JPH0684226A - Optical pickup device - Google Patents

Abstract

PURPOSE:To simplify and miniaturize a device by attaching a dielectric multilayered film to the incidental face of a light beam reflected by the recording medium of a first prism constituting a photodetector, and forming a beam splitter with the multilayered film. CONSTITUTION:Three light beams L1, L2 and L3 provided by an optical element 4 are made incident through a condenser lens 7, convex lens 8 and cylindrical lens 9 to a photodetection unit 10. Namely, the element 4 is functioned as the beam splitter for splitting a laser beam Li made incident from a light beam generating source 1 through an objective lens 5 to a magneto-optical disk 6 and a reflected laser beam Li returned from the disk 6 through the lens 5 with a dielectric multilayered film 43 formed on the incidental face part of a first prism 41. At the same time, the element is functioned as the photodetector for splitting and emitting the beam Li into the beam L1 of a P deflected component, the beam L2 of an S deflected component and beam L3 of the synthetic component of P and S deflected components with first and second prisms 41 and 42.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention makes a light beam incident on a recording medium through an objective lens and guides a reflected light beam from the recording medium to a photodetection section, and the photodetection section records information recorded on the recording medium. The present invention relates to an optical pickup device that obtains a read output of the.

[0002]

2. Description of the Related Art Conventionally, writing of information using a light beam,
As a so-called writable optical disc that can be erased and read, a perpendicular magnetic film that forms a recording layer is provided on the surface of a disk-shaped substrate, and the perpendicular magnetic film is further protected by a protective layer. Magneto-optical disks having a covered structure are known.

To write information on this type of magneto-optical disk, for example, a predetermined external magnetic field is applied to the perpendicularly magnetized film at each position of a large number of concentric circular or spiral recording tracks surrounding the central portion thereof. In this state, the recording track is scanned with a laser light beam modulated according to information to form a magnetization direction reversal region of a predetermined pattern. Note that pits for tracking / servo control are arranged in a predetermined pattern on each recording track.

Further, when reading information from a magneto-optical disk, a recording track is scanned with a laser light beam having a power smaller than that at the time of writing information, and a reflected laser light beam reflected by a perpendicularly magnetized film on the recording track is detected by a photodetector. And a read error signal, a tracking error signal, a focus error signal, or the like corresponding to the information written in the magneto-optical disk, based on the detection output of the photodetector. . The reflected laser light beam from the perpendicularly magnetized film of this magneto-optical disk causes the rotation of the polarization plane according to the magnetization direction reversal pattern in the vertically magnetized film corresponding to the written information due to the Kerr effect. . Then, for example, the orthogonal polarization component of the reflected laser light beam, that is, the P polarization component and S
The rotation of the polarization plane is detected by individually detecting and comparing the polarized components, and a read signal is formed based on the comparison output. Further, a change in the reflected laser light beam due to the pits arranged for the tracking / servo control is detected, and a tracking error signal is formed based on the detected output.
Further, a focus error signal is formed based on the position and spot shape of the reflected laser light beam on the photodetector.

As an optical pickup device for recording / reproducing information on / from this magneto-optical disk,
Various configurations have been proposed, but a typical configuration is that a reflected laser light beam is distributed by a beam splitter to a servo read optical system for servo and a read optical system for magneto-optical information. In the configuration, it is necessary to separately provide a photodetector for the reading optical system for servo and the reading optical system for magneto-optical information, which requires a lot of man-hours for alignment, and also a large number of optical parts and adjustment points. There is a problem that it is difficult to downsize the optical pickup device.

Therefore, in order to solve the above-mentioned problems, the applicant of the present invention uses a light beam from a light beam generation source through an objective lens as disclosed in JP-A-63-127436. An optical pickup device that guides the reflected light beam from the recording medium to an analyzer through a beam splitter and separates the reflected light beam into three light beams by the analyzer. I am proposing to.

This optical pickup device is constructed as shown in FIG. 6, and includes a light beam generating source 6
The laser light beam from No. 1 is incident on the beam splitter 63 as parallel light via the collimator lens 62, and is incident from the beam splitter 63 on the magneto-optical disk 65 in a focused state via the objective lens 64. The reflected laser light beam from the magneto-optical disk 65 is incident on the beam splitter 63 via the objective lens 64 and its P
The polarization component from the beam splitter 63 to the phase compensator 6
It is incident on the analyzer 67 via 6.

The analyzer 67 is constructed by laminating a first prism 68 and a second prism 69, which are respectively made of quartz, and the incident reflected laser light beam is the first light of the P polarization component. a beam L _1, a second light beam L ₂ of the S-polarized light component, three light beams L ₁ of the third light beam L ₃ of synthetic components of the P-polarized component and S-polarized light component,
It is designed to be separated into L ₂ and L ₃ .

The analyzer 67 is a beam splitter 63.
The reflected light beam from is incident on the first prism 68 and reaches the second prism 69, and the optical axis of the first prism 68 is substantially orthogonal to the optical axis of the incident reflected light beam. It is in-plane and inclined by a predetermined angle with respect to the polarization plane of the incident reflected light beam, and the optical axis of the second prism 69 coincides with the optical axis of the incident reflected light beam. It lies in a plane substantially orthogonal to each other and forms a predetermined angle with the optical axis of the first prism 68.

The three light beams L ₁ , L ₂ and L ₃ obtained by the analyzer 67 are shared by the common condenser lens 70.
The light is incident on the light detection unit 72 via. The third light beam L ₃ which is a composite component of the P-polarized component and the S-polarized component is further incident on the photodetection unit 72 via the cylindrical lens 71.

The photodetection unit 72 includes an analyzer 67.
Obtained three light beams L₁, L ₂ , L₃ Individually
It is composed of a light detection element that emits light, and
Dome L₁, L₂ , L₃ Signal processing of each detection output signal for
It is supplied to the processing unit 73.

In the signal processing unit 73, the detection output signal of the _first light beam L _{1 and} the detection output signal of the second light beam L ₂ , that is, the P-polarized component and the S-polarized component of the reflected laser light beam are mutually exchanged. Then, the read information signal S _i is formed based on the comparison output. In addition, the signal processing unit 73
, The tracking error signal S _t and the focus error signal S _f are detected from the detection output signal of the third light beam L _3.
To form.

[0013]

By the way, in the optical pickup device previously proposed by the applicant of the present application, by using an analyzer for separating the reflected light beam from the magneto-optical disk into three light beams, the conventional optical pickup device has been proposed. Although it has been possible to make the size smaller than that of the above, there is a great demand for size reduction in the magneto-optical disk recording / reproducing device, and a device smaller than this optical pickup device is required.

In view of the above-mentioned conventional circumstances, the present invention has improved the optical pickup device previously proposed by the applicant of the present invention to further downsize the optical pickup having a novel structure. The purpose is to provide a device.

[0015]

In order to achieve the above-mentioned object, an optical pickup device according to the present invention makes a light beam generation source and a light beam from the light beam generation source incident on a recording medium in a focused state. And an objective lens that receives the reflected light beam from the recording medium, a beam splitter that separates the light beam incident on the objective lens from the light beam generation source and the reflected light beam that has passed through the objective lens, and a quartz crystal, respectively. The first prism and the second prism thus formed are bonded to each other, and the reflected light beam from the beam splitter is arranged at a position where the light beam is incident from the first prism and reaches the second prism. ,
The optical axis of the first prism is in a plane substantially orthogonal to the optical axis of the incident reflected light beam, and is inclined by a predetermined angle with respect to the polarization plane of the incident reflected light beam. And the optical axis of the second prism is in a plane substantially orthogonal to the optical axis of the incident reflected light beam, and forms a predetermined angle with the optical axis of the first prism. Accordingly, an analyzer for emitting at least three light beams based on the incident reflected light beam, and a plurality of photodetector elements for individually detecting the three light beams emitted from the analyzer are incorporated. And a photodetection unit, the dielectric multilayer film is deposited on the incident surface of the light beam reflected by the recording medium of the first prism that constitutes the analyzer, and the dielectric multilayer film is formed. On the membrane Forming the beam splitter.

[0016]

In the optical pickup device according to the present invention, the first
At least 3 based on the light beam incident on the prism of
The dielectric multi-layered film attached to the incident surface of the first prism of the analyzer configured to emit the light beam of the book through the second prism records the light beam from the light beam generation source. A beam splitter that makes the light incident on the medium in a converged state and separates the light beam incident from the light beam generation source into the objective lens that receives the reflected light beam from the recording medium and the reflected light beam that passes through the objective lens from the recording medium Work as.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific embodiment of the optical pickup device according to the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment of an optical pickup device according to the present invention. The optical pickup device shown in FIG. 1 includes a light beam generating source 1 using a semiconductor laser and a diffraction grating plate 2. The laser light beam emitted via the collimator lens 3 enters the optical element 4 having the function of the beam splitter and the function of the analyzer as parallel light.

In the optical element 4, for example, as shown in FIG. 2, a first prism 41 and a second prism 42 each made of quartz are bonded together, and the incident surface of the first prism 41 is bonded. A dielectric multilayer film 43 is deposited on the portion.

Here, the first prism 41 and the second prism 42 are attached to each other with their surfaces inclined by a predetermined angle θ. Further, the optical axis A ₁ of the first prism 41 and the optical axis A ₂ of the second prism 42, is inclined a predetermined angle φ with the incident polarization plane and the same plane. Further, the second prism 42
The optical axis A _{2 of} is orthogonal or parallel to the plane of polarization of the incident light.

The optical element 4 has the laser light beam L incident on the dielectric multilayer film 43 through the collimator lens 3.
_{The i} is reflected at a ratio of the reflectance R _P for the P-polarized component and the reflectance R _S for the S-polarized component of the dielectric multilayer film 43, and is incident on the magneto-optical disk 6 in a focused state via the objective lens 5.

Reflection from the magneto-optical disk 6
Laser light beam L_jIs an optical element through the objective lens 5.
It is again incident on the dielectric multilayer film 43 of No. 4. In addition, light bee
From the light source 1 to the dielectric multilayer film 43 of the optical element 4.
Laser light beam L_iIs a part of the dielectric multilayer film 4
3 and this transmitted light beam L _kIs a photo detector
20 is incident on the photodetector 20.
Is detected by the so-called APC of the light beam generation source 1.
Output control.

The reflected laser light beam L _j incident through the objective lens 5 has the transmittance T _P for the P-polarized component of the dielectric multilayer film 43 and the transmittance T _S for the S-polarized component in the dielectric substance. The light passes through the multilayer film 43 and enters the first prism 41 that constitutes the optical element 4.

The reflected laser light beam L _j incident on the first prism 41 is the first component of the optical element 4.
And due to the difference in the refractive index between the ordinary ray component and the extraordinary ray component of the second prisms 41, 42, the first light beam L ₁ of the P polarization component, the second light beam L ₂ of the S polarization component, P The third light beam L ₃ of the combined component of the polarized component and the S-polarized component is separated into _three light beams L ₁ , L ₂ and L ₃ and emitted from the second prism 42.

The three light beams L ₁ , L ₂ and L ₃ obtained by the optical element 4 are collected by the condenser lens 7 and the concave lens 8.
And the light detection unit 1 via the cylindrical lens 9.
It is incident on 0. That is, the optical element 4 includes the dielectric multilayer film 43 formed on the incident surface of the first prism 41.
Separates the laser light beam L _i which is incident on the magneto-optical disk 6 from the light beam generation source 1 through the objective lens 5 and the reflected laser light beam L _j which is returned from the magneto-optical disk 6 through the objective lens 5. While functioning as a beam splitter, the first and second prisms 41 and 42 convert the reflected laser light beam L _j into the first light beam L ₁ of P polarization component.
And a second light beam L ₂ of the S-polarized component and a third light beam L ₃ of the combined component of the P-polarized component and the S-polarized component, divided into _three light beams L ₁ , L ₂ and L _3. It is designed to function as an analyzer that emits and outputs light.

As shown in FIG. 3, the photo-detecting unit 10 is the _first of the three light beams L ₁ , L ₂ and L _{3 obtained} by separating the reflected laser light beam L _j by the optical element 4. Beam spot BS _{1 of the} P-polarized component by the optical beam L ₁ of
And the second light beam L
_The photodetector 12 for detecting the beam spot BS ₂ of the S-polarized component by ₂ and the P by the third light beam L _3.
Beam spot B of the combined component of the polarized component and the S polarized component
A so-called four-division photodetector 13 for detecting S ₃
Are arranged with the four-division photodetector 13 positioned in the center, and the side spot BS _S1 , for detecting a tracking error by the so-called three-spot method.
A pair of photodetectors 14 and 15 for detecting BS _S2 are arranged with the four-divided photodetector 13 positioned in the center. The four-division photo detector 1
3 is composed of the respective photodetecting elements 13A, 13B, 13C and 13D.

Then, the optical pickup device of this embodiment is
In the table, the third light beam L₃ Beam spot BS by
₃To the astigmatism given by the cylindrical lens 8
By the astigmatism method based on
Each photodetector element 13A, 13B of the photodetector 13,
Each detection output signal S obtained by 13C and 13D_A，
S _B, S_C, S_DTherefore, FE = (S_A+ S_C)-(S_B+ S_D) Obtaining the focus error signal FE by
You can In addition, each photo detector of the light detection unit 10
Beam spots of P-polarized components obtained by
BS₁Detection output signal S_IAnd S-polarized component beam spot
BS₂Detection output signal S_JFrom RF_MO= S₁-S_J Output signal RF for detection of magneto-optical recording information_MO
Can be obtained. Furthermore, each of the light detection units 10
Each side spot obtained with the photo detectors 14 and 15
BS_S1, BS_S2Each detection output signal S of_E, S_FTherefore, TE = S_E-S_F The tracking error signal force TE is obtained by the following arithmetic processing.
be able to.

In the above optical pickup device, the detection output signals S _I and S _J obtained by the photodetectors 11 and 12 of the photodetection unit 10 are subjected to arithmetic processing of RF _CD = S _I + S _J. It is also possible to obtain a detection output signal RF _CD of an information signal for a compact disc which is an optical disc used only for reproducing an information signal recorded in advance as pits.

By using the optical element 4 having the function of the beam splitter and the function of the analyzer as in the optical pickup device of the first embodiment, the optical system can be downsized.

Here, in the above-described first embodiment, the optical element 4 is provided in the parallel optical path in which the laser light beam emitted from the light beam generation source 1 through the diffraction grating plate 2 is collimated by the collimator lens 3. However, the optical element 4 having the function of the beam splitter and the function of the analyzer as in the second embodiment shown in FIG. 4 may be installed in the converging optical path.

In the second embodiment, the above-mentioned first embodiment is used.
4 which are the same as those in the embodiment described above are designated by the same reference numerals, detailed description thereof will be omitted, and only different points will be described in detail. That is, in the second embodiment, the laser light beam L _i emitted from the light beam generation source 1 via the diffraction grating plate 2 is adhered and formed on the incident surface portion of the first prism 41 of the optical element 4. The collimator lens 3 is reflected by the dielectric multilayer film 43 and is incident on the collimator lens 3.
Then, the light is collimated and then is incident on the magneto-optical disk 6 through the objective lens 5 in a focused state.

Reflection reflected by the magneto-optical disk 6
Laser light beam L_jFrom the objective lens 5 to the collimator
Re-enter the dielectric multilayer film 43 of the optical element 4 via the lens 3.
The first and second pre-beams that are irradiated and constitute the optical element 4.
The first light beam L of P polarization component at₁ 
And the second light beam L of S-polarized component₂And P polarization component
Third light beam L which is a composite component of S-polarized component₃ Of three
Light beam L₁, L₂ , L ₃ The second prism 4
It is emitted from 2.

Then, the three light beams L ₁ , L ₂ , and L ₃ obtained by the optical element 4 are incident on the photodetection unit 110 via the concave lens 8 and the correction plate 30.

In the second embodiment, since the optical element 4 is installed in the convergent optical path, not only the focusing lens 7 is unnecessary but also the optical element 4 is provided as compared with the first embodiment. Astigmatism can be imparted by the correction plate 30 and the cylindrical lens 9 is not required, and an extremely small optical pickup device can be realized.

As shown in FIG. 5, the photodetection unit 110 according to the second embodiment uses a 4-division photodetector 113 for focus error detection rotated by 90 °. In addition, each photodetector 14 for tracking error detection of the photodetection unit 110,
15 is a side spot B indicated by a broken line in FIG.
S _{S1 1,} BS _S21 or side spots BS _S12 shown by a chain line, BS _S22 may be detected.

[0036]

In the optical pickup device according to the present invention, at least three light beams based on the light beams incident on the first prism are emitted through the second prism. The dielectric multilayer film deposited on the incident surface of the first prism makes the light beam from the light beam generation source incident on the recording medium in a focused state, and at the same time receives the reflected light beam from the recording medium on the objective lens. Since it functions as a beam splitter that separates the light beam incident from the generation source and the reflected light beam that passes through the objective lens from the recording medium, the function of the beam splitter and the function of the analyzer can be realized by one optical element.
The device configuration can be simplified and downsized.

[Brief description of drawings]

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

FIG. 2 is a schematic diagram showing a configuration example of an optical element used in the optical pickup device according to the present invention.

FIG. 3 is a schematic diagram showing a specific configuration example of a photodetection unit applied to the optical pickup device shown in FIG.

FIG. 4 is a configuration diagram showing a second embodiment of the optical pickup device according to the present invention.

5 is a schematic diagram showing a specific configuration example of a light detection unit applied to the optical pickup device shown in FIG.

FIG. 6 is a configuration diagram showing a conventional optical pickup device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light beam generation source 4 Optical element 5 Objective lens 6 Magneto-optical disk 10,110 Photodetection unit 41, 42 Prism 43 Dielectric multilayer film

Claims (1)

[Claims] 1. A light beam generation source, an objective lens for making a light beam from the light beam generation source incident on a recording medium in a focused state and receiving a reflected light beam from the recording medium, and the light beam generation source. A beam splitter that separates a light beam incident on the objective lens and a reflected light beam that has passed through the objective lens, a first prism and a second prism, which are respectively formed of quartz, are bonded together, and The reflected light beam from the beam splitter is arranged at a position where the reflected light beam is incident from the first prism and reaches the second prism, and the optical axis of the first prism is substantially the optical axis of the incident reflected light beam. It is in a plane orthogonal to each other, and is inclined by a predetermined angle with respect to the polarization plane of the incident reflected light beam,
The optical axis of the second prism is in a plane substantially orthogonal to the optical axis of the incident reflected light beam, and
An analyzer that makes a predetermined angle with the optical axis of the first prism and emits at least three light beams based on the incident reflected light beam, and the three detectors that emit from the analyzer. In an optical pickup device including a photodetection unit having a plurality of photodetection elements for individually detecting the light beams, a light beam reflected by the recording medium of the first prism constituting the analyzer is An optical pickup device characterized in that a dielectric multilayer film is deposited on an incident surface, and the beam splitter is formed by the dielectric multilayer film.