JP3461541B2 - Optical pickup device - Google Patents

Description

BACKGROUND OF THE INVENTION [0001] Field of the Invention The present invention is applied to a magneto-optical recording and reproducing apparatus or the like, a light detection element for reading writing or information on a recording medium such as a magneto-optical disk The present invention relates to an optical pickup device used. In order to write or read information on or from a recording medium by an optical pickup device, it is necessary to accurately position an objective lens in both a focus direction and a track direction. Further, when the recording medium is a magneto-optical disk, since the Kerr rotation of a slight polarization plane is read as a magneto-optical signal, it is weaker than a pit signal of a compact disk. On the other hand, with the recent miniaturization of magneto-optical disks, there has been a demand for miniaturization of optical pickup devices.
For this reason, the information recorded on the magneto-optical disk (magneto-optical signal) from the light reflected from the magneto-optical disk by using a diffraction grating and a three-beam Wollaston prism (3-Beam Wollaston Prism), and the displacement in the focus direction ( There is known an optical pickup device in which a single photodetector can extract a focus error signal indicating a focus shift and a tracking error signal indicating a position shift in a track direction (for example, JP-A-4-157647). . According to this conventional optical pickup device, a recording layer of a magneto-optical disk is irradiated with a light beam that has been separated into three light beams of zero-order light and ± first-order light by a diffraction grating.
As shown, each reflected light beam R ₀ , R ₁ ,
R ₂ is separated into three beams by a three-beam Wollaston prism 1 and a total of nine reflected light beams R ₀ , R ₁ , R
₂ , R ₁₀ , R ₁₁ , R ₁₂ , R ₂₀ , R ₂₁ , R ₂₂
Five of the reflected light beams R ₀ , R ₁ , R ₂ , R ₁₀ ,
The R ₂₀ is detected by a single photodetector element (see FIG. 14) 2, and utilizing the detection result focus error signal, the generation of the tracking error signal and magneto-optical signal. Accordingly, as shown in FIG. 14, the conventional photodetector 2 has a zero-order light separated by a diffraction grating and ± 1
A plurality of light receiving surfaces 3 to 7 for respectively receiving reflected light beams R ₀ , R ₁ , R ₂ corresponding to the next light and reflected light beams R ₁₀ , R ₂₀ whose traveling directions are separated by the three-beam Wollaston prism 1 are provided. The reflected light beams R ₀ , R
_1, the direction of the light receiving surface for receiving the R ₂ reflected light beam R _10, R
The direction of the light receiving surface that receives ₂₀ is arranged vertically. A conventional optical pickup device often uses a cubic beam splitter and a cylindrical lens, and the beam separation direction by a diffraction grating and the separation direction by a three-beam Wollaston prism are arranged vertically. Accordingly, in the photodetector, the tracking error signal light receiving portion and the magneto-optical signal light receiving portion are arranged perpendicular to each other. However, a conventional optical pickup device using a cubic beam splitter and a cylindrical lens has been increased in size. In view of this, an optical pickup device which has been reduced in size by using a plate-shaped beam splitter or the like which also has a function of generating astigmatism (referred to as a focus error signal) has been proposed (Oplus E No. 163, page 93). , 9
4), no diffraction grating is used in this system. Also,
In a system using a diffraction grating and the plate-like beam splitter,
A conventional photodetector in which a tracking error signal light receiving portion and a magneto-optical signal light receiving portion are arranged perpendicular to each other is not suitable for this optical system, and cannot obtain a desired signal. Therefore, the present invention has been made in view of the above circumstances, and uses a plate-like beam splitter or the like having a function of generating astigmatism to determine the direction of separation by a diffraction grating and the direction of separation by a Wollaston prism. There is an object to provide an optical pickup device using the optimal light detection element to configure the optical system to become non-orthogonal. [0010] In order to achieve the above object, the present invention is characterized in that:
The optical pickup device includes a light beam generation source that generates a light beam, a diffraction grating that separates the light beam from the light beam generation source into at least three of 0-order light and ± 1st-order light,
An objective lens receiving each reflected light beam from the recording medium while irradiating each of the light beams separated by the diffraction grating onto a recording portion of the recording medium, and each reflected light beam received by the objective lens; A Wollaston prism whose separation direction is non-perpendicular to the separation direction of the diffraction grating, and a photodetector that receives at least nine reflected light beams from the Wollaston prism, A first light receiving surface for receiving a light beam corresponding to + 1st-order light by the (S + P) wave diffraction grating by the Wollaston prism and -1st-order light by the (S + P) wave diffraction grating by the Wollaston prism. A second light receiving surface for receiving a light beam and a zero-order light which is a central light beam among the three light beams by the diffraction grating are divided and received. A third light receiving surface composed of a plurality of divided light receiving surfaces and a pair of fourth light beams independently receiving light beams on both sides of the three light beams separated by the Wollaston prism for the zero-order light by the diffraction grating. And a direction connecting the centers of the first light receiving surface and the second light receiving surface and the directions of the pair of fourth light receiving surfaces are non-perpendicular to each other , and the first light receiving surface and the first light receiving surface are not perpendicular to each other. The second light receiving surface is in front
The extension direction of the dividing line of the plurality of divided light receiving surfaces of the third light receiving surface
And a lens driving means for adjusting the position of the objective lens. According to the first aspect, the direction connecting the centers of the first light receiving surface and the second light receiving surface and the direction of the pair of fourth light receiving surfaces are different from each other. Since it is a right angle, an optical pickup device optimal for an optical system in which the direction of separation by a diffraction grating and the direction of separation by a Wollaston prism are non-perpendicular using a plate-shaped beam splitter or the like having a function of generating astigmatism. Further, by taking the difference between the light detection signal from the first light receiving surface and the light detection signal from the second light receiving surface,
For example, a tracking error signal can be generated. Further, a focus error signal can be generated by taking the difference between the light detection signals from each of the divided light receiving surfaces of the third light receiving surface. Further, by taking the difference between the light detection signals from the pair of fourth light receiving surfaces, for example, a magneto-optical signal can be generated. Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a view showing an optical system in an embodiment of the optical pickup device of the present invention. The optical pickup device 10 of the present embodiment comprises
Move the objective lens 11 in the focus direction Z and the track direction X
A lens driving unit (lens driving means) 12 (see FIG. 5), which will be described later, that adjusts the position of the lens, and an optical system block in which a plurality of optical components and the like are built. As shown in FIG. 1, this optical system block irradiates a semiconductor laser (light beam generating source) 14 for generating a laser light beam B, and irradiates a laser light beam B generated from the semiconductor laser 14 into three light beams. The light beams B ₀ , B ₁ ,
The diffraction grating 15 split into B ₂ , and the irradiation light beams B ₀ , B ₁ , and B ₂ separated by the diffraction grating 15 are partially reflected to the magneto-optical disk (recording medium) D side, and The reflected light beam R from the side passes through a plate-type polarizing beam splitter 16 that partially passes, and the irradiation light beams B ₀ , B ₁ , and B reflected by the polarizing beam splitter 16.
₂ is condensed and irradiated onto a recording layer (recording portion) of the magneto-optical disk D, and receives an reflected light beam R (R ₀ , R ₁ , R ₂ ) from the magneto-optical disk D; Each of the reflected light beams R ₀ , R ₁ , and R ₂ received by the objective lens 11 and passed through the polarizing beam splitter 16 is converted into 3
And a total of nine reflected light beams R ′ (R ₀ , R ₁ ,
3-beam Wollaston prism (3-Beam Wollaston) for generating R ₂ , R ₁₀ , R ₁₁ , R ₁₂ , R ₂₀ , R ₂₁ , R ₂₂ )
Prism) 18 and this three-beam Wollaston prism 1
The light detecting element 23 for receiving the nine reflected light beams R 'from 8 is built in. The diffraction grating 15 is, as shown in FIG.
At least the irradiation light beam B0 of the _0th- order light and the irradiation light beam B1 of the + _1st- order light are coupled with each other so that the incident beam B is spread out in a fan shape around the optical axis of the beam B by the diffraction phenomenon.
It is intended to separate into three irradiation light beam B ₂ of the primary light. Of these three irradiation light beams B ₀ , B ₁ , B ₂ , the irradiation light beams B ₁ , B _{2 on} both sides are used for generating a so-called tracking error signal. The diffraction grating 15 irradiates the polarizing beam splitter 16 with the irradiation light beams B ₀ , B ₁ , and B _{2. For the} reasons described later, the directions of the irradiation light beams B ₁ and B ₂ correspond to the plane of FIG. With respect to the direction perpendicular to the optical axis in a plane perpendicular to the optical axis. The polarizing beam splitter 16 has a function of both a reflecting plate and an astigmatism generating element.
Thus, conventionally, a cubic beam splitter and a cylindrical lens or the like are used as an astigmatism generating element in order to separate the reflected light beam from the magneto-optical disk D to the photodetector element 23 side. Since the two elements of the beam splitter and the cylindrical lens can be omitted and only one element can be used, the size can be reduced. The three-beam Wollaston prism 18
As shown in FIG. 3, a pair of triangular prisms 18a and 18b each formed of a uniaxial crystal such as quartz, rutile or calcite and having a substantially right-angled triangular cross section are joined to each other by joining their inclined surfaces 18c into a rectangular parallelepiped shape. It is composed. Also,
The three-beam Wollaston prism 18 is configured such that the crystal axis directions of the triangular prisms 18a and 18b are respectively orthogonal to the optical axis of the reflected light beam R and intersect with each other at an angle of, for example, approximately 45 degrees. Is configured. This 3
The reflected light beams R ₀ , R ₁ , and R ₂ incident on the beam Wollaston prism 18 are irradiated with the irradiation light beams B ₀ , B ₁ , and B ₂ separated by a diffraction grating 15 at an angle of approximately 45 °. As shown in the figure, when the light is incident in a state of being separated in the oblique direction 19 and passes through the inclined surface 18c of the triangular prisms 18a and 18b, as shown in FIG. is refracted, the first beam _{R 10, R 11, R 12} , P -polarized light second beam R ₂₀ is a component, R _21, R _22, and components which each of these components are synthesized as S-polarized light component ( S + P) and split into the third beams R ₀ , R ₁ , and R ₂ ,
4 to 28 are incident on a parallelogram. As shown in FIG. 4, the light detecting element 23 is a reflected light beam corresponding to the + 1st-order light, and three reflected light beams R ₁ and R whose traveling directions are separated by the Wollaston prism 18. ₁₁ and R ₂₁ , the reflected light beam R ₁
And three reflected light beams R ₂ , R ₁₂ , R ₁₂ , which are reflected light beams corresponding to the −1st order light and whose traveling directions are separated by the Wollaston prism 18.
Second light receiving surface for receiving the reflected light beam R ₂ of R ₂₂ 2
6, a reflected light beam corresponding to the 0 order light, the reflected light beam R ₀ of the center of the traveling direction 3 of the reflected light beam separated R _0, R _10, R ₂₀ by the Wollaston prism 18 A third light receiving surface 24 including a plurality of first to fourth divided light receiving surfaces 24a, 24b, 24c, and 24d that receive the divided light, and three reflected light beams R ₀ , R ₁₀ , and ₀ corresponding to the zero-order light. both sides of the reflected light beam R ₁₀ of R _20, R ₂₀
, A pair of fourth light receiving surfaces 27 that receive light independently of each other,
28. Further, each of the light receiving surfaces 24a to 24
Each of d, 25, 26, 27, and 28 outputs a light detection signal corresponding to the light intensity of the received reflected light beam to a signal processing unit 30 described later via a lead wire (not shown). Normally, the directions of the reflected light beams R ₁₀ and R _{20 and the} directions of the reflected light beams R ₁ and R ₂ are arranged vertically as shown in FIG. 14, but in this embodiment they are non-perpendicular. This is because the direction of beam deformation due to astigmatism in the flat plate beam splitter 16 is the direction shown by the dotted line in FIG.
This is because the direction of the dividing line becomes oblique, and the light receiving elements 25 and 26 for receiving the tracking error signal are usually arranged in the extending direction of the dividing line. FIG. 5 is a block diagram showing a control system of this embodiment. The optical pickup device 10 of this embodiment is
As shown in the drawing, the apparatus 10 has a control unit (control means) 29 for controlling each unit, the lens drive unit 12 is connected to the control unit 29, and the light receiving surfaces 24 to 28 are connected to a signal processing unit. 30. The signal processing section 30 generates a tracking error signal, a focus error signal and a magneto-optical signal based on the light detection signals transmitted from the respective light receiving surfaces 24 to 28, and converts the tracking error signal and the focus error signal. The signal is output to the control unit 29, and the magneto-optical signal is output to the output buffer 31. [0026] When generating a tracking error signal by the signal processor 30, the reflected light beam and the light detection signal by the first light receiving surface 25 is output that has received the R _1, the second receiving the reflected light beam R ₂ The tracking error signal is generated by taking the difference from the photodetection signal output from the light receiving surface 26 of FIG. When the focus error signal is generated, the value of the focus error signal is Fe and the value of the light detection signal from the first to fourth divided light receiving surfaces 24a to 24d is Ra, respectively, according to the astigmatism method. , Rb, Rc, Rd, it can be obtained by the following equation (1): Fe = (Ra + Rc)-(Rb + Rd) (1) As shown in FIG. 6, since the reflected light beams R ₀ , R ₁ , and R ₂ to the beam splitter 16 are converged light, the beam S ₂ below the optical axis is above the optical axis. receives a large refractive action than by the beam splitter 16 than the beam S _1. As a result, the focal point P is formed at a position displaced by y below the optical axis. When the beams S ₁ and S ₂ exit the beam splitter 16, they are parallel to the respective incident lights but are displaced, so that what should be condensed at the point Q is displaced x to the right of the point Q. Focus on the position. Further, since the influence of the refraction of the beam splitter 16 can be almost neglected in the change of the optical path as viewed from above the optical axis, the light flux after entering the beam splitter 16 is indicated by a one-dot chain line, and the condensing point is substantially at the point Q. Becomes Here, planes passing through the points P and Q and perpendicular to the lens optical axis are denoted by c and a, respectively, and a plane that bisects the plane a and the plane c perpendicularly is denoted by b. The spot (light image) on each of the planes a, b, and c is a circular segment on the plane b and orthogonal to each other on the planes a and c. Therefore, when the objective lens 11 moves away from the disk D (plane c), it becomes an ellipse flattened in the horizontal direction as shown in FIG. 8, and the value Fe of the focus error signal becomes
Takes a positive value. Also, if the objective lens 11 is a disc D
(Plane a), as shown in FIG. 9, the ellipse becomes a flattened ellipse, and the value of the focus error signal Fe
Takes a negative value. As described above, by calculating the above equation (1), it is possible to determine whether the focus is in focus, too close or too far, and further, as shown in FIG. The amount of defocus can also be recognized from the magnitude of the value Fe. When a magneto-optical signal is generated by the signal processing unit 30, the reflected light beams R ₀ , R ₁₀ and R ₂₀ separated from the zero-order light by the Wollaston prism 18 are reflected on both sides. A magneto-optical signal is generated by taking the difference between the two light detection signals output by the pair of fourth light receiving surfaces 27 and 28 that independently receive R ₁₀ and R ₂₀ , respectively. The lens driving section 12 includes a focusing coil and a tracking coil. Under the control of the control section 29, a current is supplied to these coils to generate a driving force on the coils, thereby moving the objective lens 11 in the focusing direction. The position is adjusted by following the Z and the track direction X. The control section 29 controls the lens driving section 12 based on the tracking error signal and the focus error signal output from the signal processing section 30 to control the position of the objective lens 21 in the focus direction and the track direction. Is what you do. Next, the operation of this embodiment will be described with reference to FIG. The laser light beam B generated from the semiconductor laser 14 is separated into _{first to} third irradiation light beams B ₀ , B ₁ , and B ₂ by the diffraction grating 15, and the optical axis direction is changed by the polarization beam splitter 16. It is changed and enters the objective lens 11. The objective lens 11 focuses and irradiates the incident irradiation light beams B ₀ , B ₁ , B ₂ onto the recording layer of the magneto-optical disk D. The recording layer of the magneto-optical disk D is
The so-called perpendicular magnetization is formed, and the magnetization direction is changed for each minute region in accordance with the written information signal. Then, the reflected light beams R of the irradiation light beams B ₀ , B ₁ , and B ₂ focused and irradiated on the recording layer are shown in FIG. 11 by the so-called Kerr effect according to the magnetization direction of the recording layer. Thus, the polarization direction is changed. That is, the polarization of the reflected light beam R from the region in which the magnetization direction of the recording layer is in the initial state (the region indicated by the upward arrow in the drawing), in other words, for example, the region where the recording information is “0”. The direction is the irradiation light beam B incident on the recording layer.
It is rotated by + θ _{k with} respect to the polarization directions of ₀ , B ₁ and B ₂ . Further, a region where the magnetization direction of the recording layer is inverted with respect to the initial state (a region indicated by a downward arrow in the drawing), in other words, the reflected light beam R from the region where the recording information is “1”.
Are polarized light beams B ₀ and B incident on the recording layer.
Rotated by −θ _{k with} respect to the polarization directions of ₁ and B ₂ . In this manner, the irradiation light beams B ₀ , B ₁ , and B ₂ incident on the recording layer of the magneto-optical disk D are reflected light beams whose polarization directions have been rotated according to the contents of the recording information of the recording layer. The light enters the objective lens 11 again as R ₀ , R ₁ , and R ₂ . The reflected light beams R ₀ , R ₁ , R ₂ re-entering the objective lens 11 pass through the polarization beam splitter 16 and enter the Wollaston prism 18. The Wollaston prism 18 separates each of the reflected light beams R ₀ , R ₁ , and R ₂ into three beams, and a total of nine reflected light beams R ′ (R ₀ , R ₁ , R ₂ , and R ₂₎ .
R ₁₀ , R ₁₁ , R ₁₂ , R ₂₀ , R ₂₁ , R ₂₂ ) are generated and incident on the photodetector 23. Each light receiving surface 24a to 24 of the light detecting element 23
d, 25, 26, 27, and 28 output a light detection signal corresponding to the light intensity of the received reflected light beam to the signal processing unit 30. The signal processing unit 30 generates a tracking error signal, a focus error signal, and a magneto-optical signal based on the light detection signal output from the light detection element 23, and outputs the generated signal to the control unit 29. The control unit 29 controls the lens drive unit 12 based on the tracking error signal and the focus error signal output from the signal processing unit 30 to adjust the position of the objective lens 11 in the focus direction Z and the track direction X. I do. The magneto-optical signal is used as reproduction information. The present invention is not limited to the above embodiment, but can be variously modified. For example, the recording medium targeted by the apparatus of the present embodiment is not limited to the magneto-optical disk for MO, but may be a magneto-optical disk for mini disk. Further, an optical system in which a beam splitter for separating a light beam incident on the objective lens from a light beam generation source and a reflected light beam from a recording medium passing through the objective lens and a three-beam Wollaston prism may be integrated. [0046] Also, the photodetector element 23, as shown in FIG. 12, the reflected light beam R _1, R _11, a first light receiving surface 25 for receiving the R ₂₁ ', the reflected light beam R _2, R _12, the first to fourth sub light receiving surface 24a through 24d where the second light-receiving surface 26 ', is received by dividing the reflected light beam R ₀ which receives the R ₂₂
And the reflected light beams R ₁₀ , R ₂₀
May be provided with a pair of fourth light receiving surfaces 27 'and 28' for receiving light. Thereby, the strength of the tracking error signal can be improved. According to the first aspect of the present invention, the direction connecting the centers of the first light receiving surface and the second light receiving surface and the direction of the pair of fourth light receiving surfaces are determined. Since it is non-perpendicular, using a plate-shaped beam splitter that also has the function of generating astigmatism, it is ideal for optical systems that are configured so that the separation direction by the diffraction grating and the separation direction by the Wollaston prism are non-perpendicular. Since a photodetector can be provided and a plate-shaped beam splitter can be used, the size of the optical pickup device can be reduced. [0048]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing an optical system in an embodiment of an optical pickup device according to the present invention. FIG. 2 is a principle diagram for explaining a diffraction phenomenon of a diffraction grating. FIG. 4 is a perspective view for explaining polarization by a ton prism. FIG. 4 is a diagram showing a configuration of a photodetector. FIG. 5 is a block diagram showing a control system of the present embodiment. FIG. FIG. 7 is a diagram showing a spot formed on a third light receiving surface of a photodetector. FIG. 8 is a diagram showing a spot formed on a third light receiving surface of a photodetector. FIG. 9 is a view showing a spot formed on a third light receiving surface of the photodetector. FIG. 10 is a graph showing a signal value Fe of a focus error signal and a defocus. FIG. 11 is a recording layer of a magneto-optical disk. FIG. 12 shows a light beam reflected from the object. FIG. 13 is a view showing another embodiment of the photodetector shown in FIG. 4. FIG. 13 is a perspective view for explaining polarization by a three-beam Wollaston prism. FIG. 14 is a view showing a conventional photodetector. Reference Signs List 10 optical pickup device 11 objective lens 12 lens driving unit (lens driving unit) 14 semiconductor laser (light beam generating source) 15 diffraction grating 18 three-beam Wollaston prism 23 photodetector 24 third light receiving surfaces 24a, 24b, 24c, 24d Divided light receiving surface 25 First light receiving surface 26 Second light receiving surface 27, 28 Fourth light receiving surface 29 Controller (control means) D Magneto-optical disk (recording medium) B, B ₀ , B ₁ , B ₂ irradiation The light beam _{R, R ', R 0,} R 1, R 2, R 10, R 11, R 12,
R _20, R _21, R ₂₂ reflected light beam

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B ^7/ 12-7/22 G11B 11/10-11/105

Claims (1)

(57) [Claims] 1. A light beam generating source for generating a light beam, and a light beam from the light beam generating source is separated into at least 0th order light and ± 1st order light. A diffraction grating, an objective lens for receiving each reflected light beam from the recording medium while irradiating each of the light beams separated by the diffraction grating to a recording portion of the recording medium, and receiving the reflected light beam from the recording medium. Each of the reflected light beams is separated into at least three light beams, the separation direction of which is not perpendicular to the separation direction of the diffraction grating, and a Wollaston prism; and a light detector for receiving at least nine reflected light beams from the Wollaston prism. +1 by a diffraction grating of (S + P) waves by the Wollaston prism
A first light receiving surface for receiving a light beam corresponding to the next light, a second light receiving surface for receiving a light beam corresponding to the -1st order light by a (S + P) wave diffraction grating by the Wollaston prism, and the diffraction grating And a third light receiving surface composed of a plurality of divided light receiving surfaces for splitting and receiving the zero-order light, which is the central light beam, of the three light beams, and the zero-order light by the diffraction grating is separated by the Wollaston prism. And a pair of fourth light receiving surfaces for independently receiving light beams on both sides of the three light beams, and a pair of directions connecting the centers of the first light receiving surface and the second light receiving surface. The fourth
Is non-perpendicular to the direction of the light receiving surface, and is in front of the first light receiving surface.
The second light receiving surface is a plurality of divided light receiving surfaces of the third light receiving surface.
An optical pickup device, comprising: a photodetector arranged in the extension direction of the dividing line; and lens driving means for adjusting the position of the objective lens.