JPH0668540A - Optical pickup device - Google Patents

Abstract

(57) [Summary] [Configuration] Luminous flux R ₁ emitted from the laser diode _1.
Is irradiated onto the magneto-optical disk through the polarizing oblique plate glass 2 and the objective lens 5. The reflected light flux R ₃ reflected by the magneto-optical disk is transmitted through the polarizing oblique plate glass 2 and is given astigmatism, and is split into the light fluxes R ₄ , R ₅ , and R ₆ by the 3-beam Wollaston prism 7. [Effect] A focus error signal is obtained from the central light beam R _4, and a push-pull signal that is a tracking error signal and / or an address signal is obtained from the light beams R ₅ and R ₆ on both sides.

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.

[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.

By the way, in an optical pickup device for reading out an information signal from a read-only optical disc on which an information signal is recorded by a concavo-convex pattern, an optical element that functions as both the beam splitter and the cylindrical lens is provided. A slanted plate glass is used which is arranged at an angle of about 45 ° with respect to the optical axis of the reflected light flux. The oblique plate glass is a parallel plate-shaped glass plate, and the one surface portion reflects the emitted light beam and transmits the reflected light beam to impart astigmatism to the reflected light beam. When the optical pickup device is configured using this oblique plate glass, the beam splitter and the cylindrical lens can be replaced with one optical element, so that the configuration of the optical pickup device is simplified.
It is possible to reduce the size and facilitate manufacturing.

When an optical pickup device for reading out an information signal from the magneto-optical recording medium as described above is constructed by using the oblique plate glass, one surface portion of the oblique plate glass which reflects the emitted light flux is reflected. First, it is necessary to deposit and form a polarizing film. This polarizing film is a film having different transmittance depending on the polarization direction of the light beam, and the P-polarized light beam and the S-polarized light beam with respect to the one surface portion have different transmittances on the one surface portion. In this optical pickup device, since the polarizing film is formed on the oblique plate glass, a slight change in the polarization direction due to the Kerr effect of the reflected light flux passing through the oblique plate glass is increased, which is a so-called enhancement effect. Obtainable.
If this enhancement effect cannot be obtained, it becomes extremely difficult to detect the change in the polarization direction of the reflected light flux.

However, when the polarizing film is formed on the oblique plate glass to obtain an enhancing effect,
The direction of astigmatism obtained by passing through this oblique plate glass and the direction of the gradient of the light intensity distribution for obtaining the push-pull signal will coincide. This is because the polarization direction of the irradiation light flux is set in a direction orthogonal to the recording track in order to improve the linear density of the information signal in the recording track in the recording track.
That is, in order to obtain the enhancement effect, the slanted plate glass is arranged so as to generate astigmatism in the direction along the recording track and in the direction orthogonal to the recording track.

When the direction of the astigmatism obtained by passing through the oblique plate glass and the direction of the gradient of the light intensity distribution for obtaining the push-pull signal coincide with each other, the photodetector is Becomes unable to obtain the focus error signal and the push-pull signal due to the four-divided light receiving portion located in the central portion. This is because the amount of the astigmatism and the amount of change in the light intensity distribution cannot be discriminated and detected.

Therefore, the optical pickup device as described above cannot be constructed by using the oblique glass plate on the assumption that the enhancement effect is obtained.

Therefore, the present invention has been proposed in view of the above situation, and a reflected light flux whose polarization direction is changed by a magneto-optical recording medium in accordance with an information signal recorded on the magneto-optical recording medium. Can be satisfactorily detected while obtaining an enhancement effect, and can be configured by using an oblique plate glass as an optical element that acts as a beam splitter while giving astigmatism to the reflected light flux. An object of the present invention is to provide an optical pickup device that can be simplified, miniaturized, and easily manufactured.

[0016]

In order to solve the above-mentioned problems and achieve the above-mentioned objects, the optical pickup device according to the present invention converges and irradiates a magneto-optical recording medium on which recording tracks are formed. An optical element that splits a reflected light beam, which is a light beam reflected by the magneto-optical recording medium, into three light beams that are spread in three directions in one plane according to the polarization state of the reflected light beam, and this optical element. And a photodetector having three light-receiving portions that respectively receive the three light beams divided by the above-mentioned, and the pair of light-receiving portions located on both sides of the photodetector output light from each other. Is used as a read signal of the information signal recorded on the recording track, and each is divided into two light receiving portions, and the difference signal of the light detection output obtained from each light receiving portion forming one light receiving portion. Each is made is made with push-pull signal indicative of a positional deviation between the irradiation position and the recording track of the irradiation light beam.

According to the present invention, in the above-mentioned optical pickup device, the light receiving portion located at the central portion of the photodetector is divided into four light receiving portions radially arranged at equal angular intervals, In the photodetector, a pair of light receiving portions located on both sides are divided into two light receiving portions by a dividing line forming an angle of 45 ° with respect to a dividing line dividing the light receiving portion located in the central portion. It is a thing.

Further, according to the present invention, in the above optical pickup device, the four light receiving portions forming the light receiving portion located at the central portion of the photodetector have directions corresponding to the astigmatism directions of the reflected light flux. And a pair of light receiving portions located on both sides of the photodetector are divided in a direction corresponding to the direction of the recording track on the magneto-optical recording medium.

[0019]

In the optical pickup device according to the present invention, the reflected light beam which is the light beam reflected by the magneto-optical recording medium is spread in three directions within one plane divided by the optical element according to the polarization state of the reflected light beam. Out of the three light receiving parts of the photodetector that receive the three light beams corresponding to
The pair of light receiving portions located on both sides have a difference signal of their photodetection outputs as a read signal of the information signal recorded on the recording track, and each of the light receiving portions is divided into two light receiving portions. Since the difference signals of the light detection outputs obtained from the respective light receiving portions forming the light receiving portion are respectively made push-pull signals, the light receiving portion located at the central portion can obtain the focus error signal and the like.

Further, in the above-mentioned optical pickup device, the light receiving portion located in the central portion of the photodetector is
The photodetector is divided into four light receiving portions radially arranged at equal angular intervals, and a pair of light receiving portions located on both sides of the photodetector are divided into dividing lines that divide the light receiving portion located in the central portion. When divided into two light receiving portions by a dividing line forming an angle of 45 °, the direction of astigmatism imparted to the reflected light beam by the oblique plate glass and the light intensity of the reflected light beam for obtaining the push-pull signal. The focus error signal and the push-pull signal can be independently detected even if the gradient directions of the distribution match.

Further, in the above optical pickup device, four light receiving portions forming a light receiving portion located at a central portion of the photodetector are arranged in a direction corresponding to a direction of astigmatism of the reflected light beam, When the pair of light receiving portions located on both sides of the photodetector are divided in the direction corresponding to the direction of the recording track on the magneto-optical recording medium, the focus error signal and the push-pull signal can be detected well. .

[0022]

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 is configured as an optical pickup device of a reproducing device for reproducing a so-called magneto-optical disk which is a magneto-optical recording medium. This optical pickup device
As shown in FIGS. 1 to 3, the reproduction is performed so as to oppose the magneto-optical disk 6 supported by the reproduction device, which has an optical block portion 10 made of a synthetic resin material or a metal material. It is arranged in the device.

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 (not shown) around 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 shown by an arrow T in FIG. As shown in FIGS. 1 to 3 and 5, a laser diode 1 serving as a light source, various optical elements 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, the optical block unit 10 includes an objective lens 5
Objective lens driving device 11 that supports the lens so that it can be moved.
Is installed. This objective lens driving device 11 is
When the objective lens 5 is supported by being opposed to the main surface portion of the magneto-optical disk 6 and a predetermined drive current is supplied, the objective lens 5 is moved in the optical axis direction of the objective lens 5, that is, the magneto-optical disc. A moving operation is performed in the direction of contact and separation with respect to the 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.

In this optical pickup device, the emitted light beam R ₁ emitted from the laser diode ₁ is
Irradiation is performed on one main surface portion of the oblique plate glass 2. The oblique plate glass 2 is a parallel plate glass, and is arranged with its main surface portion at an angle of 45 ° with respect to the optical axis of the emitted light flux R ₁ . The polarizing film 2a is formed on one main surface portion of the oblique plate glass 2.
Has been formed. The polarizing film 2a is a film having a different transmittance depending on the polarization direction of the incident light beam, and the transmittance of the P-polarized incident light beam and the S-polarized incident light beam with respect to the one main surface portion of the oblique plate glass 2 at the one main surface portion. Is different. In this optical pickup device, the polarizing film 2a has a transmittance Ts of the S-polarized incident light flux higher than the transmittance Tp of the P-polarized incident light flux.

The emitted light flux R incident on the polarizing film 2a
_As shown by the line P in FIG. 5, ₁ is linearly polarized in the direction of the P-polarized incident light beam with respect to the oblique plate glass 2.

The emitted light beam R ₁ is reflected by the polarizing film 2a and the optical path thereof is changed by 90 ° to become an irradiation light beam R ₂ . This irradiation light flux R ₂ is applied to the collimator lens 3
Is converted into a parallel light beam by the mirror 4, is reflected by the mirror 4, the optical path is changed, and is incident on the objective lens 5. This objective lens 5 focuses the incident irradiation light flux R ₂ on the signal recording layer of the magneto-optical disk 6 through the disk substrate.

The objective lens driving device 11 moves the objective lens 5 based on a focus error signal and a tracking error signal, which will be described later, so that the focal point of the irradiation light flux R ₂ is shown in FIG. As shown
It is always located on the recording track 12.
It should be noted that the focus error signal is the optical axis direction of the irradiation light flux R ₂ between the converging point and the surface of the signal recording layer,
That is, it is a signal indicating a distance in a direction substantially perpendicular to the surface of the signal recording layer. Further, the tracking error signal indicates the distance between the condensing point and the recording track 12 in the direction perpendicular to the optical axis of the irradiation light beam R ₂ and the recording track 12, that is, the radial direction of the disk substrate. It is a signal to show.

The cross-sectional shape of the irradiation light beam R ₂ focused on the recording track 12, that is, the recording track 1
The shape of the beam spot formed on 2 is the near field of the light beam R ₁ emitted from the laser diode 1.
It has an elliptical shape corresponding to the pattern. 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 irradiation light flux R ₂ 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.

[0033] Then, the reflected light beam R ₃ the irradiation beam R ₂ is a light beam reflected by the magneto-optical disc 6,
According to the information signal recorded on the recording track 12,
Due to the so-called Kerr effect, the polarization direction is rotated by a minute angle. The reflected light flux R ₃ is generated by the objective lens 5,
After passing through the mirror 4 and the collimator lens 3, it returns to the polarizing film 2 a on the oblique plate glass 2. Here, the reflected light flux R ₃ passes through the polarizing film 2 a and the oblique plate glass 2. At this time, the reflected light flux R ₃ is slightly swirled in the polarization direction due to the Kerr effect due to the so-called enhancing effect of the polarizing film 2a.

Reflected light beam R ₂ transmitted through the oblique plate glass ₂
Causes astigmatism due to the oblique plate glass 2.
The direction of this astigmatism, that is, the major axis direction when the cross section of the light flux becomes elliptical, is the tilt direction of the above-mentioned oblique plate glass 2,
Alternatively, it is a direction orthogonal to this inclination direction.

A reflected light beam R ₂ transmitted through the oblique plate glass ₂
Is incident on a three-beam Wollaston prism 7, which is an optical element that splits the incident light beam into three light beams that are spread in three directions in one plane according to the polarization state of the incident light beam. This 3 beam Wollaston prism 7
The prisms are formed by adhering the slant faces of a pair of triangular prisms 7a, 7b, each of which is formed of a uniaxial crystal material and formed into a right-angled isosceles triangular prism, into a cubic shape. The three-beam Wollaston prism 7, the respective triangular prisms 7a, a mutual bonding surface of 7b, the reflected light beam R ₃
Are arranged at an angle of 45 ° with respect to the optical axis.
Further, in the three-beam Wollaston prism 7, the inclination direction of the pasting surface is set to a direction rotated by 45 ° around the optical axis of the reflected light flux R ₃ with respect to the inclination direction of the oblique plate glass 2. There is. That is, as shown in FIG. 6, when the three-beam Wollaston prism 7 faces the direction opposite to the traveling direction of the reflected light flux R ₃ shown by the arrow B in FIG. 5, the diagonal direction of the lower surface of the square is shown. The polarization direction of the reflected light beam R ₃ indicated by the arrow P in FIG. 6 is arranged. The polarization direction of the reflected light flux R ₃ shown here is the polarization direction when the rotation of the polarization direction due to the Kerr effect does not occur.

The triangular prisms 7a and 7b forming the 3-beam Wollaston prism 7 are shown in FIG.
The crystal axis directions indicated by the median lines D ₁ and D ₂ are orthogonal to the optical axis of the reflected light flux R ₃ , and the crystal axis directions are at an angle of 45 °. The triangular prism 7a on the incident side of the reflected light flux R ₃ has the crystal axis direction indicated by the line D ₁ in FIG. 6 at 45 ° with respect to the polarization direction of the reflected light flux R ₃ indicated by the arrow P in FIG. Are arranged at an angle of. Further, the triangular prism 7b on the side from which the reflected light flux R ₃ is emitted has the crystal axis direction indicated by the line D ₂ in FIG. 6 at 90 ° with respect to the polarization direction of the reflected light flux R ₃ indicated by the arrow P in FIG. Are arranged at an angle of.

The three-beam Wollaston prism 7 thus arranged has the first to third split luminous fluxes R ₄ , which spread the reflected luminous flux R ₃ in three directions within one plane.
Divide into R ₅ and R ₆ . This is because the triangular prisms 7a and 7b forming the three-beam Wollaston prism 7 have anisotropy, so that S of the luminous flux incident on the three-beam Wollaston prism 7 with respect to the sticking surface is
This is because the polarization direction of the polarization plane differs between the polarization component and the P polarization component. On this sticking surface, the S-polarized component and the P-polarized component are each split into two light beams, and one of these split light beams overlaps with each other to form three light beams. . As shown in FIG. 7, the spreading directions of the divided luminous fluxes R ₄ , R ₅ , and R ₆ are the tilting directions of the adhering surface of the three-beam Wollaston prism 7.

Then, each of the divided luminous fluxes R ₄ , R ₅ , and R ₆
Is received by the photodetector 9 through the condenser lens 8. The condensing lens 8 is a concave lens, and is arranged so as to be slightly inclined with respect to the optical axis of the reflected light flux R _{3 in} the direction opposite to the inclination direction of the oblique plate glass 2.

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 the photodetection output to the outside. . As shown in FIG. 7, the photodetector 9 has first to third light receiving portions 14, 15 and 16 for respectively receiving the divided luminous fluxes R ₄ , R ₅ and R ₆ respectively. There is. The first light receiving portion 14 is formed in a substantially square shape, for receiving the first split beam R ₄ is a central light beam of said each of the divided light fluxes R _4, R _5, R _6. The second and third light receiving portions 15 and 16 are each formed in a substantially square shape, and are the second and the second luminous fluxes on both sides of the divided luminous fluxes R ₄ , R ₅ , and R ₆ . It is formed on both sides of the first light receiving portion 14 so as to receive the three divided light fluxes R ₅ and R ₆ in pairs.

In the photodetector 9, the difference signal between the photodetection outputs of the second and third light receiving portions 15 and 16 is used as a read signal of the information signal recorded in the recording track 12. . That is, the light intensities of the second and third split luminous fluxes R ₅ and R ₆ change to opposite polarities in accordance with the angle and direction of rotation of the polarization direction of the reflected luminous flux R ₃ due to the Kerr effect. Is.

Then, the second and third light receiving portions 15,
16 is divided into two light receiving portions.
The second light receiving portion 15 includes the first and second light receiving portions 13
It is divided into E and 13F. The third light receiving section 16
Are divided into third and fourth light receiving portions 13G and 13H. The second and third light receiving portions 15 and 16 are divided in a direction corresponding to the direction of the recording track 12 of the magneto-optical disk 6 shown by an arrow V in FIG.

In this optical pickup device, the reflected light beam R ₃ is perpendicular to the optical axis of the irradiation light beam R ₂ from the recording track 12 to the converging point of the irradiation light beam R ₂ and the recording track 12. Direction and distance,
That is, the light intensity distribution changes according to the change in the tracking error amount. Therefore, the second light receiving unit 15
The difference signal of the photodetection outputs obtained from the first and second light receiving portions 13E and 13F forming the above becomes a push-pull signal indicating the positional deviation between the irradiation position of the irradiation light beam R ₂ and the recording track 12. Further, the difference signal of the photodetection outputs obtained from the third and fourth light receiving portions 13G and 13H forming the third light receiving portion 16 is also deviated between the irradiation position of the irradiation light beam R ₂ and the recording track 12. Will be a push-pull signal.

That is, the light detection output from the first light receiving portion 13E is E, the light detection output from the second light receiving portion 13F is F, and the light detection output from the third light receiving portion 13G is G. When the light detection output from the fourth light receiving portion 13H is H, the push-pull signal is obtained by (EF) and (GH).

In the photodetector 9, the light receiving portions forming the respective light receiving portions 14, 15 and 16 are constructed so as to be able to independently output a photodetection signal via the plurality of terminals 9b. ing.

The push-pull signal can be used not only as the tracking error signal, but when the recording track 12 is formed with so-called wobbling, it also corresponds to the wobbling cycle. , And becomes a signal for detecting an address on the recording track 12. When the push-pull signal is used as the tracking error signal, the push-pull signals obtained from the second and third light receiving units 15 and 16 are added and used. That is, the tracking error signal is obtained by (EF) + (GH).

Then, the first light receiving portion 14 for receiving the first divided light flux R ₄ is divided into _four light receiving portions radially arranged at equal angular intervals. That is,
As shown in FIG. 7, the first light receiving portion 14 is divided into fifth to eighth light receiving portions 13A, 13B, 13C, 13D. These fifth to eighth light receiving portions 13A, 1
3B, 13C, and 13D face each other in the direction of the astigmatism in which the reflected light flux R ₃ is generated by the oblique plate glass 2.
It is arranged so as to have a pair of light receiving portions.

That is, in the photodetector 9, the second and third light receiving portions 15 and 16 are divided at an angle of 45 ° with respect to the dividing line dividing the first light receiving portion 14. Lines indicate the first and second light receiving portions 13 respectively.
It is divided into E, 13F, and third and fourth light receiving portions 13G, 13H.

In this optical pickup device, the direction and amount of the astigmatism of the reflected light beam R ₃ is determined by the light of the irradiation light beam R ₂ from the surface of the signal recording layer to the condensing point of the irradiation light beam R ₂ . It changes according to the change in the direction and distance with respect to the axial direction, that is, 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.

That is, the light detection output from the fifth light receiving portion 13A is A, the light detection output from the sixth light receiving portion 13B is B, and the light detection output from the seventh light receiving portion 13C is C, When the light detection output from the eighth light receiving portion 13D is D, the focus error signal is (A +
C)-(B + D).

The optical pickup device can also read the information signal from the read-only optical disc in which the information signal is recorded by the concavo-convex pattern. In this case, the read signal is the sum signal of the photodetection outputs from the second and third light receiving portions, that is, (E +
F) + (G + H).

The optical pickup device according to the present invention is not limited to the above-mentioned embodiment, and as shown in FIG. 8, the exiting luminous flux R ₁ is applied to the polarizing film 2a on the oblique plate glass 2. However, the light may be incident in the S-polarized state. In this case, the polarization film 2a has a transmittance Tp of the P-polarized incident light flux higher than the transmittance Ts of the S-polarized incident light flux. This optical pickup device is arranged on the recording track 12 in the same manner as the above-mentioned optical pickup device by being arranged so as to be rotated by 90 ° around the optical axis of the objective lens 5 with the above-mentioned optical pickup device as a reference. Form a beam spot.

Further, the optical pickup device according to the present invention may be constructed by using a grating (diffraction grating) for obtaining a tracking error signal. This diffraction grating is arranged between the laser diode 1 and the oblique glass plate 2 and divides the emitted light beam R ₁ into three light beams which are spread in three directions within one plane. The diverging directions of these light fluxes are substantially corresponding to the direction of the recording track 12. Then, in this case, as shown in FIG. 9, in the photodetector 9, the fourth and fifth light receiving portions 17 and 18 are formed in addition to the respective light receiving portions 14, 15 and 16. These fourth and fifth light receiving units 17 and 18
Are formed in a substantially square shape, and are formed on both sides of the first light receiving portion 14 at positions arranged in a direction corresponding to the direction of the recording track 12 shown by an arrow V in FIG. ing. These fourth and fifth light receiving parts 17, 1
Reference numeral 8 denotes a light flux of which the emitted light flux R ₁ is divided into three light fluxes by the diffraction grating and light fluxes on both sides of the three light fluxes are reflected by the magneto-optical disk 6 and reach the photodetector 9. And the fifth divided luminous fluxes R ₇ and R ₈ are received correspondingly. In this optical pickup device, the tracking error signal is obtained by (I−J), where I is the light detection output of the fourth light receiving unit 17 and J is the light detection output of the fifth light receiving unit 18. To be

Further, the optical pickup device according to the present invention may be constructed by using a so-called finite system objective lens. In this case, this optical pickup device is constructed by eliminating the collimator lens 3. That is,
The objective lens has been irradiated light beam R ₂ reflected by the main surface portion of the oblique flat glass 2 is incident in the state of the diffused light flux, the irradiation light beam R ₂ is converged onto the magneto-optical disc 6.

[0054]

As described above, in the optical pickup device according to the present invention, the reflected light beam which is the light beam reflected by the magneto-optical recording medium is divided by the optical element according to the polarization state of the reflected light beam. 3 of the photodetectors that receive the corresponding three light beams scattered in three directions in the plane
Of the light receiving parts, the pair of light receiving parts located on both sides are
The difference signal of the photodetection outputs from each other is used as a read signal of the information signal recorded on the recording track, and each light is divided into two light receiving portions, and light obtained from each light receiving portion forming one light receiving portion. The difference signals of the detection outputs are made push-pull signals.

Therefore, the focus error signal or the like can be obtained based on the photodetection output from the light receiving portion located in the central portion for receiving the central luminous flux of the three luminous fluxes.

In the above optical pickup device, the light receiving portion located in the central portion of the photodetector is divided into four light receiving portions radially arranged at equal angular intervals. When the pair of light-receiving portions located on both sides are divided into two light-receiving portions by a dividing line that forms an angle of 45 ° with respect to the dividing line that divides the light-receiving portion located in the central portion, the optical axis of the reflected light flux is obtained. Astigmatism is imparted to the reflected light flux by using an oblique plate glass which is a parallel flat glass plate arranged to be inclined with respect to the above, and further,
By forming a polarizing film on one surface of the oblique plate glass so as to obtain a so-called enhancement effect, the direction of the astigmatism and the gradient of the light intensity distribution in the reflected light beam for obtaining the push-pull signal. Even if the directions match, the focus error signal and the push-pull signal can be detected independently.

Further, in the above optical pickup device, four light receiving portions forming a light receiving portion located in the central portion of the photodetector are arranged in a direction corresponding to the direction of astigmatism of the reflected light beam, By dividing the pair of light receiving portions located on both sides of the photodetector in the direction corresponding to the direction of the recording track on the magneto-optical recording medium,
The focus error signal and the push-pull signal can be detected well.

That is, according to the present invention, the reflected light flux whose polarization direction is changed by the magneto-optical recording medium in accordance with the information signal recorded on the magneto-optical recording medium can be favorably detected while enhancing the effect. In addition, since it is possible to configure the optical element that acts as a beam splitter while providing astigmatism to the reflected light flux by using the oblique plate glass, it is possible to simplify the configuration, reduce the size, and facilitate the manufacturing. An optical pickup device capable of being provided 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 an enlarged side view of an essential part showing the configuration of the optical pickup device.

FIG. 4 is an enlarged plan view showing the shape of a beam spot formed on a magneto-optical disk 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 the configuration of a light beam splitting element that constitutes the optical pickup device.

FIG. 7 is an enlarged plan view showing a configuration of a photodetector that constitutes the optical pickup device.

FIG. 8 is a plan view showing another example of the arrangement of the optical elements forming the optical pickup device.

FIG. 9 is an enlarged plan view showing another example of the configuration of the photodetector that constitutes the optical pickup device.

[Explanation of symbols]

Laser diode 6 Magneto-optical disk 7-beam Wollaston prism 9: Photodetector 12: Recording track 13A: Fifth light receiving portion 13B:・ ・ ・ ・ ・ ・ ・ ・ Sixth light receiving portion 13C ・ ・ ・ ・ ・ ・ ・ ・ Seventh light receiving portion 13D ・ ・ ・ ・ ・ ・ ・ ・ Eighth light receiving portion 13E ・ ・ ・ ・・ ・ ・ First light receiving portion 13F ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Second light receiving portion 13G ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Third light receiving portion 13H ・ ・ ・ ・ ・・ ・ ・ ・ Fourth light receiving portion 14 ・ ・ ・ ・ ・ ・ ・ ・ ・ First light receiving portion 15 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Second light receiving portion 16 ・ ・ ・ ・..... Third light receiving section R ₂・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Illuminated light flux R ₃・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Reflected light flux R ₄・ ・ ・ ・ ・ ・ ・ ・ ・ ・ First split light flux R ₅・ ・ ・ ・・ ・ ・ ・ ・ Second split luminous flux R ₆・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Third split luminous flux

Claims (3)

[Claims] 1. A reflected light beam, which is a light beam reflected by the magneto-optical recording medium and condensed and applied to a magneto-optical recording medium on which a recording track is formed, according to a polarization state of the reflected light beam. An optical element that splits into three light beams that are scattered in three directions in one plane, and a photodetector that has three light receiving portions that respectively receive the three light beams split by the optical element. In the photodetector, a pair of light receiving portions located on both sides of the photodetector are provided with a difference signal of their photodetection outputs as a read signal of the information signal recorded on the recording track, and each of the two light receiving portions has two signals. Divided into light receiving portions, the difference signals of the photodetection outputs obtained from the respective light receiving portions forming one light receiving portion are formed as push-pull signals indicating the positional deviation between the irradiation position of the irradiation light beam and the recording track. Optical pickup apparatus comprising. 2. A photodetector located in the center of the photodetector is divided into four photodetector portions radially arranged at equal angular intervals, and a pair of photodetectors located on both sides of the photodetector. 2. The optical pickup device according to claim 1, wherein the light receiving portion is divided into two light receiving portions by a dividing line that forms an angle of 45 ° with respect to a dividing line that divides the light receiving portion located in the central portion. 3. The four light receiving portions forming the light receiving portion located at the central portion of the photodetector are arranged in a direction corresponding to the direction of the astigmatism of the reflected light beam, and both sides of the photodetector are arranged. 3. The optical pickup device according to claim 2, wherein the pair of light-receiving portions located at is divided in a direction corresponding to the direction of the recording track on the magneto-optical recording medium.