JPH08235664A - Optical pickup apparatus - Google Patents

Abstract

PURPOSE: To realize reduction in size of an apparatus by forming a readout output signal of the information recorded on a magnetooptical disc with a signal processor to which detected outputs of a plurality of light receiving sections of a photodetector. CONSTITUTION: In an optical pickup apparatus, a polarization beam splitter block 16 for isolating the linear polarized elements Rs , Rp of the reflected beam R of laser beam L by the recording medium surface 2 of the magnetooptical disc 1 and a photodetector 19 for detecting the linear polarized elements Rs , Rp are integrated into one part. Therefore, its installation space can be reduced. In addition, in this case, since a focus error is detected on the basis of each detected output obtained by each light receiving portions 17, 18 of the pohtodetector 19 without using a cylindrical leans, the apparatus as a whole can be reduced in size.

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 optically reading information recorded on a magneto-optical disk.

[0002]

2. Description of the Related Art Conventionally, as an optical disk capable of rewriting information, a perpendicular substrate such as TbFeCo having a magneto-optical effect such as a Faraday effect or a Kerr effect is formed on a transparent substrate such as glass, acrylic (PMMA), polycarbonate (PC) or the like. A magneto-optical disk is known in which a magnetized film is formed by a sputtering method or a vacuum evaporation method.

In a magneto-optical disk, a DC magnetic field is applied to a perpendicularly magnetized film formed on a transparent substrate, and a laser beam that blinks in response to an information write signal is applied to the magneto-optical disk.
An optical modulation method that reverses the magnetization of the perpendicular magnetization film according to the information write signal, or a constant laser beam is continuously irradiated to the perpendicular magnetization film, and the external magnetic field applied to the perpendicular magnetization film is modulated according to the information write signal. By doing so, information is recorded by the magnetic field modulation method in which the magnetization of the perpendicular magnetization film is inverted according to the information write signal.

In a magneto-optical disk, when a perpendicularly magnetized film on which information is recorded is irradiated with laser light, the plane of polarization of reflected light or passing light obtained through the vertically magnetized film depends on the magnetization direction of the vertically magnetized film. Since it rotates, the information recorded in the perpendicular magnetization film is optically read by detecting the polarization component of the information reading laser beam obtained through the perpendicular magnetization film.

To read the information recorded on the magneto-optical disk as described above, an optical pickup device having a structure as shown in FIG. 5, for example, is used.

This optical pickup device includes a pickup block 50, as shown in FIG. The pickup block 50 includes a semiconductor laser 51 that emits a laser beam L for reading information, an objective lens 54 that focuses the laser beam L on a perpendicularly magnetized film of the magneto-optical disk 70, that is, a recording medium surface 71, and a recording medium surface of the laser beam L. A polarization beam splitter 57 for separating the linearly polarized light component of the reflected light R by 71 and each photodetector 5 for detecting the linearly polarized light component of the reflected light R.
It is equipped with 8, 59 etc. This pickup block 5
0 is moved and operated along the radial direction of the magneto-optical disk 70 by a feeding mechanism (not shown). In addition, each of the photodetectors 58 and 59 of the pickup block 50 includes a signal processing unit 60.
It is connected to the.

The laser light L for reading information emitted from the semiconductor laser 51 is collimated by the collimator lens 52 and is incident on the beam splitter 53. The beam splitter 53 is semi-transparent to the optical axis inclined by 45 °. The light component reflected by the mirror surface 53A is applied to the recording medium surface 71 of the magneto-optical disk 70 in a focused state via the objective lens 54. The reflected light R from the recording medium surface 71 of the magneto-optical disk 70 enters the beam splitter 53 from the objective lens 54, and the passing light component passing through the semi-transparent mirror surface 53A of the beam splitter 53 passes through the focusing lens 55 and the cylindrical lens 56. Incident on the polarization beam splitter 57,
The polarization beam splitter 57 separates a linearly polarized light component, that is, a P-polarized light component Rp and an S-polarized light component Rs, and irradiates the two photodetectors 58 and 59.

Then, the P-polarized component Rp and the S-polarized component Rs of the reflected light R from the recording medium surface 71 of the magneto-optical disk 70.
The signal processing unit 60 to which the respective detection outputs of the two photodetectors 58 and 59 for detecting the It is adapted to obtain the signal RF.

Further, in this optical pickup device, in order to perform focus control of the laser light L for reading information which irradiates the recording medium surface 71 of the magneto-optical disk 70, as photodetectors 58 and 59, as shown in FIG. 4 each
Focus detection by the astigmatism method is performed using a so-called four-division detector provided with two detection regions 58a to 58d and 59a to 59d, and the signal processing unit 60 uses the photodetector 5 to detect the focus.
A focus error detection signal is formed from each of the detection outputs of 8 and 59, and the signals are added and combined to be used as a focus error signal FE for focus control.

[0010]

By the way, as described above, the reflected light R from the recording medium surface 71 of the magneto-optical disk 70 is reflected.
The two photodetectors 58 and 59 for detecting the P-polarized component Rp and the S-polarized component Rs are differentially detected with respect to the magneto-optical signal corresponding to the information recorded on the magneto-optical disk 70, and the so-called non-optical In the conventional optical pickup device for performing focus detection by the point aberration method, since the cylindrical lens 56, the polarization beam splitter 57, and the photodetectors 58 and 59 are individually installed, the structure is complicated and the number of assembly steps is large. Not only that, but the installation volume is large and it is difficult to downsize the device.

Two photodetectors 58, 58 are provided so that the P-polarized component Rp and the S-polarized component Rs of the reflected light R separated by the polarization beam splitter 57 can be accurately detected at predetermined positions.
It is necessary to individually adjust the fixed position of 59 in the three-dimensional directions of the arrows X, Y, and Z shown in FIG. 6, and there is a problem that the adjustment work requires a great deal of labor and time.

Therefore, an object of the present invention is to provide a novel optical pickup device which solves the problems of the conventional optical pickup device as described above.

Another object of the present invention is to provide an optical pickup device which can realize further miniaturization.

[0014]

The optical pickup device according to the present invention, which is proposed to achieve the above object, comprises:
A laser light source that emits laser light, an objective lens that focuses the laser light emitted by the laser light source on the recording medium surface of the magneto-optical disk, and reflected light of the laser light by the recording medium surface are incident on the recording medium surface. An optical element for separating the linearly polarized light component of the reflected light, and a photodetector provided with a plurality of light receiving portions fixedly arranged on one surface side different from the incident surface of the optical element and receiving the reflected light separated by the optical element. A signal processing unit that forms a read output signal of information recorded on the magneto-optical disk based on detection outputs from a plurality of light-receiving units of the photodetector and a focus error signal of the laser beam applied to the magneto-optical disk. It is configured with and.

[0015]

DETAILED DESCRIPTION OF THE INVENTION An optical pickup device according to the present invention will be described in detail below with reference to the drawings.

As shown in FIG. 1, the optical pickup device of the embodiment shown in the block diagram of FIG. 1 uses the perpendicularly magnetized film of the magneto-optical disk 1, that is, recording the laser beam L for reading information. A pickup block 10 that irradiates the medium surface 2 to detect the linearly polarized light component of the reflected light R, and a read output of information recorded on the magneto-optical disk 1 based on the detection output obtained by the pickup block 10. The signal processing unit 20 forms the signal RF and also forms the focus error signal FE of the laser light L with which the magneto-optical disk 1 is irradiated.

A pickup block 10 which constitutes an optical pickup device includes a semiconductor laser 11 for emitting a laser beam L for reading information, an objective lens 14 for focusing the laser beam L on a recording medium surface 2 of a magneto-optical disk 1, and a laser beam. A polarization beam splitter prism 16 for separating the linearly polarized light component of the reflected light R from the recording medium surface 2 of L and a photodetector 19 having light receiving portions 17, 18 for irradiating the linearly polarized light component of the reflected light R are provided. . The pickup block 10 is fed and operated in the radial direction of the magneto-optical disc 1 by a feeding mechanism (not shown).

The laser light L for reading information emitted from the semiconductor laser 11 is collimated by the collimator lens 12 and is incident on the beam splitter 13, which is half of the beam splitter 13 tilted at 45 ° with respect to the optical axis. The reflected light component from the transparent mirror surface 13A is applied to the recording medium surface 2 of the magneto-optical disk 1 in a focused state via the objective lens 14.
The reflected light R from the recording medium surface 2 of the magneto-optical disk 1 is incident on the beam splitter 13 from the objective lens 14, and the passing light component passing through the semi-transparent mirror surface 13 A of this beam splitter 13 is polarized through the focusing lens 15. The light is incident on the splitter prism 16.

As shown in FIG. 1, the polarization beam splitter prism 16 is formed in a trapezoidal cross section in which a second prism block 16A having an isosceles right triangle cross section and a second prism block 16B having a parallelogram cross section are butted and joined. The polarization beam splitter film 16b for separating the linearly polarized light component of the reflected light R is formed on the joint surface portion having an inclination of 45 ° with respect to the optical axis of the reflected light R incident on the incident surface 16a via the focusing lens 15. It is provided. The polarization beam splitter film 16b separates the linearly polarized light component of the reflected light R by passing the P-polarized light component Rp of the reflected light R and reflecting the S-polarized light component Rs. Then, in the polarization beam splitter prism 16, a surface 16c parallel to the polarization beam splitter film 16b is a reflecting mirror that guides the S-polarized component Rs to the first exit surface 16d, and the P-polarized light that has passed through the polarization beam splitter film 16b. The second emission surface 16e of the component Rp is formed on the same plane. The exit surfaces 16d and 16e of the polarization beam splitter prism 16 are located at equal distances in front and back with respect to the focusing position P of the reflected light R that is incident on the entrance surface 16a via the focusing lens 15.

As shown in FIG. 2, in the photodetector 19, each of the light receiving portions 17 and 18 is divided into three strips, and the linearly polarized light component Rp is located at the center position of each of the central light receiving portions 17B and 18E. , Rs are aligned with the optical axis centers of the polarization beam splitter prisms 16, and the light receiving portions 17 and 18 are arranged and fixed so as to face the emission surfaces 16d and 16e of the polarization beam splitter prism 16. That is, as shown in FIG. 2, the photodetector 19 is arranged on the lower surface side of the polarization beam splitter prism 16 so that the light receiving portions 17 and 18 face the emission surfaces 16 d and 16 e of the polarization beam splitter prism 16. Has been made. More specifically, the photodetector 19 has an incident surface 16 on which the reflected light R reflected from the magneto-optical disk 1 is incident.
It is arranged on the opposite side, which is one side different from a.

In the pickup block 10 used here, the spots SPp, SP of the linearly polarized light components Rp, Rs with which the light receiving portions 17, 18 of the photodetector 19 are irradiated.
The optical path is adjusted so that the laser beam L irradiated onto the recording medium surface 2 of the magneto-optical disk 1 is in a just focus state when s has the same diameter shown by the solid line in FIG. As a result, when the focus of the laser light L is deviated, the diameters of the spots SPp and SPs on the light receiving portions 17 and 18 reciprocally change as indicated by the broken line and the alternate long and short dash line in FIG. The light receiving units 17 and 18 obtain the detection output according to the change in the diameter of SPs.

Since the pickup block 10 has a structure in which the polarization beam splitter prism 16 is integrally arranged on the photodetector 19, the entire pickup block 10 can be handled as one component, and the optical path Adjustments can be made easily.

Further, as shown in FIG. 2, the signal processing section 20 has a circuit configuration in which each detection output A, which is obtained by one of the three-divided light receiving sections 17A, 17B, 17C of the photodetector 19,
First and second signal adders 21, 2 supplied with B and C
2 and third and fourth signal adders 23, 24 to which the respective detection outputs E, F, G obtained by the other three-divided light receiving sections 18D, 18E, 18F are provided.

The first signal adder 21 detects each detection output A,
C is added, and the addition output (A + C) is supplied to the second signal adder 22 and is also supplied to the negative side input terminal of the first operational amplifier 25. The second signal adder 22 adds the detection output B and the addition output (A + C) to obtain one of 3
The total output (RF ₁ = A + B + C) of the detection outputs A, B, C obtained by the divided light receiving units 17A, 17B, 17C is supplied to the positive side input terminal of the second operational amplifier 26. The third signal adder 23 adds the detection outputs D and F, supplies the added output (D + F) to the fourth signal adder 24, and also supplies the negative input to the third operational amplifier 27. Supplying to the edge. The fourth signal adder 24 detects the detection output E
And the addition output (D + F) are added, and each detection output D, obtained by the other three-divided photodetectors 18D, 18E, 18F
The sum total output of E and F (RF ₂ = D + E + F) is supplied to the positive side input terminal of the fourth operational amplifier 28.

Further, the first operational amplifier 25 adds the first signal from the detection output B, which is applied to its positive side input terminal and whose signal level changes according to the focus state as shown in FIG. 3 (a). By subtracting the addition output (A + C) from the device 21, one of the three-divided photodetectors 17A, 17B,
Focus error detection signal [FE _{1 as} shown in FIG. 3B based on the detection outputs A, B and C obtained at 17C.
= B- (A + C)] is formed and is supplied to the positive side input terminal of the fourth operational amplifier 28.

The third operational amplifier 27 adds the third signal from the detection output E, which is applied to its positive side input terminal and whose signal level changes according to the focus state as shown in FIG. 3C. By subtracting the addition output (D + F) from the device 23, the other three-division light receiving units 18D, 18E, 1
FIG. 3 based on each detection output D, E, F obtained at 8F.
Focus error detection signal [FE ₂ =
E- (D + F)] is formed and supplied to the negative side input terminal of the fourth operational amplifier 28.

Then, the signal processing section 20 is provided with the sum total outputs RF ₁ and RF ₁ by the second and fourth signal adders 22 and 24, respectively.
RF ₂ is subtracted and synthesized by the second operational amplifier 26 to form a magneto-optical signal RF which is output from the first signal output terminal 20A and obtained by the first and third operational amplifiers 25 and 27. By subtracting each of the focus error detection signals FE ₁ and FE ₂ , a symmetrical focus error signal FE is formed around the just focus point JP as shown in (e) of FIG. 3 to form a second signal output terminal. Output from 20B.

In the optical pickup device configured as described above, the polarization beam splitter block 16 for separating the linearly polarized light components Rs and Rp of the reflected light R of the laser light L from the recording medium surface 2 of the magneto-optical disk 1 and the linearly polarized light component. Rs,
By integrating the photodetector 19 for detecting Rp into one component, the installation space can be reduced,
Moreover, the photodetector 19 can be used without using a cylindrical lens.
Since the focus error is detected based on each detection output obtained by each of the light receiving units 17 and 18, the entire apparatus can be downsized.

Further, the polarization beam splitter block 16
And the photodetector 19 for detecting the linearly polarized light components Rs and Rp are integrated and handled as one component, and the position adjustment in the three-dimensional direction can be easily performed. In this example, the photodetector 19
Linearly polarized light components Rs obtained by the respective light receiving units 17 and 18 of
Since the read output signal RF of the information recorded on the magneto-optical disk 1 and the focus error signal FE of the laser light L applied to the magneto-optical disk 1 are differentially detected based on Rp, the in-phase removal effect is achieved. Extremely high quality read output signal RF and focus error signal FE
Can be obtained.

In the above example, the polarization beam splitter block 16 with the photodetector 19 arranged and fixed is shown in FIG.
As shown in FIG. 1, the first prism block 16A constituting the polarization beam splitter block 16 is installed by rotating it by 90 ° with respect to the optical axis of the reflected light R, and one surface of the first prism block 16A is formed into the incident surface 1.
6a 'may be used.

[0031]

As described above, in the optical pickup device according to the present invention, the reflected light of the laser light from the recording medium surface is incident, and the incident surface of the optical element for separating the linearly polarized light component of the incident reflected light is used. Is a signal processing unit to which a photodetector having a plurality of light receiving units for receiving reflected light separated by an optical element is fixedly arranged on one different surface side, and the detection outputs from the plurality of light receiving units of the photodetector are input. Since it is designed to form a read output signal of information recorded on the magneto-optical disc and a focus error signal of the laser beam applied to the magneto-optical disc, the optical element and the photodetector are integrated as one component. In addition to being easy to adjust the positions of the optical element and the photodetector, the number of constituent parts is small and the device can be downsized. Therefore, according to the present invention, it is possible to provide an optical pickup device which can be easily assembled and manufactured.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of an optical pickup device for a magneto-optical disk according to the present invention.

FIG. 2 is a block diagram showing a configuration of a signal processing unit that constitutes the optical pickup device.

FIG. 3 is a waveform diagram for explaining a focus detection operation of the optical pickup device.

FIG. 4 is a schematic diagram showing another example of a detection block used in the optical pickup device.

FIG. 5 is a configuration diagram showing a configuration of a conventional example of an optical pickup device.

FIG. 6 is an external perspective view showing a configuration of a main part of the conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magneto-optical disk 11 Semiconductor laser 14 Objective lens 16 Polarization beam splitter prism 16b Polarization beam splitter film 16c Reflective surface 16d, 16e Emission surface 17, 18 Light receiving part 19 Photodetector 20 Signal processing part

Claims (1)

[Claims] 1. A laser light source for emitting a laser beam, an objective lens for focusing the laser beam emitted by the laser light source on a recording medium surface of a magneto-optical disk, and a reflected light of the laser beam by the recording medium surface. Is incident on the optical element for separating the linearly polarized light component of the incident reflected light, and a plurality of optical elements that are fixedly arranged on one surface side different from the incident surface of the optical element and receive the reflected light separated by the optical element. A photodetector having a light receiving section, and a read output signal of information recorded on the magneto-optical disk is formed based on detection outputs from the plurality of light receiving sections of the photodetector, and the magneto-optical disk is irradiated with the read output signal. An optical pickup device comprising: a signal processing unit that forms a focus error signal of laser light.