JPH11250489A - Optical pickup optical system - Google Patents

Abstract

(57) [Problem] To provide an optical pickup optical system that realizes high-accuracy tracking control that can cope with an ultra-high-density optical disk having an extremely small track pitch. A light beam from a light source (1) is transmitted to an optical recording medium (8).
A movable mirror (4) for deflecting a light beam from a light source (1) in an optical pickup optical system for converging light thereon and guiding a light beam reflected from an optical recording medium (8) to a photodetector (11);
A relay lens (5) for focusing the light beam on the optical recording medium (8) and a relay lens system (5) for guiding the light beam reflected by the movable mirror (4) to the pickup lens (7); The lens system (5) is an optical pickup optical system comprising an afocal optical system whose angular magnification is less than unity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical pickup optical system used for recording information on an optical recording medium or reproducing information recorded on the optical recording medium.

[0002]

2. Description of the Related Art In an optical recording / reproducing apparatus for optically recording information on an optical recording medium such as an optical disk or reproducing the recorded information, a laser beam is guided to a pickup lens arranged near the optical disk. The optical disc is focused on the optical disc, information is recorded on the optical disc while the optical disc is rotated, or the laser beam reflected from the optical disc is read by a signal detection system to reproduce the information. At that time, when recording, the laser beam is traced so as to form an information track in a desired area on the optical disk, and when reproducing, the laser beam is traced so as to trace the information track formed on the optical disk. We are tracking the beam. In such an optical recording / reproducing apparatus, since eccentricity occurs inevitably during rotation of the optical disk, tracking control is performed so that the laser beam can accurately follow the information track. Conventionally, as a tracking control, the pickup lens is driven by a voice coil in a direction orthogonal to the optical axis, or the movable mirror disposed immediately before the pickup lens is swung to deflect the laser beam. The light spot position was controlled to move in the eccentric direction.

[0003]

However, with the recent increase in the density of optically recorded information, the track pitch has been dramatically reduced, and the conventional method of driving a pickup lens using a voice coil and the method of driving a pickup lens immediately before the pickup lens have been proposed. In the method of swinging the arranged movable mirror, it has been difficult to satisfy the accuracy required for tracking control. Accordingly, it is an object of the present invention to provide an optical pickup optical system that realizes high-accuracy tracking control that can cope with an ultra-high-density optical disk having an extremely small track pitch.

[0004]

According to the present invention, there is provided an optical recording medium comprising: a light source;
A movable mirror (4) for deflecting a light beam from a light source (1) in an optical pickup optical system for converging light thereon and guiding a light beam reflected from an optical recording medium (8) to a photodetector (11);
A relay lens (5) for focusing the light beam on the optical recording medium (8) and a relay lens system (5) for guiding the light beam reflected by the movable mirror (4) to the pickup lens (7); The lens system (5) is an optical pickup optical system comprising an afocal optical system having an angular magnification of less than unity.

[0005]

FIG. 1 is a sectional view showing an optical system of an optical pickup according to a first embodiment of the present invention. In FIG.
A laser beam emitted from a light source 1 composed of a semiconductor laser is converted into parallel light by a collimator lens 2, and a part of the laser beam passes through a half mirror 3 and is guided to a galvanometer mirror 4. The galvanometer mirror 4 is 45 ° with respect to the optical axis z in the reference state.
The rotation axis 4b is arranged at an angle to
It is configured to be able to swing around. The laser beam reflected by the galvanometer mirror 4 is transmitted to the first relay lens 5
a and a relay lens system 5 including a second relay lens 5b
Incident on. The first relay lens 5a is arranged so that the front focal point is located on the galvanomirror surface 4a.
Further, a first relay lens 5a and a second relay lens 5b
Constitutes an afocal optical system arranged such that the rear focal position of the first relay lens 5a coincides with the front focal position of the second relay lens 5b.

[0006] The laser beam passing through the relay lens system 5 is incident on a fixed mirror 6 arranged at an angle of 45 ° with respect to the optical axis z. The laser beam reflected by the fixed mirror 6 enters the pickup lens 7 and is focused on the surface of the optical disk 8 by the pickup lens 7. The pickup lens 7 is constituted by a single lens formed of an aspherical lens, and is disposed such that the rear focal point of the second relay lens 5b is located near the incident surface of the pickup lens 7. When the pickup lens 7 is composed of a plurality of lens groups, the second relay lens 5b may be arranged such that the rear focal point is located near the entrance pupil plane of the pickup lens 7.

[0007] The relay lens system 5 in the optical pick-up optical system of the present embodiment, the focal length f _a of the first relay lens 5a is configured to 1/3 of the focal length f _b of the second relay lens 5b. Therefore, the deflection angle of the laser beam deflected by the swing of the galvanomirror 4 is reduced to 1/3 by the relay lens system 5 and emitted. Therefore, the deflection angle of the laser beam incident on the pickup lens 7 via the fixed mirror 6 is １ ／ of the deflection angle of the laser beam emitted from the galvanometer mirror 4. The laser beam is focused on the optical disc 8 on the surface by the pickup lens 7, are tracked in the arrow T _a direction based on the deflection angle of the laser beam emitted from the galvanometer mirror 4.

Thus, in this embodiment, the galvanomirror 4
Since the deflection angle of the laser beam deflected by the laser beam is reduced to 1/3 and is incident on the pickup lens 7, even if the track pitch is, for example, 0.5 μm on the surface of the optical disk 8 condensed by the pickup lens 7, On the galvanometer mirror 4 side, tracking can be performed as if the track pitch was 1.5 μm. Therefore, the driving accuracy of the galvanometer mirror 4 can be improved by the reciprocal multiple of the angular magnification of the relay lens system 5, that is, three times. In this embodiment, the angular magnification of the relay lens system 5 is 1/3.
However, if the angular magnification of the relay lens system 5 is set to less than the same magnification, the accuracy of the tracking control can be improved.

Further, by using the relay lens system 5, the deflection angle of the laser beam emitted from the relay lens system 5 is reduced, while the beam diameter is enlarged and the laser beam emitted from the relay lens system 5 is enlarged. Is expanded three times as large as the incident beam. The optical pickup optical system of the present embodiment includes a fixed mirror 6 and a pickup lens 7.
, And a fixed optical system 21 including an optical system from the light source 1 to the relay lens system 5 and the signal detection optical system 12. Through the system 5, the fixed optical system 21
While a narrow laser beam is propagated inside, the beam diameter of the laser beam sent to the moving optical system 20 is formed to be large according to the ratio of the focal length between the first relay lens 5a and the second relay lens 5b. You.

Propagation of a thin laser beam in the fixed optical system 21 is very advantageous in making the fixed optical system 21 compact. Also, as shown in FIG.
The moving optical system 20 is moved in the radial direction (the direction of the arrow r in the figure) of the optical disk 8 by a linear motor (not shown) while tracking the surface of the optical disk 8, so that the distance between the moving optical system 20 and the fixed optical system 21 Varies greatly. On the other hand, since a laser beam having a large beam diameter is propagated between the moving optical system 20 and the fixed optical system 21, the diffraction spread of the beam diameter generated during the propagation of the laser beam is small. The configuration in which the system 5 is arranged is also effective for improving signal detection accuracy.

Next, the laser beam transmitted through the pickup lens 7 is focused on the surface of the optical disk 8, and information is recorded on the surface of the optical disk 8 at a track pitch of 0.5 μm. During recording and reproduction, the optical disk 8 is rotated by a disk motor 9 about the rotation axis 8a in the direction of arrow u, and the laser beam is rotated by the rotating optical disk 8.
A laser beam irradiated on the surface and modulated on the basis of information recorded on the surface of the optical disk 8 at the time of information reproduction is reflected. The laser beam reflected by the surface of the optical disk 8 passes through the pickup lens 7, the fixed mirror 6, the relay lens system 5, and the galvano mirror 4 in order, and is partially reflected by the half mirror 3. The laser beam reflected by the half mirror 3 is guided to a signal detection optical system 12 including a condenser lens 10 and a photodetector 11. Various tracking error detections and focusing error detections are possible by appropriately selecting the condenser lens 10 and the photodetector 11. In the optical pickup optical system according to the present embodiment, any tracking error detection method can be combined. It is possible.

FIG. 3 is a sectional view of an optical system of an optical pickup according to a second embodiment of the present invention. In this embodiment, as shown in FIG. 3, the galvanomirror 4 is arranged so as to be orthogonal to the paper surface in the reference state, and the paper surface and the galvanomirror surface 4
It is configured to be able to swing around a rotation axis 4c parallel to the line of intersection with a. Further, the entire optical pickup optical system 22 is integrally formed, and as shown in FIG. 4, a rotation shaft 23 is provided at a light source side end 22 b of the optical pickup optical system 22, and can swing about the rotation shaft 23. It is composed.
By swinging the optical pickup optical system 22 about the rotation axis 23, recording and reproduction are performed while moving the pickup lens side end 22a substantially in the radial direction r of the optical disk 8. At that time, performs tracking in the arrow T _b direction by swinging the galvano mirror 4 about the rotation axis 4c. As described above, according to the configuration of the present embodiment, it is possible to improve the accuracy of the tracking control as in the first embodiment.

FIG. 5 is a sectional view of an optical system of an optical pickup according to a third embodiment of the present invention. In the present embodiment, the optical pickup optical system according to the present invention is combined with a polarization optical system to cope with magneto-optical recording. In this embodiment, the laser beam emitted from the light source 1 is converted into linearly polarized light (p-polarized light) by the polarizer 31 and is incident on the polarization beam splitter 32. The laser beam that has passed through the polarizing beam splitter 32 is guided to the galvanometer mirror 4 and is collected on the magneto-optical disk 30 rotating in the direction of arrow u by the disk motor 9 about the rotation axis 30a in the same manner as in the first embodiment. Be lighted.

The laser beam focused on the magneto-optical disk 30 is reflected on the surface of the magneto-optical disk 30. At this time, the magnetization direction of the magneto-optical disk 30 is upward or downward depending on the presence or absence of a signal. Therefore, the plane of polarization of the laser beam is rotated left and right in accordance with the direction of magnetization and reflected by the magnetic Kerr effect. Therefore, the laser beam reflected by the magneto-optical disk 30 includes p-polarized light and s-polarized light generated in accordance with the signal recorded on the magneto-optical disk 30. reflectance R _s is using the polarization beam splitter 32 such that 20 to 30 percent reflectivity R _p for p-polarized light with respect to the 100%. The laser beam reflected by the polarization beam splitter 32 is guided to a detection optical system 33 composed of a known polarization optical system, and a signal is detected based on an output ratio between p-polarized light and s-polarized light.

[0015]

As described above, according to the present invention, the tracking accuracy can be improved by the reciprocal multiple of the angular magnification of the relay lens, and high-precision tracking can be performed even on an ultra-high-density disk with a fine track pitch. It became possible to perform control. It is also possible to reduce the size of the fixed optical system,
Further, the spread of the beam diameter due to the diffraction of the laser beam propagating between the moving optical system and the fixed optical system can be suppressed to be small, so that the signal detection accuracy can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of an optical system of an optical pickup according to a first embodiment of the present invention.

FIG. 2 is a plan view of the optical system of the optical pickup according to the first embodiment of the present invention.

FIG. 3 is a sectional view of an optical pickup optical system according to a second embodiment of the present invention.

FIG. 4 is a plan view of an optical pickup optical system according to a second embodiment of the present invention.

FIG. 5 is a sectional view of an optical system of an optical pickup according to a third embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Light source 2 ... Collimator lens 3 ... Half mirror 4 ... Galvano mirror 4a ... Galvano mirror surface 4b, 4c ... Galvano mirror rotation axis 5 ... Relay lens system 5a ... 1st relay lens 5b ... 2nd relay lens 6 ... Fixed mirror 7 Pickup lens 8 Optical disk 8a, 30a Disk rotation axis 9 Disk motor 10 Condensing lens 11 Photodetector 12 Signal detection optical system 20 Moving optical system 21 Fixed optical system 22 Optical pickup optical system 23 ... optical pickup optical system rotation axis 30 ... magneto-optical disk 31 ... polarizer 32 ... polarization beam splitter 33 ... polarization detection optical system

Claims (2)

[Claims] An optical pickup optical system for converging a light beam from a light source on an optical recording medium and guiding a reflected light beam from the optical recording medium to a photodetector, comprising: a movable mirror for deflecting the light beam from the light source. A pickup lens that condenses the light beam on the optical recording medium, and a relay lens system that guides the light beam reflected by the movable mirror to the pickup lens, wherein the relay lens system has the same angular magnification. An optical pickup optical system comprising an afocal optical system having a magnification less than twice. 2. The optical pickup optical system according to claim 1, wherein the relay lens system forms an image of the movable mirror on or near an incident surface of the pickup lens.