JPH11353694A - Optical pickup - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable recording and reproducing information with high accuracy by performing a tracking control correctly without receiving an effect due to the aberration of a lens. SOLUTION: This optical pickup is provided with a galvano-mirror 106 for scanning the laser beams emitted from a light source in a prescribed direction, an image formation lens 110 regulating the laser beams made to exit with the galvano-mirror 106 into a roughly parallel liminous flux and an objective lens 108 converging the laser beams guided with the image formation lens 110 on the recording surface of a record medium 112 and, in the pickup, the objective lens 108 is arranged by being moved in a prescribed direction by a prescribed quantity along the optical axis so as to reduce the aberration due to the lens 110. Moreover, the galvano-mirror 106 and the focal position Ff of the front side of the lens 110 are arranged by being optically matched with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup capable of performing tracking control using, for example, a galvanomirror.

[0002]

2. Description of the Related Art Conventionally, there is known an optical pickup having a telecentric optical system provided with a galvanomirror, as disclosed, for example, in Japanese Patent Application Laid-Open No. 2-2677741.

Such an optical pickup includes a galvanometer mirror for scanning a laser beam emitted from a light source in a predetermined direction, and an imaging lens for defining the laser beam emitted through the galvanometer mirror into a substantially parallel light beam. And an objective lens for condensing the laser light guided through the imaging lens on the recording surface of the recording medium. The galvanomirror and the front focal position of the objective lens are optically identical to each other. And the center of rotation of the galvanometer mirror,
The centers of the imaging lens and the objective lens are located on the same optical axis.

According to such a configuration, in a state where the laser beam is focused on the recording surface of the recording medium, the galvanomirror is rotated in a predetermined direction to thereby determine the spot position of the laser beam on the recording surface of the recording medium. Can be adjusted (tracking control), and the optical recording or optical reproduction of information on the recording surface of the recording medium is performed by condensing the laser beam on the recording surface of the recording medium while performing the tracking control. .

[0005]

By the way, in a telecentric optical system provided between a galvanomirror and a recording medium, in order to accurately optically record or optically reproduce information on the recording medium, a connection is required. The aberration of the image lens is corrected in the infinite optical system.

However, in this case, the imaging lens is
Since the finite optical system has spherical aberration, if the amount of rotation of the galvanomirror is increased in accordance with the size of the tracking control range, the spherical aberration will occur and the laser light reflected at the center of the galvanomirror will be affected. The optical axis does not cross at the front focal position of the objective lens.

For this reason, in the forward and backward paths of the laser light, the laser light passes through a position shifted from the front focal position of the objective lens. As a result, it becomes difficult to always accurately position the spot of the laser beam on the track formed on the recording surface of the recording medium, and it becomes difficult to record and reproduce information with high accuracy.

The present invention has been made to solve such a problem, and an object of the present invention is to record information with high accuracy by accurately performing tracking control without being affected by lens aberration. And to provide an optical pickup capable of reproducing.

[0009]

In order to achieve the above object, the present invention provides a galvanomirror for scanning a laser beam emitted from a light source in a predetermined direction, and a laser beam emitted through the galvanomirror. An optical lens comprising: an imaging lens that regulates the laser light into a substantially parallel light beam; and an objective lens that focuses the laser light guided through the imaging lens onto a recording medium, wherein the galvanomirror is provided. And the front focal position of the objective lens are optically coincident with each other, and the objective lens is moved by a predetermined amount in a predetermined direction along the optical axis so as to reduce aberration caused by the imaging lens. And place it.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical pickup according to an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 schematically illustrates a configuration of an optical pickup 100 according to the present embodiment, and FIG. 2 illustrates a state where the optical pickup 100 is disposed on a swing arm 102.

As shown in FIGS. 1 and 2, an optical pickup 100 according to the present embodiment includes a light source (semiconductor laser) 104 capable of emitting laser light for recording and reproduction, and a laser emitted from the light source 104. A galvanomirror 106 for scanning light in a predetermined direction, an imaging lens 110 for regulating the laser light emitted through the galvanomirror 106 into a substantially parallel light beam, and a light guided through the imaging lens 110 An objective lens 108 for condensing the laser light on a recording surface (not shown) of the recording medium 112. Then, the galvanomirror 106 and the objective lens 1
08 and the front focal position Ff are arranged so as to be optically coincident with each other.

Further, the optical pickup 10 of the present embodiment
0 is provided with a light guiding optical system 114 for guiding the laser light from the light source 104 to the galvanomirror 106,
The light guiding optical system 114 converts the laser light from the light source 104 into a parallel light beam, and converts the laser light converted into a parallel light beam by the collimator lens 116 into a front focal position F of the objective lens 108.
galvanomirror 106 optically aligned with f
And a relay lens 118 that leads to

In such an optical pickup 100, the collimator lens 116 and the relay lens 118
, The center of rotation of the galvanometer mirror 106, and the centers of the imaging lens 110 and the objective lens 108 are positioned on the same optical axis A.

In the optical path between the collimator lens 116 and the relay lens 118, the galvanomirror 10
A tracking detector 120 capable of optically detecting the tracking state by receiving the return light from 6 (reflected light reflected from the recording surface of the recording medium 112) is provided. The galvanometer mirror 106 and the imaging lens 1
An angle detector 122 capable of optically detecting the rotation angle of the galvanomirror 106 is arranged in the optical path between the angle detector 122 and the optical disc 10.

The tracking detector 120 has a beam splitter 124 for reflecting the return light from the galvanomirror 106, receives the return light reflected from the beam splitter 124, and generates an electric signal corresponding to a change in the light receiving position, ie, tracking. Light receiving element 126 that outputs a state detection signal
Are provided.

The objective lens 108 is disposed on an optical head 128 supported on the swinging tip of the swing arm 102. The objective lens 108 swings the swing arm 102 about a rotation shaft 130, and swings the swing arm 102. By swinging the moving tip in the direction of arrow S, the optical head 12
The eight objective lenses 108 can be moved in the radial direction of the recording medium 112.

According to such a configuration, in a state where the laser beam is focused on the recording surface of the recording medium 112, the swing arm 102 is swung about the rotation shaft 130,
By moving the optical head 128 along the radial direction of the recording medium 112, the spot position of the laser beam with respect to the recording surface of the recording medium 112 is coarsely adjusted (coarse tracking control), and at the same time, the galvanomirror 106 is moved with the arrow R By rotating in the direction, the spot position of the laser beam with respect to the recording surface of the recording medium 112 is finely adjusted (finely tracking control).

While such coarse and fine tracking control is being performed, the laser beam emitted from the light source 104 is transmitted to the light guide optical system 114 and the galvanometer mirror 10.
6 irradiates the reflection mirror 132 via the imaging lens 110 to the optical head 12.
The light is condensed along a track formed on the recording surface of the recording medium 112 via the eighth objective lens 108. As a result,
Optical recording or optical reproduction of information on the recording surface of the recording medium 112 is performed.

By the way, the imaging lens 11 as described above
0 is generally corrected for aberration in an infinite optical system, and has spherical aberration in a finite optical system. Therefore, if the rotation amount of the galvanometer mirror 106 is increased in accordance with the size of the tracking control range, Due to the influence of the spherical aberration, the laser light reflected at the center of the galvanometer mirror 106 does not cross the optical axis A at the front focal position Ff of the objective lens 108.

In this case, in the forward and backward paths of the laser light, the laser light is applied to the front focal position F of the objective lens 108.
It passes through a position shifted from f. In this case, since the light beam passes through different portions on the forward path and the return path, when the galvanomirror 106 is scanned, the spot moves on the light receiving element 126 of the tracking detector 120, and a tracking error signal is generated. An offset occurs.

Therefore, the optical pickup 1 of the present embodiment
3A, the objective lens 108 is moved in a predetermined direction along the optical axis A by a predetermined amount, and the front focal position Ff of the objective lens 108 is shifted, as indicated by the arrow in FIG. To reduce the effects of

As shown in FIG. 3B, the imaging lens 11
Assuming that the center of 0 (point on the optical axis A) is 0 (zero), the spherical aberration increases from the 0 point toward the lens radial direction, and eventually becomes constant (tentatively referred to as a maximum point). .

Therefore, in the present embodiment, the position of the front focal position Ff of the objective lens 108 on the optical axis A is adjusted so that spherical aberration corresponding to an intermediate value P between the zero point and the maximum point is generated. adjust. In this case, the influence of the spherical aberration by the imaging lens 110 is caused by the front focal position F of the objective lens 108.
It appears as a substantially uniform optical action on the optical axis at substantially the same location near f. As a result, the laser light guided through the imaging lens 110 crosses the optical axis at substantially the same location near the front focal position Ff of the objective lens 108 on the outward path and the return path. As described above, when the luminous flux passes through substantially the same place on the outward path and the return path, the galvanomirror 10
6, the tracking detector 120
The spot does not move on the light receiving element 126, so that no offset occurs in the tracking error signal.

As described above, according to the present embodiment, the influence of spherical aberration can be reduced only by shifting the front focal position Ff of the objective lens 108 in the predetermined direction along the optical axis by the predetermined amount. As a result, it is possible to always accurately position the spot of the laser beam on the track formed on the recording surface of the recording medium 112, and it is possible to record and reproduce information with high accuracy.

In the above-described embodiment, the position of the objective lens 108 on the optical axis A is adjusted so that a spherical aberration corresponding to an intermediate value P between the zero point and the maximum point occurs. However, the present invention is not limited to this, and the position of the objective lens 108 on the optical axis A can be arbitrarily adjusted according to the purpose of use, the use environment, and the like.

Further, a hemispherical lens (for example, an immersion lens) and a magnetic coil are added to the optical head 128, and the focused light from the objective lens 108 is further narrowed down by the hemispherical lens, whereby a recording medium (for example, a magneto-optical disk) is formed. )
The spot diameter of the laser light focused on the recording surface of the recording medium 112 is further reduced, and the optical head 128 is moved by the aerodynamic lift acting between the rotated recording medium 112 and the optical head 128. It may be configured to be slightly lifted from the camera. By combining such techniques, the spot diameter of the laser beam can be further reduced without performing focus control, and the recording density on the recording surface of the recording medium 112 can be improved.

Further, in the above-described embodiment, an example in which the optical pickup 100 having the telecentric optical system is arranged on the swing arm 102 has been described. However, the present invention is not limited to this. The head 128 may be configured to move in the radial direction of the recording medium 112, and other optical system components may be fixed.

In this case, by moving the reflection mirror 132 and the optical head 128 in the radial direction of the recording medium 112, the spot position of the laser beam with respect to the recording surface of the recording medium 112 is coarsely adjusted (coarse tracking control). At the same time, the spot position of the laser beam on the recording surface of the recording medium 112 is finely adjusted by finely rotating the galvanometer mirror 106 (finely tracking control).
Is done. By performing such coarse movement and fine movement tracking control, optical recording or optical reproduction of information on the recording surface of the recording medium 112 is performed.

[0029]

According to the present invention, it is possible to provide an optical pickup capable of recording and reproducing information with high accuracy by accurately performing tracking control without being affected by lens aberration. it can.

[Brief description of the drawings]

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

FIG. 2 is a perspective view showing a state where the optical pickup of the present invention is disposed on a swing arm.

3A is a diagram illustrating a state in which the influence of spherical aberration is reduced by moving an objective lens, and FIG. 3B is a diagram illustrating spherical aberration characteristics.

[Explanation of symbols]

 104 light source 106 galvanometer mirror 108 objective lens 110 imaging lens 112 recording medium Ff front focal position of objective lens A optical axis

Claims (2)

[Claims] 1. A galvanomirror for scanning a laser beam emitted from a light source in a predetermined direction, an imaging lens for regulating the laser beam emitted via the galvanomirror to a substantially parallel light beam, An optical pickup comprising: an objective lens that focuses laser light guided through a lens on a recording medium, wherein the galvanomirror and a front focal position of the objective lens are optically coincident with each other. An optical pickup, wherein the objective lens is arranged by being moved by a predetermined amount in a predetermined direction along an optical axis so as to reduce aberration caused by the imaging lens. 2. The objective lens is moved in a predetermined direction along the optical axis such that the laser light intersects the optical axis at substantially the same location near the front focal position of the objective lens on the forward and backward paths of the laser light. The optical pickup according to claim 1, wherein the optical pickup is moved by a predetermined amount.