JPH10149562A - Optical pickup and optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized, light weight and inexpensive optical pickup and an optical disk device using it. SOLUTION: This optical pickup 20 is provided with a light convergent means 26 converging a light beam outgoing from a light source 21 on a signal recording surface of an optical disk 11, a polarized light separating means 23 transmitting the light beam from the light source 21 through between the light source 21 and the light convergent means 26 and reflecting a return light beam from the optical disk, a light division means 23a dividing the light beam from the light source 21 and a photodetector 29 having a light receiving part light receiving the return light beam reflected by the polarized light separating means 23. Then, the polarized light separating means 23 is constituted of a parallel plane arranged obliquely for an optical axis and provided with a polarized light separating film 23a on the surface of the optical disk side, and a wave front aberration corrective lens 22 for correcting wave front aberration due to the parallel plane is arranged between the light source 21 and the polarized light separating means 23.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup for recording and / or reproducing signals from an optical disk (hereinafter, referred to as an "optical disk") such as an optical disk, a magneto-optical disk, and a phase change type disk. The present invention relates to an optical disk device provided with an optical pickup.

[0002]

2. Description of the Related Art Conventionally, an optical pickup for an optical disk is constructed, for example, as shown in FIG. In FIG. 4, an optical pickup 1 includes a grating 3a, an astigmatism correction plate 3b, a beam splitter 4, a collimator lens 5, which are sequentially arranged in the optical path of a light beam emitted from a semiconductor laser element 2 as a light source. , A prism mirror 6, an objective lens 7, and a Wollaston prism 4 a, a multi-lens 4 b, and a photodetector 8 sequentially arranged in a separation optical path of a return light beam from the optical disk reflected by the beam splitter 4. ing.

In the optical pickup 1 having such a configuration, the light beam from the semiconductor laser element 2 sequentially passes through the grating 3a, the astigmatism correction plate 3b, and the beam splitter 4, and is converted into parallel light by the collimator lens 5. After that, the optical path is bent in the direction of the optical disk by the prism mirror 6, and the object lens 7 irradiates the signal recording surface of the optical disk. The return light beam reflected by the signal recording surface again enters the beam splitter 4 via the objective lens 7, the prism mirror 6, and the collimator lens 5, and is reflected by the reflection surface.
The light is received by the light receiving surface of the photodetector 8 via the Wollaston prism 4a and the multi-lens 4b, and the recording signal is detected. At this time, by detecting the main beam and the two side beams split by the grating 3a, a tracking error signal is obtained by a so-called three-spot method, and the astigmatism imparted by the multi-lens 4b is used. Thus, a focus error signal can be obtained by a so-called astigmatism method.

Here, in order to accurately detect a reproduced signal,
In order for the light beam from the semiconductor laser element 2 to form a spot at a correct position on the signal recording surface of the optical disk and to reproduce the recorded signal accurately, the objective lens 7 is moved slightly based on a predetermined servo signal. It is supposed to be. The servo of the objective lens 7 includes a tracking servo for finely moving the objective lens 7 along the radial direction of the optical disk with respect to the recording track of the optical disk, and a direction for moving toward and away from the signal recording surface of the optical disk along the optical axis. A focus servo for finely moving the objective lens 7 is performed. These tracking servo and focus servo are performed based on the above-described tracking error signal and focus error signal.

[0005]

By the way, in the optical pickup 1 having such a configuration, a cube-shaped beam splitter in which two triangular prisms are bonded is used as the beam splitter 4. Thus, even if the incident NA (numerical aperture) of the light beam from the semiconductor laser element 2 to the beam splitter 4 is relatively large, the angle of inclination of the reflecting surface can be set relatively accurately. It is configured to be able to sufficiently cope with the angle dependence of the polarization separation performance. However, such a beam splitter 4 has a relatively large thickness due to its cube shape, so that the optical path length of the optical pickup 1 is long. Therefore, there is a problem that the entire optical pickup 1 becomes relatively large, which is contrary to the demand for miniaturization.

Further, the beam splitter formed by bonding the triangular prisms has a problem that the operation is complicated and very expensive, and the whole optical pickup 1 becomes heavy because it is relatively heavy.

SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide an optical pickup and an optical disk apparatus using the optical pickup, which are configured to be small and lightweight and reduce the manufacturing cost.

[0008]

According to the present invention, there is provided a light source for emitting a light beam, light focusing means for focusing the light beam emitted from the light source on a signal recording surface of an optical disk, A light separating means disposed between the light source and the light focusing means for transmitting a light beam from the light source and reflecting a return light beam from the optical disk; and signal recording of the optical disk reflected by the light separating means A photodetector having a light receiving portion for receiving a return light beam from the surface, wherein the light separating means is disposed obliquely with respect to the optical axis, and provided with a light separating film on the surface on the optical disk side. This is achieved by an optical pickup which is constituted by a parallel plate and in which a wavefront aberration correcting means for correcting a wavefront aberration caused by the parallel plate is provided between the light source and the light separating means.

According to the above arrangement, the light beam emitted from the light source passes through the parallel plate light separating means via the wavefront aberration correcting means, and is focused on the signal recording surface of the optical disk by the light focusing means. Then, the return light beam from the optical disc is reflected by the light separating film on the surface of the light separating means, guided to the photodetector, and the signal of the optical disc is reproduced based on the detection signal of the photodetector.

Here, the wavefront aberration generated by the transmission of the light separating means is canceled by the wavefront aberration given by the wavefront aberration correcting means, so that the wavefront aberration of the light beam transmitted through the light separating means is reduced. Thus, accurate signal reproduction of the optical disk can be performed. Here, the correction of the wavefront aberration by the wavefront aberration correcting means does not have to completely remove the wavefront aberration, but may be in a range allowable in signal detection.

Therefore, by using a beam splitter made of a parallel plate as the beam splitter, the beam splitter can be formed small, lightweight, and at low cost.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIGS. still,
Since the embodiments described below are preferred specific examples of the present invention, various technically preferred limitations are added.
The scope of the present invention is not limited to these embodiments unless otherwise specified in the following description.

FIG. 1 shows an embodiment of an optical disk device incorporating an optical pickup according to the present invention.
In FIG. 1, an optical disk device 10 includes an optical disk 11
Spindle motor 12 as a driving means for rotationally driving the motor
And an optical pickup 20 for irradiating a signal recording surface of the rotating optical disk 11 with a light beam to record a signal, reproducing a recorded signal by a return light beam from the signal recording surface, and a control unit 13 for controlling these. It has. Here, the control unit 13 includes an optical disk controller 14, a signal demodulator 15, an error correction circuit 16, an interface 1
7, a head access control unit 18 and a servo circuit 19 are provided.

An optical disk controller 14 controls the drive of the spindle motor 12 at a predetermined rotation speed. The signal demodulator 15 demodulates the recording signal from the optical pickup 20, corrects the error, and sends the signal to an external computer or the like via the interface 17. Thus, an external computer or the like can receive a signal recorded on the optical disk 11 as a reproduction signal.

The head access control section 18 moves the optical pickup 20 to a predetermined recording track on the optical disk 11, for example, by a track jump or the like. The servo circuit 19 moves the objective lens held by the biaxial actuator of the optical pickup 20 in the focusing direction and the tracking direction at the moved predetermined position.

FIG. 2 shows an optical pickup incorporated in the optical disk device 10. In FIG.
The optical pickup 20 includes a correcting lens 22 as a wavefront aberration correcting unit, a beam splitter 23 as a light separating unit, and a parallel light, which are sequentially arranged in the optical path of a light beam emitted from a semiconductor laser element 21 as a light source. A collimator lens 24 as a converting means, a prism mirror 25 as an optical path bending means and an objective lens 26 as a light focusing means, and a Wollaston prism 27 and a multi-lens which are sequentially arranged in a separated optical path by the beam splitter 23. 28 and a photodetector 29.

The semiconductor laser element 21 is a light emitting element utilizing recombination light emission of a semiconductor, and emits a predetermined laser beam.

For example, the correction lens 22 used as the wavefront aberration correcting means is a plano-convex lens in which the incident side is flat and the output side is convex, and its radius of curvature is such that the light beam transmitted through the wavefront aberration correcting lens 22 is In order to correct the wavefront aberration applied when the light is transmitted through the beam splitter 23, the wavefront aberration is selected to be reversed. Further, the wavefront aberration correcting lens 22 is a grating 22 in which a diffraction grating is integrally formed on the incident surface.
a. The grating 22a is a diffraction grating for diffracting incident light,
From the main beam composed of the zero-order diffracted light and ±
It is split into at least three light beams of a side beam composed of first-order diffracted light. Note that the wavefront aberration correction means 22 may have any configuration as long as the wavefront aberration to be removed can be reduced. Therefore, the wavefront aberration correction means 22 is not limited to the illustrated lens, and may use other optical elements as appropriate. For example, a parallel flat plate may be disposed at the same position as the wavefront aberration correcting lens 22 at a predetermined angle instead. In this case, a diffraction grating can be provided on the incident surface side of the parallel plate where the light beam enters.

The beam splitter 23 has four beams with respect to the optical axis.
A parallel flat plate that is disposed at an angle of 5 degrees, and a light separation film (a polarization separation film in the illustrated case) is provided on the plane on the emission side.
23a are formed. As a result, the light beam from the wavefront aberration correction lens 22 and the return light from the signal recording surface of the optical disk 11 are polarized and separated. That is, part of the light beam from the semiconductor laser element 21 passes through the polarization splitting film 23a of the beam splitter 23, and part of the return light beam is reflected by the polarization splitting film 23a of the beam splitter 23. ing. Since the beam splitter 23 is made of a parallel plate, a bonding operation like a conventional cube-shaped beam splitter is not required, and the beam splitter 23 can be manufactured easily and at low cost.

The collimator lens 24 is a convex lens, and in the case of the drawing, a convex lens formed by combining a concave lens and a convex lens.
Is converted into parallel light.

The prism mirror 25 is, for example, a triangular prism-shaped mirror, reflects the parallel light beam from the collimator lens 24 in the vertical direction by 90 degrees, and
The return light beam from 1 is reflected 90 degrees in the horizontal direction.

The objective lens 26 is a convex lens and focuses the parallel light beam from the collimator lens 25 on a desired recording track on the signal recording surface of the optical disk 11 that is driven to rotate. Here, the objective lens 26 is supported by a biaxial actuator (not shown) so as to be movable in a biaxial direction, that is, a focusing direction and a tracking direction.

The Wollaston prism 27 is a quadrangular prism, and emits a plurality of light beams by performing polarization separation based on a return light beam from the optical disk 11. The multi-lens 28 includes a cylindrical lens and a concave lens, and provides astigmatism to the light beam and adjusts the optical path length for detecting the focus error signal on the return light beam. Has become.

The photodetector 29 is configured to have a light receiving portion for the return light beam transmitted through the beam splitter 23.

The optical disk device 10 incorporating the optical pickup 20 according to the present embodiment is configured as described above, and operates as follows. First, the optical disk 11 is rotationally driven by the rotation of the spindle motor 12 of the optical disk device 10. Then, by moving the optical pickup 20 in the radial direction of the optical disk 11, the optical axis of the objective lens 26 is moved to a desired track position of the optical disk 11, thereby performing access.

In this state, in the optical pickup 20, the light beam from the semiconductor laser element 21 is applied to the grating 2 formed on the incident surface of the wavefront aberration correcting lens 22.
After being split into three light beams by 2a and having a wavefront aberration imparted by a wavefront aberration correction lens 22, the light beam is transmitted through a beam splitter 23 and converted into a parallel light by a collimator lens 24. And this parallel light beam is
The light is reflected by the prism mirror 25 toward the optical disk 11, and is focused on the signal recording surface of the optical disk 11 via the objective lens 26. The return light from the optical disk 11 again enters the beam splitter 23 via the objective lens 26, the prism mirror 25, and the collimator lens 24. Then, the polarization separation film 23a of the beam splitter 23
And is converged on a photodetector 29 via a Wollaston prism 27 and a multi-lens 28. Thus, based on the detection signal of the photodetector 29, the optical disk 1
1 is reproduced.

At this time, the signal demodulator 15 detects a tracking error signal by a so-called three spot method based on a detection signal from the photodetector 29 with respect to the side beam by the grating 22a, and focuses by an astigmatism method. Detect error signals. The servo circuit 19 drives and controls a biaxial actuator (not shown) via the optical disk drive controller 14 so that focusing and tracking of the objective lens 26 are performed.

Here, when the light beam from the semiconductor laser element 21 is transmitted through the beam splitter 23, which is a parallel plate, a wavefront aberration is generated. The opposite wavefront aberration previously imparted to the light beam by the wavefront aberration correction lens 22 is offset. Accordingly, the wavefront aberration of the light beam transmitted through the beam splitter 23 is reduced, and an accurate spot is formed on the signal recording surface of the optical disk 11. As a result, accurate signal reproduction of the optical disk 11 is performed.

FIG. 3 shows a second embodiment of the optical pickup according to the present invention. 3, an optical pickup 30 has substantially the same configuration as the optical pickup 10 shown in FIG. 2, and a coupling lens 31 is arranged between a semiconductor laser element 21 as a light source and a wavefront aberration correcting lens 22. It is different from the first embodiment in that a collimator lens 24 is omitted. The coupling lens 31 is a convex lens, and acts so as to reduce the incident NA (numerical aperture) on the beam splitter 23 by slightly converging the light beam from the semiconductor laser element 21.

This optical pickup exhibits the following functions and effects in addition to the effects of the first embodiment. Since a convex lens is used as the coupling lens 31, the NA of the light beam entering the beam splitter 23
Can be reduced. This makes it possible to reduce the angle dependence of the polarization separation. Therefore, even if the positioning accuracy of the inclination angle with respect to the optical axis is slightly deteriorated by forming the polarization separation film 23a on one surface of the parallel plate, the optical performance is improved. Does not deteriorate. Further, the utilization efficiency of the light beam from the semiconductor laser element 21 is improved, and the relatively large collimator lens 24 is omitted, so that the overall configuration is small. In this case, by appropriately selecting the magnification of the objective lens 26, the multi-lens 28
Since the concave lens is omitted, and the multi-lens 28 is composed of only a cylindrical lens, the number of parts can be reduced.

In the optical disk device 10 and the optical pickup 20 according to the above embodiment, the configuration of the polarization optical pickup for reproducing the magneto-optical disk is shown.
Not limited to this, compact disc (CD) and CD-R
It is apparent that the present invention can be applied to a non-polarization optical pickup and an optical disk device for OM by changing the polarization separation film of the beam splitter to a light separation film.

[0032]

As described above, according to the present invention, it is possible to provide an optical pickup and an optical disk apparatus using the same, which are configured to be small and lightweight, and at a reduced cost. .

[Brief description of the drawings]

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

FIG. 2 is a schematic plan view showing a configuration of an optical pickup in the optical disk device of FIG.

FIG. 3 is a schematic plan view showing a configuration of an optical pickup according to a second embodiment of the present invention.

FIG. 4 is a side view showing an optical system in an example of a conventional optical pickup.

[Brief description of reference numerals]

10 optical disk device, 11 optical disk, 1
2 ... Spindle motor, 13 ... Control unit, 14.
..Optical disk drive controller, 15 ... signal demodulator, 16 ... error correction circuit, 17 ... interface, 18 ... head access control unit, 20 ...
-Optical pickup, 21 ... semiconductor laser element, 2
2 ... wavefront correction lens, 22a ... grating, 23 ... beam splitter, 23a ... polarization separation film, 24 ... collimator lens, 25 ... prism mirror, 26 ... objective lens, 27 ... Wollaston prism, 28 ... Multi lens, 29 ... Photodetector, 30 ... Optical pickup, 31 ... Coupling lens.

Claims (4)

[Claims] A light source for emitting a light beam; a light focusing means for focusing the light beam emitted from the light source on a signal recording surface of an optical disc; and a light source disposed between the light source and the light focusing means; Light having a light separating means for transmitting a light beam from a light source and reflecting a return light beam from an optical disk, and a light receiving unit for receiving the return light beam from the signal recording surface of the optical disk reflected by the light separation means A light detector, wherein the light separating means is arranged obliquely with respect to an optical axis, and comprises a parallel flat plate having a light separating film on a surface on an optical disk side; and the light source and the light separating means. And a wavefront aberration correcting means for correcting wavefront aberration caused by the parallel plate. 2. A light beam splitting means for splitting a light beam from the light source into a main beam and a side beam is integrally formed on a light beam incident surface of the wavefront aberration correcting means. 2. The optical pickup according to 1. 3. Between the light source and the wavefront aberration correcting means,
2. The optical pickup according to claim 1, further comprising a convex lens for reducing an incident NA to the light separating means. 4. A light converging means for converging a light beam emitted from a light source on a signal recording surface of an optical disk via a light dividing means, and a light beam from the light source between the light source and the light converging means. Light separating means for transmitting the light beam and reflecting the return light beam from the optical disc; a light detecting means having a light receiving portion for receiving the return light beam reflected by the light separating means; A driving unit that can move to a driving unit; a calculation unit that obtains a servo signal based on a signal from a light receiving unit of the light detection unit; and a servo unit that supplies a driving current to the driving unit based on the servo signal. Wherein the light separating means comprises a parallel flat plate having a light separating film on a surface on an optical disk side, and corrects a wavefront aberration caused by the parallel flat plate between the light source and the light separating means. Optical disc apparatus characterized by fit wavefront aberration correcting means is disposed.