-order reflection light beam R _2, and, with respect to the polarization direction of the zero-order reflection light beam R ₂ 45
The direction is °. The polarization direction of the 0th-order reflected light beam R ₂ shown here is the polarization direction of the ordinary ray line segment that does not cause the rotation of the polarization direction due to the Kerr effect.

In the composite optical element 7, each of the reflected light beams R ₂ , R ₃ and R ₄ is an ordinary ray component when entering the second prism 7b through the polarizing film 7c. And an extraordinary ray component, and is divided into two split light beams that spread in two directions. That is, the 0th-order reflected light beam R ₂ is the first and second split light beams R ₅ , R ₈
Is divided into The + 1st-order reflected light beam R ₃ is split into third and fifth split beams R ₇ and R ₁₀ . Also, the above-
The primary light reflected light flux R ₄ includes the fourth and sixth split light fluxes R ₆ ,
It is divided into R ₉ . The spreading direction of the light flux by the composite optical element 7 is a direction orthogonal to the light splitting direction by the diffraction grating 2, and corresponds to the inclination direction of the polarizing film 7c with respect to the optical axis of the 0th-order reflected light flux R _2. It is the direction we did.

Then, the respective divided luminous fluxes R ₅ , R ₈ , R ₇ , R ₆ , R ₁₀ , R divided by the composite optical element 7 are used.
₉ passes through the cylindrical lens 8 which serves as an astigmatism means to generate astigmatism. In the direction of this astigmatism, that is, in the major axis direction when the cross section of the light flux is elliptical, the generatrix of the cylindrical lens 8 is line D _{2 in} FIG.
As shown by, since it is a direction rotated by 45 ° with respect to the direction corresponding to the tangential direction of the recording track 12, there is a direction rotated by 45 ° with respect to the direction corresponding to the tangential direction of the recording track 12. Become.

The divided luminous fluxes R ₅ , R ₈ and
R ₇ , R ₆ , R ₁₀ , and R ₉ are received by the photodetector 9. The photodetector 9 is a photodetection element such as a photodiode and has a light receiving surface 9a and a plurality of terminals 9b for outputting a photodetection output to the outside. On the light receiving surface 9a of the photodetector 9, the respective split light beams _{R 5, R 8, R 7} , R 6, R 10, R 9 , as shown in FIG. 8, having three converging point Two rows of condensing points are formed to condense light. At these light condensing points, three light condensing points are arranged in a direction corresponding to the tangential direction of the recording track 12 shown by an arrow V in FIG. 8, and a direction orthogonal to the direction corresponding to the tangential direction of the recording track 12. 2 rows of condensing points are formed in the. The three converging points arranged in the direction corresponding to the tangential direction of the recording track 12 correspond to the light beams divided by the action of the diffraction grating 2. Then, the two condensing point arrays arranged in the direction orthogonal to the direction corresponding to the tangential direction of the recording track 12 correspond to the light beams divided by the composite optical element 7.

As shown in FIG. 9, the photodetector 9 includes the six split light beams R ₅ , R ₈ , R ₇ , R ₆ , R ₁₀ and R _{9 described above.}
First to sixth light receiving portions 1 for respectively receiving light
It has 4, 17, 16, 15, 19, and 18.

The first light receiving portion 14 is formed in a substantially square shape and receives the first divided light flux R ₅ . Also,
The second light receiving portion 17 is formed in a substantially square shape and receives the second divided light flux R ₈ .

The third light receiving portion 16 is formed in a substantially square shape and is located on one side of the first light receiving portion 14 so as to receive the third divided light flux R _7. Is formed. The fourth light receiving portion 15 is formed in a substantially square shape and is formed on the other side of the first light receiving portion 14 so as to receive the fourth divided light flux R _6. ing. Further, the fifth light receiving portion 19 is formed in a substantially square shape, and is formed on one side of the second light receiving portion 17 so as to receive the fifth divided light flux R _10. ing. The sixth light receiving portion 18 is formed in a substantially square shape and is formed on the other side of the second light receiving portion 17 so as to receive the sixth divided light flux R _9. ing.

Then, the third and fifth light receiving portions 16,
19 are short-circuited to each other. The fourth and sixth light receiving portions 15 and 18 are also short-circuited to each other.

In the photodetector 9, the third and fifth light receiving portions 16 and 19 and the fourth and sixth light receiving portions 15 and 18 have a difference signal in their photodetection outputs from each other. It is used as a tracking error signal. That is, when the optical output signals of the third and fifth light receiving portions 16 and 19 are G and the optical output signals of the fourth and sixth light receiving portions 15 and 18 are H, the tracking error signal is ( GH).

Then, the difference signal of the photodetection outputs of the first light receiving portion 14 and the second light receiving portion 17 is used as a read signal of the information signal recorded in the recording track. That is, when the light output signal of the first light receiving portion 14 is (A + B + C + D) and the light output signal of the second light receiving portion 17 is (E + F), the read signal is (A
+ B + C + D)-(E + F). First above
And the light intensities of the second split light fluxes R ₅ and R ₈ vary in opposite polarities depending on the angle and direction of the turning of the polarization direction of the 0th-order reflected light flux R ₂ due to the Kerr effect. .

Then, the first and second light receiving portions 14,
Reference numeral 17 is divided into four light receiving portions in a state where they are radially arranged at equal angular intervals. That is, the first light receiving portion 14 includes the first to fourth light receiving portions 13A,
It is divided into 13B, 13C and 13D. The second light receiving unit 17 is also divided in the same manner. The respective light receiving portions forming the first and second light receiving portions 14 and 17 are opposed to each other in the direction of the astigmatism generated by the cylindrical lens 8 by the first and second divided light beams R ₅ and R _8. Are arranged so as to have two sets of light receiving portions.

In this optical pickup device, the direction and amount of the astigmatism of each of the divided luminous fluxes R ₅ and R ₈ are such that the emitted luminous flux from the surface of the signal recording layer to the condensing point of the emitted luminous flux R _1. Direction and distance with respect to the optical axis direction of R ₁ ,
That is, it changes according to the change in the focus error amount. Therefore, in the first light receiving section 14, the light detection outputs output from the two sets of the light receiving sections 13A, 13C, 13B, 13D facing each other through the central portion of the first light receiving section 14 are summed up. When a signal is generated and a difference signal between these sum signals is generated, this difference signal becomes the focus error signal. Similarly, with respect to the second light receiving section 17, the sum signal is generated for each of the photodetection outputs output from the two sets of light receiving sections facing each other through the central portion of the second light receiving section 17, and these sum signals are generated. When a difference signal between the sum signals is generated, this difference signal becomes the focus error signal. In this optical pickup device, the first and second light receiving portions 14 and 17 are
By adding the respective focus error signals obtained from each other, a good focus error signal in which the influence of birefringence on the disk substrate is suppressed is obtained.

That is, the light detection output from the first light receiving portion 13A is A, the light detection output from the second light receiving portion 13B is B, and the light detection output from the third light receiving portion 13C is C, Let D be the light detection output from the fourth light receiving portion 13D. Then, in the second light receiving section 17, two sets of light receiving sections facing each other via the central portion of the second light receiving section 17 are short-circuited, and the light detection output of each of these sets is E, If F, the focus error signal is obtained by (A + C)-(B + D) + (EF).

[0054] In this optical pickup apparatus, the zero-order reflection light beam R ₂ is the optical axis and the recording track 12 of the injection Idemitsu bundle R ₁ than the recording track 12 to the focal point of the light rays emitted R ₁ The light intensity distribution changes in accordance with the change in the direction and distance with respect to the vertical direction, that is, the tracking error amount. Therefore, in the first light receiving portion 14, the first and fourth light receiving portions 13A, 1
When a difference signal between the sum signal of the 3D light output signals and the sum signal of the light output signals of the second and third light receiving portions 13B and 13C is obtained, the difference signal is the irradiation position of the emitted light beam R _1. It becomes a push-pull signal indicating the positional deviation from the recording track 12. That is, the push-pull signal is (A +
D)-(B + C). Here, the gradient direction of the light intensity distribution in the 0th-order reflected light beam R ₂ is
The direction orthogonal to the tangential direction of the recording track 12 is rotated by 90 ° on the light receiving surface 9a by passing through the cylindrical lens 8.

In the photodetector 9, each light receiving portion forming each light receiving portion 14 and 17 has a plurality of terminals 9b.
The light detection signal can be independently output via the.

The push-pull signal can be used not only as the tracking error signal, but also when the recording track 12 is formed with so-called wobbling, it is also a signal corresponding to the wobbling cycle. And becomes a signal for detecting an address on the recording track 12.

The optical pickup device can also read the information signal from the read-only optical disc 6 in which the information signal is recorded by the concavo-convex pattern. In this case, the read signal is the first and second read signals.
Can be obtained by the sum signal of the light detection outputs from the light receiving portions 14 and 17, that is, (A + B + C + D) + (E + F).

The photo-detecting element according to the present invention is not limited to the above-mentioned embodiment, but as shown in FIG.
The first light receiving portion 14 is divided into two by a dividing line in a direction orthogonal to the tangential direction of the recording track 12 shown by an arrow V in FIG.
A, 20B, and the second light-receiving portion 17 is divided into two, similarly to the first light-receiving portion 14, and is constituted by third and fourth light-receiving portions 20C, 20D. May be.

In this case, in order to execute the focus error signal detection method according to the present invention, the third and sixth light receiving portions 16 and 18 or the fourth and fifth light receiving portions 15 and 19 are performed. That is, the light receiving portions facing each other with the central position of the first and second light receiving portions 14 and 17 interposed therebetween are divided into four light receiving portions that are radially arranged at equal angular intervals. ing. The third and sixth light receiving portions 16 and 18, or the respective light receiving portions that form the fourth and fifth light receiving portions 15 and 19 are the third and sixth light receiving portions.
Of the divided luminous fluxes R ₇ and R ₉ or the fourth and fifth divided luminous fluxes R ₆ and R ₁₀ have two sets of light receiving portions facing each other in the direction of the astigmatism generated by the cylindrical lens 8. Are arranged as follows.

In the photodetector 9, the third and fifth light receiving portions 16 and 19 and the fourth and sixth light receiving portions 15 and 18 have a difference signal of their photodetection outputs. It is used as a tracking error signal. That is, the total of the optical output signals of the third and fifth light receiving portions 16 and 19 is (I +
J + F), and the total of the optical output signals of the fourth and sixth light receiving units 15 and 18 is (E + G + H), the tracking error signal is (I + J + F)-(E + G +).
H).

Then, the difference signal between the photodetection outputs of the first light receiving portion 14 and the second light receiving portion 17 is used as a read signal of the information signal recorded on the recording track. That is, when the light output signal of the first light receiving portion 14 is (A + B) and the light output signal of the second light receiving portion 17 is (C + D), the read signal is (A + B)-.
It is obtained by (C + D).

In this photo-detecting element, in the third light-receiving section 16, the photo-detecting outputs output from two sets of light-receiving sections facing each other with the central portion of the third light-receiving section 16 in between. When a sum signal is generated and a difference signal between these sum signals is generated, this difference signal becomes the focus error signal. Similarly, the sixth light receiving unit 18
As for the above, if a sum signal is generated for each of the photodetection outputs output from the two light receiving portions facing each other through the central portion of the sixth light receiving portion 18, and a difference signal between these sum signals is generated, This difference signal becomes the focus error signal. In this optical pickup device, the focus error signals obtained from the third and sixth light receiving portions 16 and 18 are added to each other, so that the effect of birefringence on the disk substrate is suppressed and good focus is obtained. It is supposed to get an error signal.

That is, with respect to the third light receiving section 16, two sets of light receiving sections facing each other through the central portion of the third light receiving section 16 are short-circuited, and the light detection output of each of these sets. Are I and J. In addition, the sixth light receiving unit 1
In regard to No. 8, two sets of light receiving portions facing each other via the central portion of the sixth light receiving unit 18 are short-circuited, and the light detection outputs of these respective sets are G and H. Then, the focus error signal is obtained by (I−J) + (G−H).

Then, in this photodetector, when the difference signal between the light output signals of the first and second light receiving portions 20A and 20B is obtained in the first light receiving portion 14, this difference signal is obtained as described above. The push-pull signal indicates a positional deviation between the irradiation position of the emitted light beam R ₁ and the recording track 12. In addition, in the second light receiving section 17 as well,
When the difference signal between the light output signals of the fourth and the fourth light receiving portions 20C and 20D is obtained, this difference signal becomes a push-pull signal indicating the positional deviation between the irradiation position of the emitted light beam R ₁ and the recording track 12. That is, the push-pull signal is obtained by (AB) or (CD).

Further, as shown in FIG. 11, the photo-detecting element executes the focus error signal detecting method according to the present invention, so that the third to sixth light-receiving sections 16, 15,
Each of the elements 19 and 18 may be divided into four light receiving portions radially arranged at equal angular intervals. Each of the light receiving portions forming the third to sixth light receiving portions 16, 15, 19, and 18 has the third to sixth split luminous fluxes R ₇ and R ₇ .
₆ , R ₉ and R ₁₀ are arranged so as to have two sets of light receiving portions facing each other in the direction of the astigmatism generated by the cylindrical lens 8.

Then, in this case, the first light receiving portion 14 is divided in the direction orthogonal to the direction corresponding to the tangential direction of the recording track 12 shown by the arrow V in FIG. 11, similarly to the above-mentioned example. It is divided into two by a line and is composed of first and second light receiving portions 20A and 20B, and the second light receiving portion 1 is also provided.
Similarly to the first light receiving portion 14, the reference numeral 7 is divided into two and comprises third and fourth light receiving portions 20C and 20D.

In the photodetector 9, the third and fifth light receiving portions 16 and 19 and the fourth and sixth light receiving portions 15 and 18 have the above-mentioned difference signals of their light detection outputs. It is used as a tracking error signal. That is, the optical output signals of the third and fifth light receiving portions 16 and 19 are (I + J + R).
+ S + T + U), and the fourth and sixth light receiving portions 15,
When the optical output signal of 18 is (K + L + Q + P + G + H), the tracking error signal is (I + J + R + S).
+ T + U)-(K + L + Q + P + G + H).

Then, the difference signal between the photodetection outputs of the first light receiving section 14 and the second light receiving section 17 is used as a read signal of the information signal recorded on the recording track. That is, when the light output signal of the first light receiving portion 14 is (A + B) and the light output signal of the second light receiving portion 17 is (C + D), the read signal is (A + B)-.
It is obtained by (C + D).

In this photo-detecting element, in the third light-receiving section 16, the photo-detecting outputs output from two sets of light-receiving sections facing each other with the central portion of the third light-receiving section 16 in between. When a sum signal is generated and a difference signal between these sum signals is generated, this difference signal becomes the focus error signal. Similarly, the fourth to sixth light receiving portions 15, 19 and 18 are also output from two sets of light receiving portions facing each other through the central portions of the fourth to sixth light receiving portions 15, 19 and 18. When a sum signal is generated for each of the detected light outputs and a difference signal between the sum signals is generated, the difference signal becomes the focus error signal. In this optical pickup device, the effect of birefringence on the disk substrate is suppressed by adding all four focus error signals obtained from the third to sixth light receiving units 16, 15, 19, and 18. To obtain a good focus error signal.

That is, the third and sixth light receiving portions 1
6 and 18, the third and sixth light receiving sections 1 are mutually connected.
Two sets of light receiving portions facing each other through the central portions of 6 and 18 are short-circuited, and the light detection outputs of these sets are I, J, and
G and H. Further, with respect to the fourth light receiving portion 15, the light detection outputs outputted from the fifth to eighth light receiving portions 20K, 20L, 20Q, 20P forming the fourth light receiving portion 15 are respectively K, L, Q. , P. Then, regarding the fifth light receiving portion 19, the ninth to twelfth light receiving portions 20R, 20S, 20 forming the fifth light receiving portion 19 are formed.
The light detection outputs from T and 20U are respectively R,
S, T, U. Then, the focus error signal is (I−J) + (G−H) + (K + Q) − (L + P)
+ (R + T)-(S + U).

Then, in this photodetector, when the difference signal between the light output signals of the first and second light receiving portions 20A and 20B is obtained in the first light receiving section 14, this difference signal is obtained. The push-pull signal indicates a positional deviation between the irradiation position of the emitted light beam R ₁ and the recording track 12. In addition, in the second light receiving section 17 as well,
When the difference signal between the light output signals of the fourth and the fourth light receiving portions 20C and 20D is obtained, this difference signal becomes a push-pull signal indicating the positional deviation between the irradiation position of the emitted light beam R ₁ and the recording track 12. That is, the push-pull signal is obtained by (AB) or (CD).

The photo-detecting element according to the present invention is not limited to the above-mentioned optical pickup device but also the above-mentioned composite optical element 7
Instead of this, it can also be used in an optical pickup device having a beam splitter and an analyzer. Further, the focus error signal detection method according to the present invention can be performed not only in the optical pickup device described above, but also in an optical pickup device having a beam splitter and an analyzer in place of the composite optical element 7.

[0073]

As described above, in the optical pickup device according to the present invention, the composite optical element is emitted from the light source and is divided by the diffraction grating into at least three luminous fluxes of 0th order light and ± 1st order light. The luminous fluxes are guided to the magneto-optical recording medium side, and the luminous fluxes condensed by the condensing means on the magneto-optical recording medium and reflected by the magneto-optical recording medium are respectively divided into two directions according to the polarization states of the luminous fluxes. It is guided to the photodetector side that receives each of the light fluxes through astigmatism means that divides the light fluxes into two light fluxes that are spread and produces astigmatism in these light fluxes. That is, this composite optical element functions as both a beam splitter and an analyzer.

The photo-detecting element according to the present invention is emitted from a light source and is divided into at least three light beams of 0th order light and ± 1st order light by a diffraction grating, and each is focused on a recording track of a magneto-optical recording medium by a condensing means. Detecting means for dividing each of the light fluxes collected and reflected by the magneto-optical recording medium into two light fluxes which are spread in two directions according to the polarization state of the light fluxes, and astigmatism is generated in these light fluxes. First and second light receiving elements which are photodetection elements for receiving light via astigmatism means, and which receive correspondingly the two light fluxes of the zero-order light of the light flux that has passed through the diffraction grating. Section, a third light receiving section for receiving at least one of the two light fluxes of the light flux that has passed through the diffraction grating divided by the composite optical element, and the -1st-order light flux that has passed through the diffraction grating. The light is transmitted by the composite optical element. And a fourth light receiving portion for receiving at least one of the divided two light beams, the first
And the second light-receiving portion, in which the difference signal between the photodetection outputs is used as a read signal of the information signal recorded on the recording track, and the second light-receiving portions are arranged radially at equal angular intervals. Is divided into light receiving portions, and the difference signal between the sum signals of the light detection outputs of the two light receiving portions facing each other through the center of the light receiving portion is used as the focus error signal, and the third and fourth light receiving portions are received. In the section, the difference signal between the photodetection outputs is used as a tracking error signal. Therefore, this photo-detecting element can output a good focus error signal that is less affected by the birefringence that occurs in the magneto-optical recording medium.

Further, in the photodetection element, at least one of the first and second light receiving portions has a light detection output of a light receiving portion located on one side of the dividing line in the direction corresponding to the tangential direction of the recording track. When the difference signal between the sum signal of the push-pull signal and the sum signal of the photodetection outputs of the light-receiving portions located on the other side of the dividing line is a push-pull signal, the push-pull signal can be easily changed without changing the configuration. Can be obtained.

Further, the photodetector according to the present invention is emitted from a light source and is divided into at least three rays of 0th order light and ± 1st order light by a diffraction grating, and each of them is focused on a recording track of a magneto-optical recording medium by a converging means. Detecting means for dividing each of the light fluxes collected and reflected by the magneto-optical recording medium into two light fluxes which are spread in two directions according to the polarization state of the light fluxes, and astigmatism is generated in these light fluxes. First and second light receiving elements which are photodetection elements for receiving light via astigmatism means, and which receive correspondingly the two light fluxes of the zero-order light of the light flux that has passed through the diffraction grating. Section, a third light receiving section for receiving at least one of the two light fluxes of the light flux that has passed through the diffraction grating divided by the composite optical element, and the -1st-order light flux that has passed through the diffraction grating. The light is transmitted by the composite optical element. And a fourth light receiving portion for receiving at least one of the divided two light beams, the first
And the second light-receiving unit, the difference signal between the light-detecting outputs of the two is used as a read signal of the information signal recorded on the recording track, and the third and fourth light-receiving units of the third and fourth light-receiving units are connected to each other. Is used as a tracking error signal and divided into four light-receiving portions that are radially arranged at equal angular intervals, and two sets of light-receiving portions facing each other through the central portion of the light-receiving portion are provided. A difference signal between the sum signals of the light detection outputs of the portions is used as a focus error signal. Therefore, this photo-detecting element can output a good focus error signal that is less affected by the birefringence that occurs in the magneto-optical recording medium.

In the photodetector, at least one of the first and second light receiving portions is divided into two by a dividing line in a direction corresponding to the tangential direction of the recording track,
If the difference signal between the photodetection output of the light receiving portion located on one side of the dividing line and the photodetection output of the light receiving portion located on the other side of the dividing line is a push-pull signal, it is easy to A push-pull signal can be obtained.

In the focus error signal detecting method according to the present invention, the recording track of the magneto-optical recording medium is divided into at least 0-order light and ± 1st-order light emitted from the light source by the diffraction grating and divided by the converging means. Each of the light fluxes collected on the above and reflected by this magneto-optical recording medium,
According to the polarization state of these light fluxes, light is received by the photodetector through an analyzing means for splitting the light fluxes into two light fluxes that spread in two directions and an astigmatism means for producing astigmatism in these light fluxes. A light beam which has passed through the diffraction grating and the first and second light receiving portions which receive the two light beams corresponding to the 0th-order light of the light beam which has passed through the diffraction grating and which are divided by the composite optical element. Third light-receiving portion for receiving one of the two light beams of which the + 1st-order light is split by the composite optical element and the -1st-order light of the light beam that has passed through the diffraction grating are split by the composite optical element. A fourth light receiving portion for receiving one of the two light fluxes and a fifth light receiving portion for receiving the other of the two light fluxes obtained by dividing the + 1st order light of the light flux passing through the diffraction grating by the composite optical element. Of the light flux passing through the diffraction grating −
A sixth light receiving portion for receiving the other of the two light fluxes divided by the composite optical element, and the third and sixth light receiving portions, or the fourth light receiving portion. And any one of the fifth light receiving portions is divided into four light receiving portions in a state where the respective light receiving portions are radially arranged at equal angular intervals, and the respective light receiving portions are connected via the central portion of the light receiving portion. Then, a difference signal between the sum signals of the light detection outputs of the two light receiving portions facing each other is obtained, and these difference signals are added to each other to obtain a focus error signal. Therefore, in this focus error signal detection method, it is possible to detect a good focus error signal that is less affected by the birefringence that occurs in the magneto-optical recording medium.

Further, in the focus error signal detecting method according to the present invention, the light emitted from the light source is divided into at least three beams of the 0th order light and the ± 1st order light by the diffraction grating, and the focusing means of the magneto-optical recording medium is used. A light analyzing unit for dividing each light flux focused on the recording track and reflected by the magneto-optical recording medium into two light fluxes which are diverged in two directions in accordance with the polarization state of the light fluxes, and to these light fluxes. The light is detected by the photodetector through the astigmatism means that produces astigmatism, and the photodetector is divided by the composite optical element into the 0th-order light of the light flux passing through the diffraction grating.
A first and a second light receiving portion for receiving the corresponding light beam, and a third light beam for receiving one of the two light beams divided by the composite optical element from the + 1st-order light of the light beam passing through the diffraction grating. The + 1st-order light of the light beam passing through the diffraction grating and the fourth light-receiving part that receives one of the two light beams divided by the composite optical element A fifth light receiving portion that receives the other of the two light beams split by the composite optical element, and a − of the light beams that have passed through the diffraction grating.
And a sixth light receiving portion for receiving the other of the two light fluxes of which the primary light is split by the composite optical element, wherein the third to sixth light receiving portions are equiangularly spaced. Is divided into four light receiving portions arranged in a radial pattern with each other, and a difference signal between the sum signals of the light detection outputs of the two light receiving portions facing each other through the central portion of the light receiving portion is obtained. All four difference signals are added to obtain a focus error signal. Therefore, in this focus error signal detection method, it is possible to detect a good focus error signal that is less affected by the birefringence that occurs in the magneto-optical recording medium.

That is, according to the present invention, when the information signal recorded on the magneto-optical recording medium is read out, the focus error signal and the like can be favorably detected, and the number of parts is reduced to simplify and downsize the structure. The present invention provides an optical pickup device capable of facilitating manufacturing, provides a photodetector suitable for use in such an optical pickup device, and further detects a focus error signal in such an optical pickup device. A method can be provided.

[Brief description of drawings]

FIG. 1 is a plan view showing a configuration of an optical pickup device according to the present invention as seen through.

FIG. 2 is a side view showing the configuration of the optical pickup device as seen through.

FIG. 3 is a side view of an essential part showing the configuration of the optical pickup device.

FIG. 4 is an enlarged plan view showing a state of a beam spot formed on a magneto-optical recording medium by the optical pickup device.

FIG. 5 is a plan view showing an arrangement of optical elements that constitute the optical pickup device.

FIG. 6 is an enlarged front view showing a configuration of a composite optical element that constitutes the optical pickup device.

FIG. 7 is an enlarged front view showing a configuration of a cylindrical lens that constitutes the optical pickup device.

FIG. 8 is an enlarged plan view showing an arrangement of condensing points received by a photodetector in the optical pickup device.

FIG. 9 is an enlarged plan view showing a configuration of a photodetector according to the present invention which constitutes the optical pickup device.

FIG. 10 is an enlarged plan view showing another example of the configuration of the photodetector.

FIG. 11 is an enlarged plan view showing still another example of the configuration of the photodetector.

[Explanation of symbols]

Laser diode 2 Diffraction grating 7 Composite optical element 8・ ・ ・ ・ ・ ・ ・ Cylindrical lens 9 ・ ・ ・ ・ ・ ・ ・ ・ ・ Photodetector 13A ・ ・ ・ ・ ・ ・ ・ ・ First light receiving part 13B ・ ・ ・・ ・ ・ Second light receiving portion 13C ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Third light receiving portion 13D ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Fourth light receiving portion 14 ・ ・ ・・ ・ ・ First light receiving part 15 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Fourth light receiving part 16 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Third light receiving part 17 ・ ・ ・ ・・ ・ ・ ・ ・ ・ ・ ・ 2nd light receiving part 18 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 6th light receiving part 19 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 5th light receiving part 20A・ ・ ・ ・ ・ ・ ・ ・ First light receiving part 20B ・ ・ ・ ・ ・ ・..Second light receiving portion 20C ... First light receiving portion 20D..Second light receiving portion R ₁ ...・ Irradiated light flux R ₂・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 0th order reflected light flux R ₃・ ・ ・ ・ ・ ・ ・ ・ ・ ・ + 1st order reflected light flux R ₄・ ・ ・ ・ ・ ・ ・ ・ ・ ・Primary light reflected light flux R ₅・ ・ ・ ・ ・ ・ ・ ・ ・ ・ First split light flux R ₆・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Fourth split light flux R ₇・ ・ ・ ・ ・ ・ ・ ・・ Third split light flux R ₈・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Second split light flux R ₉・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Sixth split light flux R ₁₀・ ・ ・..Fifth split luminous flux

Claims (7)

[Claims] 1. A light source, and a light beam emitted from the light source is at least ± 0th order light.
Diffraction grating for splitting into three light beams of next light, composite optical element for guiding each of the light beams having passed through the diffraction grating to the magneto-optical recording medium side, and each light beam having passed through the composite optical element for the magneto-optical recording medium. The above-mentioned composite optical element is provided with a condensing means for condensing the light beams upward, and the above-mentioned composite optical element is divided into two light beams which are spread in two directions according to the polarization states of the light beams. An optical pickup device which is divided and is guided to the photodetector side which receives each of the light fluxes through astigmatism means for producing astigmatism in these light fluxes. 2. A magneto-optical recording medium which is emitted from a light source and is divided by a diffraction grating into at least three light beams of 0th order light and ± 1st order light and focused on recording tracks of a magneto-optical recording medium by a focusing means. Light is received via an analyzing means for dividing each reflected light flux into two light fluxes which are spread in two directions according to the polarization state of these light fluxes, and an astigmatism means for producing astigmatism in these light fluxes. Which is a photo-detecting element for receiving 0th-order light of the light flux that has passed through the diffraction grating, corresponding to the two light fluxes divided by the composite optical element.
, A third light receiving portion for receiving at least one of the two light beams obtained by dividing the + 1st-order light of the light beam that has passed through the diffraction grating by the composite optical element, and the − light beam that has passed through the diffraction grating. A fourth light receiving portion for receiving at least one of the two light beams in which the primary light is split by the composite optical element, wherein the first and second light receiving portions have a mutual light detection output. The difference signal is used as a read signal of the information signal recorded on the recording track, and is divided into four light receiving portions that are radially arranged at equal angular intervals. The difference signal between the sum signals of the light detection outputs of the two light receiving portions facing each other is used as a focus error signal, and the difference signals between the light detection outputs of the third and fourth light receiving portions are tracking errors. Signal A photo-detecting element that is formed. 3. A magneto-optical recording medium which is emitted from a light source and is divided by a diffraction grating into at least three rays of 0th order light and ± 1st order light and is condensed on a recording track of a magneto-optical recording medium by a converging means. Light is received via an analyzing means for dividing each reflected light flux into two light fluxes which are spread in two directions according to the polarization state of these light fluxes, and an astigmatism means for producing astigmatism in these light fluxes. Which is a photo-detecting element for receiving 0th-order light of the light flux that has passed through the diffraction grating, corresponding to the two light fluxes divided by the composite optical element.
, A third light receiving portion for receiving at least one of the two light beams obtained by dividing the + 1st-order light of the light beam that has passed through the diffraction grating by the composite optical element, and the − light beam that has passed through the diffraction grating. A fourth light receiving portion for receiving at least one of the two light beams in which the primary light is split by the composite optical element, wherein the first and second light receiving portions have a mutual light detection output. The difference signal is used as a read-out signal of the information signal recorded on the recording track, and the third and fourth light receiving sections use the difference signal between the photodetection outputs as a tracking error signal, and
The difference signal between the sum signals of the light detection outputs of the two light-receiving portions that are divided into four light-receiving portions that are radially arranged at equal angular intervals and that face each other through the center of the light-receiving portion. Is a photodetector element that is used as a focus error signal. 4. At least one of the first and second light receiving portions has a sum signal of light detection outputs of light receiving portions located on one side of a dividing line in a direction corresponding to a tangential direction of a recording track and the dividing line. 3. The push-pull signal is a difference signal from the sum signal of the photodetection outputs of the light receiving portions located on the other side.
The light detection element described. 5. At least one of the first and second light receiving portions is divided into two by a dividing line in a direction corresponding to the tangential direction of the recording track, and light detection of a light receiving portion located on one side of the dividing line is performed. 4. The photodetector element according to claim 3, wherein a difference signal between the output and the photodetection output of the light receiving portion located on the other side of the division line is a push-pull signal. 6. A magneto-optical recording medium which is emitted from a light source and is divided by a diffraction grating into at least three rays of 0th order light and ± 1st order light and is condensed on a recording track of a magneto-optical recording medium by a converging means. The reflected light beams are divided into two light beams which are diverged in two directions according to the polarization states of the light beams, and an astigmatism means for producing astigmatism in these light beams. It is assumed that the light is received by a detection element, and the photodetection element is a first and a second light receiving section for correspondingly receiving two light fluxes obtained by dividing the 0th order light of the light flux passing through the diffraction grating by the composite optical element. A third light receiving portion for receiving one of the two light beams divided by the composite optical element from the + 1st-order light of the light beam that has passed through the diffraction grating, and the -1st-order light of the light beam that has passed through the diffraction grating. 2 split by compound optics A fourth light receiving portion for receiving one of the light fluxes of the book,
A fifth light-receiving portion for receiving the other of the two light beams split by the composite optical element from the + 1st-order light of the light beam that has passed through the diffraction grating, and the -1st-order light of the light beam that has passed through the diffraction grating. A sixth light receiving portion for receiving the other of the two light beams split by the element, the third and sixth light receiving portions, or the fourth and fifth light receiving portions.
Any one of the light receiving parts is divided into four light receiving parts in a state where each light receiving part is radially arranged at equal angular intervals, and each of them is opposed to each other through the center part of the light receiving part. A focus error signal detecting method in which a difference signal between the sum signals of the light detection outputs of the two sets of light receiving portions is obtained and these difference signals are added to each other to form a focus error signal. 7. A magneto-optical recording medium which is emitted from a light source and is divided by a diffraction grating into at least three light beams of 0th order light and ± 1st order light and focused on recording tracks of a magneto-optical recording medium by a focusing means. The reflected light beams are divided into two light beams which are diverged in two directions according to the polarization states of the light beams, and an astigmatism means for producing astigmatism in these light beams. It is assumed that the light is received by a detection element, and the photodetection element is a first and a second light receiving section for correspondingly receiving two light fluxes obtained by dividing the 0th order light of the light flux passing through the diffraction grating by the composite optical element. A third light receiving portion for receiving one of the two light beams divided by the composite optical element from the + 1st-order light of the light beam that has passed through the diffraction grating, and the -1st-order light of the light beam that has passed through the diffraction grating. 2 split by compound optics A fourth light receiving portion for receiving one of the light fluxes of the book,
A fifth light-receiving portion for receiving the other of the two light beams split by the composite optical element from the + 1st-order light of the light beam that has passed through the diffraction grating, and the -1st-order light of the light beam that has passed through the diffraction grating. A sixth light receiving portion for receiving the other of the two light beams divided by the element, wherein the third to sixth light receiving portions are arranged radially at equal angular intervals. It is assumed that it is divided into four light receiving portions in the state, and the difference signal between the sum signals of the light detection outputs of the two light receiving portions facing each other through the central portion of the light receiving portion is obtained, and these four difference signals are obtained. A focus error signal detection method in which all are added as a focus error signal.